Section 4: Wastewater Treatment Facility Process Evaluation · Wastewater System Master Plan Update...

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Wastewater System Master Plan Update Page 4-1 City of Yuba City g:\adminasst\jobs\2005\0570009_yubacityww_mstrplnupdate\09-reports\9.09-reports\master plan\03-06\text\yuba city master plan.doc 3/10/06 11:05 AM

Section 4: Wastewater Treatment Facility Process Evaluation

4.1 Introduction This section provides information on the existing Wastewater Treatment Facility (WTF) condition assessment and performance evaluation. The evaluation was based on the current NPDES permit discharge requirements.

Current NPDES Discharge Requirements The NPDES permit no. CA0079260 was issued by the California Regional Water Quality Control Board (CRWQCB) on 6 June 2003 and defines discharge requirements for the wastewater treatment facilities. The order number is R5-2003-0085.

In accordance with the permit, the rated capacity of the wastewater treatment facilities is 7 MGD. Since the plant was recently expanded (completed in 2005), the City is in the process of appealing the current permit to have the plant rated capacity revised. Also, the City appealed to the State Water Resources Control Board (SWRCB) regarding the current effluent criteria for some effluent constituents having stringent limitations and that cannot be met with secondary or filtered treatment process.

In June 2004, the SWRCB remanded most limits back to the Central Valley Regional Water Quality Control Board (CVRWQCB) for reconsideration and granted an acute toxicity mixing zone. The CVRWQCB has started a new permit, which should be issued by fall 2006.

An abbreviated version of the current discharge requirements for the effluent disposal is presented in Table 4-1. The entire NPDES permit is included in Appendix C1, containing many other permit limits for metals and volatiles.

Table 4-1: NPDES Permit CA0079260 Effluent Requirements (6 June 2003)

Constituents Units Feather River Percolation Ponds Effluent shall not exceed the following limits from adoption until 29 February 2008 Effluent Requirements

Average Monthly

7-Day Median

Average Weekly

Average Daily

BOD(a) mg/l 30(b) 45(b) 60(b) Total Suspended Solids mg/l 30(b) 45(b) 60(b) Settleable Solids ml/l.hr 0.1 0.2 Total Coliform Organisms

MPN/100 ml 23

Total Chlorine Residual mg/l 0.01 pH - 6.5 to 8.5 6.5 to 8.5


Table 4-1: NPDES Permit CA0079260 Effluent Requirements (6 June 2003) (cont’d)

Constituents Units Feather River Percolation Ponds Receiving Water Requirements pH - 6.5 to 8.5 or change by more than 0.5 units 6.5 to 8.5 Dissolved Oxygen mg/l 7 1 (in the upper zone (1 foot)

of wastewater in the pond) Turbidity NTU No increase more than 10%

over background level No increase more than 10%

over background level

Effluent shall not exceed the following limits from 1 March 2008 forward Effluent Requirements BOD(a) mg/l 30(b) 45(b) 60(b) Total Suspended Solids mg/l 30(b) 45(b) 60(b) Settleable Solids ml/l.hr 0.1 0.2 Total Coliform Organisms

MPN/100 ml 23

Total Chlorine Residual mg/l 0.01 pH - 6.5 to 8.5 6.5 to 8.5

Receiving Water Requirements pH - 6.5 to 8.5 or change by more than 0.5 units 6.5 to 8.5 Dissolved Oxygen mg/l 7 1 (in the upper zone (1 foot)

of wastewater in the pond) Turbidity NTU No increase more than 10%

over background level No increase more than 10%

over background level

(a) 5-day, 20°C biochemical oxygen demand (BOD) (b) To be ascertained by a 24-hour composite

4.2 WTF Condition Assessment and Performance Evaluation This evaluation was focused on determination of adequacy of existing plant process units to treat current flows and to assess limitations of existing facilities. It addresses the equipment condition, redundancy and reliability.

This section provides a description of the following:

● Technical data for each unit process ● Estimated capacity of each unit process ● Current operation constraints ● Recommended improvements


4.2.1 Existing Treatment Facilities The City of Yuba City WTF is a secondary treatment plant facility with a pure oxygen activated sludge process designed to handle high BOD loadings from the local food processing facility. Secondary effluent is disinfected using chlorine gas, dechlorinated and discharged to the Feather River or percolation ponds. Currently, the plant is discharging the entire flow to the Feather River.

The facility treats the domestic/commercial wastewater flows from the City as well as the industrial flows from Sunsweet and other industries. The plant also receives septage.

The existing Yuba City wastewater treatment facilities consist of the following processes:

Liquid Treatment Train

● Headworks (Screening Facility and Pumping Station) ● Grit Basin ● Primary Clarifiers ● Pure Oxygen Aeration Basins ● Secondary Clarifiers ● Chlorine Contact Tanks ● Dechlorination tanks ● Effluent Pumping Solids Handling Train

● Sludge Thickening (DAFTS) ● Digesters ● Biosolids dewatering (belt filter press (BFP)) ● Odor Control Facilities (for headworks, primary clarifiers and dewatering building) ● Biosolids Drying Beds ● Biosolids Storage Area

4.2.2 Current Plant Operation (2001 – 2005) The current plant operation parameters were established based on a statistical analysis (Section 2, Tables, 2-3, 2-4 and 2-13) of plant influent flow and loads data taken for the period from January 2001 through August 2005, as follows:

● Average day flow: 6.0 MGD ● Peak day flow: 8.23 MGD ● Peak hour flow: 10.8 MGD ● Average influent BOD5: 380 mg/l ● Peak influent BOD5: 677 mg/l ● Average influent TSS: 221 mg/l ● Peak influent TSS: 550 mg/l


4.2.3 Condition Assessment This section contains a summary of the current condition of the unit processes for the liquid and the solids treatment streams, as well as the equipment redundancy and reliability.

The WTF condition assessment included hydraulic, mechanical, and electrical operation of the facilities. This evaluation was based on visual field investigations, existing record drawings and operational comments provided by the WTF staff.

The WTF facilities are shown in Figure 4-1.

4.2.4 Liquid Treatment Processes

4.2.4.1 Headworks Technical Data The headworks which includes influent screening and pumping, was completed in 2005 as part of the Yuba City Wastewater Treatment Facility Upgrades Contract No. 02-05.

Existing Facilities – Influent Screens

● Four screen channels ● Two (2) mechanically front- cleaned bar screens, 1/4” clear opening, each at rated capacity

of 12 MGD ● Two (2) washing and compacting equipment for screenings. Existing Facilities – Influent Pumps

The influent pumping station contains 5 Flygt Submersible Pumps:

● Pump #1 and #2: Model 3201.091-5442, 642 impeller, 35 HP. They are each rated at 2250 gpm (3.24 MGD) at 42 TDH

● Pump #3, #4 and #5: Model 3300.091-5513, 623 impeller, 75 HP. They are each rated at 4000 gpm (5.76 MGD) at 53 TDH

For the purpose of the Master Plan it was assumed that the influent pump output capacity is approximately 80% of the combined (total) pump capacities. Accordingly the estimated influent pumps output installed capacity is 19 MGD. The influent pumps output firm capacity (with one largest pump out of service) is estimated at 14.4 MGD.

There is a place for provision of two (2) 5.8 MGD pumps, in the existing structure.

The influent flow is measured by a 24-inch magnetic flow meter, which is designed to measure flow up to 30 MGD. The flow meter is located downstream of the new influent pumps in a flow meter vault, which is large enough to accommodate an additional flow meter.


The Headworks Condition Based on visual observations, the overall condition of the facility appears to be excellent, which would be consistent with a recently completed facility.

Operational Limitations Bar Screen Cleaning System

The facility staff was facing frequent failure of the automated screen cleaning system. The issues were related to start-up conditions. The brake was repaired and the screens are now operating with expected level of maintenance and the screens are considered reliable.

Grit Accumulation in the Influent Channel

Facility staff anticipates that periodic cleaning of grit in the influent channel upstream of the screens may be necessary based on prior experience with grit settling in the influent channel during low flow periods. It is anticipated that cleaning of the influent channel will be difficult because of the effort required to bypass the flow. Bypassing the flow would require plugging an upstream manhole and pumping around the influent channel or other mechanical cleaning techniques.

Conclusions It is concluded that the capacity of the existing headworks and the existing influent pumping is adequate to handle the current flow.

In addition, the facility staff may face some difficulties cleaning the influent channel because of the effort required to bypass the flow or use mechanical cleaning processes.

Recommended Improvements A provision of a flow by-pass channel would improve flow diversion from the influent channel for the periodic removal of the accumulated grit.

4.2.4.2 Grit Basin Technical Data The existing aerated grit basin was constructed in 1975. Recently (2004), hydraulic improvements were made to improve the grit basin capacity. It can handle a peak flow of 20.0 MGD at 3 minutes hydraulic retention time.

Operational Limitations Redundancy

Facility staff indicated that the grit chamber does not have a redundant grit removal system that can be used when the grit chamber is taken out of service for cleaning every six months.

Odors

The grit basin odor control equipment has been abandoned and facility staff indicated that odors from the grit basin are an issue.


The Grit Chamber Condition In general, the mechanical equipment appears to be in good operating condition. The mechanical equipment, which consists of two aeration blowers, a grit pump, and grit classifier, have been rehabilitated or replaced in the past 15 years.

Based on visual observation of the exterior of the grit basin and interior of mechanical room, the concrete structure and exposed piping appears to be in reasonably good condition and is consistent with the age of the structure.

Conclusions It is concluded that the capacity of the existing grit basin is adequate to handle the current flow. However, there is no redundant capacity and there are issues related to generation of odors. Also, the equipment is nearing its useful life.

Recommended Improvements It is recommended to install a new vortex-type grit unit and an odor control facility. Once the new unit installed, the existing aerated grit removal unit will be abandoned.

4.2.4.3 Primary Clarifiers Technical Data The primary clarifiers’ technical data are summarized in Table 4-2.

Table 4-2: Primary Clarifiers Technical Data

Technical Data Units Tanks Number of Tanks - 2 Shape - Circular Tank Diameter feet 90 Side Water Depth (SWD) feet 9.25 Area-Each sf 6,362 Volume-Each cf 58,846 Total Area sf 12,724 Total Volume gal 880,336

The two existing 90-foot diameter primary clarifiers were constructed under two different projects. The northern clarifier was constructed in 1975 as part of the original plant construction and the southern clarifier was constructed in 1999. The 1999 project also included rehabilitation of the northern clarifier (drives replacement), installation of effluent channel covers, and installation of an odor control bed for both clarifiers.


Operations Parameters The primary clarifier operations parameters are summarized in Table 4-3.

Table 4-3: Primary Clarifiers Operations Parameters

M&E(a) Guidelines Operations Parameters Units Current Operation Range Typical Number of Operating Tanks - 2 2 Minimum Surface Area of Operating Tanks sf 12,724 Average Flow to Tanks MGD 6.0 Peak Hourly Flow to Tanks MGD 10.8 Overflow Rate at Qavg gpd/Sf 472 800-1,200 1,000 Overflow Rate at Qpeak gpd/Sf 850 2,000-3,000 2,500 Detention Time at Qavg h 3.5 1.5-2.5 2 Detention Time at Qpeak h 2.0 BOD Removal Efficiency % 25 (b) 25-40 TSS Removal Efficiency % 60 (b) 50-71

(a) Metcalf and Eddy (b) calculated based on plant data The WTF BOD and TSS removal data that were used for evaluation of the primary clarifiers are included in Appendix C2.

The calculated overflow rates, detention times and BOD5 and TSS removal efficiencies indicate that the current operation parameters are well within the recommended design values.

Primary Clarifiers Condition As part of the northern clarifier rehabilitation, a coating was placed on the interior wall of the primary clarifier to protect the concrete wall. The facility staff indicated that the coating extends just below the normal water surface elevation in the clarifier. Based on visual observations the coating in the northern clarifier was in good condition. There is no visible coating on the interior wall of the southern clarifier.

Based on visual observations, both clarifiers appear to be in good operating condition. The condition of the drive mechanisms, effluent channel covers, concrete structures, walkways, and sludge and scum pumping equipment appears to be consistent with age and use.

Operational Limitations Facility staff indicated that each primary clarifier is removed from service once a year for cleaning and maintenance and every 5 to 7 years for coating. The staff also indicated that they prefer to have two aeration basins and three secondary clarifiers in operation when a primary clarifier is removed from service so that the impact of reduced primary clarifier capacity on the effluent quality is minimized.


Conclusions It is concluded that the existing clarifiers have sufficient capacity to meet current operating conditions, providing both tanks are in operation.

Recommended Improvements Provision of an additional primary clarifier would offer the operators more flexibility during maintenance without jeopardizing plant performance

4.2.4.4 Aeration Basins Technical Data The aeration basins were constructed in 1975. The aeration basins technical data are summarized in Table 4-4.

Table 4-4: Aeration Basins Technical Data

Technical Data Units Tanks Tanks Number of Tanks - 3 Shape - Rectangular Width feet 43 Depth feet 11 Length feet 172 Volume-Each cf 81,356 Volume-Each gal 610,000 Total Volume gal 1,830,000

Aeration System Number of Compressors - 4 (3 duty, 1 or stand-by) Size of Compressor - Each HP 250 Power Installed for Oxygenation HP 1000 Operating Power for Oxygenation HP 500 (2 compressors needed for

current operation) Oxygen Supply ton/day 7-12 (current operations)

28 max (4 compressors) The oxygen for use in the activated sludge process is produced in a 3-bed Pressure Swing Adsorption (PSA) oxygen generation plant. It has a capacity of 28 tons/day of 90 percent pure oxygen. The air is supplied to the PSA units from four reciprocating 250 HP compressors. The compressors are matched to the PSA units and therefore one compressor is a standby, for maximum production of 21 tons/day.


Each basin has four interconnected cells with a motor driven surface oxygenator in each cell. The horsepower for the oxygenators decreases from the first cell to the fourth cell on basin #3.

Currently only two tanks (Basins 2 and 3) are in operation. Basin 1 is out service because it does not have oxygenators in all four cells. Facility staff indicated that the gear boxes from the first two cells were relocated to the other aeration basins when the new turbine blades were installed on basin #3.

Operations Parameters The WTF MLSS data that were used for evaluation of the aeration operation parameters are included in Appendix C3.

The aeration basins operation parameters are summarized in Table 4-5.

Table 4-5: Aeration Basins Operations Parameters

M&E(a) Guidelines Operations Parameters Units

CurrentOperation Range Typical

Number of Operating Tanks - 2 Volume of Operating Tanks cf 162,712 Average Flow to Tanks (Primary Effluent-PE)

MGD 6.0

Peak Hourly Flow to Tanks (Primary Effluent-PE)

MGD 10.8

Return Sludge Rate (RAS) at Qavg Return Sludge Rate (RAS) at Qpeak

%

%

57

57

25-100

Average Flow to Tanks (PE + RAS)

MGD 9.42

Peak Hourly Flow to Tanks (PE + RAS)

MGD 14.22

BOD5 Load to tank lbBOD5/day 14,261(b) Organic Loading Rate lbBOD5/cf day 0.09 0.1-0.21 Detention Time at Qavg (incl. RAS at 57%)

h 3.1 1-3 2

Detention Time at Qpeak (incl. RAS at 57%)

h 2.1

MLSS mg/l 2054 MLVSS (at 75% MLSS) mg/l 1540 F/Mv lbBOD5/lb VSS 0.96 0.25 -1.3

(Operations Experience)

Oxygen Requirements lbO2/lbBOD5 1.4 1.1 (a) Metcalf and Eddy (b) Estimated based on 25% BOD removal in the primaries


The calculated organic loading rate, detention times, F/M and the oxygen requirements indicate that the current operation parameters are well within the recommended design values.

Based on the information provided by the plant staff, the aeration basins are operated with a lower detention time in comparison to the textbook recommendation.

Aeration System Condition Aeration Basins

A condition assessment of the aeration basins was performed in 2001 by Wist, Janney, Elstner Associates, Inc. Conclusions of the assessment (which included visual observations of aeration basin number 2 and coring of aeration basin number 1) indicated that the concrete below the normal water surface had eroded to a point where the concrete aggregate was exposed. It was also concluded that the depth of carbonation extended at least 3/8 inch beyond the eroded surface of the concrete. Based on the analysis, it appeared that the reinforcing steel within the walls had not been impacted. However, it was indicated that deterioration might compromise the reinforcing steel within five to ten years. The last time an aeration basin was taken out of service for inspection was in 2001.

According to facility staff, aeration basin number 1 cannot be used because it has been prepared for concrete repairs and also due to the absence of mechanical equipment as mentioned above.

Oxygen Generation and Storage System

Based on visual observations, the pure oxygen generation and storage system appear to be in good operating condition and according to the facility staff, it should be in service for at least the next 15 years.

Facility staff indicated that no improvements are required to upgrade the system. The plant staff also indicated that the procedure to obtain the replacement part in case of failure is efficient and reliable.

The staff also indicated that the compression ring springs for the suction and discharge valves of the compressor have required frequent replacement due to failure of the springs. The compression ring springs are replaced at least once per year. Other improvements included:

● The modification of the air intakes: During the recent plant expansion (2004) the air intake lines to each compressor were removed and in their place a single intake air manifold was installed fed by two separate plenum rooms with air filters. This was supposed to limit the noise and at the same time supply the intake air to operate the generation skid. This has proven not to be very effective and seems to have major problems with design.

● The installation of a new MCC: The oxygen generation skid and system was upgraded with a new PLC controller and automatic vent valve in 2002. The PSA cooling water tower was removed and reclaimed water is now being used to cool the compressors and air after-coolers. This was done in June 2004. Annual service and inspections are performed and will continue to be performed by contracted services. Any upgrades will occur as needed and/or recommended.


● During the recent plant expansion (2004) all PSA compressors and related equipment switchgear was replaced with new equipment.

Operational Limitations Several operational difficulties with the aeration basins were identified by the plant staff. The difficulties include:

Foam Trapping

Foam trapping is occurring in the aeration basins. It is likely that the size of the openings between each cell of the aeration basin prevents foam from exiting the aeration basin.

Hydraulic Limitations

A hydraulic bottleneck in the aeration basin is limiting the amount of sludge that can be returned to the head of the aeration basins. The facility staff believes that the three 20-inch diameter pipes that connect the aeration basin inlet box with the three aeration basins are capacity limited.

During low flow periods the plant is typically operated with only one of the three aeration basins. With one train in operation the liquid level in the aeration basin increases at the peak diurnal flow that also includes RAS flow. This results in the liquid level reaching the top of the aeration basin influent box and increased power draw on aerators.

Due to this hydraulic bottleneck the plant has had difficulties returning enough return activated sludge (RAS) to maintain process stability. The current target for mean cell residence time (MCRT) is two to three days.

Oxygen Supply

The plant staff is currently having difficulty with oxygenator operation. The water surface elevation in the cells of the aeration basins can vary and on several occasions have caused the mixers to automatically shut off. The mixers trip off when the water surface elevation changes by approximately 1/4 inch. In addition, the turbine blades on train 3 have been replaced and the newer blades (M2T high Flow) require more torque than the existing gear boxes can supply. The staff has interchanged gear boxes with an inactive basin (basin number 1) to make two basins operational.

Also, only one aeration basin (basin number 3) has sufficient oxygenation capacity to be operated alone during summer season. Basin number 2 cannot be operated alone due to insufficient oxygenation capacity (due to difficulty with oxygenator operation: original pitch blade turbine has not been replaced with newer style blade). Basin number 1 is out of service. The current aeration basin configuration does not allow the plant to remove aeration basin number 3 from service for maintenance during summer months.

The current needed oxygen capacity is estimated to 6 tons/day. The existing oxygen supply system has a capacity of 28 tons/day (installed capacity) and 21 tons/day (Firm capacity). It appears that the existing system has enough capacity to meet the current operations.


Two tanks are needed in winter months for hydraulic reasons.

Conclusions Based on the discussion above it is concluded that:

● The amount of sludge that can be returned to the head of the aeration basins is limited by the configuration of the aeration tank inlet box and the size of the incoming pipes.

● Foam trapping is observed in the aeration basins.

● There is no flexibility in operation of the aeration basins due to basin number 2 not having enough oxygen transfer capacity during summer months and basin number 1 being out of service.

● The interior concrete surfaces show corrosion.

It is finally concluded that the existing aeration basins have sufficient capacity to meet current operating conditions, providing two basins are in operation and that the oxygen supply system has sufficient capacity to meet the current operations.

Recommended Improvements It is recommended to:

● Re-route the RAS piping to alleviate the problem of amount of RAS transferred to the head of the aeration basins.

● Repair the concrete in the aeration basins. Repair alternatives are detailed in the Wist, Janney, Elstner Associates, Inc. 2001 report.

● Install mechanical equipment in basin 1.

● Increase oxygenation capacity in basin 1 and 2.

4.2.4.5 Secondary Clarifiers Technical Data The secondary clarifiers’ technical data are summarized in Table 4-6.


Table 4-6: Secondary Clarifiers Technical Data

Technical Data Units Tanks Number of Tanks - 2 1 Shape - Circular Side Water Depth (SWD) feet 15 Tank Diameter feet 90 100 Area-Each sf 6,362 7,584 Area-Total sf 20,308 Volume-Each cf 95,426 117,810 Total Volume gal 2,308,792

There are two existing 90-foot diameter secondary clarifiers and one existing 100-foot diameter clarifier. The 90-foot clarifiers were constructed in 1975 as part of the original plant construction and the 100-foot diameter clarifier was constructed in 1994. Based on visual observations, all clarifiers appear to be in good operating condition.

The Return Activated Waste (RAS) pumping system includes 4 Chicago pumps, Dry Pit, Model VPM LSC-8, 30 HP, 1175 rpm. Each pump is rated at 2400 gpm (3.45 MGD) at 30’ TDH.

For the purpose of the Master Plan it was assumed that the RAS pumps output capacity is approximately 80% of the pumps capacities. Accordingly the RAS pumps output installed capacity is estimated at 11 MGD. The RAS pumps output firm capacity, with one pump out of service, is estimated at 8.3 MGD.

The Waste Activated Waste (WAS) pumping system includes 2 Chicago pumps, Dry Pit, Model VPM 64101, 5 HP, 1160 rpm. Each pump is rated at 420 gpm (0.6 MGD) at 25’ TDH.

Operations Parameters The purpose of the secondary clarifiers is to separate the activated-sludge solids from the mixed liquor. The secondary clarifier operations parameters are summarized in Table 4-7.

The WTF RAS data that were used for the evaluation of the secondary clarifiers operation parameters are included in Appendix C4.


Table 4-7: Secondary Clarifiers Operations Parameters

M&E(a) Guidelines Operations Parameters Units Current Operation Range Typical Number of Operating Tanks none 3 2 Minimum Surface Area of Operating Tanks sf 20,308 Average Flow (includes RAS at 57% Qavg) to Tanks

MGD 9.42

Peak Hourly Flow (includes RAS at 57% Qavg) to Tanks

MGD 14.22

Overflow Rate at Qavg gpd/sf 464 400-700 550 Overflow Rate at Qpeak gpd/sf 700 1,000-1,600 1,400 Detention Time at Qavg h 5.9 2.5 Detention Time at Qpeak h 3.9

(a) Metcalf and Eddy The calculated overflow rates and detention times indicate that the current operation parameters are well within the recommended design values.

Secondary Clarifiers Condition Exposed concrete aggregate is visible in the southeast clarifier effluent channel and coating in the southwest region of the interior wall of the northeast clarifier appears to be peeling. At the time of site visit algae growth was apparent in all three clarifiers and foam was visible within all three clarifier influent baffles. Staff has indicated that the southeast clarifier (100-foot diameter) appears to perform better than the other clarifiers with regard to effluent quality. The staff also prefers the perimeter launder on the southeast clarifier versus the launder arrangement on the older 90-foot diameter clarifiers, which have launders that are located approximately six feet from the outer wall of the clarifier. It appears that algae accumulation in the 90-foot clarifier launders is higher than algae accumulation in the 100-foot diameter clarifier.

Operation Limitations Clarifier Capacity

The secondary clarifiers are routinely taken out of service for maintenance approximately once every two years. The plant staff indicated that an additional clarifier is necessary because effluent quality is noticeably impacted when one clarifier is removed from service. Discharging to the Feather River is typically stopped and the effluent is directed to percolation ponds when one clarifier is removed from service.

RAS Pumps Suction Valves

Facility staff indicated that return activated sludge (RAS) and waste activated sludge (WAS) pumping facilities are in good operating condition. According to an Equipment Evaluation that was performed by HDR Engineering, Inc. in 2001, the RAS and WAS pumping systems were overhauled in 1994 and 1995. It was identified in the evaluation that suction valves for RAS


pumps 1 through 3 were difficult to operate. Facility staff indicated that this issue has not been resolved.

Conclusions Based on Table 4-7, it is concluded that the existing clarifiers have sufficient capacity to treat the current flow and loads, providing all clarifiers are in operation.

It is also concluded that:

● The effluent discharged to the Feather River is deteriorated when one clarifier is removed from service.

● The launder arrangement on the 100-foot diameter clarifier allows for lower algae growth. ● Suction valves for RAS pumps 1 through 3 are difficult to operate. Recommended Improvements The following recommendations should be considered:

● Addition of a fourth secondary clarifier. Based on review of record drawings, it appears that the secondary clarifier influent box is configured to allow connection of a fourth clarifier

● Replacement of the launder on the 90-foot diameter clarifiers should be considered

4.2.4.6 Disinfection Facilities Technical Data The chlorine contact tank (CCT) technical data are summarized in Table 4-8.

Table 4-8: CCT and Dechlorination Basins Technical Data

Technical Data Units Tanks CCT Number of Tanks - 2 Shape - Rectangular Depth – both tanks feet 6.75 Tank 1 Length feet 1038 Width (5 lengths) feet 4 Width (1 lengths) feet 9 Volume cf 33,865 Tank 2 Length feet 692 Width feet 6 Volume cf 28,026 Volume – total (2 tanks) cf 61,891 Volume – total (2 tanks) gal 462,944 Dechlorination Basin Total Width (2 passes) ft 12 Length ft 141 Depth ft 6.75


The disinfection facilities consist of two chlorine contact tanks (CCT) and two dechlorination basins. One of the two chlorine contact tanks was constructed in 1975 as part of the original wastewater treatment plant. The newer chlorine contact tank and dechlorination basins were completed in 2001.

The dechlorination basins are located in the area between the two CCTs. Effluent from both CCTs flows into the dechlorination basin. The basin can also be bypassed when the effluent is pumped to the percolation ponds. The serpentine pathway reduces the short circuiting to promote better mixing of water and dechlorination agent. At the end of the dechlorination basin there is a splitter box, which directs the flow to two effluent pump station sumps.

Submerged induction mixers are provided at the influent of the dechlorination chamber. The first mixer is the primary feed location of the dechlorination chemical. The second mixer is used when additional dechlorination chemical is added and also where caustic soda takes place for final pH adjustment, if needed. The dechlorination chemical is added through a diffuser.

Sodium bisulfite is used for dechlorination.

Operations Parameters The contact chlorine tanks operations parameters are summarized in Table 4-9.

Table 4-9: Chlorine Contact Tanks Operations Parameters

M&E(a) Guidelines Operations Parameters Units Current Operation Range Typical

Number of Operating Tanks - 2 2 Minimum Average Flow to Tanks MGD 6.0 Peak Hourly Flow to Tanks MGD 10.8 Detention Time at Qavg min 111 30-120 30 Detention Time at Qpeak min 82 15-90 30 (a) Metcalf and Eddy The calculated detention time at the average flow is within the recommended design values.

CCT Condition The new chlorination and dechlorination equipment were installed in 2001 along with the new chlorine contact tank and dechlorination basins. Based on visual observations, the equipment appears to be in good condition. There is an existing diffused air system installed in the old contact tank. The aeration system was installed in 1998 and appears to be in good condition.

Concrete Corrosion

Exposed aggregate is visible in the older chlorine contact tank. Facility staff indicated that the erosion of the concrete may have been caused by low pH conditions caused by the industrial discharges to the facility. Recently, the pH in the influent has been relatively stable- since the implementation of an industrial pre-treatment program by the City and installation of a caustic feed system in 1996. City staff indicated that it appears the erosion of the walls was eliminated or reduced after the pre-treatment program was implemented. The City also indicated that solids


which settle in the chlorine contact tank are removed every year to prevent excessive accumulation. Staff indicated that there are more solids at the beginning of the tank.

Operational Limitations Caustic Feed System

Based on visual observations and discussions with facility staff, the caustic feed system piping is deteriorating and requires frequent repairs. It appears that the caustic is reacting with the pipe or pipe adhesive that may have been used to join the pipes and fittings. The pipes material is PVC.

Bisulfite Tank

The facility staff also indicated that the size of the existing bisulfite tanks is not adequate. Currently, the plant can only re-order bisulfite when the depth in the tanks is less than or equal to 10-inches. When the volume of bisulfite goes down to this level, the plant has had instances where the bisulfite left in the tanks was not sufficient until the arrival of the next shipment of bisulfite. This condition forced the facility to cease discharge to the Feather River and discharge to the percolations ponds.

Conclusions It is concluded that the capacity of the existing disinfection facilities is adequate to handle the current flow.

It should be noted that the caustic feed system piping is deteriorated and would require replacement.

Also, the bisulfite tank capacity is inadequate and should be replaced with a tank of larger capacity.

Recommended Improvements The following recommendations should be considered:

● Replacement of the caustic feed system piping. An evaluation of the replacement of the whole caustic system should be performed in order to resolve the pH issues

● Replacement of existing bisulfite tank with a larger one

4.2.4.7 Effluent Pumping, Metering and Outfall Structure Dechlorinated plant effluent is pumped from the WTF to either the Feather River or to 6 percolations ponds located on the east side of the Feather River.

Technical Data The effluent pumping station includes 6 pumps.


West Sump

● Pump #1 and #2: Johnston Pump, Vertical Turbine, Size 16LS, 2 Stage, 75 HP, 870 rpm. Both pumps are rated at 4800 gpm (6.91 MGD) at 46’ TDH

● Pump #3: Byron Jackson Pump, Vertical Turbine, Size 20HQO, 2 Stage, 75 HP, 890 rpm. This pump is rated at 4800 gpm (6.91 MGD) at 46’ TDH

● Pump #4: Johnston Pump, Vertical Turbine, Size 10JTA, 2 Stage, 20 HP, 1165 rpm. This pump is rated at 1550 gpm (2.23 MGD) at 32’ TDH

East Sump

● Pump # 5: Byron Jackson Pump, Vertical Turbine, Size 20 HQO, 1 Stage, 75 HP, 1190 rpm, and is rated at 4800 gpm (6.91 MGD) at 46’ TDH.

● Pump #6: Goulds Pump, Vertical Turbine, Size 20GHC, 1 Stage, 125 HP, 1180 rpm. This pump is rated at 6250 gpm (9 MGD) at 58’ TDH

For the purposes of the Master Plan it was assumed that the effluent pumps output capacity is approximately 80% of the total pumps capacities. Accordingly the effluent pumps output installed capacity is 32.51 MGD. The effluent pumps output firm capacity, with one pump out of service, is estimated at 26.0 MGD.

According to an Equipment Evaluation that was performed by HDR Engineering, inc. in 2001, Effluent Pump 1 was overhauled in 1997, Effluent Pump No. 4 was overhauled in 1998, Effluent Pump No. 2 was overhauled in 2000, and Effluent Pump No. 3 was recently overhauled.

The effluent pumps convey effluent through a Venturi flow meter located in a below-grade vault, and then through a 30-inch pipe to either the percolation ponds or to the Feather River.

The outfall pipe is approximately 5,900 feet of 30-inch and 600 feet of 24-inch ductile iron piping and Ameron wire-wrapped concrete coated piping. In the river portion of the outfall there are 40 3-inch diffusers.

A simplified hydraulic evaluation was performed to assess if the effluent pumps have sufficient head capacity to discharge the effluent through the existing outfall to the Feather River for the current conditions and it was concluded that the existing pumps have sufficient head capacity to convey the current peak flow of 10.8 MGD. Also it appears that the existing outfall will convey the peak flow up to 14 MGD, with no excessive velocities in the pipe and diffusers. However, the velocity in the existing 3-inch diffusers will be excessive for any flows higher than 14 MGD.

Effluent Pumps Condition Based on visual observations and discussions with plant staff, the pumps appear to be in good condition consistent with their recent overhaul.


Operation Limitations

The staff indicated that they have received noise complaints that appear to be related to the effluent pumps. The noise complaints came from residents approximately 300 yards to the south of the effluent pump station.

Conclusion It is concluded that the existing effluent pumps have sufficient capacity to meet current operations.

In addition, the noise emanating from the pumps has a negative impact on the residents.

Recommended Improvements A sound attenuation structure should be installed to alleviate the excessive noise emanating from the effluent pumps.

4.2.5 Solids Handling Processes

4.2.5.1 Dissolved Air Flotation Thickeners (DAFT) Technical Data The dissolved air flotation thickeners (DAFT) system was installed in 1974 and consists of two parallel tanks used for thickening waste activated sludge before sending it to the digesters.

The DAFT technical data are summarized in Table 4-10.

Table 4-10: DAFT Technical Data

Technical Data Units Tanks Number of Tanks - 2 Shape - Rectangular Surface Area sf 962 Depth feet 12 Total Volume gal 86,350

This system includes the following components: two air injection pumps, two top skimmers, two high pressure air compressors, and two thickened waste activated sludge (TWAS) pumps. The DAFT dissolution system was completely redone in 2003.


Operations Parameters The DAFT thickeners operation data are included in Appendix C5.

The DAFT operations parameters are summarized in Table 4-11.

Table 4-11: DAFT Operations Parameters

Operations Parameters Units Current Operation MOP 8 Criteria Hours of Operation h 24 Incoming Sludge Flow gpd 250,000 Incoming Sludge Concentration mg/l 5,400 Solids Loading Rate lb/sf/d 12 9.6-24 (a) Hydraulic Loading Rate gpm/sf 0.18 0.5 - 2.0 Thickened Sludge Concentration % 3.8 4

(a) without chemical addition The calculated hydraulic loading rate is within the recommended design values.

DAFT Condition Concrete Corrosion

High levels of hydrogen sulfide in the DAFT have caused accelerated corrosion of interior concrete surfaces. Only the interior surfaces of one of the two tanks have been coated. The coating in the North DAFT tank (closest to the digesters) has resolved the concrete degradation, but the South DAFT tank is in a structurally poor condition due to corrosion of the concrete surfaces.

Corrosion of the concrete is visible in the South DAFT tank in the form of exposed aggregate. Extensive cracking along interior concrete surfaces is also evident.

Tank Covers

In addition, the fiberglass covers on both tanks have deteriorated due to exposure to sunlight.

Mechanical Skimming Equipment

Overall, mechanical equipment is in poor operating condition. The chains for the upper and lower skimmers are replaced every two years, even though the manufacturer claims that these chains should last up to 10 years. The most recent replacement occurred in 2004. The chains in the North DAFT tank were replaced with new plastic chains while the chains in the South DAFT tank remained steel.

Sprockets and shafts on the chains fail frequently, and the non-corroding plastic chains installed in the North DAFT tank do not adequately support the applied load, causing it to fall off of the track frequently. Facility staff indicated that the maintenance frequency for this process is excessive and would like to switch to a less intensive method of thickening, such as parallel gravity belt thickeners.


DAFT Pumps

The thickened waste activated sludge (TWAS) pumps have been replaced at least 4 times in the last 25 years; a frequency which plant staff finds excessive. A spare pump is stored at the plant for use when one of the primary pumps is out of service for maintenance.

Operational Limitations The DAFT currently has sufficient capacity, providing all tanks are in service; however, supernatant quality tends to deteriorate as flows rise above 200 gpm increasing the potential for upset of the aeration basins. Although the current average flow to the DAFT is 174 gpm, flows exceed this amount when excess solids are wasted from the secondary clarifiers.

Performance of the DAFT system is reduced when one unit is taken out of service. The facility is unable to maintain effluent quality when a single tank is down for maintenance for longer than one week. At one point in time, the North DAFT tank was offline for 3-4 weeks, consequently resulting in increased MCRT to reduce wasting.

Conclusions It is concluded that the existing tanks are in poor operating condition due to failing covers and the overall tank corrosion. The equipment requires intensive maintenance.

It is also concluded that the existing DAFT have enough capacity to meet current operations despite the operational limitations listed above. It should be noted that the effluent quality may deteriorate when one unit is out of service for maintenance. In addition, the TWAS pumps require extensive effort to maintain.

Recommended Improvements Replacing the existing DAFT with a new DAFT system would not address the excessive staff effort operating and maintaining the units. Accordingly, replacement of the existing thickening facility by parallel gravity belt thickeners, centrifuges, or other mechanical thickening devices, would address the currently experienced excessive operational effort and provide the operators flexibility, especially when units need to be taken out of service for maintenance. A new bioscrubber would be required to treat the odors associated with the thickening process.

The existing TWAS pumps should be replaced with a different pump type that provides consistent flow during high head conditions, such as a positive displacement, or progressive cavity pump. Pump replacement should occur regardless of whether the DAFT system is replaced.

4.2.5.2 Digesters Technical Data Two anaerobic digesters were installed in 1974. The digesters technical data are summarized in Table 4-12.


Table 4-12: Digesters Technical Data

Technical Data Units Tanks Number of Digesters - 2 Diameter feet 80 Sidewall Depth feet 25 Total Volume gal 1,880,055

The digesters are currently operated in series with the West Digester operating as the primary digester and the East Digester as the secondary digester. The tanks are constructed of cast in place concrete and have steel floating covers. A digester building, housing sludge heating equipment and controls, is located between the two digesters.

The digesters pumping systems include 7 Pumps (2 mixing pumps, 2 recirculation pumps and 3 transfer pumps):

● Mixing pump #1 and #2: Hayward Gordon Pump, Dry Pit, Model XSC-16C, 20 HP, 870 rpm. Both pumps are rated at 4000 gpm (5.76 MGD) at 10’TDH and 4500 gpm (6.48 MGD) at 9’TDH

● Sludge Recirculation Pump #1 and #2: Wemco Pump, Dry Pit, Model D4K-LT-DPW, 7.5 HP, 1760 rpm. Both pumps are rated at 350 gpm (0.5 MGD) at 40’TDH

● Sludge Transfer Pump #1, #2 and #3: Moyno Pump, Dry Pit, Model 1SWG12HCDQ, 15 HP, 3500 rpm (pump #1 and #2) and 1170 rpm (Pump#3). Each pump is rated at 250 gpm (0.36 MGD) at 40 psi

Each mixing pump is dedicated to each digester. Accordingly, there is no stand-by pumping capacity available for either of the existing digester. Since the pumps are relatively new there is a low potential that these pumps will be out of service for an extensive period of time. In the future, however, a risk analysis should be performed to assess a need for the stand-by pump capacity.

The two recirculation pumps are not interconnected and they are operated continuously. In case of failure of one of these pumps, one pump cannot recycle the sludge from both digesters. Therefore, a spare pump should be provided for full redundancy.

The Sludge Transfer Pumps are for pumping the digested sludge to the dewatering equipment and are interconnected. Two pumps serve as duty pumps and one is a stand-by which can be used for pumping the sludge from either digester in case of failure of any duty pump.

Operations Parameters Both digesters are normally online; however, WTF staff is able to take one digester offline for maintenance purposes during periods when solids loading are low. Increased solids loading to the digesters caused by an increase in the plant influent solids concentration or influent flowrate will reduce the WTF’s ability to take a digester offline for routine maintenance without storing solids elsewhere in the facility.


The digesters operation data that were used for the digester performance evaluation are included in Appendix C6.

The operations parameters for both digesters are summarized in Table 4-13.

Table 4-13: Digesters Operations Parameters

Operations Parameters Units Current Operation KJ Guidelines Sludge Flow gpd 62,284 Incoming Sludge Solids Concentration % 3.25 Incoming TSS Load lb TSS/day 16,906 Incoming VSS Load lb VSS/day 14,594 VSS destroyed in Digesters lb VSS/day 5,580 VS Destruction % 53 60 Digested Sludge, % Solids % 2.25 Detention Time (a) days 30.2 > 20 Influent Sludge VS % 74 Digester VS Loading lb VS/cf-day 0.12 < 0.16 Digester Design Temperature Deg F 98 95 - 98 Sludge Recirculation Flow gpm 400

(a) Digester detention time is based on "active" volume only (does not include freeboard) The calculated VSS loading, VS destruction, and detention time are within the recommended design values.

Operations Limitations Located in the digester building are two dual-fired boilers, two hot water recirculation pumps, one transfer pump, two grinders, and associated controls. The original gas mixing system was removed in 2004 and replaced with an externally pumped mixing system. Also included in the improvements were two new boilers and heat exchangers, new sludge recirculation pumps, and gas piping modifications to convey gas to the cogeneration system. Each digester has a dedicated mixing pump located in pump pit on the south side of each digester. The cogeneration system provides sufficient waste heat to feed the heat exchangers; the hot water boilers have become a back-up system. Facility staff indicated that the digesters are currently performing well overall, without any significant maintenance or operational limitations.

Prior to the mixing system upgrade, the facility staff was taking the digesters offline every 5 to 6 years to remove accumulated grit. It is understood that operation of the new mixing system will keep debris and grit in suspension and reduce accumulation in the digesters, thereby extending the period between cleanings. This frequency of maintenance is acceptable to maintenance staff.


Digester Covers

The key operational challenge is the presence of sludge on the top of the digester covers, which is a source of odors and presents an attractant for vectors. Facility staff has experienced problems with sludge filling the voids on the underside of the floating covers and spilling over onto the deck of the covers. The floating steel covers have never been changed, but require new coatings approximately every two years. Facility staff would prefer that the floating covers be replaced with fixed covers in order to reduce maintenance costs and exposure to sludge.

Pumps

The externally-pumped mixing system provides mixing of material at the bottom of the digester; however, no provisions are in place to mix the upper layer of the digester, which generally consists of scum and foam. When the existing floating covers are replaced with fixed covers, an upper discharge nozzle should be installed in each digester to provide for adequate mixing of the entire digester both vertically and horizontally.

The other pumps and appurtenances associated with the digesters, including the recirculation pumps, sludge transfer pumps, boilers, and heat exchangers are in good condition and require minimal maintenance for continued operation.

Struvite

Struvite was encountered in various small diameter piping and attached to the recirculation pump impellers when the digesters were last offline for routine maintenance. Struvite, however, has not been encountered in the heat exchangers, and has not caused any major hydraulic restrictions where it is present. Elimination of struvite is not a priority for facility staff.

Cogeneration System

Digester gas that is produced in the secondary digester is conveyed to the cogeneration system. The cogeneration system consists of microturbines, gas compressors, chillers, a scrubber, and other associated equipment. Facility staff indicated that the gas compressors are fouling due to the use of digester gas rather than natural gas. They suspect that these compressors are sized for use with natural gas only.

Scrubber

Facility staff regenerates the scrubber media approximately every 6 to 12 months to maintain sufficient hydrogen sulfide removal upstream of the microturbines. This type of media can only be regenerated three times before requiring complete replacement. Facility staff would like to replace this unit with an alternative scrubber system that has an extended lifetime or requires less frequent regeneration.

The outlet pipe was in the media and not above it. The inlet and the outlet piping have been replaced and this should resolve the issue in the scrubber media. The need for replacement of the scrubber media will be reevaluated based on the performance of the newly installed piping system

Waste Gas Burner

Gas that is not conveyed to the cogeneration system is redirected to the waste gas burner. The burner is located on the south side of the West digester and was installed in 1974. Facility staff


indicated that the burner is in poor operating condition and should be replaced as part of the next phase of facility improvements.

Conclusion It is concluded that the existing anaerobic digestion facility is adequate to meet current operations.

The following conclusions relate to the maintenance of the existing digesters:

● Floating steel covers allow sludge to accumulate on the cover, consequently developing odors and attracting nuisance pests.

● Struvite was encountered in various small diameter piping but its elimination is not a priority for the facility staff.

● The gas compressors in the cogeneration system are fouling due to the use of saturated digester gas rather than natural gas. Digesters gas conditioning improvements are being made.

● The scrubber media require extensive maintenance and may need to be replaced with an alternative scrubber system

● The waste gas burner is in poor operating condition. The gas burner will need to be changed because of the new regulation

● The existing digester mixing system does not adequately agitate the upper scum layer due to existing location of the nozzles (too low).

Recommended Improvements Based on the noted operational limitations the following digester improvements are recommended:

● Replace floating covers with fixed steel or concrete covers in order to expand the capacity of the existing digesters and eliminate sludge overflow.

● Replace the waste gas burner.

● Add an upper discharge nozzle to the mixing system at each digester.

4.2.5.3 Dewatering System Technical Data The dewatering process at the treatment facility consists of two belt filter presses, a sludge cake conveyor, a polymer feed system, and an odor control system for the dewatering building.

The belt filter presses technical data are summarized in Table 4-14.


Table 4-14: Belt Filter Presses Technical Data

Technical Data Units Tanks Number of Filter Presses none 2 Width m 2

According to an Equipment Evaluation that was performed by HDR Engineering, inc. in 2001, the original belt filter press was partially overhauled in 1999. A second belt filter press was installed in early 2005. The second press provides full redundancy. In addition, the facility has the option to bypass the belt filter presses and discharge digested sludge directly to the sludge drying beds at approximately 1.75% solids concentration.

Operations Parameters Both filter presses were designed for the sludge flow of 130 gpm. Based on the operation experience the filter presses can handle the range of flows from 100 gpm to 175 gpm. Only one press is in service at a time. Facility staff is able to maintain a constant discharge of 15% cake with either unit. Staff has expressed a desire to replace the older unit with a new unit to gain the benefit from the inherent mechanical improvements of the new model.

The BFP operations parameters are summarized in Table 4-15.

Table 4-15: BFP Operations Parameters

Operations Parameters Units Current Operation KJ Guidelines Flow capacity per day gpd 69,364 Flow capacity per minute gpm 96 Days of operation days/wk 4 Hours of operation h/day 12 Polymer dose lb/dry ton 15 Max 15 Total capacity gpm 48 100 Solids loading rate lb/hr 1,085 1,600 The calculated solids loading rate is within the recommended design values.

BFP Condition Staff indicated that maintenance has not been significant for the original press. The belt on the original unit is replaced every one to two years, which is normal for this make and model. A new cake conveyor has been installed to handle the discharge from both units. An improved HVAC system collects the air from the room and discharges to a nearby biofilter. Minor corrosion is visible at welds in the galvanized steel frame of the original unit. Other equipment on the unit, such as rollers and guides, have experienced minor wear as expected for this type of mechanical process.

The plant staff indicated that this belt filter press is planned to be refurbished.


Conclusion It is concluded that the existing dewatering system is adequate for current operations.

Recommended Improvements Refurbish the original belt filter.

4.2.6 Odor Control Facility Three biofilters are currently installed at the facility to remove hydrogen sulfide from the following processes:

● Headworks ● Primary clarifiers ● Dewatering building There are no specific requirements for the degree of air treatment, although constant flow through the biofilters is standard practice. Staff indicated that these are relatively simple, low maintenance systems consisting of fiberglass ducting and high flow, low pressure fans and the biofliter media.

4.2.7 Septage Handling System Septage is currently discharged to the plant drain system in front of the digester building. The plant drain line connects to the plant influent line upstream of the headworks building.

A separate septage handling system is recommended to reduce the amount of rocks and debris prior to entering the headworks.

4.2.8 Main Liquid Process Piping A simplified hydraulic evaluation was performed to confirm the hydraulic capacities of the existing piping.

The existing liquid piping considered during this evaluation included:

● 24-inch grit basin influent piping ● 24-inch-36-inch grit basin effluent piping ● 30-inch primary clarifier influent piping ● 27-inch-42-inch primary clarifier effluent piping ● 20-inch aeration basins influent piping ● 20-inch and 24-inch by-pass aeration basin effluent piping ● 24-inch secondary clarifier influent piping ● 24-inch-30-inch-36-inch secondary clarifier effluent piping


The piping was evaluated for both installed and firm capacities. The firm capacity is defined as the capacity when one tank or a unit is taken out of service for maintenance or repair.

Based on this evaluation, it appeared that all the existing piping within the WTF have enough capacity to convey the current peak flow, with freeboards available between all unit processes. The hydraulic evaluation results are summarized in Table 4-16.

Table 4-16: WTF Liquid Piping Capacity

Process Units Liquid Level Units

Installed Capacity Evaluation

Firm Capacity Evaluation

10.8 MGD

10.8 MGD

Dechlorination Tanks ft 45.59 45.59 Secondary Clarifier Effluent Channel ft 46.15 46.15 Secondary Clarifier(a) ft 48.37 48.37 Available Freeboard (Secondary Clarifier)

ft 2.22 2.22

24-inch by-pass

20-inch 24-inch by-pass

20-inch

Aeration Basins Effluent Channel ft 49.33 49.8 50.47 51.5 Aeration Basins(a) ft 52.96 52.96

52.96 52.96

Available Freeboard (Aeration Basin)

ft 3.63 3.14 2.49 1.43

Aeration Basins Inlet Box ft 53.62 54.43 Primary Clarifier Effluent Channel ft 54.44 55.24 Primary Clarifier(a) ft 57.37 57.37 Available Freeboard (Primary Clarifier)

ft 2.93 2.13

Liquid Level in Primary Clarifier Split Structure

ft 54.83 56.11

Existing Weir Elevation in PC Split Structure

ft 58.07 58.07

Available Freeboard ft 3.24 1.96 Liquid Level in Grit Basin ft 55.32 56.59 Existing Weir Elevation in Grit Basin ft 60.56 60.56 Available Freeboard ft 5.24 3.97

(a) Liquid levels in structures with long weirs were assumed at the same elevation as shown on HDR drawings (WTF Upgrades, July 22, 2002; Contract #02-05; Dwg G006) for the flow of 9 MGD.


4.2.9 Yard Piping No. 3 plant water (plant treated effluent) is used for foam control spray water and irrigation purposes. The No. 3 water pumps are located at the north end of the chlorine contact tanks, with one high pressure, and one low pressure pumps available.

The water pressure at the north end of the facility is currently insufficient. Facility staff believe that during recent improvements to the facility utilities, a portion of the No. 3 water distribution system was redirected, eliminating the high pressure loop that was originally in place.

4.3 Grease Receiving Station Plant staff would like to incorporate a grease receiving station into future improvement plans for the WTF. The system would allow grease to be offloaded into a separate tank and then be pumped directly into the primary digester for gas production during the peak daily energy rate periods. Grease receiving would be entirely separate from a septage system.

4.4 Summary of the Capacity of the Unit Processes and Main Liquid Treatment Piping

The installed capacity is defined as the capacity of a unit process system, with all tanks or units in operation. The firm capacity is defined as the capacity of a unit process system when one tank or a unit is taken out of service for maintenance or repair.

Based on a simplified hydraulic evaluation performed to confirm the hydraulic capacities of the existing piping the maximum available capacity of the main liquid treatment piping was estimated. A summary of the currently available capacities is provided in Table 4-17.

Table 4-17: Main Liquid Treatment Piping Capacity

Liquid Piping Installed Capacity

(MGD) Firm Capacity

(MGD) 24-inch-36-inch grit basin effluent piping 20.7 14.4 30-inch primary clarifier influent piping 23.4 14.4 27-inch-42-inch primary clarifier effluent piping 19.8 15.3 20-inch aeration basins influent piping 26.1 16.2 20-inch aeration basin effluent piping 19.8 11.7 24-inch By-pass Aeration Basin Effluent Piping 24.6 16.2 24-inch secondary clarifier influent piping 45 15.2 24-inch-30-inch-36-inch secondary clarifier effluent piping 13 12.5 The existing unit process capacities were established through a desktop evaluation of processes using the commonly used design criteria from literature (Metcalf & Eddy, Wastewater Engineering- Treatment, Disposal, Reuse). A summary of the estimated capacities is provided in Table 4-18.


Table 4-18: Summary of the Unit Process Capacities

M&E Design Parameters

Parameters Units Current Operation

(2000-2004) Firm Capacity

Calculated Installed Capacity (based on M&E Design

Parameters) Range Typical Primary Clarifiers Number of Operating Tanks - 2 1 2 Equivalent Average Plant Flow – Based on Limiting Parameter (Average Annual Flow)

MGD 6.0 6.4 12.7

Overflow Rate at Qavg gpd/sf 472 1000 1000 800-1200 1000 Aeration Basins Number of Basins - 3 Theoretical (based on all installed basins) Number of Operating Basins 2 2 3 Equivalent Average Plant Flow – Based on Limiting Parameter (Average Annual Flow) (PE + RAS)

MGD 9.42 12.2 (theoretical) 18.2 (theoretical)

Existing conditions (based on available basins – No. 2 and 3 only)

Number of Operating Basins 2 1 (Existing conditions)

2 (Existing conditions)

Average Flow to Basins (average annual flow) MGD 9.42 6.1 12.2

Detention Time at Qavg h 3.1 2 2 1-3 1-2 (based on other plants for pure oxygen)

Secondary Clarifiers Number of Tanks - 3 2 3 Number of Operating Tanks - 3 Equivalent Average Plant Flow – Based on Limiting Parameter (Average Annual Flow)

gpd 9.42 7.4 11.2

Overflow Rate at Qavg gpd/sf 464 550 550 400-700 550


M&E Design Parameters

Parameters Units Current Operation

(2000-2004) Firm Capacity

Calculated Installed Capacity (based on M&E Design

Parameters) Range Typical Chlorine Contact Tanks Number of Basins - 2 1 2 Equivalent Average Plant Flow – Based on Limiting Parameter (Average Annual Flow)

MGD 6.0 10.1 24.1

Detention Time at Qavg Min 111 30 30 30-120 55 Dissolved Air Flotation Thickener Number of Units None 2 1 Sludge Flow Rate Gpd 250,000 213,847 427,694 Solids Loading Rate lb/sf/d 12 20 20 9.6-24 Equivalent Average Plant Flow based on Limiting Parameter (average annual flow) MGD 6.0 5.1 10.2

Digesters Number of Digesters None 2 1 Sludge Flow Rate Gpd 62,284 62,668 125,337 Equivalent Detention Time Days 30.19 15 15 15-30 15 Equivalent Average Plant Flow based on Limiting Parameter (average annual flow) MGD 6.0 6.05 12.1

Belt Filter Press Number of Units None 2 1 Influent Solids Concentration % 1.75 Flow Capacity Gpd 69,364 102,240 204,480 Solids Loading Rate lb/hr 844 1243 2487 2500-3500 3000 Equivalent Average Plant Flow based on Limiting Parameter (average annual flow) MGD 6.0 8.9 17.7

Note: The installed and firm capacities were calculated based on the historical plant data for the period 2000 to 2004.


4.5 Summary of the Condition of the Unit Processes A summary of the WTF condition assessment is summarized in Table 4-19.


Table 4-19: WTF Installed Capacity and Condition Assessment Findings

Unit Process

Installed Capacity

(MGD)

Firm Capacity

(MGD) Limitations Recommended Improvements

Screening Facility 24 12 None

Pumping Station 19.0 14.5 None

Grit Basin 20.0(a) 0 • Lack of redundancy

• Generation of odors.

• Install a new vortex-type grit unit

• Install odor control facility

Primary Clarifiers 12.7 6.4 No redundant unit: The existing clarifiers have sufficient capacity to meet current operating conditions, providing both tanks are in operation.

Provision of an additional primary clarifier would offer the operators more flexibility during maintenance without jeopardizing plant performance

Aeration Basins Theoretical (3 basins installed) Existing Conditions (2 basins available for operation)

18.2

12.2

12.2

6.1

• The amount of sludge that can be returned to the head of the aeration basins is limited by the configuration of the aeration tank inlet box and the size of the incoming pipes.

• Foam trapping observed in the aeration basins.

• No flexibility in operation of the aeration basins due to basin number 2 not having enough oxygen capacity and basin number 1 being out of service.

• The interior concrete surfaces show corrosion

• The existing aeration basins have sufficient capacity to meet current operating conditions, providing two basins are in operation.

• Re-route the RAS piping

• Basin number 1 should be considered for reparation.

• Install mechanical equipment in Basin number 1

• Repair the concrete in the aeration basins

• Increase Basin 1 and 2 oxygenation capacity.

Oxygen Supply(b) 28 tons/day 21 tons/day


Unit Process

Installed Capacity

(MGD)

Firm Capacity


Secondary Clarifiers 11.2 7.4 • Effluent quality problems when one clarifier is removed from service.

• Algae accumulation in the 90-foot clarifier launders. It is higher than the algae accumulation in the 100-foot diameter clarifier

• Suction valves for RAS pumps 1 through 3 are difficult to operate

• The existing clarifiers have sufficient capacity to treat the current flow and loads, providing all clarifiers are in operation.

• Addition of a fourth secondary clarifier.

• Rehabilitation and replacement of the launder on the 90-foot diameter clarifiers

Chlorine Contact Tanks 24.1 10.1 • The caustic feed system piping is deteriorated and would require replacement.

• The bisulfite tank capacity is inadequate and should be replaced with a tank of larger capacity

• Replace the caustic feed system piping

• Replace of existing bisulfite tank with a larger one

Effluent Pumps(c) 32.5 26.0 Noise from the pumps has a negative impact on the residents

Install a sound attenuation structure

Sludge Thickening

10.2 5.1 • The existing equipment requires intensive maintenance

• Major corrosion of tanks

• The fiberglass covers on both tanks are in a poor condition

• Mechanical equipment is in poor operating condition.

• The effluent quality significantly deteriorates when one unit is down for maintenance.

Replace the existing thickening facility by parallel gravity belt thickeners, centrifuges, or other mechanical thickening devices


Unit Process

Installed Capacity

(MGD)

Firm Capacity


Digesters 12.1 6.0 • Failure of the floating covers on the digesters

• Struvite was encountered in various small diameter piping

• The gas compressors in the cogeneration system are fouling due to the use of digester gas rather than natural gas. Improvements are being made.

• The waste gas burner is in poor operating condition

• Replace the floating covers with fixed steel or concrete covers in order to expand the capacity of the existing digesters and reduce the issues caused by exposed sludge.

• Replace the waste gas burner.

BFP 17.7 8.9 No limitations observed Refurbish the original unit

Outfall 14.0 14.0 No limitations identified

Odor Control Facility No limitations observed None

Water 3 Pressure The water pressure at the north end of the facility is currently insufficient

Loop pipeline.

Septage System A large amount of rocks and debris are entering the headworks

Install a separate septage handling system

Others

Install a new grease facility

(a) Peak flow capacity. (b) Supplemented with LOX at 11,000 gallons capacity (c) This defines the installed and firm capacity of the effluent pumps only.


4.6 Electrical Evaluation

4.6.1 Technical Data Based on the review of the available single line diagrams and load data, the electrical system technical data are summarized, as follows:

Overview The existing service to the Facility is derived from PG&E system and rated at 12kV, 3 phase, 3 wire with 1200 A bus and 1000A main circuit breaker.

The Service Switchgear distributes power to several unit substation centers at various areas of the plant. Five such units each consisting of a 12 kV primary switch, and oil filled transformer which steps down the voltage to 480V, 3 phase that is used to feed plant’s loads from several Motor Control Centers (MCC).

Standby Power At each distribution center, a standby generator is provided to serve loads in case the PG&E service fails. The generators were sized for peak loads and range from 300 to 900 kW. Automatic transfer switches are provided for transferring plant’s load from normal to standby power.

4.6.2 Evaluation A summary of the existing loads and the projected peak demand at 480 Volts are summarized in Table 4-20.

Table 4-20: Summary of Existing Loads Conditions at 480 Volts

Item Load Description HP FLA kVA PDF PD FLA PDkVA Transformer

(kVA) Generator kW (kVA)

1 Chlorine Building 837 667 0.75 628 500 1000 400 (750) 2 RAS Sludge Building 506 403 0.8 405 323 1500 600 (750) 3 Digester Building 506 403 0.67 339 270 1000 300 (375) 4 Headworks 1091 591 0.64 698 378 1000 600 (750) 5 Oxygen Generator 1638 1305 0.72 1179 940 2000 900 (1125) Totals 4578 3369 0.7 3249 2410.7 Total at 12 kV 183 130 313

Where: FLA : Full Load Amps PDkVA : Peak Demand kVA kVA : Kilovolt amps PDFLA : Peak Demand FLA PDF : Peak Demand Factor Based on this summary, the following can be concluded.


Normal Power For the current conditions the calculated peak demand is 130 A which is well below the 1000A service available at the Main service Switchgear. It is clear that the plant’s has adequate spare capacity that can be used for the operation of any appropriate additional units. A more thorough review and evaluation of the condition of the equipment and feeders would be required during the design of the specific expansion projects.

Distribution Transformers Based on peak demand data, all distribution centers are underloaded, some are below 50% under peak conditions. The existing transformers have available spare capacity that can be used for future additions.

Standby Generators The standby generators are adequate for the current loads and according to staff are in a good condition.

Some generators have spare capacity available. Depending on motor stating methods and load additions, some of theses generators could provide standby power to future additions. This has to be evaluated in more details on a case by case basis.

Service Equipment The existing 12 kV equipment includes outdoor metal clad switchgear consisting of circuit breakers that feed the major distribution centers. The Switchgear was constructed around 1974.

Operational Limitations According to plant’s staff, the area where the switchgear is located is subjected to flooding which could cause a fault that could disrupt the service to the plant.

In addition, while the PG&E services are fed from two separate lines, these two lines originate at the same substation. Switching of these lines is done by PG&E using transfer switches on their poles.

To relocate the existing service switchgear would include constructing new underground conduit system and method to tie to existing feeder once the switchgear is relocated. This could subject the plant to extended power outage. Another option includes installing new switchgear that can be installed at a new location and making a gradual tie to existing feeders. This option would require shorter outages during the transition.

Recommended Improvements Considering the age of the switchgear, it is approaching the end of its useful life and according to plant staff, spare parts are hard to get. Therefore, we recommend replacing the switchgear with new switchgear that can be installed at a location away from potential flooding.

Site Lighting Site lighting includes post top lights and door mounted fixtures that are installed on building walls. The existing light fixtures can be upgraded to more efficient lighting systems.

Section 4: Wastewater Treatment Facility Process Evaluation · Wastewater System Master Plan Update...

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Transcript of Section 4: Wastewater Treatment Facility Process Evaluation · Wastewater System Master Plan Update...