0067

TENNESSEE VALLEY AUTHORITY

Office of Natural Resources and Economic Development

DESIGN AND PERFORHANCE OF THE ARTIFICIAL WETLANDS

WASTEWATER TREATHENT PLANT AT ISELIN, PENNSYLVANIA

BY

James T. Watson, Foster D. Diodato, and Hilt Lauch

Prepared for Presentation at the

Aquatic Plants for Water Treatment and Resource Recovery Orlando, Florida, July 20-24, 1986

Conference on Research and Applications of:

Chattanooga, Tennessee

July 1986 (revised December 1986)

This article is a Government publication and is not subject to copyright.

DESIGN AND PERFORMANCE OF THE ARTIFICIAL WETLANDS WASTEWATER TREATMENT PLANT AT ISELIN, PENNSYLVANIA

J. T. Watson1, F. D. Diodato2, and M. Lauch3

ABSTRACT

The Tennessee Valley Authority (TVA) is demonstrating the use of a

marsh/pond/meadow system for treatment of municipal wastewat.ar as a low

cost system for meeting stringent National Pollutant Discharge

Elimination System (NPDES) discharge limitations. The system is modeled

after a small system at Iselin, Pennsylvania. The Iselin system was

designed and constructed by the Pennsylvania Department of Environmental

Resources, which has provided the design information and monitoring

results to TVA.

The Iselin wetlands system has a design capacity of 12,000 gpd and

consists of four key components: an aerated pond, a cattail (Typha)

marsh, a stabilization pond, and a reed canary grass (Phalaris) meadow.

Data are available on each component for each month since Harch 1983.

Average effluent concentrations for key parameters for the first 31

months of operation are: biochemical oxygen demand, 7.4 mg/l; total

suspended solids, 19 mg/l; ammonia nitrogen, 3.3 mg/l; total phosphorus,

2.6 mg/l; and fecal coliforms, 150/100 ml.

KEY WORDS

Warsh/pond/meadow treatment system; cattails (Typha) , duckweed (Lema) and reed canary grass (Phalaris); low cost system for NPDES permit compliance.

1 Program Manager, Tennessee Valley Authority, Water Quality Branch, 248 401 Building, Chattanooga, TN 37401

2 Chief, Sewage Facilities Planning Section, Pennsylvania Bureau of Water Quality Hanagement, P.O. Box 2063, Harrisburg, PA 17120

Chief, Facility Plan Development Unit, Pennsylvania Bureau of Water Quality Hanagement, P.O. Box 2063, Harrisburg, PA 17120

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INTRODUCTION

Small communities nationwide are having extreme difficulties in

providing affordable wastewater disposal that will meet state and federal

water quality regulations. Conventional and "hi-tech" methods are

generally too expensive to construct and operate.

the Kentucky Division of Water, the Tennessee Valley Authority has

initiated a project in Benton, Hardin, and Pembroke, Kentucky, to

demonstrate how small communities can provide low cost, high quality

sewage treatment with artificial wetlands. Three types of artificial

wetlands systems will be demonstrated--a marsh/pond/meadow (HPH) system,

a root zone system, and a gravel marsh system. The focus of this paper

is on the marsh/pond/meadow system.

In cooperation with

One of the difficulties TVA encountered during the planning and

design of the demonstration is the scarcity of design criteria and

performance data in the literature for artificial Wetlands. The

information that is available when viewed from a design engineer's

perspective is sketchy, at times contradictory, and generally inadequate

for determining details needed in a wetlands system to achieve various

NPDES permit limits. TVA is addressing this problem with a technology

transfer objective. A design manual identifying key criteria and their

bases will be prepared and widely distributed.

During TVA's search for information, the Pennsylvania Bureau of

Water Quality Management (BWQM) informed TVA of the data they were

collecting on a marsh/pond/meadow system at Iselin, PA.

was provided to TVA, computerized and returned to the BWQM along with an

analysis and interpretation of the system's performance. This report

summarizes the data analyses.

The data base

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TREATMENT CONCEPT AND SYSTEM DESIGN

The treatment facility serves 158 of the 300 residents of Iselin.

It consists of six components in series: pretreatment (comminution and

bar screens), an aeration cell, a cattail marsh, a stabilization pond, a

reed canary grass meadow, and a chlorination unit.

system is summarized in Table 1 and Figure 1.

The design of the

The comunitor and bypass screen removes large solids.

cell provides primary treatment through bacterial metabolism and

minimizes odors from any stale sewage entering the system.

serves as the heart of the system, providing treatment primarily through

bacterial metabolism with sedimentation, filtration, and adsorption of

solids also being important.

of the wastewater. The sand, gravel, and plants provide substrate and

conditions conducive to establishing and maintaining extremely high

concentrations of bacteria and other microorganisms. The two primary

benefits of the vegetation are believed to be to provide oxygen to the

bacteria within the root zone of the plants and to maintain longterm

permeability of the substrate.

The aeration

The marsh

The system is designed for subsurface flow

The pond is contiguous with the marsh. Riprap is used to minimize

sand and gravel losses to the pond.

pond include bacterial metabolism, plant (algae and duckweed) uptake of

nutrients, and volatilization of ammonia nitrogen during summer.

Important treatment processes in the

The meadow serves as a polishing unit. Algae from the pond are

filtered out and additional removal of organics and nutrients are

achieved through the same processes occurring in the marsh. A

chlorinator assures that permit limits for fecal coliforms are met.

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The design of the marsh and meadow was based on the results of a

similar system at the Village of Neshaminy Falls (SMC-Martin, 19801,

which is a commercial housing development near Philadelphia. This system

in turn was based on the original pioneer work performed at the

Brookhaven National Laboratory (Small, 1977, and Hendrey, et al., 1979).

SYSTEM COSTS

The construction costs for the system was $174,085 (1982 dollars) 3 which equates to $8.70/gpd ($0.033/m /day) of treatment capacity. This

cost is believed to be unusually high for an artificial wetlands system,

and it results partly from site restraints, e.g. borrow excavation and

rolled embankment quantities were high.

The unit cost for potential wetlands sites in the Tennessee Valley

is expected to be much lower. The estimate for the HPH system at

Pembroke, KP, is less than $2/gpd ($0.0076/m /day). The unit cost for

conventional, mechanical-type plants recently installed in Kentucky

ranges from about $3 to $15/gpd ($0.011 to $0.057/m /day).

3

3

The system is operated and maintained by a utility contractor.

fees have averaged $120.39/yr per customer over the first 43 months of

operation.

of January 1986. These fees include maintenance (mowing) costs for

another demonstration project, a comunity on-lot disposal system

(COLDS). The mowing costs have been extremely high. Operation and

maintenance costs are expected to be much lower for the TVA projects,

roughly equivalent to the costs of lagoon systems.

User

Monthly fees have been raised from $8.00/mo to $12.60/mo as

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PERFORMANCE EVALUATION

This report will summarize the data for key parameters often

regulated by NPDES permits: biochemical oxygen demand, total suspended

solids, fecal coliforms, ammonia nitrogen, and phosphorus. The data are

tabulated in Table 2. Effluent concentrations are depicted in Figure 2.

Performance is evaluated by parameter for each component and for the

total system. Concentration, rather than loading, forms the primary

basis for the evaluation because flow is monitored only on an

instantaneous basis at the influent and effluent. Influent flows are

highly variable and instantaneous reading may not be representative.

However, instantaneous readings on the effluent are probably

representative because the system effectively equalizes the flow.

loadings are identified, they are based on the average daily effluent

flow for the period of record (6,800 gpd(26 m /day)}.

When

3

Evapotranspiration is sufficiently large during the summer to

substantially reduce the discharge flow, probably by about 25-30% of the

influent flow. However, rainfall, storm runoff (including snow melt)

from the surrounding land, and groundwater seepage into the system at

least partially offsets the evapotranspiration on a net annual basis. 3 The average influent and effluent flows were 6,300 gpd (24 m /day)

and 6,800 gpd (26 mJ/day), respectively, from September 1983 through

September 1985. Thus, the system is operating at less than its design 3 capacity of 12,000 gpd (45 m /day).

two parallel marsh and meadow cells were used to treat the flow;

consequently, these components were typically operating near or slightly

Host of the time only one of the

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above their design hydraulic capacity. Cells were switched occasionally

which further complicates the evaluation. The aeration basin and pond

were typically loaded at about half of design hydraulic capacity.

Another key variable that must be considered in evaluating the

performance of the marsh is the type and amount of vegetation that was

present.

reproduce very well.

Kentucky Fescue 31 due to overseeding. In Cell 2, cattails were more

abundant but still sparse overall. The poor stand of cattails may be

caused by the inability to flood the cells and the toxic effect of high

ammonia concentrations (Gersberg, et al, 1986). Consequently, the data

for the marsh reflect a much less than ideal situation from a vegetation

perspective.

Although cattails were planted in each cell, they did not

In Cell 1, the predominant type of vegetation was

During July 1985, pond water was recycled back to the head of the

marsh for a three week period for one hour per day beginning July 10,

1985. Also, on August 15, 1985, boards were placed across marsh cell #I

to flood the cell and improve cattail growth (cattail density is still

sparse). These operational changes affect component performance.

An additional factor to consider in evaluating performance is the

operation of the aerators in the aeration basin. A single surface

splasher aerator was used until it failed in mid-December 1984.

Hechanical aeration was not restored until Hay 1985, when two aspirator

aerators where placed in service. Although the design of the system and

the monitoring program does not allow a sound technical evaluation of the

effects of the lack of aeration, the system performance did not appear to

I

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decrease during this period. This raises the question of the need for

the aerators, but the Iselin data are not sufficient to answer the

question.

The data are separated into two groups, "winter" data and "summer"

data, to evaluate seasonal differences. The winter season is defined as

November through April and summer is defined as Hay through October.

This parallels the seasons used by the Kentucky Division of Water for

setting effluent limitations for ammonia nitrogen.

normally less stringent during winter than summer.

Limitations are

Biochemical Oxygen Demand

The system reduces the BOD by an average of 97% (from 260 mg/l t o

7.4 mg/l). Reduction rates are similar for winter (96%) and summer

(98%). Only one month showed an average BOD above 30 mg/l (Feb. 1984,

32 mg/l), and this probably resulted from unrepresentative data because

the concomitant BOD at the point of discharge to the receiving stream was

very low. Consequently, the data indicate that the system is capable of

meeting EPA's secondary treatment standard (30 mg/l) essentially 100% of

the time. The average effluent quality exceeds secondary quality.

Each component of the system except for the pond significantly

reduces.BOD. The aeration basin and the marsh reduce BOD by about the

same quantity (around 6.7 lbs/day(3000 g/day) and 7.0 lbs/day (3200

g/day), respectively, assuming an average flow of 6,800 gpd} but the

marsh has the highest reduction percentage (88% versus 46%). The meadow

has the second highest reduction percentage (64%). The pond typically

increases BOD due to algal production.

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Differences between winter and summer reductions were relatively

small within a component except for the aeration basin which ranged from

15% during winter to 67% during summer.

factors: the difference in bacterial metabolism between winter and

summer, and the sampling methods used.

at all locations. The influent sample represents instantaneous

conditions and is not as representative of average concentrations as the

effluent sample because the basin effectively mixes and equalizes the

This is attributed to two

Single grab samples are collected

sewage.

Differences are large during each season both within a component and

from one component to another. For example, BOD reductions in the marsh

varied from 19 to 96% during summer.

reductions between the marsh and pond was 79% versus -22%. respectively.

However, the meadow typically acts as a safety net for the system so that

the wastewater discharged to the receiving stream consistently meets

permit limits.

The variation between summer

Total Suspended Solids

The system removes an average of 89% of the suspended solids (from

180 mg/l to 19 m g / l ) . The reductions are similar for winter (88%) and

summer (90%).

months of available data exceeded 30 mg/l; however, data at the final

monitoring point prior to discharge to the receiving stream revealed that

only one month exceeded 30 mg/l (August 1984, 36 mg/l). The high values

for the meadow effluent probably result from the sampling procedure.

The average effluent concentration for six of the 28

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Samples are obtained from weep holes, and solids may be scraped from the

sides or resuspended within the rock media due to the sampling personnel

walking over the cell. Consequently, the data indicate that the system

meets EPA's secondary treatment standard (30 mg/l) more than 90% of the

time (including the start-up period). The average effluent quality is

much better than secondary quality. The remaining solids probably

consist of algae and plant fragments rather than sewage particles.

Concentrations are generally highest during spring and fall when the

system's vegetative growth dynamics are in the greatest state of flux.

The marsh and the meadow are the two components that effectively

reduce solids concentrations. The marsh removes an average of about

18 lbslday (8,200 g/day) or 86% of the solids. The meadow removes about

2 . 4 lbs/day (1,100 g/day) or 69% of the remaining solids.

The largest variations occurred in the aeration basin and the pond,

ranging from increases of greater than 1,000% to reductions of 90%. This

reflects the bacterial and algal growth dynamics occurring within these

components. Very few increases in suspended solids occurred in the marsh

and meadow, reflecting the effectiveness of the rock and sand media for

filtering and settling the solids. The solids are believed to be

biologically stabilized into a permeable compost within the system.

Fecal Coliforms

Reductions in fecal coliforms approach 100% (from 1,800,000/100ml to

150/100ml). The system is highly effective during both winter and

summer. Only one spike in excess of 1,000/100ml occurred in the monthly

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geometric means for the meadow effluent.

200/100ml, which is a typical, average permit limit, during only 5 of the

29 months that were monitored. All of these occurrences were during fall

and winter months and may be related to small mammals wintering within

the system. Nests occasionally had to be removed from the meadow weep

holes.

Geometric means exceeded

All components except the aeration basin effectively reduce fecal

coliforms during each season. Host of the organisms are reduced in the

marsh with the pond and meadow serving as polishing components for the

remaining organisms. The reductions are attributed to natural die-off in

an unfavorable environment and the toxic effect of root excretions on

enteric organisms.

These results are of special significance since they indicate

artificial wetlands systems can be designed to either eliminate the need

for chlorination or minimize the chlorine dosages needed to meet permit

limits. This will provide cost and operational benefits to communities

using the technology and also benefit the receiving stream by avoiding or

minimizing the toxic by-products of chlorination. The need for

dechlorination will also be eliminated or reduced.

Ammonia Nitrogen

The system removes an average of 77% of the ammonia (from 14 mg/l to

3.3 mg/l) contained in the raw sewage. Removal is better during the

summer (93%) than winter ( 5 4 % ) . However, these removal rates have little

meaning because of the conversion of organic nitrogen to ammonia in the

aeration basin and marsh. The effectiveness of the system for ammonia

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removal is based primarily on the effluent concentrations. The average

effluent concentration is 3.3 mg/l. The concentrations vary seasonally.

During the summer the average is 1.2 mg/l and during winter the average

is 5.8 mg/l.

6.0 mg/l). Only two months exceeded 10 mg/l (January 1984, 15 mg/l, and

February 1984, 13 mg/l).

During summer only one month exceeded 4 mg/l (October 1984,

The components that effectively reduce ammonia concentrations are

the marsh, pond, and meadow. Ammonia in the marsh is converted to

nitrites and nitrates (nitrification). Reductions amount to about 56% by

concentration and 0.96 lb/day (4,400 g/day) by mass. In the pond

nitrification and volatilization (loss of ammonia as a gas) both appear

to be important. The average reduction in concentration is the highest

in the pond (60%), but on a mass basis the reduction is only about half of

that occurring in the marsh (0.44 lb/day(200 g/day)}. Nitrification

continues in the meadow with a 36% reduction in ammonia.

Differences between winter and summer reductions were relatively

small except for the pond.

winter to 86% during summer.

attributed primarily to volatilization (algal production during the

summer results in pH values as high as 11.2; the summer average was

9.2). During each season, the variation was large within all

components. For example, during winter, the reductions in the pond

ranged from -650% to 86%.

These reductions varied from 27% during

The higher reductions during summer are

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Total Phosphorus

Phosphorus is reduced by an average of 82% (from 15 mg/l to

2.6 mg/l). Reductions can be attributed to a combination of three

mechanisms: absorption onto bed substrate, compost, and liner (volclay);

plant uptake; and chemical precipitation. Reductions are higher during

summer (90%) than winter (68%). Reduced effectiveness during winter has

been reported in the literature and is caused in part by plant dormancy

and decay and a net release of precipitated phosphorus (Black, et al.,

1981, and Gearheart, et.al., 1984).

The effluent average was always under 6 mg/l except for one month,

February 1985, when the average was 16 mg/l. However, the data indicate

an increasing trend in effluent concentrations. The average effluent

concentration for the last twelve months of record (October 1984 through

September 1985) is 4.3 mg/l while for the preceding twelve months

(October 1983 through September 1984) the average was 2.1 mg/l. This may

indicate the root zone is reaching its absorption limit. It may also

reflect only normal variability due to an immature ecosystem since the

trend parallels that of ammonia nitrogen (see Figure 2).

Average concentrations were reduced in each component with the marsh

being the most effective (69%) and the aeration basin the least effective

(7%). Variability was largest within the aeration basin and the pond.

Conclusions

The marsh/pond/meadow system is capable of consistently meeting

EPA's secondary treatment standards and even more stringent standards at

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costs less than that required using conventional, mechanical-type systems

(for small communities). The system is very simple to operate and

maintain.

High quality effluent was achieved without benefit of a thick stand

of cattails, suggesting that the treatment mechanism for organic

pollutants is primarily bacterial metabolism. The marsh component

normally provides most of the treatment for the key parameters often

regulated by NPDES permit.

as a safety net for meeting permit limits. Either component could be

added as an upgrade to existing treatment facilities.

The meadow polishes the wastewater and serves

The aeration basin is effective primarily for BOD reduction. Of the

key parameters that are often regulated by NPDES permits, the pond is

effective in reducing ammonia nitrogen and fecal coliforms.

There are several potential changes that should be considered in

design of future HPH systems based on the Iselin data and data available

from other types of artificial wetlands. These include:

(1) Installation of control structures for varying the water depth

within each cell. This will improve growth and reproduction of

the marsh vegetation, may improve treatment efficiencies during

high flows, and can be used to control icing.

(2) Reduction of bottom slope, depending on the site's natural

slope. Flat slopes have been used in other gravel-based marsh

systems with good success (Gersberg, et al, 1986, and Wolverton

and HcDonald, 1982). The construction cost savings for using

slopes similar to those existing on-site may be substantial.

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(3) Use of other wetland species. Several species have been used

by other investigators. Bulrush (Scirpus) and reeds (Phragmites)

both appear to have better potential than cattails (Gersberg,

et al, 1986).

( 4 ) Replace sand substrate with gravel.

clogging of the wetland cells while maintaining high treatment

efficiencies (Gersberg, et al, 1986, and Wolverton and HcDonald,

1982).

(5) Increase the design organic and hydraulic loading rates if

ammonia limits are not low. The loading rates to each wetlands

cell was near the design rate and the treatment efficiencies were

high. However, the marsh cells did not establish a dense stand of

cattails. Better management of the vegetation should increase the

treatment capacity of the marsh through greater oxygen transfer to

the root zone and maintenance of a highly permeable root zone.

The data do not support increasing the loading rates for systems

with stringent ammonia limits.

are still lacking.

(6) Eliminate the aeration cell. Based on European experience

(Boon, 19861, primary treatment beyond screening, communition, and

grit removal is not necessary if the marsh is adequately designed

and operated.

needed to control odors if the raw sewage is septic.

(7) Revise the basis for the pond design, perhaps eliminating it.

The pond design is based on BOD removal; however, the marsh is so

effective in producing an effluent with low BODS that the pond

This will minimize

r'

Data for optimizing system design

Aeration or subsurface inlets to the marsh would be

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actually causes slight increases due to algal production.

Therefore, based on the loading rates and performance at Iselin,

the need for the pond depends on nitrogen control.

dentrification (nitrates are reduced by 82%), and volatilization

are important processes occurring within the pond. Since nitrogen

control can be effectively achieved with either a marsh or a

marsh/pond combination, an important issue is to determine the

appropriate design for each type system for optimizing nitrogen

removal and which is most cost effective.

Nitrification,

There are additional potential modifications that would increase the

operational flexibility of the system and may help optimize treatment

efficiencies, especially during stress periods resulting from such

factors as variable waste loading (low or high flows or concentrations)

or seasonal changes (fall/spring turnovers or winter icing). However,

these modifications increase the cost and complexity of the system and

should not generally be considered for the typical small community.

include: (1) recirculation of the pond or meadow effluent back to the

aeration basin or marsh, (2) piping to allow bypassing the pond or

meadow, and ( 3 ) aeration o r recirculation of the pond water to control

icing.

They

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REFERENCES

Black, S.A., Wile, I., and Hiller, G., 1981. Sewage Effluent Treatment in an Artificial Harshland, Paper presented at the 1981 WPCF Conference, Detroit, Hichigan.

Boon, A.G., 1986. Report of a Visit by Hembers and Staff of WRc to Germany (GFR) to Investigate the Root Zone Hethod for Treatment of Waste Waters, Water Research Center, Processes, Stevenage, Herts, England.

Gearheart, R.A., Finney, B.A., Wilbur, S., Williams, J., and Hull, D., 1984. The Use of Wetland Treatment Processes in Water Reuse. Future of Water Reuse, Volume 2. AWWA Research Foundation, Denver, Colorado.

Gersberg, R.H., Elkins, B.V., Lyon, S.R., and Goldman, C.R., 1986. Role of Aquatic Plants in Wastewater Treatment by Artificial Wetlands. Water Research, Vol. 20, pp. 363-368

Hendrey, G.R., Clinton, J., Blumer, K., and Lewin, K., 1979. Lowland Recharge Project. Operations, Physical, Chemical and Biological Changes, 1975-1978. Final Report to the Town of Brookhaven. BNL 27054. Brookhaven National Laboratory, Associated Universities, Inc., Upton, New York.

Small, H.H., 1977. Natural Sewage Recycling Systems. BNL 50630. Brookhaven National Laboratory, Associated Universities, Inc., Upton, New York.

SHC-Hartin, Inc., 1980. Harsh-Pond-Headow Sewage Treatment Facility, Village of Neshaminy Fall, Hontgomery Township, Hontgomery County, PA., SHC-Hartin, Valley Forge, PA.

Wolverton, B.C., and HcDonald, R.C., 1982. Basic Engineering Criteria and Cost Estimations for Hybrid Hicrobial Filter-Reed (Phragmites communis) Wastewater Treatment Concept. NASA TH-84669. National Aeronautics and Space Administration, National Space Technology Laboratories, NSTL Station, HS.

ONRED WQB 0137J

Table 1 . DESIGN OF THE ISELIN ARTIFICIAL WETLANDS SYSTEM

Cminu to r and S c r e e ?

Standard design based on manufacturers data fo r raw sewage flow Cminu to r : C l o w Model A - 8 Bypass bar screen: 2" x 1/4" (5.1 cm x 0.64 cm) w i th I" (2.5 cm) openings, manually cleaned

Aeration Cel I

Standard c i rcular design based on 50% BOD removal and complete mixing V o l m : 34,500 gallons (I30 m3) (winter conditions control the size) Depth: 5' (1.52 m) Detention time: 2.86 days Horsepower for canplete mixing: 2.3 hp (1700 W) Freeboard: 2' (0.61 m) Sidewall slope: lv:3h Liner: Hypalon

Wet I ands Marsh

AppI icat ion rate Nunber o f ce l l s Cel I lengthluidth r a t i o Media 1 i ner Freeboard Maximum Sidewater depth Slope Vegetation In le t

Outlet

50,000 gal/acre/day (470 m3/ha/day) 2 3.6811 4" ( I O cm) 2B Stone over 16" (41 cm) sand 4" (IO cm) Volclay 0.5' (I5 cm) 2.0' (61 cm) 2% Cattai Is 4" (IO cm) WC perforated header across cel I

width buried i n 28 stone French drain 9" (23 cm) stone r i p rap

Berm Slopes lv:3h Cell Divider 3' (91 cm) top width, compacted so i l

Standard design based on 50% BOD removal Detention t ime: 22 days (winter conditions control) V o l m : 264,000 gal Ions (I ,OOO m3) Depth: 5' (1.5 m) Length/width rat io: 211 Freeboard: 2' (0.61 m) Sidewall slope: Iv:Jh l iner : 4" ( I O cm) Volclay

Ch lor i nation

Meadow

100,000 ga I/acre/day (940 mJ/ha/day) 2 I .84/1 4" (IO cm) 28 Stone over 16" (41 cm) sand 4" ( I O cm) Volclay 0.5' (I5 cm) 2.0' (61 cm) 22 Reed canary grass 4"(10 cm) WC perforated header across c e l l

width, buried i n 28 stone French drain 8" (20 cm) reinforced concrete wal I with 6" (15 cm) diameter weep holes, spaced a t 4' (122 cm) intervals

I v: 3h 3' (91 cm) top width, compacted so i l

Chlorinator: Sanuri I Model 1001 Contact Tank: 1250 gal (4.7 m3) Contact Time: 120 min Required Chlorine Residual: 2.0 q/ l

Tabla 2. PERFORMANCE DATA FOR THE ARTIFICIAL WETLANDS AT ISELIN, PENNSYLVANIA

Biochemical Oxygen Demand Total Suspended Solids Percent Concentration Percent Concentration

Reduction Influent Effluent Reduction Influent Effluent - - -- Fecal Coliforms Ammonia Nitrogen Total Phosphorus

Reduction Influent Effluent Reduction Influent Effluent Reduction Influent Effluent Concentration Percent Concentration Percent Concentration Percent

- - ----- Component Season

Aeration Winter Basin Summer

15 230 200 -170 180 490 67 280 92 -67 170 290

-48 1,200,000 1,700,000 -92 13 24 7.8 12 11 60 2,600,000 1,000,000 -120 16 35 5.7 16 15

Total 46 260 140 -120 180 380 2 1 1,800,000 1,400,000 -1 10 14 30 7.0 15 13

Marsh Winter Summer

93 200 15 93 490 33 79 92 19 76 290 69

100 1,700,000 6,200 49 24 12 37 11 7.1 100 1,000,000 720 61 35 14 87 15 2.0

Total 88 140 17 86 380 53 100 1,400,000 3,700 56 30 13 69 13 4.2

Pond Winter Summer

-15 15 17 -1 6 33 38 -22 19 23 -16 69 80

48 6,200 3,200 27 12 9.1 42 7.1 4.2 12 720 630 86 14 1.9 -3 6 2.0 2.8

Total -2 0 17 20 -14 53 61 43 3,700 2,100 60 13 5.2 20 4.2 3.4

Veadow Winter Summer

50 17 8.5 45 38 21 72 23 6.5 78 80 18

92 3,200 240 36 9.1 5.8 6.8 4.2 3.9 96 630 23 38 1.9 1.2 43 2.8 1.6

Total 64 20 7.4 69 61 19 93 2,100 150 36 5.2 3.3 23 3.4 2.6

;ystem Winter Summer

96 230 8.5 88 180 21 98 288 6.5 90 170 18

100 1,200,000 240 54 13 5.8 68 12 3.9 100 2,600,000 23 93 16 1.2 90 16 1.6

Total 97 260 7.4 89 180 19 100 1,800,000 150 77 14 3.3 82 15 2.6

IOTES: Period of record: March 1983 -September 1985. Winter months include November through April. Summer months include May through October. Concentrations are the average of monthly averages except monthly geometric means are used for fecal coliforms. Units are mgll except colonies1100ml for fecal coliforms. Data are rounded to two significant digits. Monitoring locations used in the evaluation are: aemtion basin - points A and B, marsh - points B and E, pond - points E and G,

and meadow - points G and I.

105' 140'

Aerat ion Cel l

Commlnutor a 6. Screen r-'

-- IC -0

n r , rr) 0 -: Influent

in? C

Notel Dimenoions are a t the water wr face for the aeration coil and pond and a t the atone t u r f l e a for the marah and meadow.

b r-' rr)

Commlnutoi h Screen

-=j ;,iL ~

Figure I . lselln Artificial Wetlands Treatment Scheme

Figure 2. Effluent Concentrations For the lselin Artificial Wetlands

P -7 I O 0

2000

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CONSTRUCTED WETLANDS DESIGN EXAMPLE SUBSURFACE FLOW MUNICIPAL SYSTEM

TREATMENT OF PRIMARY EFFLUENT TO SECONDARY LEVELS OR SECONDARY EFFLUENT TO ADVANCED LEVELS

The design will be based on hydraulic loading rates (HLR) rather than first order kinetics because of limited information on appropriate reaction rates and constants. The references cited in the example are: (1) Steiner, G. R. and R. J. Freeman, Jr. "Configuration and Substrate Design Considerations for Constructed Wetlands Wastewater Treatment", (2) Watson, J. T., S. C. Reed, R. Kadlec, R. L. Knight, and A. E. Whitehouse. Wetlands'*, and (3) Watson, J. T. and J. Hobson. "Hydraulic Design Considerations and Control Structures for Constructed Wetlands for :

Wastewater Treatment" in Constructed Wetlands for Wastewater Treatment, D. A. Hammer, Ed. (Chelsea, MI: Lewis Publishers Inc., 1989). Washed river gravel with a nomimal size of about 3/4 aggregate) and either reeds (PhraRmites australis) or softstem bulrush (Scripus validus) will be used (see reference 1). The design flow will be 100,000 gpd (13,370 ft3/day). significant site constraints.

**Performance Expectations and Loading Rates for Constructed

** (such as /I467 AHD

It is assumed that there are no

Select an appropriate HLR: 20 acres/MGD (reference 2, table 7)

Calculate the surface area (A,) needed:

As = 20 acres/MGD * 0.1 MGD = 2 acres = 87,120 ft2

Calculate the cross-sectional area (Ac):

A, = Q/(ks*S) (Darcy's law: reference 2, equation 9)

Use a long term permeability of 260 m/day or 853 ft/day (reference 2, p. 23) and a hydraulic gradient (bed slope) of 1%.

A, = 13,370 ft3/day / (853 ft/day * 0.01) = 1,567 ft2

Calculate the system width (Us):

Use an inlet depth of 1.5 ft.

Us = 1,567 ft2 / 1.5 ft = 1,045 ft

Calculate the system length (Ls):

Ls = 87,120 ft2 / 1,045 ft = 83.4 ft (say 84 ft)

Calculate the outlet depth Do:

Do = 1.5 ft + (84 ft * 0.01) = 2.34 ft

Note: The maximum depth should not exceed 2.5 ft (the maximum effective root depth of reeds or bulrushes, reference 2, p. 22). If adjustments are needed to meet this criterion, reduce the hydraulic gradient to obtain a greater cross-sectional area and a reduced system length.

Use parallel cells to provide operational flexibility and better hydraulic control. Four cells should be adequate for this design. After rounding, the dimensions would be 261 ft. wide and 84 ft. long (each cell). Information on inlet and outlet structures is provided in reference 3 . Liners, recirculation, alternate configurations, etc. are addressed in reference 1.

04 6 OH

Constructed Wetlands Wastewater Treatment Residential Septic Tank System

Conceptual Design Basis

Example Design

Wastewater flow, Q = 150 GPD per bedroom, 20.1 FT3/D

Hydraulic Loading rate = 20 acres/MGD, 0.871 M12/GPD or 0.153 F T / D

CW cell surface area, As = 20.1 FT3/D / 0.153 FT/D = 131 ET2 per bedroom

Determine cell cross-section area, A,, using Darcy's Law:

Q = A, * Ks * S , where K, = substrate hydraulic conductivity (long term) S = hydraulic gradient (assume equivalent to bed slope)

For 3 bedrooms, Q = 60.3 FT3/D and As = 393 ET2.

Assume K, = 800 FT/D (conservative rate based on long-term clogging of the gravel)

Use S = 1%, or .01

Use 1.5 FT for cell depth, D (front of cell)

Cell width, W = A,/D = 7.5/1.5 = 5 F T

System cell length, L = As/W = 393/5 = 78.6 FT

If the in-situ soil percolation rate is 60-75 MIN/IN or faster, the total surface area is divided equally between the 2 cells. dimensions are 5 kT wide and 4 0 FT long each.

Therefore the cell

Substrate depth--cell front = 1.5 FT (18 IN) cell end = 1.5 FT + .01 (slope) * 40 FT = 1.9 FT (23 IN) average depth = 20.5 IN

If practical, the second cell should be constructed at a lower elevation than the first cell to allow independent water level control in each cell. Ideally, the top of the second cell should be at or below the bottom of the first cell. If this is not practical, lowering the water level in the first cell may be restricted by the water level in the second cell.

-2-

If the above dimensions do not f i t t he desired s i te , the dimensions can be adjusted by using d i f f e ren t hydraulic gradients , or cell bed slopes. Reducing the s lope w i l l increase t h e bed width and decrease i t s length, and increasing the slope w i l l decrease t h e bed width and increase i t s length. For example, a slope of 0.5% i n the above example r e s u l t s in:

U s e S = 0.5%, or .005

For D = 1.5 FT ( in l e t ) , W = 15.111.5 = 10 FT L = 393/10 = 39.3 FT

U s e two cells, 10 FT wide and 20 FT long each. Outlet depth f o r each cell is 1.5 ET + 0.005 * 20 FT = 1.6 FT.

WRC 0476H

CONSTRUCTED WETLANDS DESIGN EXAMPLE SURFACE FLOW SYSTEM

TREATMENT OF PRIMARY EFFLUENT TO SECONDARY LEVELS OR SECONDARY EFFLUENT TO ADVANCED LEVELS

The design is based on a flow of 100,000 gpd and a selection hydraulic loading rate (HLR).

Select appropriate HLR: 50 acres/MGD

Calculate required surface area (As):

As = 0.1 MGD * 50 acres/MGD = 5 acres = 217,800 ft2

Select length to width ratio (L/W): 20

Calculate system dimensions:

width = x ft, length = 20x ft

x * 2 0 ~ = 217,800 ft2 x = 104.4 ft, use 100 ft width

length = 217,800 ft2 i 100 = 2178 ft; use 2200 ft

Effective L/W = 22

One cell 2200 ft long by 100 ft wide

Option

Use a 4-cell serpentine system, or 4 parallel cells.

As each cell = 217,800 ft2 P 4 = 54,450 ft2

Use L/W = 10

Dimensions: lox2 = 54,450 x = 74 ft width

Length = 54,450 ft2 - 74 ft = 736 ft, use 740 ft.

Overall system size, (excluding divider dikes) is 740 feet long by 296 ft. wide (4 x 74 ft.)

Parallel cells provides better 0624 flexibility.

Use slight bed slope (0.1%), which provides a 9" difference between inlet and outlet for the 740 foot long beds.

Use dike height of three feet above bed.

Elevate inlet distributor(s1 two feet above bed on large stone.

WRC 05460

!1

1

Plan Mew of Outlet Structure wlth SwIveling Standpipe

Rotatfon !

Rotate Standplpe and Elbow to the Desired Water Level

Source: Modifled from Cooper 1

and Hobson [Ill

I Control Structure with Collapslble Tubing

Length of Pipe Sedon Correspond8 to the n DeaIred Water Wet

Control Structure wlth Swiveling Standpipe Control Structure wlth Interchangeable Sections of PIP wIth Joints Containing Elastomeric aske eta

Figure. Outlet water level control structures