Monitoring the household wastewater treatment process ...

ECOTERRA - Journal of Environmental Research and Protection

www.ecoterra-online.ro 2016, Volume 13, Issue 1

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Monitoring the household wastewater treatment process within the SIERA system 1Ioan M. Craciun, 1Vasile Ciuban, 1Daniela Ignat, 1Corina M. Berkesy, 1Grigore Vlad, 1Liviu Suciu, 2Valer Turcin

1 S.C. ICPE Bistriţa S.A., Bistrita, Romania; 2 ICPE Centru 5, Bucharest, Romania. Corresponding author: I. M. Craciun, [email protected]

Abstract. The autonomous integrated system for treating household wastewaters while reusing water and sludge planned to mitigate the environmental impact by locally using the products resulted from the wastewater treatment, to enhance the treatment efficiency by using an innovating treatment technology and to use the green energy within the process. The integrated system is composed of a mechanical-biological wastewater treatment plant with active sludge and biological ponds, of a green energy catching and storing station and of a glasshouse. This paper aims at assessing the system efficiency by monitoring its quality and energetic parameters. The outcomes of the SIERA system implementation show a 100 % sludge reutilisation degree, a 30 to 70% water reutilisation degree, a more than 97% efficiency of treating wastewaters in case of nitrogen products and a reduction in the consumption of electrical power from the national system of 50 to 90%. Key Words: wastewater treatment, reutilisation, integration, green energy.

Introduction. SIERA is an autonomous integrated system for treating household wastewaters while reusing water and sludge. The integrated system is composed of a mechanical-biological wastewater treatment plant with active sludge and biological ponds, of a green energy catching and storing station and of a glasshouse (Figure 1).

Figure 1. Overview of the integrated system.

The wastewater treatment plant combines the technology of biological treatment with active sludge and wastewater treatment by means of the biological ponds, used as a buffer tank for irrigation and conditioning in the glasshouse (Crites & Tchobanoglous 1998).

The green energy production and storing plant is composed of photovoltaic solar panels and it supplies the wastewater treatment plant and the glasshouse with electrical power (Tomescu & Tomescu 2008).

The glasshouse reuses the treated wastewater and the sludge resulted from the wastewater treatment process. It is equipped with a system of irrigation by aspersion.

The integrated system is controlled and monitored by a continuous automation and control installation in real time, which transmits the parameters of the wastewater treatment process in a SCADA system.

Overview of the integrated system. SIERA operates by the green energy generated by photovoltaic panels that cover around 86.5 sqm, with a total installed electrical power of 12.35 kWh, out of which 8.85 kWh is active energy and 3.50 kWh the operation by a photovoltaic generator. This energy is distributed to the mechanical-biological wastewater

Mechanical-biological purging station

Photovoltaic energy plant

Glasshouse Automation plant



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treatment plant with active sludge and biological ponds, whose wastewater treating yield is 35 to 45 cm/day and daily consumption of approx. 34.00 kWh, and also to the glasshouse, whose area is 200 sqm and which needs around 9.5 kWh per day (Figure 2).

Legend

Figure 2. Integrated system lay-out.

Wastewater treatment process. The wastewater treatment plant is a mechanical-biological one, complete with two successive steps of biological aeration (Figures 3 and 4). In the biological step, the wastewater treatment technology (for meeting the purged water quality conditions, according to the water pollutants technical rule NTPA 001/2002) is continuous mixed operation – type: aeration tank with complete mixture, highly efficient in withholding the organic substances from the wastewaters and which also includes the stage of nitrifying the larger amounts of nitrogen present in the household wastewaters (Dima 2005; Robescu et al 2000).

Figure 3. Wastewater treatment plant and technological pavilion lay-out.

The biological step takes place in a fabricated construction made of 4 tanks of reinforced concrete with anticorrosive protection, two 10 m3 volume cylinders for the anoxic step and two 18 m3 cylinders for the aerobic step, endowed with mixers for the water within the anoxic steps and with a system of aeration with fine bubbles (porous diffusers with an elastomeric membrane) for the aerobic steps, whose role is to provide the amount of oxygen for the development of the aerobic biological processes and for maintaining

by-pass route wastewater route purged water route current water route nutrient route pH correction reactive route

Legend

EQUIPMENT P1, P2 – transferring pumps P7, P8 – sludge pumps Mx – mixer PD1, PD2 – reactive agents pumps S1, S2 – blowers TA – automation panel A1, A2 – reactive agents tank D1 – distributor RD – distribution network RA – aeration network R1, R2 – adjustment cocks Gc – cage screen

CAPTION 1.Pumping station 2.Entrance chamber 3. Sludge thickener 4. Anoxic step 1 5. Aerobic step 1 6. Anoxic step 2 7. Aerobic step 2 8. Secondary separator 9. Water flow rate measurement chamber 10. By-pass chamber 11. Technological pavilion



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adequate hydrodynamic conditions in the aeration-agitation tank, in order to keep an optimal contact between the wastewater and the active sludge.

The recirculation of the waters with a content of nitrates and nitrites from the nitrification tanks into the anoxic ones takes place by means of a air-lift type system – flow rate: 5-10 m3/h. The wastewater is pumped into the first denitrification anoxic tank, where the water is mixed with the recirculated water from the first aerobic tank for nitrification and biological carbon removal. This mixture goes gravitationally in the first aerobic tank and from here in the second denitrification tank, where it mingles with the recirculated water from the second aerobic tank. The nitrification-denitrification processes, as well as the process of mitigating the dissolved organic substances and, partially, phosporus take place successively in these tanks. The aerobic tanks are complete with fine bubble aeration diffusers with a controlled flow rate adjusted by oxygen sensors, whereas the anoxic tanks are equipped with systems of pneumatic and mechanical mixture.

The water and active sludge mixture flows gravitationally in the secondary separator, where the solid-liquid separation by sedimentation takes place. So the nitrification gives birth to an external recirculation of the sludge from the secondary separator in the two aerobic tanks and for the denitrification there is an internal recirculation by pumping the water with active sludge from the aerobic tanks into the corresponding anoxic tanks. From the secondary separator, the sludge is absorbed by the pumps and is recirculated in the aeration tanks or, if in excess, it is evacuated and directed toward the sludge thickening tank (Figure 5).

Figure 4. The wastewater treatment plant.

Figure 5. Water, sludge and air circulation in the wastewater treatment plant.

Wastewater supply

Anoxic tank 1

Aerobic tank 1

Internal recirculation

Compressed air

Aerobic tank 2

Secondary separator

External recirculation

Technological pavilion

Discharge chamber

Internal recirculation

Anoxic tank 2

Entrance chamber Sludge water

Water flowmeter Purged water

discharge Sludge

thickener

Active sludge in excess



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Wastewater treatment plant energetic consumption. The pieces of equipment used in the purging station and the energetic consumptions, subject to their power and operating duration, are provided in the Table 1.

Table 1

Wastewater treatment plant energetic consumption

No. of pcs.

No. of

pcs

Unitary installed electr. power

Total installed electr. power

Total con-sumption

electr. power

Ope-rating hours/

day

Consumed electrical

power/day No.

Equipment name

and characteristics

Activity [kW] [kW] [kW] [h] [kWh] 1 Control and automation cabinet 1 1 0.10 0.10 0.07 24 1.68 2 Submersible mixer 2 1.00 2.00 1.20 10 12.00 3 Submersible pumps for the

transferred wastewater: Q = 10m³/h ; H = 8mCA

2 1.30 2.60 1.82 0.4 0.73

4 Separator pump : Q = 6 mc/h 1 0.50 0.50 0.35 0.1 0.04 5 Reactive agents dosing pump 1 1 0.20 0.20 0.12 0.2 0.03 6 Reactive agents dosing pump 2 1 0.02 0.02 0.01 1 0.11 7 Reactive agents dosing plant

agitator 2 0.18 0.36 0.18 12 2.20

8 Variable rotating speed blower: Q = 59 m³/h; H = 400 mbars

1 1 2.20 2.20 1.45 8 11.02

9 Thickened sludge pump 1 0.50 0.50 0.35 0.1 0.03 10 Hot air and forced convection air

heaters 1 1.50 1.50 1.43 0 0.00

11 Excess sludge recirculation/discharge pumps:

Q = 10 mc/h, H = 6 mCA

5 0.01 0.05 0.04 10 0.35

12 Indoor and outdoor lighting 1 0.30 0.30 0.21 4.4 0.93 Total Daily Consumption 14.33 7.57 29.20

The average daily electrical power needed for the glasshouse operation is approx. 4.5 kWh – irrigation, ventilation and heating for the cold season.

The annual amount of electrical power needed for the operation of the SIERA system is around 12352 kWh, out of which 8852 kWh represent the photovoltaic electrical power and 3499 kWh represent the electrical power from the national system. The monthly distribution according to the solar radiation is shown in Figure 6.

Figure 6. Solar energy consumption as percentage of total consuption. The Figure 6 shows that the photovoltaic system provides 40-50 % of electrical power in the winter months and 80-90% of electrical power in the other months of the year. Out of the yearly necessity of 12352 kWh, the photovoltaic system provides approx. 72%, the remaining 28 % being absorbed from the network. Wastewater treatment plant efficiency. After being started up and brought within the operating parameters, the station was monitored from April to October 2015. The date were processed and set out depending on the characteristics upon the discharge and on the wastewater treatment efficiency for the determined parameters: the total suspension



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matters (TSM), the chemical oxygen demand (COD), the biochemical oxygen 5 demand (BCO5D) and N-NH4 (Figures 7, 8, 9, 10) .

Figure 7. The variation of the total suspension matters (TSM), and its efficiency upon the discharge.

Figure 8. The variation of chemical oxygen demand (COD), and its efficiency upon the discharge.

Figure 9. The variation of biochemical oxygen 5 demand (BCO5D), and its efficiency upon

the discharge.

Figure 10. The variation of ammonia nitrogen (N-NH4), and its efficiency upon the discharge.



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Experimental results. The treated wastewater parameters are within the limits of the water pollutants technical rule NTPA-001, with little exceptions – at the ammonia nitrogen (Figure 10), on account of the quality of the entering waters, which sometimes exceed by far the values allowed for the sewerage waters, even though the purging efficiencies are higher, often exceeding the 93% limits prescribed in NP133: 80-90% for TSM (Figure 7), 70-97% for COD (Figure 8), 81-95% for BCO5D (Figure 9), 85-99.9% for N-NH4 (Figure 10).

The high efficiencies are reached because the wastewater treatment plant has got two consecutive biological steps, which allow the application of the Bardenpho technology or a related one, with efficiencies greater than 93%, in case of tank volumes and energy consumptions smaller than at the purging stations with one biological step.

Conclusions. By monitoring the Integrated Wastewater treatment System in a SCADA system, we may better the operation of the equipment in due time, in order to mitigate the electrical power consumptions as much as possible and to enhance the purging efficiency.

The electrical power consumption is largely provided by the photovoltaic system, which in summer can reach yields up to 90%, and because of the fact that the glasshouse no longer consumes energy for heating and ventilation. In the cold season of the year, the consumptions increase and the solar radiation decreases, the photovoltaic energy being thus reduced up to 40% of the system requirements for this application.

The treated wastewater quality falls within the limits imposed by NTPA 001, even though the wastewaters exceed by far – in case of the ammonia nitrogen even by 3 to 5 times – the limits regulated by NTPA 002. Very high efficiencies – 95% for BCO5D, 97% for COD and especially up to 99.9% for the reduction of the ammonia nitrogen, have been reached, which are outcomes that cannot be obtained in the wastewater treatment plant with one biological step.

This technology shows that the procedure and the biological wastewater treatment plant with two aeration steps and one separator, with high load aeration in the former aeration step and a full mixture in the latter one, bring forth a more than 98 % efficiency for the ammonia nitrogen, which thus accounts for the theoretical calculations laid down in the A 2014 4 00834 patent draft from 7.11.2014. References Crites R., Tchobanoglous G., 1998 small and decentralized wastewater management

systems. WCB and McGraw-Hill, New York, USA, pp. 609-627. Dima M., 2005 [Urban sewage treatment plant]. Tehnopress Publishing House, Iasi. [in

Romanian] Robescu D., Lanyi S., Robescu D., Constantinescu I., 2000 [Technologies, installations

and equipment of sewage treatment]. Technical Publishing House, Bucharest. [in Romanian]

Tomescu A., Tomescu I. B, 2008 [The direct conversion of energy]. Matrix Rom Publishing House, Bucharest. [in Romanian]



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Received: 01 March 2016. Accepted: 28 March 2016. Published online: 31 March 2016. Authors: Ioan Mircea Craciun, S.C. ICPE Bistriţa S.A., Parcului Street, No 7, 420035 Bistriţa, Romania, e-mail: [email protected] Vasile Ciuban, S.C. ICPE Bistriţa S.A., Parcului Street, No 7, 420035 Bistriţa, Romania, e-mail: [email protected] Daniela Ignat, S.C. ICPE Bistriţa S.A., Parcului Street, No 7, 420035 Bistriţa, Romania, e-mail: [email protected] Corina Michaela Berkesy, S.C. ICPE Bistriţa S.A., Parcului Street, No 7, 420035 Bistriţa, Romania, e-mail: [email protected] Grigore Vlad, S.C. ICPE Bistriţa S.A., Parcului Street, No 7, 420035 Bistriţa, Romania, e-mail: [email protected] Liviu Suciu, S.C. ICPE Bistriţa S.A., Parcului Street, No 7, 420035 Bistriţa, Romania, e-mail: [email protected] Valer Turcin, ICPE Centru, Splaiul Unirii No. 313, sect. 3, 030138 Bucharest, Romania, e-mail:[email protected] This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution and reproduction in any medium, provided the original author and source are credited. How to cite this article: Craciun I. M., Ciuban V., Ignat D., Berkesy C. M., Vlad G., Suciu L., Turcin V., 2016 Monitoring the household wastewater treatment process within the SIERA system. Ecoterra 13(1):50-56.

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