Monitoring the household wastewater treatment process within the SIERA system

Transcription

1 Monitoring the household wastewater treatment process within the SIERA system 1 Ioan M. Craciun, 1 Vasile Ciuban, 1 Daniela Ignat, 1 Corina M. Berkesy, 1 Grigore Vlad, 1 Liviu Suciu, 2 Valer Turcin 1 S.C. ICPE Bistriţa S.A., Bistrita, Romania; 2 ICPE Centru 5, Bucharest, Romania. Corresponding author: I. M. Craciun, craciunmircea@icpebn.ro 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 mechanicalbiological 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). Glasshouse Photovoltaic energy plant Automation plant Mechanical-biological purging station 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 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 50

2 treatment plant with active sludge and biological ponds, whose wastewater treating yield is 35 to 45 cm/day and daily consumption of approx kwh, and also to the glasshouse, whose area is 200 sqm and which needs around 9.5 kwh per day (Figure 2). Legend Legend by-pass route wastewater route purged water route current water route nutrient route ph correction reactive route Figure 2. Integrated system lay-out. Wastewater treatment process. The wastewater treatment plant is a mechanicalbiological 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). 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 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 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 m 3 volume cylinders for the anoxic step and two 18 m 3 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 51

3 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. Technological pavilion Wastewater supply Internal recirculation External recirculation Internal recirculation Compressed air Discharge chamber Anoxic tank 1 Entrance chamber Aerobic tank 1 Anoxic tank 2 Aerobic tank 2 Secondary separator Water flowmeter Sludge water Sludge thickener Purged water discharge Active sludge in excess Figure 5. Water, sludge and air circulation in the wastewater treatment plant. 52

4 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. No. Wastewater treatment plant energetic consumption Equipment name and characteristics No. of pcs. No. of pcs Unitary installed electr. power Total installed electr. power Total consumption electr. power Operating hours/ day Table 1 Consumed electrical power/day Activity [kw] [kw] [kw] [h] [kwh] 1 Control and automation cabinet Submersible mixer Submersible pumps for the transferred wastewater: Q = 10m³/h ; H = 8mCA 4 Separator pump : Q = 6 mc/h Reactive agents dosing pump Reactive agents dosing pump Reactive agents dosing plant agitator 8 Variable rotating speed blower: Q = 59 m³/h; H = 400 mbars 9 Thickened sludge pump Hot air and forced convection air heaters 11 Excess sludge recirculation/discharge pumps: Q = 10 mc/h, H = 6 mca 12 Indoor and outdoor lighting Total Daily Consumption 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 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 % 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 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 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 53

5 matters (TSM), the chemical oxygen demand (COD), the biochemical oxygen 5 demand (BCO 5 D) and N-NH 4 (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 (BCO 5 D), and its efficiency upon the discharge. Figure 10. The variation of ammonia nitrogen (N-NH 4 ), and its efficiency upon the discharge. 54

6 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 BCO 5 D (Figure 9), % for N-NH 4 (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 BCO 5 D, 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 patent draft from References Crites R., Tchobanoglous G., 1998 small and decentralized wastewater management systems. WCB and McGraw-Hill, New York, USA, pp 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] 55

7 Received: 01 March Accepted: 28 March Published online: 31 March Authors: Ioan Mircea Craciun, S.C. ICPE Bistriţa S.A., Parcului Street, No 7, Bistriţa, Romania, Vasile Ciuban, S.C. ICPE Bistriţa S.A., Parcului Street, No 7, Bistriţa, Romania, Daniela Ignat, S.C. ICPE Bistriţa S.A., Parcului Street, No 7, Bistriţa, Romania, Corina Michaela Berkesy, S.C. ICPE Bistriţa S.A., Parcului Street, No 7, Bistriţa, Romania, Grigore Vlad, S.C. ICPE Bistriţa S.A., Parcului Street, No 7, Bistriţa, Romania, Liviu Suciu, S.C. ICPE Bistriţa S.A., Parcului Street, No 7, Bistriţa, Romania, Valer Turcin, ICPE Centru, Splaiul Unirii No. 313, sect. 3, Bucharest, Romania, 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):