PERFORMANCE TEST OF SBR WASTEWATER TREATMENT PLANT WITH 5 PE CAPACITY

Transcription

1 PERFORMANCE TEST OF SBR WASTEWATER TREATMENT PLANT WITH 5 PE CAPACITY Nataša Uranjek Ževart 1, Tomislav Sunarič 1, Štefan Pražnikar 1, Bojan Čendak 2 1 Velenje Public Utility, Koroška cesta 37/b, 332 Velenje ( natasa.uranjek@kp-velenje.si, tomo.sunaric@kp-velenje.si, stefan.praznikar@kpvelenje.si) 2 Pipelife International, Ljubljanska 52 a, 1236 Trzin ( bojan.cendak@pipelife.si ) Abstract The efficiency and operation capacity of SBR wastewater treatment plant for household sewage was tested. Initially, operation control, technical measurements and wastewater sampling were carried out. The outflow from the plant was analyzed and the sludge from the primary tank was tested. Efficiency of the plant was compared when operating under normal conditions and when the enzyme preparation was added by the treatment plant owner. Data from monitoring was used to check the compliance of the SBR wastewater treatment plant with Slovenian legislation. Manufacturer s manuals were also checked in the field. It was established that the monitored SBR wastewater treatment plant complies with Slovenian legislation requirements. The results showed increased efficiency of the treatment plant when enzyme preparation was added. Key words: ammonia nitrogen, BOD 5, waste water treatment, enzyme preparations, COD, small waste water treatment plant, SBR treatment plant, treatment efficiency 1 INTRODUCTION In parts of Slovenia with low population density, sewage systems will never be constructed. For the wastewater treatment, small treatment plants are used to comply with the legislation related to the emission of substances in the discharge of wastewater into the environment. Today, many suppliers can be found on the market, selling wastewater treatment plants with the capacity of one or more households. In our company we decided to test the operation of several such treatment plants. In this article we are presenting the start-up and operation of one of the monitored small treatment plants. We decided to present the SBR small treatment plant produced by Pipelife. 2 TREATMENT PLANT OPERATION SBR small treatment plant Pipelife is designed for the treatment of wastewater from households or smaller companies. Its treatment capacity is 4 16 PE. A household with three members is connected to the monitored treatment plant.

2 Figure 1 Installation of SBR treatment plant Before reaching the treatment plant, wastewater is directed into the existing cesspit which serves as a sedimentation tank. In this case, the existing cesspit was used as the first reactor this term is used further in this article. From there, wastewater is pumped into the treatment plant. The treatment plant consists of two connected tanks (Figure 2). The first tank a reactor is used for sedimentation of suspended substances that flows in with fresh wastewater and excess biological sludge which is pumped back from the SBR reactor. This part of the plant functions as a sedimentation tank. From this tank, wastewater is pumped into the SBR reactor which is enabled by a floating unit where a sludge pump and a treated water pump are installed along with submersible aerators. The process of wastewater treatment takes place with the help of this floating unit and dispersed biomass in the SBR reactor. Figure 2 Treatment plant scheme The entire process is managed through a controller which leads the plant operation through four main phases (sedimentation, discharge of treated water, filling of SBR reactor, water treatment (biological treatment, denitrification and nitrification). In any given moment, the controller displays the current phase of the batch. Phases of the treatment process: Wastewater from a household flows into the first reactor where suspended particles sink to the bottom.

3 Wastewater without suspended substances (upper fraction) is pumped into the second reactor SBR reactor. When a certain water level in the SBR reactor is reached the pumping stops and part of sludge is pumped back into the sedimentation tank after that, treatment of the new batch of wastewater starts. With a slight blow of air, the content of the reactor is mixed and the denitrification phase begins. After a certain period of time, intensive aeration starts, enabling biological treatment of wastewater and nitrification processes. The air is blown into the reactor by the aerator fixed to the floating unit. After a certain period of time, aeration stops and the batch cycle is terminated by pumping the treated water from the SBR reactor into the environment. As soon as this happens, the reactor is ready for a new batch cycle. To check the efficiency of the process, part of discharged water at the outlet is saved for a sample. The device is designed to allow three cycles daily; minimal duration of one cycle is 8 hours. 3 MATERIALS AND METHODS In line with the legislation (Decree on emission of substances in waste water discharged from small municipal treatment plants, Official gazette of RS, no. 13/2), monitoring of regulatory parameters COD and BOD 5 was carried out. We also decided to measure ph, temperature, electric conductivity, dissolved oxygen and also ammonia nitrogen to establish the efficiency of methane removal. Parameters were defined by using standard methods and their modifications used in the laboratory in accordance with the SIST EN ISO/IEC 1725 standard for testing and calibration laboratories. Samples were taken once a week from the built-in sampling dish after the completed batch cycle. They were analyzed in our laboratory. Operation of the treatment plant was monitored from its startup in December 26 until July 27. In this way, treatment plant was monitored in cold as well as in warm part of the year. Treated water from the treatment plant was sampled once a week, we also carried out two samplings to establish efficiency of the treatment plant.

4 4 EXPERIMENTAL PART In Table 1 and graphs 1 through 5, the results of measurements and their comparison with legally binding values for discharge of treated water into the environment are presented: Table 1 Results of measurements during the monitoring of the SBR treatment plant operation AMMONIA NITROGEN SUSP. PARTICLES DATE TEMP. ph EL.COND. COD BOD5 C µs/cm mgo 2/L mgo 2/L mgnh 4--N/L mg/l 21 Dec Feb Feb Feb Mar Mar < Mar < Mar Apr Apr Apr < Apr May < May May May Jun Jun Jun Table 1 presents the results of measurements in the 6-months period when the operation of the treatment plant was monitored. Since an enzyme preparation was added to the treatment plant by the users to improve the functioning of the cesspit (sedimentation tank) we also checked the impact of this on wastewater treatment. Between 7 May and 4 June 27, we stopped adding the above mentioned preparation. In graphs bellow, values of individual parameters are presented, while their explanation follows in the Discussion chapter.

5 KPK NA IZTOKU KPK (mgo2/l) KPK mgo2/l MDV Graph 1 COD value at the outlet from the treatment plant compared to the limit value The Decree on emission of substances in wastewater discharged from small municipal treatment plants (Official gazette of RS, no. 13/2) defines the COD limit value at 16 mgo 2 /l and the BOD 5 limit value at 3 mgo 2 /l. 35 BPK5 NA IZTOKU 3 25 BPK5 (mgo2/l) BPK5 mgo2/l MDV Graph 2 BOD 5 value at the outlet from the treatment plant compared to the limit value

6 KPK in AMONIJEV DUŠIK NA IZTOKU (mg/l) KPK mgo2/l mgnh4-n/l Graph 3 COD values and ammonia nitrogen at the outlet from the treatment plant VREDNOSTI AMONIJEVEGA DUŠIKA NA IZTOKU IZ NAPRAVE 6 5 BREZ DODAJANJA ENCIMOV (mg NH4-N/L) AMONIJEV DUŠIK mgnh4-n/l Graph 4 The impact of adding enzymes on the concentration of ammonia nitrogen at the outlet

7 UČINEK ČIŠČENJA V % ZA KPK, BPK5 IN AMONIJEV DUŠIK učinek čiščenja ( %) feb.7 mar.7 apr.7 maj.7 jun.7 KPK učinek % BPK5 učinek % NH4-N učinek % Graph 5 Measured treatment efficiency of the treatment plant 5 DISCUSSION It is evident from Graphs 1 and 2 that the treatment plant is operating in accordance with legislation all measured values at the outlet from the treatment plant are bellow limit values for COD and BOD 5 parameters. Measured values are much below the limit values; the value of COD parameter did not exceed 1 mgo 2 /l, while the BOD 5 value was closest to the limit value at the time of the first measurement when the concentration reached 21.1 mgo 2 /l. It is evident from Graph 3 that COD and ammonia nitrogen values at the outlet of the treatment plant are in close relation. This confirms that tertiary treatment ammonia oxidation is also taking place in the plant apart from biological treatment. Measurements confirmed that ammonia transforms into another form of nitrogen. Graph 4 shows values of ammonia nitrogen at the treatment plant outlet. It is evident that the values were decreasing since the first measurement in 21 December 26, reaching values below 1 mg NH 4 -N/L between 5 March and 7 May 27. When we stopped adding enzyme preparations on 7 May 27, ammonia nitrogen values started to increase and reached the value of 26 mg NH 4 -N/L after three weeks without the preparations. After enzyme preparations were applied again, ammonia nitrogen values started to decrease again. Graph 5 shows the efficiency of water treatment which was measured during the sampling before the wastewater entered the SBR treatment plant and after the treated water was discharged. 2-hour average samples were used. The sample before treatment was taken from the cesspit (sedimentation tank) and the sample after treatment was taken at the outlet as all other samples.

8 6 OPERATING COSTS During the treatment plant testing it was established that the majority of the SBR treatment plant operating costs (.74 kwh/day) can be attributed to the use of electricity and cleaning of the sedimentation tank. Table 2 shows main operating costs at the electricity price of.8938 EUR/kWh (Elektro Ljubljana). Calculated costs do not include the control of plant's operation and monitoring of discharged treated water into the environment. Table 2 Calculation of operating costs during the monitoring DATA FOR THE CALCULATION OF OPERATING COSTS Number of operating days 24 VALUE Daily electricity use.74 Kwh/day Transportation of biological sludge hourly rate * Biological sludge treatment m3* * Prices were set by Velenje Public Utility TOTAL Operation of small treatment plants also requires daily keeping of operator's log book and regular servicing of the plant. 7 CONCLUSION Measurements of wastewater at the outlet of the Pipelife SBR small waste water treatment plant with 5 PE capacity proved that the treatment plant functions in accordance with valid legislation for this area. The measured values were considerably below the prescribed limit values for small treatment plants. It was also established that adding enzyme preparations for better functioning of the cesspit has a strong impact on the concentration of the ammonia nitrate and the overall efficiency of plant operation. More important, even without additives the plant operates well and does not require much servicing and assistance. Operating costs are not high. Control over the operation of the device can be carried out through the controller which displays the current phase of plant operation and allows adaptations regarding the quantity or load of wastewater inflow at any time. Manufacturer's operating manuals are clear and recommended controller settings are adequate. As each technological process, this treatment plant also requires regular control and maintenance, which also includes monitoring of treated water and regular cleaning of the sedimentation tank. 8 LITERATURE 1. Original user's manual written by the manufacturer of the small treatment plant 2. Decree on the emission of substances in wastewater discharged from small municipal wastewater treatment plants, Official gazette of RS, no. 13/2. 3. Henze M., Harremoës P., Jansen j.c., Arvin e., Wastewater treatment: biological and chemical processes, third edition, 22, Springer