TREATMENT OF HOSPITAL WASTEWATER USING ACTIVATED SLUDGE COMBINED WITH BIOLOGICAL CONTACTOR

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1 TREATMENT OF HOSPITAL WASTEWATER USING ACTIVATED SLUDGE COMBINED WITH BIOLOGICAL CONTACTOR ABSTRACT In wastewater treatment plant (WWTP) of Dong Thap General Hospital, an aerotank was transformed to Activated Sludge combined with Biological Contactor- ASBC for treating hospital wastewater to meet the Vietnamese standard, especially total Nitrogen factor. The transformed WWTP expressed a higher pollutants removal performance: 87.8% with COD, 71.2% with total N, 83.6% with total P, 99.98% with Coliforms. The effluent of the WWTP with ASBC meets the Vietnamese standard TCVN 5945:3005, A level. Key words: Hospital wastewater, Aerotank, Activated Sludge combined with Biological Contactor, Nitrogen removal 1. INTRODUCTION Hospitals generate on average 750 l of wastewater by bed and a day. These effluents are loaded with pathogenic microorganisms, pharmaceutical partially metabolized, radioactive elements and other toxic chemical substances. The pollutants in hospital wastewater are certain substances, such as anti-tumor agents, antibiotics and organohalogen compounds, leave mostly into WWTP. Along with these pollutants, pathogenic microorganisms in hospital wastewater are a risk for other living things and receiving waters. Therefore, researching and finding an effective and appropriate WWTP for hospital wastewater are a necessity [4]. In general, secondary biological treatment along with anaerobic sludge treatment is used to treat hospital wastewater. During outbreaks of enteric disease; however, or during warm weather, because of the pathogenic microorganisms increase, the effluent must be disinfected by chlorine dioxide (ClO 2 ). If the final effluent is discharged into costal waters close to shellfish habitats, disinfection of the effluent will be required throughout the year [5]. The factors which determine designed decisions in a hospital WWTP are: land requirement, construction cost, maintenance cost, and operation cost. According to Kumar et al., conventional suspended-growth activated sludge processes, which have been used effectively and widely to treat municipal wastewater during the last hundred years, are not always suitable for treating some wastewater flows. In our Green Tech operation conditions, this was confirmed with the WWTP in Dong Thap general hospital case because the aerotank didn t thoroughly remove total Nitrogen, total Phosphorus, Coliforms. To control this problem, we decided to improve the aerotank into Activated Sludge combined with Biological Contactor-ASBC, the treatment has been proven to remove nutrients efficiently from wastewater [4]. All improvement steps as well as treatment efficiency of each plan are described and summarize in this paper. 1

2 2. MATERIAL AND METHODS 2.1. Material Activated sludge used in hospital WWTP was taken from stable aerotanks in other WWTPs which have the similar characteristics. Biological fixed contactor material made from PVC (Fine Reputation Co. Ltd., Taiwan) with surface area 110 m 2 /m 3, and vacant space 99,2% Methods Treatment technology Figure 1: Biological fixed contactor material made from PVC Hospital wastewater Pump sum Equalization tank Raw Bar rack Fine Bar rack Hospital wastewater Pump sum Equalization tank Blower Aerotank Blower ASBC Settling tank Sludge digester Settling tank Sludge digester Chlorine Disinfection tank Chlorine Disinfection tank Receiving water Receiving water Figure 2: Outline of WWTP of Dong Thap general hospital before (left, Aerotank) and after improvement (right, ASBC) 2

3 According to Dong Thap general hospital, the WWTP with Aerotank couldn t treat 250 m 3 wastewater per day to meet the Vietnamese standard TCVN 5945:2005, A level, especially total Phosphorus and total Nitrogen are higher 2 times than the standard because the traditional aerotank can t remove effectively N in wastewater. To improve the effluent wastewater, we decided to change the aerotank to the ASBC with PVC biological contactor. The ASBC is a combination of suspended growth (activated sludge) and attached growth (biofilm). In addition, raw and fine bar racks were also installed at the beginning of pump sum and equalization tank to split garbage from wastewater to improve the removal efficiency of biological processes Investigated parameters and sample collection methods To find the treatment performance of each system, these factors were investigated: COD, BOD 5, total N, total P, and Coliforms. Here is the way to collect samples: Sterile 500 ml glass bottles were used to collect effluent sample from each stage of treatment. Duplicate samples were collected and stored in a refrigerator. After collection, all the samples were processed in Environmental Engineering Laboratory Institute of Environment and Resources, Vietnam National University-Ho Chi Minh city. 3. RESULTS AND DISCUSSION Wastewater quality results of samples in Dong Thap general hospital WWTP are showed in Table 1. Table 1: Characteristics of inlet and outlet wastewater of WWTP in Dong Thap general hospital Source: Green Tech Co., November 10, 2008 COD, BOD 5, Total N, Total P, Coliforms, MPN/100ml Inlet x10 6 Outlet of WWTP with Aerotank Outlet of WWTP with ASBC Standard TCVN 5945:2005, A level COD removal performance Figure 3 displays the COD removal efficiency of two WWTPs. The results show that the WWTP with ASBC removes organic matters more effectively than the WWTP with aerotank (87.8% comparing to 75.7%). In addition, the improvement of the WWTP helps to treat wastewater meeting the TCVN 5945:2005 standard, A level. 3

4 Figure 3: COD removal performance of 2 WWTPs, % COD treated =(COD inlet COD outlet )/COD inlet This result is explained by the installation of bar racks at the beginning of the pump sum and the equalization tank. Bar racks reduce garbage in hospital wastewater and improve the COD removal performance of the transformed system. Besides, the efficiency of ASBC is higher than that of aerotank due to the combination of activated sludge processes and attached-growth microorganisms operation in a biofilm Nitrogen removal performance Figure 4 shows the efficiency of Nitrogen removal in the transformed WWTP is higher two times than that of in the WWTP with aerotank (71.2% comparing to 37.9%), and total N in effluent meets the TCVN 5945:2005 standard, A level. Figure 4: Nitrogen removal performance of 2 WWTPs 4

5 The higher Nitrogen removal performance of the WWTP with ASBC than that of the WWTP with Aerotank has been explained by the combination of both nitrification and denitrification inside ASBC. In the ASBC, biological microorganisms living on the contactor material surface can produce biological flocs which contain both aerobic zone and anoxic zone. According to Van Huyssteen et al. (1990), this condition with both aerobic zone and anoxic zone is very compatible to Nitrogen removal processes. Meanwhile, the sludge in the Aerotank is always fixed at aerobic condition which can t completely remove all Nitrogen concentration in wastewater. For this reason, the ASBC has been believed the main factor to increase the Nitrogen removal performance. This result also shows that our changing decision from the WWTP with Aerotank to the one with ASBC is a precise choice. According to Van Huyssteen et al. (1990), the combination of both nitrification and denitrification in the Nitrogen removal processes may be explained by two possible mechanisms. First, the mixed liquor traveled away from the surface mechanical aerators, the Dissolved Oxygen-DO was depleted, creating conditions more favorable for anoxic reactions. Second, activated sludge floc can contain both aerobic and anoxic zone, as illustrated in a simplified view of a biological floc on Fig. 5 because the DO can not penetrate all the depth of the floc [3]. Nitrate produced by nitrification in the aerobic zone can diffuse into the inner anoxic zone along with substrate so that denitrification occurs within the floc depth. With the combination of nitrification and denitrification, the Nitrogen concentration in the influent wastewater was removed efficiently by the ASBC with activated sludge and biofilm on contactor material. Figure 5: Diagram of an activated sludge particle showing aerobic and anoxic zone 3.3. Phosphorus removal performance Similar to N, P factor was treated efficiently in ASBC with efficiency 83.6%, satisfying the standard. 5

6 3.4. Bacteria removal Figure 6: Phosphorus removal performance of 2 WWTPs Microorganism is one of the most important factors in the effluent of hospital WWTP, and is measured by Coliforms bacteria. The bacteria removal efficiency has a formula: -log(c n /C 0 ), where C n is the number of bacteria at time n, C 0 is the number of bacteria in the inlet. The result proves that the bacteria removal performance of the transformed WWTP is higher than that of the other one. (99.98% comparing to 99.95%). 4. CONCLUSIONS Figure 7: Bacteria removal performance of 2 WWTPs - The WWTP of Dong Thap general hospital after improved from aerotank to ASBC shows a higher efficiency in all investigated factors, especially Nitrogen. 6

7 - All factors in the outlet of the WWTP with ASBC meet the TCVN 5945:2005, A level. REFERENCES [1] Chitnis, V. et al. Hospital effluent: A source of multiple drug-resistant bacteria. Current Science, Vol. 79, No. 7, [2] Kumar, B.M. and S. Chaudhari. Evaluation of sequencing batch reactor (SBR) and sequencing batch biofilm reactor (SBBR) for biological nutrient removal from simulated wastewater containing glucose as carbon source. Wat. Sci. Technol., 48, 2003:73-9. [3] Metcalf & Eddy. Wastewater Engineering Treatment and Reuse-Fourth Edition. Mc Graw-Hill. [4] Rezace A. et al. Hospital wastewater treatment using an integrated anaerobic aerobic fixed film bioreactor. American Journal of Environmental Sciences1 (4) 2005: [5] Tsai C.T, Lin S.T. Disinfection of hospital waste sludge using hypochlorite and chlorine dioxide. Journal Applied Microbiology 1999: [6] Wen, X. et al. Treatment of hospital wastewater using a submerged membrane bioreactor. Process Biochem., 39, 2004: