Efficiency Assessment of the Anaerobic Filter Reactor Treating Rural Domestic Sewage at Different Operational Temperature and HRT

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1 Efficiency Assessment of the Anaerobic Filter Reactor Treating Rural Domestic Sewage at Different Operational Temperature and HRT John Leju Celestino LADU* 1,2 ; Xiwu LU 1 ; Ahmed M.O. KHAIRALLA 1 1 School of Energy and Environment, Department of Environmental Science and Engineering, Southeast University, Nanjing 296, P. R. China 2 College of Natural Resources and Environmental Studies, Department of Environmental Studies, University of Juba, Republic of South Sudan Abstract In this research paper, the efficiency of anaerobic filter (AF) reactor was assessed for rural domestic sewage treatment at different operational temperature and HRT with different loading rates respectively. The results revealed efficient removal of COD by the reactor, 36%, 48% and 68% at an HRT of 1, 2 and 3 days. Besides that, temperature have significant influence on the reactor performance accounting to COD removal rate of 44%, 68%, 7%1 and 78% at the temperature of 15 o C, 18 o C, 22 o C and o C respectively. Biological degradation and solids accumulation in the reactor contributed to high COD removal rate. At temperature of 15 C, 18 C and 22 C, gas production rate increases with increasing influent COD organic load up to.19,.1 and.1 kgcod/m3.d for C, 22 C and 18 C respectively. At higher loads a constant gas production of 12, 9 and 6 L/day was observed for C, 22 C and 18 C, respectively. Average gas production at 15 C for all the inflow organic loads were 1.2 L/day. The results denoted that, the lesser the organic loading rate (OLR) and the longer the HRT, the higher the removal rate. For the nutrients, at temperature 15 C, 18 C, 22 and oc, TN removal rate were 28%, 32%, 35% and 47% respectively. At the same operating temperature of 15 C, 18 C, 22 C and oc, NH4 removal were 24%, 27%, %, 38% and that of TP were 13%, 16%, % and 24% respectively. The sluggish removal of nutrients by the reactor can be attributed to the low sludge production in the anaerobic filter. The finding concluded that, the reactor efficiency was highly affected by the operating temperatures and the HRT. Keywords Anaerobic filter; rural domestic sewage; operational temperature; HRT; loading rates; biological degradation; solids accumulation; I. INTRODUCTION Anaerobic treatment nowadays is becoming popular for rural domestic sewage treatment because of its low construction, operation and maintenance costs, small land requirement, low excess sludge production and production of biogas (Tarek A. Elmitwalli et al., 2). Even though the anaerobic treatment of rural domestic sewage has been used at large scale in several hot countries, the process to date has not been applied at full scale in temperate countries. This is chiefly because of lower removal efficiencies. Also, in temperate regions, a longer hydraulic retention time (HRT) is needed due to the lower rate of hydrolysis (de Man AWA et al, 1986) and the higher amount of accumulating suspended solids (SS) in the reactor (Zeeman G, Lettinga G, 1999). Rural domestic wastewater has typically low concentrations of COD, yielding small gas production that is insufficient to heat the reactor to more favourable mesophilic temperatures (B. Lew, et al, 4). Moreover, the relatively high concentration of particulate matter present in domestic wastewater requires an initial hydrolysis step, which is significantly affected by temperature and is usually the rate-limiting step in subtropical climate regions (B. Lew, et al, 4). In tropical countries AF reactors for rural domestic sewage have found wide acceptance. There are several fullscale plants already in operation in China, Colombia, Brazil, Indonesia, India and Egypt. Several authors have experimented on AF process and found COD removals above 8% (Souza and Foresti, 1996; Chernicharo and Cardoso, 1999). Several authors observed the influence of temperature on the performance of AF reactor; among them were Sari Luostarinen et al.,7; B. Lew, et al., 4; Lettinga et al., 1981; Grin et al., 1983; Vieira and Souza, 1986; Elmitwalli et al., 1999; Elmitwalli et al., 1; Seghezzo et al.,. 548

2 A decrease in the effluent quality was also observed, together with a decline in the gas production rate. A study by Agrawal et al. (1997) revealed a decrease in gas production rate when the temperature was reduced from 27 C to C. This case study focused on the effect of temperature on the efficiency of AF reactor for rural domestic sewage treatment at different hydraulic retention times (HRT) and organic loading rates. II. MATERIAL AND METHODS In Fig. 1 a schematic diagram of the experimental setup, consisting of an AF reactor constructed of plexiglass with an effective volume of 6 litres, internal diameter of 6. cm and a height of 9 cm high (see table 1), with five sampling ports placed at different heights. The AF reactor was filled with sludge taken from Wuxi municipal wastewater Treatment Corporation. The reactor was fed with rural domestic sewage pump from southeast university campus, Wuxi. Influent, effluent samples and gas production readings were taken at different temperatures and HRT from the reactor. After every two days, samples were taken from different sampling ports of the reactor and were taken to laboratory for experimental tests for COD, TN, NH4 and TP. All analyses were performed according to Chinese standard method for determination of municipal sludge in wastewater treatment plant (s) (CJT 221-5) and according to standard methods for the examination of water and wastewater (APHA, 1995). The calculation of COD removal efficiency was base on influent COD (Martina Uldal, 8). The volatile fatty acids concentration was measured using the five-point titration method (Moosbrugger et al., 1993). The gas produced was collected and measured as described by Haandel and Lettinga (1994). COD (%) = COD inf COD eff /COD inf * Initially the reactor was operated at 26 - o C with HRT of 3 days to allow sludge acclimatization to domestic sewage. Later, the HRT was steadily reduced with the increase in organic loading rate. The HRT was further reduced after the reactor reached stable state for a period of 25 days. After the start-up was completed at C, operations of the reactor at different temperatures were also conducted. Fig.1 schematic diagram of AF reactor 549

3 Parameters Hydraulic retention time (d) Total effective volume (L) Total height (cm) TABLE 1 MAIN FEATURES OF THE OPERATED AF REACTOR Internal diameter (cm) Organic load (kg COD/m3/d) SS (mg/l) VSS (mg/l) Grey matter (mg/l) Values 1,2, VSS/SS III. ANALYTICAL PROCEDURES To examine the efficiency of the AF reactor in rural domestic sewage, the following parameters shown in table and method of testing in rural domestic sewage were used and considered to be of paramount importance for this study. The experimental test was carried for a period of four months. All the analysis was conducted in accordance with the Chinese standard method for determination of municipal sludge in wastewater treatment plant (s) (CJT 221-5) and according to the standard methods (APHA 1995). The samples were filtered through a.45-μm membrane filter before experimental analysis. The ph and temperature was measured by dissolved oxygen meter and gas production was measured by wet gas meter. The flow rate was controlled by a valve and incessantly regulated by the help of a pump. TABLE 2 TEST SAMPLES AND METHODS Sample tested Methods Temperature (oc) Dissolved oxygen meter COD (mg/l) Potassium dichromate (GB ) TN (mg/l) On the Persulfate UV Spectrophotometer (GB ) NH4 (mg/l) Nessler s reagent (GB ) TP (mg/l) UV Spectrophotometer (GB ) Gas production (L/d) Wet gas meter A. COD removal IV. RESULTS AND DISCUSSION At the start up period, the reactor performed very well resulting into COD removal of 68%. At the end of the startup period, the reactor was operated at different temperatures for a period of four Months and the HRT was steadily reduced from 3 days to 2days and then to 1 day with an increase in organic loading rate (OLR) from kgcod/m3.d. There was stability in effluent COD concentration when the HRT was gradually reduced. For HRT less than three days, the quality of effluent was greatly reduced, while at HRT longer than two days, the average COD removal was seen to be constant (around 68%), it decreased to 48% at HRT of 2days and 36% at HRT of 1 day (fig.2). The results also revealed that, the lesser the OLR, the higher the removal rate (figure 3) 55

4 COD removal (%) Gas production (L/d) COD removal (%) COD removal (%) COD removal COD removal COD removal COD removal HRT (d) OLR (kgcod/m3.d) Fig.2 Average COD removal with HRT Fig.3 Average COD removal with OLR The reduction in CODs removal rate can be explained by too short HRT to complete COD degradation. For each temperature studied the COD removal at HRT longer than 2 days decreased with the decrease in the temperature TABLE 3 (Table 1). These results suggest a much lower biodegradability at lower temperatures of a range of compounds comprising the varied composition of rural domestic wastewater. AVERAGE COD REMOVAL (%) AND GAS PRODUCED AT DIFFERENT TEMPERATURES Temperature Removal performance Gas production (L/d) 15 C C C C C 18 C 22 C. C Temperature COD removal Gas production Fig.4 Average COD removal at different temperature Gas production 15 C 18 C 22 C. C Temperature (oc) Gas production Fig.5 Average gas production at different temperature 551

5 At temperature of 15 C, 18 C and 22 C, gas production rate increases with increasing influent COD organic load, up to.19 kgcod/m3.d for C and.1 kgcod/m3.d for 22 C and 18 C respectively. At higher loads a constant gas production of 12, 9 and 6 L/day was observed for C, 22 C and 18 C, respectively. At 15 C average gas production was experimented for all the inflow organic loads was 1.2 L/day (see table 2). Base on these results, the study coincided with that of B. Lew, et al. 4, that the hydrolytic bacteria were more affected by temperature alteration than the methanogenic bacteria. As observed, the maximum gas production rate demonstrates a decrease with temperature, as with the COD removal. Nevertheless, the decrease in the maximum gas production was much more marked than the decrease in the COD removal. This B. TN removal The average concentrations of total nitrogen (TN) in the influent and effluent of AF were 32.2 and 16.7mg/L respectively. These results indicated insignificant TN removal with regards to the operating temperature conditions. incident can be explained by suspended solids accumulation in the reactor, which resulted in better COD removal. At lower temperature, solids of different characteristics were built up on top of the floc. Suspended solids can also cause formation of scum layers and sudden washout of sludge, if they are only accumulated and not stabilized within the reactor. Long hydraulic retention time and sludge retention times (HRT, SRT) and relatively low organic loading rates (OLR) are thus required (Zeeman and Lettinga, 1999).The increase in the accumulation of particulate matter in the reactor approximately equaled the decrease in the biological degradation rate with temperature and explains the same overall COD removal efficiencies attained at C, 22 C and 18 C for the reactor, as seen in Table 1. This may be attributed to the low sludge production in the anaerobic filter as reported by Barbosa et al., At temperature of 15 C, 18 C, 22 and oc, TN removal rate were 28%, 32%, 35% and 47% respectively. At the end of the startup period, the reactor removal rate was 48%. TABLE 4 AVERAGE TN REMOVAL (%) AT DIFFERENT TEMPERATURES Temperature Removal performance (%) 15 C C C. 35 C

6 TN removal rate (%) TN removal C 18 C 22 C. C TN removal Temperature (oc) C. NH4 removal The average influent and effluent concentrations of NH4 in the rural domestic sewage during the experimental tests were found to be 27.3mg/L and 17.2mg/L respectively. This also shows that, there is insignificant NH4 removal with regards to the operating temperature conditions. This Fig.5 Average TN removal at different temperatures TABLE 5 AVERAGE NH4 REMOVAL AT DIFFERENT TEMPERATURES Temperature Removal performance (%) 15 C C C. C 38 is also attributed to the inadequate production of sludge production in the reactor. NH4 removal rate of the reactor increases with increase in temperature. At temperature of 15 C, 18 C, 22 and oc, NH4 removal were 24%, 27%, % and 38% removal rate. At the end of the startup period, the average reactor removal rate was 37%. 553

7 NH4 removal (%) NH4 removal NH4 removal 5 15 C 18 C 22 C. C Temperature (oc) Fig.6 Average NH4 removal at different temperatures D. TP removal The influent and effluent concentrations of TP in the rural domestic sewage during the experimental tests were 2.1 mg/l and 1.5 mg/l respectively. The removal rate was 13%, 16%, % and 24% at temperature of 15 C, 18 C, 22 and oc. This also shows that, TP removal in the reactor is affected by temperature resulting into average removal of 29%. TABLE 6 AVERAGE TP REMOVAL (%) AT DIFFERENT TEMPERATURES Temperature Removal performance (%) 15 C C C. C

8 Efficiency (%) TP removal (%) TP removal TP removal Temperature (oc) Fig.7 Average TP removal at different temperatures COD removal TN removal NH4 removal TP removal Gas production 15 C 18 C 22 C. C Temperature (oc) Fig.8 Average COD, TN, NH4, TP removal and gas produced at different temperatures 555

9 V. CONCLUSIONS The study concludes that, the anaerobic filter reactor is efficient in removal of COD at different HRTs. Furthermore, temperature has imperative influence on the reactor performance respectively. Biological degradation and solids accumulation in the reactor contributes to high COD removal. The results signify that, the lesser the organic loading rate (OLR) and the longer the HRT, the higher the removal rates. On the other hand, low sludge production in the anaerobic filter contributed to insignificant removal of nutrients (TN, NH4, and TP). Based on the results obtained in this study, we can conclude that AF reactor is efficient at different operating temperatures and hence, can be applied for treatment of rural domestic sewage in different climatic zones. ACKNOWLEDGEMENTS Acknowledgments is extended to School of energy and environment, department of environmental science and engineering, Southeast University and to the college of Natural Resources and Environmental Studies, department of environmental studies, University of Juba for providing academic support. REFERENCES [1] Tarek A. Elmitwalli et al., (2). Treatment of domestic sewage in a two-step anaerobic filter/anaerobic hybrid system at low temperature. Water Research 36 (2) [2] de Man AWA, Grin PC, Roersma R, Grolle KCF, Lettinga G., (1986) Anaerobic treatment of sewage at low temperatures. Proceedings of the Anaerobic Treatment a Grown-up Technology, Amsterdam, The Netherlands, pp [3] Zeeman G, Lettinga G., (1999). The role of anaerobic digestion of domestic sewage in closing the water and nutrient cycle at community level. Water Sci Technol;39(5): [4] Lettinga G, Roersma R, Grin P., (1983). Anaerobic treatment of raw domestic sewage at ambient temperatures using a granular bed UASB reactor. Biotechnol Bioeng;25: [5] Uemura S, Harada H., (). Treatment of sewage by a UASB reactor under moderate to low temperature conditions. Biores Technol;72(3): [6] Agrawal, L.K., Ohashi, Y., Mochida, E., Okui, H., Ueki, Y., Harada, H. and Ohashi, A. (1997). Treatment of raw sewage in a temperate climate using a UASB reactor and the Hanging Sponge Cubes process. Wat. Sci. Tech., 36(6 7), [7] APHA (1995). Standard Methods for the Examination of Water and Wastewater. 19th edn, APHA, AWWA, WPCF, Washington DC, USA. [8] El-Gohary, F.A. and Nasr, F.A. (1999). Cost-effective pretreatment of wastewater. Wat. Sci. Tech., 39(5), [9] Elmitwalli, T.A., Zandvoort, M.H., Zeeman, G., Bruning, H. and Lettinga, G. (1999). Low temperature treatment of domestic sewage in upflow anaerobic sludge blanket and anaerobic hybrid reactors. Wat. Sci. Tech., 39(5), [] Grin, P.C., Reresma, R. and Lettinga, G. (1983). Anaerobic treatment of raw sewage at lower termperatures. In Proc. European Symposium on Anaerobic Wastewater Treatment, Noordwijkerhout, The Netherlands, [11] Lettinga, G., Roersma, R., Grin, P., de Zeeuw, W., Hulshof Pol, L., van Velsen, L., Hovma, S. and Zeeman, G. (1981). Anaerobic treatment of sewage and low strength wastewater. Proceedings of the Second International Symposium on Anaerobic Digestion, Travemunde, Germany, [12] Moosbrugger, R.E., Wentzel, M.C., Ekama, G.A. and Marais, G.V.R. (1993). Alkalinity measurement: part 1 a 4 ph point titration method to determine the carbonate weak acid/base in an aqueous carbonate solution. Water SA, 19(1), [13] Sari Luostarinen., Wendy Sanders., et al.,(7). Effect of temperature on anaerobic treatment of black water in UASBseptic tank systems [14] Seghezzo, L., Castaneda, M.L., Trupiano, A.P., Gonzalez, S.M., Guerra, R.G., Torrea, A., Cuevas, C.M., Zeeman, G. and Lettinga, G. (). Anaerobic treatment of pre-settled sewage in UASB reactors in subtropical regions (Salta, Argentina). Preprints, VI Latin-American Workshop and Seminar on Anaerobic Digestion, Recife, Brazil. pp [15] Souza, J.T. and Foresti, E. (1996). Domestic sewage treatment in an upflow anaerobic sludge blanketsequencing batch reactor system. Wat. Sci. Tech., 33(3), [16] Tilche, A. and Vieira, S.M. (1991). Domestic report on reactor design of anaerobic filters and sludge bed reactors. Wat. Sci. Tech., 24(8),

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