2016 International Conference on Environment, Climate Change and Sustainable Development (ECCSD 2016) ISBN: 978-1-60595-358-8
Up Flow Anaerobic Filter (UAF) Treatment of Rural Domestic Sewage at Different Psychrophilic and Mesophilic Temperatures John Leju Celestino LADU 1,2 , Xi-wu LU 1,* and Zhong-zhao PING 1 1School of Energy and Environment, Department of Environmental Science and Engineering, Southeast University, Nanjing, 210096, P. R. China 2College of Natural Resources and Environmental Studies, Department of Environmental Studies, University of Juba, Republic of South Sudan *Corresponding author
Keywords: Anaerobic filter, Pschrophilic, Mesophilic , Sewage, HRT.
Abstract. This empirical research paper revealed the findings from the up flow anaerobic filter (UAF) treatment of rural domestic sewage at different pschrophilic and mesophilic temperature. The reactor was operated at specific HRT of 24, 48 and 72 hours. In the first 14 days of the start-up, the results obtained from the reactor revealed good removal efficiency. At the mesophilic temperature, average COD removal reached 82.0%; while at psychrophilic temperature the reactor attained 68.7%. From the overall results, UAF reactor managed under mesophilic condition disclosed higher COD removal efficiency as compared to psychrophilic temperature which is similar to values obtained in hot regions. Experimentally, up flow anaerobic filter reactor operated at mesophilic temperature is recommended for rural domestic sewage treatment at a specific HRT of 3 days.
Introduction In recent years, gigantic urban areas are served more readily than the medium and small city areas or rural communities in domestic sewage treatment. Since the population density is less in rural areas as compared with big urban cities, a small-scale dispersed up flow anaerobic (UAF) treatment system is opted to be the best option. The conventional activated sludge process that is extensively famous for domestic sewage treatment in urban cities is a stable treatment system, but the process is not suitable and cost effective for a small-scale rural domestic sewage treatment system, hence, other systems are being selected. The concern of domestic sewage treatment has been shifting from large-scale intensive systems for urban cities, to small-scale systems necessary for rural communities. Rural domestic sewage is extremely contaminated with various pollutants that has contributed to water quality deterioration and affects the natural use of water for agriculture and other domestic uses. Hence, up flow anaerobic filter sewage treatment process has been explored as the green technology due to its efficient feasibility for treatment of low strength rural domestic sewage [1]. In addition, anaerobic process is very simple and cost effective in contrast with aerobic technology [2]. In the up flow anaerobic filter reactors, pollutants can successfully be removed if appropriate temperature, pH, and hydraulic retention time (HRT) are applied [3]. Among the operational conditions, temperature range is crucial for achieving high efficiency. Nevertheless, in temperate climate, high rate anaerobic reactors have been applied [4], in which proliferations of bacteria have been reported under psychrophilic, mesophilic and thermophilic environment [5]. The main objective of this paper is to assess the up flow anaerobic filter reactor efficiency at psychrophilic and mesophilic temperature with specific hydraulic retention time (HRT).
Seed Sludge The reactor was seeded with anaerobic sludge obtained from Wuxi municipal sewage treatment plant. The raw sludge was screened through a 600 µm sieve before seeding to remove the sand, fibers, and large pieces of debris which may inhibit the anaerobic suspended growth before seeding. The concentration of the existing sludge was estimated to be 0.30 gVSS per liter of reactor, with the initial sludge characteristics as follows: water content 85 %, VSS/ (wet sludge) 7.6 % and SMA (at ambient temp.) 0.072 gCOD/gVSS.d.
Wastewater for the Experiment The inlet sewage was mainly from a campus main manhole at Southeast university campus of Taihu Lake environmental program, in Wuxi, Jiangsu Province. Samples were collected from influent and effluent of the reactor by 3-days interval and then kept in a cold room at temperature of 4°C to avoid further degradation.
Experimental Set-ups One cylindrical Polyvinylchloride (PVC) up flow anaerobic filter with internal diameter of 10cm, a height of 200cm and wall thickness of 1cm were used in this experiment. The column was filled with a non-woven fabric filter materials and porosity of 97%. The up flow anaerobic filter reactor had an effective volume of 80 L. Water bath system was provided to control the temperature of the reactor.
Table 1. Characteristics of the studied area rural domestic raw sewage (mg/L). Parameter Min Max Average COD [mg/L] 76.8 375.5 15 6.6 pH 6.6 7.5 7.1 Table 2. Operational conditions of process at Psychrophilic temperature. Reactors HRT [hours ] Temperature [°C] UAF 24 14 48 16 72 18 Table 3. Operational conditions of process at Mesophilic temperature.
Reactors HRT [hours] Temperature [°C] UAF 24 23 48 26 72 30
Analytical Procedures All the analyses were carried out in accordance to [6, 7]. The removal rate Em of pollutants from sewage passing through the UAF bioreactors was calculated from Eq. (1):
(1)
Where Ci is the influent pollutant concentration (in mg/l) and Ce is the pollutant concentration in the effluent (in mg/l). The total removal rate of pollutant in the UAF system was calculated from the values at the inlet and the outlet of the UAF.
Results and Discussion The Influence of Temperature on Reactors’ Performance for COD Removal The up flow anaerobic filter reactor (UAF) was started at specific HRTs and different temperatures mentioned in table 2. During the first 14 days, the results obtained from the reactor showed good removal efficiency. At the same HRTs, COD removal of UAF at psychrophilic temperature reached 68.7% while at mesophilic temperature it reached 82.0% (table 3 & 4). This has revealed the higher efficiency of the reactor at mesophilic temperature (average 26 oC) as compared to psychrophilic temperature (average 16 oC). Several studies on AF treatment process at pschrophilic temperature has obtained COD removal efficiencies of (80-90%) temperatures [8], whereas at mesophilic and extreme treatment temperature of 40 oC, a 80% COD removal was obtained [9]. Table 4. Average COD concentrations in influent, effluent and removal at psychrophilic temperature.
HRT Temp [oC] Removal efficiency [%] [h] [mg/L] [mg/L] 14 24 126.3 43.13 66% 16 48 138.7 44.32 68% 18 72 140.5 39.01 72% Table 5. Average COD concentrations in influent, effluent and removal at mesophilic temperature.
Temp ( oC) HRT (h) Removal efficiency (%) (mg/l) (mg/l) 23 24 139.5 30.17 76% 26 48 144.6 24.31 83% 30 72 158.1 20.42 87% The results revealed that UAF reactor efficiency increased with increase temperature as well as increase in HRT. Increase in temperature and HRT always resulted into improved removal efficiency of up flow anaerobic reactor in regards to COD removal. This agreed with the findings of [10] who reported COD removal of 87% at temperature of 35 oC when treating pharmaceutical waste in an UAF. The high and good removal efficiencies of UAF at mesophilic temperature demonstrated that UAF reactor is efficient and can be utilize for rural domestic sewage treatment.
Summary Considering these findings, it’s empirical that the UAF bioreactor can be successfully represented as cost effective and efficient alternative of rural domestic sewage treatment.
Acknowledgement This research has been supported by major science and technology program for water pollution control and treatment (2012ZX07101-005) and national natural science foundation of China (51078074).
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