| Water pollution is a severe problem in the modern times, especially in the developing countries as well as China due to rapid economic growth and increased human activity. The rural wastewater pollution constitutes a major problem worldwide because it's usually lack of the effective and sustainable wastewater treatment systems. In recent years, there has been more attention for the developing the wastewater treatment approaches in China rural areas and protect the aquatic environment from pollution to produce an environmentally safe wastewater suitable for disposal or reuse. This research deals to study of the applicability of innovate bio-ecological treatment technology for rural domestic wastewater. The model system used in this study is essentially combined between a modified A~2/O process and constructed wetland. The modified A~2/O process consists of two stages of upflow anaerobic filter (UAF), anoxic filter (ANF) and four chambers of waterfall aeration biofilm reactor (WABR). The main objective of this study is to evaluate the performance efficiency of the bio-ecological combined system for removal of organic matter and nutrients from the rural domestic wastewater. The effect of hydraulic retention time (HRT), organic loading rate (OLR), temperature and recycle ratio of nitrifying wastewater on the treatment efficiency was assessed during the entire experimental operations. The experimental work was carried out at southeast University, Wuxi campus during two of the operation periods from June 2012 to January 2013 and from October 2013 to January 2014, respectively. The experimental study of this research mainly divided into three parts includes of performance evaluation study of the pilot scale modified A~2/O process, laboratory scale of A~2/O process and horizontal subsurface flow constructed wetland (HFCW).Pilot scale of the modified A~2/O process: In this part of the study, the pilot scale of modified A~2/O process is evaluated for the organic matter and nutrients removal.The removal efficiencies of chemical oxygen demand (COD), total nitrogen (TN),ammonium nitrogen (NH4+-N) and total phosphorus (TP) in each reactor were monitored and evaluated. The performance efficiency for each reactor was evaluated during six months at different of operation conditions. The system was exposed to domestic wastewater with COD concentration varied from 105.5 ?361.1 mg/l, TN ranged of 17.4?56.8 mg/1 and TP ranged of 0.83?4.1 mg/1.Acclimation of the anaerobic and aerobic bacteria for start- up system was achieved within 34 days and one week, respectively, depending on the stability of COD and NH4+-N removal. The UAF reactor was evaluated during two phases summer season (15th July - 15th October) and winter season (22th October - 15th January). During the first phase, the average COD removal efficiencies were ranged of 30.9%?48.12% at HRT varied between 1? 4 days corresponding OLR varied from 0.2?0.072kg. COD/ m3.day and the average temperature ranged between 19.6?30.4 ?, respectively. The maximum COD removal efficiency of 48.12% with average effluent concentration of 114.92 mg/l was realized at HRT of 3 days and an average temperature of 30.4 ?. In contrast, during the second phase, the average COD removal efficiencies were 34.5%, 38.2% , 29.1% at HRT of 3, 4, 5 days, OLR of 0.065, 0.065, 0.033 kg COD/m3.day and with the average temperature of 14.5, 10.7 and 6.1 ?, respectively. In addition, the biogas generated through the anaerobic treatment process is significantly depended on HRT, temperature, COD removal, and it was observed on average as 6.18 and 1.24 L/d during the summer and winter season, respectively. These results demonstrated that the removal efficiency improved with increasing in HRT,temperature and decreasing of OLR and the average COD removal obtained through UAF reactor operation was 42.4% and 34.7% in the first and second phase,respectively. Additionally, the biological nutrients removal was achieved through the integrated A/O process (anoxic - oxic). The average influent, effluent of TN,NH4+-N and TP concentrations at different of HRT ranged of 1? 5 hrs and recycle ratio of 2 and 3 during experimental operations of an integrated A/O process were 34.8, 26.1, 1.84 mg/1 and 11.6, 6.94 and 1.12 mg/1, respectively. The pilot scale of modified A~2/O sub-system showed a good performance efficiency for treatment process, which realized removal efficiencies of 69.4%, 69.08%, 75.5% and 46.41%with final average concentration of 65.68,11.6,6.94, and 1.12 mg/l for COD, TN,NH4+-N and TP, respectively.Laboratory scale of the modified A~2/O process: In this part of study, the laboratory scale of modif1ed A~2/O process was operated to realize two main goals included, firstly, the optimization study of the COD removal process in UAF reactor by investigating of the several operation factors such as pH, temperature,HRT and OLR influence the treatment process. Secondly, evaluated the effect of the water dropping height of the WABR on the ammonium nitrogen (NH4+-N)removal process. To achieve these goals, Taguchi orthogonal array (TOA) was applied to create the model of the experimental design and to determine the optimum combination factors to realize the maximum COD removal through UAF reactor. In addition, NH4+-N removal efficiency through WABR was investigated at different water dropping heights of 0.25, 0.3, 0.35 and 0.4 m.According to Taguchi method and based on the S/N ratios and ANOVA analysis, the results demonstrated that the optimum combination of factors with levels for achieving a maximum COD removal was A~2B3C3D1,which corresponding to pH value of 7, temperature of 25?, HRT of 36 hrs and OLR of 0.166 kg COD/m3.day. Furthermore, experimental model showed statically significant for all factors and the results demonstrated that the contribution percentage for the factors of HRT, temperature, OLR and pH on the COD removal process were 39.92%, 33.78%, 13.37% and 9.18%, respectively. The performance of UAF reactor for long term operation was evaluated during the period extend from 15th October 2013 to 15th January 2014 at different temperature and HRT.The results revealed that the average COD removal during the entire experiments ranged between 39.9% ? 56.5% with the total average COD removal of 50.8%.Moreover, to evaluate the effect of water dropping height in WABR on the NH4+-N removal efficiency, the dropping heights of 0.25, 0.3, 0.35 and 0.4 m were investigated. The results demonstrated that the DO concentration improved with the increase in water dropping height and flow rate. Furthermore, the NH4+-N removal efficiency showed increases with an increase in dropping height. The optimum water dropping height was 0.35 m. For long term operation of integrated A/O process in a laboratory scale, the results revealed that the HRT of 10 hrs,temperature of 25?, water dropping height of 0.35 m and recycle ratio of 2 were the optimum operation conditions for the performance of the A/O process to achieving maximum average removal of COD 68.3% and NH4+-N of 82.24%.Horizontal subsurface flow constructed wetland (HFCW): This is the last part of experimental study, which was operated during two phases (summer-winter)with different aquatic plants that cultivated into the constructed wetland (water spinach - Chinese celery). The performance efficiency of HFCW on nutrient removal was evaluated at different of hydraulic loading rate (HLR) and temperature. The water spinach HFCW sub-system demonstrated that the average removal efficiencies of COD, NH4+-N, TN and TP were 67.4%, 65.1%, 59.3 and 79.1%, and it was reduced with Chinese celery HFCW to 61.8%, 53.4%, 45.3%and 70.9%, respectively. The HFCW showed good growth of plants with efficient in organic matter and nutrient removal and the average effluent concentrations of COD was 32.8 mg/1, TN of 9.82 mg/1, NH4+-N of 5.04 mg/l and TP was 0.39 mg/l.Performance efficiency of the pilot scale bio-ecological combined system: In this study, the general evaluation of the bio-ecological combined system performance efficiency for rural wastewater treatment was conducted. The results showed that the average removal efficiencies of COD, TN, NH4+-N and TP through the entire system were 85.1%, 74.1%, 81.3% and 80% with final effluent concentration of 32.8, 9.82, 5.04 and 0.39 mg/1, respectively. These results demonstrated that the effluent quality in regard of COD, TN, NH4+-N and TP concentrations reached up to level (A) of Chinese sewage discharge standard (GB 18918-2002). This study revealed that the bio-ecological combined system was efficient, easy to operate, sustainable and more convenient for domestic wastewater treatment in rural areas.This research provides new ideas in the wastewater treatment beside it can bring researchers and readers to know more details about horizontal subsurface flow constructed wetland and aeration methodology by using waterfall aeration biofilm reactor which, can be applied in the wastewater systems. |
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