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Domestic wastewater treatment using immobilized sludge process An, Muhui

Abstract

This study is an initial approach for developing a small domestic wastewater treatment process using immobilized sludge. The feasibility of sludge immobilization by the PVA-boric acid method was examined. The activity and stability o f the immobilized sludge were measured. The potential of the immobilized sludge process for small scale domestic wastewater treatment was explored. In this research, the PVA-alginate-borate method was successfully used to immobilize activated sludge. The optimum final polyvinyl alcohol (PVA) concentration in the immobilized sludge was determined to be 10 ~ 12.5%. A minimal 1% of alginate was needed to prevent bead agglomeration. The effects of pH on the organic carbon removal activity by immobilized sludge were examined. A wastewater pH of 6 ~ 8 was the most favorable for application of the immobilized sludge process. The operational stability of the immobilized sludge system was also studied in a batch reactor. The effects of aeration rates and hydraulic retention time (HRT) on the treatment of domestic wastewater using the immobilized sludge process were investigated in a fluidized bed reactor. The results showed that variation of aeration rates (0.5 ~ 1.5L air/min.) and HRTs (24 ~ 6 hours) did not have any significantly adverse impacts on the removal of organic carbon, NH₄⁺ - N and TKN nor on producing a high quality of effluent. Different intermittent aeration patterns were investigated to improve total nitrogen (TN) removal. The best TN removal was above 74.4% and was achieved at an HRT of 6 hour (corresponding BOD loading rate 0.766 kg/m3 d) and aeration pattern of 1:3 (the ratio of non-aeration time and aeration time). The removal efficiencies for organic carbon, NH₄⁺ - N , TKN and TSS were not significantly affected. Simultaneous organic carbon and nitrogen removal could be realized in a single immobilized sludge reactor. The impact of various influent flow patterns on small scale domestic wastewater treatment was examined. The results showed that variation of wastewater feeding patterns ranging from 24-hour continuous feed to intermittent feed (12 and 8 hours per day) did not have any significantly adverse impacts on the removal of organic carbon, NH₄⁺ - N, TKN and TSS. However, a significant decrease in total nitrogen removal occurred. The production of excess sludge by the immobilized sludge process was experimentally demonstrated to be about 1/2 ~ 1/3 that produced by the conventional activated sludge process. The results of scanning electron microscopic analysis showed that bacteria mostly grew on the surface of immobilized sludge beads. The process performance of the immobilized sludge process in this research was as good as or better than that of other biological treatment processes for the domestic wastewater treatment. The immobilized sludge beads exhibited satisfactory mechanical stability without apparent breakage over the 180-day experiment. Thus the immobilized sludge process was demonstrated to be technically feasible for treatment of domestic wastewater on a small scale.

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