SOLUBILIZATION OF SYNTHETIC SEWAGE

Abstract

With the advent of several high-rate treatment systems, anaerobic process has emerged as a promising alternative for the treatment of different types of wastewaters. From the various systems which have been developed, the UASB reactors and /or related systems are mostly applied. One of the major features of UASB reactors is the development of the sludge of good settling properties and low sludge volume index (SVI). Further, scarcity of power supply coupled with frequent power failure make anaerobic technology an ideal choice for domestic and industrial wastewater treatment in this part of the world. The SS content of the wastewater is a primary factor that affects the performance of an anaerobic reactor. It is one of the key issues in operation and performance of UASB reactor. The SS present in the wastewater, depending on characteristics and concentration can affect the anaerobic treatment in the following ways: Reduction of SMA of the sludge due to adsorption and entrapment of poorly or non biodegradable SS. Formation of scum layers. It may counteract the formation of granular sludge. A prolonged continuous entrapment of voluminous SS in a granular sludge bed may lead to a spontaneous and sudden washout of almost the complete sludge bed. I SS (organic in nature) render difficulty in producing degradable soluble substrate for methane generation also. Therefore, when uniform conditions are applied i.e. in single phase process, optimum conditions cannot be achieved for both acidogens and methanogens. Pohland and Ghosh (1971) proposed separation of the acid forming phase from the methane forming phase by employing two separate reactors. The goal of a two phase digestion system is (i) to eliminate adverse effects of SS on methanogens (ii) to enhance anaerobic biodegradation by controlled separation of major reactions, with the ii hydrolysis and fermentation/acidification reactions contained within the first phase and the acteogenic/methanogenic reactions in the second phase. The objectives of the work embodied in the thesis are given as under: (i) To increase soluble fraction of COD in the wastewater (ii) To minimize COD reduction i.e. to check the conversion of incoming COD to methane in the solubilization reactor (iii) To decrease the SS content. To meet out these, investigations have been carried out to study: * The solubilization of Synthetic sewage. For the ease of presentation the subject matter of the thesis has been divided into following chapters. 1) Introduction 2) Literature Review 3) Materials and Methods 4) Results and Discussion 5) Conclusion References are appended at the end. Information and data relevant to the work have been incorporated as appendices. The objectives of the work along with the justification of the problem undertaken form the subject matter of Chapter-1. Chapter-2 deals with the literature review on sewage treatment by UASB process. A number of full scale plants which are in operation in India have been emphasized.. Waste solubilization has been incorporated. Chapter-3 describes the materials and methods employed in the investigations. The reactor was inoculated with 14 L ( 25% sludge occupancy) of sludge with the TSS and VSS contents of 41.1 and 19.76 g L-1 (48%) respectively. The average influent total iii COD and soluble COD to reactor were 516.8 mg I:1 and 344 mg 1.-1. Solubulization/ acidification reactor was first acclimated for 30 days (3 cycles per day of 8h each) with synthetic sewage. Afterwards, HRT was lowered step by step and reactor was operated at HRTs of 6, 4 and 2 h at a constant temperature (30±2°C). Results and discussion pertaining to different experiments performed have been organized in the Fourth Chapter of the thesis. Solubilization-fermentation of total organic matter (both soluble and particulate fractions) has been studied. Retention of SS, fermentation and clarification of fermented effluent was achieved in an UASB reactor. As a primary settler, the fermenter was able to consistently produce an effluent with low SS (< 100 mg SS 1:1) under all operating conditions tested (HRT values of 6 h to 2 h). The process was initiated at 8 h HRT which was subsequently reduced to 6h, 4h and 2 h. Observations at 8h were not recorded. The overall summary of the results of solubilization phase indicates retention of SS, fermentation and clarification of fermented effluent in a single reactor. As a primary settler, the fermenter was able to consistently produce an effluent with low SS = 82 mg 1:1 ( <100 ). At HRT of 2 h, mean (CODS) effluent / (CODs) influent was found to be 0.28, and (CODs/CODT) effluent =0.79 greater than (CODs/CODT) influent = 0.66. Mean CODT removal was 75.7% but mean SS (COD) removal was 61%. This disparity between SS and COD removal may be due to the solubilization of particulate organic matter in the wastewater. The particulate COD concentration from a mean value of 178.57 mg 1:1 was reduced to 27.144 mg 1:1 (A.-184.8%) and soluble COD concentration was reduced from a mean value of 349.46 mg 1:1 to 99 mg 1:1 (-,1 71.6% only, CODA/CODs = 027). The results obtained also show that under the HRT of 2h, an average of 0.16 mg HAc CODT was produced. The relatively low HRT (2 h) may result in compact reactor volume with good solids retention, leading to VFA production and wastewater clarification...