Efficiency of high rate treatment of low-strength municipality sewage by a pilot-scale combination system of a sedimentation tank and a down-flow hanging sponge reactor.

Down-flow hanging sponge (DHS) reactor that is sponge-based trickling filter was considered to be an alternative aerobic treatment system for low strength sewage treatment under tropical conditions. This study aims to determine the process performance of the DHS reactor combined with a pre-treatment sedimentation tank (SED) system installed at the municipality sewage treatment plant in Khon Kaen, Thailand over, 1,600 days. The DHS reactor was operated with three operational periods: low (0.2 kgBODm3 per day), high (0.5-1.3 kgBODm3 per day), and super rates (1.7-2.2. kgBODm3 per day). The results showed effective reductions in biochemical oxygen demand (BOD) and suspended solids by more than 74% and 78%, respectively, during the entire experimental period. Moreover, the final effluent met the Thailand discharge standard with an external short hydraulic retention time of 0.2 h. In addition, the combined system facilitates simultaneous nitrification and denitrification and effectively removed up to 43% of total nitrogen. The self-degradation of the organic compounds occurs owing to the retained sludge in the DHS reactor; this leads to undisputed clogging in sponge media. Therefore, the combined SED-DHS system could be an appropriate sewage treatment system for tropical conditions.

Development of appropriate technology for treatment of molasses-based wastewater.

In this study, the performance of a proposed treatment system consisting of an anaerobic process (acidification, methane fermentation) and an aerobic process (trickling filter) was evaluated for treating high concentrations of molasses-based wastewater (43-120 gCOD/L) by a continuous flow experiment. An anaerobic up-flow staged sludge bed (USSB) reactor, equipped with multiple gas solid separators, was used as the main treatment/methane recovery process. The USSB showed good efficiency of both COD removal (80-87%) and methane recovery (70-80%) at an organic loading rate of 11-43 kgCOD/m(3) day. As the influent COD concentration was increased, the organic loading rate for stable operation of the USSB was reduced due to cation inhibition. However, the COD removal efficiency of the whole treatment system (including the aerobic post-treatment process) was 96% even at an influent COD concentration of 120 gCOD/L. Use of the treated wastewater as a fertilizer and/or irrigation-water for sugarcane was evaluated by a field cultivation test. Both growth of sugarcane and emission of greenhouse gases from the field soil were measured. A relatively high methane flux (352 µgCH4/m(2) h) was observed when the treated wastewater from day 0 was used. By day 3, however, this value was reduced to the same level as the control. In addition, growth of sugarcane was satisfactory when the treated wastewater was used. The treated wastewater was found to be useful for cultivation of sugarcane in terms of both a low risk of greenhouse gas emission from the field soil and effectiveness for growth of sugarcane.

Development of a treatment system for molasses wastewater: the effects of cation inhibition on the anaerobic degradation process.

This study evaluated the process performance of a novel treatment system consisting of an acidification reactor, an upflow staged sludge bed (USSB) reactor, an upflow anaerobic sludge blanket reactor, and an aerobic trickling filter for the treatment of a high-strength molasses wastewater with a chemical oxygen demand (COD) of up to 120,000mg/L. The USSB operating at 35°C was capable of achieving an organic loading rate of 11kgCOD/m(3) day with a methane recovery of 62.4% at an influent COD of 120,000mg/L. The final effluent COD was 4520mg/L. The system was effective with regard to nitrification and sulfur removal. Fifty percent inhibition of the bacterial activity of the retained sludge by the cations was determined at 8gK/L for sucrose degradation, 16gK/L for sulfate reduction, and 12gK/L or 9gNa/L for acetoclastic methane production. Cation inhibition of anaerobic degradation reduced the process performance of the USSB.

High-rate treatment of molasses wastewater by combination of an acidification reactor and a USSB reactor.

A combination of an acidification reactor and an up-flow staged sludge bed (USSB) reactor was applied for treatment of molasses wastewater containing a large amount of organic compounds and sulfate. The USSB reactor had three gas-solid separators (GSS) along the height of the reactor. The combined system was continuously operated at mesophilic temperature over 400 days. In the acidification reactor, acid formation and sulfate reduction were effectively carried out. The sugars contained in the influent wastewater were mostly acidified into acetate, propionate, and n-butyrate. In addition, 10-30% of influent sulfur was removed from the acidification reactor by means of sulfate reduction followed by stripping of hydrogen sulfide. The USSB achieved a high organic loading rate (OLR) of 30 kgCOD m(-3) day(-1) with 82% COD removal. Vigorous biogas production was observed at a rate of 15 Nm(3) biogas m(-3) reactor day(-1). The produced biogas, including hydrogen sulfide, was removed from the wastewater mostly via the GSS. The GSS provided a moderate superficial biogas flux and low sulfide concentration in the sludge bed, resulting in the prevention of sludge washout and sulfide inhibition of methanogens. By advantages of this feature, the USSB may have been responsible for achieving sufficient retention (approximately 60 gVSS L(-1)) of the granular sludge with high methanogenic activity (0.88 gCOD gVSS(-1) day(-1) for acetate and as high as 2.6 gCOD gVSS(-1) day(-1) for H(2)/CO(2)). Analysis of the microbial community revealed that sugar-degrading acid-forming bacteria proliferated in the sludge of the USSB as well as the acidification reactor at high OLR conditions.