Sequencing Batch Reactor In Treatment Of Slaughterhouse Effluent

Abstract

Slaughterhouse wastewaters are difficult to treat because of high concentration of organic matter, nutrients and suspended solids. These materials are readily biodegradable in the environment, resulting in degradation of receiving waters and serious odor problems. Public health authorities have in the past closed four of the slaughterhouses at Dagorretti in Nairobi, Kenya because of inadequate wastewater and solid waste management systems. Conventional treatment methods such as the activated sludge process are unaffordable while waste stabilization ponds require large pieces of land that are unavailable in urban areas where most slaughterhouses are located. Slaughterhouse wastewaters are intermittent, which favor batch treatment methods including the sequencing batch reactor (SBR). The SBR is a fill-and-draw type of activated sludge system that involves a single complete-mix reactor in which all steps of the activated sludge process occur. Because the SBR combines several processes in one unit, it has minimal land requirements, which makes it suitable for urban settings where land is scarce. This study investigated the suitability of SBR in treating wastewater from Dagoretti slaughterhouses. Three bench scale SBRs were set up with a manual control mechanism for the treatment stages to evaluate the effects volumetric exchange rate on effectiveness of SBR in treating effluent from the slaughterhouses. The average raw slaughterhouse wastewater concentrations for COD, BOD5, MLSS, NH4-N, NO3-N and TP were 11947 ± 2,164; 8233 ± 2025; 1,400 ± 787; 70.3 ± 49.0; 65.2 ± 9.2 and 261 ± 39 mg/L respectively. Volumetric

exchange rate (VER) in the 30 - 50 % range did not show significant difference in the SBR treatment. Therefore, the higher VER of 50% was recommended because it gives higher of volumetric turnover compared to the lower VERs. The SBR treatment process achieved average reductions of 59, 61, 54 and 35% for chemical oxygen demand (COD), biological oxygen demand (BOD5), ammonia nitrogen (NH4-N) and total phosphorus (TP) respectively. However, the corresponding average effluent concentrations, 4884 ± 125; 3196 ± 82; 196 ± 82; 32 ± 2 and 171 ± 5 mg/L for COD, BOD5, NH4-N and TP, respectively, were above the regulatory standards for discharge to public sewers. Therefore, there is need to improve the SBR treatment through improved aeration and mixing, use of more treatment cycles and inexpensive on-line monitoring and control, or to provide supplementary treatment before discharge.