| dc.description.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. | en_US |
