Abstract
Performance of BOD removal was investigated using observed data on rural sewerage facilities with submerged biological filter. It was found that probability distribution of BOD in influent and effluent of rural sewerage facilities obeyed logarithmic normal distribution. BOD removal in anaerobic filter tank was assumed to depend primarily on two factors : BOD in influent and SS in effluent. BOD removal in contact aeration tank was also influenced by three factors, that, BOD in influent, SS and ATU - BOD in effluent. Therefore, BOD removal in anaerobic filter tank and contact aeration tank have limitation due to elution of accumulated sludge in biofilm filter. As a result, equations related to BOD removal were derived from the data regarding to BOD in influent, SS and ATU - BOD in effluent. The predicted values of BOD removal were approximately in agreement with observed values. The relation between BOD and SS or ATU - BOD in effluent was approximately linear in the range of BOD in influent of anaerobic filter tank and contact aeration tank. The relationship between BOD, SS and ATU - BOD was nearly in accord with the tendency calculated by equations which was obtained from above data. Deposited sludge thickness on the bottom had a considerable influence on SS in effluent of anaerobic filter tank. Consequently, control of sludge thickness is effective to maintain BOD removal efficiency in anaerobic filter tank.
