BOD contribution by benthalsludge deposits Part-1: Effect of sludge characteristics

Abstract

Organic matter that settles to their river bottoms is the benthalsludge deposits. Decomposition of benthalsludge deposits in streams affect the overlying waters by removal of the dissolved oxygen (DO) from the overlying waters as well as by the benthos and periphytons in the aerobic top layers of the overlying waters and by the immediate oxygen demand of the reduced substances emanating from the deeper anaerobic layers. Secondly, the benthalsludge deposits can also release organic substances and various nutrients into the overlying waters. The oxygen utilisation rate by the benthalsludge deposits may also depend on the sludge characteristics as well as the stream characteristics. In this first part of the paper, the variations of the total oxygen uptake rate in any one days duration and the rate of BOD contribution by benthalsludge in respect of different sludge characteristic parameters have been correlated and discussed. At the top layers of overlying waters, the rate of BOD contribution manifested an optimum high value at benthalsludge depth of 0.1m, and an optimum low value of initial BOD of benthalsludge top layers of around 475 mg/L. The cumulative oxygen consumption till a particular day, was lower or almost same at greater depths of benthalsludges, and manifested a low value at Kd-b value of 0.035. However, the influence of S b-o seemed to be less. The percent BOD contribution indicating the sludge age, manifested an optimum low at benthalsludge depths of 0.2m, both at the top and bottom most layers of overlying waters. The COC values at the interface showed similar trends as in the top layers of overlying waters. The rate of BOD contributions as well as percent contributions, at the interface showed an increasing trend with the Kd-b values. The rate of BOD contributions at the interface also increased with increasing Sb-o values, but the percent BOD contributions manifested an optimum low value. 2008 - Kalpana Corporation.