Sludge Accumulation in Aerated Facultative Lagoons Operating in Colder Climate

Notwithstanding the long time of retention and aeration in aerated facultative lagoons, not all the organic matter is oxidized to final products, as one would suppose. Consequently there is significant accumulation of sludge in the lagoons which should be removed periodically so as not to interfere with the mixing and overall performance of the treatment system. Recent studies confirm that sludge accumulation is more pronounced in areas where water temperatures are lower than normal. Existing mathematical models for estimating sludge accumulation are found to either under- or over-estimate the actual quantities produced. This might be due to various constraints of each model like hydraulic retention time, type of aeration, coagulant usage and, of course, wastewater characteristics. In the present study, on-site measurements of sludge accumulation were conducted in aerated lagoons operating in small municipalities in Québec. The results obtained are compared with those calculated using currently well known models. Corrections are proposed to the existing mathematical models so that future estimates can be more accurate than at present.