The following equations show the design of an extended-aeration process without nitrification and with zero-sludge yield (Ramalho 1983):
Y = sludge yield Q = influent flow rate, l/day Si = influent BOD, mg/l Se = effluent BOD, mg/l kd = sludge decay (endogenous respiration) rate, l/day X = MLVSS concentration in the aeration basin, mg/l V = basin volume, l 0 = LRT, day
These equations incorporate 0.77 since approximately 77% of the sludge produced is biodegradable. The recycling ratio (r) is calculated as follows:
where Xr = MLVSS concentration in the recycled sludge flow, mg/l.
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