Excess sludge reduction in activated sludge processes by integrating biomass alkaline heat treatment

With new EC regulations, alternative treatment and disposal techniques of t he excess sludge produced by activated sludge wastewater treatment plants h ave to be developed. To decrease activated sludge production yield, microbi al cell lysis can be amplified to enhance cryptic growth (biomass growth on lysates). Cell breakage techniques (thermal, alkaline and a combination) w ere studied to generate Ralstonia eutropha (strain model) and waste activat ed sludge lysates and to evaluate their biodegradability. Gentle treatment conditions by alkaline waste treatment (20 min at 60 degreesC and pH 10 by NaOH addition) allowed waste activated sludge to be solubilized by a two st ep process (instantaneous and post-treatment) giving a dissolved organic ca rbon released by the total suspended solids treated of 267 mgDOC.g(-1)TSS. The biodegradation of the soluble fraction of the lysates by fresh sludge r eached 75 and 90% after 48 and 350 hrs of incubation respectively. A valida tion on a laboratory scale by insertion of a liquor alkaline heat treatment loop in a biological synthetic wastewater treatment process was carried ou t. A reduction of 37% of the excess sludge was obtained without altering th e purification yield of the process.