Reduction by sonication of excess sludge production in a conventional activated sludge system: continuous flow and lab-scale reactor.
Conventional activated sludge wastewater treatment plants currently produce a large quantity of excess sludge. To reduce this sludge production and to improve sludge characteristics in view of their subsequent elimination, an ultrasonic cell disintegration process was studied. In a lab-scale continuous flow pilot plant, part of the return sludge was sonicated by low-frequency and high-powered ultrasound and then recycled to the aeration tank. Two parallel lines were used: one as a control and the other as an assay with ultrasonic treatment. The reactors were continuously fed with synthetic domestic wastewater with a COD (chemical oxygen demand) of approximately 0.5 g l(-) corresponding to a daily load of 0.35-0.50 kg COD kg(-1) TS d(-1). Removal efficiencies (carbon, particles), excess sludge production and sludge characteristics (particle size distribution, mineralization, respiration rate, biological component) were measured every day during the 56-day experiment. This study showed that whilst organic removal efficiency did not deteriorate, excess sludge production was decreased by about 25-30% by an ultrasonic treatment. Several hypotheses are advanced: (i) the treatment made a part of the organic matter soluble as a consequence of the floc disintegration, and optimised the conversion of the carbonaceous pollutants into carbon dioxide and (ii) the treatment modified the physical characteristics of sludge by a mechanical effect: floc size was reduced, increasing the exchange surface and sludge activity. The originality of this study is that experiments were conducted in a continuous-flow activated sludge reactor rather than in a batch reactor.
Vaxelaire
S
S
Laboratoire Optimisation de la Construction et Ingénierie de l'Environnement, Polytech'Savoie, Université de Savoie, 73376 Le Bourget du Lac, France.
Gonze
E
E
Merlin
G
G
Gonthier
Y
Y
D001420:Bacteria, Aerobic / Q000378:metabolism; D019149:Bioreactors; D005160:Facility Design and Construction; D010100:Oxygen / Q000378:metabolism; D010316:Particle Size; D012722:Sewage / Q000032:analysis / Q000737:chemistry*; D012995:Solubility; D013010:Sonication / Q000379:methods*; D014865:Waste Disposal, Fluid / Q000379:methods*; D018508:Water Purification / Q000379:methods*
D012722:Sewage; D010100:Oxygen