|
Large amount of municipal sewage and sludge is generated with China’s socio-economic development and urbanization. Sludge demands high treatment cost and may cause second pollution and novel methods to reduce the excess sludge is needed. Lysis- cryptic growth has receive intensive study due to its efficiency and easy-operation.This paper studied the sludge lysis by ultrasound and ozone; the sludge reduction via lysis-cryptic growth by varying operational modes; and investigated potential drawbacks of the technique and the corresponding solutions.In the process of ultrasound lysis under 1.2 W/ml, the supernatant SCOD, TN, TP, protein, polysaccharide and DNA increased with the growth of ultrasound irradiation time. Among them, SCOD, protein, polysaccharide and DNA had a similar increasing trend, and showed three growth phases: the concentration increased faster in the first 5 min, the rate of increase slowed down during 5 min to 10 min, and increased faster after 10min.Ozone can effectively dissolve sludge. When the ozone dose was 50 mgO3/gSS and the treatment time was 105 min, DDCOD was 40.3%, the sludge solid concentration and volatile solid concentration decreased by 49.1% and 45.7%, respectively. Thus, the supernatant SCOD, TN, TP, protein, polysaccharide and DNA increased by 699%, 169%, 2379%, 602%, 528%, 556%, respectively. We speculated that ozone lyzed sludge mainly by damaging of microorganism cells. Moreover, ozonation released heavy metals from particulate to water with the only exception of Cd.Through long-term sludge ozonation, ozone in the returned sludge would affect growth metabolism of activated sludge in aeration tank. In succeeding experiment, ultrasound was adopted for sludge lysis.The paper researched the effect of different operation moded on sludge reduction under 1.2 W/ml, 15 min. The upper limit of sludge disintegration was 28.0%, and when equal to or more than 28.0%, effluent standard rate of the system could not be guaranteed. Considering sludge reduction and energy comsumption, the operation mode of 14.0%×1 was better and less energy consumption which the sludge reduction reached 48%.Sludge reduction brings about some negative impacts. Sludge reduction extended sludge retention time and released some phosphorus during lysis, these lead to increasing of phosphorus concentration. In our research, the effluent TP level was in the range 3.52 mg/L, we suggested the dose of FeCl3·6H2O was 0.25 mmol/L to meet the nation one level. Ultrasonic released heavy metals from particulate to water with the only exception of Cd. Heavy metals accumlated in sludge to some extent, it was worth noting that the accumlation of Cu and Ni in ultrasonic sludge were more, but it was not found that heavy metal ions inhibit microbial metabolism.
|