Enhancing Aerobic Digestion Efficiency Of Sludge And Its Future As Liquid Fertilizer

In general, solid removal rate of aerobic digestion is about 30-40%. Toenhance sludge biodegradability, the processes of various pretreatments havebeen carried out using alkaline treatment, ultrasonic treatment and differentcombination of these two methods, followed by aerobic digestion. Odorouscompounds associated with physicochemical pretreatments are significantlyreduced during aerobic digestion. In the meantime, agricultural value ofsludge treated by the combination of pretreatment and aerobic sludge wasstudied. And the influence of NO₃^--N and NH₄⁺-N concentration on the leafsize and height of seedling was discussed.For waste sludge with described pretreatment, SCOD concentration wasgreatly increased, especially the combination of simultaneous alkaline andultrasonic treatment. SCOD concentration of sewage sludge pretreated usingsimultaneous ultrasonic and alkaline treatment increased from 347mg/l to6700mg/l in only 2 hours. The subsequent respirometer test showed thatneutral pH of the substrate yielded the highest biodegradability. Oxygenuptake for 20days increased up to 19 times by the pretreatment. Batch aerobicdigestion represented that TSS and VSS removal rates increased with theincrease of Feed/Seed ratio, and it was meaningful to use pretreated sludge asfeed sludge at the short retention time. After 40 days, SCOD concentration inthe digester B (fed with pretreated sludge) was decreased from 2600mg/l to230mg/l, which indicated that SCOD produced by pretreatment can bedegraded and that this combination was more effective than conventionalaerobic digestion in terms of VSS removal rate. In addition, the contents of allheavy metals in sludge were within the limit values in the soil, which showedthat the disposal method of land application was feasible. In the finalsemi-continuous aerobic digester, HRT 2 days was an optimal operationcondition according to VSS and SS removal rates.