Effects Of Pretreatment Methods On Excess Sludge Anaerobic Fermentation For Volatile Fatty Acids(VFAs) Accumulation And Phosphorus Release

Recently, with increasing municipal wastewater followed by urbanization, more and more waste activated sludge(WAS) produce in municipal wastewater treatment plants(WWTPs). And the sludge disposal is becoming a serious problem, almost representing up to 50% of the current operating cost of a WWTP. WAS contains a substantial amount of nontoxic organic compounds and phosphorus. However, its production has often been limited by long retention times and low degradation efficiency, which are generally associated with the hydrolysis stage of sludge. Two pretreatment methods were investigated for sludge volatile fatty acids(VFAs) accumulation and phosphorus release.The effects of ultrasound(US), Fenton, and combined US/Fenton as physicochemical pretreatment processes on the waste activated sludge(WAS) hydrolysis and acidification were investigated in the first study. The soluble carbohydrate concentrations after US/Fenton treatment were 2.36-fold, 2.17-fold and 17.11-fold more than that obtained in Fenton, US and control tests, respectively. And the corresponding concentrations of soluble protein after US/Fenton treatment were 2.43-fold, 1.47-fold and 13.37-fold more than that obtained in Fenton, US and control tests, respectively. The degree of sludge disintegration(DDCOD) in US/Fenton treatment was 15.4%, whereas it was only 9.97% and 3.18% in US and Fenton tests. In addition, particle size d50 was at 44.01μm for untreated sludge and it was almost similar with Fenton treatment(41.53 μm), but was much higher than that obtained in US(24.52 μm) and US/Fenton(22.63 μm). The maximum accumulation of volatile fatty acids(VFAs) was obtained in US/Fenton pretreatment(4594 mg COD/L), which presented obvious advantages over US(3485 mg COD/L) and Fenton(2700 mg COD/L). US/Fenton had a synergetic effect on improving the hydrolysis and subsequent acidification of WAS.The second research focused on the sludge hydrolysis and phosphorus(P) release from waste activated sludge(WAS) by pulsed electric field(PEF) pretreatment. The results showed that sludge hydrolysis and phosphorus release can be accelerated through PEF pretreatment. However, high content of metals in sewage during anaerobic fermentation was also observed along with organic matters and soluble orthophosphate(SOP) release. It was better to recover phosphorus from fermentation liquor at the first 3-4 days before phosphorus precipitation was largely formed. The Standards, Measurements and Testing(SMT) analysis showed that total phosphorus(TP) release rate in pretreated sludge was higher than that in control. Apatite P and organic P were relatively stable during the whole fermentation process. The SOP release in fermentation liquor mainly derived from non-apatite inorganic(NAIP) solubilization. The present results suggest that PEF pretreatment before anaerobic fermentation could be a promising method for sludge hydrolysis and phosphorus release.