Combining ethylene diamine tetraacetic acid and high voltage pulsed discharge pretreatment to enhance short-chain fatty acids and phosphorus release from waste activated sludge via anaerobic fermentation

Abstract

High voltage pulsed discharge has proved to be an efficient method for waste activated sludge pretreatment, however, the energy consumption of this pretreatment is always high, which hindered the practical application. In the present study, a combined ethylene diamine tetraacetic acid and high voltage pulsed discharge pretreatment method was firstly proposed to enhance short-chain fatty acids and phosphate recovery from waste activated sludge via anaerobic fermentation. The results showed that, with combined pretreatment, the soluble chemical oxygen demand and protein levels reached the maximum values of 5,639.6 ± 574 mg/L and 635.3 ± 6.6 mg/L during hydrolysis process, which were approximately 3.2- and 2.2-folds higher than those of the control, the short-chain fatty acids levels in liquid increased to 4,181.2 ± 16.3 mg/L on day 5, which was approximately 2.5-fold higher than that of the control. The analysis of short-chain fatty acids composition showed that the short-chain fatty acids in combined pretreatment systems mainly consisted of acetic and propionic acids, accounting for 67.2% of the total, indicating that short-chain fatty acids obtained in this study were favorable carbon sources for denitrification. In addition, the phosphate level in combined pretreatment experiment was 304.8 mg/L after 5 days anaerobic fermentation, which was approximately 2.8-fold higher than that of the control, suggesting that the combined pretreatment enhanced phosphate release. The possible mechanism of the combined pretreatment could be that the chelation of metal ions by ethylene diamine tetraacetic acid not only disintegrated the extracellular polymeric substances of sludge, but also led to carbon source and phosphate release simultaneously, so that the cell disruption effect could be achieved with lower voltage by latter high voltage pulsed discharge. These results indicated that the combined pretreatment could be a promising and alternative method to recover phosphorus and short-chain fatty acids from waste activated sludge via anaerobic fermentation, with the energy cost of high voltage pulsed discharge being reduced greatly.