Free ammonia-based pretreatment enhances phosphorus release and recovery from waste activated sludge

The recovery of phosphorus from waste activated sludge (WAS) was usually at low levels due to low phosphorus release. This study presents a novel, cost-effective and eco-friendly pretreatment method, e.g., using free ammonia (FA) to pretreat WAS, to enhance the phosphorus release from WAS. Experimental results showed that the phosphorus release from WAS was significantly increased after FA pretreatment at up to 189.4 mg NH3-N L−1 for 24 h, under which the released PO43--P (i.e. 101.6 ± 6.7 mg L−1) was higher than that pH 9 (i.e. 62.6 ± 4.54 mg L−1) and control (without pH and FA pretreatment) (i.e. 15.1 ± 1.86 mg L−1). More analysis revealed that the FA induced improvement in phosphorus release could be attributed to the disintegration of extracellular polymeric substances (EPS) and cell envelope of sludge cells. Moreover, the released phosphorus recovered as magnesium ammonium phosphate (MAP) was confirmed. The findings reported may guide engineers to develop an economic and practical strategy to enhance resources and energy recovery from WAS. [Display omitted] •FA pretreatment was successfully developed to enhance phosphorus release from WAS.•Variations of EPS and release of LDH and DNA indicated disintegration of EPS and cell envelope.•Phosphorus could be recovered effectively from the supernatant of FA treated sludge.•A potential and practical concept of WWTPs and WAS treatments was proposed.