Recovery and concentration of thermally hydrolysed waste activated sludge derived volatile fatty acids and nutrients by microfiltration, electrodialysis and struvite precipitation for polyhydroxyalkanoates production

Abstract

A novel chain of processes was proposed for the first time to convert thermally hydrolysed waste activated sludge (WAS) into concentrated volatile fatty acids (VFAs) and nutrient effluent stream for the production of biodegradable polyhydroxyalkanoates (PHAs). The integrated process involved a sequence of anaerobic fermentation followed by microfiltration (MF) and conventional electrodialysis (CED). The VFAs produced were primarily acetic and n-butyric acids, with concentrations of 3.27 and 4.37g/L, respectively, within a total of 11.73g/L of short chain organic acids produced from an organic loading rate of 20g VS/Lday and 2days hydraulic retention time anaerobic fermentation. MF achieved over 80% recovery rates of VFAs and ammonium. CED concentrated effectively the MF recovered stream with 92% of VFAs and ammonium transferred to the concentrated stream i.e.19.82g VFAs/L (∼32g CODVFAs/L) and ammonium of 3.02g/L. The excessive ammonium was removed through struvite precipitation before usage as substrate for PHAs production. This novel upfront process resulted in a 5-fold increase in PHA%/cell dry matter compared with the untreated thermally hydrolysed anaerobically acidified WAS stream. The results illustrate a promising market for the use of WAS through membrane and precipitation separation techniques for biomaterials production. The novel engineered processing system has much wider applications within the chemical industry and the potential for a very effective high rate methanogenesis.