Fe-enhanced primary sedimentation, acidogenic sludge fermentation and electrodialysis for resource recovery from domestic wastewater

In this study, a new chemical-biological process has been developed for municipal wastewater treatment. The new process utilises iron-based chemically enhanced primary sedimentation (CEPS) to concentrate organics and phosphorus (P) into sludge and hence reduces the load of pollutants on the downstream treatment process. A side-steam module for acidogenic sludge fermentation was applied to convert wastes in CEPS sludge to valuable resources. Results showed that over 70% of total organic carbon (TOC) and 83% of total phosphorus (TP) were removed by CEPS with an addition of 20 mg-Fe/L of FeCl3 while the total nitrogen (TN) removal efficiency was limited. Acidogenic fermentation of Fe-sludge under the mesophilic condition produced volatile fatty acids (VFAs) at a ratio of 137.7 mg-C/g-volatile solids (VS) with 12% of TP dissolution. With 1 g/L of starch addition for co-fermentation, the VFAs yield and P dissolution increased significantly to 201.3 mg-C/g-VS and 60%, respectively. However, the addition of peptones did not improve the P dissolution, due to the higher ammonium release that prevented the pH drop and acidification in the fermenter. Through the electrodialysis (ED) treatment in a five-chamber cell, 50% of ammonium in the fermented sludge liquor was concentrated into catholyte, while 35%-43% of phosphate, acetate (Ac) and propionate (Pr) were separated into anolyte.