Evaluation of the effects of chemically enhanced primary treatment on landfill leachate and sewage co-treatment in publicly owned treatment works

This study evaluated the effects of Chemically Enhanced Primary Treatment (CEPT) on co-treatment of landfill leachate and sewage in publicly owned treatment works (POTWs). Two most frequently used coagulants in CEPT, ferric chloride and aluminum sulphate, were studied. Bulk organic matter, pH variation, UV absorption, etc. were evaluated during the treatment processes. 54 %–74 % organic matter removal was achieved by ferric and aluminum coagulants. Ferric coagulant was found to perform better for organic matter removal than aluminum in most cases. Notably, ferric chloride coagulation increased the UV absorbance of treated leachate significantly by up to 10 times, while aluminum sulphate only slightly decreased it. Theoretical models are discussed to elucidate co-precipitation behaviors under various pH scenarios. It is exacerbated by the complexes formed by ferric and organic matter, which have characteristic light absorption in the UV range. The formation of such complexes is supported by the Fourier Transform Infra-Red (FTIR) spectroscopy. In addition, the volatile acids in leachate were found to play an important role in mediating pH through their buffering capacity.