Department of Civil and Environmental Engineering, University of Auckland, New Zealand
The objective of this research is to investigate the effect of four additives including iron slag (IS), works debris (WD), fly ash (FA), and lime kiln dust (LKD) on the biochemical properties of biosolids produced at Mangere Wastewater Treatment Plant (MWWTP), Auckland, New Zealand. All these additives are homogenously mixed in the laboratory with biosolids at various percentages with and without lime. All these prepared amendments are compacted into polyvinyl chloride (PVC) tubes for curing durations of 2 weeks, 4 weeks and 8 weeks. Water content (WC), volatile solids (VS), pH, total organic carbon (TOC) concentrations, proteins, carbohydrates, lipids and VFA’s (volatile fatty acids) are determined for all the samples. These parameters are analyzed initially and after 2, 4 and 8 weeks for every PVC tube. Results indicated that when biochemical changes occurred within biosolids, all of these parameters results are affected. After comparing results of all the amendments it is concluded that FA 50% with lime 20% inhibited most of the biological activities and maintained pH of biosolids at elevated level of 12 or above for 8 weeks and thus can be applied to biosolids for stabilization before land filling. FA 50% with lime 20%, like all the other additives, is added to wet biosolids on the basis of dry weight. Solid content of biosolids is around 25% so the addition of even 70% additive to wet biosolids on the basis of dry weight is very less in amount.