Effect of Various Amendments on the Solids Properties and Gas Production of Biosolids

Four additives namely iron slag (IS), works debris (WD), fly ash (FA), and lime kiln dust (LKD) are added to biosolids and their effects are investigated on the selected properties of biosolids. The biosolids used are final products of the wastewater treatment process at a Wastewater Treatment Plant (WWTP), Auckland, New Zealand. The additives are mixed manually with biosolids at different percentages. Most of the mixtures, finally called amendments has selected amount of lime in them. The amendments are placed separately into respirometer reactors (air tight bottles) for two weeks, measuring gas continuously to find out the total gas production and to analyse methane (CH4) and carbondioxide (CO2) production to completely understand the biochemical activity. Water content (WC %), volatile solids (VS %), and pH are determined before putting the amendments into the reactors and after two weeks as well. Gases that are being produced from the respirometer reactors are analysed after 5, 10 and 15 days for CH4 and CO2 percentages. After comparing results of all the amendments and comparing results of solids parameters to that of gas analysis, it is concluded that FA 50% with lime 20% inhibited most of the biochemical activities and maintained pH of biosolids at elevated level of 12 or above and thus could be applied to biosolids for stabilization before landfilling. 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.