Effect of alkalization process on changes in the chemical composition of secondary sludge

The paper addresses the problem of how the alkalization of partly dewatered (98.2% and 98.8% H2O) secondary sludge with a calcium hydroxide suspension influences the chemical composition of the organic fraction (which undergoes changes induced by hydrolysis processes). The process of sludge stabilization was assessed in terms of the COD/TOC ratio and the atomic O/C ratio. As a consequence of the hydrolysis processes, the content of proteins and fats as well as other organic substances (primarily simple acids) decreased, which manifested itself as a decrease of the oxygen and nitrogen content in the sludge being alkalized, and an increase in the value of the COD/TOC ratio, which was concomitant with a decrease in the atomic O/C ratio. It was found that treatment with low calcium hydroxide doses sufficed to stabilize the sludge. The products obtained are of no environmental nuisance and can be used for agricultural applications.