Influence of Valorization of Sewage Sludge on Energy Consumption in the Drying Process

Ewa Siedlecka,Jarosław Siedlecki

doi:10.3390/en14154511

Abstract

Valorization of digested sewage sludge generated in a medium-sized sewage treatment plant and the effect of valorization on energy consumption during sludge drying used for energy recovery are presented. Anaerobic digestion of sewage sludge reduces dry matter content compared to raw sludge. This lowers its calorific value leading to the lower interest of consumers in using it as fuel. The aim of the study was to valorize digested sewage sludge prior to drying with high-energy waste with low moisture content. The procedure led to the reduction in moisture content by about 50% in the substrate supplied for solidification and drying. The calorific value of digested sewage sludge increased by 50–80%, and the energy consumption of the drying process decreased by about 50%. Physical and chemical properties of sewage sludge and moisture content of substrates and mixtures after valorization were determined. The heat of combustion of valorized sewage sludge mixtures, their elemental composition, and ash content is investigated. Their calorific value in the analytical and working states of 10% H2O was calculated. The highest calorific value was obtained for the mixture of sewage sludge valorized with waste plastics or combined with wood dust, averaging 23 MJ/kg. A mathematical approximation of sewage sludge valorization is presented.

Highlights

Municipal sewage sludge is a by-product of the treatment of municipal and industrial wastewater [1,2]
The main component of sewage sludge is dry organic matter, which constitutes over 64% (Table 5)
The valorization of biomass waste with the waste with high calorific value ensures the possibility to carry out energy recovery in cement industry installations, in accordance with their technological requirements; 4

Summary

Introduction

Municipal sewage sludge is a by-product of the treatment of municipal and industrial wastewater [1,2]. Sewage sludge constitutes only 1–2 vol.% of treated wastewater, but its management is very complicated, and treatment costs amount to 20–60% of wastewater treatment plants’ (WWTPs’) total operating costs [3]. Sewage sludge from sewage treatment plants (STPs) is characterized by a high content of organic and inorganic substances, including microbial biomass, pathogens, nutrients N and P, and metals. They have a very heterogeneous composition [4] and a high water content up to 95–99% [5]. The water content varies according to the type of sewage sludge (Table 1).

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Conclusion