Examinations of the Effect of Ashes from Coal and Biomass Co-combustion on the Effectiveness of Sewage Sludge Dewatering

High water content and the associated large volume of waste represent a challenge to final disposal of sewage sludge. For this reason, dewatering is one of the most important stages in sewage sludge treatment. However, sewage sludge dewatering is also the most expensive and least explored process. The specific physical and chemical properties of raw sewage sludge make it impossible to obtain satisfactory dewatering effects without primary processing. Water removal efficiency can be improved with sludge conditioning by means of various technologies. Chemical conditioning, which consists in dosing organic flocculants, has been commonly used in wastewater treatment plants. Application of polyelectrolytes to sludge in order to improve its dewaterability generates high operating costs in sewage treatment plants, amounting even to several thousand PLN a month. The economic aspects have driven the development of the research on intensification of sewage sludge dewatering using various materials, including waste. Conditioning of sewage sludge with fuel combustion by-products represents an alternative to commonly used technologies. The paper presents the effect of by-products of co-combustion of hard coal and plant biomass on the efficiency of sewage sludge dewatering. The effect of ash on capillary suction time (CST), water content and specific resistance to filtration was discussed. Physical conditioning of sewage sludge led to the decrease in CST, specific resistance to filtration (SRF) and water content. An increase in filtrate volume after pressure filtration was also observed. The results obtained in the study showed that addition of waste can represent an alternative method of sewage sludge conditioning.