The paper describes practical results of four-year laboratory studies completed to estimate technically feasible conditions of upgrading an existing sludge disposal system. A minimization of sludge mass and volume together with an energy recovery improvement were main goals of these activities. The way from lab studies and simulations to full scale investments has been shown with a special emphasis on application of respirometric procedure being applied by authors. Proposed was authors’ procedure for an estimation of a digestion time prediction for sludge of specific composition. Investigations completed at existing wastewater treatment plant resulted in practical implementation to be used during the design of upgrading and extension of the digestion and energy recovery system at the plant. It was proved that proposed changes provide close to optimum conditions for process performance and the application of proposed calculation procedures was adopted by design team

The article describes problems related to intensification of energy production at a sewage treatment plant. The authors analyze anaerobic co-digestion of sludge from a water treatment plant and sewage treatment plant. The authors proposed a methodology of the research and analyzed the preliminary results, which showed that co-digestion of sewage and water sludge enhanced biogas production. The authors hope that the results of the study will provide a basis for development of methodology for sludge control and disposal.

This article investigates the possibilities of the recovery of raw materials at the Kraków–Płaszów municipal wastewater treatment plant (WWTP). The materials include sand coming with raw sewage and delivered by septic tankers, after cleaning sewage systems. Following the Regulation of the Minister of Climate (January 2020), sand from grit chambers is classified in the waste catalog as waste, with the code of 19 08 02. (Journal of Laws of 2020, item 10). The purchase of very efficient units has optimized the grit chamber operation and minimized the amount of waste generated as well as being an odor nuisance. The paper presents a mass balance for sand collected at the WWTP. Due to the use of new sand separators, the amount of this waste has been reduced by 28%. The paper presents the sieve curves of sand collected at the wastewater treatment plant and during the cleaning of sewage wells, as well as for sand mixtures. The sand mixture was prepared to allow some variations in the grain size characteristics of the sand. The graining differentiation indexes and curvature indexes were calculated. In addition, in laboratory tests, the leachability of heavy metals and the content of dry matter (DM) and dry mineral matter (DMM) were determined. The laboratory tests confirmed the reduction of organic solids to a level below 3% of dry weight; the content of heavy metals remained below the level of detection. The experiments confirmed that sand from the WWTP can be used as fine-grained aggregate in the production of concrete.