Prefiltration pilot study with drum filters

The Rya wastewater treatment plant (WWTP) in Gothenburg, Sweden, is facing new and stricter effluent requirements and an increased predicted flow and population in the coming years. A pilot study was done to evaluate drum filters as a possible space-efficient pretreatment compliment to the conventional pre-settling tanks. The pilot trials proved that the drum filter was able to reduce organic materials and phosphorous at different loads. The reduction was similar between two different pore sizes (100 and 300 μm) and the suspended solids (SS) effluent concentrations (35–200 mg/L) was similar to the conventional pre-settling tanks (40–130 mg/L). The two pore sizes had similar maximum flow capacities but the 300 μm was able to maintain that capacity for a longer time and higher influent SS concentrations. Chemical precipitation was able to increase the reduction of both SS and phosphorous. The drum filters could handle higher SS peaks during tunnel flush events while maintaining similar effluent SS concentrations as during normal operation. It became clear when analyzing the results that daily average data did not capture bypass events caused by momentaneous peaks in either influent SS or flow. Hourly data analysis is needed to correctly design and dimension a pre-filtration process with drum filters.