This paper presents a pilot-scale evaluation of an integrated approach to sludge management utilizing a combination of biological nutrient removal and biosolids alkaline hydrolysis, as well as attempts to explore the impact of recycled alkaline hydrolysates on sludge yield and anaerobic digestion. The novel concept of converting an existing conventional activated sludge (CAS) wastewater treatment plant in St. Marys, Ontario to BNR and integrating it with Lystek technology emerged to reduce sludge production and spare the plant expansion of its sludge storage facilities. In the integrated sludge management strategy, first waste activated sludge (WAS) from the BNR system is treated with Lystek technology and thereafter a portion of the Lystek-treated sludge is recycled to the BNR system and the primary digester, and the remaining sludge is pumped to storage/land application.
A pilot study was undertaken to demonstrate the effectiveness of the proposed BNR system and to assess the impact of recycling Lystek-treated sludge to the BNR system and anaerobic digester. The pilot plant produced effluent comparable to that of the full-scale plant with biological nitrification/denitrification and phosphorous removal. The addition of Lystek-treated sludge did not have a detrimental effect on the pilot plant treatment efficiency. Anaerobic respirometric studies of pilot plant WAS with the addition of Lystek-treated sludge indicated increased VSS destruction, COD removal, and methane production. At a similar SRT, the pilot plant observed yield was 0.37 gTSS/gCOD, compared to 0.66 gTSS/gCOD for the full-scale system. When combined with Lystek treatment and recycle, the integrated sludge management strategy is expected to achieve an estimated 84% reduction in volumetric sludge disposed from the site.