Effect of temperature on biogas yield increase and formation of refractory COD during thermal hydrolysis of waste activated sludge. (15th March 2020)

• Record Type: Journal Article
• Authors: Toutian, Vahid; Barjenbruch, Matthias; Unger, Tina; Loderer, Christian; Remy, Christian
• Is Part Of: Water research. Volume 171(2020)
• Publication Date: 2020-03-15
• Subjects: Thermal hydrolysis -- Biomethane potential -- Zahn-Wellens test -- Anaerobic digestion -- Sludge liquor -- Effluent COD; Water -- Pollution -- Research -- Periodicals; 363.7394
• DOI: 10.1016/j.watres.2019.115383
• Languages: English
• ISSNs: 0043-1354

Abstract

Abstract: Thermal hydrolysis (TH) increases the anaerobic biodegradability of waste activated sludge (WAS), but also refractory organic and nutrient return load to a wastewater treatment plant (WWTP). This could lead to an increase in effluent chemical oxygen demand (COD) of the WWTP. The aim of this study was to investigate the trade-off between increase in biogas production through TH and anaerobic digestion and increase in refractory COD in dewatered sludge liquors at different temperatures of TH in lab-scale. WAS was thermally hydrolyzed in temperature range of 130–170 °C for 30 min to determine its biomethane potential (BMP). After BMP test, sludge was dewatered and sludge liquor was aerated in Zahn-Wellens test to determine its non-biodegradable soluble COD known as refractory soluble COD (sCODref ). With increasing temperature in the range of 130–170 °C, BMP of WAS increased by 17–27%, while sCODref increased by 3.9–8.4%. Dewaterability was also enhanced through relative increase in cake solids by 12–30%. A conversion factor was defined through mass balance to relate sCODref to volatile solids of raw WAS. Based on the conversion factor, expected increase in effluent CODs of six WWTPs in Berlin were predicted to be in the range of 2–15 mg/L after implementation of TH at different temperatures. It was concluded that with a slight decrease in temperature, formation of sCODref could be significantly reduced, while still benefiting from a substantial increase in biogas production and dewaterability improvement. Graphical abstract: Image 1 Highlights: Biomethane potential of WAS increased with temperature of thermal hydrolysis (TH). Refractory soluble COD increased with temperature of TH. Slight decrease in TH temperature significantly reduced refractory sCOD. Impact of TH on effluent COD increase of a WWTP was predicted. Optimum TH temperature can be found for a WWTP to comply with COD discharge limit.