Optimization of alkaline hydrothermal pretreatment of biological sludge for enhanced methane generation under anaerobic conditions

• Published in: Waste management (Elmsford) Vol. 107; pp. 9 - 19
• Main Authors: Perendeci, N.A, Ciggin, A.S., Kökdemir Ünşar, E., Orhon, D.
• Format: Journal Article
• Language: English
• Published: United States Elsevier Ltd 15.04.2020
• Subjects: Alkaline hydrothermal pretreatment; Anaerobiosis; Biological Oxygen Demand Analysis; Hydrolysis; Methane; Methane generation; Process optimization; Sewage; Waste activated sludge; Hydrolysis; Methane generation; Process optimization; Waste activated sludge; Alkaline hydrothermal pretreatment
• ISSN: 0956-053X; 1879-2456
• DOI: 10.1016/j.wasman.2020.03.033

[Display omitted] •Amount of dry matter was considered in alkaline HTP optimization as an independent variable.•Alkaline HTP optimization focused on BMP as an objective function.•BMP was influenced by the interactions of reaction temperature and DM content.•Alkaline HTP increased COD leakage in the range of 200–900%.•Optimum alkaline HTP increased the methane potential of waste activated sludge up to 78%. This paper investigated the effect of alkaline hydrothermal pretreatment (HTP) on the hydrolysis, biodegradation and methane generation potential of waste activated sludge (WAS). A multi-variable experimental approach was designed, where initial solids content (1–5%), reaction temperature (130–190 °C), reaction time (10–30 min.) and caustic concentration (0–0.2 mgNaOH/mgVS) were varied in different combinations to assess the impact of alkaline HTP. This process significantly enhanced the hydrolysis of organic compounds in sludge into soluble fractions, whereby increasing the chemical oxygen demand (COD) leakage up to 200–900% with the 17–99% solubility. It boosted volatile solids (VS) biodegradation up to 40%, which resulted in a parallel increase in methane generation from 216 mLCH4/gVS to as high a 456 mLCH4/gVS methane generation basically relied on the conversion of solubilized COD. Alkaline HTP process was optimized for the maximum methane production. Optimum conditions were obtained at 190 °C reaction temperature, 10 min. reaction time, 0.2 mgNaOH/mgVS and 5% dry matter content. Under these conditions, 453.8 mLCH4/gVS was predicted. Biochemical methane potential (BMP) value was determined as 464 mLCH4/gVS supporting predictive power of the BMP model. The biodegradability compared to the untreated raw WAS was enhanced 78.2%.