Improvements in the anaerobic digestion of biological sludge from pulp and paper mills using thermal pretreatment

Abstract

The current disposal of biosludge generated in wastewater treatment has high costs and causes environmental problems, anaerobic digestion (AD) of solid waste is a promising alternative. Thermal hydrolysis (TH) is an accepted technology to enhance anaerobic biodegradability of sewage sludge, but this technology has not been developed to be used with biological sludge from industrial wastewater treatment. In this work, the improvements to the AD of biological sludge from cellulose industry when thermal pretreatment is carried out were experimentally determined. The experimental conditions for TH were 140 °C and 165 °C for 45 minutes. Batch tests were carried out to quantify methane production evaluated as biomethane potential (BMP), anaerobic biodegradability according to volatile solids (VS) consumption and kinetic adjustments. An innovative kinetic model based on the serial mechanism of fast and slow biodegradation fractions was tested for untreated waste, and parallel mechanism was also evaluated. Increases in BMP and biodegradability values according to VS consumption were determined with increasing TH temperature. The results of 241 NmL CH₄ gVS substrate⁻¹ for BMP and 65% biodegradability are reported for the 165 °C treatment. AD rate increased for the TH waste compared to the untreated biosludge. Improvements of up to 159% for BMP and 260% for biodegradability according to VS consumption were quantified for TH biosludge compared to untreated biosludge.