Enhancing biomethane production and phosphorus recovery from CEPT sludge through a low temperature thermal alkali and ozonation pretreatment processes

Abstract

Chemically enhanced primary treatment (CEPT) enhances the removal of suspended solids and phosphorus from municipal wastewater. The CEPT sludge contains many valuable resources with high energy and phosphorus to recover. The objectives of this study were to assess the behaviour and resource recovery potential of two CEPT sludges, FeCl3 coagulated (CEPT-I) sludge and FeCl3 + PACl coagulated (CEPT- II) sludge, during anaerobic digestion (AD) of the untreated, low-temperature thermal alkali (LTTA) pretreated and ozone pretreated sludge. The reactive P fraction of the untreated CEPT-I sludge and CEPT- II sludge were 30.17% and 17.40%, respectively, and a substantial fraction of the TP was in the nonreactive form. Upon ozone and LTTA pretreatment followed by AD and AD process alone, the reactive P fraction increased to 70%. The results showed comparable performance between pretreated and untreated sludge, indicating pretreatment may not be required for phosphorus release. However, the result was different regarding the organic fraction. Upon AD, the methane yield of the CEPT-II sludge was lower than the CEPT-I sludge. More specifically, the CEPT-II methane yield of the untreated sludge was 157 mL/g VSS added and increased to 230 and 218 with the LTTA and ozone pretreatment, respectively.

Keywords

• Chemically enhanced primary treatment
• P release
• Energy recovery
• Ozonation
• Low-temperature thermal alkali pretreatment and anaerobic digestion