Effect of low temperature thermochemical pretreatment on sludge reduction potential of membrane bioreactor treating primary treated dairy wastewater

In this present study, an aerobic submerged membrane bioreactor (MBR) was used to study the effect of thermochemical pretreatment on the efficiency of sludge reduction. For this purpose, two MBRs were fabricated. Between the two MBRs, one acted as a control reactor (CMBR) and the other acted as an experimental reactor (EMBR). The MBRs were operated with a mixed liquor suspended solids (MLSS) concentration in the range of 6,800-7,200 mg/L for a period of 160 days. In the EMBR, part of the MLSS was withdrawn at a ratio of 1% of Q and was pretreated by low temperature thermochemical treatment. The sludge pretreatment was carried out at 60 °C and an alkali dosage in the range of 0.49 to 0.56 mg NaOH/mg MLSS. During the pretreatment, 42% of COD solubilization and 22% of SS reduction were observed. The pretreated sludge was returned to the reactor for further degradation where it was found to be 42% reduced. During the 160 days of reactor operation, both of the MBRs maintained a relatively constant transmembrane pressure. The sludge digestion does not have any impact on the COD removal efficiency of the reactor.