Thermophilic anaerobic membrane bioreactor for pulp and paper sludge treatment

Abstract

Pulp and paper mills generate a significant amount of organic waste (primary and secondary sludge) that requires treatment and disposal. Currently, pulp and paper sludge (PPS) is either dried for incineration or used for landfilling. However, the dewatering and drying of sludge before incineration is an energy extensive process and landfilling is associated with a high cost and low public acceptance, the practices of landfilling will tend to decrease. Recently, anaerobic digestion is considered a cost-effective alternative to a small environmental footprint and has been researched widely. Similarly, anaerobic digestion of PPS has the limitations of a large reactor size, high capital cost, and reduced quality of effluent. Thus, it is highly desirable to search novel technologies for PPS treatment and disposal. In this study, a new insight was that thermophilic anaerobic membrane bioreactor (ThAnMBR) was developed for PPS treatment and disposal for biogas production because it can overcome some advantages of conventional anaerobic digestors. In this study, a laboratory-scale ThAnMBR was operated for 328 days to assess the biological and membrane performance of the ThAnMBR at different hydraulic retention times (HRTs) and different types of pulp and paper secondary sludge. In the first part of this thesis, the biological performance of ThAnMBR are discussed by effluent, organic loading rate (OLR), chemical oxygen demand (COD), biogas production rate, biogas composition, biogas yield and suspended solid destruction. The results showed that the performance of a higher HRT is better than a low HRT, but the performance of ultrasonic pretreatment on PPS does not improve all properties. In the second part of this thesis, the membrane performance of ThAnMBR was discussed by: flux, transmembrane pressure (TMP), membrane fouling, particle size distribution, extracellular polymeric substances (EPS), soluble microbial products (SMP), morphology and pore size distribution. The results suggest that ThAnMBR is feasible for PPS treatment, but the membrane fouling should be minimized. Operating ThAnMBR at a higher HRT is more attractive than at a lower HRT from the biological performance point of view.