Treatment of abattoir wastewater using a downflow expanded granular bed reactor coupled with a hybrid membrane bioreactor system

Abstract

Biological wastewater treatment processes such as activated sludge and anaerobic digestion remain the most favorable when compared to processes such as chemical precipitation and ion exchange due to their cost-effectiveness, eco-friendliness, ease of operation, and low maintenance. Since Abattoir Wastewater (AWW) is characterized as having high organic content, anaerobic digestion is slow and inadequate for complete removal of all nutrients and organic matter when required to produce a high-quality effluent that satisfies discharge standards. Multi-integrated systems can be designed in which additional stages are added before the anaerobic digester (pre-treatment), as well as after the digester (post-treatment) for nutrient recovery and pathogen removal. This can aid the water treatment plant effluent to meet the discharge regulations imposed by the legislator and allow the possibility for reuse on-site. This study aims to provide information on the principles of anaerobic digestion, aeration pretreatment technology using enzymes and a hybrid membrane bioreactor, describing their various roles in AWW treatment. Simultaneous nitrification and denitrification are essential to add after anaerobic digestion for nutrient recovery utilizing a single step process. Nutrient recovery has become more favorable than nutrient removal in wastewater treatment because it consumes less energy, making the process cost-effective. In addition, recovered nutrients can be used to make nutrient-based fertilizers, reducing the effects of eutrophication and land degradation. The downflow expanded granular bed reactor is also compared to other high-rate anaerobic reactors, such as the up-flow anaerobic sludge blanket (UASB) and the expanded granular sludge bed reactor (EGSB). Another objective of this study was to evaluate the operating costs of treating abattoir wastewater using combined biological processes. The processes were evaluated based on removal efficiency and cost of treating wastewater/KL. The process with the most removal efficiencies was the raw-AD-MBR and the effluent met the municipal discharge standards. A potential for reuse onsite for irrigation can be explored if a UV system is added and an anaerobic stage for phosphorus removal could be added before the MBR. The removal efficiencies for FOGs, TSS, COD, ammonia and E.coli were >98%, 98%, >90%, 80-90%, >97% respectively. The lab scale plant achieved that at a price of R801,40/KL.