Microbial and operational factors affecting energy recovery potential for anaerobic membrane bioreactors treating different wastewater types

Abstract

Water scarcity has become a worldwide issue that is exacerbated in developing countries due to excessive pollution of water resources. In order to allow for sustainable practices that are capable of facilitating wastewater reuse, different types of wastewater treatment systems have been implemented over the years. While wastewater systems are traditionally designed to reduce pollutants and pathogens prior to discharge, a major factor that also requires consideration is energy expenditure and recovery potential during treatment. Recently, anaerobic membrane bioreactors (AnMBRs) have been shown as having certain advantages compared to conventional aerobic systems, as well as other anaerobic treatment methods such as the up-flow anaerobic sludge blanket (UASB). Several factors affect energy recovery from AnMBRs including the influent wastewater strength and type, the operating parameters, and the adaptation of microbial communities. In that context, the overall work of this thesis assessed factors associated with energy use and recovery in an AnMBR and consist of multiple experiments treating different types of wastewaters under varying operating conditions. The first experiment treating synthetic wastewater highlighted the effect of operating three membranes with different permeate fluxes on the energy consumption of the system. The second experiment treating municipal wastewater highlighted the tipping point of energy neutrality of the system due to the low organic content of the influent. The third experiment treating poultry slaughterhouse wastewater (PSW) over three phases with decreasing hydraulic retention times (HRTs) concluded that the microbial adaptation to the high-strength wastewater can directly impact the energy produced from the system. In the PSW experiment, microbial risk-associated elements (such as pathogens and antibiotic resistance genes) were also assessed in effluents. An additional experiment conducted for olive mill wastewater reiterated the AnMBR’s capacity to successfully recover energy from complex agro-industrial wastewaters. It was found that for such high-strength wastewaters, energy expenditure for substrate heating or electrical demand is negligible in comparison to the potential variability in methane production rates achievable.