Citation:

Crone, B., G. Sorial, J. Pressman, H. Ryu, S. Keely, N. Brinkman, C. Bennett-Stamper, AND J. Garland. Design and Evaluation of Degassed Anaerobic Membrane Biofilm Reactors for Improved Methane Recovery. Bioresource Technology Reports. Elsevier B.V., Amsterdam, Netherlands, 10:100407, (2020). https://doi.org/10.1016/j.biteb.2020.100407

Impact/Purpose:

This research falls under SSWR6.03C; Transformative Technologies for Water Systems. Wastewater is often viewed as a liability to human health and the environment and treatment paradigms are focused on reducing negative impacts rather than on recovering resources, such as water and energy, for reuse. Domestic wastewater contains a significant amount of energy that, if effectively captured, could be used to power the wastewater treatment process. Anaerobic treatment of domestic wastewater metabolizes the organic material present in domestic wastewater into methane, which has a high energy density and can be used to produce electricity. However, a significant portion of the methane produced remains dissolved in solution and then evolves into the atmosphere when it is exposed to the environment thereby contributing to greenhouse gas emissions and lost potential energy. Dissolved methane can be recovered using membranes although there are significant issues with fouling which can lead to even greater energy requirements than is available in the recovered methane. In-situ degassing is a method that has been reported in the literature and can both recover methane and remove other dissolved biogases simultaneously which has been shown to improve methane yield and chemical oxygen demand removal efficiency. However, since the membranes are submerged in the reactor body (hence in-situ) where suspended solids concentrations are highest they are particularly susceptible to fouling. To overcome this limitation, a novel anaerobic treatment system that combined attached growth with non-porous hollow fiber degassing membranes was developed. Specifically, the process involves the growth of a methane producing biofilm on the shell side surface of a hollow fiber membrane for the in-situ removal of dissolved biogas constituents. This allowed for the immediate recovery of methane as it was produced, negating the liquid boundary layer and mass transfer fouling resistances. The objectives of this study included; evaluating wastewater treatment effectiveness, process improvements from dissolved biogas removal, methane recovery efficiency, and energy balance. Successful recovery of dissolved methane with minimal energy expenditure would lead to a potentially net-zero wastewater treatment system and reduce the environmental impacts of methane losses to the atmosphere. The stakeholders that would be interested in this study and could apply the results include Wastewater Treatment Utilities, OWM, DOD, Academia, and Resource Recovery Experts.

Description:

Anaerobic treatment of domestic wastewater (DWW) produces methane, which can remain dissolved in solution. Dissolved methane needs to be recovered efficiently to prevent subsequent release into the environment and allow for beneficial use as an energy product. While several membrane-based recovery systems have been reported in the literature, membrane fouling has been identified as a limiting factor. The objectives of this study were to develop and evaluate a novel attached growth anaerobic treatment system designed to emphasize the growth of the attached biofilm, rather than its removal, to optimize reactor performance. To accomplish this, a methane producing biofilm was developed on the shell side surface of submerged hollow fiber membranes, which allowed for immediate recovery of methane as it was produced, negating the liquid boundary layer and mass transfer fouling resistances. Impacts of membrane surface treatment on biofilm development were investigated as well. Average chemical oxygen demand (COD) removal was above 76% in all reactors and those with membrane surface treatment exhibited improved methane yield because of increased methanogenic activity. Between 89-96% of total methane produced was recovered via in-situ degassing without the need for fouling control or cleaning throughout 72 weeks of operation. High methane recovery efficiencies led to predictions of net positive energy yield in one reactor and significantly reduced energy demand in the other reactors. This research demonstrates the feasibility of combining attached growth anaerobic wastewater treatment processes with hollow fiber membranes for improved methane recovery.

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