Anaerobic membrane bioreactors for wastewater treatment: Challenges and opportunities

Abstract

Anaerobic membrane bioreactors (AnMBRs) have become a new mature technology and entered into the wastewater market, but there are several challenges to be addressed for wide applications. In this review, we discuss challenges and potentials of AnMBRs focusing on wastewater treatment. Nitrogen and dissolved methane control, membrane fouling and its control, and membrane associated cost including energy consumption are main bottlenecks to facilitating AnMBR application in wastewater treatment. Accumulation of dissolved methane in AnMBR permeate decreases the benefit of methane energy and contributes to methane gas emissions to atmosphere. Separate control units for nitrogen and dissolved methane add system complexity and increase capital and operating and maintenance (O & M) costs in AnMBR-centered wastewater treatment. Alternatively, methane-based denitrification can be an ideal nitrogen control process due to simultaneous removal of nitrogen and dissolved methane. Membrane fouling and energy associated with membrane fouling control are major limitations, in addition to membrane cost. More efforts are required to decrease capital and O & M costs associated with the control of dissolved methane nitrogen and membrane fouling to facilitate AnMBRs for wastewater treatment. © 2020 Water Environment Federation • Practitioner points • AnMBRs can accelerate anaerobic wastewater treatment including dilute wastewater. • Nitrogen and dissolved methane control is detrimental for AnMBR application to wastewater treatment. • Membrane biofilm reactors using gas-permeable membranes are suitable for simultaneous nitrogen and dissolved methane control. • High capital and O & M costs from membranes are a major bottleneck to wide application of AnMBRs. • Dynamic membranes could be an option to reduce capital and O & M costs for AnMBRs.

Assessing Advances in Anti-fouling Membranes to Improve Process Economics and Sustainability of Water Treatment

“…For AnMBR treatment of municipal wastewater, some claim that cleaning comprises 2–7% of OPEX . Lin and Chen et al found that the cost of chemicals to clean the AnMBR represented approximately 32.5% of OPEX, , while a different AnMBR study found the costs of cleaning chemicals to be 17% of OPEX, although it should be noted that both of these studies only evaluated costs of the AnMBR unit operation, not of an entire wastewater treatment plant (WWTP). Membrane cleaning disrupts operations and decreases efficiency and performance. , In the case of RO processes, Patil et al state that RO membrane cleaning comprised ∼33% of OPEX, while a different analysis suggests that cleaning chemical costs normally contribute about 10% to OPEX .…”

Examination of Extracellular Polymer (EPS) Extraction Methods for Anaerobic Membrane Bioreactor (AnMBR) Biomass

“…Hence, MBRs can be an attractive alternative to conventional activated sludge wastewater treatment processes to meet wastewater effluent standards (e.g., biochemical oxygen demand (BOD) and suspended solids). Membrane costs, one of the most significant expenses in membrane bioreactors, have substantially decreased in the past 20 years [3]. Furthermore, membrane maintenance technologies (i.e., fouling mitigation and membrane cleaning) allow for the use of membranes for long periods, reducing operating costs and downtime [1].…”

“…As such, anaerobic membrane bioreactors (AnMBRs) have received tremendous attention due to their energy neutrality or positive net energy benefits [8]. No aeration, less sludge production, and methane recovery and reuse can significantly reduce operating costs while improving sustainability in wastewater treatment [3]. Moreover, the membranes used for MBRs have been successfully used for AnMBRs without a significant modification of membrane materials or structures [8,9].…”

“…Membrane bioreactor fouling is primarily driven by EPS, which are a complex mixture of polysaccharides, proteins (structural proteins or exoenzymes), lipids/phospholipids, humic substances, and other intercellular polymers [1,10,11]. Unfortunately, the compositional, and functional details of EPS are not completely understood, while the literature has reported EPS characteristics [3,10,12]. EPS is also related to SMP, another major category of foulants.…”

“…Biomass-associated products of SMP originate from EPS hydrolysis [12,13]. Hence, reliable EPS characterization is very significant in the understanding of membrane fouling events and the development of foulant cleaning methods [3,12].…”