Kinetics of anaerobic methane oxidation coupled to denitrification in the membrane biofilm reactor

Optimization of the chemolithotrophic denitrification of ion exchange concentrate using hydrogen-based membrane biofilm reactors

A H2-based membrane biofilm reactor (MBfR) was used to remove nitrate from a synthetic ion-exchange brine made up of 23.8 g L-1 NaCl. To aid the selection of the best nitrate management strategy, our research was based on the integrated analysis of ionic exchange and MBfR processes, including a detailed cost analysis. The nitrate removal flux was not affected if key nutrients were present in the feed solution including potassium and sodium bicarbonate. Operating pH was maintained between 7 and 8. By using a H2 pressure of 15 psi, a hydraulic retention time (HRT) of 4 h, and a surface loading rate of 13.6 ± 0.2 g N m-2 d-1, the average nitrate removal flux was 3.3 ± 0.6 g N m-2 d-1. At HRTs of up to 24 h, the system was able to maintain a removal flux of 1.6 ± 0.2 g N m-2 d-1. Microbial diversity analysis showed that the consortium was dominated by the genera Sulfurimonas and Marinobacter. The estimated cost for a 200 m3/h capacity, coupled ion exchange (IX) + MBfR treatment plant is 0.43 USD/m3. This is a sustainable and competitive alternative to an IX-only plant for the same flowrate. The proposed treatment option allows for brine recycling and reduces costs by 55% by avoiding brine disposal expenses.

State-of-the-art management technologies of dissolved methane in anaerobically-treated low-strength wastewaters: A review

The recent advancement in low temperature anaerobic processes shows a great promise for realizing low-energy-cost, sustainable mainstream wastewater treatment. However, the considerable loss of the dissolved methane from anaerobically-treated low-strength wastewater significantly compromises the energy potential of the anaerobic processes and poses an environmental risk. In this review, the promises and challenges of existing and emerging technologies for dissolved methane management are examined: its removal, recovery, and on-site reuse. It begins by describing the working principles of gas-stripping and biological oxidation for methane removal, membrane contactors and vacuum degassers for methane recovery, and on-site biological conversion of dissolved methane into electricity or value-added biochemicals as direct energy sources or energy-compensating substances. A comparative assessment of these technologies in the three categories is presented based on methane treating efficiency, energy-production potential, applicability, and scalability. Finally, current research needs and future perspectives are highlighted to advance the future development of an economically and technically sustainable methane-management technology.

Anaerobic membrane bioreactors for wastewater treatment: Challenges and opportunities

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. 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.

A modelling study of the spatially heterogeneous mutualism between electroactive biofilm and planktonic bacteria

Microbial cooperation widely exists in anaerobic reactors degrading complex pollutants, conventionally studied separately inside the biofilm or the planktonic community. Recent experiments discovered the mutualism between the planktonic bacteria and electroactive biofilm treating propionate, an end-product usually accumulated in anaerobic digesters. Here, a one-dimensional multispecies model found the preference on acetate-based pathway over the hydrogen-based in such community, evidenced by the fact that acetate-originated current takes 66% of the total value and acetate-consuming anode-respiring bacteria takes over 80% of the biofilm. Acetate-based anodic respiration most apparently influences biofilm function while propionate fermentation is the dominant planktonic bio-reaction. Additionally, initial planktonic propionate level shows the ability of coordinating the balance between these two extracellular electron transfer pathways. Increasing the propionate concentration from 2 to 50 mM would increase the steady hydrogen-originated current by 210% but decrease the acetate-originated by 26%, suggesting a vital influence of the planktonic microbial process to the metabolic balance in biofilm. Best strategy to promote the biofilm activity is to increase the biomass density and biofilm conductivity simultaneously, which would increase the current density by 875% without thickening the biofilm thickness or prolonging the growth apparently.