Impact of oxygen on the coexistence of nitrification, denitrification, and sulfate reduction in oxygen-based membrane aerated biofilm

Recent progress using membrane aerated biofilm reactors for wastewater treatment

The membrane biofilm reactor (MBfR), which is based on the counter diffusion of the electron donors and acceptors into the biofilm, represents a novel technology for wastewater treatment. When process air or oxygen is supplied, the MBfR is known as the membrane aerated biofilm reactor (MABR), which has high oxygen transfer rate and efficiency, promoting microbial growth and activity within the biofilm. Over the past few decades, laboratory-scale studies have helped researchers and practitioners understand the relevance of influencing factors and biological transformations in MABRs. In recent years, pilot- to full-scale installations are increasing along with process modeling. The resulting accumulated knowledge has greatly improved understanding of the counter-diffusional biological process, with new challenges and opportunities arising. Therefore, it is crucial to provide new insights by conducting this review. This paper reviews wastewater treatment advancements using MABR technology, including design and operational considerations, microbial community ecology, and process modeling. Treatment performance of pilot- to full-scale MABRs for process intensification in existing facilities is assessed. This paper also reviews other emerging applications of MABRs, including sulfur recovery, industrial wastewater, and xenobiotics bioremediation, space-based wastewater treatment, and autotrophic nitrogen removal. In conclusion, commercial applications demonstrate that MABR technology is beneficial for pollutants (COD, N, P, xenobiotics) removal, resource recovery (e.g., sulfur), and N₂O mitigation. Further research is needed to increase packing density while retaining efficient external mass transfer, understand the microbial interactions occurring, address existing assumptions to improve process modeling and control, and optimize the operational conditions with site-specific considerations.

Metagenomic Insight Towards Vanillin-Mediated Membrane Biofouling Prevention: In Silico Docking Validation

Biofouling leads to water quality deterioration and higher maintenance cost for cleaning of membranes. The present study has demonstrated the application of a biomolecule (vanillin) in scrubbing and destabilizing biofilms of drinking water reverse osmosis (RO) membrane module in lab scale reactor set-up. Reverse osmosis membrane reactor was connected with tap water supply and subjected with optimal concentration of vanillin. The pressure drop was delayed by 17-20 days as compared to control reactor. Real-time PCR analysis of metagenome indicated the reduced copy number of functional biofilm-associated genes (bdlA, lasI, pgaC) in treated membrane. SEM and metagenome analysis revealed that the sticky biofilm communities shifted to loosely bound emboli after vanillin treatment. Metagenome sequence analysis revealed the inhibitory activity against major biofouling biota like members of Proteobacteria, Acidobacteria, Acnitobacteria, Bacteroidetes, Candidatus, Nitrospira, and Firmicutes. Biofouled membrane metagenome sequence was also compared with real-life (brackish water, waste water, domestic drinking water) biofouled membrane communities. In silico docking of vanillin to receptor proteins and chemical configuration simulation along with other phenolic derivatives were performed, which suggested that the autoiducer signal capability of vanillin was effective against representative broad spectrum biofilm population. Vanillin exhibited the quorum-quenching mode of action by virtue of docking towards similar amino acid (Thr 131, Ilu 214) responsible of autoinducer signal anchoring in the transcriptional regulatory proteins.

An Innovative in Situ Monitoring of Sulfate Reduction within a Wastewater Biofilm by H2S and SO42- Microsensors

Microelectrodes can be used to obtain chemical profiles within biofilm microenvironments. For example, sulfate (SO₄^2-) and hydrogen sulfide (H₂S) microelectrodes can be used to study sulfate reduction activity in this context. However, there is no SO₄^2- microelectrode available for studying sulfate reduction in biofilms. In this study, SO₄^2- and H₂S microelectrodes were fabricated and applied in the measurement of a wastewater membrane-aerated biofilm (MAB) to investigate the in situ sulfate reduction activity. Both the SO₄^2- and H₂S microelectrodes with a tip diameter of around 20 micrometers were successfully developed and displayed satisfying selectivity to SO₄^2- and H₂S, respectively. The Nernstian slopes of calibration curves of the fabricated SO₄^2- electrodes were close to -28.1 mV/decade, and the R² values were greater than 98%. Within the selected concentration range from 10^-5 M (0.96 mg/L) to 10^-2 M (960 mg/L), the response of the SO₄^2- microelectrode was log-linearly related to its concentration. The successfully fabricated SO₄^2- microelectrode was combined with the existing H₂S microelectrode and applied on an environmental wastewater biofilm sample to investigate the sulfate reduction activity within it. The H₂S and SO₄^2- microelectrodes showed stable responses and good performance, and the decrease of SO₄^2- with an accompanying increased of H₂S within the biofilm indicated the in situ sulfate reduction activity. The application of combined SO₄^2- and H₂S microelectrodes in wastewater biofilms could amend the current understanding of sulfate reduction and sulfur oxidation within environmental biofilms based on only H₂S microelectrodes.