Influences of liquid, solid, and gas media circulation in anaerobic membrane bioreactor (AnMBR) as a post treatment alternative of aerobic system in seafood industry

Exploring the Function of Quorum Sensing Regulated Biofilms in Biological Wastewater Treatment: A Review

Quorum sensing (QS), a type of bacterial cell–cell communication, produces autoinducers which help in biofilm formation in response to cell population density. In this review, biofilm formation, the role of QS in biofilm formation and development with reference to biological wastewater treatment are discussed. Autoinducers, for example, acyl-homoserine lactones (AHLs), auto-inducing oligo-peptides (AIPs) and autoinducer 2, present in both Gram-negative and Gram-positive bacteria, with their mechanism, are also explained. Over the years, wastewater treatment (WWT) by QS-regulated biofilms and their optimization for WWT have gained much attention. This article gives a comprehensive review of QS regulation methods, QS enrichment methods and QS inhibition methods in biological waste treatment systems. Typical QS enrichment methods comprise adding QS molecules, adding QS accelerants and cultivating QS bacteria, while typical QS inhibition methods consist of additions of quorum quenching (QQ) bacteria, QS-degrading enzymes, QS-degrading oxidants, and QS inhibitors. Potential applications of QS regulated biofilms for WWT have also been summarized. At last, the knowledge gaps present in current researches are analyzed, and future study requirements are proposed.

Recent advances in attached growth membrane bioreactor systems for wastewater treatment

To tackle membrane fouling and limited removals of pollutants (nutrients and emerging pollutants) that hinder the wide applications of membrane bioreactor (MBR), attached growth MBR (AGMBR) combining MBR and attached growth process has been developed. This review comprehensively presents the up-to-date developments of media used in both aerobic and anaerobic AGMBRs for treating wastewaters containing conventional and emerging pollutants. It also elaborates the properties of different media, characteristics of attached biomass, and their contributions to AGMBR performance. Conventional media, such as biological activated carbon and polymeric carriers, induce formation of aerobic, anoxic and/or anaerobic microenvironment, increase specific surface area or porous space for biomass retention, improve microbial activities, and enrich diverse microorganisms, thereby enhancing pollutants removal. Meanwhile, new media (i.e. biochar, bioaugmented carriers with selected strain/mixed cultures) do not only eliminate conventional pollutants (i.e. high concentration of nitrogen, etc.), but also effectively remove emerging pollutants (i.e. micropollutants, nonylphenol, adsorbable organic halogens, etc.) by forming thick and dense biofilm, creating anoxic/anaerobic microenvironments inside the media, enriching special functional microorganisms and increasing activity of microorganisms. Additionally, media can improve sludge characteristics (i.e. less extracellular polymeric substances and soluble microbial products, larger floc size, better sludge settleability, etc.), alleviating membrane fouling. Future studies need to focus on the development and applications of more new functional media in removing wider spectrum of emerging pollutants and enhancing biogas generation, as well as scale-up of lab-scale AGMBRs to pilot or full-scale AGMBRs.

Investigating membrane fouling associated with GAC fluidization on membrane with effluent from anaerobic fluidized bed bioreactor in domestic wastewater treatment

Effect of mechanical scouring driven by granular activated carbon (GAC) fluidization on membrane fouling was investigated using a laboratory-scaled, fluidized membrane reactor filtering the effluent from anaerobic fluidized bed bioreactor (AFBR) in domestic wastewater treatment. The GAC particles were fluidized by recirculating a bulk solution only through the membrane reactor to control membrane fouling. The membrane fouling was compared with two different feed solutions, effluent taken from a pilot-scaled, AFBR treating domestic wastewater and its filtrate through 0.1-μm membrane pore size. The GAC fluidization driven by bulk recirculation through the membrane reactor was very effective to reduce membrane fouling. Membrane scouring under GAC fluidization decreased reversible fouling resistance effectively. Fouling mitigation was more pronounced with bigger GAC particles than smaller ones as fluidized media. Regardless of the fluidized GAC sizes, however, there was limited effect on controlling irreversible fouling caused by colloidal materials which is smaller than 0.1 μm. In addition, the deposit of GAC particles that ranged from 180 to 500 μm in size on membrane surface was very significant and accelerated fouling rate. Biopolymers rejected by the membranes were thought to play a role as binding these small GAC particles on membrane surface strongly.

Polytetrafluoroethylene (PTFE) hollow fiber AnMBR performance in the treatment of organic wastewater with varying salinity and membrane cleaning behavior

PTFE hollow fiber anaerobic membrane bio-reactor (AnMBR) performance was investigated in the treatment of organic wastewater, with varying salinity and PTFE membrane cleaning behavior. The AnMBR was operated for 226 days, with a total and biological COD removal efficiency of 97.2% and 89.9% respectively, at a NaCl concentration of 35 g L^-1. A high number of Proteobacteria (38.2%) and Bacteroidetes (25.9%) were present in the system, with an increase in membrane fouling rate from 1.88 × 10¹¹ to 2.63 × 10¹¹ m^-1 d^-1 with higher salinity. The effects of soluble microbial products (SMP), extracellular polymeric substances (EPS), low molecular-weight (LMW) carbohydrates, sludge particle size and inorganic element accumulation, were evaluated on membrane fouling. Flux recovery of fouled PTFE membranes reached 91.6% with offline cleaning. Overall, results indicate that PTFE hollow fiber AnMBR provides a promising method for the treatment of saline organic wastewater.

Performance and methane fermentation characteristics of a pilot scale anaerobic membrane bioreactor (AnMBR) for treating pharmaceutical wastewater containing m-cresol (MC) and iso-propyl alcohol (IPA)

In this study, a pilot scale anaerobic membrane bioreactor (AnMBR) was operated for 80 days to treat pharmaceutical wastewater containing m-cresol (MC) and iso-propyl alcohol (IPA). The aim of the study is to investigate the performance and methane fermentation characteristics of AnMBR at different hydraulic retention time (HRT) (48, 36, 24, 18 and 12 h). The average total removal efficiencies of MC and IPA were 95%, 96% during the 80 days, which demonstrated that the AnMBR system performed well in the MC and IPA removal. The major volatile fatty acid (VFA) was found to be acetic acid, propionic acid, butyric acid, besides, the VFA accumulated apparently when HRT decreased to 12 h. The decrease of HRT led to an increase of relative abundance of methanosarcina from 13 to 33% and a decrease in biogas yield from 0.19 to 0.05 L/gCOD_removal. The biogas production was found to increase dramatically at HRT of 36 h. The trend of methane content kept stable at this stage with the average value of 78.5% which higher than other HRTs. The investigation of methanogen community showed that methanosarcinaceae was always dominant acetoclastic methanogens and methanomicrobiales was the dominant hydrogen utilizers throughout the operational period. When the HRT dropped to 12 h, the growth of the methanosarcinaceae and methanomicrobiales was observed, the amount of the methanosarcinaceae and methanomicrobiales sharply increased. After the overall research, HRT of 36 h was chosen as the most suitable operating condition due to the comprehensively preferable performance and more economical.

Long-term operation of oxygen-limiting membrane bioreactor (MBR) for the development of simultaneous partial nitrification, anammox and denitrification (SNAD) process

In this study, an oxygen-limiting membrane bioreactor (MBR) with recirculation of biogas for relieving membrane fouling was successfully operated to realize the simultaneous partial nitrification, anammox and denitrification (SNAD) process. The MBR operation was considered effective in the long-term test with total nitrogen (TN) and chemical oxygen demand (COD) removal efficiencies of 94.86% and 98.91%, respectively. Membrane fouling was significantly alleviated due to the recirculation of biogas and the membrane had been cleaned four times with a normal filtration period of 52 days. The co-existence of ammonia-oxidizing bacteria (AOB), anammox and denitrifying bacteria in MBR was confirmed by scanning electron microscopy (SEM) and fluorescence in situ hybridizations (FISH) analysis. Furthermore, AOB were found close to the granule surface, while denitrifying bacteria and anammox were in the deeper layer of granules. Potential in excellent TN and COD removal, operational stability and sustainability, as well as in alleviating membrane fouling is expected by using this oxygen-limiting MBR.

Investigation on the performance of hybrid anaerobic membrane bioreactors for fouling control and biogas production in palm oil mill effluent treatment

Three different sizes of powdered activated carbon (PAC) were added in hybrid anaerobic membrane bioreactors (AnMBRs) and their performance was compared with a conventional AnMBR without PAC in treating palm oil mill effluent. Their working volume was 1 L each. From the result, AnMBRs with PAC performed better than the AnMBR without PAC. It was also found that adding a relatively smaller size of PAC (approximately 100 μm) enhanced the chemical oxygen demand removal efficiency to 78.53 ± 0.66%, while the concentration of mixed liquor suspended solid and mixed liquor volatile suspended solid were 8,050 and 6,850 mg/L, respectively. The smaller size of PAC could also enhance the biofloc formation and biogas production. In addition, the smaller particle sizes of PAC incorporated into polyethersulfone membrane resulted in higher performance of membrane fouling control and produced better quality of effluent as compared to the membrane without the addition of PAC.