Can membrane bioreactor be a smart option for water treatment?

Recent advances and mechanisms of microbial bioremediation of nickel from wastewater

The global concern over emerging pollutants, characterized by their low concentrations and high toxicity, necessitates effective remediation strategies. Among these pollutants, pharmaceutical and personal care products, pesticides, surfactants, and persistent organic pollutants have gained significant attention. These contaminants are extensively distributed within aquatic ecosystems, posing threats to both human and aquatic physiological systems. Nickel, a valuable metal renowned for its corrosion-resistant properties, is widely utilized in various industrial processes, leading to the generation of nickel-containing waste streams, including batteries, catalysts, wastewater, and electrolyte bleed-off. Contamination of soil, water, or air by these waste materials can have adverse effects on the environment and human health. This review article focuses on the recent advancements in environmental and economic implications associated with the removal of nickel from diverse waste sources. Physicochemical technologies employed for treating different nickel-containing effluents and wastewater are discussed, alongside bioremediation techniques and the underlying mechanisms by which microorganisms facilitate nickel removal. The recovery of nickel from waste materials holds paramount importance not only from an economic standpoint but also to mitigate environmental impacts.

Wastewater Treatment of Real Effluents by Microfiltration Using Poly(vinylidene fluoride-hexafluoropropylene) Membranes

Over the last decades, the growing contamination of wastewater, mainly caused by industrial processes, improper sewage, natural calamities, and a variety of anthropogenic activities, has caused an increase in water-borne diseases. Notably, industrial applications require careful consideration as they pose significant threats to human health and ecosystem biodiversity due to the production of persistent and complex contaminants. The present work reports on the development, characterization, and application of a poly (vinylidene fluoride-hexafluoropropylene) (PVDF-HFP) porous membrane for the remediation of a wide range of contaminants from wastewater withdrawn from industrial applications. The PVDF-HFP membrane showed a micrometric porous structure with thermal, chemical, and mechanical stability and a hydrophobic nature, leading to high permeability. The prepared membranes exhibited simultaneous activity on the removal of organic matter (total suspended and dissolved solids, TSS, and TDS, respectively), the mitigation of salinity in 50%, and the effective removal of some inorganic anions and heavy metals, achieving efficiencies around 60% for nickel, cadmium, and lead. The membrane proved to be a suitable approach for wastewater treatment, as it showed potential for the simultaneous remediation of a wide range of contaminants. Thus, the as-prepared PVDF-HFP membrane and the designed membrane reactor represent an efficient, straightforward, and low-cost alternative as a pretreatment step for continuous treatment processes for simultaneous organic and inorganic contaminants' remediation in real industrial effluent sources.

Pollutant removal from cheese processing effluent using effective indigenous natural scavengers

The goal of this study was to come up with an efficient method for treating cheese production wastewater. Because the effluent has a higher concentration of organic and inorganic materials, the indigenous microbial treatment process was used to effectively remove total dissolved solids (TDS), chemical oxygen demand (COD), and color without the addition of any nutrients. The indigenous microorganisms were tested for color, TDS, and COD elimination by growing them in "nutrient broth medium" loaded with different amounts of cheese effluent. The isolates were identified by 16S rRNA sequencing, and the results revealed that strain 1 was Enterobacter cloacae, strain 2 was Lactococcus garvieae, and strains 3 and 4 were Bacillus cereus and Bacillus mycoides, respectively. After 36 h of incubation, the data were evaluated. Among all the microbes, E. cloacae reduced TDS and COD from the effluent the most (80 ± 0.2% and 87 ± 0.4% COD, respectively). When compared to individual species, consortia were more efficient (86 ± 0.2% TDS and 90 ± 0.3% COD). On treatment, the correlation coefficient "r" for TDS and COD elimination was found to be 1, resulting in a positive linear connection. The current study suggests that microbial therapies are both effective and environmentally beneficial.

Decentralized wastewater treatment in an urban setting: a pilot study of the circulating fluidized bed bioreactor treating septic tank effluent

To meet the increasing wastewater treatment demand while minimizing the land footprint of the treatment systems and plants, more efficient and compact processes are needed. The circulating fluidized bed bioreactor (CFBBR) has been proven to achieve high levels of biological nutrient removal. Past studies at the lab and pilot scale achieved 94% COD removal and 80% nitrogen removal at HRT's of 2-4 h. A collaborative project between Western University and the Guangzhou Institute of Energy Conversion (GIEC), in Guangzhou, China, further explored the treatment of municipal wastewater with the CFBBR. A pilot CFBBR, with aerobic and anoxic columns for nitrification and denitrification, was constructed at the GIEC for in-situ treatment of septic tank effluent from a residential building. Due to high concentrations of ammonia (NH₄-N), the wastewater had a COD/N ratio of 2-3. Thus, operating at a longer HRT and supplementing COD, in the form of glucose, was necessary to achieve a high nitrogen removal efficiency. The system was run both with and without supplemental COD at HRT's between 16 and 21 h, treating approximately 1000-1270 L/d. Overall, a COD removal efficiency of at least 92%, ammonia removal of 97%, and nitrogen removal of 82% was achieved. The CFBBR system achieved an effluent with BOD and NH₄-N concentrations both below 5 mg/L, a NO₃-N concentration below 15 mg/L, and a total nitrogen concentration below 25 mg/L. The compact design of this pilot-CFBBR, coupled with its high BNR performance make it an excellent option for decentralized treatment of urban wastewaters.

Analysis of the biodegradation performance and biofouling in a halophilic MBBR-MBR to improve the treatment of disinfected saline wastewater

Disinfectant-containing wastewaters have been generated from many places, including marine industries. The synthetic NaClO-containing wastewaters have been effectively treated in a saline MBBR-MBR (moving bed biofilm reactor & membrane bioreactor) system containing marine microorganisms. A low concentration of NaCl (below 100 mg/L) is not enough to kill the microorganisms, but can affect their bioactivity and induce membrane biofouling. A linear relationship has been obtained for the half-life of membrane biofouling as a function of the NaClO concentration (10-100 mg/L): [half-life] = 25-0.12 × [NaClO concentration]. The COD and NH₃-N removals are the highest at a salinity of 30 g/L for the marine bioreactors. The behaviour of the typical biofoulants, measured real-timely by fluorescence spectroscopy, can indicate the levels of membrane biofouling and microbial activity, responding to the NaClO and NaCl influences. Based on the behaviour of biofoulants, this work has also proposed a novel strategy of biofoulants monitoring for membrane antifouling, where antifouling responses can be carried out when the concentration of biofoulants significantly increases.

Performance and Microbial Community of Different Biofilm Membrane Bioreactors Treating Antibiotic-Containing Synthetic Mariculture Wastewater

The performance of pollutant removals, tetracycline (TC) and norfloxacin (NOR) removals, membrane fouling mitigation and the microbial community of three Anoxic/Oxic membrane bioreactors (AO-MBRs), including a moving bed biofilm MBR (MBRa), a fixed biofilm MBR (MBRb) and an AO-MBR (MBRc) for control, were compared in treating antibiotic-containing synthetic mariculture wastewater. The results showed that MBRb had the best effect on antibiotic removal and membrane fouling mitigation compared to the other two bioreactors. The maximum removal rate of TC reached 91.65% and the maximum removal rate of NOR reached 45.46% in MBRb. The addition of antibiotics had little effect on the removal of chemical oxygen demand (COD) and ammonia nitrogen (NH₄⁺-N)—both maintained more than 90% removal rate during the entire operation. High-throughput sequencing demonstrated that TC and NOR resulted in a significant decrease in the microbial diversity and the microbial richness MBRs. Flavobacteriia, Firmicutes and Azoarcus, regarded as drug-resistant bacteria, might play a crucial part in the removal of antibiotics. In addition, the dynamics of microbial community had a great change, which included the accumulation of resistant microorganisms and the gradual reduction or disappearance of other microorganisms under antibiotic pressure. The research provides an insight into the antibiotic-containing mariculture wastewater treatment and has certain reference value.

Micro-macro transition for numerical simulation of submerged membrane bioreactor

The objective of this work is numerical simulation of the membrane by direct analysis at micro, meso and macro level. This approach includes first a defining and modeling of a basic structural unit, after that simulation of a fragment as a representative element of the membrane structure. Then the results obtained to transfer for the entire membrane module and finally modeling of the membrane as porous media with calculated permeability. The numerical simulation was done with Ansys CFX, using the Darcy’s equation for flow through porous media with configuration of the membrane and second order backward Euler transient scheme for solving the Navier-Stokes equations.

The permeability of the membrane is determined at a micro and macro level by computer simulation for different fluids, which allows to evaluating the influence of the viscosity on the flow passing through the membrane. This micro-macro approach is quite efficient and cost-effective because it saves time and requires less computer capacity and allows direct analysis of the complex structure of the membrane modules.

Performance and microbial communities of different biofilm membrane bioreactors with pre-anoxic tanks treating mariculture wastewater

The performance of pollutant removals, activated sludge characteristics, and microbial communities of two biofilm membrane bioreactors coupled with pre-anoxic tanks (BF-AO-MBRs) (one using fiber bundle bio-carriers (FB-MBR) and the other using suspended bio-carriers (MB-MBR)) were compared at the salinity between zero and 60 g/L. At all salinities, three bioreactors showed good COD average removal efficiencies (>94.1%), and FB-MBR showed the best TN removal efficiency (90.4% at 30 g/L salinity). Moreover, FB-MBR had the faster process start-up time and better salt shock resistance. At high salinities (30-60 g/L), more extracellular polymeric substances were produced by the BF-AO-MBRs to avoid the penetration of salt and protect the bacterial community. Because of the different attachment patterns of biofilms, the microbial community structure in the FB-MBR exposed to 30 g/L salinity had higher nitrite-oxidizing/ammonia-oxidizing bacteria ratio (6.44) with more abundance of denitrifiers, which contribute to higher TN removal efficiency and lower nitrite accumulation.

A review on the applications of ultrasonic technology in membrane bioreactors

Membrane bioreactors (MBRs) have received increasing attention in the field of wastewater treatment in recent years. However, membrane fouling is the main problem of MBRs, limiting their widespread and large applications. Membrane cleaning methods can be mainly classified into four types including chemical, physical, physico-chemical and biological clean the fouled membrane. In recent years, ultrasonication has been reported as a promising cleaning technique for the membranes fouled in MBRs. Ultrasonic irradiation can clean the fouled membrane by creating important physical phenomena including microjets, microstreams and shock waves. Moreover, the ultrasonic method can be combined with other cleaning methods e.g. chemical cleaning and backwashing in order to improve the cleaning efficiency. It should be noted that the application of ultrasonic in the MBR system is not limited to the cleaning of membrane. The pretreatment of the wastewater by ultrasonic irradiation or ultrasound coupled with other methods, e.g. ozonation, prior to MBR system, can decrease the organic loading of the wastewater and subsequently postpone the fouling of the membrane. This paper critically reviews the recent advances in the applications of ultrasound in MBR systems. Emerging issues associated with application of on-line ultrasound and also hybrid on-line ultrasound for controlling the membrane fouling in MBR systems are critically reviewed. Moreover, application of the ultrasound in ex-situ form for cleaning the fouled membranes and pretreatment of wastewater prior to the MBR system is discussed.

Shape stable poly(vinyl alcohol) hydrogels with immobilized activated sludge at repeated dry-rewet cycles

The poly(vinyl alcohol) (PVA) hydrogels can be used as a non-toxic and inexpensive immobilization matrix for microbial cells with capability of degrading organic or inorganic pollutants in wastewaters. This study for the first time produced the PVA hydrogels with immobilized cells by two-stage crosslinking which have high shape stability at dry-rewet cycles and, when recovered after sequentially three 24-hr cultivations, reveal high bioactivity in wastewater treatment. The [B(OH)₃][SO₄^2-] cores inside the PVA-boric acid-sulfate hydrogels are proposed to support the immobilized cells with sufficient structure flexibility and strength to maintain hydrogel structural integrity and of sufficient recalcitrance to biological attack. Conversely, neither the PVA-boric acid hydrogels nor the PVA-borate hydrogels can be applied as organic pollutant degraders with dry storage capability. The PVA-boric acid-sulfate hydrogels are proposed as ideal matrix that can be produced and stored in dry, massive quantity and then applied latter at the same or different sites.

Forward osmosis membrane processes for wastewater bioremediation: Research needs

Increasing research and development works have been made to develop forward osmosis (FO) processes as a cost-effective substitute for energy intensive water vacuum suction facility in submerged membrane bioreactor (MBR) applications. Perceived to be a spontaneous water driven process without external applied pressures, the FO has been applied in lab and pilot scales for wastewater bioremediation. This paper reviewed the state-of-the-art developments on the FO unit, the process, and ways of enhancing process performance, particularly on the aspects of flux enhancement, flow resistance reduction, and draw solute with low reverse salt diffusion, which are relevant to enhanced osmotic MBR performance. The perspective to realize the use of FO processes in revision of currently existing energy intensive osmotic MBR processes is discussed with research needs being highlighted.