A performance evaluation of three membrane bioreactor systems: aerobic, anaerobic, and attached-growth

High-retention membrane bioreactors for sugarcane vinasse treatment: Opportunities for environmental impact reduction and wastewater valorization

Ethanol production has increased over the years, and Brazil ranking second in the world using sugarcane as the main raw material. However, 10-15 L of vinasse are generated per liter of ethanol produced. Besides large volumes, this wastewater has high polluting potential due to its low pH and high concentrations of organic matter and nutrients. Given the high biodegradability of the organic matter, the treatment of this effluent by anaerobic digestion and membrane separation processes results in the generation of high value-added byproducts such as volatile fatty acids (VFAs), biohydrogen and biogas. Membrane bioreactors have been widely evaluated due to the high efficiency achieved in vinasse treatment. In recent years, high retention membrane bioreactors, in which high retention membranes (nanofiltration, reverse osmosis, forward osmosis and membrane distillation) are combined with biological processes, have gained increasing attention. This paper presents a critical review focused on high retention membrane bioreactors and the challenges associated with the proposed configurations. For nanofiltration membrane bioreactor (NF-MBR), the main drawback is the higher fouling propensity due to the hydraulic driving force. Nonetheless, the development of membranes with high permeability and anti-fouling properties is uprising. Regarding osmotic membrane bioreactor (OMBR), special attention is needed for the selection of a proper draw solution, which desirably should be low cost, have high osmolality, reduce reverse salt flux, and can be easily reconcentrated. Membrane distillation bioreactor (MDBR) also exhibit some shortcomings, with emphasis on energy demand, that can be solved with the use of low-grade and residual heat, or renewable energies. Among the configurations, MDBR seems to be more advantageous for sugarcane vinasse treatment due to the lower energy consumption provided by the use of waste heat from the effluent, and due to the VFAs recovery, which has high added value.

Impact of textile dyes on health and ecosystem: a review of structure, causes, and potential solutions

The rapid growth of population and industrialization have intensified the problem of water pollution globally. To meet the challenge of industrialization, the use of synthetic dyes in the textile industry, dyeing and printing industry, tannery and paint industry, paper and pulp industry, cosmetic and food industry, dye manufacturing industry, and pharmaceutical industry has increased exponentially. Among these industries, the textile industry is prominent for the water pollution due to the hefty consumption of water and discharge of coloring materials in the effluent. The discharge of this effluent into the aquatic reservoir affects its biochemical oxygen demand (BOD), chemical oxygen demand (COD), total dissolved solids (TDS), total suspended solids (TSS), and pH. The release of the effluents without any remedial treatment will generate a gigantic peril to the aquatic ecosystem and human health. The ecological-friendly treatment of the dye-containing wastewater to minimize the detrimental effect on human health and the environment is the need of the hour. The purpose of this review is to evaluate the catastrophic effects of textile dyes on human health and the environment. This review provides a comprehensive insight into the dyes and chemicals used in the textile industry, focusing on the typical treatment processes for their removal from industrial wastewaters, including chemical, biological, physical, and hybrid techniques.

Numerical simulation and experimental research of fractal suspended carrier based on nonlinear equation

The geometric structure of the suspended carrier is an important factor that directly affects the effluent quality of the moving bed biofilm reactor, and it should be a valuable mathematical solution to solve the nonlinear equation through numerical simulation and experimental research. Therefore, this study has designed and prepared a coral-shaped fractal suspension carrier based on nonlinear equations and verified the effectiveness of the new carrier for sewage treatment through FLUENT numerical simulation and domestic sewage treatment experiments. The experimental results show that the coral-shaped fractal suspension carrier has a significant effect on the velocity, vortex distribution, and gas-phase distribution of the flow field in the reactor. The mass transfer dead area in the reactor is reduced, the number of vortices is significantly increased, and the fractal dimension of the carrier is negatively correlated with the flow velocity and pressure drop of the fluid. After stabilization, the average removal rates of COD and NH₄⁺-N by the reactor are 89.5% and 93.21%, respectively; the effluent quality reaches the national first-class A standard; and the sewage treatment performance is good. At the same time, this research provides a preliminary research basis for the method of solving nonlinear equations through numerical simulation and experimental research.

Energy-Efficient AnMBRs Technology for Treatment of Wastewaters: A Review

In recent years, anaerobic membrane bioreactor (AnMBRs) technology, a combination of a biological reactor and a selective membrane process, has received increasing attention from both industrialists and researchers. Undoubtedly, this is due to the fact that AnMBRs demonstrate several unique advantages. Firstly, this paper addresses fundamentals of the AnMBRs technology and subsequently provides an overview of the current state-of-the art in the municipal and domestic wastewaters treatment by AnMBRs. Since the operating conditions play a key role in further AnMBRs development, the impact of temperature and hydraulic retention time (HRT) on the AnMBRs performance in terms of organic matters removal is presented in detail. Although membrane technologies for wastewaters treatment are known as costly in operation, it was clearly demonstrated that the energy demand of AnMBRs may be lower than that of typical wastewater treatment plants (WWTPs). Moreover, it was indicated that AnMBRs have the potential to be a net energy producer. Consequently, this work builds on a growing body of evidence linking wastewaters treatment with the energy-efficient AnMBRs technology. Finally, the challenges and perspectives related to the full-scale implementation of AnMBRs are highlighted.

Modeling and Life Cycle Assessment of a Membrane Bioreactor–Membrane Distillation Wastewater Treatment System for Potable Reuse

Wastewater treatment for indirect potable reuse (IPR) is a possible approach to address water scarcity. In this study, a novel membrane bioreactor–membrane distillation (MBR-MD) system was evaluated to determine the environmental impacts of treatment compared to an existing IPR facility (“Baseline”). Physical and empirical models were used to obtain operational data for both systems and inform a life cycle inventory. Life cycle assessment (LCA) was used to compare the environmental impacts of each system. Results showed an average 53.7% reduction in environmental impacts for the MBR-MD system when waste heat is used to operate MD; however, without waste heat, the environmental impacts of MBR-MD are significantly higher, with average impacts ranging from 218% to 1400% greater than the Baseline, depending on the proportion of waste heat used. The results of this study demonstrate the effectiveness of the novel MBR-MD system for IPR and the reduced environmental impacts when waste heat is available to power MD.

Anaerobic Membrane Bioreactors for Municipal Wastewater Treatment: A Literature Review

Currently, there is growing scientific interest in the development of more economic, efficient and environmentally friendly municipal wastewater treatment technologies. Laboratory and pilot-scale surveys have revealed that the anaerobic membrane bioreactor (AnMBR) is a promising alternative for municipal wastewater treatment. Anaerobic membrane bioreactor technology combines the advantages of anaerobic processes and membrane technology. Membranes retain colloidal and suspended solids and provide complete solid–liquid separation. The slow-growing anaerobic microorganisms in the bioreactor degrade the soluble organic matter, producing biogas. The low amount of produced sludge and the production of biogas makes AnMBRs favorable over conventional biological treatment technologies. However, the AnMBR is not yet fully mature and challenging issues remain. This work focuses on fundamental aspects of AnMBRs in the treatment of municipal wastewater. The important parameters for AnMBR operation, such as pH, temperature, alkalinity, volatile fatty acids, organic loading rate, hydraulic retention time and solids retention time, are discussed. Moreover, through a comprehensive literature survey of recent applications from 2009 to 2021, the current state of AnMBR technology is assessed and its limitations are highlighted. Finally, the need for further laboratory, pilot- and full-scale research is addressed.

Comparison of soluble microbial product (SMP) production in full-scale anaerobic/aerobic industrial wastewater treatment and a laboratory based synthetic feed anaerobic membrane system

This study focused on the characterisation of soluble microbial products (SMPs) produced from a full-scale multi-stage (anaerobic/aerobic) industrial wastewater treatment plant, and contrasted them to the SMPs detected in the effluent of a lab-scale AnMBR treating synthetic wastewater to determine if there were any common solutes detected irrespective of the feed organics. Recently developed analytical methods using gas chromatography coupled mass spectrometry (GC-MS) and liquid chromatography coupled quadrupole-time-of-flight (LC-Q-ToF) for SMP characterisation in a wide molecular weight (MW) range of 30-2000 Da (Da) were applied. Samples collected from the Industrial Wastewater plant were the upflow anaerobic sludge blanket (UASB) influent and effluent, and aerobic membrane bioreactor (MBR) effluent before discharge. The GC-MS detected a spike in cyclooctasulphur in the UASB effluent, an indicator of shock-loading, which disappeared after the MBR process. Alkanes, acids and nitrogenous compounds were found to be the end-products from the GC-MS results, while LC-Q-ToF analysis revealed that eicosanoids, a group of cell-signalling molecules, were produced in the aerobic MBR, and made up 71% of its effluent. A comparison of the submerged anaerobic membrane bioreactor (SAMBR) and aerobic MBR effluents using GC-MS showed that there was only a small degree of similarity between the SMPs, comprising mainly long chain alkanes and phthalate. On the other hand, LC-Q-ToF showed a large contrast in compound composition, mostly having cell-signalling functions, which deepened our understanding of the different metabolic processes occurring in aerobic and anaerobic systems. These data could be useful for future work in various areas such as controlling quorum-sensing and biofilm formation, process optimisation and control, and microbial ecology.

Performance Evaluation of a Thermophilic Anaerobic Membrane Bioreactor for Palm Oil Wastewater Treatment

Anaerobic treatment processes have achieved popularity in treating palm oil mill effluent due to its high treatability and biogas generation. The use of externally submerged membranes with anaerobic reactors promotes the retention of the biomass in the reactor. This study was conducted in thermophilic conditions with the Polytetrafluoroethylene hollow fiber (PTFE-HF) membrane which was operated at 55 °C. The reactor was operated at Organic Loading Rates (OLR) of 2, 3, 4, 6, 8, and 10 kg Chemical Oxygen Demand (COD)/m³·d to investigate the treatment performance and the membrane operation. The efficiency of the COD removal achieved by the system was between 93-98%. The highest methane yield achieved was 0.56 m³ CH₄/kg COD_r. The reactor mixed liquor volatile suspended solids (MLVSS) was maintained between 11.1 g/L to 20.9 g/L. A dead-end mode PTFE hollow fiber microfiltration was operated with the constant flux of 3 LMH (L/m²·h) in permeate recirculation mode to separate the clear final effluent and retain the biomass in the reactor. Membrane fouling was one of the limiting factors in the membrane bioreactor application. In this study, organic fouling was observed to be 93% of the total membrane fouling.

Evidence, Determination, and Implications of Membrane-Independent Limiting Flux in Forward Osmosis Systems

A stepwise method for determining limiting flux and limiting osmotic pressure and a constant osmotic pressure method to validate the limiting flux were developed. First, five of the most commonly used FO membranes were characterized for water permeability ( A), solute permeability ( B), and structural parameter ( S). During both stepwise and constant osmotic pressure fouling experiments, membrane fouling constrained water flux to a singular, common upper limit, the limiting flux, for all membranes despite very different A and A/ B values for the membranes. Conversely, there was not an upper limit to reverse salt flux. It was observed that reverse salt flux increases as S decreases; however, this does not mean that higher S values are desirable. Higher S values (> ∼600 μm) also increase dilutive internal concentration polarization, which is recognized as the major impediment to achieving high FO water flux. For osmotic processes where membrane fouling occurs, membrane transport parameters A and B may not be useful performance indicators, and the goal of improving water flux by developing highly permeable, highly selective membranes may not be realistic. Instead, optimizing fouling mitigation strategies, hydrodynamics at the membrane surface, and membrane module configuration may be more promising alternatives for improving performance.

Appropriate technologies for upgrading wastewater treatment plants: methods review and case studies in China

Upgrading existing wastewater treatment plants (WWTPs) is a more challenging task than constructing new plants. The aim is usually to overcome overloading and to reduce pollution concentrations in the effluent. There are various methods that can be used to upgrade WWTPs. This article reviews some of the methodologies, such as inserting new tanks as additional treatment steps and modifying the WWTP by introducing new technologies. A number of effective technologies are reviewed in terms of their basic concepts, operational conditions, and treatment performances. Examples of WWTPs in China that have been successfully upgraded using these technologies are also highlighted.

White and infrared light continuous photobioreactors for resource recovery from poultry processing wastewater - A comparison

Concentrated wastewaters from agricultural industries represent a key opportunity for the upcycling of organics, nitrogen and phosphorus to higher value products such as microbial protein. Phototrophic or photosynthetic microbes very effectively capture input organics and nutrients as microbial protein. This study compares purple phototrophic bacteria (PPB) and microalgae (photosynthesis) for this purpose, treating real, high strength poultry processing wastewater in continuous photo bioreactors utilising infrared (IR) and white light (WL) respectively. Both reactors could effectively treat the wastewaters, and at similar loading rates (4 kgCOD m^-3d^-1). The infrared reactor (IRR) was irradiated at 18 W m^-2 and the white light reactor (WLR) reactor at 1.5-2 times this. The IRR could remove up to 90% total chemical oxygen demand (TCOD), 90% total nitrogen (TN) and 45% total phosphorus (TP) at 1.0 d hydraulic retention time (HRT) and recover around 190 kg of crude protein per tonne of influent COD at 7.0 kWh per dry tonne^-1 light input, with PPB dominating all samples. In comparison, the WLR removed up to 98% COD, 94% TN and 44% TP at 43-90% higher irradiance compared to the PPB reactor. Microalgae did not dominate the WLR and the community was instead a mix of microbes (algae, bacteria, zooplankton and detritus - ALBAZOD) with a production of approximately 140 kg crude protein per tonne influent COD.

Enhancing anaerobic treatment of domestic wastewater: State of the art, innovative technologies and future perspectives

Recent concerns over public health, environmental protection, and resource recovery have induced to look at domestic wastewater more as a resource than as a waste. Anaerobic treatment, owing to attractive advantages of energy saving, biogas recovery and lower sludge production, has been suggested as an alternative technology to the traditional practice of aerobic wastewater treatment, which is energy intensive, produces high excess of sludge, and fails to recover the potential resources available in wastewater. Sewage treatment by high-rate anaerobic processes has been widely reported over the last decades as an attractive method for providing a good quality effluent. Among the available high-rate anaerobic technologies, membrane bioreactors feature many advantages over aerobic treatment and conventional anaerobic systems, since high treatment efficiency, high quality effluent, pathogens retention and recycling of nutrients, were generally achieved. The objective of this paper is to review the currently available knowledge on anaerobic domestic wastewater treatment for the mostly applied high-rate systems and membrane bioreactors, presenting benefits and drawbacks, and focusing on the most promising emerging technologies, which need more investigation for their scale-up.

Bioreactors for oil sands process-affected water (OSPW) treatment: A critical review

Canada has the world's largest oil sands reservoirs. Surface mining and subsequent caustic hot water extraction of bitumen lead to an enormous quantity of tailings (volumetric ratio bitumen:water=9:1). Due to the zero-discharge approach and the persistency of the complex matrix, oil producers are storing oil sands tailings in vast ponds in Northern Alberta. Oil sands tailings are comprised of sand, clay and process-affected water (OSPW). OSPW contains an extremely complex matrix of organic contaminants (e.g., naphthenic acids (NAs), residual bitumen, and polycyclic aromatic hydrocarbons (PAHs)), which has proven to be toxic to a variety of aquatic species. Biodegradation, among a variety of examined methods, is believed to be one of the most cost effective and practical to treat OSPW. A number of studies have been published on the removal of oil sands related contaminants using biodegradation-based practices. This review focuses on the treatment of OSPW using various bioreactors, comparing bioreactor configurations, operating conditions, performance evaluation and microbial community dynamics. Effort is made to identify the governing biotic and abiotic factors in engineered biological systems receiving OSPW. Generally, biofilms and elevated suspended biomass are beneficial to the resilience and degradation performance of a bioreactor. The review therefore suggests that a hybridization of biofilms and membrane technology (to ensure higher suspended microbial biomass) is a more promising option to remove OSPW organic constituents.

Treatment of textile wastewater with membrane bioreactor: A critical review

Membrane bioreactor (MBR) technology has been used widely for various industrial wastewater treatments due to its distinct advantages over conventional bioreactors. Treatment of textile wastewater using MBR has been investigated as a simple, reliable and cost-effective process with a significant removal of contaminants. However, a major drawback in the operation of MBR is membrane fouling, which leads to the decline in permeate flux and therefore requires membrane cleaning. This eventually decreases the lifespan of the membrane. In this paper, the application of aerobic and anaerobic MBR for textile wastewater treatment as well as fouling and control of fouling in MBR processes have been reviewed. It has been found that long sludge retention time increases the degradation of pollutants by allowing slow growing microorganisms to establish but also contributes to membrane fouling. Further research aspects of MBR for textile wastewater treatment are also considered for sustainable operations of the process.

Recent developments in anaerobic membrane reactors

Anaerobic membrane reactors (AnMBRs) have recently evolved from aerobic MBRs, with the membrane either external or submerged within the reactor, and can achieve high COD removals (~98%) at hydraulic retention times (HRTs) as low as 3 h. Since membranes stop biomass being washed out, they can enhance performance with inhibitory substrates, at psychrophilic/thermophilic temperatures, and enable nitrogen removal via Anammox. Fouling is important, but addition of activated carbon or resins/precipitants can remove soluble microbial products (SMPs)/colloids and enhance flux. Due to their low energy use and solids production, and solids free effluent, they can enhance nutrient and water recycling. Nevertheless, more work is needed to: compare fouling between aerobic and anaerobic systems; determine how reactor operation influences fouling; evaluate the effect of different additives on membrane fouling; determine whether nitrogen removal can be incorporated into AnMBRs; recover methane solubility from low temperatures effluents; and, establish sound mass and energy balances.

Perspectives on anaerobic membrane bioreactor treatment of domestic wastewater: a critical review

Interest in increasing the sustainability of water management is leading to a reevaluation of domestic wastewater (DWW) treatment practices. A central goal is to reduce energy demands and environmental impacts while recovering resources. Anaerobic membrane bioreactors (AnMBRs) have the ability to produce a similar quality effluent to aerobic treatment, while generating useful energy and producing substantially less residuals. This review focuses on operational considerations that require further research to allow implementation of AnMBR DWW treatment. Specific topics include membrane fouling, the lower limits of hydraulic retention time and temperature allowing for adequate treatment, complications with methane recovery, and nutrient removal options. Based on the current literature, future research efforts should focus on increasing the likelihood of net energy recovery through advancements in fouling control and development of efficient methods for dissolved methane recovery. Furthermore, assessing the sustainability of AnMBR treatment requires establishment of a quantitative environmental and economic evaluation framework.