Immersed membrane bioreactors: an overview with special emphasis on anaerobic bioprocesses

Understanding the management of household food waste and its engineering for sustainable valorization- A state-of-the-art review

Increased urbanization and industrialization accelerated demand for energy, large-scale waste output, and negative environmental consequences. Therefore, the implementation of an effective solid-waste-management (SWM) policy for the handling of food waste is of great importance. The global food waste generation is estimated at about 1.6 gigatons/yr which attributes to an economic revenue of 750 billion USD. It can be converted into high-value enzymes, surfactants, Poly-hydroxybutyrate, biofuels, etc. However, the heterogeneous composition of food with high organic load and varying moisture content makes their transformation into value-added products difficult. This review aims to bring forth the possibilities and repercussions of food waste management. The socio-economic challenges related to SWM are comprehensively discussed particularly in terms of environmental concern. The engineering aspect in the collection, storage, and biotransformation of food waste into useful value-added products such as biofuels, advanced biomaterials, bioactive compounds, and platform chemicals are critically reviewed for efficient food waste management.

Intensification of lignocellulosic bioethanol production process using continuous double-staged immersed membrane bioreactors

Processing complexities associated with different lignocellulosic bioethanol production stages have hindered reaching full commercial capacity. Therefore, in this study efforts were made to remediate some issues associated with hydrolysis and fermentation, by the integration of immersed membrane bioreactors (iMBRs) into lignocellulosic bioethanol production process. In this regards, double-staged continuous saccharification-filtration and co-fermentation-filtration of wheat straw slurry was conducted using iMBRs at filtration fluxes up to 51.0 l.m^-2.h^-1 (LMH). The results showed a stable long-term (264 h) continuous hydrolysis-filtration and fermentation-filtration with effective separation of lignin-rich solids (up to 70% lignin) from hydrolyzed sugars, and separation of yeast cells from bioethanol stream at an exceptional filtration performance at 21.9 LMH. Moreover, the effect of factors such as filtration flux, medium quality and backwashing on fouling and cake-layer formation was studied. The results confirmed the process intensification potentials of iMBRs in tackling commonly faced technical obstacles in lignocellulosic bioethanol production.

Biohydrogen production from glucose using submerged dynamic filtration module: Metabolic product distribution and flux-based analysis

A lab scale bioreactor with the submerged polyester mesh of pore size 100 μm, was used for biohydrogen production under mesophilic condition (35 °C). The reactor was continuously fed with glucose (15 g/L) for 90 days with a hydraulic retention time (HRT), ranging from 12 to 1.5 h. Peak hydrogen yield (HY) was achieved at 3 h HRT as 3.22 ± 0.22 mol H₂/mol glucose _added and the hydrogen production rate was achieved at 2 h HRT as 54.07 ± 3.69 L H₂/L-d, respectively. When HRT was reduced to 1.5 h, the hydrogen yield decreased to 1.04 ± 0.44 mol H₂/mol glucose _added. Washout of the hydrogen producing population and metabolic flux shift to non-hydrogen producing at 1.5 h HRT might have attributed to the lower performance of the bioreactor.

Anaerobic membrane bioreactors for wastewater treatment: Novel configurations, fouling control and energy considerations

Water shortage, public health and environmental protection are key motives to treat wastewater. The widespread adoption of wastewater as a resource depends upon development of an energy-efficient technology. Anaerobic membrane bioreactor (AnMBR) technology has gained increasing popularity due to their ability to offset the disadvantages of conventional treatment technologies. However there are several hurdles, yet to climb over, for wider spread and scale-up of the technology. This paper reviews fundamental aspects of anaerobic digestion of wastewater, and identifies the challenges and opportunities to the further development of AnMBRs. Membrane fouling and its implications are discussed, and strategies to control membrane fouling are proposed. Novel AnMBR configurations are discussed as an integrated approach to overcome technology limitations. Energy demand and recovery in AnMBRs is analyzed. Finally key issues that require urgent attention to facilitate global penetration of AnMBR technology are highlighted.

Food waste-derived volatile fatty acids platform using an immersed membrane bioreactor

Volatile fatty acids (VFAs) are the key intermediates from anaerobic digestion (AD) process that can be a platform to synthesize products of higher value than biogas. However, some obstacles still exist that prevent large-scale production and application of VFAs, key among them being the difficulty in recovering the acids from the fermentation medium and low product yields. In this study, a novel anaerobic immersed membrane bioreactor (iMBR) with robust cleaning capabilities, which incorporated frequent backwashing to withstand the complex AD medium, was designed and applied for production and in situ recovery of VFAs. The iMBR was fed with food waste and operated without pH control, achieving a high yield of 0.54 g VFA/g VS_added. The continuous VFA recovery process in the iMBR was investigated for 40 days at OLRs of 2 gVS/L/d and 4 gVS/L/d without significant change in the permeate flux at a maximum suspended solids concentration of 31 g/L.

Anaerobic membrane bioreactors for biohydrogen production: Recent developments, challenges and perspectives

Biohydrogen as one of the most appealing energy vector for the future represents attractive avenue in alternative energy research. Recently, variety of biohydrogen production pathways has been suggested to improve the key features of the process. Nevertheless, researches are still needed to overcome remaining barriers to practical applications such as low yields and production rates. Considering practicality aspects, this review emphasized on anaerobic membrane bioreactors (AnMBRs) for biological hydrogen production. Recent advances and emerging issues associated with biohydrogen generation in AnMBR technology are critically discussed. Several techniques are highlighted that are aimed at overcoming these barriers. Moreover, environmental and economical potentials along with future research perspectives are addressed to drive biohydrogen technology towards practicality and economical-feasibility.

Hydrogen production by dark fermentation from pre-fermented depackaging food wastes

In this study, a specific fraction of food waste, i.e. depackaging waste, was studied as substrate for hydrogen production by dark fermentation. During storage and transport of this liquid mixture, inhibitory compounds like acids or alcohol might be produced by endogenous flora. A factorial fractional design based on the composition of the substrate was used to determine the best condition to convert this substrate into hydrogen. First results indicated that the consortium used might convert high quantity of lactate into hydrogen. A batch culture confirmed that lactate was used as the main carbon source and a global yield of 0.4mol_H2·mol_lactate^-1 was obtained. This study demonstrated the ability of the consortium tested to convert different carbon sources (carbohydrates or lactate) with good efficiency. These data represented an important parameter in the prospect of using an industrial substrate whose composition is liable to vary according to the conditions of storage and transport.

Continuous bioethanol fermentation from wheat straw hydrolysate with high suspended solid content using an immersed flat sheet membrane bioreactor

Finding a technological approach that eases the production of lignocellulosic bioethanol has long been considered as a great industrial challenge. In the current study a membrane bioreactor (MBR) set-up using integrated permeate channel (IPC) membrane panels was used to simultaneously ferment pentose and hexose sugars to ethanol in continuous fermentation of high suspended solid wheat straw hydrolysate. The MBR was optimized to flawlessly operated at high SS concentrations of up to 20% without any significant changes in the permeate flux and transmembrane pressure. By the help of the retained high cell concentration, the yeast cells were capable of tolerating and detoxifying the inhibitory medium and succeeded to co-consume all glucose and up to 83% of xylose in a continuous fermentation mode leading to up to 83% of the theoretical ethanol yield.

Effect of co-substrates on biogas production and anaerobic decomposition of pentachlorophenol

This study aims to examine the effect of different co-substrates on the anaerobic degradation of pentachlorophenol (PCP) with simultaneous production of biogas. Acetate and glucose were added as co-substrates to monitor and compare the methanogenic reaction during PCP degradation. During the experiment, a chemical oxygen demand (COD) removal efficiency of 80% was achieved. Methane (CH₄) production was higher in glucose-fed anaerobic reactors with the highest amount of CH₄ (303.3µL) produced at 200ppm of PCP. Scanning electron microscopy (SEM) demonstrates the high porous structure of anaerobic sludge with uniform channels confirming better mass transfer and high PCP removal. Quantitative real-time PCR (qPCR) revealed that methanogens were the dominating species while some sulfate reducing bacteria (SRBs) were also found in the reactors. The study shows that strategic operation of the anaerobic reactor can be a feasible option for efficient degradation of complex substrates like PCP along with the production of biogas.

Increased biohydrogen yields, volatile fatty acid production and substrate utilisation rates via the electrodialysis of a continually fed sucrose fermenter

Electrodialysis (ED) removed volatile fatty acids (VFAs) from a continually-fed, hydrogen-producing fermenter. Simultaneously, electrochemical removal and adsorption removed gaseous H₂ and CO₂, respectively. Removing VFAs via ED in this novel process increased H₂ yields by a factor of 3.75 from 0.24molH₂mol^-1_hexose to 0.90molH₂mol^-1_hexose. VFA production and substrate utilisation rates were consistent with the hypothesis that end product inhibition arrests H₂ production. The methodology facilitated the recovery of 37g of VFAs, and 30L H₂ that was more than 99% pure, both of which are valuable, energy dense chemicals. Typically, short hydraulic and solid retention times, and depressed pH levels are used to suppress methanogenesis, but this limits H₂ production. To produce H₂ from real world, low grade biomass containing complex carbohydrates, longer hydraulic retention times (HRTs) are required. The proposed system increased H₂ yields via increased substrate utilisation over longer HRTs.

Development of a submerged anaerobic membrane bioreactor for concurrent extraction of volatile fatty acids and biohydrogen production

The aim of this work was to study an externally-submerged membrane bioreactor for the cyclic extraction of volatile fatty acids (VFAs) during anaerobic fermentation, combining the advantages of submerged and external technologies for enhancing biohydrogen (BioH2) production from agrowaste. Mixing and transmembrane pressure (TMP) across a hollow fiber membrane placed in a recirculation loop coupled to a stirred tank were investigated, so that the loop did not significantly modify the hydrodynamic properties in the tank. The fouling mechanism, due to cake layer formation, was reversible. A cleaning procedure based on gas scouring and backwashing with the substrate was defined. Low TMP, 10(4)Pa, was required to achieve a 3Lh(-1)m(-2) critical flux. During fermentation, BioH2 production was shown to restart after removing VFAs with the permeate, so as to enhance simultaneously BioH2 production and the recovery of VFAs as platform molecules.

Enhanced Fermentative Hydrogen and Methane Production from an Inhibitory Fruit-Flavored Medium with Membrane-Encapsulated Cells

This study focused on the possibility of improving fermentative hydrogen and methane production from an inhibitory fruit-flavored medium using polyvinylidene fluoride (PVDF) membrane-encapsulated cells. Hexanal, myrcene, and octanol, which are naturally produced in fruits such as apple, grape, mango, orange, strawberry, and plum, were investigated. Batch and semi-continuous fermentation processes at 55 °C were carried out. Presence of 5 g/L of myrcene, octanol, and hexanal resulted in no methane formation by fermenting bacteria, while encapsulated cells in the membranes resulted in successful fermentation with 182, 111, and 150 mL/g COD of methane, respectively. The flavor inhibitions were not serious on hydrogen-producing bacteria. With free cells in the presence of 5 g/L (final concentration) of hexanal-, myrcene-, and octanol-flavored media, average daily yields of 68, 133, and 88 mL/g COD of hydrogen, respectively, were obtained. However, cell encapsulation further improved these hydrogen yields to 189, 179, and 198 mL/g COD. The results from this study indicate that the yields of fermentative hydrogen and methane productions from an inhibitory medium could be improved using encapsulated cells.

Removal and recovery of inhibitory volatile fatty acids from mixed acid fermentations by conventional electrodialysis

Hydrogen production during dark fermentation is inhibited by the co-production of volatile fatty acids (VFAs) such as acetic and n-butyric acid. In this study, the effectiveness of conventional electrodialysis (CED) in reducing VFA concentrations in model solutions and hydrogen fermentation broths is evaluated. This is the first time CED has been reported to remove VFAs from hydrogen fermentation broths. During 60 min of operation CED removed up to 99% of VFAs from model solutions, sucrose-fed and grass-fed hydrogen fermentation broths, containing up to 1200 mg l(-1) each of acetic acid, propionic acid, i-butyric acid, n-butyric acid, i-valeric acid, and n-valeric acid. CED's ability to remove VFAs from hydrogen fermentation broths suggests that this technology is capable of improving hydrogen yields from dark fermentation.

Instrumentation, control, and automation for submerged anaerobic membrane bioreactors

A submerged anaerobic membrane bioreactor (AnMBR) demonstration plant with two commercial hollow-fibre ultrafiltration systems (PURON®, Koch Membrane Systems, PUR-PSH31) was designed and operated for urban wastewater treatment. An instrumentation, control, and automation (ICA) system was designed and implemented for proper process performance. Several single-input-single-output (SISO) feedback control loops based on conventional on-off and PID algorithms were implemented to control the following operating variables: flow-rates (influent, permeate, sludge recycling and wasting, and recycled biogas through both reactor and membrane tanks), sludge wasting volume, temperature, transmembrane pressure, and gas sparging. The proposed ICA for AnMBRs for urban wastewater treatment enables the optimization of this new technology to be achieved with a high level of process robustness towards disturbances.

Fermentative hydrogen production in anaerobic membrane bioreactors: A review

Reactor design considerations are crucial aspects of dark fermentative hydrogen production. During the last decades, many types of reactors have been developed and used in order to drive biohydrogen technology towards practicality and economical-feasibility. In general, the ultimate aim is to improve the key features of the process, namely the H2 yields and generation rates. Among the various configurations, the traditional, completely stirred tank reactors (CSTRs) are still the most routinely employed ones. However, due to their limitations, there is a progress to develop more reliable alternatives. One of the research directions points to systems combining membranes, which are called as anaerobic membrane bioreactors (AnMBRs). The aim of this paper is to summarize and highlight the recent biohydrogen related work done on AnMBRs and moreover to evaluate their performances and potentials in comparison with their conventional CSTR counterparts.

Synergistic effects of pretreatment and blending on fungi mediated biodegradation of polypropylenes

Environmental issues raise concern on restrict the use of nondegradable polymers and encourage the development of degradable once. This study is carried out was to understand the rate of biodegradation of untreated and pretreated (100°C or UV for 10 days) polypropylene (PP), pro-oxidant blended (MI-PP) and starch blended polypropylenes (ST-PP) with two different fungal strains, Phanerochaete chrysosporium NCIM 1170 (F1) and Engyodontium album MTP091 (F2). About 18.8% and 9.42% gravimetric weight loss and 79% and 57% TGA weight loss (at 400°C) were observed with UV pretreated MI-PP in 1 year with F2 and F1 strains respectively. The amount of lacasse produced by the organism and biomass attached on the polymer surface are correlated with TGA weight loss (0.6-0.93). The formation of extractable oxygenated compounds and unoxidized low-molecular weight hydrocarbons are high in pretreated and blended samples. These results indicate blending and pretreatment strategy leads to an optimal waste-disposal strategy.

Biological upgrading of volatile fatty acids, key intermediates for the valorization of biowaste through dark anaerobic fermentation

VFAs can be obtained from lignocellulosic agro-industrial wastes, sludge, and various biodegradable organic wastes as key intermediates through dark fermentation processes and synthesized through chemical route also. They are building blocks of several organic compounds viz. alcohol, aldehyde, ketones, esters and olefins. These can serve as alternate carbon source for microbial biolipid, biohydrogen, microbial fuel cells productions, methanisation, and for denitrification. Organic wastes are the substrate for VFA platform that is of zero or even negative cost, giving VFA as intermediate product but their separation from the fermentation broth is still a challenge; however, several separation technologies have been developed, membrane separation being the most suitable one. These aspects will be reviewed and results obtained during anaerobic treatment of slaughterhouse wastes with further utilisation of volatile fatty acids for yeast cultivation have been discussed.

Low-temperature anaerobic treatment of low-strength pentachlorophenol-bearing wastewater

The anaerobic treatment of low-strength wastewater bearing pentachlorophenol (PCP) at psychro-mesophilic temperatures has been investigated in an expanded granular sludge bed reactor. Using an upward flow rate of 4 m h(-1), a complete removal of PCP, as well as COD removal and methanization efficiencies higher than 75% and 50%, respectively, were achieved. Methanogenesis and COD consumption were slightly affected by changes in loading rate, temperature (17-28°C) and inlet concentrations of urea and oils. Pentachlorophenol caused an irreversible inhibitory effect over both acetoclastic and hydrogenotrophic methanogens, being the later more resistant to the toxic effect of pentachlorophenol. An auto-inhibition phenomenon was observed at PCP concentrations higher than 10 mg L(-1), which was accurately predicted by a Haldane-like model. The inhibitory effect of PCP over the COD consumption and methane production was modelled by modified pseudo-Monod and Roediger models, respectively.

A practitioner's perspective on the application and research needs of membrane bioreactors for municipal wastewater treatment

The application of membrane bioreactors (MBRs) for municipal wastewater treatment has increased dramatically over the last decade. From a practitioner's perspective, design practice has evolved over five "generations" in the areas of biological process optimization, separating process design from equipment supply, and reliability/redundancy thereby facilitating "large" MBRs (e.g. 150,000 m(3)/day). MBR advantages and disadvantages, and process design to accommodate biological nutrient removal, high mixed liquor suspended solids concentrations, operation and maintenance, peak flows, and procurement are reviewed from the design practitioner's perspective. Finally, four knowledge areas are identified as important to practitioners meriting further research and development: (i) membrane design and performance such as improving peak flow characteristics and decreasing operating costs; (ii) process design and performance such as managing the fluid properties of the biological solids, disinfection, and microcontaminant removal; (iii) facility design such as equipment standardization and decreasing mechanical complexity; and (iv) sustainability such as anaerobic MBRs.