Pervaporation separation of butyric acid from aqueous and anaerobic digestion (AD) solutions using PEBA based composite membranes

Efficiently enhanced short-chain fatty acids (SCFAs) recovery from food waste condensate: Real-time wettability monitoring with supported liquid membrane contactor

Food waste condensate (FWC) is a valuable source for recovering short-chain fatty acids (SCFAs) through methods such as supported liquid membrane contactors. Containing organic compounds like acetate, propionate, and butyrate, FWC offers a rich substrate for efficient SCFA extraction. Recovering SCFAs from FWC provides notable environmental advantages, including reducing waste and generating high-value products for industries such as bioenergy and chemical production. This process not only contributes to carbon neutrality by recycling waste streams but also establishes a sustainable method for producing bio-based products from FWC. This study investigated the recovery efficiency and transport mechanisms of SCFAs from SCFA-rich wastewater (e.g., FWC) using both virgin hydrophobic PVDF membranes and membranes filled with organic extractants like tertiary amines (trihexhylamine and trioctylamine) and tertiary phosphines (trihexylphosphine and trioctylphosphine). Recovery efficiency for butyric acid was significantly improved when TOA (trioctylamine) was used, achieving 71.96 %, while acetic acid showed a lower recovery of 0.95 %, highlighting TOA's strong affinity for butyric acid due to ion-amine complex formation. The study also utilized real-time optical coherence tomography (OCT)-based monitoring to observe membrane wetting, finding that the virgin PVDF membrane was more prone to wetting and fouling, with a significant reduction in contact angle and surface energy. In contrast, the PVDF-TOA membrane demonstrated better resistance to wetting, showing minimal changes in contact angle and porosity, underscoring its potential for long-term applications in membrane contactors.

Fabrication of PEBA/HZIF-8 Pervaporation Membranes for High Efficiency Phenol Recovery

Phenol and its chemical derivatives serve as essential chemical materials are indispensable for the synthesis of many kinds of polymers. However, they are highly toxic, carcinogenic, difficult to be degraded biologically, and often found in aqueous effluents. Recovery of hazardous phenol from wastewater remains a daunting challenge. Herein, we prepared a hybrid membrane containing polyether block amide (PEBA) matrix and HZIF-8 fillers. To improve the compatibility between ZIF-8 and PEBA, ZIF-8 was modified by using polystyrene (PS) as a template to prepare porous HZIF-8. ZIF-8, composed of zinc nodes linked by the imidazole ring skeleton, is a kind of inorganic material with high hydrothermal stability, ordered pores, and hydrophobic microporous surfaces, which has a wide range of applications in membrane separation. The separation performance of the PEBA/HZIF-8 based membranes for phenol/water is improved due to the presence of PS on the surface of HZIF-8 and the imidazole ring skeleton in ZIF-8, which enhance the π-π interaction between HZIF-8 and phenol molecules. The effects of HZIF-8 content, feed phenol concentration, and feed temperature on the pervaporation performance of PEBA/HZIF-8 membranes were further investigated. The results showed that the pervaporation performance of the PEBA/HZIF-8-10 membrane was promising with a separation factor of 80.89 and permeate flux of 247.70 g/m²·h under the feed phenol concentration of 0.2 wt % at 80 °C. In addition, the PEBA/HZIF-8-10 membrane presented excellent stability, which has great prospect for practical application in phenol recovery from waste water.

Factors influencing pressure-driven membrane-assisted volatile fatty acids recovery and purification-A review

Volatile fatty acids (VFAs) are building block chemicals that can be produced through bioconversion of organic waste streams via anaerobic digestion as intermediate products. Purified VFAs are applicable in a wide range of industrial applications such as food, textiles, cosmetics, pharmaceuticals etc. production. The present review focuses on VFAs recovery methods and technologies such as adsorption, distillation, extraction, gas stripping, esterification and membrane based techniques etc., while presenting a discussion of their pros and cons. Moreover, a great attention has been given to the recovery of VFAs through membrane filtration as a promising sustainable clarification, fractionation and concentration approach. In this regard, a thorough overview of factors affecting membrane filtration performance for VFAs recovery has been presented. Filtration techniques such as nanofiltration and reverse osmosis have shown to be capable of recovering over 90% of VFAs content from organic effluent steams, proving the direct effect of membrane materials/surface chemistry, pore size and solution pH in recovery success level. Overall, this review presents a new insight into challenges and potentials of membrane filtration for VFAs recovery based on the effects of factors such as operational parameters, membrane properties and effluent characteristics.

Volatile Fatty Acid Production from Organic Waste with the Emphasis on Membrane-Based Recovery

In recent years, interest in the biorefinery concept has emerged in the utilization of volatile fatty acids (VFAs) produced by acidogenic fermentation as precursors for various biotechnological processes. This has attracted substantial attention to VFA production from low-cost substrates such as organic waste and membrane based VFA recovery techniques to achieve cost-effective and environmentally friendly processes. However, there are few reviews which emphasize the acidogenic fermentation of organic waste into VFAs, and VFA recovery. Therefore, this article comprehensively summarizes VFA production, the factors affecting VFA production, and VFA recovery strategies using membrane-based techniques. Additionally, the outlook for future research on VFA production is discussed.

Anaerobic digestion of organic waste: Recovery of value-added and inhibitory compounds from liquid fraction of digestate

Anaerobic digestion, as an eco-friendly waste treatment technology, is facing the problem of low stability and low product value. Harvesting value-added products beyond methane and removing the inhibitory compounds will unleash new vitality of anaerobic digestion, which need to be achieved by selective separation of certain compounds. Various methods are reviewed in this study for separating valuable products (volatile fatty acids, medium-chain carboxylic acids, lactic acid) and inhibitory substance (ammonia) from the liquid fraction of digestate, including their performance, applicability, corresponding limitations and roadmaps for improvement. In-situ extraction that allows simultaneous production and extraction is seen as promising approach which carries good potential to overcome the barriers for continuous production. The prospects and challenges of the future development are further analyzed based on in-situ extraction and economics.

Hydrophobic Two-Dimensional MoS2 Nanosheets Embedded in a Polyether Copolymer Block Amide (PEBA) Membrane for Recovering Pyridine from a Dilute Solution

A two-dimensional molybdenum disulfide (MoS₂) nanosheet, as a new type of inorganic material with high hydrophobicity and excellent physicochemical stability, holds great application potential in the preparation of a high separation performance organic-inorganic hybrid membrane. In this work, high hydrophobic MoS₂ was embedded in hydrophobic polyether copolymer block amide (PEBA) to prepare PEBA/MoS₂ organic-inorganic hybrid membranes. The structure, morphology, and hydrophobicity of the hybrid membrane were characterized by scanning electron microscopy, thermogravimetric analysis, contact angle goniometry, X-ray diffraction, infrared spectroscopy analysis, and atomic force microscopy. The effect of embedding of MoS₂ on the swelling degree and pervaporation separation performance of the PEBA/MoS₂ hybrid membrane was studied with a 1.0 wt % pyridine dilute solution. The results indicated that with increasing the MoS₂ content, the separation factor of PEBA/MoS₂ increased first and then decreased, while it showed a downward trend in the permeation flux. When the MoS₂ content in the PEBA/MoS₂ hybrid membrane was 10.0 wt %, the permeation flux was 83.4 g m^-2 h^-1 (decreased by 21.5% compared with the pure PEBA membrane), and the separation factor reached a maximum value of 11.11 (increased by 37.6% compared with the pure PEBA membrane). Meanwhile, the effects of feed temperature on the pervaporation separation performance of PEBA/MoS₂ hybrid membranes were also studied. In addition, as the PEBA/MoS₂ hybrid membrane has excellent thermal stability, it is expected to be a promising material for recovering pyridine from wastewater.

Microbial electrosynthesis: Towards sustainable biorefineries for production of green chemicals from CO2 emissions

Decarbonisation of the economy has become a priority at the global level, and the resulting legislative pressure is pushing the chemical and energy industries away from fossil fuels. Microbial electrosynthesis (MES) has emerged as a promising technology to promote this transition, which will further benefit from the decreasing cost of renewable energy. However, several technological challenges need to be addressed before the MES technology can reach its maturity. The aim of this review is to critically discuss the bottlenecks hampering the industrial adoption of MES, considering the whole production process (from the CO₂ source to the marketable products), and indicate future directions. A flexible stack design, with flat or tubular MES modules and direct CO₂ supply, is required for site-specific decentralised applications. The experience gained for scaling-up electrochemical cells (e.g. electrolysers) can serve as a guideline for realising pilot MES stacks to be technologically and economically evaluated in industrially relevant conditions. Maximising CO₂ abatement rate by targeting high-rate production of acetate can promote adoption of MES technology in the short term. However, the development of a replicable and robust strategy for production and in-line extraction of higher-value products (e.g. caproic acid and hexanol) at the cathode, and meaningful exploitation of the currently overlooked anodic reactions, can further boost MES cost-effectiveness. Furthermore, the use of energy storage and smart electronics can alleviate the fluctuations of renewable energy supply. Despite the unresolved challenges, the flexible MES technology can be applied to decarbonise flue gas from different sources, to upgrade industrial and wastewater treatment plants, and to produce a wide array of green and sustainable chemicals. The combination of these benefits can support the industrial adoption of MES over competing technologies.

Preparation and characterization of styrene-butadiene-styrene membrane incorporated with graphene nanosheets for pervaporative removal of 1,2,4-trimethylbenzene from water

In the present study, novel styrene-butadiene-styrene (SBS) membranes were prepared by the addition of graphene (Gr) nanosheets to the casting solution and were utilized in the pervaporative separation of a dilute solution of 1,2,4-trimethylbenzene (1,2,4-TMB) as a volatile organic compound (VOC) in water. Several characterizations such as field emission scanning electron microscopy (FESEM), X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), mechanical tensile test, and determination of water contact angle and swelling degree were conducted to investigate the properties of the prepared membranes. The results showed that with the addition of Gr the membrane thermal stability and hydrophobicity were increased while there was an optimum Gr loading to achieve the highest elastic modulus and tensile strength. Moreover, it was found that by increasing the Gr concentration up to 0.5 wt. %, the separation factor and pervaporation separation index (PSI) were increased by 250% and 43% compared to pure SBS membrane and reached 930 and 545 kg/m²h, respectively.

Selective Recovery of n-Butanol from Aqueous Solutions with Functionalized Poly(epoxide ionic liquid)-Based Polyurethane Membranes by Pervaporation

In this study, hydroxyl-terminated polybutadiene-poly(epoxide ionic liquid)-poly(urethane urea) (HTPB-PEIL-PU) membranes, HTPB-PEIL1-PU and HTPB-PEIL2-PU, were prepared by the reaction of functionalized PEIL, poly(1-methylimidazole-3-methyl-ethyloxy)hexafluorophosphate or poly(1-methylimidazole-3-methyl-ethyloxy)bistrifluoromethanesulfonimidate, respectively, with HTPB using 4,4'-diphenylmethane diisocyanate (MDI) as the chain extender. The HTPB-PEIL-PU and HTPB membranes were investigated for the selective recovery of n-butanol from aqueous solutions by pervaporation. PEIL was confirmed to be successfully embedded in the PU membranes by ¹H NMR, Fourier transform infrared, and differential scanning calorimetry measurements. According to our mechanical measurements, the HTPB-PEIL-PU membranes retain the mechanical properties of the original PU membrane. PEIL was shown to enhance the diffusion rate of n-butanol significantly based on swelling behavior tests. The pervaporation flux through the HTPB-PEIL1-PU membrane increased with increasing feed temperature and feed concentration. In contrast, the separation factor of the HTPB-PEIL1-PU membrane increased with increasing feed temperature but decreased with increasing feed concentration. In addition, the HTPB-PEIL2-PU membrane exhibited an optimal separation factor of up to 29.2 at a feed concentration of 3% and a feed temperature of 70 °C, which is superior to that (22.7) through pure HTPB membranes. Furthermore, the HTPB-PEIL1-PU and HTPB-PEIL2-PU membranes show better long-term stability than other supported ionic liquid membranes.

Performance of a biotrickling filter for the anaerobic utilization of gas-phase methanol coupled to thiosulphate reduction and resource recovery through volatile fatty acids production

The anaerobic removal of continuously fed gas-phase methanol (2.5-30 g/m³.h) and the reduction of step-fed thiosulphate (1000 mg/L) was investigated in a biotrickling filter (BTF) operated for 123 d at an empty bed residence time (EBRT) of 4.6 and 2.3 min. The BTF performance during steady step-feed and special operational phases like intermittent liquid trickling in 6 and 24 h cycles and operation without pH regulation were evaluated. Performance of the BTF was not affected and nearly 100% removal of gas-phase methanol was achieved with an EC_max of 21 g/m³.h. Besides, >99% thiosulphate reduction was achieved, in all the phases of operation. The production of sulphate, H₂S and volatile fatty acids (VFA) was monitored and a maximum of 2500 mg/L of acetate, 200 mg/L of propionate, 150 mg/L of isovalerate and 100 mg/L isobutyrate was produced.

Recovery of high-concentration volatile fatty acids from wastewater using an acidogenesis-electrodialysis integrated system

Recovery of volatile fatty acids (VFAs) from wastewater is an important route for wastewater valorization. Selective acidogenic fermentation enables an efficient production of VFAs from wastewater, whereas electrodialysis (ED) provides an effective approach to concentrate VFAs. However, these two processes have not been coupled in one single system previously. In this study, an acidogenesis-ED integrated system that coupled a continuous acidogenesis with a batch process of VFA concentration was developed for recovery of high-concentration VFAs from wastewater. Under 20.0 V voltage, the acetate was concentrated by 4-fold and the propionate and butyrate were concentrated by over 3-fold in the integrated system after 528-h operation. The declined VFAs recovery ratios at the later stage due to significant reverse diffusion indicate a need to prevent product over-accumulation. This work demonstrated the feasibility of the acidogenesis-ED integrated reactor for wastewater valorization and discussed the remaining challenges and opportunities.

Development and Characterization of New Pervaporation PVA Membranes for the Dehydration Using Bulk and Surface Modifications

In the present work, the novel dense and supported membranes based on polyvinyl alcohol (PVA) with improved transport properties were developed by bulk and surface modifications. Bulk modification included the blending of PVA with chitosan (CS) and the creation of a mixed-matrix membrane by introduction of fullerenol. This significantly altered the internal structure of PVA membrane, which led to an increase in permeability with high selectivity to water. Surface modification of the developed modified dense membranes, based on composites PVA-CS and PVA-fullerenol-CS, was performed through (i) making of a supported membrane with a thin selective composite layer and (ii) applying of the layer-by-layer assembly (LbL) method for coating of nano-sized polyelectrolyte (PEL) layers to increase the membrane productivity. The nature of polyelectrolyte type-(poly(allylamine hydrochloride) (PAH), poly(sodium 4-styrenesulfonate) (PSS), poly(acrylic acid) (PAA), CS), and number of PEL bilayers (2⁻10)-were studied. The structure of the composite membranes was investigated by FTIR, X-ray diffraction, and SEM. Transport properties were studied during the pervaporation separation of 80% isopropanol⁻20% water mixture. It was shown that supported membrane consisting of hybrid layer of PVA-fullerenol (5%)⁻chitosan (20%) with five polyelectrolyte bilayers (PSS, CS) deposited on it had the best transport properties.

Effects of nanofillers on the characteristics and performance of PEBA-based mixed matrix membranes

Mixed matrix membranes (MMMs) with superior structural and functional properties provide an interesting approach to enhance the separation properties of polymer membranes. As a matter of fact, MMMs combine the advantages of both components; polymeric continuous phase and nanoparticle dispersed phase. Generally, the separation performance of polymeric membranes suffers from an upper-performance limit. Hence, the incorporation of nanoparticles helps to overcome such limitations. Block copolymers such as poly(ether-block-amide) (PEBA) composed of immiscible soft ether segments as well as hard amide segments have been shown as excellent materials for the synthesis of membranes. Consequently, PEBA membranes have been extensively used in scientific research and industrial processes. It is thus aimed to provide an overview of PEBA MMMs. This review is especially devoted to summarizing the effects of nanoparticle loading on PEBA performance and properties such as selectivity, permeability, thermal and mechanical properties, and others. In addition, the preparation techniques of PEBA MMMs and solvent selection are discussed. This article also discusses the many types of nanoparticles incorporated into PEBA membranes. Furthermore, the future direction in PEBA MMMs research for separation processes is briefly predicted.

Recovery of mixed volatile fatty acids from anaerobically fermented organic wastes by vapor permeation membrane contactors

Volatile fatty acids (VFAs) are attractive compounds in renewable based bio-refinery industries and can be produced through anaerobic digestion of organic wastes. Nevertheless, the recovery of VFAs from anaerobically digested organic wastes is the bottleneck of the resource recovery. In this study, VFA recovery from synthetic VFA solutions and fermented organic wastes via air-filled and tertiary amine extractant-filled PTFE membranes through vapor pressure membrane contactors (VPMC) was investigated. Acetic acid was recovered with greater than 45% efficiency in all the fermented wastes. Recovery of propionic, butyric, valeric, and caproic acids through trioctylamine-filled PTFE membrane was greater than 86% and 95% from landfill leachate and fermentation broth of anaerobically digested organic waste, respectively. This study reveals that VFA separation can be effectively achieved via economic and environmental friendly VPMC system and the process is implementable as it can be coupled to a fermentation process to prevent inhibition and to recover VFAs.

Enhanced volatile fatty acids production from anaerobic fermentation of food waste: A mini-review focusing on acidogenic metabolic pathways

Recently, efficient disposal of food waste (FW) with potential resource recovery has attracted great attentions. Due to its easily biodegradable nature, rich nutrient availability and high moisture content, FW is regarded as favorable substrate for anaerobic digestion (AD). Both waste disposal and energy recovery can be fulfilled during AD of FW. Volatile fatty acids (VFAs) which are the products of the first-two stages of AD, are widely applied in chemical industry as platform chemicals recently. Concentration and distribution of VFAs is the result of acidogenic metabolic pathways, which can be affected by the micro-environment (e.g. pH) in the digester. Hence, the clear elucidation of the acidogenic metabolic pathways is essential for optimization of acidogenic process for efficient product recovery. This review summarizes major acidogenic metabolic pathways and regulating strategies for enhancing VFAs recovery during acidogenic fermentation of FW.

Effect of initial bulk density on high-solids anaerobic digestion of MSW: General mechanism

Initial bulk density (IBD) is an important variable in anaerobic digestion since it defines and optimizes the treatment capacity of a system. This study reveals the mechanism on how IBD might affect anaerobic digestion of waste. Four different IBD values: D₁ (500-700kgm^-3), D₂ (900-1000kgm^-3), D₃ (1100-1200kgm^-3) and D₄ (1200-1400kgm^-3) were set and tested over a period of 90days in simulated landfill reactors. The main variables affected by the IBD are the methane generation, saturation degree, extraction of organic matter, and the total population of methanogens. The study identified that IBD >1000kgm^-3 may have significant effect on methane generation, either prolonging the lag time or completely inhibiting the process. This study provides a new understanding of the anaerobic digestion process in saturated high-solids systems.

Biohydrogen production from used diapers: Evaluation of effect of temperature and substrate conditioning

This research assessed the viability to use disposable diapers as a substrate for the production of biohydrogen, a valuable clean-energy source. The important content of cellulose of disposable diapers indicates that this waste could be an attractive substrate for biofuel production. Two incubation temperatures (35 °C and 55 °C) and three diaper conditioning methods (whole diapers with faeces, urine, and plastics, WD; diapers without plastic components, with urine and faeces, DWP; diapers with urine but without faeces and plastic, MSD) were tested in batch bioreactors. The bioreactors were operated in the solid substrate anaerobic hydrogenogenic fermentation with intermittent venting mode (SSAHF-IV). The batch reactors were loaded with the substrate at ca. 25% of total solids and 10% w/w inoculum. The average cumulative bioH₂ production followed the order WD > MSD > DWP. The bio-H₂ production using MSD was unexpectedly higher than DWP; the presence of plastics in the first was expected to be associated to lower degradability and H2 yield. BioH₂ production at 55 °C was superior to that of 35 °C, probably owing to a more rapid microbial metabolism in the thermophilic regime. The results of this work showed low yields in the production of H₂ at both temperatures compared with those reported in the literature for municipal and agricultural organic waste. The studied process could improve the ability to dispose of this residue with H₂ generation as the value-added product. Research is ongoing to increase the yield of biohydrogen production from waste disposable diapers.

Waste biorefinery in arid/semi-arid regions

The utilization of waste biorefineries in arid/semi-arid regions is advisable due to the reduced sustainable resources in arid/semi-arid regions, e.g. fresh water and biomass. This review focuses on biomass residues available in arid/semi-arid regions, palm trees residues, seawater biomass based residues (coastal arid/semi-arid regions), and the organic fraction of municipal solid waste. The present review aims to describe and discuss the availability of these waste biomasses, their conversion to value chemicals by waste biorefinery processes. For the case of seawater biomass based residues it was reviewed and advise the use of seawater in the biorefinery processes, in order to decrease the use of fresh water.