Selective separation of nutrients and volatile fatty acids from food wastes using electrodialysis and membrane contactor for resource valorization.

Transport and selectivity parameters describe the quantity and purity of nutrients and volatile fatty acids (VFAs) separated from fermentation media. However, the complexity of fermentation media and low nutrient concentrations hinder the optimal conditions of such parameters. Exploring technologies to overcome such limitations is crucial for selectively separating VFAs from nutrients in fermented media. The objectives of this study were to investigate the: (1) flux, (2) recovery, (3) concentration factor, and (4) specific energy consumption of nutrients (NH4+, K+, NO3-, and PO43-) and VFAs (acetic, propionic, and butyric acid) via electrodialysis (ED), and (5) selectively separate the VFAs from the nutrients in the ED concentrate using a hydrophobic membrane contactor (HMC). Synthetic feed and real industrial fermented food wastes were used for ED and HMC experiments. The ED consumed 0.395 kWh/kg, recovering 64-95% of the nutrients and VFAs, corresponding to 4.1-9.4 and 0.6-22.1 g/L nutrients and VFAs, respectively. The HMC selectively separated over 94% of VFAs after ED, with <2% nutrients contamination in the final VFA stream. The results suggest that applying HMC after ED can concentrate and selectively separate VFAs from nutrients in fermented food wastes, which can be valorized for bio-based fertilizers and chemical platforms.

Removal of reactive violet 5 azodye (V5R) using bamboo, and calabash biochar.

We assess the adsorption capacity of bamboo and calabash biochar (BB and CB). Using 10-50 mg/L Reactive Violet 5 Azo dye (V5R) adsorbate, the kinetics, and adsorption isotherms are investigated. We pyrolyzed the bamboo, and calabash biomass at 500 °C, washed, and oven dried at 120 °C for 48 h. The Brunauer-Emmett-Teller (BET) method indicates that the BB and CB average pore diameters are 21.1 nm and 26.5 nm, with specific surface areas of 174.67 m2/g and 44.78 m2/g, respectively. The SEM reveals a larger granular shape of the CB having pinholes on the surface, but the BB exhibited interconnected structures like a mesh. The FTIR shows C=C, C=O, O-H, and C-O-C as the predominant functional groups on both BB and CB. The adsorption of V5R on BB and CB follows pseudo-second-order kinetics and favors Langmuir isotherm with maximum adsorption capacities of 5.106 mg/g, and 0.010 mg/g, respectively. The BB adsorbs 70.9-96% V5R, whilst CB adsorbs 0.1-0.2 % only. The results suggest that bamboo biochar has the potential to eliminate 70.9-96% of 10-50 mg/L V5R from an aqueous solution, hence suitable for removing V5R. In this study, we have also presented a prototype expected to eliminate 91.6%-99.8% of the V5R from an aqueous solution.

Surface Modifications of Anion Exchange Membranes for an Improved Reverse Electrodialysis Process Performance: A Review.

Reverse electrodialysis (RED) technology represents a promising electro-membrane process for renewable energy harvesting from aqueous streams with different salinity. However, the performance of the key components of the system, that is, the ion exchange membranes, is limited by both the presence of multivalent ions and fouling phenomena, thus leading to a reduced generated net power density. In this context, the behavior of anion exchange membranes (AEMs) in RED systems is more severely affected, due to the undesirable interactions between their positively charged fixed groups and, mostly negatively charged, foulant materials present in natural streams. Therefore, controlling both the monovalent anion permselectivity and the membrane surface hydrophilicity is crucial. In this respect, different surface modification procedures were considered in the literature, to enhance the above-mentioned properties. This review reports and discusses the currently available approaches for surface modifications of AEMs, such as graft polymerization, dip coating, and layer-by-layer, among others, mainly focusing on preparing monovalent permselective AEMs with antifouling characteristics, but also considering hydrophilicity aspects and identifying the most promising modifying agents to be utilized. Thus, the present study aimed at providing new insights for the further design and development of selective, durable, and cost-effective modified AEMs for an enhanced RED process performance, which is indispensable for a practical implementation of this electro-membrane technology at an industrial scale.

Characterization of Poly(Acrylic) Acid-Modified Heterogenous Anion Exchange Membranes with Improved Monovalent Permselectivity for RED.

The performance of anion-exchange membranes (AEMs) in Reverse Electrodialysis is hampered by both presence of multivalent ions and fouling phenomena, thus leading to reduced net power density. Therefore, we propose a monolayer surface modification procedure to functionalize Ralex-AEMs with poly(acrylic) acid (PAA) in order to (i) render a monovalent permselectivity, and (ii) minimize organic fouling. Membrane surface modification was carried out by putting heterogeneous AEMs in contact with a PAA-based aqueous solution for 24 h. The resulting modified membranes were firstly characterized by contact angle, water uptake, ion exchange capacity, fixed charge density, and swelling degree measurements, whereas their electrochemical responses were evaluated through cyclic voltammetry. Besides, their membrane electro-resistance was also studied via electrochemical impedance spectroscopy analyses. Finally, membrane permselectivity and fouling behavior in the presence of humic acid were evaluated through mass transport experiments using model NaCl containing solutions. The use of modified PAA-AEMs resulted in a significantly enhanced monovalent permselectivity (sulfate rejection improved by >35%) and membrane hydrophilicity (contact angle decreased by >15%) in comparison with the behavior of unmodified Ralex-AEMs, without compromising the membrane electro-resistance after modification, thus demonstrating the technical feasibility of the proposed membrane modification procedure. This study may therefore provide a feasible way for achieving an improved Reverse Electrodialysis process efficiency.

Assessment and remediation of pollutants in Ghana's Kete-Krachi District Hospital effluents using granular and smooth activated carbon.

The need for simple, cheaper and high performance hospital effluent treatment system in Kete-Krachi District which is adjacent to the Lake Volta has necessitated this study. This study focuses on assessing, and treating Kete-Krachi District Hospital effluent using packed granular (GAC) and smooth activated carbon (SAC). The use of activated carbon is due to its less expensive method of operation, the ease to prepare from local raw materials, high availability, and effectiveness for treating hospital effluent. The dissolved oxygen (DO), chemical oxygen demand (COD), biochemical oxygen demand (BOD), nutrient compounds (P-PO4, N-NO3), turbidity, pH, conductivity and total coliform parameters were investigated and later treated with the activated carbon. The average conductivity and P-PO4 removals were <50%. The average BOD5, COD, coliform, N-NO3, and turbidity removals for all the SAC treatments were 58.36%, 62.26%, 84.39%, 83.86%, and 50.74%, respectively. The DO also improved 3.8 times on the average. The pH of the raw and treated samples was within the limit 6.5-9. The results of this study suggest that the SAC is predominantly effective for reducing the pollutants concentrations of the hospital effluent which can result in oxygen depletion, eutrophication, algal bloom and ecosystem disturbance in the Lake Volta. It will also decrease the susceptibility of the Kete-Krachi residents to waterborne diseases as the effluents seep into the Lake.