Animal manure is often anaerobically digested for the purpose of producing biogas. The digested manure, namely digestate, can be applied onto farmlands to enhance crop yields as it is abundant in nutrients. However, intensive livestock farming brings about manure exceeding the carrying capacity of lands nearby. Technologies focused on nutrient recovery from digestate have been studied recently, while many problems and challenges still remain unsolved. In this article, these recovery technologies are reviewed and compared, and challenges are deliberated. Ammonia stripping and struvite formation are easily operated technologies in comparison with membrane technologies. Amongst membrane technologies, electrodialysis reversal and forward osmosis are promising due to their high resistance to membrane fouling. Further studies should be focused on the operational cost, disposal of solid and liquid residuals and marketization of the recovered products.

PURPOSE OF REVIEW: Membrane techniques have been employed to concentrate livestock manure effluent from anaerobic digestion to produce highly concentrated liquid organic fertilizer. This review aims to provide a comprehensive understanding on the opportunities and challenges of membrane processes in the concentration of digested effluent for their further implementation. RECENT FINDINGS: Anaerobic digestion has been deployed to convert livestock manure into biogas (energy) and digestate with high potential as biofertilizer. Digestate can be separated into a solid and liquid fraction to reduce required capacity for onsite storage. The liquid fraction, known as digested effluent, remains a vexing challenge to digestate management due to the contradiction between its continuous production and seasonal application to farmlands, particularly in developing countries. Recent investigation has demonstrated the promise of membrane techniques for the concentration of digested effluent to recover recycling water and produce nutrient-rich liquid fertilizer. These techniques mainly include hydraulically driven membrane processes (from microfiltration to reverse osmosis), forward osmosis, membrane distillation, and electrodialysis. In most cases, these membrane techniques are hybridized to enhance the concentration efficiency. Nevertheless, the practical application of these membrane processes is hindered by several technical challenges, which mainly include membrane fouling, contaminant enrichment, ammonia volatilization, and high economic input. In this paper, we critically reviewed the performance of different membrane processes in the concentration of digested livestock manure effluent. Key technical challenges and their potential countermeasures were elucidated. Furthermore, future perspectives were provided to shed light on further development of membrane concentration techniques in the field.

Seawater and brackish water desalination has been a practical approach to mitigating the global fresh water scarcity. Current large-scale desalination installations worldwide can complementarily augment the global fresh water supplies, and their capacities are steadily increasing year-on-year. Despite substantial technological advance, desalination processes are deemed energy-intensive and considerable sources of CO₂ emission, leading to the urgent need for innovative low carbon desalination platforms. This paper provides a comprehensive review on innovations in membrane processes and membrane materials for low carbon desalination. In this paper, working principles, intrinsic attributes, technical challenges, and recent advances in membrane materials of the membrane-based desalination processes, exclusively including commercialised reverse osmosis (RO) and emerging forward osmosis (FO), membrane distillation (MD), electrodialysis (ED), and capacitive deionisation (CDI), are thoroughly analysed to shed light on the prospect of low carbon desalination.

Osmotic membrane bioreactor (OMBR), which integrates forward osmosis (FO) with biological treatment process, has been recently developed to advance wastewater treatment and reuse. During OMBR operation, driven by osmotic pressure gradient, biologically treated water transports from the mixed liquor, through a semi-permeable FO membrane, into a highly concentrated draw solution. Compared to conventional MBR, OMBR has several advantages, including better product water quality, lower fouling propensity, and higher fouling reversibility. OMBR can be operated in the osmotic dilution mode when the draw solution, such as liquid fertilizers or seawater, can be reused or discharged directly. In most cases, OMBR is integrated with an additional process, commonly including reverse osmosis, membrane distillation, and electrodialysis, to form hybrid systems for sustainably reconcentrating draw solutions and producing clean water for reuse. In addition, several membrane processes, such as microfiltration, ultrafiltration, and electrodialysis, are combined with OMBR to address its inherent issue, salinity build-up in the bioreactor, and achieve resource (e.g., nutrients and energy) recovery. This review aims to provide a comprehensive understanding on the performance of OMBR and its hybrid systems in wastewater reuse and resource recovery. OMBR analogs and their performance are also systematically introduced. Key technical challenges and their potential solutions to the further development of OMBR and its hybrid systems are highlighted. This review sheds light on future research for the further development of OMBR and its hybrid systems.

As water scarcity has become a serious global issue, seawater reverse osmosis (SWRO) is considered as a promising technique to expand traditional water supplies. However, the reject brine from SWRO systems is still a major environmental concern. In this research, the monovalent selective electrodialysis (S-ED) was used to separate and recover one of the primary components, i.e., sodium chloride, from the SWRO brine, thereby avoiding the direct discharge of the brine and achieving the brine valorization. The permselectivity of selective ion-exchange membranes (IEMs) was elucidated by comparing with the standard IEMs in structure-property via membrane characterization techniques. Results indicated that the permselectivity of Selemion CSO membrane was attributed to the positive-charged layer with a low sulfonate/ammonium ratio of 1.28. Whereas the permselectivity of Selemion ASV membrane resulted from the highly cross-linked layer, according to the similar content of the fixed quaternary amines and the shift of the C‑N absorption peak. In addition, the effects of the current density and temperature on the membrane performance were studied, including permselectivity ([Formula: see text] and [Formula: see text]), Na⁺ recovery, and specific energy consumption (ESEC). Finally, the NaCl-rich brine with the total dissolved solid (TDS) value of 167.5 ± 3.3 g/L was obtained using SWRO brine with the initial TDS of 76.8 g/L. The Na⁺/Mg²⁺ mass ratio of the concentrate was 222.4, compared with the initial value of 9.7 in SWRO brine.

Membrane technology is an outstanding alternative for treating complex textile wastewaters. However, difficulties in the management of the resultant concentrate are the main disadvantage of these membrane technologies. This study is focused on the development of integrative management for membrane concentrate of textile effluent under the principle of discharge regulations that aim to achieve zero-liquid discharge (ZLD). Thus, biologically treated textile wastewater (BTTW) is fed to nanofiltration (NF) and reverse osmosis (RO) membranes with ultrafiltration (UF) pre-treatment, separately. NF concentrates (NFC) and RO concentrates (ROC) are further treated with electrocoagulation (EC) and electro-Fenton (EF) to remove COD and color. After the EC and EF steps, the electrodialysis (ED) method is used for ion removal. Operational costs of each process are calculated. Through the NF of BTTW > 65% COD and 92% color removals were achieved, whereas with the RO process, > 65% COD and 98% color removals were obtained. For NFC, > 80% COD and 91% color removal efficiencies were achieved with EC + ED processes and 57% COD and almost total color removal was achieved with EF + ED processes. For ROC, 71% COD and 85% color removals were obtained with EC + ED processes and 85% COD and 98% color removal was observed with EF + ED processes. Additionally, efficient treatment and concentrate management options were investigated for textile effluent.

An attempt has been made to improve the treatment efficiency of mature landfill leachate prior to the existing biological treatment. In this study, electrochemical oxidation (EO) was applied as a pre-treatment to remove organic contaminants and was simultaneously combined with electrodialysis (ED) to remove ionic constituents, such as ammonium and phosphate. A laboratory-scale electrochemical reactor was designed by utilizing a carbon graphite anode and a stainless steel cathode and separated by an anion exchange membrane (AEM) and cation exchange membrane (CEM), creating a three-compartment reactor. The oxidation of the organic pollutant would occur in the anodic compartment, while the targeted ammonium and phosphate ions would be migrated and accumulated in the central compartment. The treatment process was performed in a batch recirculation time of 12 h at a constant supplied current of 0.25 A and evaluated by means of the initial leachate pH (i.e., original pH value of 7.85; adjusted pH value of 5.50 and 8.50) and three different initial chloride concentrations. The higher the chloride concentration in the leachate, the higher the removal efficiency, except for total phosphate. The highest chemical oxidation demand (COD) removal was 86.2% (0.88 g W⁻¹ h⁻¹), at an initial leachate pH value of 7.85 with the addition of 2 g L⁻¹ of NaCl. Furthermore, under the same conditions, the ammonium, total phosphate, and chloride removals were 85% (0.44 g W⁻¹ h⁻¹), 89% (0.08 g W⁻¹ h⁻¹), and 83% (0.69 g W⁻¹ h⁻¹), respectively. Also, the concentrated ionic compounds in the central compartment can lower the energy consumption and can possibly be further treated or managed.

Three multiple input and multiple output-type fuzzy-logic-based models were developed as an artificial intelligence-based approach to model a novel integrated process (UF–IER–EDBM–FO) consisted of ultrafiltration (UF), ion exchange resins (IER), electrodialysis with bipolar membrane (EDBM), and Fenton’s oxidation (FO) units treating young, middle-aged, and stabilized landfill leachates. The FO unit was considered as the key process for implementation of the proposed modeling scheme. Four input components such as H₂O₂/chemical oxygen demand ratio, H₂O₂/Fe²⁺ ratio, reaction pH, and reaction time were fuzzified in a Mamdani-type fuzzy inference system to predict the removal efficiencies of chemical oxygen demand, total organic carbon, color, and ammonia nitrogen. A total of 200 rules in the IF–THEN format were established within the framework of a graphical user interface for each fuzzy-logic model. The product (prod) and the center of gravity (centroid) methods were performed as the inference operator and defuzzification methods, respectively, for the proposed prognostic models. Fuzzy-logic predicted results were compared to the outputs of multiple regression models by means of various descriptive statistical indicators, and the proposed methodology was tested against the experimental data. The testing results clearly revealed that the proposed prognostic models showed a superior predictive performance with very high determination coefficients (R ²) between 0.930 and 0.991. This study indicated a simple means of modeling and potential of a knowledge-based approach for capturing complicated inter-relationships in a highly non-linear problem. Clearly, it was shown that the proposed prognostic models provided a well-suited and cost-effective method to predict removal efficiencies of wastewater parameters prior to discharge to receiving streams.

The shortage of drinking water is a major problem in the rural areas of the Mekong Delta, especially, when surface water, a main local direct drinking water source is being threatened by pesticide pollution and salinity intrusion. A hybrid process coupling electrodialysis (ED) and nanofiltration (NF) is proposed as an effective process easy to setup in a small plant to treat complex matrix with high salinity and pesticide concentration as is the Mekong Delta surface water. Performance of the ED–NF integration was evaluated with synthetic solutions based on the comparison with a single NF step generally used for pesticide removal. Both energy consumption and water product quality were considered to assess process efficiency. The ED stage was designed to ensure a 50% removal of salinity before applying NF. As expected, the NF rejection is better in the hybrid process than in a case of a single NF step, especially for pesticide rejection. The integration of a NF stage operated with NF270 membrane consumes less energy than that with NF90 membrane but its efficiency was observed not high enough to respect the Vietnamese guidelines. Using NF90, the optimal recovery rate of the NF stage varies from 30 to 50% depending on the salt content in the feed.