Maximising resource recovery from wastewater grown microalgae and primary sludge in an anaerobic membrane co-digestion pilot plant coupled to a composting process

Treatment and recovery of phosphate from submerged anaerobic membrane bioreactor effluent using thermally treated biowaste and powder activated carbon

This study presents a novel treatment system using a submerged anaerobic membrane bioreactor (SAnMBR) followed by adsorption onto thermally treated biowaste, and ending with a final treatment using powdered activated carbon (PAC). Despite limited phosphate and ammonium ion removal during SAnMBR operation, thermally treated eggshell (EGSL) and seagrass (SG) received SAnMBR effluent and enhanced phosphate recovery, achieving removal rates of 71.8-99.9% and 60.5-78.0%, respectively. The SAnMBR achieved an 85% COD removal, which was slightly reduced further by biowaste treatment. However, significant further reductions in COD to 20.2 ± 5.2 mg/L for EGSL effluent and 57.0 ± 13.3 mg/L for SG effluent were achieved with PAC. Phytotoxicity tests showed the SAnMBR effluent after PAC treatment notably improved seed growth compared to untreated wastewater. In addition, volatile organic compounds (VOCs) were significantly reduced in the system, including common wastewater contaminants such as dimethyl disulfide, dimethyl trisulfide, phenol, p-cresol, nonanal, and decanal. Fractionation analysis of the solid fraction, post-adsorption from both synthetic and domestic wastewater, indicated that for SG, 77.3%-94% of the total phosphorus (TP) was inorganically bound, while for EGSL, it ranged from 94% to 95.3%. This study represents the first attempt at a proof-of-concept for simultaneous treatment of domestic wastewater and phosphorus recovery using this integrated system.

Nitrogen recovery from sludge centrate by membrane contactor: Influence of operating parameters and cleaning conditions

In urban wastewater treatment, the sludge generated is treated by anaerobic digestion, to be subsequently dehydrated by centrifuges. Currently, the liquid fraction obtained in this dehydration process is recirculated at the head of the treatment plant. However, its high nitrogen and phosphorus content makes it an effluent with high added value. The recovery of these nutrients could be an excellent alternative for the production of fertilizers or other industrial applications. In this study, the use of a liquid-liquid phase membrane contactor is presented as a favorable solution for the recovery of ammoniacal nitrogen from sludge centrated. The polypropylene hollow fiber membrane was evaluated considering its ammonia removal and recovery capacity. For this, different parameters were evaluated: the influence of the type and concentration of the acid solution, the wastewater pH, the flow rates of feeding and the acid stripping solution, and the contact time. Results showed that with a contact time of 65 min, ammonia removal and recovery percentages of the order of 90% were achieved. The flow rates of the stripping and feed solutions together with the acid concentration did not have a significant influence on the removal but on the recovery. Concerning used acid, sulphuric and phosphoric acid solutions achieved better results than nitric acid solution. The most critical parameter was the pH, obtaining the highest removal and recovery of ammonium at the highest pH. Finally, a stable cleaning protocol was obtained, between preventive and moderate cleanings to avoid severe cleanings, keeping the membrane at its maximum capacity.

Effects of cellulose-based bio-plastics on the aerobic biological stabilization treatment of mixed municipal solid waste: A lab-scale assessment

The aim of this work is to assess how the presence of cellulose-based bio-plastics influence the biological stabilization of mixed Municipal Solid Waste (MSW). For the scope, two cellulose acetate bio-plastics have been mixed with a synthetic mixed waste to create samples with and without bio-plastics. A self-induced biostabilization has been carried out for 7 and 14 days where temperature and off-gas have been monitored continuously. Results about temperature evolution, O₂ consumption, CO₂ production and respiratory quotient did not show a substantial difference regarding both the duration of the process and the presence of cellulose-based bio-plastics on the mixture. On the average, the temperature peak and the maximum daily O₂ consumption and CO₂ production were 52.2 °C, 35.81 g O₂/kg DM *d and 48.95 g CO₂/kg DM *d respectively. Disintegration of bio-plastics samples after 7 and 14 days were comparable (on the average 23.13%). The self-induced biostabilization gave its main contribution after 4 days and resulted almost finished at the end of the day 7 of the process. Results showed that cellulose-based bio-plastics did not give a negative effect on mixed MSW biological stabilization and suggest a possible management, aiming at energy recovery of the outputs.

Advanced organic recovery from municipal wastewater with an enhanced magnetic separation (EMS) system: Pilot-scale verification

The up-concentration process has been demonstrated as an attractive approach to carbon-neutral wastewater treatment. Innovation in the separation processes can help eliminate the current heavy dependence on gravity, and credible pilot-scale verification is crucial for application promotion. We hereby proposed a pilot-scale enhanced magnetic separation (EMS) system as an up-concentration step to maximize energy recovery from municipal wastewater. The design of EMS was based on the hypothesis that magnetic-driven separation could be a breakthrough in separation speed, and adsorption could further enhance the separation efficiency by capturing soluble substances. Jar tests confirmed the feasibility of activated carbon adsorption, which could also roughen the surface of aggregates. Further, over one-year operation of a 300 m³/d EMS equipment provided optimum operation strategies and evidence of system effectiveness. More than 80% of particulate organics and 60% of soluble organics were removed within 10 min at an energy consumption of only 0.036 kWh/m³. The characteristics of sludge were clarified in terms of organic concentration, extracellular polymeric substances composition, and micro-community analysis. The anaerobic experiments further demonstrated the potential value of the concentrated products. Surprisingly, the developed EMS system exhibited significant advantages in time consumption and space occupation, with competitive operating cost and energy consumption. Overall, the results of this study posed the EMS process for up-concentration as a potential approach to organics recovery from municipal wastewater.

Sustainable microalgal biomass valorization to bioenergy: Key challenges and future perspectives

The global trend is shifting toward circular economy systems. It is a sustainable environmental approach that sustains economic growth from the use of resources while minimizing environmental impacts. The multiple industrial use of microalgal biomass has received great attention due to its high content of essential nutrients and elements. Nevertheless, low biomass productivity, unbalanced carbon to nitrogen (C/N) ratio, resistant cellular constituents, and the high cost of microalgal harvesting represent the major obstacles for valorization of algal biomass. In recent years, microalgae biomass has been a candidate as a potential feedstock for different bioenergy generation processes with simultaneous treating wastewater and CO₂ capture. An overview of the appealing features and needed advancements is urgently essential for microalgae-derived bioenergy generation. The present review provides a timely outlook and evaluation of biomethane production from microalgal biomass and related challenges. Moreover, the biogas recovery potential from microalgal biomass through different pretreatments and synergistic anaerobic co-digestion (AcoD) with other biowastes are evaluated. In addition, the removal of micropollutants and heavy metals by microalgal cells via adsorption and bioaccumulation in their biomass is discussed. Herein, a comprehensive review is presented about a successive high-throughput for anaerobic digestion (AD) of the microalgal biomass in order to achieve for sustainable energy source. Lastly, the valorization of the digestate from AD of microalgae for agricultural reuse is highlighted.

Wastewater Valorization: Practice around the World at Pilot- and Full-Scale

Over the last few years, wastewater treatment plants (WWTPs) have been rebranded as water resource recovery facilities (WRRFs), which recognize the resource recovery potential that exists in wastewater streams. WRRFs contribute to a circular economy by not only producing clean water but by recovering valuable resources such as nutrients, energy, and other bio-based materials. To this aim, huge efforts in technological progress have been made to valorize sewage and sewage sludge, transforming them into valuable resources. This review summarizes some of the widely used and effective strategies applied at pilot- and full-scale settings in order to valorize the wastewater treatment process. An overview of the different technologies applied in the water and sludge line is presented, covering a broad range of resources, i.e., water, biomass, energy, nutrients, volatile fatty acids (VFA), polyhydroxyalkanoates (PHA), and exopolymeric substances (EPS). Moreover, guidelines and regulations around the world related to water reuse and resource valorization are reviewed.