Energy and material refineries of future: Wastewater treatment plants

Global energy consumption of water treatment technologies

Access to safe drinking water and sanitation is crucial for protecting human health and achieving many Sustainable Development Goals. However, the provision of these services requires significant amounts of energy, which are poorly quantified at the global scale. In this study, we develop a spatially explicit model framework (5 arcmin resolution) for quantifying the energy consumption of water treatment technologies globally, focusing on desalination, wastewater treatment and conventional drinking water treatment (i.e. from ground and suface water sources). We estimate that these processes required 379-1,159 TWh (1.36-4.17 EJ) globally in 2015, corresponding to 1.8-5.4% of total global electricity consumption. Individually, 189-331 TWh (0.68-1.19 EJ) were consumed for desalination, 85-279 TWh (0.31-1.00 EJ) for wastewater treatment and 105-549 TWh (0.38-1.98 EJ) for conventional drinking water treatment. The largest energetic tolls of the three technologies are found in the Middle East and North Africa (desalination), Western Europe (wastewater treatment) and South Asia (conventional drinking water treatment), where they contribute up to 18.6 %, 2.4 % and 4.7 % of the electricity consumption in these regions, respectively. Considering the identified uncertainties, the model framework can be used to represent spatially explicit patterns of energy consumption for water treatment in Integrated Assessment Models and Energy System Models. These developments enable projections of the future energy demands of water treatment technologies and a better understanding of the water-energy nexus, under global change and at multiple spatial scales.

Greywater reuse for irrigation: A critical review of suitability, treatment, and risks

Greywater accounts for approximately 75 % of domestic wastewater and generally contains fewer contaminants than domestic wastewater. Therefore, its treatment and reuse represent a promising approach to supplement irrigation demand. This study comprehensively evaluates the quality characteristics of greywater based on its source, applied treatment methods, and its potential health, environmental, soil, and agricultural impacts. Various physical, chemical, and biological treatment processes have been analysed, with the most commonly employed technologies including membrane bioreactors (MBRs), constructed wetlands, media filtration (sand, activated carbon), disinfection methods (UV, chlorine, ozone), and advanced oxidation processes. The effectiveness of these methods has been assessed concerning the intended reuse application, emphasizing the critical role of disinfection in ensuring safe irrigation use. The health and environmental implications of greywater reuse have been examined, focusing on the risks associated with pathogen contamination, detergent residues, and micropollutants, while also evaluating the efficiency of treatment processes in mitigating these risks. From an environmental perspective, the accumulation of essential nutrients such as nitrogen and phosphorus, the potential for salinity buildup, and alterations in soil microbial balance have been investigated. Regarding soil and agricultural impacts, this study analyzes how greywater reuse influences soil structure (e.g., permeability, infiltration), plant growth responses, and the accumulation of heavy metals. These findings contribute to the development of scientifically grounded recommendations for the safe and sustainable reuse of greywater within water management strategies, promoting its role as an alternative water source for irrigation.

Consistent acidogenic co-fermentation of waste activated sludge and food waste under thermophilic conditions

Acidogenic co-fermentation of waste activated sludge (WAS) and food waste (FW) under thermophilic conditions enhances process consistency, while overcoming the problem of acetic acid consumption due to growing methanogens. Two long-term continuous co-fermentation experiments were carried out with a WAS:FW mixture (70:30 % in VS) at organic loading rate of 8 gVS/(L·d). Experiment 1 assessed the impact of temperature (35 °C and 55 °C) and WAS origin (WAS_A and WAS_B) in two collection periods. Experiment 2 evaluated the consistency at 55 °C by testing three WAS origins (WAS_A, WAS_B and WAS_C) in 3 additional collection periods. Experimental results showed that at 55 °C, the solubilisation yield was enhanced compared to 35 °C, although this did not always lead to higher fermentation yield. The fermentation product profile was affected by the operating temperature, with 55 °C promoting the accumulation of acetic and butyric acids. Acetic acid consumption was only detected at 35 °C in fermenters treating WAS_A, whereas it was not observed in fermenters treating WAS_B. This consumption was prevented at 55 °C, as none of the 13 fermenters continuous operation showed acetic acid consumption. Acetic acid consumption was attributed to species midas_s_9557 (genus Methanosarcina), an aceticlastic methanogen, which did not grow under 55 °C. Temperature had a more significant effect on the microbial community structure than WAS origin. Functional redundancy was demonstrated by each fermenter having its own distinct microbial consortium while maintaining constant metabolic functions at 55 °C. Overall, the acidogenic co-fermentation of WAS and FW at 55 °C is regarded as a robust and consistent biotechnology.

Microbial augmented aerobic composting for effective phthalates degradation in activated sludge

Phthalate esters (PAEs) accumulated in activated sludge posed serious threats to agroecosystems and environment. Traditional aerobic (AE) and anaerobic (AN) composting were limited in achieving sustained PAEs degradation due to the single structure of microbial community. Here, the effectiveness and microbiological mechanisms of bacterial-augmented aerobic composting (AEB) in reducing activated sludge PAEs were investigated, with comparison of anaerobic composting (ANB). Results showed that AEB treatments significantly enhanced PAEs degradation efficiency through batch degradation experiments and microbial community analysis. At initial PAEs contamination levels of 50 mg/kg and 100 mg/kg, di-n-butyl phthalate (DBP) and di(2-ethylhexyl) phthalate (DEHP) removal rates increased by 2.11-3.93-fold and 2.18-3.36-fold, respectively. Notably, AEB treatment reshaped bacterial community structure, forming communities dominated by efficient PAEs-degrading bacteria. Network analysis revealed a more complex microbial interaction networks under AE treatment, with the numbers of node and connectivity being 1.5 and 1.8 times than that of AN treatment. Functional gene prediction indicated increased abundances of PAEs degradation-related functional groups. Environmental factor analysis demonstrated optimized conditions through pH control, oxygen supply, and active carbon-nitrogen metabolism. These findings provided important supports for safe activated sludge disposal and resource utilization.

A short bibliographic review concerning biomethane production from wastewater sludge

Biomethane production by anaerobic digestion (AD) of sludge from municipal wastewater treatment is a viable practice to valorise the residues of these plants. However, although the relevant literature is abundant, no comprehensive reviews have been recently published on this topic. Detailed information concerning the factors influencing the AD process and values of biomethane production from the sludge from municipal wastewater treatment plants (MWWTPs) on the global scale may support technicians and researchers in both the planning and the design steps of an AD process. This study proposes a systematic review and a meta-analysis of the factors that noticeably influence biomethane yield deriving from AD of sludge from MWWTP. The reported values were systematically analysed compared to the main factors driving AD, including publication year, geographical area of each study, type of digested sludge, treatment in the water line of the MWWTP, possible sludge pre-treatments, type of digestion process, hydraulic retention time (HRT) and temperature regime of the AD process. A higher biomethane production was registered in North American plants compared to countries in other continents. Older studies published between 2001 and 2005 reported lower mean values compared to the more recent experiments. A gradient of 'primary sludge' > 'mixed sludge' > 'wastewater activated sludge' was found for the mean biomethane yield in relation to the digested sludge type. The mean biomethane yields for different types of sludge on a global scale are 0.425, 0.296 and 0.176 Nm3 kg VS-1 for primary sludge, mixed sludge and waste activated sludge, respectively. Overall, the study demonstrates: (i) the very large variability of biomethane yields from AD of the residues from MWWTPs (mainly due to the different characteristics of sludge) and (ii) the non-significance of some factors (i.e. treatment in the water line, pre-treatments, type of process, HRT and temperature regime) on energy yields from the AD process.

Alum sludge-driven electro-phytoremediation in constructed wetlands: a novel approach for sustainable nutrient removal

In addition to their advantages as promising methods for wastewater treatment, CWs exhibit poor performance in terms of N and P removal efficiency in the effluent of wastewater treatment plants. By focusing on this issue, we designed CWs integrated with a biochar-doped activated carbon cloth (ACC) electrode and alum sludge from water treatment plants as a substrate to achieve concomitant organic matter and nutrient removal efficiency. Compared with the use of one layer of alum sludge in CWs (CWs-C3) with ACC electrodes inserted in two layers, which uses one layer of alum sludge, a significant improvement in removal efficiency was achieved (96% for COD; 89% for TN; and 77% for TP). The findings revealed that the application of potential accompanied by the insertion of a cathode ACC electrode into the first layer of alum sludge was beneficial for completing nitrification and facilitating denitrification in the cathode and anode regions, respectively, resulting in increased removal of organic matter and nutrients. Further evaluation revealed that the TN-TP synergetic removal mechanism was influenced by the use of Fe2+ as an electron donor and as a driving force for the development of autotrophic denitrifying bacteria to increase nitrate reduction. Additionally, the formation of FePO4 and AlPO4 and their adsorption through the interaction of FeOOH and AlOOH with phosphate constitute the main removal mechanism for TP in wastewater. Another reason for the increased removal efficiency in the CW-C3 reactor was the greater abundance and microbial diversity effectuated by the application of potential in the anode and cathode regions. In summary, a promising strategy for simultaneously promoting organic matter and nutrients and utilizing CWs on a large scale and in practical applications was proposed.

CRISPR/Cas9-Engineering for Increased Amylolytic Potential of Microbes for Sustainable Wastewater Treatment: A Review

Amylases are pivotal enzymes with extensive industrial applications, including food processing, textile manufacturing, pharmaceuticals, and biofuel production. Traditional methods for enhancing amylase production in microbial strains often lack precision and efficiency. The advent of CRISPR/Cas9 technology has revolutionized genetic engineering, offering precise and targeted modifications to microbial genomes. This review explores the potential of CRISPR/Cas9 for improving amylase production, highlighting its advantages over conventional methods. This review discusses the mechanism of CRISPR/Cas9, the identification and targeting of key genes involved in amylase synthesis and regulation, and the optimization of expression systems. Additionally, current review examines case studies demonstrating successful CRISPR/Cas9 applications in various microbial hosts. The review also delves into the integration of CRISPR/Cas9 in wastewater treatment, where genetically engineered amylolytic strains enhance the degradation of complex organic pollutants. Despite the promising prospects, challenges such as off-target effects and regulatory considerations remain. This review provides a comprehensive overview of the current advancements, challenges, and future directions in the application of CRISPR/Cas9 technology for amylase production and environmental biotechnology.

Membrane aerated biological reactors (MABRs) to enhance the biological treatment process at a WWTP

The goal of climate neutrality, under the provision of the European Green Deal, will require great efforts to wastewater treatment plants (WWTPs) to reduce and optimize their energy consumption. The utilization of membrane aerated biological reactors (MABRs) to renovate existing WWTPs could be an opportunity in this sense. In this study, the control of the flow at the outlet of a pure, open-end MABR was used as a strategy to minimize the oxygen consumption and obtain high oxygen transfer efficiencies (OTEs). OTE values of more than 80% were observed, which are not so common in the literature and are comparable to those obtained with a close-end configuration. High efficiencies (85%) were found for the removal of both COD and total nitrogen from samples of real wastewater. A techno-economic analysis, comparing a conventional activate sludge (CAS) plant with a MABR, both with a treatment capacity of 25,000 equivalent inhabitants (e.i.), found that the MABR only needed approx. 1/5 of the energy required by the CAS. A MABR plant could become a profitable investment, under a fixed return time of 5 years, compared to a CAS with a CAPEX of 123.7 k€, if the overall cost of the cassettes was inferior to 237 k€. A sensitivity analysis imposing a variation of ±50% on the input parameters (cost of blower, diffusers, electric energy, and opportunity cost of capital) demonstrated that the cost of electric energy had the highest impact on the maximum allowable value of the MABR investment, which was affected by ± 26% with respect to the value calculated in the reference scenario.

Integrating artificial intelligence modeling and membrane technologies for advanced wastewater treatment: Research progress and future perspectives

Membrane technologies have become proficient alternatives for advanced wastewater treatment, ensuring high contaminant removal and sustainable resource recovery. Despite significant progress, ongoing research efforts aim to further optimize treatment performance. Among the challenges faced, membrane fouling persists as a relevant obstacle in membrane technologies, necessitating the development of more effective mitigation strategies. Mathematical models, widely employed for predicting treatment performance, generally exhibit low accuracy and suffer from uncertainties due to the complex and variable nature of wastewater. To overcome these limitations, numerous studies have proposed artificial intelligence (AI) modeling to accurately predict membrane technologies' performance and fouling mechanisms. This approach aims to provide advanced simulations and predictions, thereby enhancing process control, optimization, and intensification. This literature review explores recent advancements in modeling membrane-based wastewater treatment processes through AI models. The analysis highlights the enormous potential of this research field in enhancing the efficiency of membrane technologies. The role of AI modeling in defining optimal operating conditions, developing effective strategies for membrane fouling mitigation, enhancing the performance of novel membrane-based technologies, and improving membrane fabrication techniques is discussed. These enhanced process optimization and control strategies driven by AI modeling ensure improved effluent quality, optimized resource consumption, and minimized operating costs. The potential contribution of this cutting-edge approach to a paradigm shift toward sustainable wastewater treatment is examined. Finally, this review outlines future perspectives, emphasizing the research challenges that require attention to overcome the current limitations hindering the integration of AI modeling in wastewater treatment plants.

Recent advancements in wastewater treatment via anaerobic fermentation process: A systematic review

This manuscript delves into the realm of wastewater treatment, with a particular emphasis on anaerobic fermentation processes, especially dark, photo, and dark-photo fermentation processes, which have not been covered and overviewed previously in the literature regarding the treatment of wastewater. Moreover, the study conducts a bibliometric analysis for the first time to elucidate the research landscape of anaerobic fermentation utilization in wastewater purification. Furthermore, microorganisms, ranging from microalgae to bacteria and fungi, emphasizing the integration of these agents for enhanced efficiency, are all discussed and compared. Various bioreactors, such as dark and photo fermentation bioreactors, including tubular photo bioreactors, are scrutinized for their design and operational intricacies. The results illustrated that using clostridium pasteurianum CH4 and Rhodopseudomonas palustris WP3-5 in a combined dark-photo fermentation process can treat wastewater to a pH of nearly 7 with over 90% COD removal. Also, integrating Chlorella sp and Activated sludge can potentially treat synthetic wastewater to COD, P, and N percentage removal rates of 99%,86%, and 79%, respectively. Finally, the paper extends to discuss the limitations and future prospects of dark-photo fermentation processes, offering insights into the road ahead for researchers and scientists.

Microalgal-bacterial consortia for the treatment of livestock wastewater: Removal of pollutants, interaction mechanisms, influencing factors, and prospects for application

The livestock sector is responsible for a significant amount of wastewater globally. The microalgal-bacterial consortium (MBC) treatment has gained increasing attention as it is able to eliminate pollutants to yield value-added microalgal products. This review offers a critical discussion of the source of pollutants from livestock wastewater and the environmental impact of these pollutants. It also discusses the interactions between microalgae and bacteria in treatment systems and natural habitats in detail. The effects on MBC on the removal of various pollutants (conventional and emerging) are highlighted, focusing specifically on analysis of the removal mechanisms. Notably, the various influencing factors are classified into internal, external, and operating factors, and the mutual feedback relationships between them and the target (removal efficiency and biomass) have been thoroughly analysed. Finally, a wastewater recycling treatment model based on MBC is proposed for the construction of a green livestock farm, and the application value of various microalgal products has been analysed. The overall aim was to indicate that the use of MBC can provide cost-effective and eco-friendly approaches for the treatment of livestock wastewater, thereby advancing the path toward a promising microalgal-bacterial-based technology.

Adsorption of Heavy Metal Ions on Alginate-Based Magnetic Nanocomposite Adsorbent Beads

Graphene oxide and its magnetic nanoparticle-based composites are a well-known tool to remove heavy metals from wastewater. Unfortunately, one of the major issues in handling such small particles consists of their difficult removal from treated wastewater (even when their magnetic properties are exploited), due to their very small diameter. One possible way to overcome this problem is to embed them in a macroscopic biopolymer matrix, such as alginate or chitosan beads. In this way, the adsorbent becomes easier to handle and can be used to build, for example, a packed column, as in a traditional industrial adsorber. In this work, the removal performances of two different embedded magnetic nanocomposite adsorbents (MNAs) are discussed. The first type of MNA is based on ferrite magnetic nanoparticles (MNPs) generated by coprecipitation using iron(II/III) salts and ammonium hydroxide, while the second is based on a 2D material composed of MNP-decorated graphene oxide. Both MNAs were embedded in cross-linked alginate beads and used to treat artificial water contaminated with chromium(III), nickel(II), and copper(II) in different concentrations. The yield of removal and differences between MNAs and non-embedded magnetic nanomaterials are also discussed. From the results, it was found that the time to reach the adsorption equilibrium is higher when compared to that of the nanomaterials only, due to the lower surface/volume ratio of the beads, but the adsorption capacity is higher, due to the additional interaction with alginate.

Impact of food waste addition in energy efficient municipal wastewater treatment by aerobic granular sludge process

Recently, one of the main purposes of wastewater treatment plants is to achieve a neutral or positive energy balance while meeting the discharge criteria. Aerobic granular sludge (AGS) technology is a promising technology that has low energy and footprint requirements as well as high treatment performance. The effect of co-treatment of municipal wastewater and food waste (FW) on the treatment performance, granule morphology, and settling behavior of the granules was investigated in the study. A biochemical methane potential (BMP) test was also performed to assess the methane potential of mono- and co-digestion of the excess sludge from the AGS process. The addition of FW into wastewater enhanced the nutrient treatment efficiency in the AGS process. BMP of the excess sludge from the AGS process fed with the mixture of wastewater and FW (195 ± 17 mL CH4/g VS) was slightly higher than BMP of excess sludge from the AGS process fed with solely wastewater (173 ± 16 mL CH4/g VS). The highest methane yield was observed for co-digestion of excess sludge from the AGS process and FW, which was 312 ± 8 mL CH4/g VS. Integration of FW as a co-substrate in the AGS process would potentially enhance energy recovery and the quality of effluent in municipal wastewater treatment.

Critical analysis on the transformation and upgrading strategy of Chinese municipal wastewater treatment plants: Towards sustainable water remediation and zero carbon emissions

In the light of circular economy aspects, processing of large-scale municipal wastewater treatment plants (WWTPs) needs reconsideration to limit the overuse of energy, implement of non-green technologies and emit abundant greenhouse gas. Along with the huge increase in the worldwide population and agro-industrial activities, global environmental organizations have issued several recent roles to boost scientific and industrial communities towards sustainable development. Over recent years, China has imposed national and regional standards to control and manage the discharged liquid and solid waste, as well as to achieve carbon peaking and carbon neutrality. The aim of this report is to analyze the current state of Chinese WWTPs routing and related issues such as climate change and air pollution. The used strategies in Chinese WWTPs and upgrading trends were critically discussed. Several points were addressed including the performance, environmental impact, and energy demand of bio-enhanced technologies, including hydrolytic acidification pretreatment, efficient (toxic) strain treatment, and anaerobic ammonia oxidation denitrification technology, as well as advanced treatment technologies composed of physical and chemical treatment technologies, biological treatment technology and combined treatment technology. Discussion and critical analysis based on the current data and national policies were provided and employed to develop the future development trend of municipal WWTPs in China from the construction of sustainable and "Zero carbon" WWTPs.