Assessment of energy use and environmental impacts of wastewater treatment plants in the entire life cycle: A system meta-analysis

Analyzing greenhouse gas emissions and influencing factors of 247 actual wastewater treatment plants in China using emission factor and operational data integrated methods (ODIM)

In response to China's policies on pollution control and carbon emission (CE) reductions, more stringent regulations have been implemented to evaluate CE in wastewater treatment facilities. In this study, we have analyzed CE from China's wastewater treatment plants (WWTPs) and influencing factor. Emission factor (EF) and operational data integrated methods (ODIM) were utilized to measure emissions, using data collected from 247 WWTPs over a 1-year period across seven regions in China. The average CE intensity was 0.45 kgCO2-eq/m3, affected by region, season, influent water quality, treatment processes, effluent discharge standards, and facilities. The scale effect was obvious only in the range of 2 × 105 m3/day. Underground WWTPs exhibited significantly higher CE compared to aboveground WWTPs. In summary, the assessment of CE in 247 actual WWTPs not only identifies emission reduction potential but also provides a scientific basis for formulating targeted emission reduction measures.

Constructed wetlands with recycled concrete for wastewater treatment in cold climate: Performance and life cycle assessment

This study investigated the technical, environmental, and economic feasibility of using recycled construction material (concrete) as substrate in constructed wetlands for cold climate decentralized domestic wastewater treatment. The wastewater treatment efficiency was examined, and life cycle assessment (LCA) and cost benefit analysis were performed. The technical feasibility was assessed in lab-scale two-stage wetland systems with recycled concrete or lava stone as substrates, which were operated at 22 °C and 5 °C with local wild plants and vegetables. The wetlands removed ∼85 % and ∼51 % of organics and ∼67 % and ∼34 % TN at 22 °C and 5 °C, respectively; no significant difference was found between concrete and lava stone. The heavy metal contents in the cultivated vegetables met WHO standards for human consumption, showing the feasibility of nutrient recovery from the treated wastewater. A comparative LCA of septic tank standalone, septic tank + constructed wetland (with recycled concrete), and gravity-driven ceramic membrane (GDCM) system was performed. This aims to illustrate the benefits of intensifying the existing treatment process (i.e., septic tank) with the constructed wetland, with an alternative membrane-based treatment technique as benchmark. The LCA results revealed that using waste materials as the substrate in constructed wetlands could reduce the environmental impact of wetlands. Installation of the wetland as posttreatment of the septic tank (1) could reduce ∼50 % of eutrophication potential without increasing global warming impact compared to the septic tank alone; (2) had ∼90 % higher global warming impact and ∼40 % lower eutrophication impact compared to GDCM. Economic analysis revealed that the total cost of septic tank + constructed wetland (0.143 €/m3) was comparable to the septic tank alone (merely 3.5 % difference), and 49 % lower than that of GDCM (with recycled membranes). Therefore, the septic tank + constructed wetland scenario could be favorable for sensitive areas with eutrophication potential regarding its technical, economical, and environmental feasibility.

An insight on pollutant removal mechanisms in phycoremediation of textile wastewater

Pollutants, including dyes and heavy metals from textile industrial discharge, adversely affect the surface and groundwater resources, and pose a severe risk to the living organisms in the ecosystem. Phycoremediation of wastewater is now an emerging trend, as it is colossally available, inexpensive, eco-friendly, and has many other benefits, with high removal efficiency for undesirable substances, when compared to conventional treatment methods. Algae have a good binding affinity toward nutrients and toxic compounds because of various functional groups on its cell surface by following the mechanisms such as biosorption, bioaccumulation, or alternate biodegradation pathway. Algae-based treatments generate bioenergy feedstock as sludge, mitigate CO2, synthesize high-value-added products, and release oxygenated effluent. Algae when converted into activated carbon also show good potential against contaminants, because of its higher binding efficiency and surface area. This review provides an extensive analysis of different mechanisms involved in removal of undesirable and hazardous substances from textile wastewater using algae as green technology. It could be founded that both biosorption and biodegradation mechanisms were responsible for the removal of dye, organic, and inorganic pollutants. But for the heavy metals removal, biosorption results in higher removal efficiency. Overall, phycoremediation is a convenient technique for substantial conserving of energy demand, reducing greenhouse gas emissions, and removing pollutants.

LCA of municipal wastewater treatment

Wastewater treatment plants play a significant role in minimizing environmental pollution by treating wastewater and reducing the release of contaminants into the environment. However, their operation can still have an environmental footprint. Therefore, Life Cycle Assessment (LCA) of wastewater treatment provides a comprehensive framework to quantify the environmental impact of plants across various categories. By conducting LCA assessments, the environmental impacts of different scenarios or treatment technologies can be compared, enabling decision-makers to identify the most environmentally friendly options. This information helps in optimizing the plant's design, operation, and resource allocation to minimize their environmental burden. The current research hypothesis was to conduct an LCA of a typical activated sludge plant in Greece, considering three different scenarios in order to provide an innovative take on wastewater treatment plant foam waste and utilize them for the production of biogas through anaerobic digestion. The assessment was carried out using OpenLCA software as well as EcoInvent v3.3. database. The study focused on the impact assessment of five categories (eutrophication potential, acidification potential, global warming potential, ozone depletion, and photochemical ozone creation). The results indicated that the baseline scenario had the highest impact on these categories, followed by Scenario I, while Scenario II had the least impact. Additionally, the cumulative energy demand assessment showed that the baseline scenario required significantly more energy compared to Scenarios I and II. However, Scenario II, which involved fine screens and utilization of biogas, exhibited the highest energy production, thereby reducing the overall energy demands for the system. Based on these findings, it is crucial for wastewater treatment facilities to actively pursue energy demand mitigation strategies by implementing energy-efficient technologies and utilizing biogas. These measures not only contribute to environmental protection but also promote a greener and more sustainable future for WWTP operations.

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.

Environmental and economic assessment of a floating constructed wetland to rehabilitate eutrophicated waterways

While the reduced carbon footprint of conventional constructed wetlands (CW) for wastewater treatment has been described in the literature, far less information is available on the economic performance of floating filters and their application for the treatment of other pressing environmental problems such as freshwater eutrophication. This investigation describes the technical characteristics and the environmental life cycle assessment (E-LCA) and a life cycle cost (LCC) analysis of a Typha domingensis floating constructed wetland (FCW) designed and constructed to rehabilitate eutrophicated waterways and which also produces biomass for animal feed. The analysis is based on a precise material, energy and economic inventory from a demonstration project built in the Alagón river basin (central Spain). The E-LCA followed a cradle-to-grave approach, used the EF3.0 impact assessment methodology and was referred to two complementary functional units related to the water treatment capacity of the floating filter: 1 m3 of treated water and 1 kg of N fixed, both over a 10-year operating cycle. Climate change emissions were estimated at 0.012 kg CO2 eq./m3, which included 0.082 kg CO2 eq./m3 caused by the construction, operation and decommissioning of the infrastructure, minus 0.070 kg CO2 eq./m3 credits from the production of fodder for animal feed. Considering its nitrogen uptake capacity, this may be represented as 0.845 kg CO2 eq./kg N. Most of this carbon footprint comes from the construction (63.2 %) and the operation (31.1 %) stages, with the former being dominated by auxiliary materials (mainly plastics and cereal straw) needed to build the infrastructure and the energy system (mainly PV panels). This same pattern is replicated in most other environmental categories and the aggregated single score. Further research is needed to quantify with precision direct CH4 and N2O emissions produced during the operation stage, whose contribution can be significant (up to 64.8 % over indirect LCA emissions). The LCC analysis resulted in discounted expenses over the 10-year cycle of 44,083 € and revenues derived from the sale of fodder for animal feed of 11,429 €, resulting in a net present value of 32,654 €. These expenses may be represented as 0.302 €/m3 of treated water (or 21.1 €/kg of N fixed). The monetary cost and environmental footprint per functional unit of floating CW are lower than those reported for other conventional small-scale wastewater treatment technologies.

Carbon emission efficiency evaluation of wastewater treatment plants: evidence from China

A scientific evaluation of the carbon emission efficiency is crucial for ensuring the sustainable development of wastewater treatment plants (WWTPs). In this paper, we applied a non-radial data envelopment analysis (DEA) model to calculate the carbon emission efficiency of 225 WWTPs located in China. The results showed that the average carbon emission efficiency of China's WWTPs was 0.59, indicating that the efficiencies of most samples still require improvement. The carbon emission efficiency of WWTPs from 2015 to 2017 decreased because of the decrease in technology efficiency. Among the influencing factors, different treating scales had positive impact on carbon emission efficiency improvement. WWTPs with anaerobic oxic process and the first-class A standard were likely to have higher carbon emission efficiency in the 225 WWTPs. By incorporating direct and indirect carbon emissions into WWTP efficiency evaluation, this study helped decision-makers and related water authorities to better understand the contribution of WWTPs to the aquatic and atmospheric environments.

Review of Latest Advances in Nature-Inspired Algorithms for Optimization of Activated Sludge Processes

The activated sludge process (ASP) is the most widely used biological wastewater treatment system. Advances in research have led to the adoption of Artificial Intelligence (AI), in particular, Nature-Inspired Algorithm (NIA) techniques such as Genetic Algorithms (GAs) and Particle Swarm Optimization (PSO) to optimize treatment systems. This has aided in reducing the complexity and computational time of ASP modelling. This paper covers the latest NIAs used in ASP and discusses the advantages and limitations of each algorithm compared to more traditional algorithms that have been utilized over the last few decades. Algorithms were assessed based on whether they looked at real/ideal treatment plant (WWTP) data (and efficiency) and whether they outperformed the traditional algorithms in optimizing the ASP. While conventional algorithms such as Genetic Algorithms (GAs), Particle Swarm Optimization (PSO), and Ant Colony Optimization (ACO) were found to be successfully employed in optimization techniques, newer algorithms such as Whale Optimization Algorithm (WOA), Bat Algorithm (BA), and Intensive Weed Optimization Algorithm (IWO) achieved similar results in the optimization of the ASP, while also having certain unique advantages.

A full-view management method based on artificial neural networks for energy and material-savings in wastewater treatment plants

Carbon neutrality has been received extensive attention in the field of wastewater treatment. The optimal management of wastewater treatment plants (WWTPs) has great significance and urgency since the serious energy and materials waste. In this study, a full-view management method based on artificial neural networks (ANNs) for energy and material savings in WWTPs was established. More than 5 years of historical operating data from two typical plants (size 40,000 t/d and 10,000 t/d) located in Chongqing, China, were obtained, and public data in the service area of each plant were systematically collected from open channels. These abundant historical and public data were used to train two ANNs (GRA-CNN-LSTM model and PCA-BPNN model) to predict the inlets/outlets wastewater quality and quantity. The overall average prediction accuracy of inlets/outlets wastewater indicators are greater than 92.60% and 93.76%, respectively. By combining the two models, more appropriate process operation strategies can be obtained 2 weeks in advance, with more than 11.20% and 16.91% reduction of energy and material costs, respectively. This proposed method can provide full-view decision support for the optimal management of WWTPs and is also expected to support carbon emission control and carbon neutrality in the field of wastewater treatment.

Sustainability Assessment for Wastewater Treatment Systems in Developing Countries

As the assessment of the economic, environmental, institutional, and social sustainability of wastewater treatment systems may have several conceivable goals and intended recipients, there are numerous different approaches. This paper surveys certain aspects of sustainability assessment that may be of interest to the planners of wastewater treatment systems. Here, the key criteria assess the system’s costs and financing, including its affordability for the users, the environmental impact, the benefits for health and hygiene, the cultural acceptance of the system and its recycled products, the technical functioning, and the administrative, political, and legal framework for its construction and operation. A multi-criteria approach may then be used to analyze possible trade-offs and identify the most suitable system for a certain location.

How are typical urban sewage treatment technologies going in China: from the perspective of life cycle environmental and economic coupled assessment

Sewage treatment is an important public service, but it consumes a lot of energy and chemicals in the process of removing wastewater pollutants, which may cause the risk of pollution transfer. To find the corresponding hot issues, this paper took the lead in integrating life cycle assessment (LCA) with life cycle costing (LCC) to evaluate four most typical sewage treatment technologies with more than 85% share in China. It is found that anaerobic/anoxic/oxic (AAO) was the optimal treatment scheme with relatively small potential environmental impact and economic load. The normalized results show that the trends of the four technologies on eleven environmental impact categories were basically the same. Marine aquatic ecotoxicity potential accounted for more than 70% of the overall environmental impact. Contribution analysis indicates that electricity and flocculant consumption were the main processes responsible for the environmental and economic burden. Overall, electricity consumption was the biggest hot spot. Sensitivity analysis verifies that a 10% reduction in electricity could bring high benefits to both the economy and the environment. These findings are expected to provide effective feedback on the operation and improvement of sewage treatment. Graphical abstract.