Sustainability Of Wastewater Treatment Plants Research Articles

Clarifying the Role of Phosphorus Management Strategies in Enhancing the Sustainability of Wastewater Treatment Plants

Clarifying the Role of Phosphorus Management Strategies in Enhancing the Sustainability of Wastewater Treatment Plants

EVALUATION OF THE CARBON FOOTPRINT IN THE TREATMENT OF URBAN WASTEWATER IN THE CANARY ISLANDS (SPAIN)

ABSTRACT: Wastewater treatment plants play an important role within the urban water cycle to prevent the natural water environment and human health from being negatively affected by human activities. However, wastewater treatment processes, such as effluent discharge and indirect emissions resulting from energy or chemical production, also negatively affect the environment. Footprints have been used to track human influence on the environment in different areas of interest and have been applied to assess the sustainability of wastewater treatment plants. In this article, a comprehensive review of footprint assessment was investigated to evaluate the wastewater treatment process in wastewater treatment plants. The review showed that carbon footprinting was used to assess the sustainability of WWTPs, and that other footprint assessment applications (such as nitrogen and phosphorus footprinting) were also introduced to assess eutrophication of water bodies. To promote the application of footprint assessment, this article regulates the study objectives, frameworks, system boundaries, data processing methods, and the resulting interpretation process. The pros and cons of the footprint assessments were discussed and investigated in detail, examining the CO2 production on each island of the Canary archipelago, and several suggestions were proposed to improve the footprint assessments. Analysis of footprint assessments at different wastewater treatment plants revealed that wastewater treatment technologies and scales had a significant impact on footprints. Furthermore, research hotspots identified using a keyword network diagram showed that the water-carbon-energy nexus was a promising direction for future studies. The purpose of the study is to improve the reduction of the carbon footprint both at the level of direct and indirect emissions factors using new tools and methodologies. Key Words: Footprint; Waste water; Canary Islands

A Review of AI-Driven Control Strategies in the Activated Sludge Process with Emphasis on Aeration Control

Recent concern over energy use in wastewater treatment plants (WWTPs) has spurred research on enhancing efficiency and identifying energy-saving technologies. Treating one cubic meter of wastewater consumes at least 0.18 kWh of electricity. About 50% of the energy consumed during this process is attributed to aeration, which varies based on treatment quality and facility size. To harness energy savings in WWTPs, the transition from traditional controls to artificial intelligence (AI)-based strategies has been observed. Research in this area has demonstrated significant improvements to the efficiency of wastewater treatment. This contribution offers an extensive review of the literature from the past decade. It aims to contribute to the ongoing discourse on improving the efficiency and the sustainability of WWTPs. It covers conventional and advanced control strategies, with a particular emphasis on AI-based control utilizing algorithms such as neural networks and fuzzy logic. The review includes four key areas of wastewater treatment AI research as follows: parameter forecasting, performance analysis, modeling development, and process optimization. It also points out potential disadvantages of using AI controls in WWTPs as well as research gaps such as the limited translation of AI strategies from research to real-world implementation and the challenges associated with implementing AI models outside of simulation environments.

New Optimization Framework for Improvement Sustainability of Wastewater Treatment Plants

Enhancing the sustainability of wastewater treatment plants (WWTPs) is crucial due to their manifold benefits, which encompass environmental preservation, cost reduction, and resource and energy conservation. The achievement of these advantages relies on the careful choice and implementation of retrofit technologies to upgrade WWTPs. However, this decision-making process is intricate, given the trade-offs between the objectives and the inherent decision uncertainties. To address these complexities, this work presents an innovative weighted multi-objective optimization (MOO) framework tailored for WWTP enhancement amid uncertain conditions. This framework comprises two phases. The first phase involves basic definition and information collection through a case-specific assessment, while the second phase includes model formulation and solver optimization, which serves as a generic tool for the weighted MOO problem. In the model formulation, a combined weighting approach that integrates expert opinions and statistical insights is introduced to assign significance to each objective. The solver optimization employs a projection-based algorithm to identify the optimal technology configuration that achieves a satisfactory and balanced improvement across multiple sustainable objectives. By applying this framework to a case plant for retrofit technology selection, the comprehensive sustainability performance, the targeting of discharged pollution, the operational cost, and the GHG emissions improved by 46.7% to 68.3%.

Phosphorus recycling from waste activated sludge using the hydrothermal platform: Recovery, solubility and phytoavailability

To address the grand challenge of increasing the sustainability of wastewater treatment plants, hydrothermal carbonization was studied as a nutrient recovery platform, transforming sludge into a valuable hydrochar. Carbonization was achieved at different temperatures (200–300 °C) and durations (30–120 min). The highest mass recovery (73%) was observed in the lowest temperature, while the lowest (49%) was obsereved at the highest temperature. Under all reaction conditions, phosphorus recovery values exceeded 80%, with the dominated fraction of inorganic-P in the hydrochar being HCl-extractable. Although HCl-extractable P is considered a moderately labile P fraction, P phytoavailability assays indicate that sewage sludge hydrochar is an excellent source for P, surpassing soluble P, likely due to its slow-release nature. We postulate that polyphosphates constitute a significant portion of this P pool. Overall, we emphasize the benefits of using HTC as a circular economy approach to convert sludge into a valuable hydrochar.

Development of a full-scale wastewater treatment plant for licorice root processing factories: A hybrid biodegradation-lime-alum-ozonation process

Liquorice is a perennial legume that grows principally in Asia, the Middle East and some parts of Europe. The sweet root extract is mainly used in the pharmaceutical, food and confectionary industries. It contains 400 compounds, including triterpene saponins and flavonoids, which are responsible for liquorice's bioactivities. The wastewater (WW) arising from the processing of liquorice can have negative environmental effects and must be treated before being discharged into the environment. Different WW treatment solutions are available. In the last years, increasing attention has been paid to the environmental sustainability of wastewater treatment plants (WWTPs).The present article discusses a hybrid biological (anaerobic-aerobic) and post-biological (lime-alum-ozone) WWTP, designed to treat 105 m3/day complex liquorice root extract WW for agricultural purposes. The influent chemical oxygen demand (COD) and biological oxygen demand (BOD5) were found to be 6000–8000 mg/L and 2420–3246 mg/L, respectively. With a biological hydraulic retention time of 8.2 days and no addition of extra nutrients, the WWTP reached a stable condition after 5 months. Over the course of 16 months, its highly efficient biological treatment reduced COD, BOD5, total suspended solids (TSS), phosphate, ammonium, nitrite, nitrate and turbidity by 86–98 %. However, the WW's colour proved resilient: only 68 % of the colour was removed by the biological treatment, necessitating a combination of biodegradation-lime-alum-ozonation processes in order to reach 98 % efficiency. Thus, this study reveals that liquorice root extract WW can successfully be treated and reused for crop irrigation.

Pilot Study of Oxic–Anoxic Process under Low Dissolved Oxygen for Nitrogen Removal from Low COD/N Tropical Wastewater

Conventionally, nitrification in biological nitrogen removal (BNR) requires high dissolved oxygen (DO) concentrations (>2 mg L−1), making the process energy intensive. Recent studies have shown that efficient ammonium removal and energy reduction can be realized by operating the nitrification at low DO concentrations (<1 mg L−1). In this study, the low-DO oxic anoxic (low-DO OA) process was operated in a pilot-scale sequencing batch reactor (SBR) over 218 days to evaluate the feasibility of nitrogen removal from low chemical oxygen demand-to-nitrogen ratio (COD/N) tropical municipal wastewater. The results revealed that the low-DO OA process attained high removal efficiency for ammonium (97%) and total nitrogen (TN) (80%) under an average DO concentration of 0.6 mg L−1. The effective TN removal efficiency is attributed to the occurrence of simultaneous nitrification–denitrification (SND) under low DO conditions. Further batch tests revealed that slowly biodegradable COD (sbCOD) in tropical wastewater can support denitrification in the post-anoxic phase, resulting in a high TN removal rate. Compared with high DO concentrations (2 mg L−1), low DO conditions achieved 10% higher TN removal efficiency, with similar ammonium and COD removal efficiency. This study is crucial in promoting the energy efficiency and sustainability of wastewater treatment plants treating low COD/N wastewater.

Water–energy–carbon synergies and trade-offs: A daily nexus analysis for wastewater treatment plants

Given the increasing interest in achieving carbon neutrality, water–energy–carbon synergy and trade-off mechanisms are critical for the sustainability of wastewater treatment plants (WWTPs). Based on daily operation data of a WWTP in southern China from 2007 to 2021, we propose a new approach to explore the water–energy–carbon (WEC) nexus of WWTPs by developing a Water–Energy-Carbon Coupling Index (WECCI) and a four-quadrant clustering (FQC) method. It is found that the WECCI increased by 10.12% after the first standard upgrade and decreased by 8.20% after the second standard upgrade, which indicates that the transformation of WWTP may lead to unexpected change in the overall performance. Based on the FQC method, 85.64% of the operation data are mainly concentrated in the WEC best synergy zone after the first standard upgrade, whereas 58.52% of the operation data are concentrated in the low carbon trade-off zone after the second standard upgrade. This study indicates that WECCI and FQC are necessary tools to quantitively assess the integrated performance of WWTPs for better understanding the complex WEC mechanisms of WWTPs, which facilitate the sustainable transition of WWTPs towards carbon neutrality.

Combined heat and power production based on sewage sludge gasification: An energy-efficient solution for wastewater treatment plants

• Energy recovery from sewage sludge through gasification is analysed. • Different solutions for combined heat and power production are assessed. • The analysis is applied to the case study of a real wastewater treatment plant. • A feasibility analysis of the proposed system is carried out. • The system appears to be economically and environmentally feasible. The main operating costs of wastewater treatment plants are related to the energy consumption and the disposal of by-products. Energy recovery from sewage sludge may be a solution to face both these challenges, improving the sustainability of wastewater treatment plants and making them an example of a circular economy. In this work, the energy and economic analysis of an integrated combined heat and power system based on sewage sludge gasification is proposed. The whole process is simulated by using the commercial software Aspen Plus®. A restricted equilibrium model is used to simulate the gasification of sewage sludge in an atmospheric fluidized bed reactor using air as a gasification agent. Syngas produced from gasification is used as a fuel in an internal combustion engine for combined heat and power production. Different solutions are compared: the internal combustion engine is supposed to be fuelled with syngas or with syngas and methane. In line with the pertinent literature on integrated biomass gasification–internal combustion engine systems, the engine is modeled by combining a compressor, a combustor and a turbine to simulate the four thermodynamic steps of an internal combustion engine. Electric and thermal energy produced by the system is used to supply a fraction of the demand for wastewater and sludge treatment. The energy analysis is carried out for a real wastewater treatment plant that serves 1.2 million of population equivalent, located in Southern Italy. The obtained results are used to carry out an energy and economic analysis, which aims at assessing the feasibility and environmental benefits of the proposed system over conventional technologies.

Exploiting the Nutrient Potential of Anaerobically Digested Sewage Sludge: A Review

The world is currently witnessing a rapid increase in sewage sludge (SS) production, due to the increased demand for wastewater treatment. Therefore, SS management is crucial for the economic and environmental sustainability of wastewater treatment plants. The recovery of nutrients from SS has been identified as a fundamental step to enable the transition from a linear to a circular economy, turning SS into an economic and sustainable source of materials. SS is often treated via anaerobic digestion, to pursue energy recovery via biogas generation. Anaerobically digested sewage sludge (ADS) is a valuable source of organic matter and nutrients, and significant advances have been made in recent years in methods and technologies for nutrient recovery from ADS. The purpose of this study is to provide a comprehensive overview, describing the advantages and drawbacks of the available and emerging technologies for recovery of nitrogen (N), phosphorus (P), and potassium (K) from ADS. This work critically reviews the established and novel technologies, which are classified by their ability to recover a specific nutrient (ammonia stripping) or to allow the simultaneous recovery of multiple elements (struvite precipitation, ion exchange, membrane technologies, and thermal treatments). This study compares the described technologies in terms of nutrient recovery efficiency, capital, and operational costs, as well as their feasibility for full-scale application, revealing the current state of the art and future perspectives on this topic.

Dynamic relationship between dissolved organic matter and soluble microbial products during wastewater treatment

Dynamics of the dissolved organic matter (DOM) and soluble microbial products (SMP) significantly affected the sustainability of wastewater treatment plants and effluent qualities. In this study, the origin, transformation, and seasonal variation of DOM components in the anaerobic/anoxic/oxic (A2O) units were illustrated with fluorescence analysis. Results show that the anaerobic process transformed humic acid-like substances (HA) and SMP into fulvic acid-like substances (FA) and aromatic proteins (AP), which indicated the decomposition of macromolecules. In cold seasons, the anoxic process turned AP to HA, SMP, and FA; but the oxic process reversed the transformation. In warm seasons, 6.0% of AP decreased while 3.1% of HA, 1.8% of SMP, and 1.0% of FA increased during the oxic process. Proteobacteria strains were isolated from the activated sludge to stimulate the SMP generation, it was found higher temperature facilitated the transformation of FA and HA (humics) to SMP and AP (proteins), which resulted more proteins presented in the wastewater DOM. These findings indicated that the treatment efficiency and DOM quality in A2O processes were influenced by influent quality and/or temperature conditions, and highlighted the generation of SMP by sludge microorganisms, based on which the corresponding strategies considering the seasonal DOM/SMP dynamics were recommended for the stringent regulation of effluents and the sustainability of the receiving water bodies. Besides, the overall fluorescence intensity was positively correlated with the quantified biopolymer contents in SMP, implying the potential of using the fluorescence-derived information to indicate more quantified DOM properties.

Measuring the eco-efficiency of wastewater treatment plants under data uncertainty

Eco-efficiency assessment is a useful tool for improving the sustainability of wastewater treatment plants (WWTPs). However, it is a complex task that requires the integration of several performance indicators into a single index. Data envelopment analysis (DEA) is established as a highly effective methodology for achieving this as it permits the integration of the service value, resource consumption and environmental impact variables as the desirable outputs, inputs and undesirable outputs, respectively. However, traditional DEA models omit uncertainties in the data that are likely to result in biased conclusions. This study pioneers the assessment of the eco-efficiency of WWTPs while accounting for the data uncertainty and integrating the greenhouse gas emissions as an undesirable output. The DEA-tolerance model was applied to compute the eco-efficiency scores for 729 scenarios for each facility tested for identifying the best- and worst-case scenarios. The WWTPs were also ranked based on their eco-efficiency scores. The results demonstrated the importance of integrating data uncertainty in eco-efficiency assessments; the performances of the WWTPs change notably based on the evaluated set of scenarios. The proposed methodological approach provides a reliable and robust framework for supporting decision-making processes.

Modeling the dynamic performance of full-scale anaerobic primary sludge digester using Anaerobic Digestion Model No. 1 (ADM1)

Anaerobic digestion is one of the most commonly accepted processes applied for the stabilization and treatment of primary sludge generated in municipal wastewater treatment plants enabling energy recovery via biogas production. Understanding and optimizing anaerobic sludge digesters play a key role in sustainability of wastewater treatment plants. Mathematical modeling of biological treatment systems provides several advantages such as better understanding of biochemical processes, interrelations of different biomass types, and impact of environmental conditions on the treatment plant performance. This research presents the modeling of a full-scale anaerobic sludge digester by implementing Anaerobic Digestion Model No. 1 with a limited number of monitored parameters. Model calibration was carried out using a long-term data set. The accuracy of the optimized parameter sets was assessed against measured data obtainedfrom the full-scale sludge digester. The model could predict the methane flow and effluent chemical oxygen demandconcentration in good agreement with the measured data. Therefore, the validated model can be used to predict full-scale sludgedigester performance under dynamic loadings, and to optimize methane production at different operation conditions.

Assessing changes in eco-productivity of wastewater treatment plants: The role of costs, pollutant removal efficiency, and greenhouse gas emissions

Improving eco-efficiency of wastewater treatment plants (WWTPs) has been identified as being essential for achieving urban sustainability. Several previous papers have evaluated the eco-efficiency of WWTPs using data envelopment analysis (DEA) models. However, those models provided only a static assessment in that they ignored possible fluctuations over time within each plant. To overcome this temporal limitation, this paper evaluates dynamic eco-efficiency (changes in eco-productivity over time) of WWTPs using the dynamic weighted Russell directional distance model (WRDDM). This approach allows one to obtain an eco-productivity change index for each major component of the WRDDM model (costs, pollutants removal, and greenhouse gas emissions). Our results illustrate that although eco-productivity improved in half of the WWTPs we assessed, there was still potential for improving some eco-efficiency components. Moreover, operational costs and greenhouse gases emissions were the main drivers reducing eco-productivity. This paper demonstrates the importance of evaluating change in eco-productivity over time and in identifying the drivers associated with those changes, both of which can be used to support decision-making focused on the sustainability of WWTPs.

Energy use and carbon footprints differ dramatically for diverse wastewater-derived carbonaceous substrates: An integrated exploration of biokinetics and life-cycle assessment

Energy neutrality and reduction of carbon emissions are significant challenges to the enhanced sustainability of wastewater treatment plants (WWTPs). Harvesting energy from wastewater carbonaceous substrates can offset energy demands and enable net power generation; yet, there is limited research about how carbonaceous substrates influence energy and carbon implications of WWTPs with integrated energy recovery at systems-level. Consequently, this research uses biokinetics modelling and life cycle assessment philology to explore this notion, by tracing and assessing the quantitative flows of energy embodied or captured, and by exploring the carbon footprint throughout an energy-intensive activated sludge process with integrated energy recovery facilities. The results indicate that energy use and carbon footprint per cubic meter of wastewater treated, varies markedly with the carbon substrate. Compared with systems driven with proteins, carbohydrates or other short-chain fatty acids, systems fed with acetic acid realized energy neutrality with maximal net gain of power from methane combustion (0.198 kWh) and incineration of residual biosolids (0.153 kWh); and also achieved a negative carbon footprint (72.6 g CO2). The findings from this work help us to better understand and develop new technical schemes for improving the energy efficiency of WWTPs by repurposing the stream of carbon substrates across systems.

How Does Scale of Implementation Impact the Environmental Sustainability of Wastewater Treatment Integrated with Resource Recovery?

Energy and resource consumptions required to treat and transport wastewater have led to efforts to improve the environmental sustainability of wastewater treatment plants (WWTPs). Resource recovery can reduce the environmental impact of these systems; however, limited research has considered how the scale of implementation impacts the sustainability of WWTPs integrated with resource recovery. Accordingly, this research uses life cycle assessment (LCA) to evaluate how the scale of implementation impacts the environmental sustainability of wastewater treatment integrated with water reuse, energy recovery, and nutrient recycling. Three systems were selected: a septic tank with aerobic treatment at the household scale, an advanced water reclamation facility at the community scale, and an advanced water reclamation facility at the city scale. Three sustainability indicators were considered: embodied energy, carbon footprint, and eutrophication potential. This study determined that as with economies of scale, there are benefits to centralization of WWTPs with resource recovery in terms of embodied energy and carbon footprint; however, the community scale was shown to have the lowest eutrophication potential. Additionally, technology selection, nutrient control practices, system layout, and topographical conditions may have a larger impact on environmental sustainability than the implementation scale in some cases.

Aplicação de indicadores de sustentabilidade para lagoas de estabilização

A escolha de uma alternativa tecnológica para tratamento de efluentes, assim como o local para implantação deve ser precedida de um estudo de sustentabilidade do ambiente. Foi proposto um método para avaliação da sustentabilidade de estações de tratamento de esgoto, baseado nas características ambientais, sociais e econômico-financeiras dessas unidades. O método foi aplicado em três ETE, constituídas por lagoas de estabilização, localizadas nos municípios de Cajati, Jacupiranga e Pariquera-Açu, todas pertencentes à bacia do Baixo Ribeira de Iguape (SP). A falta de dados para alguns parâmetros considerados na composição dos indicadores prejudicou a obtenção de valores mais realistas. O método proposto mostrou-se de fácil visualização da condição de sustentabilidade das ETE constituídas por lagoas de estabilização.