Wastewater Treatment Sector Research Articles

Start-up of an aerobic granular sludge system from stored granules: Evaluating the impact of storage period on biomass activity and stability and the effect of temperature on nitrification and phosphorus removal rates

Aerobic granular sludge (AGS) has been considered a breakthrough within the wastewater treatment sector. However, the long reactor start-up for the formation of granules is challenging and may hinder the spread of this technology. To circumvent this obstacle, inoculation of the reactors with pre-formed granules from existing plants is an interesting approach. In this context, issues related to biomass storage becomes very relevant. In this study, reactivation of aerobic granular biomass after storage was evaluated in a sequencing batch reactor (SBR) designed for achieving simultaneous organic matter, nitrogen and phosphorus removal. Two different scenarios, short (40 days) and long (180 days) storage periods, were assessed, and their influence on the granules physical properties and bioactivity was addressed. The results revealed that the granules stored for a shorter period showed higher resistance to breakage and underwent smooth color changes. On the other hand, the biomass stored for a longer period acquired a dark color and was more susceptible to disruption during reactivation. The granules stored for 6 months become swollen and exhibited an irregular morphology and fluffy structure within the first days of reactivation. Consequently, their settling properties were adversely affected, and some parameters such as the food-to-microorganism ratio had to be adjusted to prevent granules disintegration. Regarding the bioactivity of important microbial functional groups, COD removal was rapidly restored within a few days of SBR operation with the biomass stored for a shorter period. However, it took longer for the biomass stored for 180 days to reach the same performance observed for the granules stored for 40 days. A similar trend is valid for nitrification. In the experiments with sludge stored for a longer time, it took almost twice as long to reach effluent ammonium concentrations lower than 1 mg NH4+-N L−1 compared to the test using biomass stored for 40 days. Phosphate removal was strongly affected by biomass storage, especially after 180 days of inactivity, a condition found to be detrimental for polyphosphate-accumulating organisms. Finally, cycle tests were also conducted to assess substrate conversion rates for comparison between different trials and evaluate the influence of temperature (10–35 °C) on nitrification and phosphate removal rates.

Synthesis of Fly Ash-Based Zeolite and its Research Progress in Wastewater Treatment

Fly ash is the most common solid waste in the industry, and its high value-added utilization has become a hot issue of study. Carrying out the green synthesis route of zeolite as the raw material of fly ash has become an extremely important scientific significance and practical value. In this paper, the research progress of fly ash-based zeolite was introduced from three aspects, including fly ash activation method, fly ash-based zeolite synthesis method and fly ash-based zeolite in the wastewater treatment sector. The relevant applications of fly ash-based zeolite as an adsorbent material in the treatment of wastewater pollution were summarized, and the development trend has prospected.

SARS-CoV-2 spillover into hospital outdoor environments

Facing the ongoing coronavirus infectious disease-2019 (COVID-19) pandemic, many studies focus on severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) in indoor environment, on solid surface or in wastewater. It remains unclear whether SARS-CoV-2 can spill over into outdoor environments and impose transmission risks to surrounding people and communities. In this study, we investigated the presence of SARS-CoV-2 by measuring viral RNA in 118 samples from outdoor environment of three hospitals in Wuhan. We detected SARS-CoV-2 in soils (205–550 copies/g), aerosols (285−1,130 copies/m3) and wastewaters (255−18,744 copies/L) in locations close to hospital departments receiving COVID-19 patients or in wastewater treatment sectors. These findings revealed a significant viral spillover in hospital outdoor environments that was possibly caused by respiratory droplets from patients or aerosolized particles from wastewater containing SARS-CoV-2. In contrast, SARS-CoV-2 was not detected in other areas or on surfaces with regular implemented disinfection. Soils may behave as viral warehouse through deposition and serve as a secondary source spreading SARS-CoV-2 for a prolonged time. For the first time, our findings demonstrate that there are high-risk areas out of expectation in hospital outdoor environments to spread SARS-CoV-2, calling for sealing of wastewater treatment unit and complete sanitation to prevent COVID-19 transmission risks.

100% renewable wastewater treatment plants: Techno-economic assessment using a modelling and optimization approach

Renewable energies are being given increasing attention worldwide, as they are able to reduce the dependence on depletable fossil fuels. At the same time, wastewater treatment is known to be a significantly energy-intensive sector, which could potentially exploit renewable energies conversion in different forms. This study investigated the feasibility to design high renewable share wastewater treatment plants through dynamic simulations and optimization, aiming to move towards greener and energy-wise wastewater remediation processes. The main aim of the work was achieved by integrating photovoltaic systems with wind turbines, multi-energy storage technologies, i.e., batteries and hydrogen systems, and reverse osmosis tertiary treatment to absorb the power production surpluses. It was supposed that, in the newly proposed scenario, most of the plant electricity need would be covered by renewable energy. The optimization problem was multi-objective and found the trade-off solutions between minimizing the net present cost and maximizing the renewable share. In the first part of the study, the model was developed and applied to a medium-scale Italian municipal wastewater treatment plant. Model generalization was successively accomplished by applying the model to different locations and plant scales across the world. For all the investigated scenarios and cases, the optimal system integration was to design a renewable and storage system with a renewable share of 70%, corresponding to the lowest net present cost. The developed model is highly flexible and can be applied to other relevant case studies, boosting for a more sustainable wastewater treatment sector, enhancing at the same time local renewable energy conversion.

COVID-19 Lockdown Disruptions on Water Resources, Wastewater, and Agriculture in India

The COVID-19 pandemic has disrupted daily activities across multiple sectors globally. The extent of its impact on the global economy and its key sectors, especially water, wastewater, and associated sectors such as agriculture, is still unclear. In this paper, the preliminary impacts of COVID-19 on water resources of India, especially on the river water quality, water usage in domestic and commercial sectors, wastewater treatment sector, and agriculture sector, are discussed. The limitations in the functioning of the existing system and management of water resources are identified. The need for improvements to strengthen the water resources monitoring and developing process-based models are highlighted. This paper also discusses the need for further investigation to identify the extent of impact and contributing factors to improve our understanding of the natural system for preparing, monitoring, and implementing the policies to manage the water resources during any pandemic/epidemics in the future.

Outdoor microalgae‐based urban wastewater treatment: Recent advances, applications, and future perspectives

AbstractAlthough microalgae‐based wastewater treatment has been traditionally carried out in extensive waste stabilization ponds, recent trends focus on the use of microalgae to apply the circular economy principles in the wastewater treatment sector due to the capacity of algae to absorb carbon dioxide while recovering nutrients from sewage. To this aim, the development of new intensive microalgae‐based systems with higher efficiency and level of process control is required. Results obtained for these systems at lab scale are generally promising. However, upscaling to outdoor conditions is often uncertain. Some advances have been made in terms of applying open systems at large scale. However, there are still some issues related to land requirements and the economic feasibility and robustness of the process that have to be overcome to widely implement these systems. This article aims at describing the main design and operating factors regarding outdoor microalgae cultivation. It will also explain some microalgae cultivation technologies to treat wastewater, showing their advantages, disadvantages, and the possibility to treat different wastewater streams with microalgae cultures. Future perspectives of this biotechnology will be commented as well.This article is categorized under: Engineering Water > Engineering Water

The Impact of Water Quality Management Policies on Innovation in Nitrogen and Phosphorus Technology

The purpose of this study is to examine the effects on innovation of environmental regulations aimed at reducing eutrophication. We focus on innovations in nitrogen and phosphorus management technology in the wastewater treatment sector and the agricultural sector. Patent data from Sweden over a 50-year period is used as a measure of innovation. We estimate a negative binomial regression model in a reduced form and by the use of control-functions, taking into account environmental regulation as well as more general determinants of innovation. Our results suggest that increased regulation has induced innovation in the wastewater treatment sector, both in the long and short run. The short-run effect was estimated to 40–70% in the years immediately following the introduction of new environmental regulations. A corresponding effect could not be identified in the agricultural sector. The difference between the sectors is likely explained by differences in policy design, where performance standards are applied in the wastewater sector, while design standards and technology-specific subsidies dominate in the agricultural sector.

Treatment of real domestic sewage in a pilot-scale aerobic granular sludge reactor: Assessing start-up and operational control.

Aerobic granular sludge (AGS) has been considered a breakthrough in the wastewater treatment sector given its key characteristics, such as excellent settleability, simultaneous removal of organic and nutrient pollutants, and compactness. However, the formation of granules often delays the start-up of granular-based systems, especially in large-scale settings. This study addressed the start-up of a pilot-scale AGS sequencing batch reactor (SBR) treating domestic sewage, monitored for over 280days. The challenges faced during aerobic granulation using a mixture of activated sludge and anaerobic granular sludge as inoculum and the performance of the reactor on organic matter, nitrogen, and phosphorus removal were discussed. Results showed that robust and stable granules were formed after an initial period of around six months, with the settling time playing a key role on granules development. At least 80% of granules had a diameter greater than 0.2mm and 60% >1mm. In general, the reactor achieved high nitrogen removal efficiency, as well as satisfactory removal of soluble COD. However, total COD abatement was impaired by the various episodes of suspended solids loss with the effluent. Overall, this study demonstrated that the reactor was efficient in the treatment of domestic sewage, but its performance was adversely affected from sudden changes in the influent quality. PRACTITIONER POINTS: Aerobic granular sludge (AGS) applied to small-scale domestic sewage treatment. The control of sludge age in AGS can be a problem due to short sedimentation times. High DO to maintain aerobic granulation can economically make the process economically unfeasible in tropical countries. A sludge with excellent sedimentation properties was obtained. However, maintaining the granule over time is a challenge.

Government Guarantee Decisions in PPP Wastewater Treatment Expansion Projects

Public private partnership (PPP) models are often used in delivering wastewater treatment (WWT) projects. When existing PPP projects need expansion due to higher demand for WWT, in many cases, the expansion may involve a new PPP contract involving a new concessionaire. Expansion PPPs have unique challenges as the sharing of responsibilities and risks can become complex. The complexities are further exacerbated when there are government guarantees involved. Structuring inappropriate guarantees can often lead to high costs for the government. This study focused on the choice of government guarantee in PPP expansion projects in the WWT sector by examining two popular guarantee mechanisms: minimum revenue guarantee and exclusive right. A decision model was developed and applied in a real WWT expansion PPP project in China to illustrate the optimal guarantee under varying circumstances related to service demand, expected unit price, and the existing guarantees in the existing PPP project. The contribution of the study lies in the applicability of the model to facilitate better decisions for the government in selecting the optimal guarantee mechanism in PPP expansion projects.

How lessons from an evolving comprehensive approach for water and sanitation can improve artisanal and small-scale mining environmental initiatives

Environmental risk mitigation strategies employed in developing communities to address mercury pollution from artisanal and small-scale gold mining (ASGM) have largely failed to meet community needs, resulting in their abandonment. In contrast, the water and wastewater treatment sector has gained more traction, introducing sustainable and community supported water treatment strategies. This paper discusses why initiatives in water and wastewater treatment in developing communities are succeeding while initiatives in ASGM environmental risk mitigation are falling short. Selected case studies illustrate that water and wastewater treatment project success is contingent on the inclusion of a fully comprehensive approach that considers the socio-economic and ecological context of communities and individuals along with behavior change interventions. These elements of successful WASH projects were then applied to past ASGM environmental projects to determine their applicability to the sector. By adopting the core traits of successful water and wastewater treatment projects in developing communities, a framework can be developed for ASGM projects that, when applied correctly, could lead to measurable impact and long-term sustainability.

Unconventional Excess Heat Sources for District Heating in a National Energy System Context

District heating (DH) is an important technology in future smart energy systems as it allows for an efficient implementation of various renewable energy sources. As DH develops towards lower temperatures and renewable electricity production increases, new types of heat sources become relevant. Thus, the aim of this article is to assess the potential for utilizing four unconventional excess heat (UEH) sources in DH systems, namely: Data centers, wastewater treatment, metros and service sector buildings. The main method used to assess the UEH potentials is an energy system analysis focusing on the availability and economic feasibility of utilizing the UEH sources in national contexts. The analysis consists of 2015 and 2050 scenarios for Germany, Spain and France. The results show a potential for utilizing the UEH potentials in all three countries, both in 2015 and 2050 systems. The potentials are highest in the 2050 scenarios, primarily due to larger DH shares. Furthermore, the potentials are limited by competition with other heat supply sources, conjunction with heat demands and feasible heat pump operation. In conclusion, the four UEH sources could impact the local DH systems, but in a national energy system context they are expected to play a minor role.

Regional dimensions of the South Korean water-energy nexus

The linkage between water and energy, the water-energy nexus, is site specific. An integrated management approach to both resources begins with understanding a region’s water-energy nexus. This study built an inventory of water and energy consumption in 17 South Korean regions at each stage of the urban water cycle from 2012 to 2017, estimated the water-related energy intensities, and compared those values across regions. Additionally, this study conducted a series of regression analyses to identify the influences of various factors on water-related energy consumption. This study found regional variance in the total energy intensity as well as in the energy intensities at different stages of the water cycle. Both energy consumed and energy intensities generally increased over the study period. The findings show that greater attention should be paid to energy consumption in the water sector, especially in the wastewater treatment sector. In addition, the regression analyses revealed that management of energy intensity is the most impactful way to reduce energy consumption in the water sector. The positive impacts on water pollution and water consumption also bolster the necessity of water conservation efforts. This study presents regional priorities related to the water-energy nexus and provides water-related energy intensity benchmarks that local governments can use. The findings highlight the necessity of an integrated approach to water and energy.

Staged electrochemical treatment guided by modelling allows for targeted recovery of metals and rare earth elements from acid mine drainage

Acid mine drainage (AMD) is a challenge for current and legacy mining operations worldwide given its potential to severely harm ecosystems and communities if inadequately managed. Treatment costs for AMD are amongst the highest in the industrial wastewater treatment sector, with limited sustainable options available to date. This work demonstrates a novel chemical-free approach to tackle AMD, whereby staged electrochemical neutralisation is employed to treat AMD and concomitantly recover metals as precipitates. This approach was guided by physico-chemical modelling and tested on real AMD from two different legacy mine sites in Australia, and compared against conventional chemical-dosing-based techniques using hydrated lime (Ca(OH)2) and sodium hydroxide (NaOH). The electrochemical treatment demonstrated the same capacity than Ca(OH)2 to neutralise AMD and remove sulfates, and both were significantly better than NaOH. However, the electrochemical approach produced less voluminous and more easily settleable sludge than Ca(OH)2. Moreover, the staged treatment approach demonstrated the potential to produce metal-rich powdered solids with a targeted composition, including rare earth elements and yttrium (REY). REY were recovered in concentrations up to 0.1% of the total solids composition, illustrating a new avenue for AMD remediation coupled with the recovery of critical metals.

A Mini-Review of Urban Wastewater Treatment in Greece: History, Development and Future Challenges

Although Greece has accomplished wastewater infrastructure construction to a large extent, as 91% of the country’s population is already connected to urban wastewater treatment plants (WWTPs), many problems still need to be faced. These include the limited reuse of treated wastewater and of the surplus sludge (biosolids) produced, the relative higher energy consumption in the existing rather aged WWTPs infrastructure, and the proper management of failing or inadequately designed septic tank/soil absorption systems, still in use in several (mostly rural) areas, lacking sewerage systems. Moreover, the wastewater treatment sector should be examined in the general framework of sustainable environmental development; therefore, Greece’s future challenges in this sector ought to be reconsidered. Thus, the review of Greece’s urban wastewater history, even from the ancient times, up to current developments and trends, will be shortly addressed. This study also notes that the remaining challenges should be analyzed in respect to the country’s specific needs (e.g., interaction with the extensive tourism sector), as well as to the European Union’s relevant framework policies and to the respective international technological trends, aiming to consider the WWTPs not only as sites for the treatment/removal of pollutants to prevent environmental pollution, but also as industrial places where energy is efficiently used (or even produced), resources’ content can be potentially recovered and reused (e.g., nutrients, treated water, biosolids), and environmental sustainability is being practiced overall.

Quantifying urban wastewater treatment sector's greenhouse gas emissions using a hybrid life cycle analysis method – An application on Shenzhen city in China

Substantial amounts of greenhouse gas (GHG) emissions generated at urban wastewater treatment plants (WWTP) are gaining increasing appreciation. Improving upon the commonly used Process-Based Life-Cycle Analysis (PLCA) and Environmentally-Extended Life-Cycle Analysis (EIO-LCA) models, we construct a Hybrid Life Cycle Analysis (HLCA) model and quantify both direct and indirect GHG emissions at the operational stage of WWTPs in Shenzhen, one of the fastest urbanizing cities in the world. Data are collected from 26 wastewater treatment plants in Shenzhen, out of all 32, covering 5 commonly used wastewater treatment technologies in China, i.e. Sequencing Batch Reactor, Oxidation Ditch, Biological Filter, AAO-MBR and AAO. The results show that WWTPs using AAO-MBR technology have the highest GHG emission intensity, averaging 0.79 tons per m3, primarily due to its large electricity intensity required. WWTPs using other technologies emit 0.27 to 0.39 tons of GHGs per m3 of wastewater treated. GHG emissions associated with electricity use occupy the largest share, ranging from 65 to 75%. Therefore, transforming the energy structure of the electric power sector to low-carbon sources can reduce WWTPs operational GHG emissions. In total, GHG emissions from Shenzhen's urban wastewater sector have increased from below 0.5 million tons in 2012 to over 0.6 million tons in 2017. Inter-model comparison shows that EIO-LCA substantially underestimates the urban wastewater sector's GHG emissions using the water sector's average parameters while PLCA also results in minor underestimations due the omission of indirect emissions in the production stage of chemicals and other material inputs.

Towards the Implementation of Circular Economy in the Wastewater Sector: Challenges and Opportunities

The advancement of science has facilitated increase in the human lifespan, reflected in economic and population growth, which unfortunately leads to increased exploitation of resources. This situation entails not only depletion of resources, but also increases environmental pollution, mainly due to atmospheric emissions, wastewater effluents, and solid wastes. In this scenario, it is compulsory to adopt a paradigm change, as far as the consumption of resources by the population is concerned, to achieve a circular economy. The recovery and reuse of resources are key points, leading to a decrease in the consumption of raw materials, waste reduction, and improvement of energy efficiency. This is the reason why the concept of the circular economy can be applied in any industrial activity, including the wastewater treatment sector. With this in view, this review manuscript focuses on demonstrating the challenges and opportunities in applying a circular economy in the water sector. For example, reclamation and reuse of wastewater to increase water resources, by paying particular attention to the risks for human health, recovery of nutrients, or highly added-value products (e.g., metals and biomolecules among others), valorisation of sewage sludge, and/or recovery of energy. Being aware of this situation, in the European, Union 18 out of 27 countries are already reusing reclaimed wastewater at some level. Moreover, many wastewater treatment plants have reached energy self-sufficiency, producing up to 150% of their energy requirements. Unfortunately, many of the opportunities presented in this work are far from becoming a reality. Still, the first step is always to become aware of the problem and work on optimizing the solution to make it possible.

Cross-sectoral synergy between municipal wastewater treatment, cement manufacture and petrochemical synthesis via clean transformation of sewage sludge

The municipal wastewater treatment sector requires sustainable management of sewage sludge to fundamentally contribute to building zero-waste cities.

IMPROVED MOBILE BED BIOFILM REACTORS TO TREAT CELLULOSIC WASTEWATERS

The wastewater treatment sector is a very dynamic field, in continuous development. New technologies are developed, or the existing ones are improved [1]. An efficient biological treatment is based on solid small plastic pieces (biofilm carriers) on which different types of microorganisms attach, develop and grow. This technology is known as Moving Bed Biofilm Reactor (MBBR) technology [2]. The most common materials used for the biofilm carriers’ realization are based on high density polyethylene. This technology is not yet applied for the treatment of the cellulosic wastewaters, since cellulose is hard to be removed by using conventional microorganisms that are usually used in biological wastewater treatment. Some of the authors propose an improved material for carriers to be used in tertiary treatment for textile, paper-mill or tannery wastewaters [3]. The biofilm carriers are adapted for fungal activity. The selected fungal strains (White Root Fungi) capable of removing cellulose from wastewaters [4] will be immobilized on special biofilm carriers. The improved carrier is designed to be used in a MBBR and to favour fungal development in the presence of competing bacteria. Several laboratory experiments related to the fungal attachment on the improved carriers were realized and the results are presented in the paper.

Anthropogenic methane plume detection from point sources in the Paris megacity area and characterization of their δ13C signature

Mitigating anthropogenic methane emissions is one of the available tools for reaching the near term objectives of the Paris Agreement. Characterizing the isotopic signature of the methane plumes emitted by these sources is needed to improve the quantification of methane sources at the regional scale. Urbanized and industrialized regions such as the Paris megacity are key places to better characterize anthropogenic methane sources. In this study, we present the results of the first mobile surveys in the Paris region, assessing methane point sources from 10 landfills (which in the regional inventory are the main emission sector of methane in the region), 5 gas storage sites (supplying Paris) and 1 waste water treatment (WWT) facility (Europe's largest, second worldwide). Local atmospheric methane concentration (or mixing ratio) enhancements in the source plumes were quantified and their δ13C in CH4 (further noted δ13CH4) signature characterized. Among the 10 landfills sampled, at 6 of them we detected atmospheric methane local enhancements ranging from 0.8 to 8.5 parts per million (ppm) with δ13CH4 signatures between −63.7 ± 0.3 permils (‰) to −58.2 ± 0.3‰. Among the 5 gas storage sites surveyed, we could observe that 3 of them were leaking methane with local methane concentration enhancements ranging from 0.8 to 8.1 ppm and δ13CH4 signatures spanning from −43.4 ± 0.5‰ to −33.8 ± 0.4‰. Dutch gas with a δ13CH4 signature of −33.8 ± 0.4‰ (typical of thermogenic gas) was also likely identified. The WWT site emitted local methane enhancements up to 4.0 ppm. For this site, two δ13CH4 signatures were determined as −51.9 ± 0.2‰ and −55.3 ± 0.1‰, typical of a biogenic origin. About forty methane plumes were also detected in the Paris city, leading to local concentration enhancements whose origin was in two cases interpreted as natural gas leaks thanks to their isotopic composition. However, such enhancements were much less common than in cities of North America. More isotopic surveys are needed to discriminate whether such urban methane enhancements are outcoming from gas line leaks and sewer network emanations. Furthermore, our results lead us to the conclusion that the regional emissions inventory could underestimate methane emissions from the WWT sector. Further campaigns are needed to assess the variability and seasonality of the sources and of their isotopic signature, and to estimate their emissions using methods independent of the inventory.

The Bioconversion of Sewage Sludge to Bio-Fuel: The Environmental and Economic Benefits.

This paper aims to analyze the economic feasibility of generating a novel, innovative biofuel—bioenergy—obtained from deposit bio-components by means of a pilot installation of sewage sludge bio-conversion. Fuel produced from sewage sludge biomass bears the potential of being considered a renewable energy source. In the present study, 23 bioconversion cycles were conducted taking into consideration the different contents, types of high carbohydrate additives, moisture content of the mixture as well as the shape of the bed elements. The biofuel was produced using post fermentation sewage sludge for industrial energy and heat generation. Based on the presented research it was concluded that the composite biofuel can be co-combusted with hard coal with the optimal percentage share within the range of 20–30% w/w. Sewage sludge stabilized by means of anaerobic digestion carried out in closed fermentation chambers is the final product. The average values of the CO2, CO, NO, NOx and SO2 concentrations in flue gas from co-combustion of a bioconversion product (20% w/w) and coal were 5.43%, 1903 ppm, 300 ppm, 303 ppm and 179 ppm, respectively. In total, within a period of 4.5 years of the plant operation, 1853 Mg of fuel was produced and successfully co-combusted with coal in a power plant. The research demonstrated that in the waste water treatment sector there exists energy potential in terms of calorific value which translates into tangible benefits both in the context of energy generation as well as environmental protection. Over 700,000 Mg of bio-sewage sludge is generated annually in Poland. According to findings of the study presented in the paper, the proposed solution could give 970,000 Mg of dry mass of biomass qualified as energy biomass replacing fossil fuels.