Modern Wastewater Treatment Plants Research Articles

Strategies for mitigating nitrous oxide production and decreasing the carbon footprint of a full-scale combined nitrogen and phosphorus removal activated sludge system

Nitrous oxide (N2O) emitted from biological nutrient removal activated sludge systems contributes significantly to the total carbon footprint of modern wastewater treatment plants. In the present study, N2O production and emissions were experimentally determined in a large-scale plant (220,000 PE) employing combined nitrogen (N) and phosphorus (P) removal. As a modelling tool, the Activated Sludge Model 2d (ASM2d) was extended with modules describing multiple N2O production pathways and N2O liquid-gas transfers. The new model was calibrated and validated using the results of laboratory experiments and full-scale measurements. Different operational strategies were evaluated following the proposed model-based procedure. Heterotrophic denitrification was found to be the predominant pathway of N2O production under both anoxic and aerobic conditions. This behaviour could primarily be attributed to the predominant abundance of heterotrophic denitrifiers over nitrifiers. Simulations revealed that the optimal solution for minimizing liquid N2O production is to set the dissolved oxygen concentration in the aerobic zone from 1 to 2 mg O2/L and to enhance the mixed liquor recirculation rate (MLR) (>500% of the influent flowrate) while not compromising effluent standards. Regarding the actual conditions, the potential reduction in the carbon footprint was estimated to be 10% by applying the proposed operational strategy. The results suggest that considerable improvements can be achieved without substantial upgrades and increased costs.

Continuous-flow aerobic granulation in plug-flow bioreactors fed with real domestic wastewater

This pilot study was designed to explore the feasibility of achieving successful aerobic granulation in continuous flow infrastructure like that existing in modern wastewater treatment plants (WWTPs). Results demonstrated that aerobic granulation of activated sludge can be achieved in plug-flow reactors (PFRs) fed with primary effluent from a domestic WWTP with seasonal temperature variation between 10 and 22.5 °C. It took about 90 days during the reactor startup to reach a state of sustained aerobic granulation. The characteristics of aerobic granules formed were comparable to those measured in sequential batch reactors (SBRs). The feast-to-famine concentration profiles measured in the plug-flow pilot reactors were found to be in line with those present in the full-scale treatment trains, lending support to the feasibility of converting existing infrastructure to continuous flow aerobic granulation systems. A selection pressure based on settling velocity (Vs) was applied in a Vs selector to retain bioparticles with Vs greater than ~9–9.75 m h−1. It was theorized that an external Vs selection pressure would be necessary but would not be the sole condition sufficient to drive aerobic granulation. The alternating feast-to-famine internal selection provided by the PFRs is also believed to be a required condition to transform biomass from flocs toward dense and compact aerobic granules. While the pilot-scale Plug-flow Aerobic Granulation (PAG) reactor achieved similar COD and NH3 removal efficiencies as the full-scale WWTP treatment train, its effluent from Vs selector contained an average of 138 mg L−1 total suspended solids (TSS) as a result of the biomass ‘wash-out” by the Vs selection pressure. Pilot results suggest a second clarifier for polishing, in addition to the Vs selector, may be needed in a full-scale application of the technique unless other downstream processes (flocculation, sedimentation, filtration) are provided to reach final water quality goals.

Innovative graphene microbial platforms for domestic wastewater treatment

Supplying clean water to fulfill human requirements is one of this century’s priorities. Global water resources are barely aligned with the rising demand, which is further aggravated by rising population, climate change and water quality problems. Consequently, there is a persistent need for innovative technologies to valorize unconventional water resources such as domestic wastewater. Graphene holds promising prospects in developing domestic wastewater treatment to qualitatively enhance treatment efficiency and quantitatively increase water supply. This review highlights the existing wastewater treatment processes along with their challenges according to South Australian wastewater treatment plants (WWTPs) which are representative of many modern WWTPs. The discussion will also cover the current and potential applications of graphene for domestic wastewater treatment, as well as obstacles and research priorities required for commercialization.

Comprehensive stabilization of all streams of solid residues formed during sewage sludge thermal treatment – Case study

Abstract Modern wastewater treatment plants are currently struggling with the problem of processing and ecological management of sewage sludge. Thermal utilization is a frequently used practice of excess sludge utilization especially in large wastewater treatment plants, which seems to be a quite promising concept. However, during thermal treatment, fractions of ashes and dusts are generated. Such wastes, especially the dust fraction, can be potentially harmful to the environment. Therefore, the mentioned wastes should be stabilized. In this paper, a comprehensive method of stabilization is presented. Ash fraction, produced during sewage sludge thermal treatment, is used for dust fraction stabilization, hence no other solid medias, except cheap, commercially available cement, have to be used for stabilization. Laboratory and industrial scale trials were performed. Based on the results of the conducted research it can be stated that dust and ash fractions obtained from one facility can be stabilized together and the final product is safe for the environment since no potentially toxic elements are leached from the materials. There is a potential for improving the proposed method of stabilization to create fully environmentally safe construction materials.

Pharmaceuticals and personal care products (PPCPs) in Arctic environments: indicator contaminants for assessing local and remote anthropogenic sources in a pristine ecosystem in change

A first review on occurrence and distribution of pharmaceuticals and personal care products (PPCPs) is presented. The literature survey conducted here was initiated by the current Assessment of the Arctic Monitoring and Assessment Programme (AMAP). This first review on the occurrence and environmental profile of PPCPs in the Arctic identified the presence of 110 related substances in the Arctic environment based on the reports from scientific publications, national and regional assessments and surveys, as well as academic research studies (i.e., PhD theses). PPCP residues were reported in virtually all environmental compartments from coastal seawater to high trophic level biota. For Arctic environments, domestic and municipal wastes as well as sewage are identified as primary release sources. However, the absence of modern waste water treatment plants (WWTPs), even in larger settlements in the Arctic, is resulting in relatively high release rates for selected PPCPs into the receiving Arctic (mainly) aquatic environment. Pharmaceuticals are designed with specific biochemical functions as a part of an integrated therapeutically procedure. This biochemical effect may cause unwanted environmental toxicological effects on non-target organisms when the compound is released into the environment. In the Arctic environments, pharmaceutical residues are released into low to very low ambient temperatures mainly into aqueous environments. Low biodegradability and, thus, prolonged residence time must be expected for the majority of the pharmaceuticals entering the aquatic system. The environmental toxicological consequence of the continuous PPCP release is, thus, expected to be different in the Arctic compared to the temperate regions of the globe. Exposure risks for Arctic human populations due to consumption of contaminated local fish and invertebrates or through exposure to resistant microbial communities cannot be excluded. However, the scientific results reported and summarized here, published in 23 relevant papers and reports (see Table S1 and following references), must still be considered as indication only. Comprehensive environmental studies on the fate, environmental toxicology, and distribution profiles of pharmaceuticals applied in high volumes and released into the Nordic environment under cold Northern climate conditions should be given high priority by national and international authorities.

Multi-objective performance assessment of wastewater treatment plants combining plant-wide process models and life cycle assessment

Abstract Multi-objective performance assessment of operational strategies at wastewater treatment plants (WWTPs) is a challenging task. The holistic perspective applied to evaluation of modern WWTPs, including not only effluent quality but also resource efficiency and recovery, global environmental impact and operational cost calls for assessment methods including both on- and off-site effects. In this study, a method combining dynamic process models – including greenhouse gas (GHG), detailed energy models and operational cost – and life cycle assessment (LCA) was developed. The method was applied and calibrated to a large Swedish WWTP. In a performance assessment study, changing the operational strategy to chemically enhanced primary treatment was evaluated. The results show that the primary objectives, to enhance bio-methane production and reduce GHG emissions were reached. Bio-methane production increased by 14% and the global warming potential decreased by 28%. However, due to increased consumption of chemicals, the operational cost increased by 87% and the LCA revealed that the abiotic depletion of elements and fossil resources increased by 77 and 305%, respectively. The results emphasize the importance of using plant-wide mechanistic models and life cycle analysis to capture both the dynamics of the plant and the potential environmental impacts.

Enterobius vermicularis as a Novel Surrogate for the Presence of Helminth Ova in Tertiary Wastewater Treatment Plants.

Significant effort has gone into assessing the fate and removal of viruses, bacteria, and protozoan parasites during wastewater treatment to provide data addressing potential health risks associated with reuse options. Comparatively less is known about the fate of parasitic worm species ova in these complex systems. It is largely assumed that these helminths settle, are removed with the sludge, and consequently represent a relatively low risk for wastewater reuse applications. However, helminths are a highly diverse group of organisms that display a wide range of physical properties that complicate the application of a single treatment for helminth reduction during wastewater treatment. Moreover, their diverse biological and physical properties make some ova highly resistant to both disinfection (i.e., with chlorine or UV treatment) and physical removal (settling) through the wastewater treatment train, indicating that there may be reason to broaden the scope of our investigations into whether parasitic worm eggs can be identified in treated wastewater. The ubiquitous human parasitic nematode Enterobius vermicularis (pinworm) produces small, buoyant ova. Utilizing a novel diagnostic quantitative PCR (qPCR), this study monitored E. vermicularis presence at two full-scale wastewater treatment plants over the course of 8 months and demonstrated incomplete physical removal of E. vermicularis ova through tertiary treatment, with removal efficiencies approximating only 0.5 and 1.6 log10 at the two wastewater treatment plants based on qPCR. These findings demonstrate the need for more-diverse surrogates of helminthic ova to fully assess treatment performance with respect to reclaimed wastewaters.IMPORTANCE Helminths, despite being a diverse and environmentally resistant class of pathogens, are often underestimated and ignored when treatment performance at modern wastewater treatment plants is considered. A one-size-fits-all surrogate for removal of helminth ova may be inappropriate to adequately assess risk and ensure public safety when treated and partially treated wastewaters are encountered. This study argues for the use of human pinworm as a conservative indicator of the presence of helminth ova due to its small size, buoyancy, prevalence in humans, and environmental resistance.

Removal of several pesticides in a falling water film DBD reactor with activated carbon textile: Energy efficiency

Bio-recalcitrant micropollutants are often insufficiently removed by modern wastewater treatment plants to meet the future demands worldwide. Therefore, several advanced oxidation techniques, including cold plasma technology, are being investigated as effective complementary water treatment methods. In order to permit industrial implementation, energy demand of these techniques needs to be minimized. To this end, we have developed an electrical discharge reactor where water treatment by dielectric barrier discharge (DBD) is combined with adsorption on activated carbon textile and additional ozonation. The reactor consists of a DBD plasma chamber, including the adsorptive textile, and an ozonation chamber, where the DBD generated plasma gas is bubbled. In the present paper, this reactor is further characterized and optimized in terms of its energy efficiency for removal of the five pesticides α-HCH, pentachlorobenzene, alachlor, diuron and isoproturon, with initial concentrations ranging between 22 and 430 μg/L. Energy efficiency of the reactor is found to increase significantly when initial micropollutant concentration is decreased, when duty cycle is decreased and when oxygen is used as feed gas as compared to air and argon. Overall reactor performance is improved as well by making it work in single-pass operation, where water is flowing through the system only once. The results are explained with insights found in literature and practical implications are discussed. For the used operational conditions and settings, α-HCH is the most persistent pesticide in the reactor, with a minimal achieved electrical energy per order of 8 kWh/m3, while a most efficient removal of 3 kWh/m3 or lower was reached for the four other pesticides.

A model and tool to calculate life cycle inventories of chemicals discharged down the drain

The aim of this article is to present a new model and tool to calculate life cycle inventories (LCIs) of chemicals discharged down the drain. Exchanges with the technosphere and the environment are attributed for based on the predicted behaviour of individual chemicals in the wastewater treatment plant (WWTP) and following discharge to the aquatic environment, either through the treated effluent or directly when there is no connection to WWTP. The described model is programmed in a stand-alone spreadsheet, WW LCI. The model includes treatment in a modern WWTP and sludge disposal as well as the greenhouse gas (GHG) and nutrient emissions from degradation in the environment. The model fundamentals are described, and its application is shown with six industrial chemicals: sodium carbonate, ethanol, tetraacetylethylenediamine (TAED), diethylenetriamine penta(methylene phosphonic acid) (DTPMP), zeolite A and sodium tripolyphosphate (STPP). This application considers two scenarios: Germany, with full connection to WWTP, and a generic direct discharge scenario. The scenario with WWTP connection is assessed with WW LCI as well as with the wastewater treatment model developed for ecoinvent. Results are presented for key LCI flows and for life cycle impact assessment (LCIA), focusing on GHG emissions, freshwater ecotoxicity and marine and freshwater eutrophication. GHG emissions predicted by WW LCI differ to those predicted by the ecoinvent model, with the exception of sodium carbonate. For zeolite A and DTPMP, WW LCI predicts GHG emissions 330 higher and 12.5 times lower, respectively. Eutrophication scores are lower for WW LCI as the German scenario considers more optimistic nutrient removal rates than the default ones from the ecoinvent model. Freshwater ecotoxicity is mainly driven by the magnitude of the USEtox characterization factors; however, the ecoinvent model cannot accommodate chemical-specific toxicity assessments. When WW LCI is used to compare a direct discharge scenario with the German scenario, differences are found in all three impact categories. WW LCI provides a comprehensive and chemical-specific inventory, constituting an advance over previous models using generic descriptors such as biological oxygen demand. This level of detail comes at the price of an increased effort for collecting input data as well as the need to identify individual chemicals in wastewater prior to the assessment. The LCIs generated through this model can then be applied in the context of LCA studies where each chemical contributes to the total life cycle impacts of a product or service.

Methane Component of the Modern WWTP Biogas as an Alternative Energy Source

This paper presents an analysis of the company for the production of soft drinks wastewater treatment plants (WWTP) and indicators on biogas as a byproduct. Shown new technology of anaerobic reactors and cleaning properties of the main product - the anaerobic sludge, from which biogas released. Offered to re-evaluate the potential of using methane component of biogas. The proposed approach for the use of biogas would allow such enterprises to carry out a comprehensive approach to solving the problems of energy efficiency and the use of the significant potential of secondary energy resources.

The development of aCurve: a rich internet application for process analysis at Käppala WWTP

In modern wastewater treatment plants (WWTPs) the demand for advanced process control is a prerequisite for a smooth and energy efficient operation of the plant. Most large WWTPs have distributed control systems (DCS) and advanced supervisory control and data acquisition systems installed for operation and supervision of the plant. Normally the DCS is sufficient for the operators to run the plant efficiently. However, data is also often wanted by others than the operators (e.g. research engineers, students, scientists or consultants) for analysis and reporting or to perform different calculations. At Käppala a new web based program, aCurve, has been developed to meet such needs. The program is a so-called Rich Internet Application and is accessible via internet and requires no desktop installation. The main features of the program are rapid presentation of graphs, easy zoom, changing resolution, performing calculations and plotting the results and simple statistics (e.g. mean values, integration, maximum and minimum values). If advanced calculations are acquired, the data is easily exported as an xlsx-file for use in Microsoft Excel or other software capable of reading the Office Open XML SpreadsheetML File format. aCurve can also produce automatically updated reports that are built in Microsoft Excel. This makes the reporting function flexible and any user with Excel knowledge can create and edit a report with a professional result. The reports can easily be shared throughout the organization. The program has replaced other expensive and complex desktop application that were previously used at the Käppala WWTP. Process and laboratory data that can be used for follow up of plant performance has now become available for a greater part of the staff which improve the quality assurance of reported data to authorities and researchers.

Appraisal of changes in sewage sludge management

A positive energy balance caused by accelerated production of CH4 and additional financial benefits associated with shorter retention times, reduction in volumes, easier dewatering, enhanced hygiene, etc., are the reasons why most modern wastewater treatment plants are newly equipped with hydrothermal pretreatment units. This study examined how the changes in composition of the pretreated sewage sludge fermentation residues manifested themselves in subsequent processing by pyrolysis, both in terms of technology and financial impacts. It has been found that concentrations of heavy metals and other hazardous inhibitors might increase; however, the overall biotoxicity is lower due to their immobilization in the charred mass. Moreover, charring of the fermentation residues results in significant financial as well as technological benefits.

Removal of atrazine in water by combination of activated carbon and dielectric barrier discharge

Efficiency of modern wastewater treatment plants to remove or decompose persistent contaminants in low concentration is often insufficient to meet the demands imposed by governmental laws. Novel, efficient and cheap methods are required to address this global issue. We developed a new type of plasma reactor, in which atrazine decomposition by atmospheric dielectric barrier discharge (DBD) in dry air is combined with micropollutant adsorption on activated carbon textile and with extra bubbling of generated ozone. Investigation of reaction kinetics and by-product analysis shows that increasing input power with a factor 3.5 leads to deeper atrazine oxidation without significantly changing energy yield of atrazine removal. By-products of first and later generations are detected with HPLC–MS analysis in water and adsorbed on the activated carbon textile. Our reactor is compared in energy efficiency with reactors described in literature, showing that combination of plasma discharge with pollutant adsorption and ozone recycling is attractive for future applications of water treatment.

Electricity generation and struvite recovery from human urine using microbial fuel cells

ABSTRACTBACKGROUNDUrine is an abundant waste product which requires energy intensive treatment processes in modern wastewater treatment plants. However urine can be utilised as fertiliser in the form of struvite. Microbial fuel cells (MFCs) are a promising technology for treating waste while producing electricity. Combining these two approaches, a 3‐stage MFC/struvite extraction process system was developed and its feasibility tested in order to maximise urine utilisation in terms of electricity generation and struvite recovery.RESULTSIn the first stage, while generating electrical energy, MFCs accelerated urea hydrolysis, which was beneficial for the struvite precipitation process in the following stage. After collecting struvite by adding magnesium into the initial effluent, the supernatant was used at the final stage for additional power and more efficient COD reduction. In total, 82% of PO43−‐P and 20% of COD of undiluted human urine were removed by the 3‐stage system. Also 14.32 W m−3 (absolute power: 358 µW) and 11.76 W m−3 (absolute power: 294 µW) of power was produced from the 1st and 3rd stages of the system, respectively, during operation.CONCLUSIONThis work shows how MFCs and struvite precipitation could be integrated for both energy generation and resource recovery from urine, leading to a more sustainable energy future. © 2014 Society of Chemical Industry

Selecting sewage sludge treatment alternatives in modern wastewater treatment plants using environmental decision support systems

The importance of the sewage sludge treatment within the field of wastewater treatment plants (WWTPs) suggests new dimensions of analysis where the relevance of economic criteria combined with the associated environmental issues are increasing the sludge management complexity. For supporting the decision process and for comparative purposes, this study assesses five alternative configurations for sludge treatment, namely: mesophilic and termophilic anaerobic digestion plus composting, incineration, gasification, and supercritical water oxidation (SCWO). The global warming potential (GWP) and the annual cash flow of each alternative are used to estimate a composite indicator for each alternative. Stakeholders' preferences are integrated into the assessment through the development of five scenarios prioritizing economic or environmental aspects. A case study for a 1 million person equivalent WWTP proved that SCWO is the most adequate option if economic and environmental criteria are considered equally important. However, if the economic assessment is prioritized over the environmental one, thermophilic anaerobic digestion followed by composting turned out to be the most appropriate option. The proposed approach contributes to the implementation of more suitable sewage sludge treatment lines since it provides an indicator for each alternative embracing economic and GWP issues.

Applications of ozone for modern wastewater treatment

Modern Wastewater Treatment Plants (WWTPs) efficiently eliminate organic pollution down to Biological Oxygen Demand (BOD) and Suspended Solids (SS) values of less than 30 mg/l. However, these treated effluents still contain biologically Persistent Organic Matter (POM), characterised by a Chemical Oxygen Demand (COD) of between 50 and more than 100 mg/l. Industrial WWTP effluents have COD concentrations of several hundred mg/l. Under certain conditions of discharge imposed to the effluent, POM abatement is necessary. Elimination of pathogenic micro-organisms, i.e., disinfection and inhibition of acute toxicity, is also required. Another class of toxic compounds, Micro-Pollutants (MPs), present in WWTP effluents in much lower concentrations, µg/l even ng/l, has become a serious matter of concern. Ozonation, as a complementary stage in the treatment sequence of a WWTP, alone or in combination with biofiltration, has been demonstrated by multiple laboratory–pilot tests and existing operating plants to be an efficient and economically sound technology for the abatement of and POM and MPs and for disinfection. The purpose of this essay is to present ozone with its state-of-the-art features, from a qualitative as well as a quantitative aspect, with examples of modern applications for improved wastewater treatment.

Effect of cerium dioxide, titanium dioxide, silver, and gold nanoparticles on the activity of microbial communities intended in wastewater treatment

Growth in production and use of nanoparticles (NPs) will result increased concentrations of these in industrial and urban wastewaters and, consequently, in wastewater-treatment facilities. The effect of this increase on the performance of the wastewater-treatment process has not been studied systematically and including all the microbial communities involved in wastewater treatment. The present work investigates, by using respiration tests and biogas-production analysis, the inhibitory effect of four different commonly used metal oxide (CeO 2 and TiO 2) and zero-valent metal (Ag and Au) nanoparticles on the activity of the most important microbial communities present in a modern wastewater-treatment plant. Specifically, the actions of ordinary heterotrophic organisms, ammonia oxidizing bacteria, and thermophilic and mesophilic anaerobic bacteria were tested in the presence and absence of the nanoparticles. In general, CeO 2 nanoparticles caused the greatest inhibition in biogas production (nearly 100%) and a strong inhibitory action of other biomasses; Ag nanoparticles caused an intermediate inhibition in biogas production (within 33–50%) and a slight inhibition in the action of other biomasses, and Au and TiO 2 nanoparticles caused only slight or no inhibition for all tested biomasses.

Effect of Pressure, Water Depth and Water Flow Rate on Oxygen Saturation Level in Activated Sludge Process

Problem statement: The role of aeration in activated sludge process is to provide oxygen to microorganisms as they assimilate the organic carbon compounds and digest a portion of them to carbon dioxide and water, sulfate and nitrate compounds. The water aeration equipment used in this process consumes as much as 60-80% of total power requirements in modern wastewater treatment plants. Approach: The objective of this study is to enhance the oxygen transfer in aeration tank in activated sludge process by increasing pressure inside the part of aeration tank to increase the saturation level of dissolved oxygen in wastewater. The diffuser cap model is the experimental model which was used to show the effect of increasing pressure on oxygen transfer level. Three cases were considered, the first used without diffuser cap, the second with diffuser cap and the third with diffuser cap and plastic strips. Results: Obtained results show that in case of using the model with diffuser cap enhanced the oxygen level by about 5% than in case of without diffuser cap while that of adding plastic strips enhanced the oxygen level by about 7%. The variation of water flow showed that increasing water flow rate from 1-2 L min-1 decreased the oxygen saturation level by about 6%. Furthermore, increasing water depth from 15-60 cm increased the oxygen level by about 40%. Conclusion: The diffuser cap model showed that the increase of pressure and water depth increased the dissolved oxygen level while increasing water flow rate decreased the dissolved oxygen level.

Aplicações de cromatografia líquida de alta eficiência para o estudo de poluentes orgânicos emergentes

Emerging organic pollutants (EOP) include many environmental contaminants based on commercial products such as pharmaceuticals, personal care products, detergents, gasoline, polymers, etc. EOP may be candidates for future regulation as they offer potential risk to environmental and human health due to their continual entrance into the environment and to the fact that even the most modern wastewater treatment plants are not able to totally transform / remove these compounds. High performance liquid chromatography is recommended to separate emerging organic pollutants with characteristics of high polarity and low volatility, especially pharmaceuticals, from environmental matrices.

Design and development of decentralized water and wastewater technologies: a combination of safe wastewater disposal and fertilizer production

Modern wastewater treatment plants are often inappropriate for communities in developing countries. Such communities lack the funding, resources and skilled labour required to implement, operate, and maintain these plants. This research was conducted to investigate and establish an appropriate wastewater treatment system for the district of Gunung Kidul, Indonesia. Due to its lack of water during the dry season, this district is considered one of the poorest areas in the nation. First, wastewater was stored in septic tank units for a retention time of 26 days. Anaerobic conditions occurred, resulting in an 80% reduction of initial COD. The retained sludge was well stabilized with great potential, if dewatered, for reuse as fertilizer. Consequently, supernatant was separated for experiments consisting of lab scale aerobic sand filtering unit. Through filtration, further removals of COD (about 30%) and pathogens were achieved. Rich in nitrogen, the resulting effluent could be used for irrigation and soil conditioning. With faecal sludge and also a mixture of septic sludge and food waste, the hydrolysis stage of anaerobic digestion was examined. This paper discusses the laboratory findings in Karlsruhe and the design and implementation of a treatment system in Glompong, Indonesia.