RESUMEN
Two-compartment electrodialytic extraction (2C-ED) is a one-step process for the simultaneous phosphorous extraction and separation of heavy metals from sewage sludge ash (SSA). The process is driven by an applied electric DC field, which can be supplied from renewable sources. The proof-of-concept of the method was conducted in small laboratory cells; however, upscaling to a continuous 2C-ED process, which additionally can treat SSA suspensions at a low liquid-to-solid (L:S) ratio, requires a new design. This paper presents such a new design. In principle, ED consists of two compartments separated by a cation exchange membrane. One compartment contains a suspension of SSA in water and the anode. A cathode is placed in the other compartment. Electrolysis at the anode acidifies the suspension causing the dissolution of phosphorous and heavy metals. The heavy metals are separated from the suspension by electromigration into the catholyte, whereas the dissolved phosphorous remains in the dispersion solution. In the new design, the SSA was suspended in a tube-shaped reactor with the cation exchange membrane covering the outside. The reactor was placed in a container with the catholyte. Periodically turning off the reactor kept SSA in suspension even at a low L:S ratio without corners and pockets where the SSA otherwise tends to settle. Five 2C-ED experiments were conducted with 1.5 to 3 kg SSA at varying currents and durations. Up to 89% P was extracted. The extracted P was concentrated in the dispersion solution of the SSA suspension, where the obtained P-related concentrations of heavy metals were far below the limiting values for spreading on agricultural land. The experiments underlined that treating the SSA in a suspension with a low L:S ratio is advantageous. A comparison to previous laboratory experiments in small cells treating 50 g SSA shows a significantly more efficient use of the applied current in the new reactor setup. Thus, the new reactor design for 2C-ED fulfilled the set criteria for the operation and did additionally result in a higher efficiency than the laboratory setups, i.e., the design can be the first step towards an upscaling.
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Metales Pesados , Aguas del Alcantarillado , Eliminación de Residuos Líquidos/métodos , Fósforo , CationesRESUMEN
We present an assessment of greenhouse gas emissions from urban wastewater treatment plants in Europe. We propose a quantification in terms of emission factors (kilograms of carbon dioxide equivalents (CO2e) per population equivalent (PE) and year) taking into account all phases of wastewater treatment, from the construction of the infrastructure to the discharge of treated effluents. The assessment includes (1) life-cycle emissions of infrastructure; (2) emissions of dissolved methane in the sewer networks; (3) direct emissions of nitrous oxide and methane from the treatment processes; (4) emissions due to COD and nitrogen in the effluents; (5) indirect emissions due to the generation of electricity and the production of reagents; and (6) emission credits due to energy recovery or biomethane export associated with the anaerobic digestion of sludge. Our estimated emissions range between approximately 50 and 125 kg CO2e/PE/y depending on the type of treatment plant, of which about 20 to 40 are embedded in the infrastructure. We estimate that direct nitrous oxide emissions and indirect electricity emissions are the main contributors in the operation phase, followed by direct methane emissions. By extrapolating these emissions to the ensemble of the European Union's wastewater treatment plants, we estimate a cumulative emission of about 35 million tonnes CO2e/year, of which ca. 14 are due to the infrastructure. We analyse various scenarios to reduce emissions, showing that the efficient use of electricity at the plant and the decarbonisation of electricity would significantly help to improve the CO2e footprint of the WWTPs. In particular, the recovery of methane from biogas and the decarbonisation of electricity may reduce emissions below 27 million tonnes CO2e/year. Extending N removal to the whole territory for all plants above 10,000 PE may contribute to decrease direct nitrous oxide emissions.
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Gases de Efecto Invernadero , Aguas Residuales , Efecto Invernadero , Metano/análisis , Óxido Nitroso/análisis , Eliminación de Residuos LíquidosRESUMEN
The activated sludge wastewater treatment process has been thoroughly researched in more than 100 years, yet there are still operational challenges that have not been fully resolved. Such a challenge is the control of filamentous bulking caused by the overgrowth of certain filamentous bacteria. In this study, we tested different mitigation strategies to reduce filamentous bulking, caused by two common filamentous genera found in full-scale water resource recovery facilities (WRRF), Candidatus Microthrix and Candidatus Amarolinea. PAX dosing, ozone addition, hydrocyclone implementation, and the addition of nano-coagulants were tested as mitigation strategies in four parallel treatment lines in a full-scale WRRF over three consecutive years. Unexpectedly, the activated sludge settleability was not affected by any of the mitigation strategies. Some of the strategies appeared to have a strong mitigating effect on the two filamentous species. However, detailed analyses of the microbial communities revealed strong recurrent seasonal variations in all four lines, including the control line which masked the real effect. After removing the effect of the seasonal variation by using a time-series decomposition approach, it was clear that the filamentous bacteria were mostly unaffected by the mitigation strategies. Only PAX dosing had some effect on Ca. Microthrix, but only on one species, Ca. Microthrix subdominans, and not on the most common Ca. Microthrix parvicella. Overall, our study shows the importance of long-term monitoring of microbial communities at species level to understand the normal seasonal pattern to effectively plan and execute full-scale experiments. Moreover, the results highlight the importance of using parallel reference treatment lines when evaluating the effect of mitigation strategies in full-scale treatment plants.
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Actinobacteria , Microbiota , Bacterias , Estaciones del Año , Aguas del Alcantarillado/microbiología , Eliminación de Residuos Líquidos/métodosRESUMEN
To reduce greenhouse gas emissions and promote resource recovery, many wastewater treatment operators are retrofitting existing plants to implement new technologies for energy, nutrient and carbon recovery. In literature, there is a lack of studies that can unfold the potential environmental and economic impacts of the transition that wastewater utilities are undertaking to transform their treatment plants to water resource recovery facilities (WRRFs). When existing, literature studies are mostly based on simulations rather than real plant data and pilot-scale results. This study combines life cycle assessment and economic evaluations to quantify the environmental and economic impacts of retrofitting an existing wastewater treatment plant (WWTP), which already implements energy recovery, into a full-scale WRRF with a series of novel technologies, the majority of which are already implemented full-scale or tested through pilot-scales. We evaluate five technology alternatives against the current performance of the WWTP: real-time N2O control, biological biogas upgrading coupled with power-to-hydrogen, phosphorus recovery, pre-filtration carbon harvest and enhanced nitrogen removal. Our results show that real-time N2O control, biological biogas upgrading and pre-filtration lead to a decrease in climate change and fossil resource depletion impacts. The implementation of the real-time measurement and control of N2O achieved the highest reduction in direct CO2-eq emissions (-35%), with no significant impacts in other environmental categories. Biological biogas upgrading contributed to counterbalancing direct and indirect climate change impacts by substituting natural gas consumption and production. Pre-filtration increased climate change reduction by 13%, while it increased impacts in other categories. Enhanced sidestream nitrogen removal increased climate change impacts by 12%, but decreased marine eutrophication impacts by 14%. The reserve base resource depletion impacts, however, were the highest in the plant configurations implementing biological biogas upgrading coupled with power-to-hydrogen. Environmental improvements generated economic costs for all alternatives except for real-time N2O control. The results expose possible environmental and economic trade-offs and hotspots of the journey that large wastewater treatment plants will undertake in transitioning into resource recovery facilities in the coming years.
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Eliminación de Residuos Líquidos , Purificación del Agua , Biocombustibles , Aguas Residuales , Recursos HídricosRESUMEN
This work aims to obtain full-scale N2O emission characteristics translatable into viable N2O control strategies and conduct full-scale testing of the proposed N2O control concepts. Data of a long-term monitoring campaign was first used to quantify full-scale N2O emission and probe into the seasonal pattern. Then trends between N2O production/emission and process variables/conditions during typical operating cycles were revealed to explore the dynamic N2O emission behavior. A multivariate statistical analysis was performed to find the dependency of N2O emission on relevant process variables. The results show for the first time that relatively low/high N2O emission took place in seasons with a decreasing/increasing trend of water temperature, respectively. Aerobic phase contributed to N2O production/emission probably mainly through the hydroxylamine pathway. Comparatively, heterotrophic bacteria had a dual role in the anoxic phase and could be responsible for both net N2O production and consumption. Incomplete denitrification might contribute mainly to the N2O production/emission in the anoxic phase and the accumulation of N2O to be significantly emitted in the following cycle due to the competition between different denitrification steps for electron donors. Therefore, properly extending the length of anoxic phase could serve as a potential control means to regulate N2O accumulation in the anoxic phase. The full-scale testing not only verified the efficacy of reduced dissolved oxygen set-point in reducing N2O emission by 60%, but also confirmed the proposed concepts of control over the aerobic and anoxic phases collectively.
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Aguas del Alcantarillado , Aguas Residuales , Reactores Biológicos , Desnitrificación , Óxido NitrosoRESUMEN
We investigated the possibility of applying performic acid (PFA) and peracetic acid (PAA) for disinfection of combined sewer overflow (CSO) in existing CSO management infrastructures. The disinfection power of PFA and PAA towards Escherichia coli (E. coli) and Enterococcus was studied in batch-scale and pre-field experiments. In the batch-scale experiment, 2.5 mg L(-1) PAA removed approximately 4 log unit of E. coli and Enterococcus from CSO with a 360 min contact time. The removal of E. coli and Enterococcus from CSO was always around or above 3 log units using 2-4 mg L(-1) PFA; with a 20 min contact time in both batch-scale and pre-field experiments. There was no toxicological effect measured by Vibrio fischeri when CSO was disinfected with PFA; a slight toxic effect was observed on CSO disinfected with PAA. When the design for PFA based disinfection was applied to CSO collected from an authentic event, the disinfection efficiencies were confirmed and degradation rates were slightly higher than predicted in simulated CSO.
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Desinfectantes/análisis , Desinfección/métodos , Formiatos/análisis , Ácido Peracético/análisis , Eliminación de Residuos Líquidos/métodos , Aguas Residuales/microbiología , Contaminantes Químicos del Agua/análisis , Drenaje de Agua/métodos , Aguas Residuales/química , Microbiología del AguaRESUMEN
The objective of this paper is to demonstrate the full-scale feasibility of the phenomenological dynamic influent pollutant disturbance scenario generator (DIPDSG) that was originally used to create the influent data of the International Water Association (IWA) Benchmark Simulation Model No. 2 (BSM2). In this study, the influent characteristics of two large Scandinavian treatment facilities are studied for a period of two years. A step-wise procedure based on adjusting the most sensitive parameters at different time scales is followed to calibrate/validate the DIPDSG model blocks for: 1) flow rate; 2) pollutants (carbon, nitrogen); 3) temperature; and, 4) transport. Simulation results show that the model successfully describes daily/weekly and seasonal variations and the effect of rainfall and snow melting on the influent flow rate, pollutant concentrations and temperature profiles. Furthermore, additional phenomena such as size and accumulation/flush of particulates of/in the upstream catchment and sewer system are incorporated in the simulated time series. Finally, this study is complemented with: 1) the generation of additional future scenarios showing the effects of different rainfall patterns (climate change) or influent biodegradability (process uncertainty) on the generated time series; 2) a demonstration of how to reduce the cost/workload of measuring campaigns by filling the gaps due to missing data in the influent profiles; and, 3) a critical discussion of the presented results balancing model structure/calibration procedure complexity and prediction capabilities.
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Simulación por Computador , Modelos Químicos , Eliminación de Residuos Líquidos/métodos , Contaminación del Agua/análisis , Purificación del Agua/métodos , Análisis de la Demanda Biológica de Oxígeno , Estaciones del Año , Temperatura , Movimientos del Agua , Contaminantes Químicos del Agua/análisisRESUMEN
A model for the description of the SS distribution in a full-scale recirculating activated sludge WWTP was developed. The model, based on conservation principles, uses on-line plant data as model inputs, and provides a prediction of the SS load in the inlet to the secondary clarifiers and the SS distribution in the WWTP as outputs. The calibrated model produces excellent predictions of the SS load to the secondary clarifiers, an essential variable for the operation of the aeration tank settling (ATS) process. A case study illustrated how the calibrated SS distribution model can be used to evaluate the potential benefit of ATS implementation on a full-scale recirculating WWTP. A reduction of the maximum SS peak load to the secondary clarifiers with 24.9% was obtained with ATS, whereas the cumulative SS load to the clarifiers is foreseen to be reduced with 22.5% for short rain events (4 hours duration) and with 16.6% for long rain events (24 hours duration). The SS distribution model is a useful tool for off-line studies of the potential benefits to be obtained by introducing ATS on a recirculating WWTP. Finally, the successful operation of the ATS process on the full-scale plant is illustrated with data.