Small Wastewater Treatment Plants Research Articles

Design of the installation of a small wastewater treatment plant using a Tubular Biological Reactor in the Xochimilco canals

This work proposes the generation of a preliminary project based on the biological treatment process called the Tubular Biological Reactor (RBT), to treat the wastewater discharges that contaminate the Xochimilco canals. The main focus of the work is: through the use of the FEL methodology to generate a design for the installation of a small wastewater treatment plant and thus be able to establish a treatment train based on RBT technology and thus translate it into a diagram of process blocks, subsequently constructing the Process Flow Diagram (DFP) which includes the pre-treatment equipment and main treatments that make up the treatment train, a material balance was prepared that considers urban wastewater as effluent in the tributary of the plant, the systems analyzed in the mass balance are; pretreatment, the sludge produced by the biological reactor as well as its treatment, the aeration systems and the disinfection of the effluent. To comply with NOM- 003- SEMARNAT-1997. With the complete mass balance, the pipeline and instrumentation diagram (DTI) was built and a Layout diagram was made to locate the equipment, this methodology allowed to generate a design that can be applied at various points of the Xochimilco channels, mainly where sewage discharges occur. wastewater treatment; tubular biological reactor.

Integrated Design of a Small Wastewater Treatment Plant - A Case Study from Thailand

Integrated Design of a Small Wastewater Treatment Plant - A Case Study from Thailand

Impact of a methane emission tax on circular economy scenarios in small wastewater treatment plants.

This paper analyzes the impact of methane emissions taxation on the recovery of the investments required for implementing technologies that use biogas energy in small wastewater treatment plants (WWTPs) in Brazil. It is based on the hypothesis that the adoption of a national methane emission tax policy would encourage small WWTPs to become sustainable power plants. The procedure involved 173 anaerobic plants to analyze: (a) methane production; (b) available useful energy; (c) investments and avoided costs for implementing STHIL system (thermal drying sludge) and motor generator (electricity generation); (d) financial impact for two scenarios (C1: no emissions tax; C2: with tax). Positive environmental and financial results were observed for WWTPs, varying according to the period of time analyzed for both technologies. Investments must be made in cogeneration in anaerobic WWTPs for achieving satisfactory results. Taxation must not be viewed simply as a punitive instrument; on the contrary, it should be seen as a tool to encourage continuous process improvement. The circular economy may support the enlargement of the wastewater collection and treatment system, guaranteeing widespread sanitation conditions in urban areas. However, the actual implementation of a methane emission tax in Brazil still requires many rounds of discussion among sanitation companies, government, and civil society, to establish emission limits, and unit taxes, as well as to consolidate a carbon trade to follow through with this decision in the sanitation sector.

A Treatment Reliability-Based Method for Supporting Infrastructure Asset Management of Wastewater Treatment Plants

A simple and consolidated reliability-based method widely used to unveil the real reliability and stability of wastewater treatment plants (WWTPs) is herein proposed to trigger decision making on operational improvements and asset management for maintaining or improving treatment effectiveness, reliability, and efficiency. Five-year data (2015–2019) from 16 Portuguese activated sludge WWTPs were used. For the 73% of the yearly data which fitted a lognormal distribution, Niku’s coefficient was computed to assess the plant annual reliability for biological oxygen demand (BOD5), chemical oxygen demand (COD), and total suspended solids (TSS). The standard deviation of the annual concentrations was used to characterize the plant stability, and the maximum standard deviations allowed to comply with the European discharge requirements for urban WWTPs were derived. The results demonstrate extended aeration WWTPs were more reliable and stable than conventional aeration WWTPs (0.98 reliability vs. 0.82 for BOD5, 0.97 vs. 0.91 for COD, and 0.94 vs. 0.89 for TSS). Furthermore, the lower reliabilities and stabilities were found for the smaller WWTPs. These results are important for strategic asset management for designing and rehabilitation of the wastewater treatment system. At tactical and operational levels, for resources’ allocation and operating conditions set up, the computed WWTP’s coefficient of variation allows establishing the mean effluent concentrations required for compliance with a given reliability for different scenarios of discharge requirements.

Role of wastewater treatment plants in pollution reduction - evaluated by grey water footprint indicator

The study assesses the pollution discharged from 251 wastewater treatment plants (WWTPs) throughout the Odra river basin in the Czech Republic. The development of pollution production over a period of 15 years (2004–2018) together with a number of WWTPs in the Odra river basin were analyzed. The grey water footprint (GWF) of discharged pollution was determined both in terms of individual size categories of WWTPs and in terms of the parameter that most affects the level of pollution. The share of the small WWTPs size categories (up to 2,000 PE) on the total GWF value of discharged pollution is only 8%, although these are the most numerous. The share of the WWTPs of the size category > 10,000 PE on the total GWF value of discharged pollution is 82%. Total phosphorus (at large WWTPs) and ammonium nitrogen (at small WWTPs) were identified as the key pollutants that most determine the value of the grey water footprint of discharged pollution.

Techno-Economic Evaluation of Ozone Application to Reduce Sludge Production in Small Urban WWTPs

In Chile, small wastewater treatment plants (WWTPs) (treatment capacity of less than 4,800 m3/d) are normally not designed with consideration for the potential valorization of generated sludge. For this reason, they are generally operated at high solids residence times (SRT) (15 d) to promote the decay of biomass, promoting less sludge production and reducing the costs associated with biomass management. Operation at high SRT implies the need for a larger activated sludge system, increasing capital costs. The implementation of a sludge-disintegration unit by ozonation in future WWTPs could enable operation at an SRT of 3 d, with low sludge generation. In this work, we evaluate how the implementation of a sludge-ozonation system in small WWTPs (200–4000 m3/d) would affect treatment costs. Four scenarios were studied: (1) a current WWTP operated at an SRT of 15 d, without a sludge ozonation system; (2) a WWTP operated at an SRT of 15 d, with a sludge-ozonation system that would achieve zero sludge production; (3) a WWTP operated at an SRT of 3 d, with a sludge-ozonation system that would provide the same sludge production as scenario 1; (4) a WWTP operated at an SRT of 15 d, with a sludge-ozonation system that would achieve zero sludge production. Economic analysis shows that the treatment costs for scenarios 1 and 2 are similar, while a reduction in cost of up to 47% is obtained for scenarios 3 and 4.

OPERATIONAL EFFICIENCY AND ENVIRONMENTAL IMPACT OF WASTEWATER TREATMENT PLANTS IN LITHUANIAN RURAL AREAS

The aim of the paper was to determine the operational efficiency and environmental impact of five small wastewater treatment plants (WWTPs) in Ukmergė district. The efficiency of these WWTPs, reconstructed by applying the same vertical flow labyrinth technology was calculated according to the most important pollution indicators: biochemical oxygen consumption in 7 days (BOD7), total phosphorus (TP) and total nitrogen (TN) in period 2017-2020. It was found that the lowest operational efficiency of Taujėnai wastewater treatment plant was according to BOD7 (94-96%). The lowest treatment efficiency of total nitrogen was determined in Dainava WWTP (88-95%). The highest treatment efficiency according to total phosphorus was in Šventupė WWTP (86-92%), the lowest in Žemaitkiemis WWTP (72-85%). In order to evaluate the impact of wastewater treatment plants on the environment, their Life Cycle Assessment (LCA) was performed. Sludge from wastewater treatment process has been found to have the highest environmental impact and fuel consumption for transport the lowest. Of the five wastewater treatment plants examined, the Vidiškiai wastewater treatment plant has the largest impact on the environment, and Šventupė WWTP has the lowest.

Energy Consumption and Carbon Footprint of Greek Wastewater Treatment Plants

Wastewater treatment plants (WWTPs) exhibit significant energy consumption and produce large amounts of Greenhouse Gas emissions (GHG emissions). Energy efficiency and reduction in GHG emissions in WWTPs have become important issues, especially in view of the climate crisis. The core objective of this work is to assess the energy and carbon footprint of Greek WWTPs and to propose methods to improve energy efficiency and reduce GHG emissions. Data were collected from 31 Greek WWTPs with an average treatment capacity between 250 and 3,650,000 population equivalents (PE). The total population served by the 31 WWTPs was over 6,000,000, which is more than half of the population in Greece with access to WWTPs. Based on the results, the annual average energy consumption for small, medium and large WWTPs equals 137 kWh/PE, 48 kWh/PE and 32 kWh/PE, respectively. Accordingly, annual average GHG emissions, both biogenic and non-biogenic in small, medium and large WWTPs are equal to 207 kgCO2e/PE, 144 kgCO2e/PE and 89 kgCO2e/PE, respectively. Annual average on-site GHG emissions are equal to 56.5 kgCO2e/PE, while the average off-site GHG emissions account for 16.9 kgCO2e/PE. Based on the results, acceptable and attainable targets for WWTPs energy consumption and GHG emissions are proposed.

Impacts of wastewater treatment plants on benthic macroinvertebrate communities in summer and winter

Treated effluent from municipal wastewater treatment plants (WWTPs) is a major source of contamination that can impact population size, community structure, and biodiversity of aquatic organisms. However, because the majority of field research occurs during warmer periods of the year, the impacts of wastewater effluent on aquatic communities during winter has largely been neglected. In this study, we assessed the impacts of wastewater effluent on aquatic benthic macroinvertebrate (benthos) communities along the effluent gradients of two WWTPs discharging into Hamilton Harbour, Canada, during summer and winter using artificial substrates incubated for 8 weeks. At the larger of the two plants, benthic macroinvertebrate abundance was higher and diversity was lower at sites downstream of the outfall compared to upstream sites in both seasons. Whereas at the smaller plant, the opposite was observed, abundance increased and diversity decreased with distance from the outfall in both seasons. While the impacts of wastewater on benthic communities were largely similar between seasons, we did detect several general seasonal trends – family diversity of macroinvertebrates was lower during winter at both WWTPs and total abundance was also lower during winter, but only significantly so at the smaller WWTP. Further, benthic macroinvertebrate community composition differed significantly along the effluent gradients, with sites closest and farthest from the outfall being the most dissimilar. Our contrasting results between the WWTPs demonstrate that plants, with different treatment capabilities and effluent-receiving environments (industrial/urban versus wetland), can dictate how wastewater effluent impacts benthic macroinvertebrate communities.

First Demonstration of Nitrate Reduction Using Woodchip Bioreactor Technology at a Small Community Wastewater Treatment Plant

Eutrophication can be accelerated by excess amounts of reactive Nitrogen (Nr) entering aquatic ecosystems. Historically, the circa 1960 Bolton Wastewater Treatment Plant, Warren County, New York (USA), discharged plant effluent for final polishing to natural sand infiltration beds, which entered the groundwater and then tributaries to Lake George. The absence of a denitrification unit process at the Bolton facility resulted in the construction of a woodchip bioreactor and a corresponding demonstration project to evaluate denitrification of plant effluent prior to sand bed discharge. This Denitrifying Bioreactor (DNBR) installation was the first real time, in-situ application of this “green technology” for a small wastewater treatment plant world-wide. The Bolton DNBR reduced nitrate-nitrogen concentrations in the tertiary effluent by 38% when compared with untreated tertiary effluent. Here we show that wastewater denitrification using this passive, environmentally compatible technology offers a low-cost, effective tool for small community wastewater treatment plants where excess Nr is problematic. Combined with diligent plant operator attention, this innovative treatment should move beyond concept into full scale field applications for other small community wastewater treatment plants globally, using lessons learned at the Bolton facility.

Economic evaluation of a small wastewater treatment plant under different design and operation scenarios by life cycle costing

High-performance wastewater treatment technologies suited to the urban environment remain largely inaccessible to developing countries due to financial constraints. Instead, inadequate technologies are being used that adversely affect the quality of water resources and limit their sustainability. One high performing technology that offers possible solution is a packaged version of the integrated fixed-film activated sludge (IFAS) system consisting of a 20 m3 aerobic reactor and a 4.2 m3 settlement tank. The present work has investigated aspects of this typically-expensive solution that can be economized to improve its uptake in these countries. To achieve this a life cycle cost analysis (LCCA) was performed and potential savings identified. The results obtained show that the life cycle cost is $0.31/m3 and that costs primarily occurred at the construction stage (11.9%) and the operation and maintenance stage (88.1%) with negligible disposal costs. A reduction of up to 42.4% in construction costs were shown to be accessible by adopting other materials such as high-density polyethylene (HDPE) or to a lesser extent glass-fibre reinforced polymer (GFRP). The greatest single cost in the life cycle was found to be incurred by aeration (48.9%), requiring expenditure of $0.15/m3, however the use of intermittent aeration (IA) could reduce this further to $0.08/m3. Further work is suggested to investigate the broader sustainability of the different aeration strategies in light of these economic results.

SARS-CoV-2 RNA surveillance in large to small centralized wastewater treatment plants preceding the third COVID-19 resurgence in Bangkok, Thailand

Wastewater surveillance for SARS-CoV-2 RNA has been a successful indicator of COVID-19 outbreaks in populations prior to clinical testing. However, this has been mostly conducted in high-income countries, which means there is a dearth of performance investigations in low- and middle-income countries with different socio-economic settings. This study evaluated the applicability of SARS-CoV-2 RNA monitoring in wastewater (n = 132) to inform COVID-19 infection in the city of Bangkok, Thailand using CDC N1 and N2 RT-qPCR assays. Wastewater influents (n = 112) and effluents (n = 20) were collected from 19 centralized wastewater treatment plants (WWTPs) comprising four large, four medium, and 11 small WWTPs during seven sampling events from January to April 2021 prior to the third COVID-19 resurgence that was officially declared in April 2021. The CDC N1 assay showed higher detection rates and mostly lower Ct values than the CDC N2. SARS-CoV-2 RNA was first detected at the first event when new reported cases were low. Increased positive detection rates preceded an increase in the number of newly reported cases and increased over time with the reported infection incidence. Wastewater surveillance (both positive rates and viral loads) showed strongest correlation with daily new COVID-19 cases at 22–24 days lag (Spearman's Rho = 0.85–1.00). Large WWTPs (serving 432,000–580,000 of the population) exhibited similar trends of viral loads and new cases to those from all 19 WWTPs, emphasizing that routine monitoring of the four large WWTPs could provide sufficient information for the city-scale dynamics. Higher sampling frequency at fewer sites, i.e., at the four representative WWTPs, is therefore suggested especially during the subsiding period of the outbreak to indicate the prevalence of COVID-19 infection, acting as an early warning of COVID-19 resurgence.

Environmental life cycle impacts of small wastewater treatment plants: Design recommendations for impact mitigation

The objective of this study was to quantify potential mitigation of environmental impacts from the operation and construction of wastewater treatment plants (WWTP) from implementing specific design recommendations. The study investigated small WWTPs, many of which are serving slow growing or declining populations. Life Cycle Assessment methodology was used to evaluate and compare the inventory and environmental impacts of nine small WWTP case studies. Detailed inventory data was collected from the facilities’ engineering design plans and utility bills. One recommended practice was to avoid significant overdesign by planning for no lower than a 75% capacity utilization by the facilities’ end-of-life. A theoretical correction to a 75% capacity utilization was estimated to mitigate 0.4% of lifetime electricity usage and 1% of secondary process concrete for every 1% reduction in design average flow rate. Relatedly, a 0.4% mitigation in the Carcinogenic and Global Warming impacts could be achieved for every 1% reduction in design average flow toward a 75% capacity utilization. Other suggested practices were focused on conveyance, namely, to minimize non-process facility area and to use polyvinyl chloride pipe instead of ductile iron pipe where possible. The latter practice was estimated to mitigate between 1.1 and 4.8% of the Carcinogenic impact in the nine case studies.

Wastewater-Based Epidemiology of Enteric Viruses and Surveillance of Acute Gastrointestinal Illness Outbreaks in a Resource-Limited Region.

Acute gastrointestinal illness (AGI) continues to be an important cause of morbidity and mortality among all ages. This study applied the principles of wastewater-based epidemiology for the preventive identification of potential outbreaks of acute viral gastroenteritis and hepatitis A by analyzing the presence of human enteric viruses in influents of small municipal wastewater treatment plants (WWTPs) handling domestic sewage, together with public health reports of acute diarrheal and hepatitis A disease in Costa Rica during 2013. Raw wastewater samples were collected during four seasonal periods with different rainfall levels. The presence of five human enteric viruses (rotavirus A, norovirus GI, norovirus GII, enterovirus, and hepatitis A virus) was studied by endpoint and real-time polymerase chain reaction in influents of five WWTPs. Cases of AGI were analyzed using historical public health reports of endemic levels and quartile ranges for each administrative and territorial area where the WWTPs are located and for its surrounding counties. A tendency for a higher rate of positive viral tests was present 1 week before an increase of AGI cases. Epidemiological weeks categorized as Outbreak (above the 75th percentile) and Success (below the 25th percentile) showed statistically significant differences in terms of positive viral test rates (Wilcoxon test, P = 0.05). Virological monitoring of wastewater in small WWTPs is an appropriate model for epidemiological surveillance of diarrheal and hepatitis A diseases in low- and middle-resource countries.

ANALYSIS OF HEAT RECOVERY FROM WASTEWATER USING A HEAT PUMP ON THE EXAMPLE OF A WASTEWATER TREATMENT PLANT IN THE ŚWIĘTOKRZYSKIE VOIVODESHIP IN POLISH

Currently, sources from which renewable energy could be generated are being sought worldwide. One of these sources could be wastewater. This article shows how heat can be recovered from wastewater, using a small wastewater treatment plant in Świętokrzyskie voivodeship as an example. It analyses the temperature of wastewater in the reactor, in the sewage system and the ambient temperature for each month. The principle of heat pump operation was presented. Then, the amount of heat energy that can be recovered from wastewater was calculated for each month.

Microplastic retention in small and medium municipal wastewater treatment plants and the role of the disinfection.

Wastewater treatment plants (WWTPs) efficiently retain microplastic particles (MPs) generated within urban areas. Among the wastewater treatment steps, disinfection has not been characterized for its potential MPs retention activity, although it has been reported that processes used to abate the bacterial load could also affect MPs concentration. For this reason, we evaluated the MPs concentration across the overall wastewater treatment process and before and after the disinfection step in four small/medium WWTPs located in the north of Italy. Most of the MPs found in the samples were fibers or fragments, smaller than 500 μm, mainly composed of polyethylene, polypropylene, or polyethylene terephthalate. The retention efficiency at the outlets was higher than 94% in all the plants analyzed. More interestingly, the disinfection treatments adopted by the different WWTPs reduced MPs concentration from a minimum of 9.1% (UV treatment) to a maximum of 67.6% (chlorination), promoting a further increase of the overall retention efficiency of the WWTPs from 0.4 to 0.7%. Quantitatively, the disinfection contributes to the MPs reduction in the outlets by retaining 0.5-6.7 million MPs per day, in WWTPs that discharge 2.7-12 million MPs per day. The results of the present work underline the importance of a careful choice of the steps that constitute the wastewater treatment, including disinfection, in order to minimize MPs discharge into the natural ecosystems.

Energy efficiency assessment of China wastewater treatment plants by unit energy consumption per kg COD removed

ABSTRACT Unit energy consumption per kg pollutant removed (kWh/kgCODremoved) is used for the first time in assessing and ranking the sustainability of main treatment technologies of 1215 wastewater treatment plants (WWTPs) in China. The metric better measures the sustainability of main treatment technologies in WWTPs than unit energy consumption per cubic meter treated (kWh/m3). The energy consumption data of these WWTPs were selected from the database of 1399 WWTPs to evaluate the energy efficiency of different treatment technologies. 80.3% of the WWTPs applied anaerobic-oxic plus anaerobic–anoxic–oxic, oxidation ditch, and sequencing batch reactor as main technologies. Statistical analysis shows that the unit energy consumption of WWTPs decreases with increasing design flow rate, operation loading rate, and influent COD concentration. For example, the average unit energy consumption of SBR decreases from 2.76 kWh/kgCODremoved to 0.83 kWh/kgCODremoved when the design flow rate increases from less than 10,000 m3/d to 100,000–200,000 m3/d. The mean unit energy consumption of SBR decreases from 1.71 kWh/kgCODremoved to 1.32 kWh/ kgCODremoved and 2.85 kWh/ kgCODremoved to 0.63 kWh/kgCODremoved as the operation loading rate and COD removal increase from 40% to 100% and from less than 150 mg/L to over 450 mg/L, respectively. SBR has the lowest unit energy consumption among all the technologies. Therefore, SBR might be the most appropriate technology in small and medium-scale WWTPs in China. Regression equations were developed to predict the unit energy consumption for sustainable design treatment trains by input variables such as design flow rate, operation loading rate, and influent COD concentration.

Aquatic tardigrades in Poland – a review

Abstract The diversity, distribution and ecology of aquatic Tardigrada in Poland remain poorly known. We reviewed the literature focused on tardigrades in Poland and recognized only 15 aquatic taxa which were reported from various freshwater and marine habitats. Among them, 12 are freshwater and three are marine taxa. Hypsibius dujardini is Poland’s most widely-distributed hygrophilous species, but it re presents rather a complex of cryptic species and their diagnosis requires integrative approaches. Most reports of aquatic tardigrades in Poland are accidental findings mostly from water bodies in Tatra Mountains or from lakes in Masurian Lake District. Some species were also reported from small ponds or wastewater treatment plants in other regions like Małopolska or Wielkopolska Provinces.

Bionor sewage sludge technology – Biomass to fertiliser and a soil addition

Wastewater treatment plants play a key role in preserving the resources of the environment, as well as human health. The applied technological system of a wastewater treatment plant determines the efficiency of wastewater and sewage sludge treatment, but also energy efficiency and operating costs. The aim of the presented work is to analyse the technological unconventional system of a small wastewater treatment plant with some modifications generating ecological profits, mainly the fertiliser, biomass or peat substitution (“biosolids factory” concept). The modification of the technological system consists in the application of sewage microfiltration, conditioning of sewage and sludge with cellulose material and application of short-term thermo-composting (Bionor technology). The use of a belt filter for suspension separation reduces the load on activated sludge bioreactors and aerobic stabilisation. The basic modification is the use of thermo-composting of separated sewage sludge with the addition of a structure-forming agent (straw pellet). Importantly, no precipitating or flocculating chemical substances or agents are used in this technology. The technology used enables the processing of sewage sludge into biomass with high fertilising and energy potential. In the following work, the Life Cycle Assessment (LCA) of a wastewater (and sewage sludge) treatment plants was made, comparing different possible concepts of sewage sludge management. The LCA was performed on five applied sewage sludge treatment scenarios: incineration of biomass (S1); biomass as a fertiliser product – “fertiliser substitution” (S2); biomass as a soil addition - “peat substitution” (S3); biomass as both fertiliser and a soil addition - “fertiliser and peat substitution” (S4); and biomass as a filling without any substitution benefits - “no specific use” (S5). The LCA analyses of the Bionor sludge technology applied in the wastewater and sewage sludge treatment plant confirm the environmental benefits and minimise the environmental impact with conventional solutions. The fertiliser and peat substitution scenario cause the least impact on climate change. This scenario was found as beneficial for avoiding net CO2 emissions (−5.8 kg CO2 eq/1 m3 wastewater) and eutrophication potential (−1.7 to −2.0 kg N2O eq/1 m3 wastewater, −2.78 to −3.0 PO4 eq/1 m3 wastewater). The eco-toxicity study also showed low impact potentials for a land application scenario. Incineration of biomass yields higher environmental impacts than any application scenario (13.8 kg CO2 eq/1 m3 wastewater). The LCA analysis confirmed that the peat substitution scenario was found as the most valuable.

Promoting Sustainability: Wastewater Treatment Plants as a Source of Biomethane in Regions Far from a High-Pressure Grid. A Real Portuguese Case Study

Wastewater treatment plants (WWTP) located in regions far from a high-pressure grid can produce renewable biomethane, which can partially substitute the natural gas locally consumed. However, the economic viability of implementing biomethane plants in WWTP has to be guaranteed. This paper uses the discount cash flow method to analyze the economic viability of producing biomethane in a WWTP located in Évora (Portugal). The results show that, under the current conditions, it is unprofitable to produce biomethane in this WWTP. Since selling the CO2 separated from biogas may result in an additional income, this option was also considered. In this case, a price of 46 EUR/t CO2 has to be paid to make the project viable. Finally, the impact of potential government incentives in the form of feed-in premia was investigated. Without selling CO2, the project would only be profitable for feed-in premia above 55.5 EUR/MWh. If all the CO2 produced was sold at 30 EUR/t CO2, a premium price of 20 EUR/MWh would make the project profitable. This study shows that the economic attractiveness of producing biomethane in small WWTP is only secured through sufficient financial incentives, which are vital for developing the biomethane market with all its associated advantages.