Small-scale Wastewater Treatment Plants Research Articles

When does infrastructure hybridisation outperform centralised infrastructure paradigms? – Exploring economic and hydraulic impacts of decentralised urban wastewater system expansion

We explore the dynamics of centralised and decentralised wastewater infrastructure across various scenarios and introduce novel insights into their performance regarding structural vulnerability, hydraulic capacity, and costs. This study determines circumstances under which infrastructure hybridisation outperforms traditional centralised infrastructure paradigms. We combined system analysis to map out the modelling problem with the model-based exploration of the transition space using the novel TURN-Sewers model. System diagramming was used to identify the parameters or combinations of parameters that significantly influence the performance indicators being assessed. This allowed the creation of relevant simulation scenarios to identify circumstances where a decentralised sewer system could outperform a centralised one. TURN-Sewers was applied to model the infrastructure maintenance and generation of new infrastructure over 20 years for a municipality on the Swiss Plateau, considering a population growth rate of 0.03 a−1. Results show that decentralisation in expansion areas with higher densification can outperform the hydraulic performance and structural vulnerability of expanding centralised sanitary wastewater infrastructure. Decentralised systems can also offer economic advantages when capital expenditure costs for small-scale wastewater treatment plants are significantly reduced compared to current costs, particularly at higher discount rates, e.g. reaping effects of economies of scale. The findings of this study emphasise the potential of transition pathways towards decentralisation in urban water infrastructures and the value of models that allow the exploration of this transition space.

Machine learning facilitated the conceptual design of an alum dosing system for phosphorus removal in a wastewater treatment plant

Wastewater treatment plants (WWTPs) face challenges in controlling total phosphorus (TP), given more stringent regulations on TP discharging. In particular, WWTPs that operate at a small scale lack resources for real-time monitoring of effluent quality. This study aimed to develop a conceptual alum dosing system for reducing TP concentration, leveraging machine learning (ML) techniques and data from a full-scale WWTP containing incomplete TP information. The proposed system comprises two ML models in series: an Alert model based on LightGBM with an accuracy of 0.92, and a Dosage model employing a voting algorithm through combining three ML algorithms (LightGBM, SGD, and SVC) with an accuracy of 0.76. The proposed system has demonstrated the potential to ensure that 88.1% of the effluent remains below the TP discharge limit, which outperforms traditional dosing methods and could reduce overdosing from 61.3 to 12.1%. Furthermore, the SHapley Additive exPlanations (SHAP) analysis revealed that incorporating the output features from the previous cycle and utilizing the results of the Alert model as the input features for dosage prediction could be an effective method for data with limited information. The findings of this study have practical applications in improving the efficiency and effectiveness of TP control in small-scale WWTPs, providing a valuable solution for complying with stringent regulations and enhancing environmental sustainability.

In-situ sulfite treatment promotes solid reduction during aerobic digestion of waste activated sludge: Feasibility for small-scale wastewater treatment plants

Aerobic digestion remains the preferred choice for small-scale wastewater treatment plants (WWTPs) in some developing countries, largely due to economic viability and operational simplicity. The escalating production of waste activated sludge (WAS) has prompted small-scale WWTPs to improve efficiency. To address this issue, this study employed an in-situ sulfite treatment as a non-intrusive method to augment aerobic digestion. With sulfite-enhanced solubilization and hydrolysis, a 3.6-fold increase in degradation was achieved. Both sludge dewatering properties and pathogens inactivation were improved. Microbial community analysis revealed a preferential enrichment of Actinobacteriota and Firmicutes during sulfite treatment. The desktop scaling-up estimation suggests that implementing this treatment yielded operational cost savings exceeding 40 %. In summary, in-situ sulfite treatment offers a cost-effective strategy for WAS management in small-scale WWTPs.

Socio-Hydrological Approach for Water Resource Management and Human Well-Being in Pinglin District, Taiwan

Despite being a limited resource, pollution, poor management, and other drivers like climate change make available water unsuitable and insufficient for human consumption and ecosystem maintenance. Therefore, a transdisciplinary approach is needed for managing this precious resource. The overall aim of this paper is to address water inequalities and improve human well-being using an integrated approach of key informant interviews, hydrological modeling, and the payment of ecosystem services (PES) scheme in Pinglin District, Taiwan. This site is an upstream area of Feicui Reservoir, which protects the downstream tap water supply. Key informant interviews were conducted to identify the gaps in and challenges to water resource management. This was followed by a scenario-based hydrological simulation using a Water Evaluation and Planning (WEAP) tool to project future water quality by the year 2050 (using biochemical oxygen demand and total coliform content as key indicator parameters) and to trace the factors responsible for water pollution. Survey analysis of key informant interviews depicts that this area is facing several challenges, such as lack of water infrastructure, agricultural subsidy, construction restrictions, etc., which cumulatively cause water scarcity in the upstream regions. On the other hand, hydrological simulation results show that population decline and climate change under an RCP 8.5 scenario will have an enormous negative impact on water quality. The concentrations of BOD and E. coli in river water will expand by 110.1% and 117.3%, respectively, by 2050 compared to 2018. Finally, the results of the study suggest that the PES scheme can play a positive role in enabling integrated water resource management. For example construction of a small-scale wastewater treatment plant in the upstream area will reduce the total E. coli concentration by up to 90%. While the initial cost of construction will be taken care of by the government, the operation and management cost of this infrastructure will be covered by people living downstream, who need to pay only $0.10 per year per person. The obtained results should be vital for both the stakeholders and decision-makers in this region.

Ensemble machine learning approach for examining critical process parameters and scale-up opportunities of microbial electrochemical systems for hydrogen peroxide production

Hydrogen peroxide (H2O2) production in microbial electrochemical systems (MESs) is an attractive option for enabling a circular economy in the water/wastewater sector. Here, a machine learning algorithm was developed, using a meta-learning approach, to predict the H2O2 production rates in MES based on the seven input variables, including various design and operating parameters. The developed models were trained and cross-validated using the experimental data collected from 25 published reports. The final ensemble meta-learner model (combining 60 models) demonstrated a high prediction accuracy with very high R2 (0.983) and low root-mean-square error (RMSE) (0.647 kg H2O2 m−3 d−1) values. The model identified the carbon felt anode, GDE cathode, and cathode-to-anode volume ratio as the top three most important input features. Further scale-up analysis for small-scale wastewater treatment plants indicated that proper design and operating conditions could increase the H2O2 production rate to as high as 9 kg m−3 d−1.

Artificial Intelligence-Assisted Prediction of Effluent Phosphorus in a Full-Scale Wastewater Treatment Plant with Missing Phosphorus Input and Removal Data

Although artificial intelligence (AI) such as machine learning (ML) and deep learning (DL) has been recognized as an emerging and promising tool, its application becomes challenging with incomplete data collection. Herein, in the absence of the influent phosphorus load and chemical dosage data for phosphorus removal, we employed ML/DL models to predict effluent phosphorus using nine-year data from a small-scale wastewater treatment plant. Attempts were made to select essential model input features from 42 variables by using Pearson correlation analysis to reveal internal correlations among variables. First, five ML regression models were used to predict the effluent phosphorus load, and a maximum coefficient of determination (R2) of 0.637 was achieved with the support vector machine model. Then, the DL model named long short-term memory could predict phosphorus load in one-day advance with an R2 value of 0.496. Finally, on the basis of the historical data, an anomaly alarm design was proposed to minimize the chance of exceeding the discharge permit and achieved a maximum accuracy of 79.7% to predict the phosphorus concentration after comparing seven ML classification models. This study provides an example of applying AI for process improvement and potential cost reduction with incomplete data sets.

Assessment in treatment efficiency of a small-scale municipal wastewater treatment plant with activated sludge

Abstract In this paper, the treatment efficiency of a small-scale wastewater treatment plant (WWTP) with activated sludge was analysed in order to examine the impact of variations in the composition of incoming raw municipal wastewater. The characteristics of the wastewater were analysed with respect to COD, BOD5 and TSS values and loading during the two years, 2018 and 2019. The mixed liquid suspended solid (MLSS), sludge volume index (SVI), food to microorganism ratio (F/M), sludge age and hydraulic retention time (HRT) were used for evaluation of the performance of WWTP. Removal percentage is in the order of TSS > BOD5 > COD during 2018, while in 2019 is in the order BOD5 > TSS > COD. However, better values of removal efficiency for COD, BOD and TSS are obtained in 2019, which is connected to lower oscillation values of MLSS and SVI index. Biodegradability ratio of raw and treated wastewater, plant reliability factor (RF) and equivalent number of inhabitant (ENI) were determined. In addition, the economic cost of small-scale wastewater treatment plant (WWTP) with activated sludge was evaluated and discussed.

Biological treatment of municipal wastewater using fixed rope media technology: Impact of aeration scheme

This paper characterized a new fixed rope media system to upgrade decentralized and small-scale wastewater treatment plants. A primary effluent of municipal wastewater was treated using two pilot-scale reactors equipped with full-scale sized fixed rope media technology, one of the reactors was aerated using a coarse bubble tube and the other using a custom fine bubble aeration system. The study examined the impact of the aeration scheme and intensities and the COD/NH 3 -N ratio on ammonia and COD removal rates, excessive biofilm growth, slough-off, and microbial communities’ composition. The average biofilm ammonia and COD removal rates ranged from 0.23 ± 0.15 to 0.38 ± 0.26 gNH 3 -N/m 2 .d and 1.35 ± 0.95 to 3.05 ± 1.21 gCOD/m 2 .d, respectively. The fine and coarse bubble reactors showed comparable carbon oxidation rates; however, the fine bubble reactor showed a higher nitrification rate than the coarse bubble reactor at lower aeration intensities despite the similar dissolved oxygen concentration. Correspondingly, an increase in COD/NH 3 -N and excessive biofilm growth decreased the NH 3 -N removal performance but did not affect the COD removal efficiency. Further analysis of the microbial communities composition revealed that the reactors supported a relatively substantial amount of AOB (55 and 63%) and denitrifying bacteria (36 and 21%) with a relatively lower NOB (7 and 8%) and anammox (1 and 8%) species in the fine and coarse bubble aeration reactors, respectively. Overall this study demonstrated the feasibility of one stage fixed rope media to treat COD and ammonia and meet treatment objectives, thus providing an alternative solution to decentralized and smaller plant upgrades. • Ammonia and COD removal efficiency of innovative fixed rope media technology was evaluated. • Different aeration schemes showed minimal impact on the DO concentration but impacted removal performances. • C/N ratio influenced NH 3 -N removal but not COD removal. • Slough off did not impact COD removal; however, it enhanced ammonia removal. • Reactor with the fine bubble aeration supported a relatively higher fraction of denitrifying bacteria.

Design of 50KLD Sewage Treatment Plant

Abstract: Sewage treatment is a type of wastewater treatment which aims to remove contaminants from sewage to produce an effluent that is suitable for discharge to the surrounding environment or an intended reuse application, thereby preventing water pollution from raw sewage. Canteen of every academic organization need a lot of clean water, and it generates equivalent amount of wastewater every hour which is neither purified nor reused. Due to water scarcity, the recycling and reusing of wastewater become very essential. The present study describes the simple and Cost-effective method for the design of a smallscale wastewater treatment plant for the purification of wastewater generated by canteen of Ma’din College. The present study involves the Analysis of pH value, total solid , total Suspension solid , hardness,Acidity , oil fat and grease , chloride ,BOD,DO etc. The Sampling of the waste water have been done in different times of the day to have an Average data of measure parameters.

Intermittent Microaeration Technology to Enhance the Carbon Source Release of Particulate Organic Matter in Domestic Sewage

Domestic sewage treatment plants often have insufficient carbon sources in the influent water. To solve this problem, the commonly used technical means include an additional carbon source, primary sludge fermentation, and excess sludge fermentation, but these methods are uneconomical, unsustainable, and not applicable to small-scale wastewater treatment plants. Intermittent microaeration technology has the advantages of low energy-consumption, ease of application, and low cost, and can effectively promote anaerobic digestion of municipal sludge; however little research has been reported on its use to enhance the carbon sources release of particulate organic matter (POM) from domestic wastewater. Therefore, the effect of intermittent microaeration on the carbon source release of POM was evaluated in this study, with POM as the control test. The results showed that the release concentration of soluble chemical oxygen demand (SCOD) was the highest on day 4 under microaerobic conditions, and the concentrations of SCOD, NH4+-N, and PO43−-P in the liquid phase were 1153, 137.1, and 13 mg/L, respectively. Compared with the control group, the SCOD concentration increased by 34.2%, and the NH4+-N and PO43−-P concentrations decreased by 18.65% and 17.09%, respectively. Intermittent microaeration can effectively promote the growth of Paludibacter, Actinomyces, and Trichococcus hydrolytic fermentation functional bacteria. Their relative abundances increased by 282.83%, 21.77%, and 23.47%, respectively, compared with the control group. It can simultaneously inhibit the growth of acetate-type methanogenic archaea, Methanosaeta and Methanosarcina, with a decrease in relative abundances of 16.81% and 6.63%, respectively. The aforementioned data show that intermittent microaeration can not only promote the hydrolysis of POM, but can also reduce the loss of acetic acid carbon source, which is a cost-effective technical way to enhance the release of a carbon source of particulate organic matter in domestic sewage.

Quantification and qualification of the urban domestic pollution discharged per household and per resident.

The research study aims to analyze the discharges of solely domestic wastewater from 15 single-family dwellings. This sizable dataset, containing over 300 unique and insightful data points, makes it possible to accurately qualify the raw wastewater in terms of concentrations, volumes and pollutant loads. Findings quantify the extremely wide data variability. As such, for single-family households of fewer than six residents, it is suggested not to use the standard P.E. pollution value as the design load, but rather a load range defined by the interval [10th percentile, 90th percentile] of the data distribution, i.e. [123; 568 L·d- 1] and [30; 281 g BOD5·d-1], respectively, for the daily hydraulic and organic loads. Also, an analysis of the hydraulic peak factor would tend to lobby in favor of a collective sewer solution. For subdivisions and residential zones with little economic activity and similar French lifestyle, the daily domestic pollution per resident is now determined with the values: 40 g suspended solids, 94 g carbon oxygen demand, 40 g five-day biochemical oxygen demand, 6.7 g NH4+-N, 10.4 g Kjeldhal nitrogen, and 1.2 g total phosphorus for a volume of 83 L. Those data could be used to optimize design and operation of decentralized or small-scale wastewater treatment plant.

Performance of a post-nitrification process with carriers for residual ammonia nitrogen removal in secondary effluent, aimed at small-scale wastewater treatment plants

Performance of a post-nitrification process with carriers for residual ammonia nitrogen removal in secondary effluent, aimed at small-scale wastewater treatment plants

The purification of wastewater on a small scale by using plants and sand filter

The canteen and laboratory of every academic organization need a lot of clean water, and it generates equivalent amount of wastewater every hour which is neither purified nor reused. Due to water scarcity, the recycling and reusing of wastewater become very essential. The present study describes the simple and cost-effective method for the design of a small-scale wastewater treatment plant for the purification of wastewater generated by household, canteen and laboratory of an academic institute. The current study explored the process of phytoremediation by Typha latifolia L. and Canna indica L. for removal of metal ions and phosphate ions from the wastewater. The partially treated water after phytoremediation was further purified by sand filtration. The various water quality parameters (pH, hardness, dissolved oxygen, chemical oxygen demand, turbidity, total dissolved solids and metal ions) of the treated and untreated water were analyzed. It was observed that there are significant reduction in hardness, turbidity and chemical oxygen demand and increase in dissolved oxygen value. The treated water can be reused for various household works and agriculture.

Plastic bottles waste as attached growth media in the removal of organic and nutrients for small-scale wastewater treatment

Biofilm carriers play an important role in attached growth systems for wastewater treatment processes. The purpose of this study is to study the ability of plastic polyethylene terephalate (PET) waste bottles in wastewater treatment for small scale residential. Then its performance is compared with some communal Wastewater Treatment Plants (WWTPs) that use other supporting media and those that do not use media. The study was conducted at five WWTP locations in the city of Padang, West Sumatera. The results show that the WWTP that uses supporting media in organic and nutrient removal in wastewater treatment on a small scale WWTP is better than the one that does not use the supporting media.

Investigation of the Prevalence of Antibiotic Resistance Genes According to the Wastewater Treatment Scale Using Metagenomic Analysis.

Although extensive efforts have been made to investigate the dynamics of the occurrence and abundance of antibiotic resistance genes (ARGs) in wastewater treatment plants (WWTPs), understanding the acquisition of antibiotic resistance based on the WWTP scale and the potential effects on WWTPs is of relatively less interest. In this study, metagenomic analysis was carried out to investigate whether the WWTP scale could be affected by the prevalence and persistence of ARGs and mobile genetic elements (MGEs). As a result, 152 ARG subtypes were identified in small-scale WWTP samples, while 234 ARG subtypes were identified in large-scale WWTP samples. Among the detectable ARGs, multidrug, MLS (macrolide–lincosamide–streptogramin), sulfonamide, and tetracycline resistance genes had the highest abundance, and large and small WWTPs had similar composition characteristics of ARGs. In MGE analysis, plasmids and integrons were 1.5–2.0-fold more abundant in large-scale WWTPs than in small-scale WWTPs. The profile of bacteria at the phylum level showed that Proteobacteria and Actinobacteria were the most dominant bacteria, representing approximately 70% across large- and small-scale WWTPs. Overall, the results of this study elucidate the different abundances and dissemination of ARGs between large- and small-scale WWTPs, which facilitates the development of next-generation engineered wastewater treatment systems.

Biotechnological wastewater treatment in small-scale wastewater treatment plants

The article analyses the results of ten months of operations of two small-scale wastewater treatment plants. Both wastewater treatment plants were one-block facilities, operating on the basis of activated sludge in accordance with the same technological scheme and having an identical hydraulic load. The difference between the plants was that one was 1.3 times smaller than the other, was better insulated and had a longer sludge retention time, with excess sludge having to be removed less often. The smaller plant purified waste more effectively in terms of the parameters of chemical oxygen demand, biochemical oxygen demand over five days, suspended solids, ammonium nitrogen, and total phosphorus. The efficiency level in regard to removing ammonium nitrogen in the small plant given the winter temperature conditions was high (98–99%). In the treated effluent, the amount of remaining ammonium nitrogen was just 0.1–0.6 mg/L. Helpful factors were the long sludge retention time and the concentration of activated sludge, which reached up to 6.5 g/L. Excess sludge was removed from the small plant only twice in ten months. The amount of phosphorus remaining in the treated effluent was on average 1.06 mg/L. Comparing the two plants, a 20% greater effectiveness in elimination of phosphorus (82%) was achieved in the smaller plant, which used four times less electrical energy. The analysis results are useful for the further improvement of small biological wastewater treatment plants.

Governance Arrangements for the Scaling Up of Small-Scale Wastewater Treatment and Reuse Systems – Lessons From India

Environmental pollution and increasing water scarcity are key features of the urban landscape of India today. The extension of centralised sewerage networks cannot keep up with city growth, and alternative sanitation systems are needed for citywide inclusive sanitation (CWIS). The government of India mandated larger buildings to be equipped with small-scale wastewater treatment plants (SSTP). This resulted in the emergence of a large number of technology and service providers, and in the implementation of thousands of private SSTPs. However, this quick scaling up was not accompanied by the development of appropriate governance arrangements. As a result, a significant proportion of SSTPs underperform and do not meet the effluent standards. Through a systematic analysis of governance arrangements around SSTPs, this contribution analyses the scaling up process of small-scale wastewater management and reuse at building level in India, in particular in the state of Karnataka and the city of Bengaluru. This paper identifies the gaps in this multi-level, polycentric governance framework and investigates which arrangements are needed to enable the performance of SSTPs on the ground and to create the necessary synergies between the relevant governmental agencies, the private sector and civil society. The scaling up of SSTPs in India mainly followed a market governance approach within a governance environment that is traditionally very hierarchical. The authors argue that hybrid governance arrangements, blending hierarchical, market and network governance are needed to foster market regulation and stakeholder coordination, and increase the performance of the sector. They conclude that an efficient governance of SSS requires the creation of dedicated SSS units at state and city level, and the development of an online platform collating all databases, streamlining and supporting processes from establishment to monitoring, and allowing meaningful collaboration between stakeholders. Through the case study of India, this paper contributes to understand the governance arrangements necessary for the successful scaling up of decentralised sanitation systems, and how to fulfil the potential of alternative solutions for sustainable urban water management. It contributes to governance studies by substantiating the concept of hybrid governance approach and proposing concrete measures to make it work for such distributed systems.

Trace metal requirements for anaerobic co-digestion of sewage sludge from rural areas and food waste in Japan

Abstract For small-scale wastewater treatment plants in rural areas (WWTPRs) of Japan, reducing sludge disposal costs is an important issue. Co-digestion of sludge from WWTPRs and food waste is a promising method of reducing maintenance costs and producing energy resources such as methane. In this study, co-digestion experiments using sludge and kitchen garbage were conducted to investigate the stability of the co-digestion from the perspective of trace metal requirements. The gas production rate and pH were stable in the digester with HRTs of 140–70 days. With a HRT of 30 days, the pH gradually dropped from 7.0 to 6.5, and VFA accumulated up to a concentration of 2,200 mg/L, indicating process failure. Cobalt (Co) concentration was approximately one-tenth of the required amount reported by a previous study. When Co was added to the digester, the pH and gas production rate became stable even with a higher VS loading rate. Therefore, the unstable situation was attributed to a lack of Co in the sludge. The Co concentration of sludge from WWTPRs in Japan is generally low, similar to the sludge used in this study. The addition of Co is required for stable co-digestion of sludge from WWTPRs and food waste.

Function and biomass production of willow wetlands applied in the polishing phase of sewage treatment in cold climate conditions

Willow wetlands can offer a low-cost solution for recovery of nutrients contained in sewage water and simultaneously produce plant biomass, which can be used in energy production. Willow (Salix spp.) is considered an excellent crop for this purpose, due to its good nutrient uptake and biomass production. Although willow wetlands have been used in sewage treatment in e.g. Denmark, Sweden and southern Finland, their use in northern regions is challenging due to the detrimental effects cold climate conditions can have on plant survival rates and wastewater purification efficiency. In this study, a pilot constructed wetland in northern Finland receiving effluent from a small-scale wastewater treatment plant was investigated. Four willow varieties were planted (Gudrun, Karin, Klara and one local variety) and retention of nutrients in the wetland and willow plant survival rate, biomass production and nutrient uptake were evaluated. Good retention of nutrients (e.g. Tot. N 66–86% and Tot. P 30–87%) was achieved throughout the study period. After two growing seasons, the variety Gudrun showed the best survival rate and significantly higher biomass production (5.7 t/ha) than Karin, Klara and the local variety (1.7, 3.0 and 0.02 t/ha, respectively). Thus, willow wetlands are suitable systems for nutrient recovery from pre-treated wastewater in cold climate regions. However, the willow variety used should be chosen carefully, as there can be significant differences in survival rate and biomass production between varieties.

Indicators for sustainability assessment of small-scale wastewater treatment plants in low and lower-middle income countries

Wastewater treatment in low and lower-middle income countries is often limited by lack of local technical expertise, institutional capacity, and financial resources, making it challenging to reach SDG6-target 6.3, i.e. halving the proportion of untreated wastewater. Several studies suggest sets of sustainability indicators for assessing the planning and/or operation of WWTPs. However, existing standard indicators are typically focused on the context of high and upper-middle income countries, whereas low and lower-middle income countries face other types of issues. The development of a contextualized set of relevant and effective sustainability indicators to support the planning and/or operation of small-scale WWTPs in low and lower-middle income countries is crucial. This study develops a contextualized set of sustainability indicators for small-scale wastewater treatment plants in Bolivia, which is classified as a lower-middle income country. Indicators were identified using a literature review combined with empirical studies using focus groups with managers and operators, as well as, workshops with experts. The aim of the focus groups and workshops was to acquire an understanding of the local context and identify relevant sustainability indicators. The practical investigation took place at five sites in Cochabamba, Bolivia. The results suggest that sustainability assessment of WWTPs in low and lower-middle income countries should emphasize the institutional dimension (e.g. Institutional capacity, Interactions, and Information) and the technical dimension (e.g. Sewage network functionality and Expertise) alongside indicators in the social, economic and environmental dimensions.