Small Wastewater Treatment Plants Research Articles

Energy autarky of small scale wastewater treatment plants by enhanced carbon capture and codigestion – A quantitative analysis

Municipal wastewater treatment plants (WWTPs) can achieve energy self-sufficiency (autarky) while complying with increasing discharge standards. We evaluated three energy-positive wastewater treatment scenarios classified as “Basic”, “Moderate”, and “Advanced” configurations. A quantitative mass and energy balance model was developed to analyze the energy recovery potentials of these configurations. Enhanced COD capture, codigestion with locally available biodegradable wastes, and aeration energy optimization were considered as the main approaches to achieve an energy autarky or energy-positive status. Data from existing operating plants were used to validate the model performance. This paper presents a detailed quantitative analysis of two (basic and moderate) energy-neutral or energy-positive wastewater treatment configurations. In addition, a novel and practically feasible energy-positive wastewater treatment scheme incorporating advanced solids separation is presented with energy analysis and a case study. This model can be useful to quickly assess the energy recovery potential of small scale wastewater treatment systems.

Catchment scale analysis of occurrence of antibiotic resistance genes in treated wastewater

Antibiotic resistance poses a significant health risk for humans and animals. Wastewater treatment plants (WWTPs) are among the key sources of antibiotic resistance genes (ARGs) in the natural environment. The aim of this study was to analyze the occurrence and seasonal variations of ARGs in treated wastewater flowing to the Pilica River or its tributaries. Samples of treated effluents were collected from 17 WWTPs assigned into three groups based on their population equivalent (PE): <2000, 2000–9999 and 15,000–99,999. Samples were collected four times at two-month intervals between November 2017 and July 2018. The occurrence of the 16S rRNA gene, class 1 integrase (intl1) gene and genes encoding resistance to beta-lactams (blaTEM, blaOXA, blaSHV, blaCTX-M), tetracyclines (tetA, tetB, tetC, tetD, tetE), fluoroquinolones (aac(6′)-Ib-cr), macrolide, lincosamide and streptogramin (MLS) antibiotics (ermF, linA) and sulfonamides (sul1) was determined by standard PCR. All of the analyzed ARGs, excluding blaSHV, were detected in treated wastewater. The prevalence of ARGs was more frequently in spring and rarelier in summer. Antibiotic resistance genes were most frequently detected in treated wastewater flows out from small WWTPs (class I, PE <2000).

The Possibility of Using Spent Coffee Grounds to Improve Wastewater Treatment Due to Respiration Activity of Microorganisms

Spent coffee ground (SCG) may affect wastewater treatment processes due to high coffee consumption worldwide. The impact of the main chemical compounds present in SCG on respiration activity of sewage sludge was investigated. The results showed approximately two times higher respiration in the samples where various types of SCG were present in comparison with samples without SCG. During intense microbial metabolism, statistically significant (p &lt; 0.05) decreases in caffeine, total polyphenols, and chlorogenic acid contents after processing and in filtrate was observed. The monitored compounds (caffeine, polyphenols, and chlorogenic acid) deteriorated due to their probable inclusion in microbiological metabolism. Increase in respiration activity of microorganisms in the presence of cheap waste material such as coffee grounds can help to improve wastewater treatment. The research was focused on spent coffee grounds’ impact on the respiratory activity of microorganisms in the activated sludge taken from small and large wastewater treatment plants. The impact was measured in more detail due to the inclusion of different coffee species (Robusta and Arabica) in diverse concentrations. The novelty of the study can also be seen through the literature overview, where information cannot be found about SCG influence on the respiration activity of microbial communities, and data on the possible SCG aerobic degradation or utilization by a sewage sludge bacterial consortium has also never been reported. The study has shown the possibility of improving wastewater treatment due to respiration activity of microorganisms in the presence of cheap waste material such as coffee grounds.

The role of concentrations gradients on phosphorus and iron dynamics from chemically-dosed horizontal flow wetlands for tertiary sewage treatment.

This study examined the dynamics of iron (Fe) and phosphorus (P) transformations from the surface sludge accumulated in tertiary horizontal flow (HF) treatment wetlands (TW) chemically dosed for P removal. Site surveys showed P was stored in HF TW with and without artificial aeration on average, with instances of P release in the non-aerated site. Controlled experiments revealed storing TW surface sludge for over 24 hours resulted in limited oxygen and nitrate concentrations, resulting in both P and Fe release. The rate of P release increased with increasing water-sludge P concentration gradients, and the reaction could take as little as 10 minutes. Convection had no impact on P transformation rates. The findings suggest mitigation strategies could include the manipulation of the biogeochemical environment by managing oxygen and nitrate concentrations within the wetlands. A better understanding of links between Fe, P, and nitrate is needed to test proactive mitigation strategies for small wastewater treatment plants.

Presence of Mycobacterium avium Subspecies paratuberculosis Monitored Over Varying Temporal and Spatial Scales in River Catchments: Persistent Routes for Human Exposure.

Mycobacterium avium subspecies paratuberculosis (Map) was monitored by quantitative PCR over a range of temporal and spatial scales in the River Tywi catchment. This study shows the persistence of Map over a 10-year period with little change, which correlates with the recognised levels of Johne’s disease in British herds over that period (aim 1). Map was quantified within the river at up to 108 cell equivalents L−1 and was shown to be consistently present when monitored over finer timescales (aim 4). Small wastewater treatment plants where the ingress of human-associated Map might be expected had no significant effect (aim 2). Map was found for the first time to be located in natural river foams providing another route for spread via aerosols (aim 5). This study provides evidence for the environmental continuum of Map from the grazing infected animal via rain driven runoff through field drains and streams into main rivers; with detection at a high frequency throughout the year. Should Map need to be monitored in the future, we recommend that weekly or monthly sampling from a fixed location on a river will capture an adequate representation of the flow dynamics of Map in a catchment (aim 3). The human exposure to Map during this process and its impact on human health remains unquantified.

A sludge purging procedure that increases the robustness of upflow anaerobic sludge blanket reactors in sewage treatment

This work proposes a sludge purging procedure from upflow anaerobic sludge blanket reactors in small wastewater treatment plants. The following characteristics of the anaerobic sludge supported its development: specific methanogenic activity, biodegradability and dewaterability. The sludge samples from the reactor blanket zone presented low specific methanogenic activity, low biodegradability and good dewaterability. On the other hand, sludge samples from its bed zone showed higher biodegradability and specific methanogenic activity, as well as equivalent dewaterability and excellent sedimentability. These characteristics indicate that the common practice of sludge purging from the bed zone is a mistake and must be avoided. Nevertheless, the sludge blanket usually presents high water contents (total solids < 3%), which can overload hydraulically the drying beds. To prevent this problem, the sludge purge from the blanket zone should be fractionated into three discharges of lower volume during the first 3 days of the dewatering cycle.

Factors affecting SVI in small scale WWTPs

This paper analyses factors associated with bulking in 195 small scale wastewater treatment plants (WWTPs) in Estonia. Operational data from each plant were collected and analysed statistically. The key factors associated with bulking were infiltration into sewage pipes, the type and purpose of process reactor, operational practices and influent characteristics. Both anaerobic fraction and volumetric fraction of the anaerobic reactor compared to the aerobic reactor resulted in a positive correlation with sludge volume index (SVI) <150 ml/g values. Good operation and maintenance practice as well as an operator's competence play a crucial role in bulking prevention. Using the 30 minute settling test (V30) as the single process control parameter can mislead an operator's judgement in process control strategies and cause effluent violations. Misjudgements in process control decisions can lead to unwanted conditions in small WWTPs (e.g. excessive chemical addition favoured bulking). Use of instrumentation, control and automation helped to keep the process conditions more stable and reduce the probability of bulking. Analyses of variance showed that the factors associated with Microthrix parvicella growth were long solids retention time (SRT), low food-to-microorganism ratio (F/M) and lack of carbon content compared against nitrogen and phosphorus contents.

Pollution and Sustainability Indices for Small and Medium Wastewater Treatment Plants in the Southwest of Spain

Two indices have been defined in this work to measure the pollution load that a Wastewater Treatment Plant (WWTP) receives and the efficiency of the process it carries out from the overall perspective of pollution removal and energy efficiency. The aim is to provide two performance parameters which could be used to characterize both the working conditions of a WWTP and how well it treats the pollution it receives. In this way, they may be used to compare the behavior of different plants in a certain geographical area. Forty-five WWTPs in the Southwest of Spain were studied to find out the most significant information that is to be used to identify and define both indices. Seven of the variables recorded were used to define each one. Their values were calculated for the whole set of plants studied. The results showed that most of the plants received a low pollution load. Only six of them suffered from a high pollution load, probably because of farms and food industries located in their surroundings. Only three plants showed a poor efficiency, while 23 of them presented a very good one.

Struvite Phosphorus Recovery from Aerobically Digested Municipal Wastewater

Small, municipal wastewater treatment plants (WWTPs) that use aerobic digestion treat approximately 40% of the discharged wastewater in the USA, and yet they are an overlooked source of recoverable P. There are no known reports of small, aerobic WWTPs recovering P through struvite (MgNH4PO4·6H2O) precipitation for repurposing as a mineral fertilizer, even though some large WWTPs with anaerobic digestion are. Four small WWTPs in north Florida, USA, with treatment capacities from 371 to 2650 m3 wastewater d−1 and incoming P loads from 2 to 14 kg d−1 were investigated for their potential to produce struvite from digester filtrates. A chemical equilibrium model was used to predict the feasibility of struvite production and the results compared with actual WWTP filtrate measurements. Filtrates from aerobic digesters were able to form struvite if solution pH was increased by ≤1 pH unit. Depending on the WWTP, P recovery in filtrates through struvite precipitation ranged from 27–57% by mass at pH 8.5, via NaOH additions or air sparging. Increasing filtrate Mg concentrations improved P recovery up to 97%. Based upon these results, small WWTPs using aerobic digestion will be able to lower their P waste output through recovery as struvite fertilizer.

Sewage sludge processing and management in small and medium-sized municipal wastewater treatment plant-new technical solution

Although sewage sludge generated by most large wastewater treatment plants is treated as waste, this ‘waste’ is both a source of energy and nutrients. Moreover, mainly in the small and medium-sized installations of municipal wastewater treatment plants is produced sewage sludge that meets the standards for soil application. Unfortunately, the overly simplified operating systems of small wastewater treatments plants cannot provide the satisfactory content of water in sewage sludge for energy recovery purposes. Therefore, new solutions for sewage sludge treatment are required. The study presents an innovative, energy effective, wastewater treatment and sewage sludge processing in one operational sequence, with significant energy consumption decrease and autothermal biomass production. Current research contains detailed technical information about the novel integrated waste water treatment plant and sewage sludge treatment installation as well as cost analysis in comparison to conventional treatments.The aim of this study was to evaluate the operation of the one prototype line for wastewater and sewage sludge treatment and the assessment of the obtained biomass and fertilizer.This new technology is a solution for small and medium-sized municipal wastewater treatment plants and is leading to change the conception of wastewater treatment process as a whole and is resolving the management of sewage sludge at the place where it is generated. In described process the sewage sludge is adequately treated by the installation apparatus and can be used in two ways: as a source of pathogen-free compost, or as a biomass and feedstock for simple thermal installation. Obtained sewage sludge can be recycled as biomass for combustion with the remaining ash acing as a plant nutrient-rich source (soil properties enhancer). Finally, in a modified wastewater treatment process, an odorless and stabilized compost or biomass for thermal energy recovery can be obtained and utilized directly at the place of origin. This alternative system allows for the systematic (and technological) adjustment of already existing, upgraded and newly-designed wastewater treatment plants. This new and innovative technology driven by assumptions about the best possible use of the resources and energy, allows for a more sustainable functioning of the treatment plant. The present study provides a significant insight into closing carbon, nitrogen, phosphorus, potassium and energy loops in wastewater treatments system.

Influence of variability in the amount of inflow wastewater pollution concentration in small sewer system (case study)

The aim of study was the analyze of the impact of hydraulic load on the changes in the concentration of pollution indicators in raw sewage in years 2009-2014 in the small wastewater treatment plant. Qualitative analysis for raw sewage was included three parameters: total suspension solid, BOD and COD. The characteristics relation between the concentration of pollution indicators in raw sewage (depend variable) from the hydraulic load(independent variable) was presented by the Pearson linear correlation. In the 6 year study period were collected 32 samples of raw wastewater. Based on the result of linear regression analysis, showed that along with the increasing amount of wastewater in the sewer decrease the concentration of pollutions in raw wastewater. For total suspension solid, increase by 1 m3 of quantity of raw sewage inflowing to wastewater treatment plant, causes a decrease in the concentration of this indicator by 0,53 g·m-3. For the both organic indicators (BOD and COD), the was found that an increase of 1 m3 the amount of raw sewage inflowing to wastewater treatment plant, caused a decrease of 0,75 gO2·m-3 BOD value and 0,66 gO2·m-3 COD value in raw sewage.

Reduction of Environmental Pollution Applying Decentralised Wastewater Treatment Systems in Small Communities

Small size wastewater treatment plants are widely used as a decentralised treatment solution in regions, where the access to the sewer system is not available or the connection to an existing system is not economically sound like in small communities (e.g. schools, hospitals, army camps, etc.). The local treatment of wastewater can be performed by small size units applying activated sludge or attached growth biomass. In this paper the performance and operation of a process unit applying conventional activated sludge is analysed. For this purpose, a simulation tool with mass balance modelling was used. In the model, various influent wastewater qualities were set in order to examine their effect on each process. Operational parameters were fine-tuned to increase the capacity by utilising additional aeration. As a result, it can be stated that the nominal capacity of the treatment unit is overestimated; in the Central European region, due to the wastewater characteristics, the examined treatment unit could handle 40% of the nominal capacity.

Is Turkey Still a Reliable Ally? The Case of the Black Sea

Small size wastewater treatment plants are widely used as a decentralised treatment solution in regions, where the access to the sewer system is not available or the connection to an existing system is not economically sound like in small communities (e.g. schools, hospitals, army camps, etc.). The local treatment of wastewater can be performed by small size units applying activated sludge or attached growth biomass. In this paper the performance and operation of a process unit applying conventional activated sludge is analysed. For this purpose, a simulation tool with mass balance modelling was used. In the model, various influent wastewater qualities were set in order to examine their effect on each process. Operational parameters were fine-tuned to increase the capacity by utilising additional aeration. As a result, it can be stated that the nominal capacity of the treatment unit is overestimated; in the Central European region, due to the wastewater characteristics, the examined treatment unit could handle 40% of the nominal capacity.

Management of sewage sludge energy use with the application of bi-functional bioreactor as an element of pure production in industry

The increase in sewage sludge makes it necessary to improve the direction of sewage sludge management policy and disposal, which requires a larger amount of incineration or land reclamation. It was shown that the result of methane fermentation, which is a more complex process of extracting energy contained in waste. High costs of implementation of sludge processing technology and low efficiency of sewage treatment plants in which sewage sludge is insufficient to recover energy from them, have a negative impact on the development of energy generation from sediments. The model waste system for energy is characterized, which includes two stages. The proposed solution can be applied to small wastewater treatment plants and it is justifiable to use the concept of bi-functional bioreactors in which anaerobic and aerobic processes can be carried out with much lower construction and maintenance costs. The use of bioreactors allows to exclude the energy demand needed to stabilize sewage sludge at a low cost compared to the expenditure that is currently incurred by disposal. The proposed solution works perfectly with industrial plants, due to the possibility of their creation in the time of the creation and application of a circular economy.

A novel method for rapid assessment of the performance and complexity of small wastewater treatment plants

A novel method for rapid assessment of the performance and complexity of small wastewater treatment plants

Small but with big impact? Ecotoxicological effects of a municipal wastewater effluent on a small creek

Municipal wastewater treatment plants (WWTPs) discharge micropollutants like pharmaceuticals, pesticides, personal care products or endocrine disrupting chemicals but also nutrients. Both can adversely influence the freshwater ecosystem and may finally affect the ecological conditions. Many studies focus on the potential impact of large WWTPs even if smaller ones are more common, often less efficient and discharge into small creeks or the upper reaches of rivers. As a result, the receiving waters are characterized by relatively high shares of treated wastewater. Thus, the primary objective of this study was to investigate the ecotoxicological effects of a small WWTP on freshwater amphipods and mollusks in a small creek using an active and passive monitoring approach, accompanied by laboratory experiments (LE). In vitro assays with recombinant yeasts and the microtox assay with Aliivibrio fischeri were performed in parallel to determine the endocrine potential and the baseline toxicity. The evaluation of the effects of the analysed WWTP was possible due to its shutdown during our study and the application of the same in vivo and in vitro assays before and after the shutdown. During the operation of the WWTP the discharge of treated wastewater caused significantly higher mortalities and lower reproduction of the anaylsed invertebrates in the active and passive montoring as well as in the LEs. Furthermore, the amphipod species assemblage in the creek was affected downstream of the WWTP effluent. Besides, the endocrine activity and baseline toxicity were significantly higher downstream of the effluent. After the shutdown of the WWTP, the in vitro activity levels and adverse in vivo effects in the receiving water recovered quickly with no significant differences downstream of the former WWTP effluent compared to the upstream station. Furthermore, the previously disturbed amphipod species assemblage recovered significantly with a shift in favor of Gammarus fossarum downstream of the effluent. These biological results are consistent with a marked decline by 81.5% for the detected micropollutants in the receiving creek after the shutdown which points to a prominent role of micropollutants for the observed effects.

Environmental and economic assessment of electro-dewatering application to sewage sludge: A case study of an Italian wastewater treatment plant

The objective of this study is to evaluate the feasibility of implementing electro-dewatering (EDW) as an add-on unit to the existing conventional dewatering units with the aim of increasing the final dry solids content and reducing the subsequent handling and energy costs of sewage sludge management. The assessment was carried out by focusing on a case study, a small wastewater treatment plant (WWTP) in the Milan metropolitan area. Various indicators were used to evaluate the environmental impact and economic performance. Primary data, such as operating data from the case study WWTP and economic data from an EDW equipment manufacturer, were extracted and used in the modelling. Four scenarios were set up and compared, which address the current and future sludge management schemes in Italy.The results suggest that it is environmentally and economically feasible to implement the EDW upgrade if the sludge disposal follows the incineration route. More specifically, when small WWTPs deliver their EDW-dewatered sludge to a centralised incineration facility, this will enable to reduce the global warming impact of the system up to 135 kg CO2-eq. per dry tonne of sludge. In addition, good profitability (incremental return on investment > 15.1%) can be obtained when the market disposal cost is above 30.5–39.6 € per wet tonne of sludge. Based on our recent market survey, the sludge disposal price is well above the break-even values.

Small sewage wastewater treatment plants for domestic wastewater

Small sewage wastewater treatment plants are used for treatment of domestic wastewater from individual residential houses, small schools, roadside cafes, restaurants, small railway stations, camping sites, etc., where there is no centralized sewage network. In cases when there is a limited space for the installation of small-scale treatment facilities, authors suggest using of septic tanks and drainage wells. Sewage effluents are collected with gravity force, without using electricity. Usage of proposed constructions does not cause pollution of soils and underground water horizons. Sanitary environment is stable and predictable.

Ambient-temperature co-digestion of low-solids municipal and industrial waste mixtures: Insights from molecular analyses

ABSTRACTThe performance of ambient temperature anaerobic co-digestion was investigated for mixtures of six substrates: canned tomato and salsa waste, portable toilet waste, septic tank waste, winery waste, beer and cider waste, and fats, oils, and grease (FOG). Laboratory semi-continuous reactor studies and molecular biological analyses revealed that beer/winery, and tomato/FOG/winery/beer mixtures resulted in the best performance in terms of biogas production (515 and 371 mL CH4/g VS, respectively) and methanogenic populations. A portable toilet/septage mixture resulted in the overall poorest performance and inhibition of microbial activity was evident. Average methane content was ~70% for all mixtures tested. The findings of this study reveal that healthy methanogen populations were present, further supporting the feasibility of biogas production via the novel feedstock mixtures in ambient temperature lagoons.Implications: Disposal of septic tank waste and other high chemical oxygen demand (COD) 10 industrial food processing waste at a small wastewater treatment plant is uncommon, because it can upset the treatment process and requires additional power for treatment. Ambient-temperature covered lagoon digesters can be an alternative low-cost technology for co-digestion of these recalcitrant waste streams while generating bioenergy. The results of this study demonstrated that there is potential for implementation of unheated covered lagoon digester systems 15 for conversion of liquid wastes for production of renewable biomethane while eliminating the need to treat these wastes at a wastewater treatment plant.

Enhanced Pollution Removal with Heat Reclamation in a Small Hungarian Wastewater Treatment Plant

Enhanced Pollution Removal with Heat Reclamation in a Small Hungarian Wastewater Treatment Plant