Decentralized Wastewater Treatment Research Articles

Thermal swing intermittently-operated biological activated carbon filtration for rapid, non-sewered treatment of psychrophilic black water

TS-IOBAC filtration is an energy-efficient biological treatment process for decentralized wastewater treatment in cold climates.

Optimizing Scale for Decentralized Wastewater Treatment: A Tool to Address Failing Wastewater Infrastructure in the United States

Wastewater systems (sewered or on-site septic tanks) are failing across the U.S. Economically disadvantaged populations, communities of color, tribal lands, and rural/peri-urban areas are especially vulnerable. Efficient deployment of public and private capital to assure appropriate service levels and affordability is a critical need. We present a modeling framework to identify economically optimal wastewater network layout and component sizes. Six system configurations are considered, which include gravity versus pressurized collection system flow and treatment of septic effluent versus raw wastewater. A case study for Uniontown, Alabama─a community that has been in national news for the failure of their wastewater infrastructure─is presented. We find that a decentralized network that separates and stores solids on-site, prior to conveyance to a cluster-scale treatment site, has a fraction of the capital and operating cost of a centralized system that is currently proposed. Broader implications are discussed.

Study of Treating Wastewater with a Laboratory Benchtop Septic Systems

Efficient wastewater treatment technologies are needed to curb water scarcities and prevent the spread of diseases and contamination of water sheds. Decentralized wastewater treatment systems or respectively septic systems are easy to afford and handle – especially in rural areas. In this research a developed 19.9 l (5 gal.) laboratory septic system containing 15 l (3.96 gal.) of liquid was operated at a temperature of 18°C (64.4°F) with wastewater collected from a primary clarifier of a local wastewater treatment plant. The laboratory study included a hydraulic retention time of 30-, 10- and 5-day with and without addition of bacteria from an anaerobic sludge blanket reactor and commercially available bacteria for enhancement of septic systems.
 Operating the laboratory septic system at a 10-day HRT showed the best performance for all system operations with and without enhancement bacteria in comparison n to 30- and 5-day HRT.
 The developed laboratory septic system proved to be a valuable way to investigate septic systems performance on a laboratory scale.

Municipal wastewater treatment with corrugated PVC carrier anaerobic baffled reactor.

The anaerobic baffled reactor (ABR) is a promising solution for decentralized wastewater treatment due to its low operation cost as compared to the activated sludge process, but it requires comparatively higher hydraulic retention time (HRT). This ultimately increases land requirement, capital and construction cost of treatment plant. This study investigates performance of ABR using polyvinyl chloride (PVC) corrugated pipe as carrier media to improve biomass retention capacity and treatment performance of reactor with the aim to reduce HRT. Comparative performance of two ABRs with and without carrier media was analyzed under mesophilic conditions (35 ± 1 °C) for organics and total suspended solids (TSS) removal at HRTs of 24, 18, 12, 8, 6 and 4 h. Results showed that at HRTs of 24-08 h, the organics removal performance of the carrier anaerobic baffled reactor (CABR) was better than ABR and was in the range of 77-81% for CABR as compared to 64-70% for ABR. However, on further decrease in HRT to 6 h, CABR sustained the treatment with organics removal of 80%, while ABR performance reduced to 58%, creating a performance difference of 38%. Average total suspended solids (TSS) removal was in the range of 76-83% at all HRTs for both reactors. Therefore, this study identified CABR with PVC carrier media as an effective low-HRT reactor for organics and SS removal with less land area requirement.

Simultaneous nitrification and denitrification in a novel rotating self-aerated biofilm reactor for decentralized wastewater treatment

Decentralized wastewater pollution in rural areas has become a serious problem for the rural environment. In this study, a novel rotating self-aerated biofilm reactor was developed for decentralized wastewater treatment without any aeration equipment. After the long-term operation of 110 days, the removal efficiency reached to 96.06 % (COD), 98.06 % (NH4+-N), and 62.58 % (TN) in the last phase. Under high dissolved oxygen level, the simultaneous nitrification–denitrification (SND) maintained at a stable ratio of 62.53 % and the denitrification rates reached over 28.37 mg/L/h. With the organic loading rate increased, key nitrogen functional bacterial communities such as anoxic denitrifiers (Thiothrix, Flavobacterium, Pseudoxanthomonas, Aquimonas and Azoarcus) and aerobic denitrifiers (Hydrogenophaga, Zoogloea and Terrimonas) increased obviously. Overall, microbial analysis and nitrogen metabolism pathway indicated that an integration of SND process was achieved in this single reactor by the combined action of nitrification, denitrification and comammox without any aeration equipment.

Combining a novel biofilm reactor with a constructed wetland for rural, decentralized wastewater treatment

A novel waterfall aeration biofilm reactor integrated with a constructed wetland (WABR-CW) system was developed to meet the challenge of decentralized wastewater treatment with a focus on nutrient removal. In a lab-scale experiment of 70 days, the WABR-CW showed a high removal efficiency for COD (85–98 %), NH4+-N (100 %), TN (60–90 %) and TP (85 %-95 %), even when different organic loading rates (OLR) were used. The CW was responsible for improving the overall performance in view of an increased nutrient removal. The CW offers denitrification capacity when the OLR is not optimal for the WABR. Based on the lab-scale experiment, a pilot-scale WABR-CW was built and tested for aquaculture wastewater treatment and reuse. A total of 63 m3 wastewater was treated of which 56.7 m3 was reused. Furthermore, the microbial structure of the WABR-CW system was investigated. A metabolic analysis highlighted the N and C metabolic pathways and functional genes distribution in the WABR-CW system. Next generation sequencing not only linked the pollutants removal performance and microbial encoding genes but also disclosed the potential ability of WABR-CW to treat more polluted and more complex wastewater. The outcomes of this study provide scale-up results and a better understanding of the functioning of the WABR-CW.

Investigation of mechanisms of an upflow-downflow siliceous sand filtration system for surfactants bathroom grey water treatment.

Sustainable decentralized wastewater treatment systems (DEWATS) at the local level are considered as a smart alternative for small communities particularly in arid areas. The present study examines the mechanisms of an upflow-downflow Siliceous Sand (SS) filtration system involved in surfactants bathroom grey water treatment. In order to get a better understanding of the mechanisms involved in surfactants removal, particle size distribution and Fourier transform infrared (FTIR) spectroscopy of the SS particles were performed. Optimization of the upflow-downflow SS filtration system, operated following operational conditions of hydraulic load rate (HLR) and SS amounts, results indicates an average removal efficiency (ARE) of 93.7% reached with respect to surfactants removal. Results showed also that the resulting silicate materials react with surfactants in a cooperative assembly process involving the interaction of SS particles with surfactants aggregates. Brunauer, Emmett and Teller (BET) surface area, pore volume (Vp), and pore size were found to be significantly reduced post-filtration with respectively 3.39%, 24.31%, and 21.86% reduction. From FTIR spectroscopy analysis of the Sulfonates, Silanol and Silane functional groups appear to be involved in mesoporous constructed micelle organization for surfactants removal. Such geo-materials could be green and sustainable for various applications in water and environmental engineering.

Viability of waste heat capture, storage, and transportation for decentralized flowback and produced water treatment

The use of waste heat has been proposed to reduce the energy footprint of membrane distillation for flowback and produced water (FPW) treatment. However, its feasibility has not been fully understood for FPW treatment. Accordingly, this study performs systematic assessments through thermodynamic modelling of waste heat capture, storage, and transportation for decentralized FPW treatment at well pads located in the Denver-Julesburg Basin. A wide range of sensible, phase-change, and thermo-chemical storage materials were assessed for their effectiveness at the utilization of waste heat from on-site hydraulic fracturing engines and natural gas compressor stations, in order to overcome the temporal or spatial mismatch between waste heat availability and FPW generation. Our results show that the type of storage material being used can have a high impact on the efficiency of waste heat utilization and the treatment capacity of membrane distillation. Sensible storage materials only utilize sensible heat capacities, while phase-change materials have improved performance because they are able to additionally store latent heat. However, sensible and phase-change storage materials lose 11–83% of heat due to conversion inefficiencies caused by their changing temperatures. Thermo-chemical materials, on the other hand, have the highest potential for use because they collect and release heat at constant temperatures. We identified three thermo-chemical storage materials (magnesium sulfate, magnesium chloride, and calcium sulfate) with the best efficiencies due to their elevated discharge temperatures which reduce the energy consumption of membrane distillation. In addition, these materials have high volumetric energy storage density, which enables capture and transportation of waste heat from remote locations such as natural gas compressor stations to the well sites, yielding up to 70% reduction in transportation costs relative to moving FPW to centralized treatment facilities at natural gas compressor stations. Our study, for the first time, demonstrates the importance of selecting appropriate energy storage material for leveraging low-grade thermal energy such as waste heat to power membrane distillation for decentralized wastewater treatment.

Renewable Electricity and Hydrogen Production via Decentralized Wastewater Treatment Systems

Urban wastewater could be converted into energy if microbial electrochemical technologies (METs) like microbial dual-chamber electrolysis cells (MDEC) or microbial fuel cells (MFC) are applied as a treatment method. Mathematical modelling of MFC and MDEC for wastewater treatment and energy recovery has been developed in this study. The Radaue method has been used to solve ordinary differential equations (ODEs), and the model outputs were successfully validated with previous experimental and modelling data. A case study in Montreal, Canada, has also been considered for testing the application of METs on an urban scale with a total daily wastewater flow of 75,000 L/day. The results show that from 1 m3 of wastewater, MDEC and MFC can generate 0.077 kg H2 and 0.033 kWh, respectively.

Full-scale application and performance of a new multi-self-reflow decentralized Wastewater treatment device: Impact of hydraulic and pollutant loads

Decentralized treatment of wastewater in rural areas usually has several challenges, which include large fluctuations in pollutant concentration and water quantity, complicated operation and maintenance of conventional biochemical treatment equipment, resulting in poor stability and a low compliance rate of the wastewater treatment process. In order to solve the above problems, a new integration reactor is designed, which uses gravity and aeration tail gas self-reflux technology to realize the reflux of sludge and the nitrification liquid, respectively. The feasibility and operation characteristics of its application for decentralized wastewater treatment in rural areas are explored. The results demonstrated that, under constant influent, the device showed strong tolerance to the shock of pollutant load. The chemical oxygen demand, NH4+-N, total nitrogen and total phosphorus fluctuated in the ranges of 95–715 mg/L, 7.6–38.5 mg/L, 9.32–40.3 mg/L and 0.84–4.9 mg/L, respectively. The corresponding effluent compliance rates were 82.1%, 92.8%, 96.4% and 96.3%, respectively. When the wastewater discharge was non-constant and the maximum single-day Qmax/Qmin reached 5, all indicators of the effluent met the relevant discharge standard. The integrated device also demonstrated high phosphorus enrichment levels in its anaerobic zone; the concentration of phosphorus reached a maximum of 26.9 mg/L, which created a good environment for phosphorus removal. The microbial community analysis showed that sludge digestion, denitrification, and phosphorus-accumulating bacteria all played an important role in pollutant treatment.

Avaliação de desempenho de uma estação de tratamento de esgoto movida a energia solar (SBR de dois estágios) operada em regiões de clima tropical

ABSTRACT This article investigates the performance behaviour of a small decentralized wastewater treatment plant with a capacity of up to 50 population equivalents powered by solar energy. The two-stage sequencing batch reactor (SBR) consists of a photovoltaic (PV) system to deliver energy, a battery storage for night operation and two reactor tanks. In the experimental period of 157 days, the wastewater inflow was increased from 3 to 4.5 and 6 m3.d−1, with sludge ages of 32 ± 2 d in the beginning and 21 ± 2 d in the end. The results corresponding to the different phases indicated high efficiency and stability of the system with domestic wastewater, reaching efficiencies of the test periods of 93 ± 2%, 86 ± 4% and 93 ± 6% for removal of chemical oxygen demand, nitrogen and phosphorus, respectively. In the last 51 days, aeration in the night was interrupted for three hours to save energy and study the behaviour of extended non-aerated phases. A shortening of the aeration phases can help to extend the lifetime of batteries and reduce operational costs, while limiting values in the outlet are still met.

Optimization model for cost estimation of decentralized wastewater treatment units

In this study, an optimization model, which is a combination of Genetic algorithm (GA) and geographical information system (GIS) was used to find minimum construction, operation, and flow reuse cost ( Fmin) . This Fmin model will be used for the estimation of the constructional and operational costs of decentralized wastewater treatment units [DTUs] and can be used for the estimation of reusing treated municipal wastewater flow for irrigation purposes in Sulaimani city, Iraq as well. In the optimization processes, an objective function technique was used based on data from 31 small-sized DTU and the costs of reusing their effluents in 827 deferent sizes green areas [GRs] across the city. A transportation matrix model of size [31x827] was built to find the Fmin for conveying the required flow from the DTUs to the GRs destinations. Also, optimum required pipe lengths and routes for the treated flow conveying were found using GIS Network Analysis – Origin-Destination (OD) Matrix Tools. The results showed that the proposed model could successfully obtain an optimal solution. The algorithm is flexible enough to consider a variety of scenarios and compare the best options.

The material politics of living in close proximity to our wastewaters: A case of decentralisation in the Netherlands

This paper investigates how decentralised wastewater treatment initiatives experiment with ways to live in close proximity to wastewater and their potentiality for a future with less polluting wastewater. In the Netherlands, there is a contested political debate about whether centralised or decentralised technologies are better. Rather than engaging in this deliberative political debate, we articulate a less visible and more material politics by tracing different ways of ordering wastewater treatment in practice. Drawing on fieldwork with inhabitants, scientists, and engineers who have brought wastewater treatment ‘close to home’, we examine the turn to decentralisation as a material object of enquiry which, in turn, shapes our engagement with pollutants, technologies, and a range of non-human actors. We ask: What kinds of living together in close proximity to our waste do such decentralised experiments allow for?

The Role of Carbon to Nitrogen Ratio on the Performance of Denitrifying Biocathodes for Decentralized Wastewater Treatment

Bioelectrochemical systems with denitrifying biocathodes have been of interest for the removal of nitrate in decentralized wastewater treatment applications. Only a few studies have directly focused on this application, but the removal rates have been very low. This study evaluated the operational parameters that affect the nitrate removal of two-chambered microbial fuel cells (MFCs) with a biocathode, particularly, the carbon to nitrogen ratio (C:N) and proton diffusivity across electrode chambers. The results show that proton diffusion across a proton exchange membrane is not a limiting step in nitrogen removal performance. At C:N ratios of 4 and 8, biocathodes with a continuously supplied carbon source at the anode were able to achieve complete nitrogen removal at a rate of 0.97 ± 0.21 and 1.15 ± 0.13 mg N L−1 d−1, respectively. However, as the C:N ratio increased from 4, 8, 16, and 32, the electrode potentials decreased accordingly. Ratio 4 C:N had a cathodic reduction potential of +66.1 ± 5.3 mV vs. SHE and dropped to −78.6 ± 9.8 mV vs. SHE at 32 C:N. The cathode electrode potential can be controlled by way of the carbon concentrations at the anode, which can have major indirect implications on the evolution of cathodic microbial communities that have preference to particular ranges of reduction potentials. The cathodic biofilms in this study were dominated by the phyla Proteobacteria, Acidobacteria, Bacteroidetes and Nitrospirae, which are known to have key denitrifying microorganisms. The genus Stenotrophomonas was found in abundance within the attached cathode biofilm and to a lesser extent in the suspended biomass. Vibrio, Acidobacteria_Gp4, Nitrosomonas, and Candidatus Competibacter were also cultivated in both the suspended and attached biomass. Nitrospira was only found in the attached biofilm. Regardless of operational scheme, nitrogen removal was improved at low C:N ratios, with 8 C:N having the best performance overall. This indicates that higher C:N ratios than were previously explored (>4 C:N) provide sufficient coulombs to facilitate denitrification at the cathode even while the anodic CEs remain low. Reactor design modifications should be considered to fully support robust denitrifying communities, enhancing the overall nitrogen removal for decentralized wastewater treatment applications.

Waste Water Treatment Performance of Two Vertical Flow Constructed Wetlands for Agricultural Reuse in Jordan: Enhancing Nitrogen Removal

This study demonstrates the treatment performance of two vertical flow constructed wetlands (VFCWs) for decentralized wastewater treatment plants in Jordan, for reuse purposes to meet the WHO regulations for reuse in agriculture and the Jordanian standards (JS 893/2006). The first system is a recirculating VFCW that has shown high removal efficiency of COD, TSS, and CBOD5 over the study period, conforming to the JS (Category A). Whereas, the Total Nitrogen (TN) and Nitrate (NO3-) removal were limited (55 and 44 mg/L) over the baseline monitoring, conforming to the JS Category-B (TN: 70 mg/L and NO3-N: 45 mg/L). Therefore, the system was modified by converting the recirculation tank into attach growth tank (using electric conduit pipes as plastic media). TN concentration reduced effectively of 40 mg/L, conforming to the JS category-A (TN: 45 mg/L), whereas, NO3–N concentration reduced to 37 mg/L, conforming to the JS Category-B (TN: 45 mg/L). Over the study period, E. coli reduction were constant, 2 log10 reduction, conforming to the JS category C (more than 1000 MPN/100 mL). The second system is two-stage VFCW that has shown high removal efficiency of COD, TSS, and BOD5, conforming to the JS Category-A over the study period. But, TN and NO3–N concentrations were limited (55 and 44 mg/L), conforming to the JS Category-B, due to insufficiency of carbon source to promote denitrification (high BOD5 removal by first filter). Thus, the two-stage VFCW was modified with raw wastewater step-feeding application to the intermediate pump shaft before the second stage filter. The results of operational modification showed a small significant improvement in TN removal (p = 0.005); TN and NO3–N concentrations were reduced to 52 and 50 mg/L, respectively; conforming to the JS Category-B. Higher E. coli removal was observed in the two-stage system than the recirculating system, with an overall average removal of 4.5 log10 units, conforming to the JS category B (less than 2.0 log10 units). While, E. coli reduction influenced negatively by step-feeding modification, conforming to the JS category C

Integrated application of macrophytes and zooplankton for wastewater treatment

The increasing amount of sewage has become a serious concern globally, demanding sustainable solutions. The constructed wetland system (CWS) can be installed at the wastewater discharge site and properly screened bio-purifiers can be used for efficient wastewater treatment. Filter-feeding zooplankton have the potential to graze on bacteria and reduce biological oxygen demand. However, higher suspended particles choke the zooplankton filtering appendages. An integrated application of zooplankton and macrophytes can solve the problems by reducing contaminants and providing the surface area for zooplankton to take refuge. Using three different approaches: (a) screening of natural bio-purifiers through time series study, (b) assessment of sewage treatment potential of screened bio-purifiers in the CWS and, (c) evaluation of the growth potential of screened bio-purifiers in untreated wastewater, this study explored the combined use of macrophyte and zooplankton in the CWS. The 3-year time series study in the vicinity of the wastewater discharge area recorded the zooplankton, Brachionus angularis and Moina macrocopa as highly indicative zooplankton. The top two highly indicative macrophytes are Typha and Phragmites. Under laboratory conditions, the population growth rates of B. angularis and M. macrocopa were significantly higher in wastewater without any external nutrient source than those in control with algae as a food source. The integrated application of zooplankton (B. angularis and M. macrocopa) macrophytes (Typha and Phragmites) in CWS yielded upto 56% reduction in the total bacterial count and upto 92% reduction in BOD along with substantial increase in the DO level. The present results strongly suggested the use of CWS planted with macrophytes and inoculated by zooplankton. The usefulness of this system is further supported by the natural occurrence of selected species, as it is easy to maintain, has low installation cost, and excellent efficiency in treating wastewater. As both the zooplankton species are preferred live feed for rearing of fish larvae, the present results suggested the use of zooplankton and macrophytes for treatment of wastewater, reduction of sludge, and harvest of live feeds for the aquaculture industry to augment circularity and promote decentralized wastewater treatment.

P07-51 Environmental aspects and application experience of textile fiber filters in decentralized wastewater treatment in Crete, Greece

P07-51 Environmental aspects and application experience of textile fiber filters in decentralized wastewater treatment in Crete, Greece

Environmental synergies in decentralized wastewater treatment at a hotel resort.

Climate change and water scarcity are clearly related environmental problems, making them global environmental issues. Accordingly, the water cycle management deserves a revision in its approach, integrating the concept of circular economy within an efficient and sustainable management of water resources and the design of wastewater facilities. In this sense, newly engineered decentralized facilities have emerged as a viable option for the treatment of segregated wastewater flows. The design has not only integrated the wastewater treatment function, but also resource recovery, such as water reclamation for agricultural and irrigation activities, fertigation, fertilization and energy sustainability. Based on these premises, the concept of decentralized wastewater management deserves the same degree of attention and development that has so far been reserved for conventional centralized management systems. Therefore, this paper proposes a progressive substitution of the business-as-usual scenario or centralized system by applying a small-scale wastewater management scheme performing a more efficient resource and water recovery in a medium-sized 4-5-star resort hotel. The spotlight was a membrane technology for the anaerobic digestion of the blackwater instead of the greywater treatment. A favorable environmental profile was found for the decentralized scenario under two circumstances: a large system boundary including the beneficial environmental impacts of the products and, based on the results obtained from a sensitivity analysis, an energy demand for the operation of the AnMBR lower than 2kWh·m-3. The global warming potential results (around 9%) were even for such high demand and much larger benefits were obtained for other impact categories (94% for SOD and 98% for LU). Nevertheless, the operation (gate-to-gate approach) of these on-site recovery facilities is far from being optimized and further research should follow to decrease the 39.8% difference in the global warming potential between decentralized and centralized systems.

Life cycle impact assessment and life cycle cost assessment for centralized and decentralized wastewater treatment plants in Thailand

This research investigates the cost-effectiveness of four sludge treatment scenarios for centralized (C) and decentralized (D) wastewater treatment plants (WWTP) using life cycle cost assessment (LCCA). The environmental impacts and costs are quantified by Stepwise2006. The most environmentally and financially viable WWTP construction option for Bangkok, Thailand (2022–2031) is determined in terms of LCCA and net present value (NPV). The environmental costs of D-treatment scenarios are lower than those of C-treatment scenarios. The total environmental costs of C- and D-fertilizer scenarios are lower than those of C- and D-dewatering scenarios. The net cash flow per functional unit of C-WWTPs is higher than that of D-WWTPs. The C-fertilizer scenario is the most environmentally and economically viable treatment scenario due to the lowest LCCA deficit (−5.58 THB2020 per m3 treated effluent). Composting should thus be adopted for treating sludge. The most environmentally and financially viable WWTP construction option is option I (building four C-WWTPs within 10 years) due to the lowest LCCA deficit (−19925 million THB2020) and smallest financial loss (NPV = −6309.96 million THB2020). Essentially, the local administration of the capital should adopt option I as a guideline in formulating the wastewater treatment management policy of 2022–2031.

Optimized titania nanotubes photoanode mediated photoelectrochemical oxidation of ammonia in highly chlorinated wastewater via Cl-based radicals

Efficient removal of low-concentration ammonia from chlorinated wastewater is a challenge for decentralized wastewater treatment due to its notorious environmental effect and lethal influence on aquaculture. Photoelectrocatalytic (PEC) oxidation process is considered as an efficient and environment–friendly approach, whereas a low-cost and stable photoanode is crucial. In this study, TiO2 nanotubes (TNTs) photoanode (Ar–TNT–500 °C) with excellent physicochemical and photoelectrochemical properties was prepared by optimizing the parameters of anodization, including the voltage/times of anodization and the atmosphere/temperature of heat treatment. During the synthesis, the electrochemical and heat treatment processes promoted the formation of oxygen vacancies (OV) on the TNTs surface and enhanced its electrocatalytic activity. The optimized Ar–TNT–500 °C photoanode could selectively convert ammonia to N2 (86%) and a small amount of nitrate (14%). Radical quenching and probe experiments confirmed that the ClO produced by rapid quenching of OH and Cl by free chlorine dominated the selective degradation of ammonia in the synergistic process of photocatalysis and electrocatalysis. The cycle of chlorine-based radicals (ClO and Cl) and Cl− provided a continuous and efficient ammonia oxidation system, because chlorine-based radicals could efficiently and selectively oxidize ammonia and reduce the production of toxic (per) chlorate.