Browsing by Author "Dotro, Gabriela"
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Item Open Access Adaptation of two-stage vertical flow constructed wetlands for treating unscreened sewage in the UK.(Cranfield University, 2019-03) Khomenko, Olha; Bajón Fernández, Yadira; Dotro, GabrielaThe UK water industry has made a priority of embracing low energy sewage treatment, making of two-stage vertical flow constructed wetlands (VFCWs) a plausible alternative to conventional systems. However, for successful implementation of the technology in the UK a further understanding of any required adaptations in its design and operation is required, in particular linked to the UK use of spot sampling regulation of treated effluents and differences in rain profile affecting hydraulic loads in combined sewers. There is also a paucity of information regarding required time for full maturation of the technology and of performance during early operation. In response, the first UK full-scale WWTP based on two-stage VFCWs was built in Derbyshire, UK, and closely monitored during the initial three years of operation, allowing investigation of the system performance and robustness. The efficacy of the system for removal of total suspended solids (TSS), BOD₅ and NH₄ +- N has been evaluated by composite and spot samples analysis. The technology was found to efficiently remove pollutants to the level of 6 ± 3 mg·L⁻ ¹ , 5 ± 2 mg·L⁻ ¹ and 5.8 ± 3.8 mg·L⁻ ¹ for TSS, BOD₅ and NH₄+- N, for 24 hour composite samples. After one year of operation the system was retrofitted with forced aeration on the second stage, which enabled a higher ammonia removal with concentrations in final effluent of 95th percentile concentration of 5.3 mg∙L⁻ ¹comparing to 9.6 mg∙L⁻ ¹achieved in the system with passive aeration. The first stage filters were observed to be hydraulically limited during the first year of operation, with a hydraulic conductivity (HC) of <5.7× 10⁻⁶ m∙s⁻ ¹ which caused prolonged ponding occurrence. This in turn led to poor re-oxygenation of the first stage filter beds and low mineralization of the sludge layer deposited on its surface, which was characterized by TS and VS content of 11.5% ± 1.9% and 64.5% ± 7.3% respectively. A more mineralised sludge layer was present after three operational years, with HC <4.9 × 10⁻⁴ m∙s⁻ ¹ and sludge properties of 20.4% ± 3.5% TS and 62.3% ± 3.5% VS. These values are comparable to data reported for two-stage VFCWs operated in France and ponding was minimal after three years, suggesting this as the required length for system maturation. Close monitoring of the system during the first three years of operation evidenced the need to adapt rotating period lengths according to system age and sludge layer properties. Resting periods of up to 14 days were required for the young system to encourage sufficient hydraulic conductivity of the sludge layer, while the conventional 3.5 days feed/ 7 days rest cycle is appropriate after three years of operation. The influence of sludge properties on permeability was assessed in laboratory experiments, as well as artificial modifications of the sludge surface that could sustain increased permeability and accelerate sludge layer mineralisation. A positive impact of increased VS on permeability was found, with an increase in VS from 60% to 75% improving permeability from 6.14 × 10⁻ ¹⁷ m∙s⁻ ¹ to 2.00 × 10⁻ ¹⁶ m∙s⁻ ¹ in samples with TS of 9% and from 2.06E × 10⁻ ¹⁷ m∙s⁻ ¹ to 1.25 × 10⁻ ¹⁶ m∙s⁻ ¹ in samples with TS 15%. A greater relative contribution to permeability of preferential flow pathways (PFPs) present in the sludge layer than of sludge properties (TS, VS) was observed. PFPs were scarce in the young full scale primary VFCWs, which was believed to be the reason for their poor hydraulic acceptance. A positive effect on PFP formation and sludge drying rate was observed when artificially modifying the sludge layer by application of secondary activated sludge or by making initial cuts on its surface. Artificial modifications of the sludge layer could be implemented in full-scale systems to improve hydraulic acceptance and re-oxygenation, to shorten maturation of primary filters and to maintain prolonged operational periods without desludging.Item Open Access Analysis of phosphorus flux in reed beds at chemically dosed wastewater treatment works(Cranfield University, 2014-05) Barak, Jan; Dotro, Gabriela; Jefferson, BrucePhosphorus (P) as a macronutrient contributes to eutrophication. In the UK, iron (Fe) and aluminium (Al) salt dosing is a well-established wastewater treatment strategy for its removal. Small works with a population equivalent (p.e.) under 2,000 often employ horizontal subsurface flow constructed wetlands (HSSF CWs) as a means for subsequent tertiary (3°) treatment. Although these significantly improve the final effluent’s quality, P release has, on occasions, been observed. This study attempts to contribute to a better understanding of P flux mechanisms in reed beds and to outline a mitigation strategy countering P release. The literature review identified that, in given circumstances, the P concentration gradient, redox conditions, pH and Fe cycling are key potential factors governing P flux. The field survey revealed that secondary (2°) P effluent concentration negatively correlated with P release from the reed bed. In laboratory scale sludge reactor series, P concentration in wastewater was observed to be buffered by molecular diffusion driven by a concentration gradient in the sludge-wastewater interface. The instantaneous equilibrium point appeared to lie in 0.1 to 0.5 mg/L interval in the first 10 minutes, shifting to 1 mg/L in the next 8 hours and higher in the later stages. In biologically active systems, the shift of the equilibrium point seemed to be dominated by changes in redox potential linked to simultaneous microbial utilisation of oxygen (O2) and nitrate (NO3 - ), eventually leading to a reduction of Fe (III) and sulphate (SO4 2- ), with subsequent P release. The start of Fe (III) reduction coincided with reductive depletion of nitrate-nitrogen (NO3-N) below 1 mg/L. In systems with limited biological activity, P release was linked to disassociation from Fe-P compounds under decreasing pH. In an experiment assessing hydrodynamics, an increase was recorded in Fe and P flux fluctuation due to convection. Based on the findings, maintaining hydraulic residence time (HRT) under 24 hours and reed bed influent in concentrations above 0.5 mg/L total phosphorus (TP) and 15 mg/L NO3-N is proposed as a means to prevent or delay P release.Item Open Access Assessing the potential for tertiary nitrification in sub-surface flow constructed wetlands(Taylor and Francis, 2016-06-10) Butterworth, Eleanor; Richards, Andrew; Jones, Mark; Dotro, Gabriela; Jefferson, BruceThe challenge of how to maintain or improve wastewater treatment performance without causing an excessive increase in energy or costs is increasingly focussed towards ammonia. On small sewage treatment works, solutions have historically been energy intensive: to divert waste to a larger plant, add a polishing step to the end of the process flow sheet or upgrade and replace upstream processes. Constructed wetlands (CWs) offer a low energy alternative to meet these challenges. This review explores oxygen transfer theory; nitrification performance of existing CW systems, and the key affecting factors to be considered when implementing the technology for tertiary treatment upgrades. Future perspectives include the use of artificial aeration and greater consideration of vertical sub-surface flow systems as they achieve the nitrification capacity in a smaller footprint than horizontal flow systems and, where suitable hydraulics permit, can be operated under very low energy demand.Item Open Access Assessment of activated sludge, membrane bioreactors and vertical flow wetlands for upgrading sewage treatment works(Taylor & Francis, 2016-11-29) Le Corre Pidou, Kristell; Dotro, Gabriela; Jefferson, BruceThis paper demonstrates that utilising a vertical flow (VF) wetland after a conventional activated sludge (CAS) delivers equivalent or better effluent quality to a membrane bioreactor (MBR) based on a side-by-side pilot trial. The CAS was operated under the solids retention times (SRT) of 6, 12, and 20 days, with the effluent from each pilot plant fed onto a soil aquifer treatment column to better understand their water reuse application potential. Results showed an upgraded CAS + VF system could deliver effluents with median values of 34 mgO2.L–1, 7 mg.L–1 and 1.9 mg.L–1 for organics, solids and ammonia nitrogen, respectively, which were statistically similar to those from the MBR. Water reuse standards were achieved by the upgraded system for most parameters, with the exception of total coliform removal. The upgraded system delivered superior metal removal when compared to the CAS. An economic analysis showed upgrading a CAS with a VF wetland was more favourable than investing in an MBR system for example works of 5000 and 50,000 population equivalents if the VF system was operated at hydraulic loading rates of 0.03 m.d–1 and 0.08 m.d–1, respectively. This was delivered for a tenth of the carbon footprint of the MBR treatment.Item Open Access Assessment of tertiary reed beds in chemically-dosed wastewater treatment plants for phosphorus removal(Cranfield University, 2013-03) Prieto Fort, Raul; Jefferson, Bruce; Dotro, GabrielaEutrophication is one of the problems affecting the environmental quality standards of fresh waters. Phosphorus (P) is considered a main nutrient contributing to this. In the UK, the Water Industry is responsible for c. 50% of the total phosphorus load to freshwater ecosystems. Within this, small wastewater treatment plants (WwTPs) (<2,000 population equivalent) have a significant role since they represent 75% of all WwTPs in the UK. The current option for P removal from wastewater is chemical precipitation through the dosing of iron (Fe) salts in combination with a tertiary filtration treatment step. This study aims to determine the transformation processes whereby tertiary reed beds permanently store or release iron and phosphorus in chemically-dosed sites to provide recommendations regarding the conditions where reed beds can be used as such final filtration treatment in small WwTPs. This was carried out through sampling campaigns in 14 full-scale tertiary reed beds. Chemically-dosed WwTPs with tertiary reed beds can perform satisfactorily achieving phosphorus removals above 85% and average P and Fe final effluent concentrations of 0.7 mg P/L and 0.2 mg Fe/L, respectively, both well below consents (2 mg TP/L and 4 mg Fe/L). The majority of the total phosphorus in the reed bed influents was associated to either suspended solids or dissolved fractions, whereas 60¬90% of the effluent TP is in the dissolved form. Occasional episodes of phosphorus release from the reed bed can occur, as evidenced in an increase in soluble reactive phosphorus in the effluent. The main mechanism for trapping of Fe and P in mature beds was settlement of suspended particles, with phosphorus and iron concentrations in the accumulated sludge being up to 55.9 g P/kg dry matter and 246.6 g Fe/kg DM. The removal of particulate pollutants was successful in the reed beds studied, but colloidal and dissolved particles passing through the beds untreated. This could compromise the use of reed beds with future tightening P consents if the current chemical dosing practices are unchanged.Item Open Access Coagulation–flocculation process with metal salts, synthetic polymers and biopolymers for the removal of trace metals (Cu, Pb, Ni, Zn) from municipal wastewater(Springer, 2018-07-02) Hargreaves, Andrew J.; Vale, Peter C. J.; Whelan, Jonathan; Alibardi, Luca; Constantino, Carlos; Dotro, Gabriela; Cartmell, EliseTo ensure compliance with regulatory standards, it is important to examine the potential of treatment technologies to enhance trace metal removal from wastewater. This study investigated the effectiveness of coagulation–flocculation at removing trace metals from humus effluent with ferric chloride (FeCl3), the synthetic polymer polyethyleneimine (PEI) and the biopolymers chitosan and floculan. Effluent samples were collected from a trickling filter treatment works operating in the UK and contained 21 ± 4 μg/L Cu, 0.8 ± 0.1 μg/L Pb, 4 ± 1 μg/L Ni and 43 ± 9 μg/L Zn. The influence of coagulant dosage and the velocity and time of the slow mixing stage were studied via a series of jar tests. Chitosan and PEI had a moderate effect on the removal of trace metals (≤ 35%). FeCl3 removed 48% Cu, 56% Pb and 41% Zn at the optimised dose of 0.10 mg/L. At the optimised dose of 0.25 mg/L, floculan removed 77% Cu, 68% Pb and 42% Zn. The dominant mechanism for particle removal by FeCl3 was enmeshment in the precipitates (i.e. sweep flocculation), whereas, for floculan, inter-particle bridging was the dominant removal mechanism. Overall, FeCl3 and floculan were found to be most effective at removing trace metals from wastewater.Item Open Access Constructed wetlands as nature-based solutions in managing per-and poly-fluoroalkyl substances (PFAS): evidence, mechanisms, and modelling(Elsevier, 2024-07-15) Savvidou, Pinelopi; Dotro, Gabriela; Campo, Pablo; Coulon, Frederic; Lyu, TaoPer- and poly-fluoroalkyl substances (PFAS) have emerged as newly regulated micropollutants, characterised by extreme recalcitrance and environmental toxicity. Constructed wetlands (CWs), as a nature-based solution, have gained widespread application in sustainable water and wastewater treatment and offer multiple environmental and societal benefits. Despite CWs potential, knowledge gaps persist in their PFAS removal capacities, associated mechanisms, and modelling of PFAS fate. This study carried out a systematic literature review, supplemented by unpublished experimental data, demonstrating the promise of CWs for PFAS removal from the influents of varying sources and characteristics. Median removal performances of 64, 46, and 0 % were observed in five free water surface (FWS), four horizontal subsurface flow (HF), and 18 vertical flow (VF) wetlands, respectively. PFAS adsorption by the substrate or plant root/rhizosphere was deemed as a key removal mechanism. Nevertheless, the available dataset resulted unsuitable for a quantitative analysis. Data-driven models, including multiple regression models and machine learning-based Artificial Neural Networks (ANN), were employed to predict PFAS removal. These models showed better predictive performance compared to various mechanistic models, which include two adsorption isotherms. The results affirmed that artificial intelligence is an efficient tool for modelling the removal of emerging contaminants with limited knowledge of chemical properties. In summary, this study consolidated evidence supporting the use of CWs for mitigating new legacy PFAS contaminants. Further research, especially long-term monitoring of full-scale CWs treating real wastewater, is crucial to obtain additional data for model development and validation.Item Open Access Data subset for Chapter 3: Particle sizing data(Cranfield University, 2022-12-13 12:33) Brown, Gareth; Jefferson, Bruce; Dotro, Gabriela; MacAdam, JitkaThe particle sizing dataset as underlying the data presenting in the study 'Impact of low temperatures on anaerobic hydrolysis in passive treatment systems such as septic tanks' measured on a Malvern mastersizer, for the batch tests run a 5, 15 37 degrees celcuis and a sample prior to digestion.Item Open Access Data Supporting Chapter 3: Extracellular Enzyme Activity(Cranfield University, 2022-12-13 12:34) Brown, Gareth; Jefferson, Bruce; MacAdam, Jitka; Dotro, GabrielaThe raw and processed data of thhe extracellular lipase activity supporting the study 'Impact of low temperatures on anaerobic hydrolysis in passive treatment systems such as septic tanks'Item Open Access Data Supporting: A whole life cost and carbon perspective of alternatives to septic tanks utilising nature based solutions(Cranfield University, 2022-12-13 12:33) Brown, Gareth; Jefferson, Bruce; MacAdam, Jitka; Dotro, GabrielaThe data summary alongside the costing calculation and lifecycle inventory for the study 'A whole life cost and carbon perspective of alternatives to septic tanks utilising nature based solutions'Item Open Access Developing the next generation of treatment flowsheets for rural wastewater(Cranfield University, 2022-12) Brown, Gareth; Jefferson, Bruce; MacAdam, Jitka; Dotro, GabrielaSeptic tank systems (STS) are one of the most common wastewater treatment systems in the world however these systems are becoming antiquated, struggling to meet tighter consent, needing frequent desludging and venting greenhouse gases to the environment. A flowsheet to tackle these issues was proposed consisting of an enhanced septic tank (EST) and a constructed wetland (CW). The proposed flowsheet was assessed by examining the underlying mechanisms, testing the flowsheet at pilot scale and assessing the cost and carbon implications of the flowsheet. A key aim of the thesis is to decrease the maintenance of the flowsheet to once every 5 to 7 years. The maintenance of septic tank is due to desludging, as the tank needs to be emptied when the sludge bed reaches a certain height. The desludging of a septic tank is dependent on the hydrolysis rate within the reactor. Batch studies into anaerobic digestion found that low operating temperatures in septic tanks impact the hydrolysis rate. However, temperature is not the dominant factor of hydrolysis and optimisation of mass transfer between hydrolytic microorganisms and degradable particulates can increase the hydrolysis rate by 200%. A pilot scale study investigated using baffles to promote hydraulic mixing within a septic tank. The presence of hydraulic mixing due to the baffles increased the hydrolysis rate constant of a septic tank from 0.0089 d⁻¹ to 0.035d⁻¹, extending the time between desludging from 4.9 to 6.7 years. The proposed flowsheet is a lower cost treatment system than a conventional package treatment system (e.g. submerged aerated filter) over a 30 year life time and leads to a significant reduction in lifetime carbon emissions compared to a STS. The cost and carbon reduction of the flowsheet make the flowsheet a viable abatement technique.Item Open Access Education in ecological engineering – A need whose time has come(Springer, 2021-06-12) Dale, Glenn; Dotro, Gabriela; Srivastava, Puneet; Austin, David; Hutchinson, Stacy; Head, Peter; Goonetilleke, Ashantha; Stefanakis, Alexandros; Junge, Ranka; Fernández L., José A.; Weyer, Vanessa; Truter, Wayne; Bühler, Devi; Bennett, John; Liu, Hongbo; Li, Zifu; Du, Jianqiang; Schneider, Petra; Hack, Jochen; Schönborn, AndreasThe Importance of Ecological Engineering in Society In this paper, the importance of ecological engineering education is discussed in relation to the perceived need of our society to address global challenges of sustainable development. The perceived needs of industry, practitioners, educators and students for skills in ecological engineering are also discussed. The Importance and Need for Ecological Engineering Education The need for integrative, interdisciplinary education is discussed in relation to the scope of ecology, engineering and the unique role of ecological engineering.Item Open Access Impact of aeration on macrophyte establishment in sub-surface constructed wetlands used for tertiary treatment of sewage(Elsevier, 2016-02-27) Butterworth, Eleanor; Richards, Andrew; Jones, Mark; Brix, Hans; Dotro, Gabriela; Jefferson, BruceThe effect of artificial aeration on plant growth in constructed wetlands in terms of above and below ground biomass and nutrient uptake of two macrophyte species Phragmites australis and Typha latifolia was carried out to provide quantitative, mechanistic evidence to support any differences between the plant species establishment. Pilot scale systems were built and supplied with different intensities of aeration and corresponding controls, with supporting evidence from two full scale operational sites. Results show T. latifolia was more impacted by aeration than P. australis when comparing against their respective non-aerated controls, evidenced in reduced height, growth rate and leaf length. However, the impact was less visible due to T. latifolia's faster growth rate compared to P. australis. Micro and macronutrient uptake by each species had no discernible pattern, preventing the identification of a definitive mechanism to explain the retarded growth. However, results suggest a synergy between iron and manganese may be at play.Item Open Access Impacts of coagulation-flocculation treatment on the size distribution and bioavailability of trace metals (Cu, Pb, Ni, Zn) in municipal wastewater(Elsevier, 2017-10-25) Hargreaves, Andrew J.; Vale, Peter C. J.; Whelan, Jonathan; Alibardi, Luca; Constantino, Carlos; Dotro, Gabriela; Cartmell, Elise; Campo, PabloThis study investigated the impact of coagulation-flocculation treatment on metal form and bioavailability in municipal wastewater. Real humus effluent samples were separated into particulate, colloidal and truly dissolved fractions before and after treatment with either ferric chloride (FeCl3) or the biopolymer Floculan. Results revealed that both reagents effectively (≥48%) eliminated Cu, Pb and Zn from the particulate fraction and removed Cu and Zn from the colloidal fraction in conjunction with colloidal organic carbon (COC). Although organics in the truly dissolved fraction were resistant to removal, Floculan reduced Cu in this fraction by 72% owing to the complexation of free Cu ions to phenol and amino groups along the polymeric chains, revealing an additional removal pathway. In fact, COC removed in the CF process by Floculan was replaced with truly dissolved compounds, input as a result of this reagents organic composition. Floculan, therefore, reduced the soluble concentration of Cu and Zn without changing the DOC concentration, thus reducing the bioavailability of these metals in treated effluent. FeCl3 did not reduce the bioavailability of target metals, thus did not deliver any environmental benefit. This work provides important information for the selection and development of high performance coagulants to improve metal removal.Item Open Access Influence of sludge layer properties on the hydraulic behaviour of gravel-based vertical flow constructed wetlands for primary treatment of sewage(Elsevier, 2019-07-09) Khomenko, Olha; Dotro, Gabriela; Jefferson, Bruce; Coulon, Frederic; Bajón Fernández, YadiraSludge accumulation on the first stage of French design vertical flow constructed wetlands has been reported to improve treatment performance by favouring even sewage distribution on the beds' surface and increasing water retention time. However, due to its relatively low permeability, sludge layer can restrict the hydraulic capacity of the wetlands, requiring careful consideration of the feeding and resting strategy in order to avoid system ponding. This study aimed to elucidate the impact that sludge layer properties have on its permeability and investigate artificial modifications that could enhance it. A positive impact of increased organic matter content on sludge permeability was observed, with a 3-times permeability increase for a 15 percentage points higher volatile solids content. The opposite effect was observed for total solids, where an increase of 19 percentage points led to a drop of 1.6 × 10−16 m2 on permeability. The impact of different surface modifications on drying kinetics and sludge layer properties was studied as a means to accelerate sludge layer mineralisation. Artificial modifications that modify surface tension of the sludge layer have been proved to achieve greater permeability and faster mineralisation of the sludge, with potential to achieve higher hydraulic acceptance and reduced operational costs (lower sludge accumulation) if implemented in full scale vertical flow constructed wetlands.Item Open Access Mercury and antimony in wastewater: fate and treatment(Springer Verlag, 2016-02-23) Hargreaves, Andrew J.; Vale, Peter C. J.; Whelan, Jonathan; Constantino, Carlos; Dotro, Gabriela; Cartmell, EliseIt is important to understand the fate of Hg and Sb within the wastewater treatment process so as to examine potential treatment options and to ensure compliance with regulatory standards. The fate of Hg and Sb was investigated for an activated sludge process treatment works in the UK. Relatively high crude values (Hg 0.092 μg/L, Sb 1.73 μg/L) were observed at the works, whilst low removal rates within the primary (Hg 52.2 %, Sb 16.3 %) and secondary treatment stages (Hg 29.5 %, Sb −28.9 %) resulted in final effluent concentrations of 0.031 μg/L for Hg and 2.04 μg/L for Sb. Removal of Hg was positively correlated with suspended solids (SS) and chemical oxygen demand (COD) removal, whilst Sb was negatively correlated. Elevated final effluent Sb concentrations compared with crude values were postulated and were suggested to result from Sb present in returned sludge liquors. Kepner Tregoe (KT) analysis was applied to identify suitable treatment technologies. For Hg, chemical techniques (specifically precipitation) were found to be the most suitable whilst for Sb, adsorption (using granulated ferric hydroxide) was deemed most appropriate. Operational solutions, such as lengthening hydraulic retention time, and treatment technologies deployed on sludge liquors were also reviewed but were not feasible for implementation at the works.Item Open Access Partitioning and removal of per- and polyfluoroalkyl substances (PFAS) in full-scale surface flow treatment wetlands with different upstream wastewater treatment(Elsevier, 2025-03-01) Sarti, Chiara; Souleymane, Ayisha Affo; Dotro, Gabriela; Cincinelli, Alessandra; Lyu, TaoThe performance of treatment wetlands (TWs), as a nature-based solution, in mitigating persistent per- and polyfluoroalkyl substances (PFAS) and their interactions with existing treatment flowsheets remain unclear. This study investigated PFAS removal in two full-scale surface flow TWs treating secondary effluent from different domestic wastewater treatment plants (WWTPs). The systems demonstrated their capacities to safeguard natural water bodies by achieving discharge levels of the legacy PFOS (4–4.6 ng L−1) and PFOA (1.79–3.27 ng L−1) with removal efficiencies of 29%–38% and 15%–34%, respectively. Further upstream and downstream water quality monitoring in receiving waters is required to accurately evaluate PFAS contributions from WWTP effluents. Partitioning behaviour analysis revealed that sediment adsorption was the dominant removal pathway, achieving removal rates 16–61 times higher than plant uptake for PFOS and 1.8–6 times higher for PFOA. Sediment iron content, depth, and bulk density were positively correlated with PFAS sequestration, highlighting their importance in controlling PFAS mobility. PFOS accumulation in the sediment was greater in the TW for the WWTP dosing with ferric sulphate than the WWTP without chemical dosing (2.80 mg m−2 y−1 vs. 1.34 mg m−2 y−1). Notably, a conventional mass balance analysis was challenged by the transformation of PFAS precursors into terminal compounds, including PFOS and PFOA, potentially inflating input concentrations and contributing to mass imbalance during treatment. Further research is necessary to address these complexities, but the findings are encouraging for the use of TWs as scalable, eco-friendly solutions for mitigating PFAS pollution and are instructive for optimising wetland design and operation to safeguard aquatic ecosystems.Item Open Access Performance of four full-scale artificially aerated horizontal flow constructed wetlands for domestic wastewater treatment(2016-09-16) Butterworth, Eleanor; Richards, Andrew; Jones, Mark; Mansi, Gabriella; Ranieri, Ezio; Dotro, Gabriela; Jefferson, BruceA comparison of the performance of four full-scale aerated horizontal flow constructed wetlands was conducted to determine the efficacy of the technology on sites receiving high and variable ammonia loading rates not yet reported in the literature. Performance was assessed in terms of ammonia and solids removal, hydraulic conductivity and mixing patterns. The capability of systems to produce ammonium effluent concentrations <3 mgNH4 + -N/L was observed across all sites in systems receiving variable loadings between 0.1 and 13.0 gNH4 + -N/m2 /d. Potential resilience issues were observed in relation to response to spike loadings posited to be due to an insufficient nitrifying population within the beds. Hydraulic conductivity and flow mixing patterns observed suggested deterioration of the reactor effective volume over time. Overall, the study demonstrates the efficacy of the technology where ammonium removal is required on small sites receiving high and variable flow rates, with adequate removal of organics and solids, but no significant benefit to the long term hydraulics of the system.Item Open Access Phosphorus removal in surface flow treatment wetlands for domestic wastewater treatment: Global experiences, opportunities, and challenges(Elsevier, 2024-10-01) Lyu, Tao; Headley, Tom; Kadlec, Robert H.; Jefferson, Bruce; Dotro, GabrielaTreatment Wetlands (TWs) are widely used for the treatment of domestic wastewater, with an increasing emphasis on provision of multiple co-benefits. However, concerns remain regarding achieving stringent phosphorus (P) discharge limits, system robustness and resilience, and associated guidance on system design and operation. Typically, where P removal is intended with a passive TW, surface flow (SF) systems are the chosen design type. This study analysed long-term monitoring datasets (2–30 years) from 85 full-scale SF TWs (25 m2 to 487 ha) treating domestic sewage with the influent load ranging from 2.17 to 54,779 m3/d, including secondary treatment, tertiary treatment, and combined sewer overflows treatment. The results showed median percentage removals of total P (TP) and orthophosphate (Ortho P) of 28% and 31%, respectively. Additionally, median areal mass removal rates were 5.13 and 2.87 gP/m2/yr, respectively. For tertiary SF TWs without targeted upstream P removal, 80% of the 44 systems achieved ≤3 mg/L annual average effluent total P. Tertiary SF TWs with targeted upstream P removal demonstrated high robustness, delivering stable effluent TP < 0.35 mg/L. Seasonality in removal achieved was absent from 85% of sites, with 95% of all systems demonstrating stable annual average effluent TP concentrations for up to a 30-year period. Only two out of 32 systems showed a significant increase in effluent TP concentration after the initial year and remained stable thereafter. The impact of different liner types on water infiltration, cost, and carbon footprint were analysed to quantify the impact of these commonly cited barriers to implementation of SF TW for P removal. The use of PVC enclosed between geotextile gave the lowest additional cost and carbon footprint associated with lining SF TWs. Whilst the P-k-C* model is considered the best practice for sizing SF TWs to achieve design pollutant reductions, it should be used with caution with further studies needed to more comprehensively understand the key design parameters and relationships that determine P removal performance in order to reliably predict effluent quality.Item Open Access Pollution prevention in wastewater networks: development of a biological early warning device(Cranfield University, 2016-06) Black, Gary; Dotro, Gabriela; Nocker, Andreas; Coulon, FredericA biological early warning system (EWS) was developed to screen wastewater containing nitrification inhibitors and identify nitrifying bacteria activity reduction without relying on absolute values of sensor signals. To do so, numerous sensors were evaluated using a tiered approach to aid the analysis and made it easier to convey the current state of the technology. The research then produced a framework for the development of an EWS and the applicability of sensors to the wastewater matrix. The research identified a need for the development of a strategy and guidance that can help in the prevention and detection of nitrification inhibitors. Initial tests focussed on sewer biofilm N2O emissions, however, despite average nitrification rates of 19.5 g-NH4 + - N.m- 2 .d- 1 the response was unreliable due to inadequate control. To address this, a circulating floating bed biofilm reactor (CFBBR) was designed as a sidestream. The CFBBR biofilm’s toxicity response was compared to the sewer biofilm, a 2850 mg.L- 1 MLSS culture and a 10.5 mg.L- 1 MLSS culture (with equivalent biomass concentration to the CFBBR biofilm). The cultures responded differently with an inhibitory effect scale of Cu2+ > ATU > Ni2+ > Cr6+ for CFBBR biofilm, ATU > Cu2+ > Ni2+ > Cr6+ for 2850 mg L- 1 MLSS, ATU > Ni2+ > Cr6+ > Cu2+ for 10.5 mg.L- 1 MLSS and ATU > Cu2+ > Cr6+ > Ni2+ for sewer biofilm. This was firstly attributed to suspended growth nitrification stimulation by Cu2+ doses up to ~45 mg.L- 1 resulting in a lower inhibitory effect. Secondly, very high Cr6+ and Ni2+ doses were required for biofilm nitrification inhibition, due to diffusion limitations and slow transport through cell membranes. The CFBBR biofilm response to heavy metals was characterised through N2O and CO2 spikes and a post shock emissions recovery period was observed with the trend Ni2+ > Cr6+ > Cu2+ . A 10 minute hydraulic retention time allowed quick detection and steady state nitrification rates of 0.4 g-NH4 + -N.m- 2 .d- 1 despite high organic loading rates. Additionally, a suspended growth based monitor (Nitritox) was assessed as an inlet works toxicity detector. Incorporation of a Nitritox with a CFBBR based sewer monitor offered increased robustness over a CFBBR only system and was shown to be viable system in catchments >200,000 population equivalent. This information is useful to water utilities so that they can plan for and experiment with upset early warning protocols. It is also useful to manufacturers as they can determine product performance needs.