CERES :: Browsing by Author "Jefferson, Bruce"

Browsing by Author "Jefferson, Bruce"

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Open Access
Achieving drinking water compliance levels for metaldehyde with an acclimated sand bioreactor
(Elsevier, 2020-07-06) Rolph, Catherine A.; Jefferson, Bruce; Brookes, Adam; Hassard, Francis; Villa, Raffaella;
Metaldehyde removal was delivered to below the 0.1 µg L-1 regulatory concentration in a laboratory scale continuous upflow fluidised sand bioreactor that had undergone acclimation through selective enrichment for metaldehyde degradation. This is the first reported case of successful continuous flow biological treatment of metaldehyde from real drinking water sources treating environmentally realistic metaldehyde concentrations. The impact of the acclimation process was impermanent, with the duration of effective treatment directly related to the elevated concentration of metaldehyde used during the enrichment process. The efficacy of the approach was demonstrated in continuous flow columns at both laboratory and pilot scale enabling degradation rates of between 0.1 and 0.2 mg L-1 h-1. Future work needs to focus on optimisation of the sand bioreactor and the acclimation process to ensure viability and feasibility of the approach at full scale
Open Access
Aeroterrestrial and freshwater microalgae biofilms: deposition and growth in aqueous and non-aqueous systems.
(2016-12) Ledwoch, Katarzyna; Villa, Raffaella; Jefferson, Bruce
Non-suspended microalgal cultivation methods have gained an interest over the last decade. In contrast to traditional cultivation systems, where microalgae are grown in highly diluted suspensions, microalgae grow concentrated in biofilms over a particular substrate. Growth in biofilms gives higher biomass concentrations of end products and decreases overall water and energy consumption. However, there are research gaps in the field of biofilm formation and growth. The studies on material and strain properties and their effects on microbial attachment are very limited. So far, a small number of strains and materials have been tested, leading to many contradictory conclusions. In this thesis the primary colonisation of 36 material-strain pairings was tested and related to topographical and physicochemical properties of substrates. Experimental data was also confronted against properties of microalgal strains. Further microalgal biofilm development in aerial conditions, and its relation to substrate properties, was analysed for the first time. To address some of the sustainability issues associated with microalgal cultivation, a novel Humid Biofilm-Based Reactor (HBBR) was also proposed. This novel method focused on growing microalgae in a humid atmosphere enriched with nutrients. The natural phenomenon of biofilm development in aerial humid conditions was a working principle of the system, resulting in higher biomass concentrations than in other non-suspended reactors proposed so far. Using mist instead of a liquid medium significantly minimised the water consumption. No presence of a liquid medium in the reactor enabled easier maintenance of the system and improved light distribution. Growth trial in this novel reactor and its comparison to reference systems showed that HBBR was a promising way of culturing microalgae with higher growth rates, lower water and nutrient consumption, more effective light distribution and easier maintenance of the system.
Open Access
Aged-engineered nanoparticles effect on sludge anaerobic digestion performance and associated microbial communities
(Elsevier, 2017-07-23) Eduok, Samuel; Ferguson, Robert M. W.; Jefferson, Bruce; Villa, Raffaella; Coulon, Frederic
To investigate the potential effect of aged engineered nanoparticles (a-ENPs) on sludge digestion performance, 150 L pilot anaerobic digesters (AD) were fed with a blend of primary and waste activated sludge spiked either with a mixture of silver oxide, titanium dioxide and zinc oxide or a mixture of their equivalent bulk metal salts to achieve a target concentration of 250, 2000, and 2800 mg kg− 1 dry weight, respectively. Volatile fatty acids (VFA) were 1.2 times higher in the spiked digesters and significantly different (p = 0.05) from the control conditions. Specifically, isovaleric acid concentration was 2 times lower in the control digester compared to the spiked digesters, whereas hydrogen sulfide was 2 times lower in the ENPs spiked digester indicating inhibitory effect on sulfate reducing microorganisms. Based on the ether-linked isoprenoids concentration, the total abundance of methanogens was 1.4 times lower in the ENPs spiked digester than in the control and metal salt spiked digesters. Pyrosequencing indicated 80% decrease in abundance and diversity of methanogens in ENPs spiked digester compared to the control digester. Methanosarcina acetivorans and Methanosarcina barkeri were identified as nano-tolerant as their relative abundance increased by a factor of 6 and 11, respectively, compared to the other digesters. The results further provide compelling evidence on the resilience of Fusobacteria, Actinobacteria and the Trojan horse-like effect of ENPs which offered a competitive advantage to some organisms while reducing microbial abundance and diversity.
Open Access
Algae reactors for wastewater treatment
(Cranfield University, 2016-02) Whitton, Rachel Louise; Jefferson, Bruce; Villa, Raffaella
The onset of the Water Framework Directive (WFD) will challenge water utilities to further reduce their wastewater phosphorus discharges to < 0.5 mg.L- 1 . Whilst conventional treatments, such as chemical dosing, are able to meet these new discharge consents, the strategies are representative of a linear economy model where resources are unrecovered and disposed. An alternative solution which can contribute to the aspiration of a circular economy is microalgae. Microalgae are ubiquitous in wastewater environments and assimilate phosphorus during their growth, to residual concentrations complementary of the WFD. Furthermore, microalgal biomass can be anaerobically digested to produce biomethane offering the potential for an energy neutral approach. However, uptake of microalgal systems are lacking in the UK through limited knowledge of operation; and the belief that such solutions are synonymous to large, shallow open ponds with extensive treatment times. The development of alternative microalgal reactors are increasingly investigated to overcome these implementation challenges. Of these, immobilised microalgae has shown great potential; and whilst within its infancy demonstrates the greatest opportunity for development and optimisation. This thesis determines the critical operational parameters that influence the remediation efficacy of immobilised microalgae for tertiary nutrient removal; including species selection, biomass concentration, treatment period and lighting; with recommendations for optimal performance. These recommendations are then applied to the design and operation of an immobilised bioreactor (IBR) to understand the key design and operating components that influence the overall economic viability. In doing so, the potential for an IBR to be economically viable, within the next decade, in comparison to traditional approaches are discussed.
Open Access
Ammonia recovery from brines originating from a municipal wastewater ion exchange process and valorization of recovered nitrogen into microbial protein
(Elsevier, 2021-06-18) Guida, Samuela; Van Peteghem, Lotte; Luqmani, Ben; Sakarika, Myrsini; McLeod, Andrew; McAdam, Ewan J.; Jefferson, Bruce; Rabaey, Korneel; Soares, Ana
A hollow fibre membrane contactor (HFMC), and two vacuum thermal stripping processes, a rotary evaporator (VTS) and multi-component system (MVTS) were compared for their ability to recover ammonia (NH3) from ion exchange (IEX) regeneration brines. The IEX was a 10 m3/day demonstration scale plant fed with secondary municipal wastewater. The 10% potassium chloride regeneration brine was used multiple times leading to ammonium (NH4+-N) saturation (up to 890 mg N/L). When treating the saturated IEX brine, the highest NH3 mass transfer coefficient for the HFMC, MVTS and VTS were 0.6, 0.7 and 0.1 h−1, respectively, compared to values between 1.7 and 3.5 h−1, when treating a synthetic solution. The highest NH3 recovery was obtained with the HFMC (99.8%) and the ammonium sulphate produced was characterised for impurities, presenting high quality. Concentrated ammonium (NH4+-N) solutions (0.5–3.1 g N/L) were obtained from the MVTS and VTS processes. To further valorise the recovered NH4+-N solution produced from the MVTS process, this was used as a substrate for microbial protein (MP) production. Limited differences were observed for production rate (specific growth rate 0.092–0.40 h−1), protein yield (0.021–0.18 g protein/g acetate-CODconsumed) and protein content (0.073–0.87 g protein/g cell dry weight) between recovered and commercial nitrogen (N) sources, indicating that recovered N from IEX can serve as a substrate for MP production. This study demonstrates a comprehensive N management solution for wastewater applications, leading to a range recovered products. These combined technologies can contribute to the local economy, whilst delivering to the ambitious NET-ZERO and circular economy targets.
Open Access
Ammonium and phosphorus removal and recovery from wastewater through the ion exchange process.
(2020-07) Guida, Samuela; Soares, Ana; Jefferson, Bruce
Challenges to implement circular economy principles in the wastewater cycle are connected to the need of reducing nutrients (ammonium as NH₄⁺-N, and phosphorus as PO₄-P) in treated effluent whilst enabling their recovery in an environmentally sustainable way. Conventional biology-based technologies fail to address these challenges by having high greenhouse gases footprint and offering limited possibilities for nutrient recovery. The aim of this work was to underline the mechanisms of removal and recovery of NH₄⁺-N and PO₄-P from wastewater through the ion exchange (IEX) process in order to optimise the removal efficiency and maximise the recovery from IEX regenerant brines (sodium hydroxide and potassium chloride), when working at demonstration scale over an extended period of time. The IEX process was tested in a 10 m³/day demonstration plant for 2.5 years using Zeolite-N and a hybrid anion exchanger (HAIX) for the removal of NH₄⁺-N and PO₄-P at empty bed contact times of 10 and 5 min, respectively. The operation at demonstration scale confirmed the resilience and consistency of the IEX process and the possibility to maintain high effluent quality (<0.3 mg PO₄-P/L and <1 mg NH₄⁺-N/L) despite changes in influent concentration (i.e. <0.006-26 mg NH₄⁺-N/L) and extended operational period (up to 63 consecutive adsorption/regeneration cycles with HAIX). Additionally, the regenerant brines were reused multiple times and nutrients could be recovered as high purity ammonium sulphate and hydroxyapatite using a hollow fibre membrane contactor for ammonium recovery and simple precipitation with calcium hydroxide and filtration for phosphorus recovery. The results obtained from this work additionally highlighted the need of an automated system to start the regeneration when the desired effluent quality is reached, the need of a nearly solids-free influent and high mechanical strength media to avoid media packing and losses. This work significantly moved the IEX process higher in the technology readiness level (from level 5 to level 7) for mainstream wastewater treatment with the advantages of simple operation, consistency, resilience and lower environmental impact (-25% cumulative energy demand, - 66% global warming potential, -62% marine eutrophication potential) compared to traditional biological processes.
Open Access
Anaerobic membrane bioreactors for municipal wastewater treatment
(Cranfield University, 2006-08) Fawehinmi, Folasade; Jefferson, Bruce
Anaerobic treatment has historically been considered unsuitable for the treatment of domestic wastewaters. The work presented in this thesis focuses on the incorporation of membranes into the anaerobic bioreactor to uncouple solid retention time and hydraulic retention time. This in turn prevents biomass washout and allows sufficient acclimatisation periods for anaerobes. However, the exposure of membranes to anaerobic biomass comes with its own inherent problems namely fouling. Fouling was found to take place in two stages; a rapid phase characterised by solid and bacterial cell deposition and a slow phase characterised by the travel of colloidal matter to the membrane surface. Gas sparging was also found to attenuate fouling to a considerable extent despite the fact that biomass characteristics were critical factors in the fouling of the system. In addition, side stream membranes showed differing characteristics to submerged membranes. A comparison of anaerobic membrane bioreactors to conventional anaerobic systems and aerobic membrane bioreactors highlighted the advantage of this system over other comparable technologies. The anaerobic membrane bioreactor is less energy intensive than the aerobic membrane bioreactor, fouls differently to this system and achieves much better performance than would be seen if conventional anaerobic systems were used in the treatment of domestic or municipal wastewaters.
Open Access
Analysis of phosphorus flux in reed beds at chemically dosed wastewater treatment works
(Cranfield University, 2014-05) Barak, Jan; Dotro, Gabriela; Jefferson, Bruce
Phosphorus (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.
Open Access
Application of activated carbon fabric for the removal of a recalcitrant pesticide from agricultural run-off
(Elsevier, 2022-01-08) Cosgrove, Stephanie; Jefferson, Bruce; Jarvis, Peter
Removal of pesticides from agricultural run-off close to the point of application has the potential to prevent or reduce the pollution of water sources used for drinking. This research considered the novel application of activated carbon (AC) fabric as a sorbent material for removal of pesticides from field run-off. AC fabric was tested for the removal of the molluscicide pesticide metaldehyde under a range of flow rates at both laboratory and pilot scale. Metaldehyde at an initial concentration of 10 μg/L was removed effectively from deionised (DI) water and real source water by the AC cloth under all conditions tested, reaching removal of 1375 and 876 μg/g (equivalent to 169 and 264 mg/m2), respectively. The adsorption followed pseudo-second order kinetics (k2 of 29.9 and 34.8 g/μg min for the AC fabric and GAC), providing rapid removal of metaldehyde within the first 5 min of contact. In single pass and flow through conditions, stabilised removal of 46% metaldehyde was achieved by the AC fabric bundle for treatment of 700 L of real water in a pilot scale flume. This equated to removal of 454 μg/m2, although significantly more removal would be expected over longer duration testing given the stabilised removal and the equilibrium capacity of the fabric seen during the batch isotherm testing. The work provides evidence to show that AC fabric could be used in the catchment to reduce peak loads of pesticides in sources used for drinking water.
Open Access
Application of microbubbles to ozonation for drinking water treatment.
(Cranfield University, 2022-11) John, Alexander; Jarvis, Peter; Carra ruiz, Irene; Jefferson, Bruce
Ozonation is a widely used water treatment process that is used to oxidise contaminants as well as disinfect water. Conventional ozone contactors have a large energy requirement and deep tanks to ensure adequate mass transfer. As a result, the delivery of ozone into water is an energy intensive and expensive process. The use of microbubbles in water treatment is a new technology that has been shown to significantly improve gas-liquid contacting processes. Microbubbles have diameters ranging from 1 – 100 µm, whereas conventional bubbles used in typical ozone contactors have diameters ranging from 2 – 6 mm. Due to their small size, microbubbles have a larger interfacial area and a lower rise velocity than conventional bubbles. Therefore, ozone in the gas phase may be transported more efficiently into the liquid phase. Despite the favourable properties of microbubbles, the mechanism by which microbubbles outperform conventional bubbles is not fully understood, with various conflicting interpretations having been presented in the literature. This work is comprised of several direct-comparison studies of microbubble and conventional bubble ozonation systems under identical conditions. Experiments were normalised for both input and effective ozone dose in order to determine a number of critical performance parameters including: hydroxyl radical production, volumetric mass transfer coefficient, ozone self-decomposition, rate and extent of compound removal and bromate formation. Overall, the observed performance enhancement was attributed to an increase in the volumetric mass transfer coefficient through the combination of an increase in bubble specific interfacial area and a decrease in the mass transfer coefficient. When normalised to effective ozone dose, no enhancement in hydroxyl radical production or increase in bromate formation was observed. In addition, the generation of microbubbles results in a distribution of bubbles containing both micro- and nanobubbles. It was concluded that in order to optimise the overall ozonation process, emphasis should be placed on understanding how to manage the size distribution of the microbubble fraction as the risk of residual ozone from nanobubble survival was deemed insignificant. These findings were then applied to the design of microbubble contactors to determine the economic viability of microbubble generation when applied to ozonation at full scale compared with a conventional bubble ozone contactor.
Open Access
Are microbubbles magic or just small? a direct comparison of hydroxyl radical generation between microbubble and conventional bubble ozonation under typical operational conditions
(Elsevier, 2022-01-24) John, Alexander; Carra, Irene; Jefferson, Bruce; Jodkowska, Monika; Brookes, Adam; Jarvis, Peter
The application of microbubbles for water treatment is an emerging technology which has been shown to significantly enhance gas–liquid contacting processes. When applied to ozonation, microbubble technology has been shown to enhance mass transfer and the speed and extent of compound removal compared with conventional bubbling techniques. One explanation as to why microbubble systems outperform conventional systems is that microbubbles shrink, collapse and spontaneously generate hydroxyl radicals which is thought to enhance the speed of compound removal. This study compared microbubble (mean diameter 37 μm) and conventional bubble (mean diameter 5.4 mm) ozonation systems under identical conditions. The experiments were normalised for effective ozone dose to determine whether microbubble ozonation generated significantly more hydroxyl radicals than conventional bubble ozonation. 4-chlorobenzoic was used as the hydroxyl radical probe and the proportion of hydroxyl radicals generated for a given effective ozone dose was quantified. The •OH-exposure to O3-exposure (the ) was used to compare the systems. The ratio of the mean to mean was 0.73, 0.84 and 1.12 at pH 6, 7 and 8 respectively. Statistical assessment of the showed that there was no significant difference between the bubble systems. No evidence was found to support the hypothesis that microbubble systems generate more •OH. Instead, the level of •OH-exposure is linked to the effective dose and pH of the system and future designs should focus on those factors to deliver •OH based benefits.
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, Bruce
The 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.
Open Access
Assessing the potential of enhanced primary clarification to manage fats, oils and grease (FOG) at wastewater treatment works
(Elsevier, 2020-04-20) Collin, Thomas Denis; Cunningham, Rachel; Asghar, Mohammed Qasim; Villa, Raffaella; MacAdam, Jitka; Jefferson, Bruce
Daily, sewage treatment works (STWs) receive large volumes of fats, oils and greases (FOG), by-products of food preparation. To increase FOG removal at STW, conventional primary sedimentation tanks (PSTs) can be enhanced using chemical coagulant or through dissolved air flotation (DAF) techniques. This work aimed to assess the potential benefits of enhanced primary treatment for FOG removal through an energy and costs analysis. To achieve this, a five-year sampling programme was conducted monthly at 15 STWs measuring FOG concentrations in crude and settled sewage (i.e. after primary treatment). In addition, two DAF pilot systems were trialled for four months and their performance, in terms of FOG removal, was assessed and compared to that of a control primary clarifier. Across the 15 STWs, influent FOG concentrations were found at 57 ± 11 mg.L−1. Chemical coagulants dosed prior to PSTs increased FOG removal rates on average to 71% whilst traditional sedimentation only achieved 50% removal. Effluent FOG concentrations were found between 12–22 mg.L−1 and 19–36 mg.L−1 respectively. By contrast, DAF achieved FOG effluent concentrations on average at 10 ± 4 mg.L−1 corresponding to 74% removal from a relatively low influent concentration of 40 ± 30 mg.L−1. Thus, enhanced primary treatments have the potential to reduce organic load to secondary treatment and increase energy generation through anaerobic digestion. The overall net energy balance was estimated at 2269 MWh.year−1 for the DAF compared to 3445 MWh.year−1 for the chemically-enhanced PST making it a less financially attractive alternative. Yet, in the case where the works require upgrading to accommodate flow or load increases, DAF appeared as a sensible option over sedimentation offering significantly lower capital costs and footprint. In relation to FOG management, upgrading all STWs is not realistic and will require understanding where the benefits would be the highest.
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, Bruce
This 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.
Open Access
Assessment of municipal waste compost as a daily cover material for odour control at landfill sites.
(Elsevier Science B.V., Amsterdam., 2005-01-01T00:00:00Z) Hurst, C.; Longhurst, Philip J.; Pollard, Simon J. T.; Smith, Richard; Jefferson, Bruce; Gronow, Jan R.
The ability of municipal waste compost as a daily cover material to reduce the odorous emissions associated with landfill surfaces was investigated. Trials were carried out using landfill gas, a certified sulphurous gas mix and ambient air as a control. Odorous gas was passed through portable test column filled with compost at different densities (590 kg/m3 and 740 kg/m3). Gas samples were taken from the inlet, outlet and at varying column depths and examined using a combination of sensory analysis (olfactometry) and a novel analytical method (Transportable Selected Ion Flow Tube – TSIFT). Results for the trials using landfill gas showed a 69% odour reduction (OU/m3) through the column for compost with a bulk density of 590 kg/m3, and a reduction of 97% using compost with a bulk density of 740 kg/m3. TSIFT analysis showed an overall decrease in the concentration of terpenes, and sulphurous compounds in the outlet gas from the column for both bulk densities. No significant trend could be identified for the concentrations at different depths within the column. Results show the ability of compost to reduce landfill odours under differing conditions. The inconclusive data provided by TSIFT analysis may be due to the analysis of compounds that are not contributing to odour, and thus highlights the potential for synergetic effects and the importance of sensory measurement when examining odorous emission
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, Gabriela
Eutrophication 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.
Open Access
Ballasted flotation with glass microspheres for removal of natural organic matter
(Taylor & Francis Inc., 2013-01-23) Jarvis, Peter; Martin, John; Winspear, Tracey; Jefferson, Bruce
Low density microspheres were used to float flocs formed from the coagulation of natural organic matter (NOM) using ferric sulphate coagulant. Microspheres were visually observed to be incorporated into the floc structure during the coagulation phase. In comparison with conventional flotation with air bubbles, the residual turbidity after flotation using the microspheres was very favourable and did not impact on overall NOM removal. Spheres of the lowest density and largest particle size gave the most rapid floc clearance, but the residual turbidity after 10 minutes flotation was similar for all of the spheres investigated. The results of this work have shown that floating microspheres offer an effective, energy efficient alternative to conventional dissolved air flotation for removal of flocs containing high concentrations of NOM.
Open Access
Bioaugmentation of pilot-scale slow sand filters can achieve compliant levels for the micropollutant metaldehyde in a real water matrix
(Elsevier, 2022-01-14) Castro-Gutierrez, V. M.; Pickering, Laura; Cambronero-Heinrichs, J. C.; Holden, B.; Haley, J.; Jarvis, Peter; Jefferson, Bruce; Helgason, T.; Moir, J. W.; Hassard, Francis
Metaldehyde is a polar, mobile, low molecular weight pesticide that is challenging to remove from drinking water with current adsorption-based micropollutant treatment technologies. Alternative strategies to remove this and compounds with similar properties are necessary to ensure an adequate supply of safe and regulation-compliant drinking water. Biological removal of metaldehyde below the 0.1 µg•L−1 regulatory concentration was attained in pilot-scale slow sand filters (SSFs) subject to bioaugmentation with metaldehyde-degrading bacteria. To achieve this, a library of degraders was first screened in bench-scale assays for removal at micropollutant concentrations in progressively more challenging conditions, including a mixed microbial community with multiple carbon sources. The best performing strains, A. calcoaceticus E1 and Sphingobium CMET-H, showed removal rates of 0.0012 µg•h−1•107 cells−1 and 0.019 µg•h−1•107 cells−1 at this scale. These candidates were then used as inocula for bioaugmentation of pilot-scale SSFs. Here, removal of metaldehyde by A. calcoaceticus E1, was insufficient to achieve compliant water regardless testing increasing cell concentrations. Quantification of metaldehyde-degrading genes indicated that aggregation and inadequate distribution of the inoculum in the filters were the likely causes of this outcome. Conversely, bioaugmentation with Sphingobium CMET-H enabled sufficient metaldehyde removal to achieve compliance, with undetectable levels in treated water for at least 14 d (volumetric removal: 0.57 µg•L−1•h−1). Bioaugmentation did not affect the background SSF microbial community, and filter function was maintained throughout the trial. Here it has been shown for the first time that bioaugmentation is an efficient strategy to remove the adsorption-resistant pesticide metaldehyde from a real water matrix in upscaled systems. Swift contaminant removal after inoculum addition and persistent activity are two remarkable attributes of this approach that would allow it to effectively manage peaks in metaldehyde concentrations (due to precipitation or increased application) in incoming raw water by matching them with high enough degrading populations. This study provides an example of how stepwise screening of a diverse collection of degraders can lead to successful bioaugmentation and can be used as a template for other problematic adsorption-resistant compounds in drinking water purification.
Open Access
Biogas enhancement with membranes
(Cranfield University, 2014-04) McLeod, Andrew J.; McAdam, Ewan; Jefferson, Bruce
Biogas is generated during anaerobic digestion (AD) of sewage sludge at wastewater treatment works (WWTW) and consists of approximately 50-70 % methane (CH4) balanced primarily by carbon dioxide (CO2). It is commonly used directly as a fuel gas for the renewable generation of electricity on-site by combined heat and power (CHP) engines. However, as a result of governmental incentivisation, biogas possesses a greater value when applied to the national gas grid as a natural gas substitute. However, this requires enhancement of the CH4 content to that comparable to natural gas by selective removal of CO2; a process known as biogas upgrading. This thesis explores the potential of hydrophobic micro-porous hollow fibre membrane contactors (HFMCs) to biogas upgrading. HFMCs allow non-dispersive contact between the biogas and a liquid solvent for the preferential absorption of CO2, which is conventionally facilitated by packed-column gas scrubbing technology. However, recent gas absorption literature has demonstrated many practical and operational advantages of HFMCs, which suggests they may be effective for biogas upgrading at WWTW. In this thesis, HFMCs were used to explore the mechanism and controllability of the undesirable co-absorption of CH4, known as methane slip. This was found to be attributable to the phase limiting mass transfer, with liquid-limited physical absorption in water exhibited 5.2 % slip whereas gas-limited chemical absorption displayed just 0.1 %. Ammonia-rich wastewaters were investigated as sustainable chemical absorbents using HFMCs and exhibited comparable chemically enhanced absorption to analogue synthetic ammonia solutions. The recovery of the subsequent reaction product (ammonium bicarbonate) by crystallisation facilitated by the membrane was also examined. The potential of this approach was summarised within two hypothetical wastewater flowsheets, where upgrading using a return liquor absorbent acts as a return liquor treatment and where ion exchange allows 100 % application of wastewater derived ammonia to biogas upgrading. These both offered potential economic advantages versus conventional flowsheets with 100 % biogas application to CHP.
Open Access
Biogas upgrading by chemical absorption using ammonia rich absorbents derived from wastewater
(IWA Publishing, 2014-09-18) McLeod, Andrew J.; Jefferson, Bruce; McAdam, Ewan J.
The use of ammonia (NH3) rich wastewaters as an ecological chemical absorption solvent for the selective extraction of carbon dioxide (CO2) during biogas upgrading to ‘biomethane’ has been studied. Aqueous ammonia absorbents of up to 10,000 gNH3 m−3 demonstrated CO2 absorption rates higher than recorded in the literature for packed columns using 20,000–80,000 g NH3 m−3 which can be ascribed to the process intensification provided by the hollow fibre membrane contactor used in this study to support absorption. Centrifuge return liquors (2325 g m−3 ionised ammonium, NH4+) and a regenerant (477 gNH4+ m−3) produced from a cationic ion exchanger used to harvest NH4+ from crude wastewater were also tested. Carbon dioxide fluxes measured for both wastewaters compared reasonably with analogue ammonia absorption solvents of equivalent NH3 concentration. Importantly, this demonstrates that ammonia rich wastewaters can facilitate chemically enhanced CO2 separation which eliminates the need for costly exogenic chemicals or complex chemical handling which are critical barriers to implementation of chemical absorption. When testing NH3 analogues, the potential to recover the reaction product ammonium bicarbonate (NH4HCO3) in crystalline form was also illustrated. This is significant as it suggests a new pathway for ammonia separation which avoids biological nitrification and produces ammonia stabilised into a commercially viable fertiliser (NH4HCO3). However, in real ammonia rich wastewaters, sodium bicarbonate and calcium carbonate were preferentially formed over NH4HCO3 although it is proposed that NH4HCO3 can be preferentially formed by manipulating both ion exchange and absorbent chemistry.