DORA :: Browsing by Author "Villa, R."

Browsing by Author "Villa, R."

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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, R.
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
Assessing the potential of enhanced primary clarification to manage fats, oils and grease (FOG) at wastewater treatment works,
(Elsevier, 2020-04-20) Collin, T.D.; Cunningham, R.; Asghar, M.O.; MacAdam, J.; Jefferson, B.; Villa, R.
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
Biohydrogen production from fermentation of organic waste, storage and applications
(Elsevier, 2022-10-10) El Bari, H.; Lahboub, N.; Habchi, S.; Rachidi, S.; Bayssi, O.; Nabil, N.; Mortezae, Y.; Villa, R.
Biohydrogen is a carbon-free alternative energy source, that can be obtained from fermentation of organic waste, biomass-derived sugars, and wastewater. This article reviews the current processes for fermentative biohydrogen production from biomass including its appropriate storage and transport challenges. The review showed that a comparison of fermentation pretreatment methods across the literature is complicated and that fermentability tests are necessary to determine the best combination of pretreatment/feedstock. Operational parameters, such as temperature, pH, macro/micronutrients addition are widely dependent on the type of fermentation and microorganisms used and hence their content need to be tailored to the process. For immobilized cells, the range of hydrogen production rate values reported for granulation processes using mixed microbial cultures, were higher (13–297 mmol H2/L h) than those reported for entrapment (1–115 mmol H2/L h) and adsorption (3–83 mmol H2/L h), suggesting an achievable and sustainable route for full-scale applications. A purification phase is mandatory before the final use of biohydrogens. Sorption techniques and the use of membranes are the most widely used approaches. Pressure swing adsorption has the highest recovery rate (it reaches 96%). In addition, storage of biohydrogen can have several forms with varying storage capacities (depending on the form and/or storage materials used). The transport of biohydrogen often faces technical and economic challenges requiring optimization to contribute to the development of a biohydrogen economy.
Open Access
Characterisation and energy assessment of fats, oils and greases (FOG) waste at catchment level
(Elsevier, 2020-01-13) Villa, R.; Collin, C.; Cunningham, R.; Jefferson, C.
Several of the waste materials that have a negative impact on the sewer system are produced by fats, oils and greases (FOG) discharged from commercial and domestic kitchens. These materials accumulate at different points in the sewer catchment, from kitchens to pumping stations, sewers and sewage treatment works (STWs), and comprise oily wastewater, floating agglomerates and hard deposits. Despite their detrimental effects, these waste materials have a high calorific content and are an ideal feedstock for energy recovery processes. So far, the overall volume of each type of waste and their physical-chemical properties in relation to their collection point are unknown. However, from a management point of view, knowledge on each feedstock quality and volumes is necessary to develop an economic viable solution for their collection and for energy recovery purposes. In this study, FOG wastes collected from households, food service establishments (FSEs), sewage pumping stations, sewers and STWs, were compared to sewage sludge in terms of organic contents and energy potentials. As expected, FOG recovered at source (households and FSEs) were ‘cleaner’ and had a higher energy content. Once mixed with wastewater the materials changed in composition and lost some of their energy per unit mass. Our results showed that around 94,730 tonnes.year-1 of these materials could be recovered from the Thames Water Utilities’ catchment, one of the most populated in the UK. These materials could produce up to 222 GWh.year-1 as biogas, close to double of what is produced with sewage sludge digestion and around 19% of the company energy needs. Finally, even with over six million households in the catchment, the results showed that most of the FOG waste was produced by FSEs (over 48,000 premises) with an estimated average of 79,810 tonnes.year-1 compared to 14,920 tonnes·year-1 from private households. This is an important outcome as recovery from FSEs will be cheaper and easier if the company decides to implement a collection system for energy recovery.
Open Access
Characterisation of food service establishment wastewater and its implication for treatment
(Elsevier, 2019-10-08) Gurd, Caroline; Villa, R.; Jefferson, B.
Essential for the selection of a reliable treatment system is the characterisation of the effluent to treat. Kitchen wastewater (KWW) from food service establishments (FSEs) is a strong organic and fat-rich effluent whose characterisation has not been sufficiently addressed. KWW composition is highly variable and linked to the FSE’s size, the type of meals prepared and the amount of water used during the cleaning. COD, TSS and fat content (FOG) are the most common parameters found in literature. However, other physical and chemical parameters (e.g. temperature, pH, oil droplets characteristics and trace elements), correlated to commercial kitchen cleaning practices rather than the specific effluent, but equally influential on the treatment efficiencies of both physical and biological methods, have hardly been investigated. A comprehensive characterisation of wastewaters from three food service establishments was used to generate data to support the selection of appropriate FOG mitigation methods. Two novel analytical methods were used to quantify the proportion of emulsified FOG and associated droplet size from different kitchen washing effluents. The results showed that more than 90% of the FOG from the dishwasher effluent and around 35% of sink one was emulsified, with droplet sizes less than 100 μm, well below the removal capabilities of conventional grease interceptors, but easily removed using biological means. From the WW composition results, a formula for predictive modelling was derived to represent average organic matter composition for kitchen wastewater as C20H38O10N, applicable in remediation processes. These results offer a good starting point for the design, operation, and optimisation of wastewater treatment systems of oil-rich KWW.
Embargo
Dealing with Missing Data in the Smart Buildings using Innovative Imputation Techniques
(IEEE, 2021-11-16) Pazhoohesh, Mehdi; Javadi, Mohammad Sadegh; Gheisari, Mehdi; Aziz, Saddam; Villa, R.
Data quality plays a crucial role in the context of smart buildings. Meanwhile, missing data is relatively common in acquired datasets from sensors within the smart buildings. Poor data could result in a big bias in forecasting, control and operational services. Despite the common techniques to handle missing data, it is essential to systematically select the most appropriate approach for such missing values. This paper aims to focus on the lift systems as one of the essential parts in the smart buildings by exploring the most appropriate data imputation methods to handle missing data and to provide its service and allow a better understanding of patterns to issue the correct control actions based on forecasted models. The imputed data is not only investigated statistically but also modelled through machine learning algorithm to explore the impact of selecting inappropriate imputation techniques. Seven imputation techniques deployed on datasets with three level of missing values including 10%, 20% and 30% and the performance of methods examined through the normalized root mean square error (NRMSE) approach. In addition, the interaction between imputation techniques and a machine learning algorithm, namely random forest were examined. Findings from this paper can be employed in identifying an appropriate imputation technique not only within the lift datasets, but smart building context.
Open Access
Determination of fats, oils and greases in food service establishment wastewater using a modification of the Gerber method
(Wiley, 2018-11-13) Gurd, C.; Jefferson, B.; De Castro Rodriguez, C.; Villa, R.
Discharges from food service establishments (FSEs) are a major source of fat, oil and grease (FOG) which cause blockages in sewer networks. Previous research has identified that current methods are unsuitable for quantifying FOG in FSE wastewater owing to interference from surfactants in detergents, and protein from food residuals which emulsify FOG. A novel quantification method, based on the dairy industry Gerber method, has been developed which negates the impact of surfactants. Moreover, the method allows free and emulsified oil to be quantified separately providing greater insight into FOG management strategies. Trials in synthetic and real FSE wastewaters indicate the novel method is more reliable than standard liquid–liquid and solid phase extraction in FOG‐rich systems.
Open Access
Dry anaerobic digestion of organic waste: A review of operational parameters and their impact on process performance.
(Elsevier, 2019-12-24) Rocamora, I.; Wagland, S.; Villa, R.; Simpson, E. W.; Fernandez, O.; Bajón-Fernández, Y.
Dry digestion is a suitable technology for treating organic wastes with varying composition such as the organic fraction of municipal solids waste. Yet, there is a need for further research to overcome some of the disadvantages associated with the high total solids content of the process. Optimisation of inoculum to substrate ratio, feedstock composition and size, liquid recirculation, bed compaction and use of bulking agents are some of the parameters that need further investigation in batch dry anaerobic digestion, to limit localised inhibition effects and avoid process instability. In addition, further attention on the relation between feedstock composition, organic loading rate and mixing regimes is required for continuous dry anaerobic digestion systems. This paper highlights all the areas where knowledge is scarce and value can be added to increase dry anaerobic digestion performance and expansion.
Open Access
Energy potential of household fats, oils and grease waste
(Wiley, 2021-07-01) Collin, Thomas; Cunningham, Rachel; Deb, Melanie; Villa, R.; MacAdam, Jitka; Jefferson, Bruce
In comparison to fats, oils and grease (FOG) found in commercial and industrial effluents, very little is known about FOG discharged at household level. To address this shortcoming, household FOG production was calculated following a year-long monthly collection at 2.3 kg/year per household, equivalent to 0.8 kg/year per capita. In the United Kingdom, these numbers translate in an annual estimated FOG production of 62 380 tonnes. Physico-chemical characterization of household FOG showed promising results for biodiesel production. Biomethane yield was measured at 875 mL CH4/g VSadded, twice as much that of sewage sludge, making it a desirable substrate for anaerobic digestion. It was thus estimated that energy recovery from household FOG through anaerobic co-digestion or biodiesel production could generate about 490 GWh/year in the United Kingdom. However, insights from participants revealed that most of this waste is currently not recovered, requiring the development of schemes fitting with households' routine to maximize collection rates.
Open Access
Ensiling for anaerobic digestion (AD): a review of key considerations to maximise methane yields
(Elsevier, 2020-09-25) Villa, R.; Ortega Rodriguez, Leila; Fenech, Cecilia; Anika, Ogemdi Chinwendu
Growth in anaerobic digestion (AD) has expanded the use of silage to preserve crops intended for renewable energy generation. Preservation of seasonal crops and their residues is critical in a process that needs continuous feeding. Whilst the impact of different crops and harvesting times on methane formation is relatively well understood, to date the specific considerations for maximising methane yields through management practice have been largely ignored. The present paper reviews the current state of knowledge on silage practice for biogas production and specifically on the factors affecting methane yields of ensiled crops, as well as their influence on the silage quality, and provides suggestions for further research in the field. Data shows that ensiling is able to conserves 93% of crops gross energy when good practices are followed. Shorter chop length (7-10 mm), lower DM feedstock (20-35%) and lower compaction values (less than 250 kg/m3) are used to achieve higher biogas yields. Increase biogas production can also be obtained by managing the organic acids production with the preferential formation of acetic acid and ethanol instead of lactic acid via enzymatic or microbial additives. The review outcomes show that more research is required to provide a clear-cut distinction between the requirements for ensiling crops for AD versus crops for animal feed.
Open Access
An exploratory study of the impact and potential of menstrual hygiene management waste in the UK
(Elsevier, 2022-02-11) Blair, Lucie A. G.; Bajón -Fernández, Yadira; Villa, R.
An estimated 15 million people in the UK menstruate over the span of approximately 37.5 years, using every year around 3.3 billion units of single-use menstrual management products (MMPs) (i.e. pads and tampons). A more circular design and sustainable management of these products could greatly reduce their waste and environmental impacts. This research is an exploratory study into the current menstrual products, waste and systems in the UK. The study found that an estimated 28,114 tonnes of waste is generated annually from menstrual products, 26,903 tonnes from disposable products of which about 4% (3,363 tonnes) is lost in the environment by flushing. The less sustainable products within those studied are disposable pads, which are the main contributors to menstrual waste volumes in the UK (21,094 t/y) and produce around 6,600 tCO2 eq. of GHG. Replacing disposable MMPs with reusable would reduce waste production by 22,907 t/y and avoid about 7,900 tCO2 eq. of GHG. In addition, even a simple better waste management process, such replacing landfill with thermal treatment, would further reduce emissions by around 5,000 tCO2 eq. of GHG and produce every year approximately 5,500 MKh with incineration and 18,000 MKh with gasification.
Open Access
From full-scale biofilters to bioreactors: engineering biological metaldehyde removal
(Elsevier, 2019-05-21) Rolph, Catherine A.; Jefferson, Bruce; Brookes, Adam; Choya, Andoni; Iceton, Gregg; Hassard, Francis; Villa, R.
Polar, low molecular weight pesticides such as metaldehyde are challenging and costly to remove from drinking water using conventional treatment methods. Although biological treatments can be effective at treating micropollutants, through biodegradation and sorption processes, only some operational biofilters have shown the ability to remove metaldehyde. As sorption plays a minor role for such polar organic micropollutants, biodegradation is therefore likely to be the main removal pathway. Here, the biodegradation of metaldehyde was monitored, and assessed, in an operational slow sand filter. Long-term data showed that metaldehyde degradation improved when inlet concentrations increased. A comparison of inactive and active sand batch reactors showed that metaldehyde removal happened mainly through biodegradation and that the removal rates were greater after the biofilm was acclimated through exposure to high metaldehyde concentrations. This suggested that metaldehyde removal was reliant on enrichment and that the process could be engineered to decrease treatment times (from days to hours). Through-flow experiments using fluidised bed reactors, showed the same behaviour following metaldehyde acclimation. A 40% increase in metaldehyde removal was observed in acclimated compared with non-acclimated columns. This increase was sustained for more than 40 days, achieving an average of 80% removal and compliance (< 0.1 µ L-1) for more than 20 days. An initial microbial analysis of the acclimated and non-acclimated biofilm from the same filter materials, showed that the microbial community in acclimated sand was significantly different. This work presents a novel conceptual template for a faster, chemical free, low cost, biological treatment of metaldehyde and other polar pollutants in drinking water. In addition, this is the first study to report kinetics of metaldehyde degradation in an active microbial biofilm at a WTW.
Metadata only
Impacts of microalgae pre-treatments for improved anaerobic digestion: Thermal treatment, thermal hydrolysis, ultrasound and enzymatic hydrolysis
(Elsevier, 2014-08-06) Villa, R.; Ometto, Francesco; Quiroga, Gerardo; Psenicka, Pavel; Whitton, rachel; Jefferson, Bruce
Anaerobic digestion (AD) of microalgae is primarily inhibited by the chemical composition of their cell walls containing biopolymers able to resist bacterial degradation. Adoption of pre-treatments such as thermal, thermal hydrolysis, ultrasound and enzymatic hydrolysis have the potential to remove these inhibitory compounds and enhance biogas yields by degrading the cell wall, and releasing the intracellular algogenic organic matter (AOM). This work investigated the effect of four pre-treatments on three microalgae species, and their impact on the quantity of soluble biomass released in the media and thus on the digestion process yields. The analysis of the composition of the soluble COD released and of the TEM images of the cells showed two main degradation actions associated with the processes: (1) cell wall damage with the release of intracellular AOM (thermal, thermal hydrolysis and ultrasound) and (2) degradation of the cell wall constituents with the release of intracellular AOM and the solubilisation of the cell wall biopolymers (enzymatic hydrolysis). As a result of this, enzymatic hydrolysis showed the greatest biogas yield increments (>270%) followed by thermal hydrolysis (60–100%) and ultrasounds (30–60%).
Open Access
Influence of light regime on the performance of an immobilised microalgae reactor for wastewater nutrient removal
(Elsevier, 2019-10-23) Whitton, Rachel; Ometto, Francesco; Pidou, Marc; Jefferson, Bruce; Villa, R.
Microalgae immobilised within a resin shaped into beads have demonstrated the ability to remediate nutrients from wastewater effluents within hydraulic retention times as low as 3 h. Methods to further optimise performance consider parameters relating to the bead with the impact of external conditions seldom investigated. Light is an essential parameter for microalgal growth with its effect on suspended cultures well documented. This work explores the influence of light on nutrient remediation by immobilised microalgae in order to recommend an optimal lighting solution for an immobilised microalgae technology based on Scenedesmus obliquus encapsulated within calcium-alginate beads. White light (400–700 nm) at a photon flux density (PFD) of 200 μmol∙m−2∙s−1 was determined optimal when illuminating a packed bed configuration. When considering phosphate, these conditions supported a remediation rate of 10.7 (± 0.01) mgP∙h−1∙106 beads−1 in comparison to 10.2 (± 0.01) and 10.1 (± 0.01) mgP∙h−1∙106 beads−1 for the blue (465 nm) and red (660 nm) spectra respectively. Although similar performance was demonstrated, light transmission trials determined white light to penetrate to greater bed depths resulting in a larger photoactive zone. A PFD of 200 μmol∙m−2∙s−1 was regarded as optimal when considering performance, attenuation depth and effective use of total supplied light. In addition, photoperiods trials determined lighting periods <12 h extended the overall treatment time.
Open Access
Inhibitory mechanisms on dry anaerobic digestion: Ammonia, hydrogen and propionic acid relationship
(Elsevier, 2023-02-28) Rocamora, Ildefonso; Wagland, T. Stuart; Hassard, Francis; Villa, R.; Peces, Miriam; Simpson, Edmon W.; Fernández, Oliver; Bajón-Fernández, Yadira
Inhibitory pathways in dry anaerobic digestion are still understudied and current knowledge on wet processes cannot be easily transferred. This study forced instability in pilot-scale digesters by operating at short retention times (40 and 33 days) in order to understand inhibition pathways over long term operation (145 days). The first sign of inhibition at elevated total ammonia concentrations (8 g/l) was a headspace hydrogen level over the thermodynamic limit for propionic degradation, causing propionic accumulation. The combined inhibitory effect of propionic and ammonia accumulation resulted in further increased hydrogen partial pressures and n-butyric accumulation. The relative abundance of Methanosarcina increased while that of Methanoculleus decreased as digestion deteriorated. It was hypothesized that high ammonia, total solids and organic loading rate inhibited syntrophic acetate oxidisers, increasing their doubling time and resulting in its wash out, which in turn inhibited hydrogenotrophic methanogenesis and shifted the predominant methanogenic pathway towards acetoclastic methanogenesis at free ammonia over 1.5 g/l. C/N increases to 25 and 29 reduced inhibitors accumulation but did not avoid inhibition or the washout of syntrophic acetate oxidising bacteria.
Open Access
Liquid-phase hydrogenation of bio-refined succinic acid to 1,4-butanediol using bimetallic catalysts
(Springer Nature, 2019-04-24) Baidya, P.K.; Sarkar, U.; Sadhukhan, S.; Villa, R.
Development of a Crotalaria juncea based biorefinery produce large quantity of waste glycerol after trans-esterification of the juncea seeds. This glycerol, after purification, is used as a substrate for producing succinic acid on a microbial route. Hydrogenation of this bio-refined succinic acid is carried out under high pressure in order to produce 1,4- butanediol (BDO) using a batch slurry reactor with cobalt supported ruthenium bimetallic catalysts, synthesized inhouse. It is demonstrated that, using small amounts of ruthenium to cobalt increases the overall hydrogenation activity for the production of 1,4-butanediol. Hydrogenation reactions are carried out at various operating temperatures and pressures along with changes in the mixing ratios of ruthenium chloride and cobalt chloride hexahydrate, which are used to synthesize the catalyst. The Ru-Co bimetallic catalysts are characterized by XRD, FE-SEM and TGA. Concentrations of the hydrogenation product are analyzed using Gas chromatography-Mass spectrometry (GC-MS). Statistical analysis of the overall hydrogenation process is performed using a Box-Behnken Design (BBD).
Open Access
Looking through the FOG: microbiome characterization and lipolytic bacteria isolation from a fatberg site
(Microbiology Society, 2021-12-06) Court, E.K.; Chaudhuri, R.R.; Kapoore, R.V.; Villa, R.; Pandhal, J.; Biggs, C.A.; Stafford, G.P.
Sewer systems are complex physical, chemical and microbial ecosystems where fats, oils and grease (FOG) present a major problem for sewer management. Their accumulation can lead to blockages (‘Fatbergs’), sewer overflows and disruption of downstream wastewater treatment. Further advancements of biological FOG treatments need to be tailored to degrade the FOG, and operate successfully within the sewer environment. In this study we developed a pipeline for isolation of lipolytic strains directly from two FOG blockage sites in the UK, and isolated a range of highly lipolytic bacteria. We selected the five most lipolytic strains using Rhodamine B agar plates and pNP-Fatty acid substrates, with two Serratia spp., two Klebsiella spp. and an environmental Acinetobacter strain that all have the capacity to grow on FOG-based carbon sources. Their genome sequences identified the genetic capacity for fatty acid harvesting (lipases), catabolism and utilization (Fad genes). Furthermore, we performed a preliminary molecular characterization of the microbial community at these sites, showing a diverse community of environmental bacteria at each site, but which did include evidence of sequences related to our isolates. This study provides proof of concept to isolation strategies targeting Fatberg sites to yield candidate strains with bioremediation potential for FOG in the wastewater network. Our work sets the foundation for development of novel bioadditions tailored to the environment with non-pathogenic Acinetobacter identified as a candidate for this purpose.
Open Access
Managing full-scale dry anaerobic digestion: semi-continuous and batch operation
(Elsevier, 2022-06-24) Rocamora, I.; Wagland, S.; Rivas Casado, M.; Hassard, F.; Villa, R.; Peces, M.; Fernández, O.; Bajón-Fernández, Y.
Dry anaerobic digestion usually results in inhibitors accumulation, which can be solved by adapting operation. Multiple strategies targeting increased stability are implemented in full-scale, but impacts are poorly documented. Two full-scale dry AD plants treating organic fraction of municipal solid waste (OFMSW) were investigated: a semi-continuous plant with compost addition and a batch plant testing different percolate recirculation strategies and inoculum to substrate ratios. Regression tree analysis was used to evaluate the effect of these strategies on methane yields and inhibitors accumulation. Compost addition in the semi-continuous plant reduced volatile fatty acids content but dropped methane flow up to 10 % when compost constituted over 10.1 % in weight of the incoming feedstock. This reduction was linked to the limited availability of easily degradable material in the compost. In batch dry AD, methane yields increased as percolate recirculated raised up to a range of 182–197 m3 (0.342–0.363 m3/t of biomass mix). Recirculation of higher percolate volumes reduced methane production, probably linked to pile compaction and inhibitors accumulation. The ratio of OFMSW, digestate and woodchip (bulking agent) fed was determinant, and methane production was higher when digestate was over 43.1 %, waste between 45 % and 47.5 % and woodchip over 8.2 % in weight in as received basis. Woodchip influenced percolation through the pile and supported reduced total ammonia levels of 3.2 g/l when kept over 8.2 %, which raised to 5.2 g/l for lower values.
Open Access
A new conceptual model of pesticide transfers from agricultural land to surface waters with a specific focus on metaldehyde
(Royal Society of Chemistry, 2020-02-04) Whelan, M.J.; Ramos, A.; Villa, R.; Guymer, I.; Jefferson, B.; Rayner, M.
Pesticide losses from agricultural land to water can result in the environmental deterioration of receiving systems. Mathematical models can make important contributions to risk assessments and catchment management. However, some mechanistic models have high parameter requirements which can make them difficult to apply in data-poor areas. In addition, uncertainties in pesticide properties and applications are difficult to account for using models with long run-times. Alternative, simpler, conceptual models are easier to apply and can still be used as a framework for process interpretation. Here, we present a new conceptual model of pesticide behaviour in surface water catchments, based on continuous water balance calculations. Pesticide losses to surface waters are calculated based on the displacement of a limited fraction of the soil pore water during storm events occurring after application. The model was used to describe the behaviour of metaldehyde in a small (2.2 km2) under-drained catchment in Eastern England. Metaldehyde is a molluscicide which has been regularly detected at high concentrations in many drinking water supply catchments. Measured peak concentrations in stream water (to about 9 micro g L-1) occurred in the first few storm events after application in mid-August. In each event, there was a quasi-exponential decrease in concentration during hydrograph recession. Peak concentrations decreased in successive events - responding to rainfall but reflecting an effective exhaustion in soil supply due to degradation and dissipation. Uncertain pesticide applications to the catchment were estimated using land over-analysis of satellite data, combined with a Poisson distribution to describe the timing of application. Model performance for both the hydrograph (after calibration of the water balance) and the chemograph was good and could be improved via some minor adjustments in assumptions which yield general insights into the drivers for pesticide transport. The use of remote sensing offers some promising opportunities for estimating catchment-scale pesticide applications and associated losses.
Open Access
Novel insight on the impact of enzymatic addition on organic loading rate in anaerobic digestion
(Springer, 2022-01-29) Villa, R.; Jantová-Patel, Jana; Bajón Fernández, Yadira
Addition of enzymes to anaerobic digesters (ADs) has been reported as beneficial to the hydrolytic step of the process. Additional benefits have been described for bioadded reactors such as improved dewatering and lower energy requirements. This work aimed to assess the long-term and unaccounted effects of enzymatic addition on sludge digestion. Enzymes’ impacts were tested using different addition modes (bulk or gradual addition) and during operational changes on reactors operated for 295 days. Enzyme added in bulk, generated a 14% increase in biogas production (144 ml/gVSadded) compared to control (126 ml/gVSadded), whereas the same amount of enzyme added gradually produced a 10% increase (139 ml/gVSadded). These values however, where higher when the OLR was increase from 3 to 5.5 kg VS/(m3∙d): 257, 212 and 149 ml/gVSadded for the enzyme added in bulk, the enzyme added gradually and the control respectively. Specific biogas yields (SBY), higher in bioadded reactors, were significantly different between control reactors and those reactors dosed in bulk. Furthermore, following OLR increase, the mode of enzyme addition resulted in different increases in gas production rate (GPR) when the enzyme was added in one dose compared to control and to a gradual addition, 121%, 32% and 93% respectively. These results offer a new hypothesis on the impact of bioadditions to AD during changing operational conditions, suggesting a potential stabilising effect of the enzymes in continuous systems.

Browsing by Author "Villa, R."

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