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Professor Raffaella Villa

Job: Professor of Environmental Bioengineering - Interim Associate Dean of Research and Innovation

Faculty: Computing, Engineering and Media

School/department: School of Engineering and Sustainable Development

Address: ²ÝÁñÊÓƵ, The Gateway, Leicester, LE1 9BH, United Kingdom

T: 0116 255 1551

E: raffaella.villa@dmu.ac.uk

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Personal profile

Professor Raffaella Villa joined ²ÝÁñÊÓƵ in 2019 as Reader in Environmental Engineering. Prior to that she worked at Cranfield, Stirling, Exeter and the University of Milan (Italy).

Raffaella has worked on microbial bioengineering for the last 20 years. Her major contributions relate to the delivery of the next generation biotechnological processes that combine protection and production for a more circular bioeconomy, such as bioremediation and high-value products from waste. This is achieved by understanding the common science in the two areas (protection and production) on how to control and enhance specific functions of microbial communities by manipulating operative conditions to increase process yields and stability, with increasing emphasis on the concept of the “waste biorefinery”.

Raffaella has published over 60 research papers, books and conference proceedings with substantive contributions to waste biotransformations, bioremediation and anaerobic digestion.

Research group affiliations

Institute of Energy and Sustainable Development (IESD)

Publications and outputs


  • dc.title: Inhibitory mechanisms on dry anaerobic digestion: Ammonia, hydrogen and propionic acid relationship dc.contributor.author: Rocamora, Ildefonso; Wagland, T. Stuart; Hassard, Francis; Villa, R.; Peces, Miriam; Simpson, Edmon W.; Fernández, Oliver; Bajón-Fernández, Yadira dc.description.abstract: 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. dc.description: open access article

  • dc.title: Towards a risk ranking for improved management of fats, oils and greases (FOG) discharges from food outlets dc.contributor.author: Collin, Thomas; Cunningham, Rachel; MacAdam, Jitka; Villa, R.; Jefferson, Bruce; Jeffrey, Paul dc.description.abstract: The understanding of fats, oils, and greases (FOG) pathways in commercial kitchens is relatively poor. In this contribution, we extend our understanding of how FOG is perceived and managed by those working within food service establishments (FSEs). A questionnaire (n = 107) exposes awareness of and experiences with FOG and characterises two important behaviours: kitchen appliance cleaning regimes and waste management practices. Findings demonstrate that awareness of issues caused by FOG in sewer networks is independent of job role or position and that a majority of respondents (74%) are acquainted with the impacts of poor FOG management. Application of a risk ranking approach revealed a low risk of emissions from waste frying oils and exposed behaviours which can serve to reduce FOG emission potential including pre-rinsing of plates and cleaning of fryers and extraction hoods. Critically, 69% of FSEs had no means of managing their FOG emissions. We conclude that sampled FSEs were generally unaware of the relative contribution of FOG sources, thereby limiting their ability to respond to the behavioural and technological options available for minimising its impact. The risk ranking developed in this paper could be used to suggest efforts to reduce and mitigate FOG emissions from FSEs. dc.description: open access article

  • dc.title: Biohydrogen production from fermentation of organic waste, storage and applications dc.contributor.author: El Bari, H.; Lahboub, N.; Habchi, S.; Rachidi, S.; Bayssi, O.; Nabil, N.; Mortezae, Y.; Villa, R. dc.description.abstract: 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. dc.description: open access article

  • dc.title: Prospects of low and zero-carbon renewable fuels in 1.5-degree net zero emission actualisation by 2050: A critical review dc.contributor.author: Chinwendu Anika, O.; Nnabuife, S.G.; Bello, A.; Okoroafor, E.R.; Kuang, B.; Villa, R. dc.description.abstract: The Paris Climate Agreement seeks to keep global temperature increases under 2° Celsius, ideally 1.5° Celsius. This goal necessitates significant emission reductions. By 2030, emissions are expected to range between 52 and 58 GtCO2e from their 2016 level of approximately 52 GtCO2e. This review paper explores a number of low and zero-carbon renewable fuels, such as hydrogen, green ammonia, green methanol, biomethane, natural gas, and synthetic methane (with natural gas and synthetic methane subject to CCUS both at processing and at final use) as alternative solutions for providing a way to rebalance transition paths in order to achieve the goals of the Paris Agreement while also reaping the benefits of other sustainability targets. The results show renewables will need to account for approximately 90% of total electricity generation by 2050 and approximately 25% of non-electric energy usage in buildings and industry. However, low and zero-carbon renewable fuels currently only contributes about 15% to the global energy shares, and it will take about 10% more capacity to reach the 2050 goal. The transportation industry will need to take important steps toward energy efficiency and fuel switching in order to achieve the 20% emission reduction. Therefore, significant new commitments to efficient low-carbon alternatives will be necessary to make this enormous change. According to this paper, investing in energy efficiency and low-carbon alternative energy must rise by a factor of about five by 2050 in comparison to 2015 levels if the 1.5 °C target is to be realised. dc.description: open access article

  • dc.title: Managing full-scale dry anaerobic digestion: semi-continuous and batch operation dc.contributor.author: Rocamora, I.; Wagland, S.; Rivas Casado, M.; Hassard, F.; Villa, R.; Peces, M.; Fernández, O.; Bajón-Fernández, Y. dc.description.abstract: 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. dc.description: open access article

  • dc.title: An exploratory study of the impact and potential of menstrual hygiene management waste in the UK dc.contributor.author: Blair, Lucie A. G.; Bajón -Fernández, Yadira; Villa, R. dc.description.abstract: 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. dc.description: open access article

  • dc.title: Novel insight on the impact of enzymatic addition on organic loading rate in anaerobic digestion dc.contributor.author: Villa, R.; Jantová-Patel, Jana; Bajón Fernández, Yadira dc.description.abstract: 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. dc.description: The file attached to this record is the author's final peer reviewed version. The Publisher's final version can be found by following the DOI link.

  • dc.title: Looking through the FOG: microbiome characterization and lipolytic bacteria isolation from a fatberg site dc.contributor.author: Court, E.K.; Chaudhuri, R.R.; Kapoore, R.V.; Villa, R.; Pandhal, J.; Biggs, C.A.; Stafford, G.P. dc.description.abstract: 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. dc.description: open access article.

  • dc.title: Dealing with Missing Data in the Smart Buildings using Innovative Imputation Techniques dc.contributor.author: Pazhoohesh, Mehdi; Javadi, Mohammad Sadegh; Gheisari, Mehdi; Aziz, Saddam; Villa, R. dc.description.abstract: 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. dc.description: The Publisher's final version can be found by following the DOI link.

  • dc.title: Energy potential of household fats, oils and grease waste dc.contributor.author: Collin, Thomas; Cunningham, Rachel; Deb, Melanie; Villa, R.; MacAdam, Jitka; Jefferson, Bruce dc.description.abstract: 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. dc.description: open access article

Research interests/expertise

Professor Villa's research interests include:

applied microbial processes across the fields of wastewater treatment (bioremediation) and energy from waste (anaerobic digestion and algae);

waste biotransformation;

environmental engineering.

Qualifications

PGCert in Academic Practice (Cranfield University)

PhD in Food Biotechnologies, Universitá di Milano (Italy)

BSc and MSc in Food Sciences and Technologies, Universitá di Milano (Italy)

²ÝÁñÊÓƵ taught

ENGT5268 Environmental Management and Policy

Honours and awards

Personal Marie Curie Post-Doctoral Fellowship (EU FP5), Stirling University 2000

MIUR (Ministry of Education, Universities and Research) Personal Advancement Fellowship (1995)

Membership of external committees

Member of the Editorial Board of ICE Water Management ()

Editor in Chief of Environmental Technology Reviews ()

Membership of professional associations and societies

Member of the Society for Applied Microbiology

Recent research outputs

See link to Orcid and Scopus profiles

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