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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. [ABSTRACT FROM AUTHOR]

• 10 UK biogas plant methane emission rates were estimated. • Total methane emissions were in range of 0.1 to 58.7 kg hr -1. • The percentage of losses relative to the calculated production rate ranged from 0.02 to 8.1%. • Biogas plants may averagely account for up to 1.9% of total methane emissions in the UK. The rising number of operational biogas plants in the UK brings a new emissions category to consider for methane monitoring, quantification and reduction. Minimising methane losses from biogas plants to the atmosphere is critical not only because of their contribution of methane to global warming but also with respect to the sustainability of renewable energy production. Mobile greenhouse gas surveys were conducted to detect plumes of methane emissions from the biogas plants in southern England that varied in their size, waste feed input materials and biogas utilization. Gaussian plume modelling was used to estimate total emissions of methane from ten biogas plants based on repeat passes through the plumes. Methane emission rates ranged from 0.1 to 58.7 kg CH 4 hr-1, and the percentage of losses relative to the calculated production rate varied between 0.02 and 8.1%. The average emission rate was 15.9 kg CH 4 hr-1, and the average loss was 3.7%. In general, methane emission rates from smaller farm biogas plants were higher than from larger food waste biogas plants. We also suggest that biogas methane emissions may account for between 0.4 and 3.8%, with an average being 1.9% of the total methane emissions in the UK excluding the sewage sludge biogas plants. [ABSTRACT FROM AUTHOR]

Anaerobic digestion (AD) is a long-established method for treating wastewater sludge and has been extensively researched, but there remains a lack of generic or practical modelling tools to guide operators and maximise the energy output. Detailed kinetic models have been developed, but are too complex as practical tools for industrial level application. A multi-level model of biogas yield (BY) was therefore developed based on operational data from 72 full-scale sites in the UK showing a wide range of AD performance. The model focused on the controllable operational parameters that are currently monitored at full-scale, including: temperature, hydraulic retention time and dry solids content in the feed sludge. The model effectively described performance variations in BY of full-scale processes, and provides a practical management tool to aid decision support to improve AD efficiency and net energy balance. Image 1 • Up to 7 years of operational data from 72 full-scale AD sites was examined. • A practical, operationally based sewage sludge MAD biogas model was developed. • AD performance was significantly correlated to major operational process variables. • Effects of operational parameters on BY with THP are equivalent to conventional MAD. • Optimisation strategies are proposed to improve the overall AD energy balance. [ABSTRACT FROM AUTHOR]

• 240 TWh.year−1 could be generated from food outlets' FOG in the London area. • FOG collected further away from source were richer in water and other contaminants. • FOG demonstrated high biomethane potentials. • Lipids accounted for most of the organic in FOG. • A shift from unsaturated to saturated fats was noticed from source to end point. 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. [ABSTRACT FROM AUTHOR]