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Bioaerosols are released in elevated quantities from composting facilities and are associated with negative health effects, although dose-response relationships are unclear. Exposure levels are difficult to quantify as established sampling methods are costly, time-consuming and current data provide limited temporal and spatial information. Confidence in dispersion model outputs in this context would be advantageous to provide a more detailed exposure assessment. We present the calibration and validation of a recognised atmospheric dispersion model (ADMS) for bioaerosol exposure assessments. The model was calibrated by a trial and error optimisation of observed Aspergillus fumigatus concentrations at different locations around a composting site. Validation was performed using a second dataset of measured concentrations for a different site. The best fit between modelled and measured data was achieved when emissions were represented as a single area source, with a temperature of 29°C. Predicted bioaerosol concentrations were within an order of magnitude of measured values (1000–10,000CFU/m3) at the validation site, once minor adjustments were made to reflect local differences between the sites (r2>0.7 at 150, 300, 500 and 600m downwind of source). Results suggest that calibrated dispersion modelling can be applied to make reasonable predictions of bioaerosol exposures at multiple sites and may be used to inform site regulation and operational management.

The “Reinvent the Toilet Challenge” set by the Bill & Melinda Gates Foundation aims to bring access to adequate sanitary systems to billions of people. In response to this challenge, on-site sanitation systems are proposed and being developed globally. These systems require in-situ thermal treatment, processes that are not well understood for human faeces (HF). Thermogravimetric analysis has been used to investigate the pyrolysis, gasification and combustion of HF. The results are compared to the thermal behaviour of simulant faeces (SF) and woody biomass (WB), along with the blends of HF and WB. Kinetic analysis was conducted using non-isothermal kinetics model-free methods, and the thermogravimetric data obtained for the combustion of HF, SS and WB. The results show that the devolatilisation of HF requires higher temperatures and rates are slower those of WB. Minimum temperatures of 475 K are required for fuel ignition. HF and SF showed similar thermal behaviour under pyrolysis, but not under combustion conditions. The activation energy for HF is 157.4 kJ/mol, relatively higher than SS and WB. Reaction order for HF is lower (n = 0.4) to WB (n = 0.6). In-situ treatment of HF in on-site sanitary systems can be designed for slow progressive burn.

With the increase in composting as a sustainable waste management option, biological air pollution (bioaerosols) from composting facilities have become a cause of increasing concern due to their potential health impacts. Estimating community exposure to bioaerosols is problematic due to limitations in current monitoring methods. Atmospheric dispersion modelling can be used to estimate exposure concentrations, however several issues arise from the lack of appropriate bioaerosol data to use as inputs into models, and the complexity of the emission sources at composting facilities. This paper analyses current progress in using dispersion models for bioaerosols, examines the remaining problems and provides recommendations for future prospects in this area. A key finding is the urgent need for guidance for model users to ensure consistent bioaerosol modelling practices.

Poor sanitation is one of the major hindrances to the global sustainable development goals. The Reinvent the Toilet Challenge of the Bill and Melinda Gates Foundation is set to develop affordable, next-generation sanitary systems that can ensure safe treatment and wide accessibility without compromise on sustainable use of natural resources and the environment. Energy recovery from human excreta is likely to be a cornerstone of future sustainable sanitary systems. Faeces combustion was investigated using a bench-scale downdraft combustor test rig, alongside with wood biomass and simulant faeces. Parameters such as air flow rate, fuel pellet size, bed height, and fuel ignition mode were varied to establish the combustion operating range of the test rig and the optimum conditions for converting the faecal biomass to energy. The experimental results show that the dry human faeces had a higher energy content (∼25MJ/kg) than wood biomass. At equivalence ratio between 0.86 and 1.12, the combustion temperature and fuel burn rate ranged from 431 to 558°C and 1.53 to 2.30g/min respectively. Preliminary results for the simulant faeces show that a minimum combustion bed temperature of 600±10°C can handle faeces up to 60wt.% moisture at optimum air-to-fuel ratio. Further investigation is required to establish the appropriate trade-off limits for drying and energy recovery, considering different stool types, moisture content and drying characteristics. This is important for the design and further development of a self-sustained energy conversion and recovery systems for the NMT and similar sanitary solutions.

The impact of bioaerosol emissions from urban, agricultural and industrial environments on local air quality is of growing policy concern. Yet the risk exposure from outdoor emissions is difficult to quantify in real-time as microbial concentration in air is low and varies depending on meteorological factors and land use types. While there is also a large number of sampling methods in use, there is yet no standardised protocol established. In this review, a critical insight into chemical fingerprint analysis of microbial volatile organic compounds (MVOC) is provided. The most suitable techniques for sampling and analysing MVOCs in outdoor environments are reviewed and the need for further studies on MVOCs from outdoor environments including background levels is highlighted. There is yet no rapid and portable technique that allows rapid detection and analysis of MVOCs on site. Further directions towards a portable GC–MS coupled with SPME or an electronic nose are discussed.

Bioaerosols are ubiquitous in ambient air but there have been increasing concerns about their human exposure and to health impact due to ever increasing environmental emissions from sources such as biowaste and intensive agriculture facilities (Borlée et al. 2015). However, the knowledge on their risk of exposure to the public is limited mainly due to a lack of emission characterisation, in part due to the limitation of conventional methods for the detection and characterisation of ambient bioaerosols. Among emerging techniques, fluorescence spectroscopy has shown promise in detecting and broadly classifying bioaerosols (Pan et al. 2015). This paper provides the preliminary results of a study that aims to demonstrate the potential of a fluorescence based bioaerosol sensor unit to detect and quantify these in real time with a view to developing and advancing bioaerosol exposure assessment methodologies to various environmental sources.

All crops that are eaten raw can present a microbiological risk to consumers. Disease outbreaks in the United Kingdom and United States have illustrated that ready-to-eat crops can be a vehicle for the transmission of gastrointestinal disease. Irrigation water has been implicated as a possible source of microbiological contaminants. Over two-thirds of irrigation water applied to UK salad crops is abstracted from rivers and streams. Many of these are subject to a continuous input of faecal contamination from sewage treatment works as well as intermittent inputs from livestock and sewer overflows. In this paper, we show how geospatial techniques can help to assess the relationships between treated effluent discharges and abstractions and thus provide a new insight into local-scale assessments of irrigation water quality. The extent to which the approach can inform risk assessments and decision-making at the farm scale is demonstrated using a case-study catchment in eastern England.

A novel enzymatic hydrolysis test (EHT) has been evaluated as a surrogate for conventional microbial biodegradability methods, using 37 assorted organic waste samples collected from diverse sources. The results of the EHT method are compared with those obtained from two conventional tests; the 4 day aerobic DR4 and 100 day anaerobic BM100 test methods currently applied in England and Wales. The EHT is based on the enzymatic hydrolysis of cellulosic materials and can be completed in less than 24 hours. Linear regression for 37 samples against the BM100 data showed the DR4 provided a correlation coefficient of r = 0.58; the EHT method gave a correlation of r = 0.62 for the total DOC release; and r = 0.77 for the DOC released from enzymatic hydrolysis. The correlations suggest that the EHT method may be better suited to a wider range of waste types when correlating with anaerobic BM100 test results since it more closely mimics the full extent of decomposition rather than that from the readily biodegradable fraction.

A novel and rapid biodegradability test method has been developed based on the enzymatic hydrolysis of cellulose. The test method consists of three phases, in which the first two phases consist of the pH buffer addition, and then autoclaving of the mixture and the final phase is the addition of the enzyme mixture and incubation. An initial investigation was carried out to determine the optimum conditions for the enzymes using standard commercial cellulose as the substrate. The optimised test was then applied to a wide range of organic waste samples including untreated and treated MSW derived mixed BMW, and specific wastes such as waste wood, packaging waste (cardboard), turkey feathers and green waste. The DOC released by enzymatic hydrolysis indicates that this could give an indication of the sample biodegradability. However the DOC released in phases 1 and 2 may also contain some biodegradable components (depending on the extent of biological treatment applied to the waste sample) and these would need to be differentiated from the non-biodegradable DOC and used together with the DOC from phase 3 to give the best possible biodegradability indication.

Headline. Although no evidence to link the irrigation of salads to disease outbreaks in the UK has been found, the industry should be seen to be taking the issue of irrigation water quality seriously. The strategy should be to take proactive measures to pre-empt the adoption of unnecessarily cautious standards within grower protocols. - Background and expected deliverables. Concerns have been expressed by some of the major supermarkets that salad vegetables may become contaminated with pathogens as a result of crop irrigation using poor quality water sources. As salads are likely to be eaten raw and will have received a minimal level of processing there are fears that consumers may be put at risk if irrigation water quality is not controlled. To assure product quality and to protect consumer confidence, some supermarkets may set stringent irrigation water quality standards in future grower protocols. Product quality is of paramount importance to growers, processors, retailers and consumers alike. However, the salad growing industry advocates a proportionate, science-based approach to the development of grower protocols rather than the adoption of an excessively precautionary principle. The aim of this project was to generate the baseline information needed by the industry to respond in a positive way to the concerns of retailers. The findings should help to inform the decisions and actions necessary to demonstrate and assure the quality of these products. The work should also support and contribute to the broader commercial objectives of the HDC regarding the efficient use of water. - Summary of the project and main conclusions. The following research tasks were undertaken in pursuit of the project’s aim. 1 A review of literature relating to the microbiological quality of irrigation water and of salad crops. 2 A survey of current UK irrigated salad production to assess current usage and underlying trends. 3 An evaluation of the technological and economic feasibility of on-farm water treatment options. 4 An analysis and discussion of the data collected and development of recommendations for the industry. The main conclusions of this work are: Irrigation water is one of many potential sources of contamination of salads. No published direct evidence has been found to link the irrigation of salads to disease outbreaks in the UK. However, there is a clear potential for this to occur. Published laboratory trials have shown that pathogens associated with poor quality irrigation water may survive on lettuce until harvest. Epidemiological investigations (not from UK) have indicated a link between disease and poor quality irrigation water. On occasions, some UK salad crops are probably irrigated with water of a lower microbiological standard than that recommended for comparable uses (e.g. reuse of wastewater for irrigation and bathing). The actual extent to which this occurs should be quantified and reviewed. The lack of guidance on irrigation water quality is a deterrent to proper water quality monitoring as most growers are unsure how they should respond to the data that is generated. This situation should be corrected as a matter of priority. It is reported that some of the multiple retailers in the UK favour a standard for irrigation water close to that which would meet the requirements for drinking water (i.e. absence or infrequent presence of E. coli in 100 ml water). Our review of standards suggests that this may be an unnecessarily cautious and expensive option. A grower faced with doubts about water quality appears to have four options: Demonstrate existing water is of adequate quality; Treat existing water; Change water source; Relocate crop. A site specific water resources study should be undertaken before assuming that treatment is necessary. Where water quality cannot be assured by management or sourcing strategies, treatment technologies may be considered. Of the many options, three technologies are likely to be suitable: ultra-violet (U/V) treatment, thermal treatment, and sand filters. U/V is considered to be attractive when taking all of the factors into account. Thermal treatment is the most rigorous and reliable. With heat recovery, such treatment could be viable in some cases. Sand filters offer the most farmer-friendly solution but these systems offer less assurance of water quality. - Financial benefits. There are no direct financial benefits to be gained by growers from this work. It may be prudent for growers to take proactive measures to improve monitoring procedures to pre-empt the adoption of unnecessarily cautious (and costly) standards in future grower protocols. - Action points for growers. There is likely to be increasing scrutiny of the microbiological quality of irrigation water. It is advised that growers review their monitoring strategy as a matter of priority. Regular sampling of water sources, at least monthly during the irrigation season, for faecal indicator bacteria would be a good start. The development of such a dataset would aid future decisions regarding the acceptability of particular sources.