Lisa M. Avery

Survival of E. coli O157:H7 in organic wastes destined for land application

Aim:  To determine the persistence of Escherichia coli O157 in contrasting organic wastes spread to land and to assess the potential environmental risk associated with the disposal of these wastes to land.

Persistence of Escherichia coli O157 on farm surfaces under different environmental conditions.

Aims:  To compare the persistence of Escherichia coli O157 on a variety of common faecally contaminated farmyard material surfaces (wood and steel) under different moisture and temperature regimes.

Impacts of residence time during storage on potential of water saving for grey water recycling system.

Grey water recycling has been generally accepted and is about to move into practice in terms of sustainable development. Previous research has revealed the bacteria re-growth in grey water and reclaimed municipal water during storage. However, in most present grey water recycling practices, impacts of water quality changes during storage on the systems performance and design regulation have not been addressed. In this paper, performance of a constructed wetland based grey water recycling system was analysed by taking the constraint of residence time during storage into account using an object based household water cycle model. Two indicators, water saving efficiency (WSE) and residence time index (RTI), are employed to reflect the systems performance and residence time during storage respectively. Results show that WSE and RTI change with storage tank volumes oppositely. As both high WSE and RTI cannot be achieved simultaneously, it is concluded that in order to achieve the most cost-effective and safe solution, systems with both small grey and green tanks are needed, whilst accepting that only relatively modest water saving efficiency targets can be achieved. Higher efficiencies will only be practicable if water quality deterioration in the green water tank can be prevented by some means (e.g. disinfection).

Survival of Escherichia coli O157:H7 in the rhizosphere of maize grown in waste-amended soil.

Aims:  To assess whether the persistence of Escherichia coli O157:H7 in soil amended with cattle slurry and ovine stomach content waste is affected by the presence of a maize rhizosphere.

ULTRAVIOLET (UV) DISINFECTION OF GREY WATER: PARTICLE SIZE EFFECTS

Abstract The impact of water quality on the ultraviolet (UV) disinfection of grey water was investigated with reference to urban water reuse. Direct UV disinfection of grey water did not meet the stringent California State Title 22 criteria for unrestricted urban water reuse due to the presence of particulate material ranging from <1 to ≥2000 μm in size. Grey water was manipulated by settling to produce fractions of varying particle size distributions and blending was employed post‐disinfection to extract particle‐associated coliforms (PACs). The efficacy of UV disinfection was found to be linked to the particle size of the grey water fractions. The larger particle size fractions with a mean particle size of 262μm and above were observed to shield more coliforms from UV light than did the smaller particles with a mean particle size below 119μm. Up to 70% of total coliforms in the larger particle size fractions were particle‐associated following a UV dose (fluence) of 260mJ·cm−2 and would remain undetected by standard coliform enumeration techniques. Implications for urban water reuse are discussed and recommendations made for grey water treatment to ensure removal of particle‐associated indicator bacteria and pathogens prior to UV disinfection.

Leaching of bioluminescent Escherichia coli O157:H7 from sheep and cattle faeces during simulated rainstorm events

Aims:  Development of a novel inoculation technique to improve the current methods of determining the leaching of Escherichia coli O157:H7 from faeces.

Clay mineral type effect on bacterial enteropathogen survival in soil

Enteropathogens released into the environment can represent a serious risk to public health. Soil clay content has long been known to have an important effect on enteropathogen survival in soil, generally enhancing survival. However, clay mineral composition in soils varies, and different clay minerals have specific physiochemical properties that would be expected to impact differentially on survival. This work investigated the effect of clay materials, with a predominance of a particular mineral type (montmorillonite, kaolinite, or illite), on the survival in soil microcosms over 96 days of Listeria monocytogenes, Salmonella Dublin, and Escherichia coli O157. Clay mineral addition was found to alter a number of physicochemical parameters in soil, including cation exchange capacity and surface area, and this was specific to the mineral type. Clay mineral addition enhanced enteropathogen survival in soil. The type of clay mineral was found to differentially affect enteropathogen survival and the effect was enteropathogen-specific.

Prevalence and survival of potential pathogens in source-segregated green waste compost

Composting of source-separated green waste (SSGW) is essential to meet the EU Landfill Directive target and agricultural land is considered a significant market for the resulting composts. A critical review of the literature was performed to evaluate the potential for pathogens to enter the composting process via SSGW feedstocks and the likelihood of their survival of the composting process and subsequent application to land. This is discussed in the context of application of other organic wastes to land. It was concluded that zoonoses such as verotoxigenic Escherichia coli and Salmonella spp. are unlikely to survive and effective composting process, whereas spore forming organisms are more resistant to composting but are also ubiquitous in the environment. Adherence to existing guidelines, such as those for farm yard manures, is likely to provide a rational degree of health protection for humans and livestock.

Risk assessment of the use of PAS100 green composts in sheep and cattle production in Scotland

A generalized quantitative risk assessment for the use of source-segregated green waste (SSGW) compost use in livestock production is presented. This assessment focussed on potential risks associated with a specific product, PAS100 compost that meets the UK publicly available specification 100 and represents the majority of compost available for use in extensive Scottish livestock systems. A hazard screening approach was used to identify all potentially hazardous agents present in compost. A total of 497 potentially hazardous agents were screened, with 147 finally put forward for quantitative risk assessment. Scenarios modelled in the assessment included surface application of compost to grazing land and also incorporation into soil and subsequent uptake by fodder crops. Risk estimates were compared to those associated with six comparator materials, including various sludges, slurries and farm yard manures. Overall, five potentially hazardous agents (PCB28, PCB138, PCB153, 1,2,3,4,6,7,8-HpCDD, Clopyralid) returned a hazard quotient >1 but within margins of uncertainty, indicating that further investigation may be required. Within the limitations of available information, SSGW compost was found to pose less risk to grazing livestock, or the environment, than other commonly-used soil amendments. While this assessment relates to a specific product/standard used in the UK, the methodology could easily be applied to other composts/products/situations. Therefore these results have wider applicability.

Heat and lime-treatment as effective control methods for E. coli O157:H7 in organic wastes

Land-application of abattoir wastes is economically appealing and may provide an effective means of closing the nutrient cycling loop. This practise is constrained, however, by legislation which necessitates pre-treatment to remove pathogenic micro-organisms prior to land-spreading. Here we investigated whether heat-treatment or lime addition could eliminate Escherichia coli O157:H7 from three contrasting abattoir wastes. We found that treatment at 60 degrees C for 10 min effectively eradicated the organism while treatment for the same length of time at 50 degrees C led to 2-4 log reductions, but not a complete kill. Temperatures of 72 degrees C induced waste solidification rendering its use impractical. The potential for re-growth in heat-treated and untreated wastes was also investigated. Survival was significantly greater in heat-treated wastes, although the difference was less than half a log unit in magnitude. This effect of heat-treatment on pathogen survival appeared to be ameliorated when wastes were mixed with soil. No viable E. coli O157:H7 cells were recovered from any waste after application of lime (CaO) at a rate of 10 gl(-1), even after enrichment. Our results indicate that pasteurisation-style or liming treatments may provide a suitable alternative method for reducing pathogen loads in abattoir wastes, so that they can be applied to land with minimal biological risk.