Gillian H. Drew

Biodrying for mechanical-biological treatment of wastes : A review of process science and engineering

Biodrying is a variation of aerobic decomposition, used within mechanical-biological treatment (MBT) plants to dry and partially stabilise residual municipal waste. Biodrying MBT plants can produce a high quality solid recovered fuel (SRF), high in biomass content. Here, process objectives, operating principles, reactor designs, parameters for process monitoring and control, and their effect on biodried output quality are critically examined. Within the biodrying reactors, waste is dried by air convection, the necessary heat provided by exothermic decomposition of the readily decomposable waste fraction. Biodrying is distinct from composting in attempting to dry and preserve most of biomass content of the waste matrix, rather than fully stabilise it. Commercial process cycles are completed within 7-15 days, with mostly H(2)O((g)) and CO(2) loses of ca. 25-30% w/w, leading to moisture contents of <20% w/w. High airflow rate and dehumidifying of re-circulated process air provides for effective drying. We anticipate this review will be of value to MBT process operators, regulators and end-users of SRF.

Production and Quality Assurance of Solid Recovered Fuels Using Mechanical—Biological Treatment (MBT) of Waste: A Comprehensive Assessment

The move from disposal-led waste management to resource management demands an ability to map flows of the properties of waste. Here, we provide a comprehensive review of how mechanical–biological treatment (MBT) plants, and the unit processes that comprise them, perform in relation to management of material flows, while transforming inputs into output fractions. Focus is placed on the properties relating to the quality of MBT-derived fuels. Quality management initiatives for refuse-derived fuels (RDF) or solid recovered fuels (SRF) are reviewed and SRF quality from MBT plants is assessed through a statistical analysis of published data. This can provide a basis for a targeted reduction in pollution load from solid MBT outputs and subsequent end-user emissions. Our analysis, among else, (1) verifies the difficulty of chemical separation solely by mechanical means; (2) illustrates the trade-off between achieving a high quality of recoverable outputs and the quantity/properties of reject material; and (3) indicates that SRF quality could respond to legislative requirements and market needs, if specific improvements (reduction of Cl, Cu, and Pb content) are achieved. Further research could enhance the confidence in the ability of MBT plants to produce a quality-assured SRF suitable for specific end-users, without contradicting the wider requirement for an overall sustainable management of resources.

Spatial variations in airborne microorganism and endotoxin concentrations at green waste composting facilities.

The emission and dispersal of bioaerosols from open-air commercial composting facilities continues to be contentious. A meta-dataset enumerating cultivable microorganism emission and downwind concentrations is not yet available. A dataset derived from repeated and replicated field studies over a period of two years at two commercial composting facilities is presented. The data characterises patterns in Aspergillus fumigatus, actinomycetes, Gram-negative bacteria and endotoxin emission and downwind concentrations. For all bioaerosols, compost agitation activities had a significant impact on concentrations; levels were variable up to 600 m downwind from site. Bioaerosols declined rapidly from source and exhibited a secondary peak 100-150 m from site boundary. All bioaerosols were found downwind from site in elevated concentrations. Compared to those found 100 m upwind, levels were significantly higher at 180 m downwind for A. fumigatus; at 300-400 m for actinomycetes and Gram negative bacteria, and at 100 m for endotoxins. Periodically, elevated concentrations could be found for all bioaerosols at distances further downwind. The evidence provided by this data set provides operators and regulators of facilities with reliable data to inform the location, risk assessment and bioaerosol sampling strategies of commercial composting facilities.

Temporal and spatial changes in the microbial bioaerosol communities in green-waste composting.

In this study, the microbial community within compost, emitted into the airstream, downwind and upwind from a composting facility was characterized and compared through phospholipid fatty acid analysis and 16S rRNA gene analysis using denaturing gradient gel electrophoresis and bar-coded pyrosequencing techniques. All methods used suggested that green-waste composting had a significant impact upon bioaerosol community composition. Daily variations of the on-site airborne community showed how specific site parameters such as compost process activity and meteorological conditions affect bioaerosol communities, although more data are required to qualify and quantify the causes for these variations. A notable feature was the dominance of Pseudomonas in downwind samples, suggesting that this genus can disperse downwind in elevated abundances. Thirty-nine phylotypes were homologous to plant or human phylotypes containing pathogens and were found within compost, on-site and downwind microbial communities. Although the significance of this finding in terms of potential health impact was beyond the scope of this study, it clearly illustrated the potential of molecular techniques to improve our understanding of the impact that green-waste composting emissions may have on the human health.

A critical review of classification of organisations in relation to the voluntary implementation of environmental management systems

The need and ability of an organisation to manage and control its impact on the environment has been hotly debated in recent times. However, the uptake of certificated environmental management systems (EMS), specifically BS EN ISO 14001 (ISO 14001) (British Standards Institution, 2004), is becoming more prevalent, even though evidence of the individual benefits is less clear. Furthermore, reports are often limited and anecdotal in their discussion of the true barriers that organisations experience during the certification and management of their EMS. Presently organisations are commonly classified simply according to size and the barriers they experience when implementing an EMS successfully. This system of classification is not sufficient to understand the multifaceted environments within which modern organisations operate. This paper reviews existing classification methodologies relevant to environmental management so as to determine whether opportunities exist for their practical application in this sector. It begins with an introduction to EMS and existing discussions regarding implementation is provided before a more detailed consideration of organisational size, the integration and development of environmental management within an organisation, then cladistics and quality management systems (QMS) are reviewed as potential opportunities for classification. This shows that whilst numerous methods are available, none function beyond the theoretical, or that the classes provided restrain the description of the complex tasks. Central to differences faced by organisations are insights to the true hurdles that each experience when implementing an EMS. It is shown here how the manipulation of techniques from the more mature field of Energy Management may offer a direction for the development of robust classes. A valuable outcome is that these methods produce classifications that are fit for purpose to better support organisations through the implementation and management of their EMS.

Identifying Uncertainty in Environmental Risk Assessments: The Development of a Novel Typology and Its Implications for Risk Characterization

ABSTRACT Environmental risk analysts need to draw from a clear typology of uncertainties when qualifying risk estimates and/or significance statements about risk. However, categorizations of uncertainty within existing typologies are largely overlapping, contradictory, and subjective, and many typologies are not designed with environmental risk assessments (ERAs) in mind. In an attempt to rectify these issues, this research provides a new categorization of uncertainties based, for the first time, on the appraisal of a large subset of ERAs, namely 171 peer-reviewed environmental weight-of-evidence assessments. Using this dataset, a defensible typology consisting of seven types of uncertainty (data, language, system, extrapolation, variability, model, and decision) and 20 related sub-types is developed. Relationships between uncertainties and the techniques used to manage them are also identified and statistically evaluated. A highly preferred uncertainty management option is to take no action when faced with uncertainty, although where techniques are applied they are commensurate with the uncertainty in question. Key observations are applied in the form of guidance for dealing with uncertainty, demonstrated through ERAs of genetically modified higher plants in the European Union. The presented typology and accompanying guidance will have positive implications for the identification, prioritization, and management of uncertainty during risk characterization.

Endotoxin emissions from commercial composting activities

This paper describes an exploratory study of endotoxin emissions and dispersal from a commercial composting facility. Replicated samples of air were taken by filtration at different locations around the facility on 10 occasions. Measurements were made of endotoxin and associated culturable microorganisms. The inflammatory response of cell cultures exposed to extracts from the filters was measured. Endotoxin was detected in elevated concentrations close to composting activities. A secondary peak, of lesser magnitude than the peak at source was detected at 100-150 m downwind of the site boundary. Unexpectedly high concentrations of endotoxin were measured at the most distant downwind sampling point. Extracted endotoxin was found to stimulate human monocytes and a human lung epithelial cell line to produce significant amounts of pro-inflammatory cytokines. On a weight basis, endotoxin extracted from the composting source has a greater inflammatory cytokine inducing effect than commercial E. coli endotoxin.

Morphological classification of bioaerosols from composting using scanning electron microscopy

This research classifies the physical morphology (form and structure) of bioaerosols emitted from open windrow composting. Aggregation state, shape and size of the particles captured are reported alongside the implications for bioaerosol dispersal after release. Bioaerosol sampling took place at a composting facility using personal air filter samplers. Samples were analysed using scanning electron microscopy. Particles were released mainly as small (<1 μm) single, spherical cells, followed by larger (>1 μm) single cells, with aggregates occurring in smaller proportions. Most aggregates consisted of clusters of 2-3 particles as opposed to chains, and were <10 μm in size. No cells were attached to soil debris or wood particles. These small single cells or small aggregates are more likely to disperse further downwind from source, and cell viability may be reduced due to increased exposure to environmental factors.

Sensitivity of predicted bioaerosol exposure from open windrow composting facilities to ADMS dispersion model parameters

Bioaerosols are released in elevated quantities from composting facilities and are associated with negative health effects, although dose-response relationships are not well understood, and require improved exposure classification. Dispersion modelling has great potential to improve exposure classification, but has not yet been extensively used or validated in this context. We present a sensitivity analysis of the ADMS dispersion model specific to input parameter ranges relevant to bioaerosol emissions from open windrow composting. This analysis provides an aid for model calibration by prioritising parameter adjustment and targeting independent parameter estimation. Results showed that predicted exposure was most sensitive to the wet and dry deposition modules and the majority of parameters relating to emission source characteristics, including pollutant emission velocity, source geometry and source height. This research improves understanding of the accuracy of model input data required to provide more reliable exposure predictions.

Use of dispersion modelling for Environmental Impact Assessment of biological air pollution from composting: progress, problems and prospects

With the increase in composting asa 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.