Krivtsov, V., Dacombe, P., Kozenko, E.P., Zotova, E.A, Pak, L.N., Heaven, S. and Banks, C.J. (2008) Contemporary applications of the interdisciplinary waste management research: Case studies of algal biodiversity in the WSP and energy footprint of municipal wastes. International Journal of Energy, Environment, and Economics, 15 (3-4), 183-204.
Abstract
This paper describes two interdisciplinary waste management case studies coordinated by the University of Southampton. The first case study addresses the issue of algal species composition in wastewater treatment facilities situated in Kazakhstan. Algal populations in four experimental waste stabilisation ponds fed at surface loading rates from 50-300 kg BOD ha-1 day-1 were monitored for seven months, including a period between late November and mid March when the ponds were frozen. Cell counts and species identification were performed five times a week and biomass concentration was estimated weekly. During winter only very small numbers of algae were observed in samples taken from below the ice. Once the ice melted there was a rapid increase in algal numbers linked with rising water temperature. It was also apparent that cell numbers increased at a faster rate in the pond with the lightest winter load. During the whole period of operation the algal population was dominated by a small number of species, with 80% of the cell count attributable to no more than 3 species in each pond, but there were considerable differences between ponds. When considered as biomass rather than cell numbers, single species dominance was even more apparent apart from in one pond where diversity increased significantly. In line with other studies, there is an indication that higher loadings result in lower diversity. With the current set of results, it was difficult to interpret changes in the population structure as a function of loading or any other analytical determinant. However, there is an indication that the system appears to be dominated by small species in the initial warm up period, maturing to greater species diversity, and larger species, by mid summer.
The second case study describes a project set up to understand, quantify and model energy usage associated with the collection, separation, processing and disposal of Municipal Solid Wastes. It illustrates the energy footprint analysis using data on the paper/card fraction within household waste. The mass and energy balances for the different processes/stages involved with dealing with the waste stream in Southampton are simulated using a specially designed model. The model starts from the point where the material becomes ‘waste’ and follows it through until disposal and/or processing. It accounts for recycling via bring-sites (both recycling banks and Household Waste Recycling Centres) and also via kerbside collection schemes, and disposal via landfill and thermal recovery of heat. Critically, the model not only takes into account the energy consumed during processing/disposal but also transport energy consumption. The results show that the major source of energy savings from paper/card recycling is from increased use of the recycled material in paper/card manufacture, due to the decrease in energy required to produce paper from this material. There is an ~5% reduction at a maximum recycling rate of ~52%, compared to the present-day rate (18.1%,) with recycling through the PaperChain? scheme (only collects newspaper/magazines/leaflets).
The savings increase to ~9% (at ~87% recycling rate) if a city-wide dry recyclables scheme is introduced to replace the PaperChain scheme. This increase is largely due to the fact that more sub-categories of paper/card are collected by the dry recyclables scheme.
In terms of energy consumption, incineration without recycling would be the preferred waste management option. However, the calorific value of the residual waste stream is not significantly affected by removal of paper/card through increased recycling. Thus, a combination of recycling and incineration of the residual waste would also be an option.
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