Welcome to this May 2012 issue of Waste and Resource Management which comprises four papers of interest to the water industry and waste practitioners alike. The privatised water industry in England and Wales is now in the fifth asset management period (AMP5) and turns over in excess of £10 billion per annum. Each AMP brings further challenges for capital and operational efficiency and new challenges to establish a sustainable business amidst pressures of climate change, rising sea levels, and a desire to reduce carbon dioxide emissions while achieving improved environmental standards. These papers illustrate the research and innovation taking place within the sector to address these challenges.
The first paper by Halliday et al. (2012) describes research to determine the feasibility of using sewage sludge ash (SSA) as a replacement material for cement or fine aggregate in cement-based concretes. As a by-product of the incineration of sewage sludge arising from the treatment of wastewater from domestic and industrial sources, SSA has historically been seen as a waste rather than a resource. In the study SSA was collected from ten fluidised bed incinerators processing sewage sludge. Having confirmed the suitability of the chemical and physical properties of the material for use in concrete, it was found that the use of SSA as cement replacement in structural concrete detrimentally affected the compressive strength development. However, when used as a fine aggregate in foamed concrete the effect was beneficial to strength and thermal properties.
Rizzardini et al. (2012) describe a study to assess sewage sludge from ten small wastewater treatment plants in north-east Italy, most of which employ activated sludge treatment and have predominantly domestic catchments. Recognising the potential value of dried sludge in terms of nitrogen and phosphorous, the sludge was analysed for nutrients, inorganic and, importantly, organic contaminants and was found to be of largely consistent composition irrespective of the catchment characteristics or the effluent treatment process employed. Organic contaminants such as linear alkylbenzene sulphonates (LAS) can reach high levels but are easily degraded. Provided EU limits are observed and locally accepted strategies are put in place such material can be usefully discharged to land.
The paper on Esholt wastewater treatment scheme by Marsden et al. (2012) describes a very large capital project on a site which had been in use for 100 years. During the project opportunities to save materials and maximise energy recovery were sought out and realised. The 5-year scheme is described from the feasibility study through design, construction and commissioning. It included pilot plant work, physical and computational modelling, an innovative procurement method where good ideas were shared by unsuccessful tenderers, challenging of traditional design standards, off-site prefabrication of equipment to improve safety on site, and careful planning of commissioning. These factors were all used to successfully manage risk and minimise the resources required for construction.
The final paper on reusing material from trench excavation by Carrera et al. (2012) describes a study to develop a prototype vehicle for processing as-dug material to enable it to be recycled and reused at site, reducing disposal costs, avoiding the need for importing quarried backfill and reducing transport impacts. A process was developed to generate material to provide good quality backfill comprising shredding and screening, assessment for moisture and quality and conditioning using a cement/pulverised fly ash mixture. This process was tested, optimised and scaled to enable it to be mounted on a lorry. On-site trials were undertaken and a prototype developed which was found to work well under most conditions with the exception of handling very wet, plastic clay.
These papers all relate to the practical application of the waste hierarchy within the water sector and illustrate what can be achieved across wider industry to deliver a more sustainable economy provided research, innovation and learning are written up by researchers and practitioners and disseminated effectively through journals such as Waste and Resource Management.
