Bauxite residue (Red mud) as a pulverised fuel ash substitute in the manufacture of lightweight aggregate

This study looked at the potential of bauxite residue or red mud to be used in the manufacture of lightweight aggregate in replacement of pulverised fuel ash (PFA), commonly used as a way of recycling problematic wastes. The percentage replacements of red mud with PFA were as follows: 25, 31, 38, 44 and 50%. These were blended in a mix with waste excavated clay and sewage sludge – all from the Chongqing municipality in China. Lightweight pellets were produced using a Trefoil rotary kiln and were sintered to 1200 °C. Results showed that 44 % bauxite residue replacement produced lightweight pellets with the highest compressive strength, highest density and largest water holding capacity. This would be expected in materials with a low level of silicates, which causes insufficient glass phase viscosity and therefore poor bloating during firing; producing an aggregate with a higher density but with open pores that allowed for larger water absorption. All ratios of red mud aggregates were significantly reduced in pH after firing to around pH 8, and this reduced the leachability of the aggregates to levels below those set by the European landfill directive (2003/33/EC)

Are microbial communities in green roof substrates comparable to those in post-industrial sites?—a preliminary study.

Green roofs have been implemented on new buildings as a tool to mitigate the loss of post-industrial or brownfield land. For this to be successful, the roofs must be designed appropriately; that is with the right growing media, suitable substrate depth, similar vegetation and with a comparable soil microbial community for a healthy rhizosphere. This study compared soil microbial communities (determined using phospholipid fatty acid or PLFA analysis) of two extensive green roofs and two post-industrial sites in Greater London. It was found that green roof rootzones constructed using engineered growing media are not depauperate, but can have an abundant soil microbial community that in some cases may be more diverse and numerous than communities found in brownfield areas. In this preliminary study, one green roof supported abundant soil microbial communities that were dominated by gram negative and aerobic bacteria, whilst fungal abundance was similar across all sites analysed. Furthermore, ratios of fungal: bacterial PLFA’s were larger from post-industrial sites but overall were consistent with bacterial dominated soils typical of early successional habitats