Birgitte Lilholt Sørensen

Filtration characterisation and specific surface area measurement of activated sludge by Rhodamine B adsorption

Abstract Rhodamine B adsorption was used to measure the specific surface area of activated sludge. The surface area occupied by the Rhodamine B molecule was calibrated by measuring its adsorption onto polyvinyl chloride (PVC) granules. The area occupied was found to be dependent on pH and conductivity of the solution. To verify the measurements other uniform materials were used. The surface area of wood flour and an activated carbon were measured with satisfactory results. Micropores (

Applying cake filtration theory on membrane filtration data

Conventional cake filtration theory is used in this paper to analyse membrane filtration data on activated sludge published by Benitez et al. (1995). In contrast they used boundary layer modelling for handling the data. Firstly the conventional cake filtration theory is shown to be equivalent to the boundary layer model in principle but more complete in its description. Secondly the data analysis is performed and a systematic deviation, which cannot be explained, seems to be involved in the data used. The data are corrected for this and reanalysed according to conventional cake filtration theory. The activated sludge is shown to be highly compressible.

Environmental and resource implications of phosphorus recovery from waste activated sludge.

Phosphorus is an essential mineral resource for the growth of crops and thus necessary to feed the ever increasing global population. The essentiality and irreplaceability of phosphorus in food production has raised the concerns regarding the long-term phosphorus availability and the resulting food supply issues in the future. Hence, the recovery of phosphorus from waste activated sludge and other waste streams is getting huge attention as a viable solution to tackle the potential availability issues of phosphorus in the future. This study explores the environmental implications of phosphorus recovery from waste activated sludge in Denmark and further elaborates on the potential availability or scarcity issue of phosphorus today and 2050. Life cycle assessment is used to assess the possibility of phosphorus recovery with little or no environmental impacts compared to the conventional mining. The phosphorus recovery method assessed in this study consists of drying process, and thermal gasification of the waste activated sludge followed by extraction of phosphorus from the ashes. Our results indicate that the environmental impacts of phosphorus recovery in an energy efficient process are comparable to the environmental effects from the re-use of waste activated sludge applied directly on farmland. Moreover, our findings conclude that the general recommendation according to the waste hierarchy, where re-use of the waste sludge on farmland is preferable to material and energy recovery, is wrong in this case. Especially when phosphorus is a critical resource due to its life threatening necessity, lack of substitution options and potential future supply risk originating due to the high level of global supply concentration.