Assessing dewatering performance of drinking water treatment sludges David I. Verrelli 1 , David R. Dixon, Peter J. Scales* Particulate Fluids Processing Centre, Department of Chemical and Biomolecular Engineering, The University of Melbourne, Victoria 3010, Australia article info Article history: Received 13 May 2009 Received in revised form 11 October 2009 Accepted 29 October 2009 Available online 3 November 2009 Keywords: Alum Ferric Coagulation Sludge Dewatering Filtration abstract A comparison of the dewaterability of a range of water treatment plant sludges has been completed through computation of dewatering performance indicators for a diaphragm filter press. Real parameter data, obtained from the characterisation of alum and ferric sludges, generated under precisely controlled conditions, was used for input to a phenomenological model. Comparisons of dewaterability based on throughput curves largely agree with previous analysis of the underlying parameter data. The difference in approach provides a quantification of benefit. Greater throughputs and output concen- trations are predicted at the lowest coagulant doses and at pH w 6. Typical industrial cloth resistances consistently reduce throughput by a factor of 3–7, but the assessment of relative benefit is shown to be insensitive to this parameter. Quantitative agreement of the predictions with observed performance can be attained. Finally, the twin effects of solids loading and dewaterability are assessed together, showing that each has a significant influence on the required filter surface area. This quantification shows that high coagulant doses adversely affect both of these aspects, leading to filter area requirements larger than might otherwise be expected. ª 2009 Elsevier Ltd. All rights reserved. 1. Introduction The problem of what to do with sludges produced in conventional coagulation processes for potable water treat- ment has received sporadic attention over several decades (Neubauer, 1968). Concern has steadily risen due to the countervailing demands to supply water satisfying increas- ingly stringent requirements and to reduce waste disposal costs and environmental impacts. The sludges themselves are typically quite inert. Particular motivations include the desire to reduce loss of water held in the sludge matrix, throughput optimisation d i.e. maximisation of sludge dewatering rate for a given dewater- ing device d and the increasingly limited (and expensive) options available for disposal. The ultimate objective is to maximise the quality and minimise the quantity of sludge while assuring the quality of the treated water. It is widely known that sludge properties vary over time at a given water treatment plant (WTP) and also differ between WTPs. This variation can be attributed to variation in the quality of the raw water and to differences in the coagulation regime d the latter often determined largely by the former. To assess the impact of individual changes in the treat- ment conditions, it is important to have an objective means of * Corresponding author. Tel.: þ61 3 8344 6480; fax: þ61 3 8344 4153. E-mail addresses: david.verrelli@csiro.au (D.I. Verrelli), drdixon@unimelb.edu.au (D.R. Dixon), peterjs@unimelb.edu.au (P.J. Scales). 1 Current affiliation: CSIRO, Clayton, Victoria 3168, Australia. Available at www.sciencedirect.com journal homepage: www.elsevier.com/locate/watres water research 44 (2010) 1542–1552 0043-1354/$ – see front matter ª 2009 Elsevier Ltd. All rights reserved. doi:10.1016/j.watres.2009.10.036