Combining physical and chemical pre-treatment processes to reduce running costs and sludge volumes in municipal WWTP’s

Dunnewijk, J. and Kluit, A., Nijhuis Water Technology, The Netherlands



Laboratory and pilot scale tests were done on waste water that originated from the influent and effluent of the primary sedimentation at the municipal WWTP of Rijn&IJssel in Etten (The Netherlands). By combining a primary sedimentation with a flocculation/flotation system, TSS reductions of 95-100 [%] and COD reductions of 39-79 [%] can be achieved. Combination of both processes reduce chemical requirements by a factor of 4 compared to a single flocculation/flotation system by which these reductions also could have been achieved. The COD removal, reduces the COD load to the aerated biological reactor on average by 59 [%] and thus will lead to a similar reduction in aeration and electrical requirements. The removed TSS can be digested for the production of 0.15 [Nm3 biogas] per [m3] of treated waste water. This can deliver 0.38 [kWh] heat and 0.34 [kWh] electrical energy per [m3] of treated waste water.


sewage, primary treatment, flocculation, flotation, COD reduction, utility consumption, energy recovery


END-O-SLUDG – – is an EU FP7 project that aims to provide novel process options that may be used in improved system solutions in line with EU energy policies and climate change mitigation strategies. In this context, the key issues to be addressed include energy and sludge volume reduction in order to lower the running costs of a Waste Water Treatment Plant (WWTP). Nijhuis Water Technology, one of the END-O-SLUDG partners, has a particular interest in the development of more efficient processes for enhanced solid removal in primary treatment that would ultimately result in a net reduction in the sludge mass, overall.

The two goals of this paper are:  initially, to show if a chemical pre-treatment – such as flocculation/flotation – can give a more efficient separation. Secondly, showing that the combination of physical – such as primary sedimentation – and chemical pre-treatments leads to lower chemical requirements of the chemical pre-treatment.

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