In The Netherlands a research project is presently conducted, which has the objective to identify new, more sustainable sewage treatment scenarios which are based on physical-chemical pretreatment. After collecting possible treatment scenarios by means of literature research and contacts with international experts the identified scenarios are evaluated on sustainability and costs. For evaluating the sustainability, the following sustainability criteria (derived from the Life Cycle Assessment methodology) are used: energy balance, final sludge production, effluent quality, the use of chemicals and space requirement (footprint). Within this paper the use of these criteria is illustrated and discussed by means of two example scenarios and a reference scenario. The calculation results for the two example scenario's show that physical-chemical pretreatment leads to energy saving when biological post treatment is applied. Besides, more energy can be generated through sludge digestion, due to an increased sludge production. However, the increased particle removal also leads to an increased final sludge production after digestion which will have to be disposed of and to a relatively high consumption of chemicals.

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