Discover the Editor’s Choice: from each issue of leading journal, Water Science & Technology, the Core Team of Editors will select one outstanding paper to make Open Access and share across IWA Publishing platforms.


IWA Publishing is pleased to announce that the 8th Editor's Choice paper, selected by Wolfgang Rauch, is now Open Access (CC BY NC-ND):

How does greywater separation impact the operation of conventional wastewater treatment plants?

Carlo Morandi, Heidrun Steinmetz

Water Science & Technology, April 2019; 79 (8): 1605–1615. DOI:


Why was this paper selected as the Editor's Choice?

"Source separation of the wastewater streams has been a topic of considerable interest over the last 2 decades, mostly dealing with either greywater – or urine separation. Numerous papers have focused on treatment processes and resource recovery of the separated waste streams, pointing out the benefit of such decentralized wastewater management schemes. However, in most industrialized countries a centralized treatment scheme already exists and as such the infrastructure is not abandoned easily. Hence, if source separation is implemented in traditional centralized treatment schemes, the effect also needs to be considered for the existing infrastructure. Undeservedly, this issue has not really found much attention in the literature until now.

The paper by Morandi and Steinmetz addresses the effect of large-scale greywater separation on the operation of a traditional wastewater treatment system. Here, the term separation indicates that greywater is treated decentrally (e.g. onsite) and no longer reaches the treatment plant. The authors use an integrated model of the total treatment plant, including sludge management and recycle streams, to point out mass and flow volume balance in this system. Starting from the traditional wastewater composition as given in (German) guidelines and textbooks, greywater separation gradually shifts the C to N ratio (typically > 3.5) to less favorable proportions. However, as long as the greywater separation is less than 17% the overall effect (including energy requirements) is positive for plant performance. If more greywater is treated decentrally the denitrification process is hampered and from 35% separation onwards even alternative process solutions have to be evaluated. In terms of source separation, the obvious choice would be to include additionally urine separation. The authors point out that – from the point of view of the treatment plant operation – source separation of 50% of the greywater should go hand in hand with 50% of urine separation.   

My choice to select this paper as the Editor Choice Paper from the current issue is based on the relevance of the topic and the pragmatic but still scientifically convincing approach to demonstrate the issue. The paper is well structured and does not attempt to make it a superficial complex reading. I enjoyed reading a paper that represents scientific innovation for a topic of practical relevance and hope that this also applies to the readers of this issue of Water Science & Technology."

Wolfgang Rauch, Editor-in-Chief


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