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Thursday, September 29, 2011

Greywater Mythbusting

One of the papers at the 12th International Conference on Urban Drainage, Porto Alegre, Brazil, 11-16 September 2011 dispelled some myths about the impacts of greywater reuse on sewer systems. The myths typically focus on (1) pirating of wastewater for greywater reuse will cause blockage of sewers due to the reduced volume/velocity of wastewater in pipelines, and (2) pirated flows will change the wastewater quality to the point that the wastewater treatment plants cannot efficiently treat the wastewater.

Effects of on-site greywater reuse on municipal sewer systems 
by R. Penn, M. Schütze and E. Friedler


On-site greywater reuse (GWR), in the urban sector, reduces urban demand of fresh water resources. In the last years research on GWR has generally overlooked the effects that GWR may have on municipal sewer systems. This paper discusses and quantifies these effects. The effects of GWR, positive and negative, were studied by modeling a representative urban sewer system. Five GWR scenarios were modeled and analysed using the SIMBA simulation system. The results show that as expected as GWR increases, the flow, velocity and proportional depth decrease. Nevertheless, the reduction is not evenly distributed but mainly occurs during the morning and evening peaks. Further, it is indicated that as a result of the GWR, blockages rate of sewers is not expected to increase. The results support the possibility to construct new sewer systems with smaller pipe diameters. The analysis shows that as the penetration of GWR system increases, concentrations of pollutants increase too, but at a rate lower than proportional reduction of sewage flow. 

Where to go from here?

More analyses should be performed also on other sewer networks. As dual-flush toilets are increasingly being used, their effect will be topic of a subsequent paper. Furthermore, analyses of the effects of greywater reuse measures on wastewater treatment efficiency would merit further research.

Read the paper here.
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It is difficult to separate, at times, the myth from the truth.  
~ American Artist Bob Kane  

1 comment:

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