Investigation of the effect of green roofs upon water quality

 

Tom Liffen is conducting a research project which investigates the effect of green roofs upon water quality.  The project also discusses the various benefits of green roofs (including habitat creation) and the policy tools that can assist their establishment.  The work is a collaboration between the Department of Environment, Food and Rural Affairs (Defra) and King’s College London.  The final report will be used as a resource by Defra, where Tom has been placed for three months, and submitted as the dissertation for his M.Sc in Aquatic Resource Management.

It is Tom’s hope, and that of the department, that this project will be used to guide the government’s future strategy of encouraging the incorporation of green roofs so that they become a common feature of urban environments.

The runoff Tom will collect will be tested for various indicators of pollution (such as metals and nitrogen) and compared to that of traditional roofs and uncontaminated rainwater, hopefully to provide some indication of how well the green roof is filtering water.

Tom is also helping me to find the answers to two other questions: (1) whether there is any serious bacterial buildup in underground water storage tanks particularly where there are a lot of birds feeding on the roof (2) how to achieve the clearest looking water for use in flushing lavatories.

With regard to the second question, we have already found that the water gently skimmed off the top of the tank is much clearer than water coming out of the garden tap. The latter is as discoloured as water taken after stirring up sediment in the bottom of the tank. I was told to expect this previously by Lutz Johnen, (a German-born expert on water recycling who has brought his excellent products and knowledge to the UK with his firm Aquality) when he came to look at my British ‘Envireau’ system sold by Klargester. Lutz had previously pointed out that my British designed system pumps water out of the base of the tank, stirring up sediment in the process. This is yet another example of the UK being years behind Germany and Austria in environmental thinking, design and products. I have now ordered a floating intake for my pump from Aquality and look forward to reporting an improvement in the quality of the rainwater pumped out of the tank. I am also investigating using a large cartridge filter to ‘polish’ the water before it goes into the lavatories.

Further research outcomes will be posted here in due course.

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