Are you really telling us that anno2020 most of treatment plant design is based on theoretical criteria; usually generic data that can be up to 20 years old ?
Published by Caroline Figueres, strategic advisor water, ICT4D, Cap Dev
2 Comments
Hi Caroline,
Many thanks for your comment and in answer to your question.
Treatment plants up to 1,000 population equivalent for commercial applications are generally designed around British Water code of practice (4). This gives manufacturers theoretical loading rates produced for various applications. This code of practice has changed little over the last 15-20 years with primarily a reduction in the amount of water used per person, from 200 lts per person down to 150litres per person. The BOD and ammonia however have remained fairly constant, as this is the load calculated for biological treatment the only thing that has really changed is retention time in both the primary and clarification stage. These figures were originally agreed by the British Water PTP focus group, primarily made up of package plant manufacturers, with some European influence. The code of practice produced is referenced by the E.A., SEPA and natural Resources Wales. This is the source data or guide for a large number of plants both domestic and commercial. Larger commercial plants on green field sites tend to be designed on these parameters as true effluent strengths can not be measured until the development is complete, existing sites, usually industrial (dairies etc) can be designed using site data as they tend to already exist.
Having established where the guidance started as to effluent strength we then looked at loading requirements of the biological phase, ie how much capacity do you need to grow sufficient bacteria to oxidise the effluent down to the correct standard for environmental discharge. When dealing with Utilities a large percentage have set figures generally based on data and information produced some time ago, up to 20 + years, especially for traditional technologies. With regards SAF in a lot of instances we are prescribed the loading rates in mg/l of contaminant removed per square meter of media provided, an arbitrary figure for air requirements based on the square meterage of the surface area of the plant is used ie15m3 of air per M2, again this can be in excess of 20 years old, it has however meant that they have ended up with an over conservative design but not consider advancements in traditional technologies or changes in how we consume and contaminate water.
So for traditional technologies used for over 20 years the base design criteria has changed little, obviously this does not apply to new technologies, however these have to be well proven before adoption by the Utilities. This is an important sector as it influences both development and design. Whilst I am not saying ALL technologies, processes and companies follow these guide lines a large majority do, especially when designing sites for up to 10,000 population, this represents around 95% installed in the UK with the remaining being large purpose designed municipal works.
Published by Andrew Baird
Natasha Wiseman over to you!
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