The second day of the eco sewage and sanitation course was on sewage treatment. My advice for anyone taking this course next year is, don’t get drunk the night before!! The friday night party feeling took over me and I spent the entire Saturday with a hangover, you guessed it, looking at shit (all self-inflicted of course).
Nevertheless I still managed to concentrate (I think) and gain an understanding that actually sewage treatment really can be life and death and is something that needs to be taken seriously. There’s all sorts of nasties – pathogens, viruses and so forth as wells as eutrophication causing nutrient overloads. Other environmental impacts of sewage include storm sewage overflows (which if you ever go surfing in Cornwall you will know about – the day after the storm its like tampon city in the atlantic ocean).
There’s all sorts of ways of measuring the quality of effluent so you know how clean it really needs to be, such as turbidity (suspended solids – lovely phrase), odour measuring ammonia and biotic classifications, which measure the biology of the water (as certain organisms live in dirty water etc.)
I never knew how much food waste contributes to excess nutrients in the water ways, as a vegan I get quite used to blaming animal farmers on things like that but now I know to scrape my plate before washing up that’s for sure!
Things to think about if you want to set up an independent sewage treatment system:
- physical aspects e.g. land area, soils, water table, levels, discharge point
- client acceptability – how proactive do they have to be?
- regulations – there’s all sorts to consider such as pipework requirements and gradients, do your research!
This removes suspended soils from water (which can be prevented with the compost loo of course) otherwise main systems include septic tanks and aquatron separators (which are the business!). These things separate out the urine and let the solids fall down to be composted, and they’re pretty exciting to look at if you’re a sanitation junkie like Judith. There’s all sorts of other elements to consider however like floating crusts, sinking solids, sludge management… can you see how this was difficult with a hangover?
The aim of secondary treatment is to treat liquids to a discharge standard. Similar factors influence this also, such as soil porosity, the height of the water table, cost and effluent quality requirements and so forth.
Options include systems that filter, such as leachfields and soakaways, drainage bounds, wetlands and so forth, otherwise there are package treatment plans, trench arches, anaerobic digestion and pond systems.
Filters are vital to mechanically remove solids but also to create a cosy place to live for microorganisms (biofilms – sounds like a german organic soya yoghurt or something!). We explored each of the above in turn which have their own advantages and disadvantages.
We also explored the degree of centralisation within systems, for example do we really need to design off-grid sewage systems for single households or should design them on a community level? Judith recommends mains sewage if you have the option, however with new developments regularly, especially low impact developments, it is useful to have an understanding of the alternatives to the mains.