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Waste-water management and environmental sustainability

I met with an MP yesterday and she was interested in more information regarding waste-water management, specifically the links with environmental sustainability. Does WaterAid have any existing information on this?

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If you want to know what WA does specifically, then others can reply. I know some WA partners who have done interesting work, indeed OPP in Pakistan who has installed condominium sewers for about 2 million people; they have focused on the community-level sewers which then go into municipal mains sewers and so they haven’t dealt directly with treatment (although often discussed it with authorities to make sure they fit in plans).

Another one is CCI in Tanzania who also does housing; as part of a 500-unit peri-urban housing development, they have added a sanitation system consisting of 1) pour-flush toilets in homes, leading to 2) septic tanks (1 for 10 houses), which separate solids and liquids, and then the effluent (liquid portion) is transported by 3) small-diameter sewers to 4) constructed wetlands (i.e. a concrete square with gravels and plants on top), where the plants effectively treat the effluent, which is then discharged into a river (as it meets regulation and WHO requirements). Some of that treated wastewater is also used on community gardens. It’s a good example of decentralised treatment (as mains sewers in Dar es Salaam are 20km away and there would be 2 rivers to cross).

As a general approach, what you depends heavily on whether people are using flush toilets or dry toilets. In the latter case you have to deal with excreta management (emptying, treating, reusing compost), in the first case, it depends if people are using pit toilets (same emptying issue) or toilets connected to septic tanks / sewers. Only in this case do you have to deal with “blackwater”, i.e. wastewater contaminated with excreta, which is the most annoying (“greywater”, i.e. wastewater from your kitchen or shower, is easier to treat, although still an issue). Then for treatment, you can choose between treating solids and liquids together (most annoying, you need bigger sewers), or liquids only (in which case you need a septic tank to intercept solids). And you can also choose between centralised systems (all sewers in a given area converging towards a big treatment unit), or decentralised (a community-level system not connected to the municipal mains). And indeed you would try to view “waste as a resource”, i.e. treated solids can make compost, and waste-water, with suitable first treatment, can be re-used for irrigation (there are tons of guidelines on that matter).

All these involve communal decision-making, so this is something you would decide with authorities & communities… our Sanitation Framework (p. 22 onwards) describes such systems.

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Most of the sanitation options used are on-site dry or those that use limited quantities of water (pour flush). There don’t tend to be the interconnected sewerage networks that you need to accumulate large quantities of wastewater so we tend to focus on faecal sludge management rather than wastewater management per se but there are exceptions. Orangi Pilot Project in Pakistan is one. There are also examples of decentralised wastewater treatment facilities in Nepal.

On the wastewater reuse front we have got a small number of programmes in Nepal who use wastewater from washing utensils for watering of kitchen gardens. The approach makes use of a natural gradient in these communities. There may be other larger scale examples that form part of urban programming.

I’m copying in Ada, Timeyin and Remi who will know more than I do about this.

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