Sewer Pipe Power: Urban Renewables

Generating energy from waste is one of the mantras of sustainability. You'd be surprised what power sources we can find when we start exploring the dark corners of our infrastructure. Thanks to things like waterborne sewage, many of us get rid of our waste so easily we can almost forget that it was ever there. There's a grimy alchemy to the whole energy-from-waste process that shows us what we can do with things we'd rather not think about.

Energy from waste was a central part of the fabled (and now seemingly abandoned) Ecotopia that the UK-based firm Arup was to build in China. It's also part of the headline sustainability features of Vancouver's Olympic village. But projects in Durban, South Africa, show that opportunities exist in almost any city – not just glossy new developments.

Since early 2008, South Africa has been in the midst of a debilitating electricity crisis (see the previous post). Durban itself has no significant energy generation capacity. It gets all of its power from a coal fired national grid that – as well as being highly unstable – is one of the largest single emitters of greenhouse gases in the world. With everyone looking for a lasting solution, it seemed like the time was right for innovative energy projects.

Surprisingly, the main driver so far has been the city's Department of Water and Sanitation (DWS). While the local electricity utility remains focused on stop-gap efficiency campaigns, it's the people responsible for providing drinking water and taking away sewage who are pioneering urban renewables. They are putting in place a complementary pairing of biogas and hydro power projects that will criss-cross whole sections of the city.

Hydro and Micro-Hydro
Because of the city's hilly terrain, the water distribution system has more pressure than it can handle. Water from dams descends into the city, building pressure that needs to
be cut by as much as two thirds in some parts of the system. Right now, that pressure gets dissipated by hot and noisy pressure release valves. Soon, a series of hydro turbines integrated directly into the piping system will be turning it into electricity.

Large and micro scale turbines will yield enough power for between 10 000 and 30 000 low-cost houses (7 – 22 megawatts) depending on the extent of the roll out. The main yield will come from one large turbine installed in sync with the already plann
ed construction of a new western aqueduct. The rest will come from as many as 100 small turbines put in at other high pressure points in the system. Construction is set to start next year, and the power will come online in 2012.

Biogass & Algae Biodiesel
DWS also has plans to upgrade and expand the existing generation systems that capture gas produced by the biodigesters that break down sewage. Beyond meeting the needs of the treatment works themselves, the plants will store biogas and generate electricity to sell to the grid at peak times. In partnership with AGAMA energy they are also putting in place smaller scale applications of the same system in peri-urban communities. The set up makes it possible to provide low-cost waterborne sewage, treat effluent on site, produce cooking gas and to generate a high grade fertilizer that can be used for local agriculture.

At the same time, in partnership with a local university, DSW is looking at ways to generate biodiesel from algae grown on waste water remediation ponds. They hope to enter commercial production within a year. A special type of local grass that can be grown on the same ponds is also being looked into for its oil producing potential.

On Not Being Bored
The technologies are interesting, but even more interesting is how the department – with no mandate to generate electricity – came to see these opportunities and act on them. While many of the officials that I talked to in the city were generally interested in “doing something about climate change” they all fell back on the common refrain that it wasn't “what I'm paid to deal with.”

In DWS though, the answers were different. One of the managers working on the energy projects told me, laughing, “ I can design a water main with my eyes closed. There is nothing more anyone can teach me about infrastructure planning in terms of water or designing for water. I can do it. In life you need more than that, you need something that is going to interest you and stop you from yawning.”

-- In the next Durban post: More on organizational culture and retrofitting cities for sustainability.

For more on my time in Durban see:
pt.1 Durban and the Climate Future
pt.3Climate Change? Not my job.

[image: turbine & AGAMA biogass digester being built]


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This is a blog for news and views on the future of sustainable cites. A major revamp is in the works. Until then I am keeping this version up as an archive of my past writing.

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