A fortnight ago I was fortunate to take part in some of the 2014 centenary celebrations of the 1914 invention of activated sludge in Manchester. The day before the centenary conference we kicked off with a fascinating – and not quite as smelly as expected – visit to Davyhulme sewage works kindly organised by site owners, United Utilities.

The 1.2 million population equivalent Davyhulme site is so large that UU had laid on a bus for the tour. Our first stop was at the inlet screenings area, complete with sample ‘rags’ in a wheelbarrow (‘not all toilet paper’, our host stressed):

Photo: Covered screens for one of the treatment lanes at Davyhulme sewage works.
Photo: Covered inlet screens for one of the treatment lanes at Davyhulme sewage works; typical screened out ‘rags’ shown in the wheelbarrow in the foreground.
Photo: Display board at the inlet screen, one of several prepared by UU for the Centenary; the inlet screens are marked number 1 on this site map.

The display board told us that two of three main sewers feeding Davyhulme from parts of Manchester are huge – one is a 10ft gravity sewer; the other is 13ft in diameter. The plant can also treat up to 714 megalitres a day and has an additional 105 megalitres of storm tank storage (that were originally primary settlement tanks).

Our guide, Lee Donnellan, at various points during the tour, showed us samples of the flow through the plant, like this one from the works inlet:

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Photo: Bottled sample of the sewage from the inlet lane in the background.
Photo: Bottled sample of the sewage from the inlet lane you can see in the middle ground.

Then it was time to see the activated sludge tanks, which sit next to a much newer BAFF (Biological Aerated Flooded Filter) plant at Davyhulme:

Photo: The activated sludge process in action at Davyhulme.
Photo: The activated sludge process in action at Davyhulme (the novelty that was published by inventors Ardern and Lockett in 1914 was to use certain ‘micro-organisms suspended in the sewage without the need for large filter beds’ as described in the display board shown below).

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Photo: Display boards describing the invention and operation of the activated sludge process at Davyhulme.
Photo: UU’s display boards describing the invention and operation of the activated sludge process at Davyhulme.

Lee then showed us more sewage samples taken at various points as they pass through the works, right up to the stage of cleaned, fully treated effluent that is discharged from the works:

Photo: Samples of the sewage sludge from inlet to discharge. The third picture is from the activated sludge tanks.
Photo: (L to R) Samples of the sewage from inlet to discharge. The third sample is from the activated sludge tanks.

We also had a quick look at the BAFF plant, installed at Davyhulme in 1999 according to the display boards to address ammonia levels that were harmful to aquatic life in the Manchester Ship Canal:

Photo: Display board about the BAFF plant at Davyhulme.
Photo: Display board about the BAFF plant at Davyhulme.
Photo: Housing for the blowers to aerate the BAFF plant at Davyhulme.
Photo: Building housing the energy-sapping air blowers that aerate the BAFF plant at Davyhulme.
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Photo: Treated flow leaving the BAFF plant at Davyhulme ready for discharge into the nearby Manchester Ship Canal.

Next up was the £100 million sludge recycling plant that was finished at Davyhulme in 2013. At the time it was the world’s largest thermal hydrolysis plant; it’s now the 2nd biggest due to the fact that a larger one has been commissioned in Washington, DC.

Photo: Panorama pics of the very large thermal hydrolysis plant at Davyhulme, treating sludge at high temperature then enabling biogas production for energy recovery.

The size, noise, heat and rather concentrated smell of this thermal hydrolysis area is hard to convey with pictures alone! Some members of the tour party also had concerns about this plant’s longevity given its operational stresses. At present though it seems like a laudable effort to get renewable energy out of the works and higher quality sludge for application to land.

Photo: Odour control at Davyhulme.
Photo: Odour control at Davyhulme.

There was an emphasis on continuous – and very expensive – development of the site throughout the tour. Notably a £200 million investment is now starting. This is to address the age, condition and performance of large parts of the historic site, given that much of it has been in place and not radically re-vamped for decades. There was also a forward-looking emphasis on what the next 100 years might hold – a theme that carried over into the actual conference the following day.

Photo: Map of the 100 square km area covered by Davyhulme sewage works.
Photo: Map of the 100 square km area covered by Davyhulme sewage works.
Photo: Display board explaining another £200 million investment is now starting as part of the plant's next 100 years!
Photo: Display board announcing another £200 million investment to launch Davyhulme’s next 100 years!

The conference began with some audience participation led by Prof. James Alleman in the chair. First he asked the audience how many of them had actually worked on an activated sludge plant; most hands went up (not mine!) showing that it was really a community of practitioners at the event. Second, he asked about lengths of service and age from the audience. This reached people in their eighties whose relatives had been based at Davyhulme in early years, and people with well over 30 years of service in the field of activated sludge:

Photo: Prof. Alleman marshalling a remarkable series of shows of hands about years of service in the field of activated sludge.
Photo: Prof. Alleman marshalling a show of hands for the audience’s impressive years of service in activated sludge.

A number of points struck me during the conference presentations:

  • This was a rare gathering of a niche community of dedicated people from around the world who have devoted decades of their lives to the study and improvement of a world-spanning treatment process;
  • It’s important to celebrate taken-for-granted, flush-and-forget, no doubt unpalatable to most, but nevertheless vital, world-changing technology and system innovations like this;
  • There’s been a mixture of tradition and conservatism interspersed with a few bursts of energy and innovation in the activated sludge area – seemingly pretty consistent with our general view of innovation in the water sector here; and
  • An interesting range of exhibitors (mainly suppliers) at the conference exemplified continued invention and innovation in the sector, although some had had familiar problems in getting any large-scale uptake from UK water utilities.

One surprise for me from the conference content was about the UK/US litigation that had ensued very shortly after the invention of activated sludge. It didn’t slow the process’ rapid adoption, remarkable given that this legal action could have been barrier enough let alone the fact that this was also a time of world war. Dr Nigel Horan told us how the original inventors and collaborators for activated sludge – particularly Weizmann and the Mumfords at the University of Manchester, Ardern and Lockett at the Manchester Rivers Department, manufacturers Jones and Attwood, and ‘knowledge broker’ Gilbert Fowler – had fundamental disagreements about intellectual property that led to various court cases.

Photo: A historical shot of Davyhulme from the conference displays.
Photo: A historical shot of Davyhulme from the conference displays.

There was also nostalgia during some presentations for apparently lost ‘golden ages’ of research and exploration in the water sector, of the sort that were seen to be no longer possible due to post-privatisation competition, among other things. One example quoted by Dr Horan was the remarkable 17-year long investigation of sewage options during the 1898-1915 Royal Commission on Sewage Disposal. Clearly no such modern effort of this scale exists; there was a feeling at the conference that this may be holding the industry back in the face of the many challenges it faces (e.g. carbon footprint, energy and chemical dependency, affordability, climate change resilience).

Overall though it was a great event. I really enjoyed my time on the tour and at the conference. I know the sector has a habit of talking more about innovation than doing it, but this was I feel a worthwhile celebration of fundamental change. Hopefully reflection upon its circumstances and consequences may spur similar improvements by the time this band of enthusiast engineers and scientists gather again (albeit the younger ones!) for the next milestone in the history of activated sludge.

Duncan Thomas

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