NOT A NORMAL CLUB OUTING – AND THERE WAS NO FISH
On a very sleety and cold February (2010) afternoon, Mike, Fen and I went on a tour of East Calder Sewage Treatment Works to find out more about what is discharged into the River.
We were very warmly welcomed at the works by Veolia Regional Operations Manager, Simon Wigglesworth. Simon gave us a guided tour of the works and explained how the mixed sewage surface and foul water sewage is treated, separated and processed before being discharged at the outfall into the River Almond.
The sewage, by the time it reaches the outfall, has gone on a complicated journey through endless routes of pipe-work into chamber after chamber – attacked by bacteria – grit, sludge, phosphorus, fat and water separated, ammonia removed - finally passing through sand filters to leave the site cleaner than it went in. In fact due to the type of contract Veolia have, the waste is cleaner than SEPA requires.
Whilst the weather was not pleasant, the amount of the rain demonstrated the problem when the capacity of 724 litres/second (2600 cubic metres /hr.) of incoming sewage is exceeded by a large amount of large of rainfall. This excess passes through 6mm screens and is then held in storm water storage tanks to be treated later. Each tank holds in excess of 2000 cubic metres. The regular flow passes on to the full treatment plant, having solids (6mm screens) and grit removed at the inlet. The storm water storage tanks have a settling effect and sludge is collected and treated later in the process. The retention time in the tank allows solids to settle. Once the tanks are full the settled overflow passes to the River, which by the sheer nature of the heavy flow, should already be in flood, increasing the dilution. Not ideal, but we have to remember that without the plants’ treated water the River Almond could well be no more than a burn.
All recovered sludge is transported elsewhere for further treatment: grit and solids are sent to landfill.
So what did we learn:-
The site is well managed and has made a significant investment to improve the operation, £1.6m to be exact, increasing the plant capacity from 550 litres/second (2009) to 724 litres / second.
The vast majority of the water entering the River Almond has been thoroughly processed. However an amount of untreated, screened and settled, effluent is discharged in heavy weather – but should be dilute and the river should be in flood due to the rain fall.
There are certain liquids and chemicals that the Works (which is there to treat sewerage) cannot get rid of effectively – anionic detergents (in washing and dishwasher powder), oil and grease (including cooking), paint etc. Some things which go in the top end come out the bottom end.
So when considering the effect on the River Almond, the Works appear to be doing their duty to ensure that the outflow is as good a quality as possible. We might want look at our own actions in respect of what we put into the sewer system to ensure we are doing as much as we can.
We didn’t catch any fish but did get a very welcome cup of coffee after our tour.
Many thanks to Simon for his time and hospitality.
Alison Brooks
I’m happy to hear that there is a high level of treatment at the plant although I feel that further investment is required if the Almond is to meet the WFD requirements in the future. The fact that there is still untreated waste pouring into the Almond is deeply regrettable.
Quote:
“without the plants’ treated water the River Almond could well be no more than a burn”
This seems a poor attempt to justify the overflow of untreated waste into the river during heavy rainfall.
Douglas
Hi Douglas,
Untreated waste is not in any way an ideal solution and I am not here justifying it. But just to clarify the points you raised from our visit to the works:
There may be other measures that could be done to treat the overflow or have larger tanks (not sure – not my field), but whilst there is a combined sewage system there is always likely to be times when the sewage works will not be able to deal with the overflow. We were told that the works are designed to take three times the flow likely after a 7 day dry period (with no rain) and to design the system to run at peak would involve a works which would, for the majority of the time, run considerably under capacity. If we could turn back the clock, combined systems would not ever have been considered but that is unlikely to change for existing infrastructure. Lets hope that SUDS works for the future.
The point about capacity was that there had been discussion in the past about piping all the treated water to Seafield for outflow into the Forth. One of the reasons not to do this was that (again because it is a combined system) it would also take all the rainwater, which in an ideal world would permeate through the soil into the river system, would be taken away and what would be left of the river. I did not intend for this comment to have been made in relation to the overflow of untreated, but relates to flow of treated water back into the river system and was not a justification for the untreated overflow.
My guess is that the works will not go away and that the peak flow is the issue – any ideas?
Alison
Hi Alison,
SUDS is a step in the right direction however my understanding is that it only applies to new developments. I would like to see existing systems upgraded to comply with the standards required for new developments. I believe the most cost effective way of doing this would be to introduce more basins (flood storage reservoirs) that could better deal with high levels of rainfall. If the rainfall was diverted away from the treatment plant into basins it could then permeate in a more natural way.
Increasing capacity at the plants is expensive but there are things that could be done to improve water quality that require less investment. The installation of a phosphorus stripping plant at every treatment site could reduce the amount of phosphates discharged into the river by as much as 95%. This is only going to deal with reducing the amount of phosphates of future processed effluent. The large volumes of phosphates that already exist in the in the rivers sediment and how to deal with that would be far more costly.
Douglas