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
