Sewage treatment in East Kilbride Scotland a case study

East Kilbride is located about 15 km south-east of Glasgow in an area of high ground. It is one of Scotland's 'new towns' and was built to take the overspill of Glasgow's population. Originally it was a small village of a few hundred people, but it expanded very rapidly from 1944. Now it is one of Scotland's largest towns with a population of about 85,000 people. As it was built on a hill, the drainage from the town flows in two directions from the high point. In the west side of the town, the sewage flows to Philipshill sewage treatment works (STW), whilst the eastern side's wastewater goes to Allers STW.

The effluent from Allers STW flows into a small tributary of the River Clyde called the Rotten Calder Water (so-named because of the two main streams in the catchment, the Rotten Burn and the Calder Water, and not because of its condition!). When the town was small, the effluent made little impact on the quality of the river, but as it expanded, the flow rate of the effluent made an increasingly large contribution to the river flow. In 1996, in the long dry spell in July and August, the river flow diminished but the effluent flow remained the same. Downstream of the effluent discharge point, the flow rate of the river was composed of 75 per cent sewage effluent.

Although the Allers STW was modernized and expanded to keep pace with the amount of sewage it had to purify, nevertheless the effluent quality was not good and the Rotten Calder Water started to live up to its name. The results in Table 5 are for some selected determinands of the river upstream and downstream of the effluent point.

The effluent was clearly having a bad effect on the river, and the variety of aquatic life was very reduced downstream of the effluent. The trout

Table 5. Chemical quality of the Rotten Calder Water upstream and

downstream of the effluent point of Allers STW,

summer 1996

Concentration (in mg/l)

Determinand

Upstream

Downstream

BOD

2.5

4.0

Dissolved oxygen

8.8

7.6

Ammonia nitrogen

0.28

8.6

Nitrate nitrogen

1.2

1.7

Chloride

60.0

77.0

that used to live in the river had long since disappeared and there were complaints about the smell of the river in summer months.

The problem for the local authority which manages the STW was that, however good the treatment given to the sewage before discharge, there would always be a lack of clean river water to dilute the effluent. It was eventually decided that the only solution was to divert the effluent away from the Rotten Calder Water and discharge it where it would receive more dilution. This work started in 1995 and was completed at the end of 1996. Now the effluent flows into the River Clyde where it is diluted at least 50 times, even when there are low summer flows. The effects of this on the quality of the Rotten Calder have been dramatic as shown in the results for the survey carried out at the beginning of 1997 in Table 6.

Table 6. Chemical quality of the Rotten Calder Water upstream and

downstream of the former discharge point of Allers STW, February 1997

Concentration (in mg/l)

Determinand

Upstream

Downstream

BOD

1.6

2.3

Dissolved oxygen

11.8

11.5

Ammonia nitrogen

0.08

0.05

Nitrate nitrogen

2.4

2.4

Chloride

29

32

Now that the major source of pollution has been removed from the river, it is expected that the trout will return and the variety of aquatic life will increase.

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  • Karin
    How can you determine the quality of a river that has sewage effluent upstream?
    9 years ago

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