The connection between the treatment and disposal of raw (untreated) sewage and the improved health of a community had been established by the 19th century. The River Clyde and other watercourses had become polluted, though nothing much was done until the Caledonian Railway Company won permission to construct underground railway lines beneath Glasgow�s streets. As part of the works, they had to reconstruct the sewers, at a cost of about �200,000.

The sewer work formed part of Glasgow Corporation�s main drainage scheme, covering an area of some 10,000ha divided into three parts, each with its own treatment works. The Dalmarnock plant was the first of these � it was authorised by statute in 1891 and construction began in 1893.

The works cost around �100,000 to construct. The formal opening took place on 2nd May 1894. The other two plants � at Dalmuir (NS477710) and Shieldhall (NS536663) � opened in 1904 and 1910 respectively.

The Dalmarnock works were designed by Danish engineer Gustav Valentine Alsing (1836-96), an acknowledged expert on chemical precipitation, and constructed under his supervision. Glasgow Corporation employed Alsing as a consulting engineer from about 1892 until his death.

Sewage treatment then, as now, involved separating out the solid component (sludge) of raw effluent � in this case a mixture of industrial and domestic waste, with the mass of suspended matter varying from 0.3g to 14g per litre. Effluent entered the works through three 1.2m wide channels, where floating matter was screened out and burned in furnaces.

The screened sewage then flowed into catch pits where sand, grit and heavy solids settled out and were transported by worm screws in V-shaped conduits in the base of the pits to a collecting tank. The solid material was taken away for disposal on railway wagons. The Caledonian Railway had a siding on site.

Originally, the liquid effluent flowed via a mixing chamber to 24 precipitation tanks, each with a capacity of 368,000 litres. Once precipitation was completed, the fluid was aerated and passed through 60 coke filters, covering about 1.2ha. Then it passed through sand filters before being discharged into the river.

Within a few years this system was found to be inadequate and the coke filters were abandoned. The precipitation tanks were put into continuous use with under-surface flow, though the same two chemicals were used to promote precipitation � aluminium sulphate and hydrated lime (calcium hydroxide).

The sludge from the precipitation process was mixed with more lime and fed into filter presses for dewatering, resulting in filter or sludge �cakes�, which were also transported off site by rail. In 1897, a Cumnor drying plant was installed, producing sludge cakes that were marketed as Globe Fertiliser for agricultural use. By 1911 around 32,500 tonnes were being sold each year.

In around 1900, an experimental plant was set up to test bacterial sewage treatment. One of the larger precipitation tanks, with a surface area of 357 sq m and a capacity of 909,000 litres, was converted into an open septic tank and eight bacteria beds were built. Further research into the use of more efficient biological filtration occurred from 1913, with the inauguration of two hectares of filter beds.

Though the fertiliser was a useful by-product of the treatment process, demand did not take up the entire production. From 1915, surplus undried sludge was pumped into a purpose-built boat and taken downriver daily for discharge into the Firth of Clyde off Garroch Head. In later years, chemical fertilisers were used more widely than those derived from sewage, and production of Globe Fertiliser ceased in 1935.

To help with the disposal of sludge, in 1914 a 9.6km long, 229mm diameter pipeline was laid beneath Glasgow�s streets between Dalmarnock and Shieldhall treatment works. This pumping main conveyed untreated sludge, which was then shipped from Shieldhall for marine disposal between the Isles of Bute and Arran. In line with a European Union directive banning the dumping of sewage at sea, the last sludge boats sailed from Shieldhall in December 1998.

British engineers had developed in 1913 a method for the treatment of screened sewage, called the activated sludge process. It aerated the sludge and introduced bacteria and protozoa to form a flocculated mass of organic matter that could be removed easily. By the mid-1930s the works were reaching the end of their useful life. So in 1937, an experimental plant using the Simplex Activated Sludge Process was installed to try the new technique.

However, it was not until 1962-8 that a full activated sludge plant was constructed on site. It has 1.7m deep aeration tanks served by 178mm diameter diffusers. The plant cost about �4m and was designed by consulting engineer Babtie, Shaw & Morton.

Research: ECPK

"Glimpses of Old Glasgow" by Andrew Aird, Aird & Coghill, Glasgow, 1894

"Obituary: Gustav Valentine Alsing, Died 1896", in Minutes of ICE Proceedings, Vol.127, pp.387, London, January 1897

"Disposal of Sewage" by A.B. McDonald, in Report of the Proceedings, International Engineering Congress, Glasgow, 1901

"Discussion: Glasgow Main Drainage" by W.C. Unwin et al, in Minutes of ICE Proceedings, Vol.189, pp.239-268, London, January 1912

"Discussion: Some Developments in the Activated-Sludge Process" by James McNicholas et al, in ICE Proceedings, Vol.23, pp.435-449, London, November 1962

"Discussion: A Comprehensive Scheme for Sewage Sludge Disposal in North-Western England" by J. Hayes et al, in ICE Proceedings, Vol.55, pp.743-753, London, September 1973

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