Sewage farm

By the 1870s, the lower parts of Nottingham were regularly affected by flooding of polluted water from the River Leen, as a consequence of six parishes adjacent to the town discharging raw sewage into the river. Marriott Ogle Tarbotton had become the Borough Engineer for Nottingham in 1859, and in 1872 the Nottingham and District Sewerage Act was obtained, which enabled the Nottingham and Leen District Sewerage Board to be created. Tarbotton became the Sewerage Board engineer, in addition to his other duties, and set about building sewers and sewage pumping stations to convey effluent from the city to Stoke Bardolph. The Borough Extension Act of 1877 enabled the offending parishes to be incorporated into Nottingham, and the Borough to take over the responsibilities of the Sewerage Board.^[8][9]

The Corporation leased 638 acres (258 ha) of agricultural land from Earl Manvers at first.^[9] A deed from 1878 states that John Elliot Burnside leased the farm, now known as Stoke Farm, to the Mayor, Alderman and Burgesses of the Borough of Nottingham for a period of 60 years, at an annual rent of £135.^[10] It was situated immediately to the north of the church building,^[11] and was known to have good drainage, allowing the sewage to be spread over the land, where it seeped into the soil. The farm was subsequently purchased. Tarbotton was responsible for the construction of the sewage farm, and the first stage became operational on 17 June 1880. However, he did not see it completed, as he suffered a stroke while attending a meeting of the Sewage Farm Committee on 4 March 1887, and died two days later. Additional land adjacent to the original site was acquired, some of which was in the neighbouring parish of Bulcote. The farm produced milk from cattle kept on the land, and was also a centre for pedigree shire horses and pigs.^[8][9]

Plans for a new sewage treatment works were drawn up in 1928, to be situated further to the west. Work on a combined scheme for main drainage and sewage disposal works began in 1936. New piping was constructed, and a new pumping station at Sneinton was commissioned, to bring additional sewage to the farm. New buildings housed preliminary treatment facilities, before the effluent was spread on the land.^[12] During the 1950s, the works were extended to include secondary treatment, by the addition of an activated sludge plant and final settlement tanks.^[13] In 1974, responsibility for the plant was transferred from the City of Nottingham to Severn Trent Water Authority, one of ten regional water authorities established under the terms of the Water Act 1973 to manage water resources in England and Wales.^[14]

By the early 2010s, the site was the second-largest managed by Severn Trent Water, serving around 500,000 domestic customers, and the equivalent of another 200,000 due to discharges from trade customers. It was also treating waste from a local animal rendering plant, which entered the works separately.^[13] The secondary treatment facilities were reaching the end of their working life, and as a result of the Urban Waste Water Treatment Directive, the levels of phosphorus in the final effluent needed to be reduced.^[13] A conventional solution would have involved extensive reconstruction of the facilities and the addition of another activated sludge plant,^[15] but a more innovative approach was taken, which enabled much of the existing infrastructure to be reused, and the size of the activated sludge plant to be reduced. This was achieved by ammonia and phosphorus removal before the liquor entered the activated sludge plant. Removal of these substances has another beneficial effect, as it significantly reduces blockages in pipes due to the precipitation of struvite, or magnesium ammonium phosphate. The solution adopted produces half a tonne of phosphorus per day,^[16] and was £19.2 million cheaper than the cost of a conventional solution. Operational costs are also £165,000 per year lower.^[17]

The process of using anaerobic digestion to treat sewage sludge has been used on Severn Trent sites since the 1950s, and Stoke Bardolph works uses a biomethane plant to turn the gas produced by the digestion process into biomethane. This is then supplied to the national gas network. The plant runs continuously, and produces around 500 cubic metres (18,000 cu ft) of biomethane per hour from 1,000 cubic metres (35,000 cu ft) of biogas. The gas is washed, compressed and an odour is added to it before it is pumped into the gas network. In 2017, the site was partially self-sufficient, producing some 38 percent of its energy needs in this way, and Severn Trent hope to increase this to 50 percent by 2020.^[18]

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