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A process for the elimination of septicity based on controlled addition of nitrate to sewer networks is developed. The process is registered as the NutrioxTM process. The work described in this paper gives the results of a full scale trial in the UK. The trial was set up and managed by Norsk Hydro and independently monitored and evaluated by the Water Research Centre Environmental Management (WRc). The results showed that dosing of nitrate was very effective for suppression of hydrogen sulphide in a rising main. During nitrate dosing the average level of hydrogen sulphide at the works inlet was 0.24 mg/l, with a daily variation within the range of 0-0.4 mg/l. Without nitrate addition the average background level of hydrogen sulphide was 4.2 mg/l, with a daily variation of 1-10 mg/l. The dosing was accomplished without significant breakthrough of nitrate to the treatment works. Dosing of nitrate resulted in an increased removal of soluble BOD across the rising main, but no significant change in total BOD or COD was registered at the treatment plant during the nitrate dosing. The nitrification process in the biological filters at the treatment plant was improved during the dosing period.

J. A. Hobson (1858–1940) was an English economist and early socialist, whose writings on capitalism and industrialism influenced Lenin and Trotsky, and were highly regarded by John Maynard Keynes. Imperialism, published in 1902, is considered his most important work. Employed as a war correspondent by the Manchester Guardian to report on the Second Boer War, he became convinced that imperial expansion was driven by the desire to find new markets and investment opportunities, resulting in capitalistic exploitation of the colonies. He argued that imperial policies were a fundamental cause of international conflict, as greed led to aggression and militarism. While modern critics have seen weaknesses in his arguments, such as his failure to examine the development of the British Empire out of early private trading enterprises, Hobson was a very influential and prolific writer and social theorist, who helped shape British welfare policy in the twentieth century.

The use of Nutriox® and ferric chloride to suppress hydrogen sulphide and odour generation in rising mains is evaluatd in a pilot scale study. Without chemical dosing the hydrogen sulphide built up to the commonly predicted levels after six months. Thereafter, addition of both Nutriox® and ferric chloride to sewage entering the rising main totally suppressed the formation of H2S. Nutriox also nearly totally suppressed the odour measured olfactometrically. The use of ferric salt at near stoichiometric levels effectively removed dissolved sulphide. Odour removal was generally good though on occasions reduction of dissolved sulphide levels to below 0.1 mg/l was not guaranteed to be accompanied by near total suppression of odour generation. The use of ferric ions at stoichiometric levels, after H2S and odours have formed in the rising main, also eliminated the dissolved sulphide. When used in this way, a significant residual odour potential, 110,000 ou/m3 remained in the sewage. The simultaneous reductions of odour and hydrogen sulphide observed in this study implied an apparent threshold odour concentration of 0.1 ppb for H2S, significantly lowr than most values quoted in the literature.

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