CONTROLLED DOSING OF NITRATE FOR PREVENTION OF H2S IN A SEWER NETWORK AND THE EFFECTS ON THE SUBSEQUENT TREATMENT PROCESSES

A process for the elimination of septicity based on controlled addition of nitrate to sewer networks is developed. The process is registered as the Nutriox(TM) 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.