The technology of step-feed nitri-denitrification in municipal wastewater treatment: the analysis of options and case record

Summary

The experience of MY PROJECT JSC in designing biological treatment facilities (aeration tanks) at the municipal treatment facilities of the Russian Federation with the use of step-feed nitri-denitrification is considered. Over the past 10 years more than 20 treatment facilities have been upgraded and built with the introduction of a step-feed scheme; the author of the article made a personal commitment in commissioning of more than 10 biological treatment facilities for municipal and industrial wastewater processing. In order to observe the data confidentiality, no data is provided on the chemical analysis of the operation of structures; however, with the help of mathematical modeling, the specific features of the implementation of step-feed denitrification are shown. The key process engineering aspects of the implementation of the schemes of a step-feed process with a different number of stages (two and three), cases of the need to use or reject nitrate recycling, as well as using, where applicable, an additional substrate (methanol) with particularly stringent requirements to the nitrogen concentration at the effluent discharge are considered. Traditionally, it is believed that the scheme of step-feed denitrification is designed for nitrogen removal; however, additional positive modifications of step-feed denitrification have been also considered that provide for arranging biological removal of phosphorus. The design of an anaerobic zone upstream the first denitrification cascade (D1), the use of step-feed denitrification in the implementation of the process scheme of the University of Johannesburg (JHB), as well as the arrangement of step-feed of return sludge are considered.

Key words

biological treatment , nitrification , denitrification , aeration tank , biological phosphorus removal , step-feed technology