The retrofitting of an extended aeration process to optimise biological nitrogen removal in liquid industrial wastes

The paper deals with the optimization of the platforms for liquid industrial wastes and wastewater treatment; in particular, the retrofitting of an existing extended aeration process and its conversion to biological nitrogen removal are performed. Three different experimental phases are carried out in order to select the best final solution. First, the full scale plant and its performances are analysed; then, a nitrification/predenitrification process with separate biomass is experimented after solving the structural problems connected with air distribution and flow equalisation. This approach reveals non satisfactory performances in nitrogen removal for two reasons: the limited nitrification in the first step, exerting the role of a simultaneous nitrification denitrification process, the low nitrates feedback to the denitrification step, in order to avoid hydraulic overloading of secondary settlers. The third investigated solution is an alternating two-step oxic-anoxic process with separate biomass. The results demonstrate that the main removal of carbon and nitrogen occurs in the first step while the second one exerts a finishing function. The two steps and the complete use of readily biodegradable carbon of the influent assure a cheaper and reliable solution.