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 industria l wastes and wastewater treatment; in particular, the retrofitting of an ex isting 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 pr ocess with separate biomass is experimented after solving the structural pr oblems 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 simult aneous nitrification denitrification process, the low nitrates feedback to the denitrification step, in order to avoid hydraulic overloading of second ary settlers. The third investigated solution is an alternating two-step ox ic-anoxic process with separate biomass. The results demonstrate that the m ain removal of carbon and nitrogen occurs in the first step while the secon d one exerts a finishing function. The two steps and the complete use of re adily biodegradable carbon of the influent assure a cheaper and reliable so lution.