NOVELTY - A water quality estimation method involves preparing three collection containers. A thickened sludge containing phosphorus accumulation storage microbe is supplied into the first container. A nutrient substance and thickened sludge are put into the second container. Inflow sewage and thickened sludge are put into third container. A phosphoric-acid concentration in the filtration solution is measured by filtering solution among each container. A phosphorus accumulation microbe reactivity organic-acids concentration is calculated by arithmetic-processing of the phosphoric-acid concentrations.    USE - For estimating the organic acid concentration of inflow sewage, waste water, or human waste.    ADVANTAGE - The method can measure, with sufficient precision and in a short time, the amount of PRA in the inflow sewage.    DETAILED DESCRIPTION - The water quality estimation method of inflow sewage by the phosphorus elution out of activated sludge, involves preparing three collection containers of predetermined capacitance. A thickened sludge containing phosphorus accumulation storage microbe obtained at the concentration process is supplied into the first collection container. A nutrient substance and thickened sludge are put into the second container. A predetermined amount of inflow sewage (as measurement sample) and thickened sludge are put into third collection container. A phosphoric-acid concentration in the filtration solution is measured by filtering a solution among each collection container after anaerobic process is carried out at predetermined time progress. A phosphorus accumulation microbe reactivity organic-acids concentration is calculated by arithmetic-processing of the phosphoric-acid concentration in the filtration solution obtained from the first and second collection container, and the phosphoric-acid concentration of the sample in the filtrate corresponding to the third collection container. INDEPENDENT CLAIMS are included for:    (1) nutrient addition apparatus in the sewage complete treatment apparatus; and    (2) sewage complete treatment apparatus, such as AO or A2O processing apparatus.    DESCRIPTION OF DRAWING(S) - The figure shows the processing flow of water quality estimation method of the inflow sewage by the phosphorus elution out of the activated sludge (Drawing includes non-English language text).