Bio-mineralization of organic matter in dairy wastewater, as affected by pH. The evolution of ammonium and phosphates

This work is focused on the use of nutrients from dairy wastewaters as fertilizers, studying the optimum operational conditions for the bio-mineralization of the nitrogen organic matter. Wastewaters from 1500 to 2500 mg COD/l and at alkaline pH of between 8.5–12 were studied, in an aerobic biological treatment at a bench scale. The temperature was maintained at 30°C. In some experiments, the COD was reduced at the same time as nitrification. An increase of the organic load produced a delay in the appearance of the ammonium, though the concentrations reached were greater than with lower loads. The phosphate profiles was parallel to that of ammonium. However, the ammonium becomes exhausted as a consequence of the release of ammonium, as ammonia, to the atmosphere and of consumption by the microorganisms, whose metabolic requirements for ammonium are greater that those for phosphate. The experiments with an initial COD of 1500 mg/l and pH of 10.5 completed nitrification within the 30-day test period. The maximum concentrations of ammonium were reached when the initial pH was 8.5. On the other hand, the highest rates of protein hydrolysis were recorded at initial pH of 10.5 and 11.0 units. Part of the nitrogen present in milk was lost as ammonia when the initial pH was 11.5 and 12.0.