Changes in the Nutrients from a Dairy Wastewater in Batch-Reactor at High pH and Organic Load

M. D. Coello Oviedo, D. Sales Márquez and J. M. Quiroga Alonso

Abstract
Dairy effluents comprise mainly milk, alkaline washing wastes, and water. In accordance with the characteristics of this type of industrial wastewater, a biological treatment was applied in a batch reactor. This work is centred on the use as fertilizers of nutrients from dairy wastewater, and studies the effect that the time of an initial anoxic stage has on mineralization of the organic matter of a dairy wastewater. The experiment was carried out using milk and water mixtures from the secondary sedimentation tank of a wastewater treatment plant (WWTP) that were inoculated with micro-organisms found naturally in wastewater (adapted to 30 °C) and in activated sludge systems. The operational conditions were 4000 mg L–1 COD, alkaline pH of 11.5, and temperature of 30 °C Six experiments were performed, varying only the period without initial aeration. The results are discussed in two stages: 1 Degradation of the organic matter. The organic load is reduced and mineralized, liberating ammonium and phosphate. This stage lasts approximately 10 days. It is affected by the period without initial aeration; highest degradation is achieved using periods of 48 hour without initial aeration, ensuring a greater microbial acclimation and hydrolysis of the organic matter. In contrast, NH4+ liberation is independent of whether aeration is applied from the start or after 6 or 48 hours. In no case was it advantageous to use a period of 10 hours without initial aeration. 2 Nitrification. There is hardly any organic matter, and the ammonium is nitrified by nitrifying bacteria. Nitrification is not affected by the conditions of a prior stage without initial aeration, but it is affected by light, pH, and the concentration of phosphorus. Highest nitrate concentrations are obtained when the concentration of phosphorus in the medium is highest and pH is lowest. pH affects both the solubilization of calcium phosphate precipitated and the phosphate-phosphate monoacid balance.

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Keywords
activated sludge, microbial activity, toxicity, heavy metals