Application of a combined biological and chemical system for the treatment of phosphorus-containing wastewater from the food industry

Abstract

Coagulants can be dosed at different points during the wastewater treatment process to achieve phosphorous removal. Addition of metal coagulants on the aeration basin (simultaneous precipitation) involves lowest cost; however, inert solids reduce the volatile solids percentage which can be deleterious to the biological process. The general objective of the present study was to analyze the feasibility of P removal in a wastewater model system of the dairy industry using simultaneous precipitation in a laboratory-scale activated sludge reactor by addition of ferric chloride. Results showed that the addition of a high dose Fe:P (molar ratio)= 1.9-2.3:1 on the aeration basin of the reactor caused a progressive enrichment of the sludge with inorganic solids. This phenomenon, which involved a gradual deterioration of the environmental quality of the biological system, led finally to a strong decline of the reactor performance. The organisms associated to flocs (crawling ciliates and attached ciliates) were the more sensitive to these changes. A mathematical model allowed the estimation of the concentration of total fixed suspended solids as well as the decrease in the abundance of these organism groups as a function of time of Fe(III) application, considering the influent flow rate, the influent Fe concentration, and the waste flow rate of the sludge. The Shannon-Wiener diversity index and the sludge biotic index (SBI) can early predict the decreasing of the system performance due to metal salts overload. The simultaneous application of the proposed mathematical model and the biological indices guarantee a successful control of systems operated with phosphorous simultaneous precipitation by Fe(III).