Influence of biogenic elements on the rate of biological wastewater treatment

Abstract

The rate of biological wastewater treatment is governed by the growth and enzymatic activity of activated sludge and biofilm communities and depends on the supply of nutrients – carbon, nitrogen and phosphorus – and of trace elements. The aim is to quantify the effect of nutrient availability on treatment kinetics and to develop an engineering algorithm for correcting wastewater composition. A model experiment was carried out on three typical objects: a municipal treatment plant with a moderate phosphorus deficiency, dairy-plant local facilities with a severe combined nitrogen and phosphorus deficiency, and an anaerobic UASB reactor with a cobalt and nickel deficiency. After a corrective additive was introduced up to the target ratio BOD:N:P = 100:5:1 or to trace-element replenishment, the oxidation rate, sludge volume index, residual pollutant concentrations and – for the anaerobic reactor – the specific methane yield and volatile fatty acid concentration were recorded over 14–20 days. Targeted replenishment of the deficient element restores process kinetics within one to two weeks: under a moderate phosphorus deficiency the BOD treatment rate increased more than twofold, under a combined nitrogen and phosphorus deficiency the volumetric BOD removal rate increased about sixfold, and under a cobalt and nickel deficiency the previously arrested methanogenesis was restored. The novelty lies in relating specific types of nutrient imbalance to the measured response of dissimilar systems and in formulating an algorithm for diagnosing and correcting nutrient supply, suitable for increasing plant throughput without reconstruction.