Forced ammonia stripping from livestock wastewater: The influence of some physico-chemical parameters of the wastewater

Abstract

In highly alkaline aqueous solutions (pH >10), the main form of dissolved ammoniacal nitrogen is the unionized free ammonia. Free ammonia, being a gaseous molecule, is easily stripped out from the solution. Increasing wastewater pH is frequently used to force ammonia removal. Herein, the effect of the variation of some physico-chemical characteristics of liquid cattle wastewater on ammonia stripping was investigated. The results show that at pH 11.5, ammonia volatilization and consequently its removal through stripping, was not affected by the variation of total solids (1-10%), alkalinity (2,500-20,000 mg/L as CaCO3) and electrical conductivity (20-50 mS/cm), or by the alkali type (NaOH, KOH and Ca(OH)2) employed to increase pH. The only parameter which affected ammonia stripping rate was the variation of the concentration of bedding material (straw 0.5-5%). The results suggest that the process of forcing ammonia stripping rate at high pH is unaffected and is not limited by the variation of any of the investigated parameters, except bedding material. The parameter kOLa (1/min) of the mass transfer model of ammonia stripping regarding the control experiments (raw wastewater without increasing pH) was ca. 0.0002, while by increasing pH it increased more than 20-fold (0.004 to 0.0045).