Effect of pH adjustment, solid–liquid separation and chitosan adsorption on pollutants’ removal from pot ale wastewaters

Abstract

Pot ale is a wastewater from the whisky industry which is produced in large volumes and causes significant environmental concern. This study investigates the degree of COD, phosphorus, ammonia and copper removal obtained from pot ale using solid–liquid separation, carried out in the range of pH values 3.4–9.0. This study also investigates the removal of the same pollutants, from the liquid phase after solid–liquid separation, obtained by adsorption on unmodified chitosan, in a range of pH values. By solid–liquid separation, a removal of up to 14% of the COD, 60% of free phosphate, 45% of total phosphorus, 65% of ammonia and >80% of copper was obtained. In general, the highest removal of the pollutants was observed at alkaline pH values. Adsorption with chitosan, at an initial pH of the wastewater equal to 5, allowed only a modest COD removal, up to 10%, and up to 35% removal of free phosphate. When the initial pH of the wastewater was adjusted to 7, no removal of COD and phosphorus was observed with chitosan, while adsorption at more acidic pH values was impossible due to formation of a thick paste with water. Adsorption capacity for COD and phosphorus correlated well with the final pH after chitosan addition, and it was shown to decrease sharply with increasing pH. Overall, this study shows that solid–liquid separation removes a significant fraction of the pollutants in pot ale, while chitosan might only be effective after chemical modifications (e.g. cross-linking) which improve its stability at acidic pH.