Assessing Struvite Formation Potential at Wastewater Treatment Plants

Abstract

Wastewater treatment plants, especially those employing secondary treatment and anaerobic sludge digestion, have historically encountered phosphate precipitates, one of the commonest being struvite, that foul and encrust the sludge return lines, and the associated pumps and valves. This growth of 'uncontrolled' struvite increases pumping and maintenance cost, as well as reduces the overall capacity of the plant piping system in terms of lost hydraulic capacity and lowered biological treatment capacity. Although uncontrolled formation of struvite can be a nuisance, however, controlled production of struvite can prove beneficial to treatment plants. This is accomplished through reducing maintenance costs, as well as providing extra revenue from the sale of the struvite crystals as fertilizers. This paper investigates what can and should be done before struvite-related problems hamper efficient operation of the treatment plant. A case study carried out at a wastewater treatment plant showed the influence of nutrient loading in cases where nutrient treatment is not carried out. The three locations investigated all has a supersaturation value greater than unity; this indicated that struvite formation potential was high. The amount of phosphorus and nitrogen looping within the treatment plant was as high as 21% and 20%, respectively.