Process and Economic Benefits of Sidestream Treatment

Sidestream nitrogen and phosphorus loads from wastewater treatment plants that perform nutrient removal and have anaerobic digestion typically account for 15–20 percent of influent nitrogen, and 20–30 percent of influent phosphorus. Since dewatering is typically not a continuous process, but rather performed in shifts, there are significant nutrient peaks to the secondary processes for a portion of the day. These nutrient peaks can cause upsets in the secondary processes, leading to higher effluent nitrogen and phosphorus concentrations. Capturing and treating sidestream flows before mixing with the influent is often economical because of the high concentration of nutrients, warm temperature, and small volume that needs to be treated. There are many benefits to sidestream treatment, such as increasing the factor of safety on nitrification and biological phosphorus removal, which in turn allows lower nutrient limits to be achieved with conventional technology. In addition, many of the sidestream treatment processes achieve nutrient removal using more energy- and cost-efficient pathways; and create sustainable end products such as fertilizer.This paper presents process and economic information about several viable sidestream treatment technologies using case studies. From these case studies, several conclusions were developed. First, implementing sidestream treatment can defer larger capital investments needed to meet stringent nutrient limits. Second, nitritation/deammonification is the lowest cost alternative among biological nitrogen removal alternatives for sidestream treatment. Third, there is significant variation in operating costs among sidestream treatment alternatives. Finally, there is significant variation in the business models and costs of struvite precipitation processes being marketed today. It is expected that over time these business models will become more similar as a result of market preference.