Phosphorus Removal by Chemical Precipitation in Wastewater Treatment Plants

The EU regulations limit the total phosphorus (P) concentration to 2 mg/L in the discharge effluent from wastewater treatment plants to minimize the negative impacts of nutrients in the ecosystems. This study focuses on monitoring and removal of P in the municipal wastewater treatment plant in Baiona, NW Spain. P is removed in the plant by precipitation as ferric phosphate with the continuous addition of ferric chloride. The FeCl 3 dose is adjusted with periodic phosphate analysis in the discharge effluent. This procedure results in a large excess of FeCl 3 dosage due to the daily and seasonal variations of P in the wastewater (2.5–8 mg/L). The excess dosage ensures compliance with the P legal limit but increases the consumption of FeCl 3 and the associated costs. In this study, we tested the benefits of P concentration monitoring in the discharge effluent with an automated analyzer to optimize the dosage of FeCl 3 . The automated analyzer determines the P concentration every 2 h and uses this information to adjust the FeCl 3 dosage to the real needs. This mode of operation minimizes FeCl 3 consumption while ensuring compliance with the legal P discharge limit. Comparing the reagent consumption of 1 year of operation with the previous year with no automated analyzer, the consumption was cut back by 50%. The savings in precipitation reagent can compensate the analyzer installation cost in just 2 years of operation, confirming the rapid return of the investment. Besides, the P precipitation system with the automated analyzer showed stable operation throughout the year under different wastewater flow and P concentration conditions, confirming the system reliability and efficiency in maintaining consistent P removal performance.