AWWA WQTC64062

For over a year PWN Water Supply Company North-Holland applies UV/H₂O₂ treatment (540 mJ/cm²; 6 mg/L H₂O₂) for organic contaminant control and primary disinfection at her treatment facility Andijk (20 MGD; 3000 m³/h) for the production of drinking water. Before implementation of UV/H₂O₂, organic contaminant control was achieved by granular activated carbon (GAC) filtration with an empty bed contact time of 30 minutes. Primary disinfection was achieved by breakpoint chlorination. The original process had to be upgraded in view of the presence of polar compounds and pathogenic micro-organisms such as protozoa. Before full scale implementation, the UV/H₂O₂ technology was investigated on batch and pilot scale in a five year research project. The impact of retrofitting the existing treatment process with UV/H₂O₂ was monitored on pilot scale for two years. The year before the UV/H₂O₂ process became operational, monitoring results from the existing process with breakpoint chlorination were gathered. The monitoring program was continued after the plant was retrofitted. This program covered pesticides such as atrazine, bentazone and AMPA, the complexing agent EDTA, the halogenated carboxylic acid TCA, emerging substances such as NDMA, pharmaceuticals such as carbamazepine and pathogenic micro-organisms such as viruses. Comparing the lab scale and pilot plant data with the results of one year monitoring the performance of the full scale UV/H₂O₂ process, leads to the conclusion that the full scale UV/H₂O₂ process performs as expected and satisfies all quality standards. By implementation of UV/H₂O₂, the role of the existing GAC filters changed significantly. In the original treatment train with breakpoint chlorination, the main function of the GAC filters was adsorption of organic micropollutants, especially THM's. After implementation of UV/H₂O₂, the objectives of the GAC filters are to quench the residual H₂O₂, to convert the formed nitrite into nitrate and biodegradation of oxidation products, thereby obtaining biological stable water. Parameters such as THM's, H₂O₂, nitrate and nitrite, AOC in the treatment process have been monitored before and after the retrofitting of the facility with UV/H₂O₂. The effect of the transformation from adsorptive to biological GAC filter was consistent with earlier pilot results. The level of biological stability of the produced water is comparable before and after the implementation of UV/H₂O₂. THM's adsorbed by the GAC during breakpoint chlorination desorbed over a period of about one year. The retrofitted Andijk facility with UV/H₂O₂ as nonselective barrier against organic micro pollutants and primary disinfection step in combination with biological GAC filters has proven to be a robust solution for the production of safe and reliable drinking water from surface water. PWN has decided to implement the UV/H₂O₂ process at her facility Heemskerk (40 MGD; 6000 m³/h) as well. Includes 6 references, tables, figures.