AWWA ACE63020

AWWA ACE63020 Characteristics of Waste Streams Generated by Anion Exchangers
Conference Proceeding by American Water Works Association, 06/01/2006

Roberts, Aaron

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The use of anion exchange technology by water utilities and industries for waterpurification has many applications including removal of organic carbon, nitrates, sulfides,sulfates, and other anions. Typically, anion exchangers are operated in a forward-flowmode until the resin becomes saturated and breakthrough occurs. The majority of weakbaseanion exchanges are operated by exchanging chloride for anions in the water source.To regenerate anion exchange systems, the resin is equilibrated with a brine solution.Resin regeneration consists of five phases: backwash, draindown, addition of brinesolution, slow rinse, and fast rinse. The waste streams generated by regeneration includethe backwash water and the brine. These waste streams share different characteristicsthat make each one unique. One unique characteristic that differentiates the two streamsis the amount of chlorides present. Chloride levels in backwash water reflect the chlorideconcentration of the water source and are typically below 50 mg/L. Chlorideconcentrations in the brine can exceed 15,000 mg/L. Discharge of brine solutions towastewater treatment facilities may impact treatment effectiveness. In addition, theadditional chloride loading may impact reclaimed water characteristics.There are reasons waste streams could affect the wastewater treatment process. It isproven through research that chloride levels over 20 mg/L in wastewater can cause thegrowth rate of bacteria in the activated sludge process to reduce. With the high chloridelevels in the brine, slow rinse, and fast rinse, the activated sludge process could be altereddepending on how high the chloride levels are in each waste stream generated. Thesehigh chloride levels along with high sodium levels are caused by salt that is present in thebrine solution. The brine causes a loading of chlorides and sodium that can change thechemical characteristics of the waste stream. The real impact that the waste streams willhave on the wastewater is the volume generated by each waste stream duringregeneration. The larger volumes of waste stream for the brine, slow rinse, and fastrinsed coupled along with the high chloride and sodium levels could be harmful to thewastewater treatment process and also could affect the reclaimed water as well asirrigation. Includes 5 references, table, figures.