AWWA WQTC69408

Decreasing regulations on nutrient limits worldwide are requiring careful process considerations to provide reliable nutrient removal in reuse plants. A key design concern of the 13.2 MGD Gibson Island Advanced Water Treatment Plant (AWTP) in Brisbane, Australia, is removal of nitrogen from influent levels as high as 5.4 mg/l as N to 0.8 mg/l as N in the treated water. Reverse osmosis is a key process technology integral to achieving the low level of nitrogen. Understanding nitrogen rejection of commercially available reverse osmosis (RO) elements was required to become more precise as design advanced. While RO manufacturer projection software may be an effective way in which to predict rejection of nitrate and ammonia, it does not predict the removal of organic nitrogen. Since organic nitrogen is one of the constituents that comprise total nitrogen, projection software is unable to confirm its concentration in treated water. Additionally, organic nitrogen varies greatly in different secondary effluent sources, and is highly dependent on industrial waste contributions. The objective of this study was to discuss the methods of determining RO nitrogen rejection and provide information on the results of those methods applied to a specific project. Of most importance, and a driver to have reverse osmosis, is the need to reduce Total Nitrogen to 0.8 mg/L as N. Total nitrogen is comprised of organic nitrogen, ammonia, nitrate, and nitrite compounds. Nitrate is the only compound that can be modeled for rejection by reverse osmosis. Therefore, to accurately predict the amount of organic nitrogen that would be rejected by the full-scale AWTP, a pilot study was conducted. Furthermore, each reverse osmosis manufacturer has different rejection properties, so the pilot study had to evaluate several manufacturers to understand the rejection that could be achieved. Two pilot studies were conducted to model the nitrogen rejection for the AWTP, a single element RO pilot and a demonstration pilot designed similar to the full-scale. Includes tables, figures.