Feasibility Study of Granular Activated Carbon for Dissolved Organic Nitrogen Removal from Wastewater Treatment Plant Effluent
AuthorMayorga, Alexander Robinson
Civil and Environmental Engineering
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Some wastewater treatment plants must meet very low concentrations of total nitrogen in their discharged water with the maximum daily load at Truckee Meadows Water Reclamation Facility (TMWRF) being 500 lbs/day for total nitrogen. For this project, data previously collected from influent and final effluent were analyzed to establish trends of dissolved organic nitrogen (DON) concentration and total organic nitrogen (TON) concentrations throughout the year. These measurements indicate significant portions of DON contributing to the TON in both influent and effluent samples; with the influent DON composing 44% of the influent TON, and the effluent DON composing 91.5% of the effluent TON. Treatment processes aimed at removing dissolved organic nitrogen may serve to reduce TON in the effluent and provide a factor of safety so treatment plants do not exceed daily limits of total nitrogen loads. Determining DON behavior throughout the treatment processes of TMWRF was accomplished by collecting samples from the influent, primary effluent, secondary effluent, denitrification effluent, and final effluent. DON concentrations varied greatly throughout the first three processes while denitrification and final effluent were the most stable and consistent having averages of 1.25±0.18 mg N/L and 1.21±0.19 mg N/L, respectively. Granular activated carbon (GAC) was used as a treatment process for the removal of DON from the final effluent. Analysis for overall effectiveness of this approach includes testing seven GAC products from various suppliers and examining them using isotherm experimentation to determine amounts of DON removed from the final effluent. Based on the isotherm data, three products were selected for column testing. A final GAC product was then selected and used to optimize the column operational parameters. A 12-minute empty bed contact time (EBCT) with an aspect ratio of 30:1 exhibited the best performance and removed 29% of DON in the column life. The GAC adsorbed 6.17 mg-N for every gram of GAC when operated to 6,000 bed volumes. Microbial activity occurred in both column tests and may have metabolized some DON. Regeneration of GAC was performed thermally at 850 oC and chemically with formic acid. The regenerated GAC performance was analyzed using the Freundlich isotherm curve. An economic evaluation on a full-scale column operating was done using the column test results and design parameters. The economic evaluation was done for a column to treat 1 million gallons per day of final effluent from TMWRF and would have an estimated annual cost of $600,000 per year without regeneration. Adsorption of DON onto GAC has revealed to be effective and have potential for wastewater treatment at TMWRF.