Carbon Diversion, Partial Nitritation/Anammox Enrichment, and Ammonium Capture as Initial Stages for Mainstream Ion Exchange-Deammonification Process

Eutrophication is a concerning environmental problem worldwide that results in algae blooms, oxygen depletion, damages to aquatic life and public health, water quality issues, and loss of aesthetics in water reservoirs. Nutrient (e.g., nitrogen and phosphorus) discharges from wastewater, agricultural, urban, and residential runoff promote eutrophication in receiving water bodies. In terms of nitrogen removal, conventional biological nitrogen removal (BNR) is a common technique used in many wastewater treatment plants (WWTP). However, BNR requires aeration for nitrification and organic carbon input for denitrification. In WWTP, the aeration represents a considerable investment in terms of energy costs. Recent technologies involve applying environmental conditions that favor the growth of specialist microorganisms to lessen the need for aeration in WWTP to develop energy-saving solutions for ammonium removal. Deammonification (or PN/A) is a process that implies having both partial nitritation and anaerobic ammonium oxidation (anammox), carried out by ammonia oxidizing microorganisms (AOM) (including ammonia oxidizing bacteria (AOB) and archaea (AOA)) and anammox bacteria, respectively. The partial nitritation process uses AOM to partially oxidize ammonium (NH4+) to nitrite (NO2-). The anammox process converts NH4+ and NO2- into nitrogen gas (N2), under anaerobic conditions. Because anammox are slow-growing and sensitive to environmental conditions, such as dissolved oxygen and microbial activity inhibitors, they are also less competitive for substrates in the presence of other microbial groups. Since its discovery in the 1980s, the deammonification process is still challenging in mainstream wastewater. This research aims to investigate a novel strategy to implement deammonification in mainstream wastewater. The goal of this research is to develop environmental conditions to favor the microbes that facilitate deammonification and suppress the activities of other competing microbial groups. The project aims to successfully implement deammonification through carbon diversion pretreatment to reduce organic matter content using Chemically Enhanced Primary Treatment (CEPT), ammonium capture by ion exchange (IX) with zeolite, and bacterial enrichment for partial nitritration, and anammox. In the next stage of this research, deammonification will be used for zeolite bioregeneration. CEPT involves a coagulation-flocculation process with iron chloride and an alkalinity source. Wastewater samples from the Northwest Regional Water Reclamation Facility (NWRWRF) in Hillsborough County, FL, were used for the CEPT process in both jar tests and a larger scale CEPT reactor. Inorganic nitrogen (N), total suspended solids (TSS), total volatile solids (VSS), chemical oxygen demand (COD), pH, alkalinity, and turbidity were measured from the wastewater influent and the CEPT effluent. The IX process included batch and column studies with zeolite to remove ammonium from synthetic wastewater and CEPT effluent. Data analysis included equilibrium isotherms and breakthrough curves. AOM enrichment was performed in a mother reactor under a sequencing batch operation, with a synthetic feed containing 200 mg/L NH4+-N. The inoculating sludge for the AOM enrichment was recirculated activated sludge (RAS) from NWRWRF. Anammox enrichment was performed in a mother reactor under a sequencing batch operation, with a synthetic feed containing 180 mg/L NH4+-N and 220 mg/L NO2--N. The inoculating sludge for the anammox enrichment was biofilm from a landfill leachate sequencing batch biofilm reactor (SBBR). The results from the project are as follows: Jar tests achieved \u3e90% TSS and VSS removal, with 30 and 40 mg/L iron chloride, and greater than 30% soluble COD removal with 100 mg/L iron chloride. Alkalinity and pH were influencing factors affecting CEPT performance. Due to low COD removal with typical iron chloride doses, higher coagulant doses were employed for the larger CEPT reactor. Greater than 50% COD removal was achieved at a larger scale with 270 mg/L iron chloride and 100 mg/L sodium hydroxide as an alkalinity source. Overall measurements of N, COD/N ratio, pH, and alkalinity consumption were favorable to the downstream IX-PN/A process. For the IX assessment, treatment with chabazite resulted in a high ammonium removal in both batch studies and column tests based on the masses of chabazite. There is strong evidence of ion competition for the breakthrough curve that can decrease the IX capacity. Factors influencing the breakthrough curve are the flow rate and fraction of chabazite in the adsorptive media. The AOM enrichment with synthetic wastewater resulted in substrate consumption of NH4+, with a maximum ammonium removal rate of 26 mg N/L/d. The anammox enrichment with synthetic wastewater resulted in substrate consumption (or even depletion) of NH4+ and NO2-, with a maximum ammonium and nitrite removal rate of 27 and 35 mg N/L/d. The key findings for the enrichments were based on controlling dissolved oxygen, pH, alkalinity, and concentrations of organic matter, ammonium, nitrite, nitrate, free ammonia, and free nitrous acid for a single-stage deammonification process. For the next stage of this research, additional studies are needed to determine the optimum conditions for the transition between ion exchange and bioregeneration based on the amount of chabazite, flow rate, presence of competing ions, and influent wastewater volume to reach the breakpoint