Engineering SND Wastewater Treatment in the Classroom Sarah Sanford 1, Ann Sager 2, Sarina Ergas 2 1. T.R. Robinson; 2. Department of Civil and Environmental Engineering, University of South Florida For more information about the program visit: The Water Awareness Research and Education (WARE) Research Experience for Teachers (RET) is funded by the National Science Foundation under award number Abstract Objectives Background Approach Results References Conclusions As population centers continue to expand, global impacts on water quality pose risks to human health and natural ecosystems. Many wastewater treatment plants (WWTP) in Florida remove nitrogen from wastewater via simultaneous nitrification-denitrification (SND); however, understanding of the chemical kinetics underlying SND is limited (Jimenez, et al. 2014, Knapp 2014). This study sought to recreate SND at the bench scale for the purpose of improving SND kinetic models. Influent samples were subjected to alternating periods of aeration (DO 0.3–1 mg/L) over 16 hours to mimic aeration over time in lieu of space. Ammonium (NH 4 + ), nitrite (NO 2 - ), and nitrate (NO 3 - ), levels were analyzed via ion chromatography. Preliminary results indicate NO 2 - and NO 3 - production occurred during aerobic periods, NO 2 - was consumed immediately upon production, and total nitrogen levels decreased, indicating SND was achieved. The study was then used to develop a collaborative learning unit where students are challenged to design and build a functional bench-scale wastewater treatment system. The unit contains 3 components: (1)E-Module: delivery of background content and design scenario. (2)Lab: Students construct a bench-scale wastewater treatment system; analyze levels of NH 4 +, NO 2 -, and NO 3 - in synthetic influent and effluent. (3)Field Trip: Students collect effluent from a regional WWTP, and analyze NH 4 +, NO 2 -, and NO 3 levels for comparison to experimental results. Figure 4. SND vs. Time WWTPs typically remove excess nitrogen from wastewater via nitrification of ammonia into nitrites and nitrates (NH 4 + → NO 2 - → NO 3 - ) and denitrification of nitrates (NO 3 - → N 2 ) in separate aerobic and anaerobic bioreactors (Fig. 1.a). SND is a variation of this method wherein nitrification and denitrification occur within the same bioreactor under moderate to low oxygen levels (Fig. 1.b). Because current understanding of SND kinetics is limited, utilization of SND is not widespread (Jimenez, et al. 2014), despite significant benefits in terms of reduced energy consumption and expenditures. Figure 1. Segregated Nitrification-Denitrification vs. SND SND Experimentation: Samples of influent (raw sewage) and return activated sludge (RAS) were obtained from Falkenburg AWWTP, Tampa, Florida. Per trial, two replicate bioreactors containing 2L influent and 2L RAS were combined, dosed with ammonium chloride to 25 mg N/L, and subjected constant mixing using a electric stirrers. Aeration (DO 1.0 mg/L) was provided in alternating 4 hour intervals, with 4 hour breaks (DO 0.3 mg/L), using common aquarium equipment. Dissolved oxygen levels were monitored with a dissolved oxygen probe. Collaborative Learning Unit: Bringing complex engineering experiences into the classroom requires consideration on several levels, including safety, and applicability to curriculum. To deepen student’s understanding of how wastewater treatment is accomplished, groups of students are challenged to design an construct a functional wastewater treatment system utilizing traditional nitrification-denitrification or SND. Figure 2. SND Experimental Set Up (Fig. 2). Bioreactors were sampled every 2 to 4 hours for NH 4 +, NO 2 -, and NO 3 - levels over a 16 hour period. Samples were analyzed via ion chromatography. Unit Completion Create lesson plan that encompasses the E-module and classroom lab Develop E-module for background content & design scenarios Adapt methodology and materials for classroom use Develop methodology to recreate SND on a bench scale SND Experiments From Lab to Classroom E-Module Development Nitrification NH 4 + → NO 2 - → NO 3 - Denitrification NO 3 - → N 2 Denitrification Mechanical aerators Effluent a) Traditional Nitrification- Denitrification b) Simultaneous Nitrification- Denitrification Influent SND Experimentation: Preliminary results indicate nitrification occurred primarily during aerobic periods, evidenced by decreases in NH 4 + and increases in NO 3 - with denitrification occurring during anaerobic periods, evidenced by decreasing NO 3 -. Increases in NH 4 + during anaerobic periods is likely the result of decomposition of organic solids. Nitrites were consumed immediately upon production, regardless of DO level, and total nitrogen levels decreased, meaning SND was achieved (Fig. 4). Difficulty maintaining DO levels during both aerated and non-aerated intervals was the largest obstacle to obtaining consistent results, and was the likely the result of normal biological processes within the bioreactors and equipment issues. The complete unit is composed of 3 components: (1)E-Module: delivery of background content and a design scenario to model a WWTP with maximum nitrogen removal via traditional nitrification-denitrification or SND. (Fig. 3) (2)Lab: Students construct a functional bench-scale wastewater treatment system; analyze levels of NH 4 +, NO 2 -, and NO 3 - in influent and effluent. To avoid pathogen transmission, synthetic wastewater is used. (3)Field Trip: Students collect effluent from a regional WWTP, and analyze NH 4 +, NO 2 -, and NO 3 - levels for comparison to experimental results. Figure 3. Nitrogen Cycle E-Module Aerobic Anaerobic SND Experimentation: The methodology implemented during this study will be utilized in further investigations focused on modelling the biological and chemical kinetics underlying SND. Collaborative Learning Unit: Complex engineering problems can be adapted for the classroom with considerations regarding applicability and safety. Critical to implementing such units is first-hand knowledge of current research, adequate planning time, and access to resources. Nitrification NH 4 + → NO 2 - → NO 3 - DenitrificationNO 3 - → N 2 Denitrification NO 3 - → N 2 Jimenez, J., Wise, G., Burger, G., Du, W., Dold, P. (2014) “Mainstream Nitrite-Shunt with Biological Phosphorus Removal at the City of St. Petersburg Southwest WRF.” Proc. WEFTEC2014, New Orleans, LA, Sept 27- Oct 1, 2014, Knapp, L. (2014) Study of Process Control Strategies for Biological Nutrient Removal in an Oxidation Ditch, MS Thesis, Dept. Civil & Environmental Engineering, University of South Florida. Sager, A., Knapp, L., Ergas, S., Iranipour, G. (2015) “Process Control Strategies for Biological Nutrient Removal in an Oxidation Ditch.” Proc. Florida Water Resources Conference, Orlando, FL, May 5 th, Nitrate production Nitrate consumption