Performance of Passive Wastewater and Groundwater Nitrex TM Nitrogen Removal System. Pio Lombardo

Transcription

1 Performance of Passive Wastewater and Groundwater Nitrex TM Nitrogen Removal System Pio Lombardo ABSTRACT Excessive nitrogen levels caused by inadequate wastewater treatment pose a threat to the ecological health of water resources in the United States. Very few appropriate options currently exist for nutrient removal from decentralized wastewater flows. Conventional nutrient removal technologies, including carbon feed systems for nitrogen removal are generally operator intensive and complex. Decentralized wastewater management systems utilizing nutrient removal technologies provide a wastewater management option that is cost effective and protective of the environment, and avoids the need for centralized sewering. Based upon research at the internationally acclaimed University of Waterloo, the new, patented, innovative NITREX TM technology fulfills this need. Also the passive NITREX TM technology, which is a wood based reactive media, has been demonstrated to be capable of reducing wastewater total nitrogen levels to less than 3 mg/l and nitrate levels below.1 mg/l N. The NITREX TM technology can be incorporated into permeable reactive barriers (PRB) to remove nitrate-nitrogen from groundwater. The longevity of the NITREX TM filter is estimated to be 2+ years with little operation and maintenance requirements. The NITREX TM Filter is the only known passive treatment technology to provide virtually complete single-pass nitrate removal to produce an effluent quality that meets the new stringent surface water discharge criteria for nitrogen. The paper will present the results of independent EPA and State sponsored performance evaluations of Nitrex TM wastewater nitrogen removal systems in Oregon, Montana, and Cape Cod, MA and field monitoring data from residential and commercial installations. Moreover the results from a pilot project installed in summer 25 will be presented demonstrating the effectiveness of the NITREX TM permeable reactive barrier on Cape Cod for groundwater treatment. Testing and field applications show that the NITREX TM technology can achieve high process reliability and strong performance in both wastewater and groundwater applications. INTRODUCTION This paper presents the results of a number of independent testing programs of nitrogen removal systems. In these testing programs, the passive NITREX TM Filter system has demonstrated the ability to produce a wastewater effluent with a TN less than 3 4 ppm. The NITREX TM Filter has been evaluated in the following testing programs: * Pio Lombardo, PE, President of Lombardo Associates, Inc. of Newton, MA, Phone Number: (617) , pio@lombardoassociates.com Page 1 of 17

2 LaPine, Oregon National Decentralized Wastewater Treatment and Disposal Demonstration Project funded by EPA evaluating 15 alternative, innovative denitrification systems. The Project is being performed by the Oregon Department of Environmental Quality, U.S.G.S. and the Deschutes County Environmental Heath Division. Project is ongoing. See The LaPine Oregon Project evaluated two NITREX TM Filters at the residences of Flemming and Stone. Montana Department of Natural Resources evaluation of three on-site denitrification systems in Polson, MT. Project performed from Nov to Aug. 22. (Dupuis, MT DNR, 21) Massachusetts Septic System Test Center, Otis Air Force Base Cape Cod, MA (21-25) University of Rhode Island 6, gpd facility in Mashpee, MA Groundwater nitrate removal systems in Falmouth, MA Seven additional installations in Canada for individual and cluster wastewater systems, along with golf course and farmland runoff treatment systems (since 1997) A schematic of the NITREX TM Filter system is presented on Figure 1. Figure 1: NITREX TM Filter system Septic Tank Nitrifying System NITREX TM Filter Drain field Page 2 of 17

3 The Nitrex nitrogen removal mechanisms consist of ammonification and nitrification in a sand filter or other aerobic treatment system that provides complete nitrification as follows: Organic Nitrogen NH4 + NH O2 2 H+ + H2O + NO3- Denitrification in the Nitrex filter occurs by heterotrophic denitrification using the NITREX TM media as a slow release carbon source by the following reaction: 4NO CH2O 2N2 + 5CO2 + 3H2O + 4OH - As stated in the EPA Nitrogen Control Manual (1993), in nitrification: 4.6 mg oxygen required/mg nitrogen oxidized 7.1 mg CaCO3 alkalinity depleted/mg nitrogen oxidized.1.15 mg net volatile solids/mg nitrogen oxidized in denitrification (anaerobic conditions required) 2.9 mg oxygen liberated/mg nitrogen reduced 3.6 mg CaCO3 alkalinity recovered/mg nitrogen reduced net volatile solids removed/mg nitrogen reduced is dependent upon carbon source and can be similar to other biological systems For nitrification, alkalinity can become the limiting factor and is often added in high rate systems and in low alkalinity waters. With higher nitrogen strength wastewater and in low alkalinity waters, alkalinity may limit complete nitrification and thereby restrict nitrogen removal in heterotrophic denitrification systems. For wastewaters with 4 6 TN, alkalinity levels need to be mg/l for single pass filters and some other treatment processes. With recirculating media filters, the alkalinity requirements are reduced as the recirculating media systems regenerate some alkalinity and thereby net alkalinity requirements for complete nitrification are reduced. Typical alkalinity sources are (EPA, 1993): 1.8 mg CaCO3 alkalinity added/mg CaO (quicklime) added 1.2 mg CaCO3 alkalinity added/mg NaOH (caustic) added In biological denitrification, carbon feed/availability is usually the limiting factor and TN levels cannot generally be < 1 mg/l without a carbon feed system. As shown on Table 1, the passive NITREX TM Filter system was determined to be the best performing nitrogen removal system based upon testing 15 technologies at the LaPine, Oregon project ( ), as it achieved an effluent TN quality of 3 ppm. All data for all the tested systems is publicly available at the above web site and was subjected to extensive QA/QC procedures performed by the Oregon Department of Environmental Quality. Page 3 of 17

4 Technology Total Nitrogen Quality (mg/l) Technology Mean TN Standard Deviation 1 NITREX Biokreisel AX RX Amphidrome EnviroServer FAST, w/o RV Nayadic Dyno Puraflo Lined Sand Filter Bottomless Sand Filter NiteLess Septic Tank IDEA Figures 2 through 7 present the LaPine Total Nitrogen Test Results for septic tank effluent, sand filter effluent and NITREX TM Filter system effluent and NITREX TM Filter effluent temperature for the LaPine Flemming residence, Stone Residence and Polson, MT site, respectively. As can be seen from Figures 2 7, the NITREX TM Filter system was able to consistently produce an effluent with a total nitrogen of less than 3 4 ppm. As it is known that denitrification slows with lower temperatures (EPA, 1993), the NITREX TM Filter systems did exhibit less than complete denitrification during cold wastewater periods. The data shows that denitrification in the NITREX TM Filter system occurs at reduced rates when wastewater temperatures are below 48 F. The lower reaction rate at lower temperatures can be addressed with longer detention times in the Nitrex filter. Page 4 of 17

5 Figure 2 - La Pine, Oregon Fleming Residence Total Nitrogen Influent & Nitrex Quality Total NItrogen TN (mg/l) /1/2 1/9/21 4/19/21 7/28/21 11/5/21 2/13/22 5/24/22 Date 9/1/22 12/1/22 3/2/23 6/28/23 Septic Tank Sand Filter Nitrex Figure 3 - La Pine, Oregon Fleming Residence, Wastewater Temperature Temperature (C) Temp (C) Nitrex /1/2 1/9/21 4/19/21 7/28/21 11/5/21 2/13/22 5/24/22 Date 9/1/22 12/1/22 3/2/23 6/28/23 Page 5 of 17

6 Figure 4: La Pine, Oregon Stone Residence Wastewater Temperature Temperature (C) 25 2 Temp (C) 15 1 Nitrex 5 1/1/2 1/9/21 4/19/21 7/28/21 11/5/21 2/13/22 5/24/22 Date 9/1/22 12/1/22 3/2/23 6/28/23 Figure 5: La Pine, Oregon Stone Residence Total Nitrogen Influent & Nitrex Quality Total NItrogen TN (mg/l) Septic Tank Sand Filter Nitrex 1 1/1/2 1/9/21 4/19/21 7/28/21 11/5/21 2/13/22 5/24/22 Date 9/1/22 12/1/22 3/2/23 6/28/23 Page 6 of 17

7 Figure 6: Polson, MT Total Nitrogen Influent & Nitrex Quality Total NItrogen TN (mg/l) Septic Tank Sand Filter Nitrex Jan- Jan- Jan- Jan- Feb- Feb- Feb- Mar- Mar- Date Figure 7: Polson, MT Wastewater Temperature 3 25 Temperature (C) Temp (C) Nitrex Jan- Jan- Jan- Jan- Feb- Feb- Feb- Mar- Date Page 7 of 17

8 Figure 8: Mashpee, MA 5,75 gpd NITREX Wastewater Systems Page 8 of 17

9 Recent data for the 5,75 gpd design flow Nitrex system in Mashpee, MA is presented below: McShane Main Street Villages - Mashpee Design Flow 5,75 gpd MDL Septic Tank Waterloo Nitrex COMMENTS 1-May-6 BOD Nitrex TM Filter removed all nitrate TSS Waterloo Biofilter did not completely nitrify mg/l NH3 -N TKN Ammonia as N Nitrite as N.1 <.2.68 <.2 Nitrate as N.2 < <.4 Org-N Calculated TN - Calcualted Alkalinity ph Valves need repaired and by taking off line not needed NitrexTM Filter modules, effluent BOD expected to be reduced to be < 3 MDL Septic Tank 14-Jun-6 Waterloo Nitrex COMMENTS BOD 2 32 < Nitrex TM Filter removed all nitrate TSS Waterloo Biofilter did not completely nitrify mg/l NH3 -N TKN Insufficient recirculation in the Waterloo appears to be the cause Ammonia as N of the not complete nitrification as alkalinity was virtually completely Nitrite as N.1.29 <.1 consumed and ph reduced to 6.6. Nitrate as N <.2 4. Valves need repaired and by taking off line not needed NitrexTM Org-N Calculated Filter modules, effluent BOD expected to be reduced to be < 3 TN - Calcualted <7. Alkalinity ph MDL Septic Tank 18-Jul-6 Waterloo Nitrex BOD 2 65 TSS 1 TKN.5 Ammonia as N.2.23 Nitrite as N.1 Nitrate as N.2 <.4 Org-N Calculated TN - Calcualted Alkalinity 1 ph.1 COMMENTS 1. System adjustments made on July 11 appear to be working to reduce ammonia from Biofilter and BOD from Nitrex MDL Septic Tank 26-Jul-6 Waterloo Nitrex BOD TSS TKN Ammonia as N Nitrite as N.1 <.2 <.2 Nitrate as N.2 16 <.4 Org-N Calculated TN - Calcualted Alkalinity ph COMMENTS 1. System adjustments appear to be working to reduce ammonia from Biofilter and BOD from Nitrex Date May 1, 26 June 14, 26 July 18, 26 Total Nitrogen < 5. mg/l < 7. mg/l < 2.6 mg/l Page 9 of 17

10 Nitrex performance at the Massachusetts Alternative Septic System Test Center over five years has been a median of 5.1 m/l TN and a mean of 6.4 mg/l of which 2.9 mg/l has been due to incomplete ammonia nitrification by the recirculating sand filter. Page 1 of 17

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12 Summary of Nitrex Use Results Numerous installations have shown Nitrex TM filter systems to achieve <3-5 mg N/l No maintenance required Wastewater Temperatures above 4 to 48 F optimal - lower temp requires larger systems. In colder climates, system insulation is important The Nitrex TM Permeable Reactive Barrier (PRB) Groundwater Treatment has been used for groundwater nitrate removal (Robertson, W.D. and J.A. Cherry. 1997) and was recently tested by the Woods Hole Marine Biological Laboratory at two coastal installations in Falmouth, MA (Cape Cod) under a project funded by the Cooperative Institute for Coastal and Estuarine Environmental Technology (CICEET) funded by NOAA. Figure 9 illustrates how a PRB operates in removing nitrogen by creation of a reactive zone in the groundwater in which heterotrophic denitrification occurs. Figure 9 Permeable Reactive Barrier for Groundwater Nitrate Removal Freshwater Aquifer PRB Coastal area PRB Page 12 of 17

13 Figure 1 The benefits of the PRB are: Treats all sources of N Immediate impact on water quality Significant cost savings potential Localized recharge to aquifers PRB Demonstration systems were installed in July 25, Figure 1, adjacent to the Childs River and Waquoit Bay as illustrated in Figures 11 and 12. Groundwater nitrate levels from mg/l have been reduced to non-detect levels. Figure 11 Childs River The project interim results are presented at and indicate that groundwater nitrate has been eliminated by the PRB installations. Page 13 of 17

14 Figure 12 Waquoit Bay Nitrex Design Build Delivery Mechanism Footprint and not to exceed Budget provided at no cost to assess project feasibility Phase I services development of fixed cost, final design and permitting Phase II installation, start-up and performance certification Individual residences only available on volume basis Costs Nitrex Unit only - single family home $4, installed Large systems sized based upon: Minimum Temperature Total N to be removed i.e. from 2 to 5 ppm of N Total System costs for residential applications: New System $18, - $24, Comparison with Membrane Bioreactors Generally 25+ % savings on capital costs 4+ % savings on annual O&M costs Nitrex TM Treatment Systems Capital Costs (Design, Install, & Start-Up) Flow TN Requirement Total Cost/gpd 6, < 1 $167, $ ,5 < 1 $267, $ , < 7 $45, $3. 3, < 7 $85, $28.33 Turnkey Price Includes Engineering and Construction Page 14 of 17

15 OPERATION AND MAINTENANCE AND DISCUSSION The NITREX TM Filter systems have not required any maintenance (Rich, 23). These installations have demonstrated the ability of passive NITREX TM Filter system to consistently achieve a high degree of nitrogen removal during full-scale operation. During start-up elevated BOD occur as illustrated in the following Figures. However, initial elevated BOD values have not been a problem in drainfields. As can be seen in the Figures, the BOD is virtually all soluble as the TSS levels are extremely low, typically < 5 mg/l. In cases where low BOD concentrations are required, a post-polishing step is provided. During longer-term operation, BOD stabilizes to < 2 mg/l depending on factors such as actual flow. Current filter designs incorporate hydraulic controls and recycle lines to reduce the start-up period. Monitoring evidence indicates complete nitrate removal can be achieved (<.1 mg/l) while maintaining BOD <2 mg/l. Nitrex TM BOD Start-up occurred in winter for LaPine sites, 2nd peak occurred during warmer weather. Mashpee site is only one with hydraulic controls -adjusted at day LaPine Stone Data LaPine Fleming MA Otis Data Mashpee, MA BOD (mg/l) Days After Start-Up Page 15 of 17

16 Nitrex TM TSS 1 9 Start-up occurred in winter, 2nd peak occurred during warmer weather TSS (mg/l) LaPine Stone Data LaPine Fleming MA Otis Data Mashpee, MA Days After Start-Up REFERENCES: Crites, R. and G. Tchobanoglous, Small and Decentralized Wastewater Management Systems, McGraw Hill, Boston, MA. Robertson, W.D. and J.A. Cherry Long Term Performance of Waterloo Denitrification Barrier. Land Contamination & Reclamation, Vol. 5 No. 3, pp Robertson, W.D., D.W. Blowes, C.J. Ptacek and J.A. Cherry. 2. Long-term performance of in situ reactive barriers for nitrate remediation. Ground Water 38: U.S. EPA (Environmental Protection Agency) Nitrogen control manual. Technical report EPA/625/R-93/1, Washington, DC. Page 16 of 17

17 Valiela, I., M. Geist, J. McClelland and G. Tomasky. 2. Nitrogen loading from watersheds to estuaries: Verification of the Waquoit Bay nitrogen loading model. Biogeochem. 49: Page 17 of 17