ENGINEERING OWTS FOR NUTRIENT REMOVAL. Simon Farrell, PE, REHS JVA Consulting Engineers March 27, 2015 CPOW mini conference

Transcription

1 ENGINEERING OWTS FOR NUTRIENT REMOVAL Simon Farrell, PE, REHS JVA Consulting Engineers March 27, 2015 CPOW mini conference 1

2 Overview of presentation Why focus on nutrient removal? Brief review of nitrogen cycle Definitions Traditional OWTS (single family home) Basic observations - increase nutrient removal Design of OWTS for nitrogen removal Design fundamentals for nitrogen removal Conduct your own evaluation 3 items to focus on 2

3 Why focus on nutrients? Transition from ISDS disposal to OWTS for treatment Significant progress over the last few years OWTS designs are not typically focused on nutrient removal Nitrogen and phosphorus Why not? National and State trend dischargers focused on nutrient removal Start with Municipal WWTF Smaller dischargers, OWTS, non-point sources 3

4 Regulatory Considerations - Colorado CDPHE Regulation 85 Nutrients Management Control Regulation effective September 2012 New WWTF: TP 0.7 mg/l, TIN 7 mg/l CDPHE Regulation 43 On-site Wastewater Treatment System Regulation effective June 2013 Treatment Level 2N = >50% TN reduction, TL3 = mg/l TN TL3N = 20 mg/l TN Control Regulations / Watershed Protection Districts Control Regulation 74 - Bear Creek Reservoir, TP < 1.0 mg/l 4

5 Chemistry review Nitrogen Cycle Organic Nitrogen = CO(NH2) 2 Urea Ammonium = NH 4 + pka = 9.25 Nitrite = NO 2 - Nitrate = NO 3 - Nitrogen gas = N 2 triple bond, inert 78% of atmosphere 5

6 Redox Chemistry / Microbiology Aerobic Requires Alkalinity Nitrification NH O 2 NO 3- + H + + H 2 0 Stoichiometry: 7.14 mg/l alkalinity as CaCO 3 per 1 mg/l NH 4 Anoxic Requires Carbon Source Denitrification: NO 3- + C 6 H 12 O 6 + H + N 2 (g) + CO 2 (g) + H 2 0 6

7 Nitrogen Cycle Common Terms Ammonia (really NH 4 + for most wastewaters) Total Nitrogen (TN) sum of all forms of nitrogen Total Inorganic Nitrogen (TIN) Ammonia, Nitrite, Nitrate Total Kjeldahl Nitrogen (TKN) Organic plus Ammonia 7

8 Nitrogen Fate s Organic N Denitrification: NO C 6 H 12 O 6 Nitrification + H + N 2 (g) + CO 2 (g) + H 2 0 Ammonium NH + NH O 2 NO 3- + H + + H cm Vadose zone? Capillary fringe Groundwater zone 8

9 Best Practices for Traditional OWTS - septic tank followed by STA Open infiltrative surface that allows the transfer of oxygen Trenches with chambers Reflected in Reg. 43 with incentives Keep the infiltrative surface shallow in the soil horizon Drip dispersal, NDDS Target the rhizosphere very biologically active 9

10 Best Practices for Traditional OWTS 10

11 Advanced Treatment OWTS design specifically for nitrogen removal Numerous technologies are available Orenco Advantex AX-100, AX MAX, AX-RT Biomicrobics MicroFAST, BioBarrier, ABC-N HOOT Systems H-series, Hoot-NR, Hoot ANR All based on the same fundamentals 11

12 Fundamentals of N removal in OWTS 1. Have realistic expectations on influent nitrogen concentrations - Particularly important for onsite systems 2. Focus on nitrification first - Requires oxygen and alkalinity 3. Denitrification - Requires anoxic conditions and carbon 12

13 Influent Levels of Nitrogen Untreated Domestic Wastewater Source: MetCalf and Eddy 5 th Edition Total Nitrogen (low strength) Total Nitrogen (medium strength) Total Nitrogen (high strength) 23 mg/l 35 mg/l 69 mg/l Application Types Source: Orenco Design Criteria TKN (Type 1 residential) TKN (Type 2 commercial) mg/l mg/l What is the objective? 50% nitrogen removal (NSF 245 standard) 10 mg/l TIN at end of pipe 13

14 Focus on nitrification first Nitrification: NH 4+ to NO 3 - Requires aerobic conditions Methods? Requires alkalinity Average Alkalinity: mg/l (Civil Engineering reference manual Michael Lindeburg) Municipal Application School Influent TKN 35 mg/l Influent TKN 100 mg/l Alkalinity required 250 mg/l Alkalinity required 714 mg/l 14

15 Denitrification Denitrification: NO - 3 to N 2 (g) Requires anoxic conditions Requires carbon source Methods? 15

16 Summary - nutrient removal in OWTS is coming. 1. Have realistic expectations on influent nitrogen concentrations - Particularly important for onsite systems - Determine the end goal 50% reduction or 10 mg/l 2. Focus on nitrification first - Requires oxygen and alkalinity 3. Denitrification - Requires anoxic conditions and carbon 16

17 JVA Consulting Engineers Thank you JVA! Mid-size Engineering Firm (approx. 90 people) Offices in Boulder, Ft. Collins, Winter Park, Glenwood Springs and soon to be Denver Focused on small to mid-size water and wastewater systems (1,000 gpd to 2 MGD) Team of engineers focused on decentralized and onsite wastewater treatment 17

18 Questions 18