Wastewater Nitrogen Characteristics, Treatment and Removal Options. Bob Smith, Orenco Systems, Inc. GEC 2013

Transcription

1 Wastewater Nitrogen Characteristics, Treatment and Removal Options Bob Smith, Orenco Systems, Inc. GEC 2013 ##/##/#### #1

2 Nitrogen Nitrogen (N 2 ) in the environment exists primarily in the earth s atmosphere as a colorless, tasteless, and generally inert gas Air, by volume, is composed of about 78.08% nitrogen, with oxygen (O 2 ) following at about 20.95% Nitrogen is assimilated (absorbed/digested) and/or fixed from the air in living things ##/##/#### #2

3 Nitrogen Soil bacteria and ocean algae are primary fixers; nitrogen gas N 2 > Organic-N Nitrogen is a constituent of DNA and therefore, an essential element for life. Carbon, Oxygen, Nitrogen, Hydrogen, and Phosphorus, by weight, compose over 99% of microbial cell structure. ##/##/#### #3

4 Nitrogen in Urine and Feces Urine contributes about 75%+ of the nitrogen found in domestic wastewater Feces contributes about 20% ± of the nitrogen. Source separation can be an effective strategy. ##/##/#### #4

5 Nitrogen Family Organic nitrogen Organic-N Ammonium nitrogen NH + 4 Ammonia nitrogen NH 3 -N Nitrite nitrogen NO 2 -N Nitrate nitrogen NO 3 -N ##/##/#### #5

6 Total Nitrogen (TN) TN = Organic N + NH 3 -N + NO 2 -N + NO 3 -N Total Inorganic Nitrogen TIN = NH 3 -N + NO 2 -N + NO 3 -N ##/##/#### #6

7 Total Kjeldahl Nitrogen (TKN) TKN = Organic-N + NH 3 -N Therefore Organic-N = TKN - NH 3 -N And TN = TKN + NO 2 -N + NO 3 -N ##/##/#### #7

8 Ammonification Ammonification is the transformation of organic nitrogen to ammonium (NH 4 ) and ammonia (NH 3 ) inorganic forms, depending on ph levels. The initial phase of ammonification occurs in the septic environment of the primary tankage (70% ±) and about 3/4 th of the remaining organic nitrogen is converted to ammonia through the secondary aerobic process. ##/##/#### #8

9 Ammonification Urea is transformed to ammonia as follows: CH 4 N 2 O + H 2 O > 2NH 3 + CO 2 ##/##/#### #9

10 Nitrification Nitrification is the microbial conversion of ammonium to nitrate. Nitrification is a two-phase process that occurs in the highly aerobic environment of secondary and advanced treatment processes ##/##/#### #10

11 Nitrification In the first phase, ammonium oxidizing autotrophic bacteria known as nitrosomonas convert ammonia to nitrite in the following manner 2NH nitrosomonas > 2NO H + + 2H 2 O. In the second phase of nitrification, a nitrite oxidizing bacteria known as nitrobactor converts nitrite to nitrate as follows: 2NO nitrobactor > 2NO 3 - ##/##/#### #11

12 Denitrification Denitrification is the microbial utilization of nitrate under anoxic conditions. Denitrification is a multi-stage process where nitrate (NO 3- ) is reduced to nitrogen gas (N 2 ), which is liberated back into the atmosphere after rising to the liquid surface in tiny bubbles. ##/##/#### #12

13 Alternate Metabolic Pathways Anammox is an anaerobic ammonia oxidation process where nitrite and ammonia react and are converted to nitrogen gas and water, as follows NH NO 2 - > N 2 gas + 2H 2 O The nitrite supply must be steady, and can be provide through partial nitrification or denitrification. ##/##/#### #13

14 Typical Residential-Strength Influent* From Building Sewer BOD 5 mg/l TSS mg/l TN mg/l G&O mg/l TP mg/l Raw Influent * Small and Decentralized Wastewater Management Systems, Crites & Tchobanoglous, p. 180, ##/##/#### #14

15 Commercial Concentrations Commercial workplace flows typically ranging 6 to 12 gpd/person, or higher depending on the type of facility. With current practices to utilize water conserving low flow fixtures, commercial concentrations, after primary treatment, are likely to be in the order of 400 to 500 mg/l± BOD to 220 mg/l± TKN 50 to 70 mg/l± TP These concentrations correlate well with field-measured concentrations from offices, rest stops, manufacturing and other similar facilities where the primary wastewater flows is primarily from toilets and urinals. ##/##/#### #15

16 Nitrification What s Needed Adequate aeration volume for solids retention time (SRT > 8-10 days typical of suspended growth) Sufficient aeration capacity for needed dissolved oxygen (DO) concentration (4.57 mg O 2 /mg NH 3 -N) Sufficient alkalinity/ph, (7.14 mg alkalinity as CaCO 3 per mg NH 4 -N oxidized ph >6) No significant toxicity (e.g. trace organics, chlorides, ) Temperature control above 45 F ##/##/#### #16

17 Oxygen Availability in Air 275 mg/l oxygen in free air, which directly interfaces with the biomass... in contrast to 9 mg/l DO holding capacity of water for oxygen transfer ##/##/#### #17

18 Nitrification Limiting Factors: High organic concentrations BOD, COD, etc Lack of sufficient dissolved oxygen DO greater than 2 mg/l is preferred Insufficient alkalinity filtrate CaCO 3 should be around 100 mg/l or greater Low ph maintain greater than 6, with optimum range between 7.2 and 9 Low Temperature should be 10 C or higher Toxic Inhibitors e.g., high chloride levels (keep below 180 mg/l) ##/##/#### #18

19 Nitrifier Population vs BOD 5 /TKN ratio Ratio of Carbon to Nitrogen Percentage of Total Population % % 5.5 5% % ##/##/#### #19

20 Nitrification Reaction Rate vs BOD/TKN Nitrifier Fraction f n ; Nitrification Rate R n R n 0.2 f n C/N Ratio ##/##/#### #20

21 Effect of DO on Nitrification DO greater than 2 mg/l is preferred 1.00 DO Effect on Nitrification DO, mg/l ##/##/#### #21

22 Effect of ph on Nitrifiers Filtrate alkalinity (CaCO 3 ) should be maintained at mg/l or greater for optimum nitrification Maintain ph above 6, with optimum between 7.2 and 9 for nitrification ph effect on Nitrification Rate R n ph ##/##/#### #22

23 Temperature Effect on Nitrifiers Winter effluent temperature should be 10 C or higher 2.50 Temperature Effect on Nitrification Growth Rate µ n T, C ##/##/#### #23

24 Nitrification with Packed Bed Filters Packed bed filters have demonstrated a strong ability to reduce residential strength ammonia (40 to 55 mg/l) by 98 to 99% When that expected level appears to degrade by 5% or more, servicing is likely necessary, as well as an investigation into flow and strength capacities and/or other inhibiting factors (like over use of household cleaners, carpet cleaning, insufficient alkalinity, ph drop, etc.). ##/##/#### #24

25 Packed Bed Filter Biofilms At the surface and within the top 6 inches±, matter is trapped and the greatest biofilm accumulation occurs The top zone is mostly responsible for solids and organic reduction Heterotrophic bacteria are primarily responsible for reducing organic matter ##/##/#### #25

26 Packed Bed Filter Biofilms Oxygen is diffused from the air that fills the unsaturated voids into the effluent and biofilms. (Oxygen concentration in air 275 mg/l) After the carbonaceous demand is met in the upper levels of the media, inorganic constituents such as ammonia (NH 3 ) is reduced to nitrate (NO 3 ) by autotrophic bacteria conversion of ammonia to nitrate) in the lower region of the media ##/##/#### #26

27 Typical PBF Recirculation Configuration ##/##/#### #27

28 TEST CENTER SUMMARY AdvanTex Effluent Averages Total N mg/l NH 3 -N mg/l Total P mg/l Duration NSF/ANSI Standard (64%) 0.9 (96%) - 7 months NSF/ANSI Standard 40 Testing with UV Novatec Nitrogen Removal Testing Rotorua District Council Approval Testing 13 (66%) months 10 (70%) year 14(78%) 0.2 (99%) 8 (36%) 13 months Rotorua (78%) 0.6 (96%) ##/##/#### #28

29 FIELD TESTING SUMMARY AdvanTex Effluent Averages (no. of SFRs) Total N mg/l NH 3 -N mg/l Total P mg/l Duration NSF Pennsylvania Testing Program (11) 17 (68%) 1.7 (96%) years Virginia Approval Testing Program (13) months Jefferson County, CO Health Dept Permit Testing (43) Skaneateles, NY Demonstration Project (2) years 7 months years 2 months La Pine, OR Demonstration Project (3) 17 (74%) (18%) 2 years 7 months Rhode Island Demonstration Project (5) year 4 months Maryland BAT Testing AX20 (12) 17 1 year 5 months Maryland BAT Testing AX20RT (12) year ##/##/#### #29

30 Typical AdvanTex Recirc-Filters 60 to 70 % total nitrogen reduction without supplemental inputs To reach concentrations below 10 to 15 mg/l, apply specific engineering practices for nitrogen removal ##/##/#### #30

31 Two-Stage PBF Configuration ##/##/#### #31

32 PFB w/ Pre-Anoxic Denite-Recirculation Loop ##/##/#### #32

33 Denitrification Key Limiting Factors: Insufficient organic concentrations [C/N ratio ranges from 4 to 8 g BOD 5 / g (NO 3 -N)] Excessive dissolved oxygen (anoxic DO < 1 mg/l optimum DO < 0.3 mg/l) Temperature (keep above 45 F preferably 50 F) ##/##/#### #33

34 Effect of DO on Denitrification 1.20 DO Effect on Denitrification DO, mg/l ##/##/#### #34

35 Why Recirculate Treated Effluent? To optimize wastewater treatment To blend and dilute influent concentrations, which promotes more efficient hydrolysis To introduce nitrified effluent where there is a free carbon concentration and potential for supporting denitrification. To accomplish greater ammonia and total nitrogen removal To accomplish greater carbon reduction through denitrification utilization of 4 or more mg BOD 5 per mg nitrate removed. ##/##/#### #35

36 Supplements for Nitrogen Removal The effectiveness of nitrification is very dependent upon alkalinity/ph, and the effectiveness of denitrification is very dependent on an organic food source both of which often requires a chemical feed system designed to consistently dispense appropriate quantities of various buffering and carbon based compounds. Chemical feed systems provide a common and effective low cost means for disinfection. ##/##/#### #36

37 Supplemental Alkalinity Buffering Compounds Compounds Alk-Ratio ppm/ppm CaCO 3 Soda Ash 1.06 Acetate 0.82 Hydrated Lime 0.74 Quick Lime 0.56 Bicarbonate 1.68 Caustic Soda 0.80 Magnesium Hydroxide 0.50 ##/##/#### #37

38 Supplemental Carbon Sources Methanol (CH 3 OH) : 6.6 lb/gal 1,118,000 mg/l COD Ethanol (CH 3 OH) : 6.8 lb/gallon 1,650,000 mg/l COD MicroC (CH 3 CO 2 Hxx): 9.56 lb/gal 600,000 mg/l COD Acetic Acid (CH 3 OOH): 8.8 lb/gal 1,120,000 mg/l COD ##/##/#### #38

39 System Description Multiple Pass, packed bed Engineered textile Combines Textile filter media Recirculation tank Discharge tank Textile Media Recirculation Side Discharge Side ##/##/#### #39

40 Applications Repairs and retrofits Small sites and poor soils Sites that require shallow bury Residential Strength Wastewater (up to and including 500 gpd) ##/##/#### #40

41 Questions? ##/##/#### #41