Nitrogen Removal Using Saturated Upflow Woody Fiber Media

Transcription

1 Nitrogen Removal Using Saturated Upflow Woody Fiber Media 2017 Onsite Wastewater Mega Conference October 24, 2017 Larry Stephens, P.E. Acknowledgement Some of this material comes from Stewart Oakley, Department of Civil Engineering California State University, Chico as part of the University Curriculum Development for Decentralized Wastewater Management, with content edited for this presentation

2 Chemistry of Nitrogen Nitrogen can exist in nine various forms in the environment due to seven possible oxidation states: Nitrogen Compound Formula Oxidation State *Organic nitrogen Organic-N -3 *Ammonia NH 3-3 Ammonium ion NH *Nitrogen gas N 2 0 Nitrous oxide N 2 O +1 Nitric oxide NO +2 Nitrite ion NO Nitrogen dioxide NO 2 +4 *Nitrate ion NO

3 The Nitrogen Cycle in Soil-Groundwater Systems Transformation of the principal nitrogen compounds in soilgroundwater systems (Organic-N, NH 3 -N, NH 4+ -N, N 2 -N, NO 2- -N, and NO 3- -N) can occur through five key mechanisms in the environment: Fixation Ammonification Synthesis Nitrification Denitrification

4 Biological Nitrification Nitrification is the biological oxidation of NH 4+ to NO 3- through a two-step autotrophic process by the bacteria Nitrosomonas and Nitrobacter: Nitrosomonas Step 1: NH /2O 2 NO H + + H 2 O Nitrobacter Step 2: NO /2O 2 NO 3 -

5 Environmental Effects of Nitrogen Discharges Health Effects from Groundwater Contamination with Nitrates Methemoglobinemia most often cited concern Carcinogenesis Birth Defects Surface Water Pollution with Nitrogen Eutrophication Oxygen Demand through Nitrification Ammonia Toxicity to Aquatic Organisms

6 Sources of Nitrogen Discharges to Groundwater Agricultural Activities: Can be a significant source of nitrate in groundwater from... Excessive or inappropriate use of nitrogen-based nutrient sources: Commercial fertilizers Animal manures Types of crops utilized (Fixation in legumes) Atmospheric Deposition Onsite Wastewater Systems

7 Control of Nitrogen Discharges from Onsite Systems Public health agencies have tried to minimize the impact of nitrate from septic systems by: Limiting the number of onsite systems in a given area (i.e. control lot sizes) Promoting alternative onsite treatment technologies that provide nitrogen removal

8 Nitrogen Dynamics in Septic Tank-Soil Absorption Systems Septic Tanks: The removal of Total-N within septic tanks is on the order of 10 to 30%, with the majority being removed as particulate matter through sedimentation or flotation processes. Because of the septic tank's anaerobic (very little oxygen) environment, nitrogen exists principally as Organic-N and NH 3 -N/NH 4+ -N (TKN).

9 Nitrogen Dynamics in Septic Tank and Soil Absorption Systems Subsurface Absorption Trenches: Nitrogen can undergo several transformations within and below subsurface absorption trenches: Adsorption of NH 4+ -N in the soil Volatilization of NH 3 -N in alkaline soils at a ph above 8.0 Nitrification and subsequent movement of NO 3- -N towards the groundwater Biological uptake of both NH 3- N/NH 4+ -N and NO 3- -N Denitrification if the environmental conditions are appropriate

10 Water flow through a trench Infiltrative Surface: Where water enters the soil Biologically Active Zone: Commonly called the biomat, is where the majority of the treatment occurs Vadose (unsaturated) Zone: Zone that provides additional aerobic treatment, disperses water, adsorbs pollutants (eg, phosphorus). (NITRIFICATION HAPPENS HEAR) R.J. Otis

11 Figure 7: Nitrate Nitrogen Concentrations in Septic Tank Effluent and Vadose Zone Receiving Nitrified Effluents Nitrate Nitrogen Concentration, mg/l as N Vadose Zone Beneath Trench Septic Tank Effluent Jun-96 Jul-96 Aug-96 Sep-96 Oct-96 Nov-96 Dec-96 Jan-97 Feb-97 Mar-97 Apr-97 May-97 Date Source: NDWRCDP

12 How Biological Denitrification Can Occur in an Onsite System NO 3- can be reduced to N 2 gas under ANOXIC (very low oxygen) conditions, through heterotrophic biological denitrification as shown in the following unbalanced equation: Heterotrophic Bacteria NO Organic Matter N 2 + CO 2 + OH - + H 2 O

13 Water flow through a trench Infiltrative Surface: Where water enters the soil Biologically Active Zone: Commonly called the biomat, is where the majority of the treatment occurs Vadose (unsaturated) Zone: Zone that provides additional aerobic treatment, disperses water, adsorbs pollutants (eg, phosphorus). (NITRIFICATION HAPPENS HEAR) R.J. Otis

14 Denitrification A large variety of heterotrophic bacteria can use nitrate in lieu of oxygen for the degradation of organic matter under anoxic conditions. If O 2 is present, however, the bacteria will preferentially select it instead of NO 3-. Thus it is very important that anoxic conditions exist in order that NO - 3 will be used as the electron acceptor. A carbon source (food) is required as the electron donor for denitrification to occur.

15 Treatment Processes for Onsite Nitrogen Removal Systems Sequential Nitrification/Denitrification Processes: (Figure 10) STEP Nitrification (aerobic process) Conversion of Organic N and Ammonia to Nitrite and then Nitrate STEP Denitrification (anerobic/anoxic process) Conversion of Nitrate to Nitrogen Gas

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17 Biological Nitrification ph and Alkalinity Effects: The optimum ph range for nitrification is 6.5 to 8.0. Nitrification consumes about 7.1 mg of alkalinity (as CaCO 3 ) for every mg of NH 4+ -N oxidized. In low alkalinity wastewaters there is a risk that nitrification will lower the ph to inhibitory levels.

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19 Biological Nitrification Temperature Effects: Temperature has a significant effect on nitrification that must be taken into consideration for design. In general, colder temperatures require longer cell residence times in suspended-growth systems and lower hydraulic loading rates in attached-growth systems due to slower growth rates of nitrifying bacteria.

20 Summary Nitrogen Removal Nitrogen removal first requires oxidation to nitrate nitrification Aerobic process Slow growing bacteria requires long cell residence time Uses up alkalinity Following oxidation to nitrate denitrification required Anaerobic process (anoxic conditions - very low DO) Requires food source carbon Produces some alkalinity Both processes are temperature sensitive

21 Examples of Onsite Nitrogen Removal Technologies Suspended Growth: Aerobic units w/pulse aeration Sequencing batch reactor Attached Growth: Single Pass Media Filters (SPMF) Recirculating Media Filters (RMF) RMF w/anoxic Filter RMF or Other Aerobic Treatment Followed by Anoxic Filter w/external carbon source RUCK system Note: This is not intended to be an exhaustive list.

22 Treatment Processes for Onsite Nitrogen Removal Table 1 Examples of Onsite Biological Nitrogen Removal from the Literature Total-N Removal Effluent Total-N Technology Examples Efficiency, % mg/l Suspended Growth: Aerobic units w/pulse aeration Sequencing batch reactor Attached Growth: Single Pass Sand Filters (SPSF) Recirculating Sand/Gravel Filters (RSF) Multi-Pass Textile Filters RSF w/anoxic Filter RSF w/anoxic Filter w/external Carbon Source RUCK System

23 Recent Research Using An Upflow, Saturated, Organic Media Source water is aerobically well-treated effluent utilizing geotextile packed-bed filters Upflow using pump/pressure feed to control contact time Saturated media to limit oxygen and create anoxic conditions Bio-degradable organic media as a carbon source (food source for bacteria)

24 Credits This research was financially supported by Craig Cihak of Craig s Cruisers, a private business owner planning to build a privately owned, public wastewater treatment system to serve a resort community in western Michigan. The research was conducted at a wastewater treatment facility owned by Brookfield Township in Eaton County, MI that serves homes around Narrow Lake and is operated by SCS Systems, LLC.

25 Source of aerobically treated (nitrified) wastewater effluent from existing treatment works Supply line to test equipment

26 Test Apparatus VIEW OF THE TEST APPARATUS SHOWING THE TEST CONTAINER AND THE FEED CONTROL VALVES AND PLUMBING

27 Test Column Assembly Shredded Bark Mulch Media Placed Over TRM Turf Reinforcement Matting Placed Over Stone in Bottom Stone Placed in Hopper Bottom Around Inlet

28 Test Column Assembly Test Container Filled with Shredded Bark Mulch Media 1 Layer of Stone Over TRM (Overflow Shown) Media Size Another Layer of TRM Over Media

29 Wastewater Feed Assembly Test Container with Organic Media Low voltage motorized valve controlled by programmable timer Influent Sampling Tap Pressure Control Valve Influent Feed Line with Nitrified Effluent Electrical Feed From Programmable Timer Transformer

30 Test Column Overflow Assembly Overflow at Top Test Container with Media Effluent Discharge Flow Media Averages 24 in Diameter and is Approximately 33 in Depth Gross Volume is ~ 75 Gallons Effluent Sampling Tap

31 Schematic of Treatment System for N Removal STEP Tanks Primary Treatment Secondary Treatment Using Media Filters Anoxic Denitrification Reactor Nitrification Occurs Here To Final Dispersal Soil Component

32 Background Information 1. Media Non-treated shredded bark mulch 2. Reactor commissioned ~ Dec. 1 st, Initial setting for empty bed contact time of 2 days (empty bed = container volume without media) 4. Changed flow settings to increase empty bed contact time to 3.2 days on July 29, 2016

33 Results...

34 Warm Weather Results...

35 Other results of interest... Explanation of BOD Change?

36 What would this look like for a home system? Septic Tank Nitrification Denitrification Secondary Aerobic Treatment NO3 Anaerobic Bark Mulch Reactor N2 Sizing Criteria Denit. reactor upflow 2. Fed by pump, overflow by gravity to drainfield 3. 3 days EBCT = 500 to 750 gallon container To Final Dispersal Soil Component EXPECTED RESULT... < 10 mg/l Nitrate and T.I.N.

37 Upsized Denitrification Filter Design for 100,000 GPD

38 Or... Consider this? THIS MAY ROCK YOUR WORLD!!!

39 Let s think about what happens beneath those mound systems we have been installing over the last 30 years!

40 Prepared surface beneath mound, leaving topsoil in place! Stone Bed Sand Fill Original grade and topsoil

41 Nitrification Aerobic Conditions

42 Denitrification Saturated anaerobic or anoxic conditions Organic topsoil as a carbon source

43 Questions? Larry Stephens, P.E. Stephens Consulting Services, P.C. Haslett, MI