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TRANSCRIPT
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
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 NH3 -3
Ammonium ion NH4+ -3
*Nitrogen gas N2 0
Nitrous oxide N2O +1
Nitric oxide NO +2
Nitrite ion NO2- +3
Nitrogen dioxide NO2 +4
*Nitrate ion NO3- +5
The Nitrogen Cycle in Soil-Groundwater
Systems
Transformation of the principal nitrogen compounds in soil-
groundwater systems (Organic-N, NH3-N, NH4+-N, N2-N, NO2
--N,
and NO3--N) can occur through five key mechanisms in the
environment:
Fixation
Ammonification
Synthesis
Nitrification
Denitrification
Biological Nitrification
Nitrification is the biological oxidation of NH4+ to NO3
- through a
two-step autotrophic process by the bacteria Nitrosomonas
and Nitrobacter:
Nitrosomonas
Step 1: NH4+ + 3/2O2 NO2
-- + 2H+ + H2O
Nitrobacter
Step 2: NO2- + 1/2O2 NO3
-
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
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 nutrientsources:
• Commercial fertilizers
• Animal manures
• Types of crops utilized (Fixation in legumes)
Atmospheric Deposition
Onsite Wastewater Systems
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
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 NH3-N/NH4+-N (TKN).
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 NH4+-N in the soil
Volatilization of NH3-N in alkaline soils at a pH above 8.0
Nitrification and subsequent movement of NO3- -N towards
the groundwater
Biological uptake of both NH3-N/NH4
+-N and NO3- -N
Denitrification if the environmental conditions are
appropriate
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
Figure 7: Nitrate Nitrogen Concentrations in Septic Tank Effluent and
Vadose Zone Receiving Nitrified Effluents
0
10
20
30
40
50
60
70
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
Nit
ra
te N
itro
gen
Co
ncen
tra
tio
n, m
g/L
as
N
Vadose Zone Beneath Trench
Septic Tank Effluent
Source: NDWRCDP
How Biological Denitrification
Can Occur in an Onsite System
NO3- can be reduced to N2 gas under ANOXIC (very low oxygen)
conditions, through heterotrophic biological denitrification as
shown in the following unbalanced equation:
Heterotrophic
Bacteria
NO3- + Organic Matter N2 + CO2 + OH- + H2O
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
Denitrification
A large variety of heterotrophic bacteria can use nitrate in
lieu of oxygen for the degradation of organic matter under
anoxic conditions.
If O2 is present, however, the bacteria will preferentially
select it instead of NO3-. Thus it is very important that anoxic
conditions exist in order that NO3- will be used as the
electron acceptor.
A carbon source (food) is required as the electron donor for
denitrification to occur.
Treatment Processes for
Onsite Nitrogen Removal Systems
Sequential Nitrification/Denitrification Processes:
(Figure 10)
STEP 1 --- Nitrification (aerobic process)
Conversion of Organic N and Ammonia to Nitrite
and then Nitrate
STEP 2 --- Denitrification (anerobic/anoxic process)
Conversion of Nitrate to Nitrogen Gas
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 CaCO3) for
every mg of NH4+-N oxidized.
In low alkalinity wastewaters there is a risk that nitrification will
lower the pH to inhibitory levels.
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.
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
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.
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 25-61 37-60
Sequencing batch reactor 60 15.5
Attached Growth:
Single Pass Sand Filters (SPSF) 8-50 30-65
Recirculating Sand/Gravel Filters (RSF) 15-84 10-47
Multi-Pass Textile Filters 14-31 14-17
RSF w/Anoxic Filter 40-90 7-23
RSF w/Anoxic Filter w/External Carbon Source 74-80 10-13
RUCK System 29-54 18-53
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)
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.
Source of aerobically treated
(nitrified) wastewater effluent
from existing treatment works
Supply line to
test
equipment
Test Apparatus
VIEW OF THE TEST APPARATUS
SHOWING THE TEST CONTAINER
AND THE FEED CONTROL VALVES
AND PLUMBING
Turf Reinforcement
Matting Placed Over
Stone in Bottom
Stone Placed in Hopper
Bottom Around Inlet
Shredded Bark Mulch
Media Placed Over
TRM
Test Column Assembly
Test Column Assembly
Another Layer of
TRM Over Media
1” Layer of Stone Over TRM
(Overflow Shown)
Test Container Filled
with Shredded Bark
Mulch Media
Media Size
Wastewater Feed Assembly
Low voltage motorized
valve controlled by
programmable timer
Influent
Sampling Tap
Pressure
Control Valve
Influent Feed Line
with Nitrified Effluent
Transformer
Test Container with
Organic Media
Electrical Feed From
Programmable Timer
Test Column Overflow Assembly
Test Container
with Media
Overflow at Top
Effluent Discharge
Effluent Sampling
Tap
Flow
Media Averages 24” in Diameter and is
Approximately 33” in Depth
Gross Volume is ~ 75 Gallons
Secondary Treatment
Using Media Filters
Nitrification Occurs Here
Anoxic Denitrification
Reactor
To Final Dispersal
Soil Component
Schematic of Treatment System for N Removal
STEP
Tanks Primary
Treatment
Background Information
1. Media – Non-treated shredded bark mulch
2. Reactor commissioned ~ Dec. 1st, 2015
3. 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
Results . . .
Warm Weather Results . . .
Other results of interest . . .
Explanation of BOD Change?
Secondary
“Aerobic”
Treatment
Anaerobic
Bark Mulch
Reactor
To Final Dispersal
Soil Component
Septic
Tank
What would this look like for a home system?
Nitrification Denitrification
NO3 N2
Sizing Criteria ---
1. Denit. reactor – upflow
2. Fed by pump, overflow by
gravity to drainfield
3. 3 days EBCT = 500 to 750
gallon container
EXPECTED RESULT . . .
< 10 mg/l Nitrate and T.I.N.
Upsized Denitrification Filter Design
for 100,000 GPD
THIS MAY ROCK YOUR WORLD !!!
Or . . . Consider this?
Let’s think about what happens beneath
those mound systems we have been
installing over the last 30 years!
Stone Bed
Sand Fill
Original grade
and topsoil
Prepared surface
beneath mound, leaving
topsoil in place!
Aerobic
ConditionsNitrification
Saturated anaerobic or
anoxic conditions----------------------------------------------------
Organic topsoil as a
carbon source
Denitrification