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TRANSCRIPT
Agricultural Mineral Soil Additives for Passive Nitrate
Removal, &
Phosphorus Removal Using Low Energy Electrochemistry
NOWRA Onsite Wastewater Mega-Conference
Christopher Jowett
October 24, 2017
Outline
3
• Talk #1 – Nitrate Removal
• Pilot testing
• Effects on treatment
• HRT results
• Sulphate production
• Talk #2 – Phosphorus Removal
• P removal in natural systems
• Mimicking nature with Waterloo EC-P
• Test results & mineral formation
• Other benefits
Agricultural Mineral Soil
Additives for Passive Nitrate Removal
Residential Nitrogen Removal
1. Single-Pass Waterloo Biofilter
• 25 – 35% TN removal
• Internal carbon source of wastewater
2. Double-Pass Waterloo Biofilter
• 50 – 65% TN removal
• Septic tank carbon source through recirculation
3. WaterNOx Anoxic Filtration Denitrification Add-On
• 80 – 95% TN removal
• Proprietary external carbon source
4. Nox-LS Autotrophic Sulphur-Limestone Add-On
• 90 – 95% TN removal
• Sulphur-oxidizing bacteria reduce nitrate5
• EPA lab study using agricultural sulfur at Cornell University, 1978
• Recent Florida & MASSTC work using wood chips + agricultural sulfur
• FULL-SCALE PERFORMANCE OF A TWO-STAGE BIOFILTRATION SYSTEM FOR REDUCTION OF NITROGEN
Damann Anderson, Josefin Hirst, Richard Otis, Elke Ursin, and Daniel Smith, 2014
• PILOT STUDY OF TWO-STAGE BIOFILTRATION FOR REDUCTION OF NITROGEN FROM OWSJosefin Hirst, Damann Anderson, and Daniel Smith, 2014
Autotrophic So + CaCO3
Denitrification
Damann Anderson at
residential demonstration
site near Tampa Florida
6
• Nitrification consumes alkalinity to buffer lower pH
• Adequate alkalinity must exist for thorough nitrification to occur
• Nitrification in soft water areas may require alkalinity chemical
addition
Nitrification is Key
7
• Water conservation is a problem – more TKN, not so much alkalinity
Nitrification is Key
Insufficient Alkalinity due to Water Conservation
0
20
40
60
80
100
0 100 200 300 400 500 600
TK
N
mg
/L
Days Lapsed
TKN Total NWaterless urinals
installed Day 80 –
increased TKN
without increasing
alkalinity
Automatic alkalinity
dosing installed
Day 380 –
nitrification back to
normal
8
NOx-LS Testing
• Autotrophic Sulphur Denitrification
Units
• Received 60 – 240 L/day of nitrified
Waterloo Biofilter effluent
• Hydraulic Retention Times of 8 – 34
hours
• NO2,3-N Loading Rate = 3.7 g/day =
13.2 g/m2/day
Pilot Test at Rural School
10
• Excellent immediate denitrification
• Consistent very low TN
• No increase in TSS
• Marginal increase in BOD
• Monitor SO4 to keep <500 mg/L; though 1000-1500 mg/L is upper limit
Pilot Test at Rural School
1.1S0 + NO3- + 0.76H2O + 0.4CO2 + 0.08NH4
+ =
0.08C5H7O2N + 1.1SO42- + 0.5N2 + 1.28H+
S0 + O2 + H2O = H2SO4 sulphuric acid
S0 + NO3 + H2O = N2 + H2SO4
CaCO3 + H2SO4 = HCO3- + OH- + CO2 + Ca+2 + SO4
-
Ca+2 + SO4- + 2H2O = CaSO42H2O gypsum ?
Acid produced, pH buffered by dissolving limestone.
Sulphate produced, monitor for aesthetic purposes.
Nitrogen gas is non-reactive. Can form
insoluble bubbles that impede hydraulic flow.
11
• Evolution of nitrogen species and sulphate through the treatment train
Pilot Test at Rural School
Erin Lift Station Raw Sewage
pH DO Temp cBOD TSS TKN Sulphate Alkalinity
mg/L ˚C mg/L mg/L mg/L mg/L mg/L
Mean 7.1 1.1 13.6 124.0 41.9 66.9 119.1 --
Median 7.1 1.0 14.0 112.0 33.5 65.1 120.0 --
Biofilter Effluent
pH DO Temp cBOD TSS TKN NO3-N NO2-N TN Sulphate Alkalinity
mg/L ˚C mg/L mg/L mg/L mg/L mg/L mg/L mg/L mg/L
Mean 7.1 7.53 14.2 4.4 2.1 1.7 32.7 0.15 34.5 119.6 --
Median 7.1 7.84 14.5 4.0 2.0 1.3 27.1 0.03 30.0 120.0 --
Limestone + Sulphur Effluent
pH DO Temp cBOD TSS TKN NO3-N NO2-N TN Sulphate Alk'y
mg/L ˚C mg/L mg/L mg/L mg/L mg/L mg/L mg/L mg/L
Mean 6.9 0.93 16.6 9.3 2.7 1.73 1.68 0.19 3.59 418 192
Median 6.9 0.85 16.5 4.0 2.0 0.90 0.06 0.03 2.22 405 177
N = 35-5012
• NOx-LS minimal effect on TSS
Treatment Effects
1
10
100
0 200 400 600 800
TSS
mg/
L
Days Lapsed
Biofilter TSS
WaterNOx-LS TSS
Raw Sewage TSS
13
• NOx-LS marginally increases cBOD; easily removed in limestone polisher
Treatment Effects
1
10
100
1000
0 200 400 600 800
cBO
D m
g/L
Days Lapsed
WaterNOx-LS cBOD Raw Sewage cBOD Limestone Polisher
14
• Total Nitrogen depends on sewage TKN + Biofilter NO3-N + Nox-LS HRT
• Generally TN < 10 mg/L when HRT > 12 hours
TN Removal
0.1
1.0
10.0
100.0
1000.0
0 100 200 300 400 500 600 700
Tota
l Nit
roge
n m
g/L
Days Lapsed
Biofilter TN NOx-LS TN Raw Sewage TKN
15
• TN% removal was high and remained consistent until HRT was lowered to
8.4 hours
• Performance improved immediately when HRT was increased again
HRT Analysis
16
• Linear relationship between mass of sulphate produced and mass of nitrate +
DO removed
Sulphate Production
y = 1.43x + 9.32R² = 0.915
0
20
40
60
80
0 10 20 30 40 50
Sulp
hat
e P
rod
uce
d g
/day
NO2,3 + DO Removed g/day
17
• Basic reaction:
2.5 S0 + CO2 + NO3 + H2O + 2.5 O2 = CH2O + 1/2 N2 + 2.5 SO4
2.5 SO4 = 2.5 S0 + CO2 + NO3 + H2O + 2.5 O2 – (CH2O + 1/2 N2)
SO4 = (2.5 S + CO2 + NO3 + H2O + 2.5 O2 - CH2O - 1/2 N2)/2.5
Mass SO4 = 96
Mass (NO3 + DO) = 56.8
Slope = SO4/(NO3 + DO) = 96/56.8 = 1.69
Sulphate Production
Theoretical Slope = 1.69 with intercept = 0.0
Actual Slope = 1.43 with intercept = 9.32
Actual Slope = 1.77 if set intercept = 0.0
Values from influent & effluent only, not within the reactor
(likely need to include CO2 + NH3,4) 18
• Suction lysimeters sampled internal pore water at 20” + 10” depths
• Internal reactor data fits theoretical slope = 1.69 if intercept is artificially set to
zero (more data needed)
Internal Reactions
y = 1.691xR² = -0.236
0
10
20
30
0 5 10 15 20
Sulp
hat
e P
rod
uce
d g
/day
NO2,3 + DO Removed g/day
Pore Water Results
19
• 10” depth sample shows
peaks in
• cBOD (biomass?)
• TSS
• Alkalinity
• TKN
• NH4
• SO4
• sulphide
• Corresponds with a low of
pH and nitrate
• Shows reactions occurring
that are lost looking at just
influent & effluent samples
Internal Reactions
20
• Before use showing smooth surface
SEM of Media
Pristine S0 surface at 50 μm SEM scale Agricultural S0 pastille ~ 3 mm diameter
21
• After use showing dissolution pits indicating biochemical reaction with oxygen
and nitrate-rich water
SEM of Media
Corrosion ‘caries’ texture common in
S0 at depth = 20” near source of NO2,3
Caries texture rare in S0 at depth = 10”
further from source of NO2,3
Different 50 μm SEM scale
22
• Agricultural sulfur and limestone successful at high
levels of TN removal
• HRT of 8 – 12 hours minimum needed without
substantial nitrate breakthrough
• pH fully neutralized and little TSS/BOD addition
• Internal reactions analogous to ‘oxidation-reduction roll-
front deposit’ in the natural environment
• Nitrate advances through ‘rock’ both nitrate and DO
reduced as sulphur oxidized
Conclusions
23
Phosphorus Removal Using
Low Energy Electrochemistry
Phosphorus Removal
• Industry issue
• A lot of discussion
• Not a lot of action… so far
• Technology exists now
Lake Erie algae bloom, 2013
Freshwater Lake Northern Ontario, 2015
Lake Okeechobee FL algae bloom, 2016
Lake Okeechobee FL outflow to the coast,
2016
25
Natural Removal of Phosphorus in Soils
• Iron rich B Horizon soils, yes
• Preferential pathways
• Unknown when iron is used up
• Clean sand and iron poor soils, somewhat
• Low levels ~20-25% TP
• Loosely adsorbed & easily leached out
• Clean sand or filtration medium, yes
• If Fe ions added by EC-P
26
Natural Soil Processes in ‘B horizon’
Ferric minerals:
Goethite α-FeOOH – yellowish brown
Hematite α-Fe2O3 – bright red
Lepidocrocite γ-FeOOH – bright orange
Maghemite γ-Fe2O3 – red to brown
Ferrihydrite 5Fe2O39H2O – reddish brown
Strengite FePO42H2O
Ferrous minerals:
Siderite FeCO3
Vivianite Fe3(PO4)28H2O
Pyrite FeS2
Phosphorus is leached down and adsorbed onto Fe-hydroxides, then mineralized as
insoluble FeSO4 crystalline mineral cements
27
Replicating B Horizon Soil in Clean Sand
Sand Filter Foam Filter
Go straight to the ‘mineralization’ step in otherwise non-reactive media:
What we are trying to do is bring together soluble ions to react together:
3 + 2PO43- = (PO4)2 (vivianite) or
+ PO43- = (PO4) (strengite)
28
Phase Diagram for Fe-PO4 minerals
High
O2
Low
O2
Biomat
Septictank
Groundwater Likely pathway is septic tank, anaerobic biomat, to
aerobic groundwater, leaving Fe-PO4 minerals
scattered in soil or filtration medium
29
Waterloo EC-P & Testing
Replicating Nature with EC-P
31
EC-P Electrodes
Early Retrofit Testing at School in Ontario
Commercial Installation at
Provincial Park in Manitoba Residential Installation at Lakefront Cottage
32
Smart Panel Control
EC-P Control
• Variable intensity settings
• Variable operational schedules
• Controls rest of the system as well
• Automatic ‘away‘ shutdown mode (pump
required)
Smart Panel Benefits
• Remote control & live monitoring
• Instant email notifications
• Cellular or Ethernet connections
• Reduced O&M costs
• Peace of mind33
Waterloo EC-P Field Study Results
1. Compare to Single-Pass Sand Filter no EC-P
TP >3.6 mg/L after 24” C-33 sand = 20-25% removal
2. Generic Recirculating Sand Filter with EC-P;
TP = 1.1 mg/L at lower iron dissolution = 82% removal
TP = 0.51 mg/L at higher iron dissolution = 92% removal
TP = 0.58 mg/Lin a second study = 91% removal
3. Residential Biofilter with EC-P;
TP = 0.61 mg/L = 96%
4. Public School Biofilter with EC-P;
TP = 0.53 mg/L = 92%
5. Septic Tank + Soil Leach Field with EC-P;
TP = 0.11 mg/L after 300 mm of sandy loam soil = 98%
TP = 0.05 mg/L after 600 mm of sandy loam soil = 99%
TP = 0.03 mg/L after 900 mm of sandy loam soil > 99%
Arithmetic averages34
• Ontario-style leachfield with pan lysimeters at 12”, 24”,
36” depths
Multi-Year Testing at MASSTC
0
0.2
0.4
0.6
0.8
1
1.2
0 200 400 600 800 1000 1200
TP m
g/L
Days Lapsed
300 mm pan lysimeter results
35
EC-P + Soil Depth Removal
0.01
0.1
1
10
0 100 200 300 400 500 600 700 800
TP m
g/L
Days Lapsed
C3 Septic 12" PAN 24" PAN 36" PAN
36
Mimicking Nature?
Al chemicals produce Al + K + P concentrations, but no apparent
crystallinity in SEM
37
Mimicking Nature?
EC-P Fe addition forms octahedral crystalline structures
38
Mineral Formation SEM & XRD scans identify CaC2O4
oxalate mineral weddellite (left) and Fe-PO4 mineral vivianite (right)
39
Mineral FormationXRD scans identify CaC2O4 oxalate mineral
weddellite and Fe-PO4 mineral vivianite
40
It’s nice to see chemistry theory predict what reactions will occur, in this case formation of vivianite
High
O2
Low
O2
Biomat
Septic
tank
Groundwater
41
Other Benefits
• Conventional Strategy – Separation as Sludge
• Dose chemicals to separate out & concentrate P in sludge
• High P sludge pumped out & treated again at WWTP
• pH buffering chemical normally required
• Waterloo EC-P Strategy – Precipitation of Fe-P Minerals
• No chemicals
• Allow FE-P ions to bond meet in anaerobic environment
• Form insoluble crystalline minerals in aerobic environment
• No additional sludge, no subsequent re-treatment
New Strategy
43
No pH Impact
1
10
0 100 200 300 400 500 600 700
pH
un
its
Days Lapsed
School Septic, Polisher & Area Bed – pH
Polisher Area Bed
Septic Tank Raw Sewage
EC-P Day 372
44
• Will this method plug the leachfield?
Long Term
To estimate the volume of Fe-P minerals precipitated in a soil leach field, an Ontario example is used of a 4-person residence with ~2.63 kg TP loading per year.
Assuming that all P is removed in the leach field as oxidized strengite FePO4·2H2O (16.6% P & density of 2840 kg/m3) and none in the anoxic septic tank, this technology will crystallize out 15.8 kg strengite per year or 15.8 ÷ 2840 = 0.0056 m3 of Fe-P minerals.
Field experience shows that the iron staining on sand grains penetrates to at least 0.3 – 0.5 m depth in sandy soil and assumed somewhat less in clay-rich soils.
In 100 m of 0.6-m wide trench in sandy loam soil of ~30% porosity, this technology will occlude 0.0056 m3 or 1 – 2% of the available 7.2 m3 pore space in the upper 0.3 – 0.5 m of leach field over a period of 20 years.
In 500 m trench in clay-rich soil, only 0.2 – 0.4% of the available ~30% porosity will be occluded.
For 1.0 m depth of synthetic filtration media such as peat, foam or textile, Fe-P minerals will occupy less than 5% of available porosity over a 20-year period at peak flow rates.
45
• Silicate material used as filtration media receiving septic tank
effluent + EC-P
• Removed and mixed with soil as fertilizing soil amendment
• Greenhouse corn growth & soil leaching studies performed
• Soil only (control)
• silicate material
• super phosphate
• STE + silicate + EC-P
• STE + silicate
15 plants of each 5 treatments
Potential for Recovery
46
Potential for Recovery
0
4
8
12
16
20
Soil(control)
Soil + vsm Soil +Mineral P
STE-EC-P +Soil
STE + vsm +Soil
Tiss
ue
Ph
osp
ho
rus
Per
cen
t D
iffe
ren
ce
1 2 3 4 5
EC-P Highest P uptake
0
20
40
60
80
100
Soil(control)
Soil + VSM Soil +Mineral P
Soil + VSM(STE/EC-P)
Soil + VSM(STE)
Hei
ght
cm
1 2 3 4 5
EC-P Tallest plant height
47
Potential for Recovery
EC-P Most biomass
0
20
40
60
Soil (control) Soil + vsm Soil +Mineral P
STE-EC-P +Soil
STE + vsm +Soil
Dry
Bio
mas
s Pe
rcen
t D
iffe
ren
ce 1 2 3 4 5
48
• Clean sand removes up to 35% TP (loosely)
• Iron-rich soils remove more
• Possible to mimic iron-rich soils using clean sand or
other filtration medium such as foam
• Insoluble vivianite crystals formed with EC-P
• Suitable for individual homes with other benefits
including potential for resource recovery
Conclusions
49
Thank you for your attention!