Transcript No Slide Title

Evaluation of alternative technologies for
upgrading wastewater treatment plants in
Minnesota for new phosphorus limits
H. David Stensel
University of Washington
Gary M. Grey
George J. Kehrberger
Hydroqual
11th Annual Education Seminar
Central States Water Environment Association
April 4, 2006
Upgrading WWTPs for phosphorus
removal

Phosphorus effluent limits of <1.0 mg/L P expected in general
for state of Minnesota

Minnesota Science and Economic Review Board
– Identify the most appropriate cost effective phosphorus
reduction strategies for retrofitting existing treatment
plants for different types of biological treatment
processes

Developed a protocol to systematically evaluate the
effectiveness of phosphorus removal alternatives for various
types of plants

Apply protocol to evaluate phosphorus removal alternatives
for different types of WWTPs
Summary of Treatment Plant Characteristics


Different Sizes 0.5 – 19.1 MGD
8 Different Biological Treatment Processes
3 Activated sludge
2 Biological nutrient removal
2 Oxidation ditches
2 High purity oxygen
1 Trickling filter
4 Combined trickling filter & activated sludge
2 Lagoon systems
1 Rotating biological contactor
Continued Summary of Treatment Plant
Characteristics




5 Plants with tertiary treatment (filters)
5 Plants dewater sludge
14 Plants land apply waste sludge
Nutrient Requirements





11 Plants monitor only for phosphorus
7 Plants monitor only for ammonia nitrogen
14 Plants receive industrial wastewater
4 Plants have 1 mg/L phosphorus discharge limit
8 Plants have discharge limit for ammonia
Protocol used for phosphorus Removal
plternatives evaluation

Ehanced Biological Phosphorus Removal
(EBPR) Only

Chemical precipitation only

EBPR +chemical addition

Key site-specific information was obtained
for evaluation
Goals of retrofit process evaluations for
P removal




Tank volumes required for process configuration
selected – i.e. anaerobic, anoxic, aerobic
Feasible retrofit modifications within existing facility
Sludge production and P recycle
Effect of pre-activated sludge processes on design
and performance




Primary treatment
Trickling filter
P removal possible with EBPR
Chemical dose required for P removal and alkalinity
control
Impact of wastewater characteristics
Influent
Parameter
>BOD
>TSS
>Total P
On Chemical
Treatment
On
EBPR
>Tank volume
>Tank Volume
>Sludge production >Sludge Production
>Tank volume
>Tank Volume
>Sludge production >Sludge Production
>Chemical dose
>Effluent P conc.
>BOD/P
<Effluent P conc.
>rbCOD/P
<Effluent P conc
<Temperature
>Tank volume
>Tank volume
rbCOD=soluble readily biodegradable COD-VFA source
Impact of wastewater characteristics
(continued)
Influent
Parameter
On Chemical
Treatment
On
EBPR
>TKN, NH3
>Effluent P conc.
<BOD/TKN
>Effluent P conc.
>Loading
variations
>Effluent P conc.
EBPR Protocol
WWT
Character.
If nitrification
locate and size
anoxic tank
Size & Locate
Anaerobic
Tank
Select
SRT
Determine
amount of
P removed
Evaluate
Costs
Chemical addition
option
Chemical Addition Only Protocol
WWT
Character.
Determine
chemical
dose
Determine P
used in
biotreatment
Identify
dose
points
Determine
chemical
Sludge
produced
Evaluate
Costs
EBPR Protocol
Size & Locate
Anaerobic
Tank
Size – 1.0 Hour detention time
Ability to add to Existing System depends
On existing design, capacity, and layout
PC
AT
SC
Anaerobic
PC
AT
SC
Easier to
Add to
Plug flow
Tanks with
Enough
capacity
For some systems layout is not
Compatible for fitting into existing tanks
Size & Locate
Anaerobic
Tank
AN
SC
AT
Oxidation Ditch and High Purity Oxygen (HPO)
require an external tank
HPO tanks
PC
AN
AT
SC
EBPR Protocol
Select
SRT
EBPR
Nitrification: NH3 to NO3
Function
of
temperature
SRT@100C
SRT@150C
EBPR
5.1 days
4.1 days
Nitrification
15.1 days
9.3 days
Tank volume needed is related to
SRT and BOD removed
(Net solids yield, Yn)(Flow)(BODr)SRT
Volume 
MLSS concentration
Primary treatment lowers Yn
Primary treatment with chemicals lowers Yn more
Use of anaerobic zone in EBPR produces lower
SVI and thus allows higher MLSS concentration
3500 mg/L possible
EBPR Protocol
Nitrate reduced to N2 in anoxic tank
Less nitrate to anaerobic zone
1 mg/L NO3-N robs 0.70 mg/L P removal
Saves energy – use NO3 produced
Improves sludge settling
If nitrification
locate and size
anoxic tank
ANAEROBIC
EFFL.
INFL.
ANOXIC
AEROBIC
WAS
EBPR Protocol
If nitrification
locate and size
anoxic tank
•Typically 10-20% of aerobic volume
•More influent TKN, more nitrate; larger tank
•Less influent BOD/TKN; larger tank
•Less soluble BOD; larger tank
ANAEROBIC
EFFL.
INFL.
ANOXIC
AEROBIC
WAS
EBPR Protocol
Determine
amount of
P removed
NO3
P is removed by phosphorus
accumulating organisms (PAOs)
and exits system in waste sludge
Anaerobic
Anoxic and/or
Waste sludge
Aerobic
P release
P uptake
Influent
rbCOD
Influent
particulate
BOD
-Carbon storage-PHB
-poly P storage
How much P is removed by microbes?
P removal =f(PAO growth from rbCOD, % P in cells)
RPAOs
Y(Δ(ΔrbCOD(8.34)

 lb/d PAOs produced
(1  bPAO * SRT)
RPAOs 0.25  0.002SRT
P removal, mg/L 
Q
+ P removed for cell synthesis
Assumes 25% dry wgt of PAOs=P
Processes that deprive PAOs of rbCOD
Denitrification


in anaerobic zone
Nitrate (NO3) may be present
in return activated sludge
1 mg/L NO3-N uses ~ 7 mg/L
equivalent to 0.70 mg/L P
removal by EBPR
Trickling
 -kD 


n


e  (Q/A) 
filter treatment prior to
activated sludge in combined
S e  So
systems
QS o
TF loading (lb/d - ft 3) 
 Effluent rbCOD can be at very
AD
low concentration
 Depends on influent rbCOD
concentration and trickling
filter loading
EBPR Protocol
Evaluate
Costs
Preliminary costs only
external tankage needed
retrofit existing tanks for A2O process
recycle lines and pumps
mixers
chemical feed equipment and storage
O&M for mixing, pumping, labor
Some things not included?
site specific issues
aeration design
solids processing
Capital Cost (Sept. 2004 US$)
General Preliminary Capital Costs
Curves Used
$4,500,000
A2O Retrofit w/ External Tanks
$4,000,000
AO Retrofit w/ External Tanks
$3,500,000
AO Retrofit w/ Existing Tanks Baffled
$3,000,000
$2,500,000
$2,000,000
$1,500,000
$1,000,000
$500,000
$0
0
5
10
15
Plant Design Flow (MGD)
Figure 4.9 – Preliminary Budgetary Retrofit Capital Costs – Enhanced Biological
Phosphorus Removal
20
General Preliminary Operating Cost
Curves Used
$180,000
A2O Retrofit w/ External Tanks
O&M Cost (Sept. 2004 US$/yr)
$160,000
AO Retrofit w/ External Tanks
$140,000
AO Retrofit w/ Existing Tanks
Baffled
$120,000
$100,000
$80,000
$60,000
$40,000
$20,000
$0
0
2
4
6
8
10
12
14
16
18
Plant Design Flow (MGD)
Figure 4.10 – Preliminary Budgetary O&M Costs – Enhanced Biological
20
What if EBPR does not provide enough
P removal?

Provide chemical addition at secondary effluent
or in primary treatment

Provide additional rbCOD (volatile fatty acid) by
purchase of organics or produce VFA by on-site
fermentation
primary
AN
WPS
VFA
Fermenter
Aerobic
SC
WAS
To digester or other
Fermenter Design Assumptions

Primary clarifier solids removal


Influent TSS = 200 mg/L
65% TSS removal

Primary sludge = 3% solids

SRT = 3 days in gravity thickener fermenter

VFA production = 0.15 g VFA/g TSS applied

Elutriation returns 70% of VFA produced

Additional P removal = 1 g P/ 12 g VFA added

Sugar cost = $0.18 per lb COD
Impact of obtaining rbCOD (VFA) from on-site
primary sludge fermenter
7.0
$/lb P removed with fermenter VFA
$/lb P removed with Alum
$/lb P removed with Sugar
$ / lb P r e m ov e d
6.0
5.0
4.0
3.0
2.0
1.0
0.0
0
5
10
15
Flow, Mgal/d
20
25
Chemical Addition Only Protocol
WWT
Character.
Determine P
used in
biotreatment
Identify
dose
points
Al or Fe
Al or Fe
PC
waste
Biological
Process
SC
waste
Effect of dose point on chemical requirement
8.0
Molar Al/P ratio
7.0
6.0
Al=(Al/P)(Pr)
Final P removal
Al/P = 1.5 to 2.0
5.0
4.0
Al/P = 1.0 to 1.2
3.0
P
o
Primary
2.0
1.0
0.0
0.0
1.0
2.0
3.0
Soluble P, mg/L
4.0
5.0
Chemical Addition Only Protocol
Determine
chemical
dose
-0.4437
Molar Al/P ratio  1.75(P
)
•At dose point select effluent P
•From curve get Al/P ratio
•(Infl P- Effl P)Al/P ratio = Al dose, mg/L
•For primary step select effluent P
so that Al/P ratio ~ 1.0 M/M
•Evaluate alkalinity consumed by alum/ferric addition
•0.45 g alkalinity (as CaCO3) used per g alum
Chemical Addition Only Protocol
Determine
chemical
Sludge
produced
3 modes of sludge production
AlPO4
Precip.
3.93 g/g P
Al(OH3)
Precip.
0.23 g/g P
Increased Primary
sludge removal
%TSSr=65(0.0021*Al+1.0)
Impact of chemical addition to primary
clarification step




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

Decreases overall chemical dose
Removes more suspended solids
 % TSS removal from 65 to 90%
Removes more BOD
 % BOD removal from 35 to 65%
Removes more on non degradable VSS
More primary sludge production
Decreases load to activated sludge process
Increases capacity of activated sludge process
 More volume available for retrofit to biological
phosphorus and nitrogen removal
Chemical Addition Only Protocol
Cost Factors






.
$0.10 per lb of Alum as Al2(SO4)3 18H2O
$0.30 per lb of alkalinity as soda ash
$180 per dry ton of solids processing and
disposal
$0.08 per kilowatt-hr
Labor at $20/hour
Present worth at 20 years and 5% interest
rate
Capital Cost (Sept. 2004 US$)
Capital cost for chemical feeding
$360,000
$330,000
$300,000
$270,000
$240,000
$210,000
$180,000
$150,000
$120,000
$90,000
$60,000
$30,000
$0
0
5
10
15
Plant Design Flow (MGD)
Figure 4.11 – Preliminary Budgetary Retrofit Capital Costs – Chemical Precipitation
20
Alternative Analyses at Level of Facility
Planning
Costs not included in analyses

Specific site conditions





Land availability for expansion
Layout constraints for addition of tanks and
piping
Needed improvements to existing system
Hydraulic profile limitations
Additional sludge handling and disposal
equipment
EBPR Retrofit Analysis




Add anaerobic contact tank – 1.0 hour HRT
Is nitrification required or occurrring?
 If yes, provide anoxic tank and recycle for A2O
process
 If no, use lower SRT and A/O process
Does activated sludge follow a trickling filter
 Determine if sufficient rbCOD remains after
trickling filter to allow EBPR
• If not, bypass trickling filter
• Or use chemical treatment only
Evaluate with single or two point chemical addition
Chemical Addition Retrofit Analysis

Determine possible chemical dose points

Evaluate chemical dose for different dose
point options

Determine sludge production

Determine alkalinity depletion

If nitrification system, consider alkalinity addition
to maintain system pH
Summary of P Removal Alternatives
Selection for Attached Growth Systems
System
Trickling Filter
Detroit Lakes
RBC
Brainerd
Lagoons
Redwood Falls
Thief River Falls
Selected
Alternative
Feed
BOD/P ratio
Chemical (no action)
NA
Chemical
NA
Chemical
Chemical
NA
NA
Summary of P Removal Alternative
Selection for Combined Systems
System
Selected
Alternative
Feed
BOD/P ratio
Trickling/Activated Sludge
Faribault
Marshall
Glencoe (w/ Industry)
Glencoe (w/o Industry)
Little Falls
Chemical
EBPR + Chemical
Chemical
EBPR + Chemical
Chemical
12
28
20
40
36
Summary of P Removal Alternative
Selection for Activated Sludge Systems
Selected
Alternative
Feed
BOD/P ratio
Conventional
Alexandria Lake
New Ulm
Chemical
EBPR + Chemical
27
23
Grand Rapids
Nutrient limited
>100
BNR
St. Cloud
Fergus Falls**
EBPR + Chemical
EBPR
23
26
System
** - demonstrated and proven for P < 1.0
mg/L
Summary of P Removal Alternative
Selection for Activated Sludge Systems
System
Oxidation Ditch
Wadena
Whitewater River
High Purity Oxygen
Moorhead
Rochester**
Selected
Alternative
Feed
BOD/P ratio
Chemical
EBPR + Chemical
22
46
EBPR
Chemical
32
30
** - demonstrated and proven for P < 1.0
mg/L
Major Factors Effecting EBPR Selection








EBPR higher capital – lower operating costs
Influent wastewater Characteristics
 BOD/P ratio and soluble BOD fraction (rbCOD)
Aeration tank configuration that is easily retrofitted for
anaerobic tank addition and anoxic tanks by baffles
Less sludge production with EBPR
Recycle flows from digesters or anaerobic unit processes less
favorable for EBPR
Sludge processing and disposal methods
 Sludge holding and land application with minimal recycle
good for EBPR
 Aerobic thickening processes
Chemical treatment easier to implement and quicker
Most EBPR applications also require chemical equipment and
addition