solving a winter-time phosphate removal problem

Examples of Work (1) Problem Solving

PCBWORKS

This presentation highlights work done as Tertiary Plant Team Chemist at the APS

Water Reclamation Facility at Palo Verde(examples contain no real plant data; values left out or altered)

. . . .

•The Water Reclamation Facility

provides water for the Palo Verde Nuclear

Generating Station– domestic & ultra pure water made from site

deep-well water– ‘process’ water made from City of Phoenix

sewage treatment effluent at Tertiary Plant

Goals

Major tasks as tertiary plant team chemist: – 1) Improve sludge acid digestions – 2) Explain phosphate removal problems – 3) Systematize chemical additions

Problem (1)

Acid digests of plant solids contained a gel that could not be removed. Such a gel could interfere with analyses.

•(FYI) Solids in 1st Stage Clarifier

Reaction zone solids (RZ)

Recycle solids / sludge(SL)

Effluentflow

slakedlime

influent effluent

Launderers gather effluent

Sludge outudge out

rake

Slaked

lime

Launderers gather effluent

influent

effluent

Approach

• Ran tests, consulted with chemists, lab techs• Did a literature search of digestion methods• Wrote program ‘Dgstcalc’ to do calculations

Scope

• Ran 22 digestions in 7 months • Accounted for up to 99% of plant sludge

Mechanics of DGSTCALC

• Input: sample mass/volume, ions • Output: assumed compounds, groups, ions

• Feedback/ QA: standard deviation, spike%, blank, digestion & analysis replicates, separations checks

Example: DGSTCALC OutputREACTION ZONE SUSPENDED SOLIDS DIGEST

Sample: FC3SL Temp: 22.00Date: 1/30 Type: grabTime: 08:00 Analysis: "limestone analysis"

average mass % rel std dev blank % rep(1)% rep(2)% spike %(assumed species)CaCO3 xxxxxxx 62.83 3.58 0.01 5.88 3.09 103.00Mg(OH)2 xxxxxxx 19.86 0.52 0.01 1.64 0.90 100.00SiO2 xxxxx 5.25 13.08 0.52 26.16 13.08

(ions)PO4 xxxx 3.85 0.87 0.00 3.15 1.55 101.00Fe xxxx 0.11 0.43 0.64 3.13 0.67 102.00SO4 xxxx 0.77 2.07 0.00 1.47 4.19 103.00

GROUPINGS ppm % QA ppm %TSS xxxxxx Cmpds xxxxxxx 87.85volatiles xxxxxx 12.36 Ions xxxxxxx 4.73Ca/Mg 1.84 Na Check 3.30Ca+Mg 82.68 SiO2 after 26.50

spike % transfer 100.72

Feedback Loops

Procedure checked four ways: – digestion by digest replicate (rep1) – analysis by analytical replicate (rep2)

– separations by Na and SiO2 checks

– matrix interference by spike recovery

Results and Benefits

• Coworker mentioned silicates often cause problems

• Found method that makes silicates acid insoluble • Filtered out silica, solving ‘gel’ problem and

ensuring better digestion numbers

Problem (2)

• The plant had had difficulty for some time (> ten years) controlling phosphate to specifications during the winter months. While many theories were advanced, what variables were involved was not known.

Approach • Worked closely with engineers, mechanics,

operators, and lab techs • Focused on entire system to include as man

many variables as possible• Did calculations, ran jar tests, used histor-ical

& current plant data & ran process tests to look at data from many points of view

•(FYI) Schematic Tertiary Plant System

Clarifier Feed Sump (FCIN)

1st Stage Clarifiers (FC1-6)

2nd Stage Clarifiers (FC7-12)

Gravity Filters

Trickling Filters (TF) (bacteria remove NH3, alkalinity,organics)

To Reservoir & Nuclear Units

Plant influent from Phoenix (WPIN)

(lime removes Ca, Mg, SiO2, PO4)

(CO2 & Soda Ash remove excess Ca)

Lines back from rest of plant

Scope

Spent >1 year gathering and analyzing data:– Trickling Filter performance– 1st Stage sludge chemical/physical characteristics

– 1st Stage effluents – Organics throughout plant

Graphing

• The following slides show different views of one graph: starting with the simplest, overall picture and adding details to expose the apparent causes of the problem . . .

Phosphates out of SpecSimplest View of Problem

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date

vario

us, s

cale

d va

lues

phosphate in effluentvolatiles

in reaction zone

volatiles in sludge recycle change in

plant solids

phosphatespec

Immediate Cause Volatiles (Organics in Suspended Solid form) in Reaction Zone

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date

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phosphate in effluent

volatiles in reaction zone

volatiles in sludge recycle

change in plant solids

timeline: high (dissolved) organics in influent

key point: organics only become a problem when they interact with plant solids to form volatiles

Showing Data Points to Evaluate Goodness of Fit

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volatiles in sludge recycle change in

plant solids

- emphasis on fit of 1/16 to 3/16 period- see next graph for view of fit of volatiles curves

Original, unsmoothed data (scaled to fit in same area of graph only)

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phosphate in effluentvolatiles in

reaction zone



What "Change in Solids" Represents

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change in plant solids(summarizes many sludge physical parameters -- plum colored lines)

12/1

4/95

1/24

/96

3/6/

96

4/18

/96

5/28

/96

12/1

4

12/2

7 1/4

1/11 1/23 1/31 2/

9

2/21 2/29 3/12 3/21 3/28 4/10 4/24 5/

1 5/9

5/16 5/28 6/

4

-10

-5

0

5

10

15

20

phosphate peak

sl volatilespeak

rzvolatilespeak

hi wpinfgorganics

rz solidstransition

true timeline

virtual (control)timelines

change in solids matrix

3D View illustrates solids matrix

Change in Solids Due to a Larger Pattern,Temperature Induced Change in Density of Water

9/8 10/28 12/17 2/5 3/26 5/15

reaction zone temperature





HYPOTHESIS

Phosphate removal problems caused by interaction of organics with plant solids to form volatiles during temperature induced change in density.

Towards a Practical Solution

• Substituting individual clarifier effluent data for average clarifer effluent phosphate shows that all clarifiers did not react the same way

Individual Clarifier Effluent Phosphates

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key point: clarifier 3 adjusted to volatiles more quickly than other clarifiers

clarifier 3 phosphate

What made clarifier 3 different?

– 1) on recal lime feed rather than purchased, pebble lime

– 2) higher viscosity of recycled solids– 3) higher cycling (ratio recycle to reaction zone

solids)

Clarifier 3 Compared to other Clarifiers

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date

vario

us, s

caled

value

s

clarifier 3 cycling and viscosity

other clarifiers improved when they began to 'look more like' 3

average of all clarifiers(including 3)

TESTING

• With the aid of plant operators, a number of “process tests” were run to determine if other clarifiers could be made to “look like” clarifier 3

Testing on Clarifier 4 (Also on recal lime)

6/24 7/14 8/3 8/23 9/12 10/2 10/22

date

process test run by plant operator: 9/13

X



QUALIFICATIONS

• tests were not run during the winter season • other tests run on clarifiers on pebble lime

were not so successful • “process tests” are tests without real

controls, still . . .

Solution and Benefits

• The results suggest that solids control is the key to phosphate control in winter

• My friends at Palo Verde assure me that they no longer have a winter phosphate problem

• Benefit: extending the life of Nuclear Power Plant water systems $$$$$$$$$$$

•Problem (3)

• Chemical additions were determined largely by effluent quality.

Approach

• Focused on head of plant to eliminate variables, but later included rest of plant for completeness

• Wrote program, FC_Chem, to do calculations

Scope

• Ran program 67 times over 6 months• Accounts for up to 95% of 1st stage solids

Mechanics of FC_CHEM

• Inputs:• plant flows and chemical additions• lab data: influent, jar test, clarifier effluents

• Outputs:• lime demand, CO2 & soda ash demand• excess calcium, free carbonate & total solids

format: INPUT/analysis INPUT/computer/data STUFFED NUMBERdate: (hypothetical example)

PLANT FLOWS LIME ADDITION

flow:kgpm 60 LIME CONCENTRATION pumpstroke (count)time: 1 min A- mls 4.4 sta A 0.22 8vol/liters 227 B- mls 4 sta B 0.24 8

C- mls 4.3 sta C 0.29 9clarifier flows sta D 0.29 9fc1 10 normality 1.0123 sta E 0.27 10fc2 10 sta F 0.55 18fc3 10 A- spg 1.1100fc4 10 B- spg 1.1100 variance 0.1fc5 10 C- spg 1.1200fc6 10

FINFG/C LDT FC1EFF FC2EFF FC3EFF FC4EFF FC5EFF FC6EFF

pH xxx xxx xxx xxx xxx xxx xxx xxxp-alk/CaCO3 xxx xxx xxx xxx xxx xxx xxx xxxm-alk/CaCO3 xxx xxx xxx xxx xxx xxx xxx xxxPO4 xxx xxx xxx xxx xxx xxx xxx xxxMg as CaCO3 xxx xxx xxx xxx xxx xxx xxx xxxSiO2 xxx xxx xxx xxx xxx xxx xxx xxxCaCO3 xxx xxx xxx xxx xxx xxx xxx xxxNH3 xxx xxx xxx xxx xxx xxx xxx xxxTIC xxx xxx xxx xxx xxx xxx xxx xxxTOC xxx xxx xxx xxx xxx xxx xxx xxxTSS(rz) xxx xxx xxx xxx xxx xxx xxx xxx

Example: FC_Chem Output LIME DEMAND format: mg/l as CaCO3

Calculated-Influent Values & Chem Eqns. calc. 675

Lime Demand Titration calc. 666analysis 685

Lime Demand on Clarifiers calc analysisclarifier 1 698 667clarifier 2 700 650clarifier 3 705 668clarifier 4 668 705clarifier 5 650 700clarifier 6 667 698

average 681 681

Report Format

• Results calculated using: – influent data – jar test data – clarifier data

• Lab data presented with calculations

Feedback Loops

• Calculational methods may be compared for insights into system

• Lab analysis confirms calculated value (and vice versa) or signals need to investigate

Benefits

• Uses systems approach • Makes fine-tuning easier• Potential for huge chemical savings $$$$$$

$$$$$$$$$$$$$$$$$$$$$$$$$$$

Accomplishments

When I left APS after 3 years as Tertiary Team Chemist, I had – 1) achieved clean digestions – 2) resolved phosphate problem– 3) systematized plant chemical additions

Thank You!

• Thank you for viewing my presentation• Thanks to the members of WRF Tertiary

Treatment Team for their invaluable help and to APS for a wonderful job

Peter Charles Bierly

solving a winter-time phosphate removal problem

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