Presentation by Sacramento Regional WWTP engineers about $200,000 a year savings, improved Nocardia control and improved effluent quality by SRTmaster operation
1. Automating Control in
Biological Reactors for
Diurnal Loading
Joshua Nurmi, Jeremy Boyce, Mick Berklich
Sacramento Regional Wastewater Treatment Plant
2. Sacramento Regional Wastewater
Treatment Plant
•Came online in 1982 replacing 22 existing
wastewater treatment plants.
•Service area of more than 250 sq miles with
roughly 1.3 million residents.
•SRWTP treats approximately 150 MGD ADWF and
is capable of treating up to 400 MGD peak hour
flow.
•Plant effluent is discharged into the Sacramento
River.
•Largest Treatment Plant in Northern California
4. Process
Overview
High Purity Oxygen
Secondary Treatment
Plant
5. Secondary Process
• High Purity Oxygen
Facility
• Carbonaceous Oxidation
Stage 4 Stage 3 Stage 2 Stage 1
T8
T7
(CO) Tanks T6
– 8 North Tanks, 4 South
T5
T4
South CO Deck Stage 1 Stage 2 Stage 3 Stage 4
T
12
• Secondary Clarifiers North CO Deck
T
T3
11
T
T2
10
T
– 24 total clarifiers
T1
9
SOI
NOI
• On-site oxygen generation PE1 PE2
facility
6. Secondary Wasting
• RAS Classifying Selectors
• Classifying Selector draws off surface flow from the
return activated sludge (RAS) stream prior to reentering
the COTs.
• Waste activated sludge (WAS) is conveyed to the
solids handling process by a dedicated set of variable
speed pumps.
• Mixed Liquor and Secondary Scum wasting
• Mixed liquor surface foam waste and SST scum tie into
waste lines downstream of WAS pumps.
7. Activated Sludge Control
• Previous Method
• Secondary Process was previously controlled by
regulating the amount of sludge wasted each day
based on a Mean Cell Residence Time target.
• Waste set point was only adjusted once per day, diurnal
loading was not taken into consideration.
• Grab samples unable to accurately represent
secondary process.
• Solids “snap shot” of solids inventory
• Taken by different operators each shift and from
day to day
• Some samples analyzed in lab, some in the field
9. Nocardiaform Problems
• SRWTP has historically been subject to
Nocardia blooms during warmer summer
months.
• Due to the design of the CO tanks Nocardia
can become entrapped on the water surface.
• Past studies have shown that the most
effective method for controlling Nocardioform
populations at SRWTP is to increase the food
to microorganism ratio (F/M) as influent
temperature increases.
10. Nocardioform Impacts
• Digester Impacts:
• Foam on digester covers
• Trash/Debris short circuiting digestion and
sent to SSBs
• Secondary Treatment Impacts:
• Pump shutdowns
• CO Tank overflows
• Excess suspended solids in the effluent
11. Study Objective
• Phase I: TSS Analyzer Field Test
– Purpose: Determine if total suspended solids analyzers
can provide accurate data to the SRT Control software
• Phase II: SRT Control
– Purpose: Use a stream of online data to adjust the
waste activated sludge set point in real time
12. Phase I: TSS Analyzer Field Test
• Investigate following parameters:
– Maintenance: minimum cleaning
and calibration requirements.
Optimum settings for self cleaning
systems.
– Accuracy: validate the relative
accuracy of the analyzers while
operating at optimal cleaning and
calibration intervals.
– Response Time: determine how
quickly the analyzers respond to
significant concentration changes.
13. Phase I: Conclusions
• Three of the four meters tested provide
accurate data when properly cleaned and
calibrated and adequately respond to sudden
process changes.
• When cleaned/calibrated 2x week the
analyzers consistently read within +/- 100 mg/l
for MLSS and +/- 300 mg/l for RAS.
14. Phase II: SRT Control Pilot
• Objective: Employ and evaluate an SRT
Control system to automate the activated
sludge flow.
• Benefits:Under steady state conditions
controlling SRT can control F/M which can
prevent:
• High F/M ratios: poor effluent quality
• Low F/M ratios: Nocardia, increased
aeration demand per pound destroyed
15. SRT Control Setup
• Five TSS Meters
• RAS, WAS and 3 MLSS Channels
• Flowmeters (8 total)
• 6 WAS Thickeners (existing), 2 WAS lines (new)
• New FMs needed to account for ML and scum
flows.
• SRT Master
• Takes values from all the flowmeters and
suspended solids meters and calculates a waste
set point (based on an SRT set point) every 15
minutes.
16. Average Daily SRT – Previous Control Method
2.5
2
SRT (Days)
1.5
1
0.5
0
Average Daily SRT - with SRT Control
2.5
2
SRT (Days)
1.5
1
0.5
0
17. Daily BOD F/M Ratio – Previous Control Method
3.5
3
2.5
2
F/M
1.5
1
0.5
0
Daily BOD F/M Ratio – with SRT Control
3.5
3
2.5
2
F/M
1.5
1
0.5
0
24. SRT Pilot Test Conclusions
• Variability in daily average SRT and F/M
were decreased significantly.
• Intraday SRT is more stable with the
controller
• Secondary effluent quality less variable.
• Better Nocardia bloom control.
25. Lessons Learned
• Meter Problems
• All meters need to be monitored closely to ensure
that they are providing accurate data. Meter errors
(Primarily Flow) could cause the controller to over or
under calculate the wasting.
• High BOD loads
• In addition to variable diurnal loads the plant is
occasionally subject to high BOD loads. The SRT
controller does not directly measure BOD and the
high load will result in elevated F/M values.
26. Acknowledgments
• Alex Ekster, SRTMaster
• SRWTP Operations Staff
• Mike Mulkerin, SRCSD
• Glenn Bielefelt, SRCSD
• Steve Ramberg, SCRSD
30. MLSS Variability Comparison
180
160
140
120
Variability in MLSS (ppm)
100
+160 ppm
80
60
+80 ppm
40
20
0
Avg MLSS Range w/o SRT Control Avg MLSS Range w/SRT Control
Editor's Notes
Fifth largest in the state, largest inland discharger in california.
No Equalization and flow is over 80% residential – without inflow/infiltration there is significant diurnal flow fluctuations. Fairly small combined stormdrain/sewer sections from older parts of sacramento.
Briefly describe the process, mention that we’ll be primarily discussing the Carbonaceous Oxidation Tanks
Typically operate with eight tanks in service. Typically use 120 tons of oxygen per day.
This makes calculating SRT difficult because the scum flows are not accounted for at the pumps. Prior to bringing on SRT controller the scum loading was not accounted for in the waste set point.
During Nocardia Blooms samples were being drawn up through the foam layer and could not be accurate due to the foam in the samples. Waste set point would still be set based on these samples which could cause the waste set point to be too low or high.
This slide demonstrates the variations in day to day MLSS (in turn SRT and F/M) due to the single waste set point that may have been adjusted using bad data.The variability in MLSS and therefore F/M would increase Nocardia problems
Trash/debris lifts with the foam to the top at once rather than staying suspended in the digester.Digester foaming is compounded by wasting nocardia and increasing wasting to the digesters to remove nocardia from the secondary system.Foam comes through thiefholes and could result in spills/violations
Historically TSS analyzers have been inaccurate and made SRT calculations difficult. So the first phase of the study was to ensure that there were new TSS analyzers available that could send accurate data to the SRT Control Software (SRTMaster).
The picture shows typical growth over a 1 week period that would require the analyzer to be cleaned and calibrated.
It was later determined that the fourth supplied analyzer had failed and provided inaccurate data throughout the course of this phase of the study.Upon concluding phase I and determining that TSS analyzers could provide accurate data, phase II of the project was implemented.
Need both a RAS and WAS meter to account for the scum load.Due to the configuration of the North/South CO Decks TSS meters were required in all three MLSS channels.2 WAS lines allow u to calculate the differential between pump flow and total flow which represents the scum load.
Introduce Results
This is a representative day of the average diurnal turbidities before and after the SRT controller was brought online. The variability in turbidity decreased from +2 to +1.
The Pre-SRT Nocardia is the four year average prior to bringing the SRT controller online and the blue line is the first year with SRT control. Not only are we controlling the preventing the major peaks in Nocardia but also the duration of the nocardia season.
Intraday F/M is more dependent on diurnal flows and
Alex Ekster developed the SRTMaster software used during this study and provided technical support throughout.Mike Mulkerin and Steve Ramberg for there additional contributions to the study.