CWD BALDWIN PLANT NEW RESIDUALS HANDLING SYSTEM

Transcription

1 CWD BALDWIN PLANT NEW RESIDUALS HANDLING SYSTEM OTCO Water Workshop March, 2011 Frank Woyma Plant Manager Nick Pizzi Vice-President EE&T ENVIRONMENTAL ENGINEERING & TECHNOLOGY, INC.

2 Objectives Review the components and operating practices of the Baldwin WTP Review new residuals handling components at Baldwin WTP Identify some critical operating practices regarding these components Discuss the need for close operational control of Residuals Treatment as a Unit Process Take a closer look at recycle treatment options

3 Glossary SFBW Spent filter backwash water FTW Filter to waste Untreated SFBW and FTW SFBW before EQ and clarification Treated or clarified SFBW Supernatant/decant from SFBW clarifiers EQ Equalization

4 Baldwin WTP Baldwin WTP is a conventional treatment plant Source: Lake Erie Intake Tunnel: 9 foot diameter pipe, >5 miles long Plant Treatment Capacity: 130 MGD Average day: 70 MGD Alum/Polymer blend, Liquid Hypochlorite, Activated Carbon, H 2 SiF 6, Phosphoric Acid, NaOH Mixing and flocculation, sedimentation, dual-media filtration, disinfection On site clearwell capacity: 130 MG Distribution Capability: Low Service Gravity Feed from 130 MG Reservoir First High, Second High Pumping

5 Baldwin WTP Water Quality Source water ph Alkalinity mg/l Hardness mg/l Turbidity <10 ntu on average, occasional spiking to 100 ntu TOC 3 mg/l TSS 2-8 mg/l, some spikes to 150 mg/l Finished water ph Alkalinity mg/l Hardness mg/l Turbidity <0.10 ntu 99 percent of time Cl 2 residual 1.5 mg/l TTHMs ug/l, HAA ug/l

6 Typical Solids Generation With low source water ntu, solid residuals created (roughly) equally from the coagulant added plus the source water turbidity Example for a raw turbidity of 8 ntu (b value = 1.2), a 3mg/L dose of Activated Carbon, a coagulant dosage of 20 mg/l as dry-basis alum, and raw flow of 85 MGD, the pounds of solids (S) per day produced would be: S = (8.34 x 85MGD) X ((0.44 x 20mg/L) + (8ntu x 1.2) + 3mg/L)) = 15,170 pounds dry solids Of course the solids are suspended in lots of water (residuals) Facilities needed to handle those residuals

7 Main Residuals Stream Characterization SFBW and FTW Typically a high-volume lowsolids stream 0.5 % solids for SFBW Typical backwash uses 225,000 gallons Plant may wash up to 10 filters in a day FTW generates 45,000 gallons Streams are treated and sent back to head of plant Solids are mixed and thickened, then wasted Sedimentation Basin Blowdown Typically a medium-volume higher-solids stream There are 4 sed basins Basins are decanted resulting in a stream of up to 7.2 MGD % solids then come off the bottom At long cleaning intervals, as much as 600,000 + pounds of solids may accumulate in each basin between cleanings Potential impact on water quality, and on NEORSD

8 Five Residuals Streams Main residuals streams 1. FTW 2. SFBW 3. Sed. Basin cleaning (two-step process) Decant (mudvalve closed) Solids (mudvalve open) Other residuals streams 4. Overflow and leakage from Baldwin Finished Water Reservoir 5. Overflow from recycle tanks

9 Five Streams Three Fates 1. FTW 2. Untreated SFBW 3. Sed. Basin Decant 4. Sed. Basin Solids 5. Reservoir Leakage and Recycle Overflow South Control Building and Gate Houses 1. Sludge Storage Tanks then NEORSD EQ and Treatment 3. Recycle Water Storage then to Head of plant 2. Doan Brook NPDES

10 Overview of Residuals Handling During Normal Operations During Sedimentation Basin Cleaning Decant Period Blowdown Period Its Potential Effect on Operations Recycle Treatment Polymer Use Permanganate Use

11 Residuals Handling During Normal Operations (No Sed. Basin Cleaning)

12 Normal Operations (no Sed. Basin Cleaning) FTW Untreated SFBW South Control Building EQ and Treatment Recycle Water Storage

13 EQ and Treatment Untreated SFBW polymer EQ SFBW Clarifier Recycle (next slide) FTW Underflow typically routed direct to mixing chamber and controlled sewer discharge, but can be routed to sludge storage tanks if needed (see slide after the next one) Note: EQ feeds clarifier at 2000 gpm without polymer, and 4600 gpm with polymer impacts rate at which EQ empties and therefore how often filters can be washed

14 Recycle of Treated SFBW (and Treated FTW) Overflow and drainage from finished water reservoir Sodium bisulfite (dechlorination) Treated SFBW Recycle Water Tanks overflow Gatehouse #10 Discharge to Doan Creek KMnO 4 Recycle Pump Station Rapid mix Note: Recycle Rate is kept at 5% of incoming raw water flow so will impact the rate at which Recycle Tanks empty

15 Solids Storage and Controlled Sewer Discharge Normal Operations (no sed. basin cleaning) 1 Underflow from SFBW clarifier 2 or Sludge Storage Tanks (2) Mixing Chamber Sewer (NEORSD) 1 2 = direct to mixing/discharge = sludge storage Recirculation (mixing) Pumps Note: Sewer Discharge limits are shared with Nottingham Plant and so discharge must be coordinated

16 Residuals Handling During Sed. Basin Cleaning (Decant period - mudvalve closed)

17 Sed. Basin Cleaning FTW and SFBW generated during sed. basin cleaning Whether sed. basin cleaning is occurring or not, FTW and SFBW will continue to be generated FTW and SFBW can not be routed separately from decant or underflow from sed. basins during sed. basin cleaning, so wherever sed. basin cleaning residuals are sent, the FTW and untreated SFBW will be routed to the same place Sed. basin cleaning phases Decant period At the start of sed. basin cleaning for a specific basin the clear water is decanted from the top of the basin while the mud valve in the basin remains closed FTW, untreated SFBW, and decant are all routed to recycle during this period, bypassing SFBW equalization (EQ) and clarification Solids blowdown period At completion of decant period: 1) decant valves are closed, 2) mudvalve is open, and 3) all residuals (FTW, untreated SFBW, and sed. basin underflow) are routed to the sludge storage tanks, bypassing SFBW EQ and clarification Summary FTW and SFBW volumes need to be accounted for when evaluating volumes of decant sent to recycle or basin underflow sent to solids storage FTW and untreated SFBW generated during sed. basin cleaning will not be equalized or clarified

18 Sed. Basin Cleaning Decant Period Mud Valve Closed FTW Untreated SFBW Sed. Basin Decant South Control Building Recycle Water Storage

19 Recycle During Sed. Basin Decant Period Untreated SFBW + FTW Decant Overflow and drainage from finished water reservoir Recycle Water Tanks overflow Gatehouse #10 Sodium bisulfite (dechlorination) Discharge to Doan Creek Treated SFBW 1 KMnO 4 Recycle Pump Station Rapid mix 1 = no new untreated SFBW or FTW sent to EQ during decant period, but water remaining in EQ from previous periods continues to be released to SFBW clarifiers (until EQ tank empties)

20 Residuals Handling During Sed. Basin Cleaning (Decant completed mudvalve open)

21 Sed. Basin Cleaning FTW and SFBW generated during sed. basin cleaning Whether sed. basin cleaning is occurring or not, FTW and SFBW will continue to be generated (plant tries to minimize backwashes) FTW and SFBW can not be routed separately from decant or underflow from sed. basins during sed. basin cleaning, so wherever sed. basin cleaning residuals are sent, the FTW and untreated SFBW will be routed to the same place Sed. basin cleaning phases Decant period At the start of sed. basin cleaning for a specific basin the clear water is decanted from the top of the basin while the mud valve in the basin remains closed FTW, untreated SFBW, and decant are all routed to recycle during this period, bypassing SFBW equalization (EQ) and clarification Solids blowdown period At completion of decant period: 1) decant valves are closed, 2) mudvalve is open, and 3) all residuals (FTW, untreated SFBW, and sed. basin underflow) are routed to the sludge storage tanks, bypassing SFBW EQ and clarification Summary FTW and SFBW volumes need to be accounted for when evaluating volumes of decant sent to recycle or basin underflow sent to solids storage FTW and untreated SFBW generated during sed. basin cleaning will not be equalized or clarified

22 Sed. Basin Cleaning Decant Finished Mud Valve Open FTW Sludge Storage Tanks Untreated SFBW South Control Building Sed. Basin Solids

23 Solids Storage and Controlled Sewer Discharge During Cleaning of One Sed. Basin (decant finished, mud valve open) Untreated SFBW Underflow (one basin being cleaned) FTW South Control Building Sludge Storage Tanks (2) Mixing Chamber Sewer (NEORSD) Recirculation (mixing) Pumps See earlier slide

24 Recycle During Sed. Basin Underflow Period Overflow and drainage from finished water reservoir Sodium bisulfite (dechlorination) Recycle Water Tanks overflow Gatehouse #10 Discharge to Doan Creek Treated SFBW 1 KMnO 4 Recycle Pump Station Rapid mix 1 = no new untreated SFBW or FTW sent to EQ during sed. basin cleaning, but water remaining in EQ from previous periods continues to be released to SFBW clarifiers (until EQ tank empties)

25 Implications of Residuals Handling Operations on Finished Water Production (i.e., water quality and operations)

26 Inter-relationship Between Residuals Handling and Finished Water Production One Way to Look at It Production of Finished Drinking Water Residuals Handling You can choose to think of water treatment and wastewater treatment as two separate issues

27 Inter-relationship Between Residuals Handling and Finished Water Production Another Way to Look at It Production of Finished Drinking Water Residuals Handling But there are times when they impact each other and overlap

28 Inter-relationship Between Residuals Handling and Finished Water Production A More Accurate Way to Look at It Residuals Handling Clarification Disinfection Production of Finished Drinking Water Other processes Coagulation Filtration In fact, poor operations in one may impact the ability to do the other

29 Examples: Inter-relationship Between Residuals Handling and Plant Operations Basins cleaning intervals can be as short as 21 days or as long as 6 months The longer the interval, the more solids accumulation Means that sedimentation basins are being used as sludge storage basins also, and that can impact water quality and overwhelm NEORSD at discharge The shorter the interval, the more often laborers have to haul hoses and dewater the basins, and the more often SFBW goes untreated SFBW can be treated with polymer or not With polymer, there is expense and need to control feed equipment Without polymer, SBFW clarifiers have to operate more slowly, so EQ builds up and impacts the frequency at which filters can be washed Difficult operational choices have to be made

30 Residuals Handling Issues Impacting Recycle SFBW clarification rate EQ volume and frequency of backwash Decant period during sed. basin cleaning As noted previously, the untreated SFBW and FTW can not be routed separately from decant during sed. basin cleaning Therefore, decant sent to recycle tanks will include any untreated SFBW and FTW generated during this period

31 Residuals Handling Issues Impacting Recycle SFBW Clarification Rate SFBW clarification rate and EQ volume are related Higher rate, less EQ volume needed EQ tank full, higher SFBW clarification rate needed Higher SFBW clarification rate results in poorer turbidity removal Poorer turbidity removal means more solids returned in recycle (i.e., now you have to remove the particles again) SFBW clarifiers without tubes/plates and or no polymer generally should be operated <0.3 gpm/sf, if possible Polymer (correct type and dose) improves SFBW clarifier performance at all rates But use of correct polymer type and dose becomes more critical as clarification rate increases

32 Recycle Treatment

33 Treatment of Recycle Water Previously, we showed polymer and permanganate location Remember that: EQ sends untreated SFBW to clarifiers Water is dosed with polymer prior to entrance of clarifier Clarifiers send: Decant to recycle system Decant is dosed with permanganate prior to recycle Thickened sludge to sludge storage and disposal

34 Polymer Were is the new Polymer System? EQ Tank #1 and Polymer

35 Purpose of Polymer Use Polymers are used in water treatment to help settle solids prior to filtration Polymers are used to condition filters to help them ripen more efficiently Polymers are used to condition sludge for eventual disposal Can reduce the space and size of equipment needed Important when attempting to treat high volume/low solids streams Can allow for more rapid sludge treatment

36 Important Factors for Operators Amount of SFBW to be treated Dosage Time needed to treat Before and after solids percentages An understanding of the liquid/solid stream to be treated SFBW has a high volume to low solids ratio Polymer will allow rapid solids removal so that water can go back to head of plant Less loading on Doan Brook and NEORSD

37 Unit Process Polymer Feed Polymer must be activated before use. Polymer dosage will vary, but will usually be in the range of 0.05 to 0.20 mg/l The table shows how much neat polymer is needed to produce various percentages of activated polymer. Do not feed neat polymer directly to the SFBW stream. Feed neat polymer to activation chamber. Plant operators will feed the activated polymer into the SFBW stream coming into the backwash clarifiers. Polymer sp gr =1 so a ml is a mg 0.1% is 1,000 mg/l The suspension you make is typically 30% active (you must verify it s strength with supplier) Therefore dosage is calculated as 30% of the activated material you feed. (discuss) Polymer may not activate well at lower temperatures so warmed water may be necessary 70 degrees F is best Neat polymer percent Mls of neat /L At that temperature, Cationic polymers deliver a 90% efficiency, other may be as low as 60-70% efficiency, or if too cold, polymer may not activate at all

38 Type of polymer Important Choices Cationic polymers activated at proper temperature yield 90% efficiency Anionic and nonionic polymers yield perhaps 60-70% Example: anionic polymer does is 0.4 mg/l per jar test, you may need 0.6 mg/l to get good results Temperature of activation and feed water Try for 70 degrees F At lower temperatures polymer may not activate at all

39 Flow Schematic for Polymer Process Polymer Feed Backwash Clarifiers EQ Tank #1 Polymer is activated and fed into SFBW stream coming from EQ into Backwash Clarifiers Sludge to Transfer pumps Supernatant to recycle Backwash clarifiers accept treated SFBW and allow solids to settle Sludge from backwash clarifiers is pumped to sludge storage tanks by using the transfer pumps Liquid stream from backwash clarifiers goes back to recycle water tanks then to head of plant

40 Polymer Equipment Acrison model 530 AA95 Polymer Feed System Milton Roy LMI fee pump 55 gallon drums of polymer Spill containment Pallet Scale for measuring amount used

41 Where is the new Permanganate System? Permanganate Feeder Gatehouse #8 Permanganate

42 Purpose of Permanganate Use Control Tastes and Odors Remove color Control biological growth in treatment plants Remove iron and manganese Control the formation of THMs and other DBPs by oxidizing precursors Reduce the demand for other oxidants

43 Important Factors for Operators Flow (or volume) to be treated (which should be 5% of raw water flow) Dosage Time or distance for a complete reaction Location in relation to other pre-treatment chemicals Chemistry of the water Temperature of the water Solubility as it relates to temperature

44 Unit Process - Permanganate Potassium Permanganate is a purplish-black powder that operators dissolve in water at 1-4% strength for feeding to the process. The permanganate day tank is 150 gallons. The table shows the amount of Potassium Permanganate powder needed to create 1, 2, 3, and 4 percent solutions of the chemical for usage. CWD will use Potassium Permanganate supplied in 330 pound drums. The drums sit on a scale so that operators can use the weight-loss method for accurate solution strength. The SOP recommends a 2% strength for permanganate as it is less soluble in colder water. 2% is 20,000 mg/l. Solution Percent 1% 2% 3% 4% lb lb/gal lb lb/gal lb lb/gal lb lb/gal At that dilution, a permanganate solution is close to the density of water.

45 Example Permanganate Dosage If the recycle flow to the head of the plant is 4 MGD. The operator makes a stock solution of 2% permanganate and feeds 20 gallons over a period of 6 hours. What is the dosage in mg/l? Step 1: figure the pounds per MG added 20 gals X pounds/gal = 3.34 pounds fed 4 MGD X 1day/24 hours X 6 hours = 0.99 MG treated 3.34 pounds / 0.99 MG = 3.37 pounds / MG Step 2: figure the dosage in mg/l 3.37 pound/mg / 8.34 = 0.40 mg/l Fed

46 Flow Schematic and Flow Quantities To 60 inch Raw Water Main (Head of plant) Meter Vault Gate House No. 8 From Recycle Water Tanks And Pumps Flow from Recycle Water Tanks goes through a meter vault on to Gatehouse #8 Flow is treated with Potassium Permanganate Flow is kept to 5% of instantaneous Raw Water flow Flow goes back to head of plant

47 Permanganate Equipment Spill containment pallet Weigh scale for one drum Two eductor pumps (one for use and one spare) 150 gallon HDPE mix tank 1 Lightnin model X5P25 mixer 2 Milton Roy metering pumps

48 Questions? Acknowledgements Richard Brown, P.E., EE&T Damon Roth, P.E., EE&T