plant optimization at north table mountain water and sanitation district presented by: rick jeschke...
TRANSCRIPT
PLANT OPTIMIZATION AT NORTH TABLE MOUNTAIN WATER AND
SANITATION DISTRICT
Presented By:
Rick Jeschke P.E.
District Engineer/Manager
NTMW&SD Background
District formed in November 1958 Publicly owned Run by an elected 5 member Board 3200 service connections Serves a population > 10,000
NTMW&SD Water Plant
Originally constructed in 1962 Major upgrades
• 1985 pump station• 1986 new filters• 1997 Actiflo ballasted floc system• 1999 MIOX chlorination system• 2001 new filters
NTMW&SD Water Plant
Surface water plant Plant rated at 15 MGD Yearly output 650 to 700 MG Actiflo ballasted floc treatment MIOX on-site chlorination system 8 multi media filters
Stage 1 D/DBP Requirements
Prompted by the EPA December 1998 TTHM MCL was set at 0.080 mg/L HAA5 MCL was set at 0.060 mg/L Chlorite MCL was set at 1.0 mg/L Bromate MCL was set at 0.010 mg/L Systems with a population over 10,000 had
to be in compliance by January 1, 2004
NTMW&SD DBP
In 1997 NTMW&SD average DBP were• TTHM 0.063 mg/L• HAA5’s 0.0404 mg/L• Chlorite and Bromate were below DL
The District felt that these values were to close to the MCL so plant upgrades were proposed
DBP Treatment Methods
Oxidation• Ozone• Chlorine dioxide• UV
Aeration Activated carbon Synthetic resins Remove precursors
Actiflo Ballasted Floc Process
Coagulated with alum Microsand and polymer are added next Destabilized suspended solids bind to the
microsand through polymer bridges Maturation to form micro sand ballasted
floc Sludge/microsand sent to hydrocyclones to
separate the microsand from the sludge
NTMW&SD Actiflo Plant
Construction started Sept. 1997 Online May 1998 Two 7.5 MGD trains Each train 19 feet by 48 feet Total max detention time 21 minutes Total max settling time 10 minutes Designed for 24 GPM/ft squared
Actiflo TTHM Reduction
Pre Actiflo TTHM levels 0.063 mg/L Post Actiflo TTHM levels 0.041 mg/L TTHM levels reduced by 35%
Actiflo HAA5 Reduction
Pre Actiflo HAA5 levels 0.040 mg/L Post Actiflo HAA5 levels 0.028 mg/L HAA5’s levels reduced by 31%
Actiflo Microscopic Particulate Analysis (MPA) Reduction
Pre Actiflo 3 to 4 log removal Post Actiflo 4 to 5.5 log removal before
filtration Post Actiflo 6 to 6.7 log removal after
filtration
Clarified Turbidity
June
July
Aug
Sep
t
Oc
tN
ov
Dec Ja
n
Feb
Ma
rch
Apr
il
Ma
yMONTH
0
1
2
3
4
5
6
7
NTU
CONVENTIONAL
ACTIFLO
CLARIFIED NTU
Filtered Turbidity
JuneJuly
AugSept
OctNov
DecJan
FebMarch
AprilMay
MONTH
0.04
0.05
0.06
0.07
0.08
0.09
NTU
CONVENTIONAL
ACTIFLO
FILTERED NTU
Standard Plate Count (SPC)
Raw water SPC are 5/mL to 200/mL Clarified SPC are 2/mL to 16/mL Recycling sand not contributing to SPC
Sand Carryover
During initial startup some sand carry over was observed
After three days no sand carry over was observed
Sand carryover filtered out easily
Sand Consumption
Hydrocyclones are not 100% efficient Sand loss is approximately 4 pounds per
million gallons produced Equates to $0.40/MG Sand purchased 12 tons at a time Sand costs $0.10/pound delivered
Sand Abrasion
Online since May 1998 Six years of operation No wear on SS pipe No wear on hydrocyclones After six years lead pump liners were
replaced
MIOX at NTMW&SD
Before MIOX the District used chlorine gas Safety was the main factor in the decision to
go to on-site generation. On-site generation eliminated the storage
space for bleach On-site generation meant that the chlorine
would only be made when needed (with the system fully automated)
MIOX On-Site Chlorine Production Electrolysis of salt water to
generate chlorine practiced commercially for > 100 years
Chlorine produced at large chlor-alkali plants, packaged, and sold Chlorine gas cylinders Sodium hypochlorite drums Calcium hypochlorite tablets
Within past 30 years, developed smaller equipment to generate sodium hypochlorite on-site by same process
On-site generation uses only salt, water, and electricity Eliminates hazardous chemicals Heart of technology is the electrolytic cell
How the Cell Works Brine -- NaCl dissolved in H2O Positive ions are drawn to the
cathode; negative ions are drawn to the anode
Apply power Possible electrolytic reactions
Anode:
2 Cl- ==> Cl2 + 2e-
HOCl + H2O ==> ClO2 + 3H+ + 3e-
2H2O ==> O2 + 4H+ + 4e-
O2 + H2O ==> O3 + 2H+ + 2e-
Cathode:
2H2O + 2e- ==> H2 + 2OH-
Hydrolysis in Bulk:
Cl2 + H2O ==> HOCl + Cl- + H+
On-Site Chlorine Generation Advantages
Safety• No hazardous chemicals used, generated
stored, or transported• Chlorine concentration approx. 0.37-0.40%• No potential for chlorine leak• No possibility of forming chlorine gas
cloud by mixing with water• No combustible combinations
On-Site Generation Advantages (continued)
Regulatory Ease• No RMP• No HAZMAT training• No SCBA equipment• No “two man rule” for changing out cylinders• No chlorine scrubber, as required by Uniform
Fire Code• No DOT trucking requirements• No corrosion due to chlorine off-gassing
On-Site Generation Advantages (continued)
Cost Savings• Operating costs depend on cost of salt and
power• Cost of power offset by not purchasing chlorine• Lower than bleach or calcium hypochlorite
• Lower than ozone, UV, or ClO2
• Lower liability
On-Site Generation Advantages (continued)
Freshness and Consistency of Solution• Generated on-site as need• Shelf-life is a non-issue• No need to change dilution or mixing ratios• No degradation to chlorite or chlorate on shelf
MIOX at NTMW&SD
Three 50 pound per day cells One 100 pound per day cell Bulk salt storage Storage capacity of up to 600 gallons of
MIOX solution
MIOX TTHM Reduction
With the Actiflo system reducing the TTHM by 35%, no further improvement was expected using MIOX
Pre-MIOX TTHM levels 0.041 mg/L Post-MIOX TTHM levels 0.023 mg/L TTHM levels reduced by 44%
MIOX HAA5’s Reduction
With the Actiflo system reducing the HAA5’s by 35%, no further improvement was expected using MIOX
Pre-MIOX HAA5 levels 0.028 mg/L Post-MIOX HAA5 levels 0.016 mg/L HAA5’s levels reduced by 43%
NTMW&SD Chlorine Dosage
District policy is to maintain a minimum 0.4 mg/L residual in the distribution system
Pre-MIOX residual leaving the plant was 1.1 mg/L
Post-MIOX residual leaving the plant 0.8 mg/L
Chlorine dosage reduced by 27%
NTMW&SD Lime Dosage
MIOX is near pH neutral Chlorine gas has a low pH Post-MIOX the lime dosage reduced by
50%
MIOX System Maintenance
Amps and volts checked daily Pressure at cell checked daily Combined chlorine concentration checked
daily Individual MIOX cell concentration
checked monthly Hardness checked weekly
MIOX System Maintenance (continued)
Orifices are checked for blockages weekly Flows through the cells are checked twice
per month Cartridges Filters are changed out twice per
year
MIOX Cell Acid Cleaning
MIOX cells are acid cleaned twice per year Cleaned with a 50/50 HCl solution Allowed to sit for 15 minutes Rinsed with softened water Entire process takes approximately 1 hour
Miscellaneous MIOX Information
Important to buy highest quality salt Salt received in 25 ton bulk shipments 25 tons of salt costs $1,600 including
delivery MIOX provided a list of recommended
spare parts
Total TTHM Reduction
Pre-Actiflo and pre-MIOX TTHM levels 0.063 mg/L
Post-Actiflo and post-MIOX TTHM levels 0.023 mg/L
TTHM levels reduced by 63% in total
Total HAA5 Reduction
Pre-Actiflo and pre-MIOX HAA5 levels 0.040 mg/L
Post-Actiflo and post-MIOX HAA5 levels 0.016 mg/L
HAA5 levels reduced by 60% in total