1. Control and Disinfection II. Optimizing Chemical Disinfections
Gerry Mackie
Water Systems Analysts
Guelph, Ontario, Canada
N1H 7B2

2. Optimizing Disinfection with Non-oxidative Chemical Control
The key is in the timing

3. Key Variables for Infestations
Biotic Variables
The mussel’s life cycle and development rate
Number of generations
Adult filtration rates
Adult body condition
Factors affecting the larval and adult densities and development rates
“Trophic variables”
Chlorophyll a
Abiotic Variables
“Chalk” variables
[Ca] pH
Alkalinity
Hardness
“Trophic” variables
[PT]
[N compounds]
Secchi depth
Conductivity
Temperature

4. Optimizing the use of chemicals
Timing the biology of the mussels to the seasonal toxicity of the control agent
Biology
Larval development rate and settlement periods
Adult filtration activity
Adult body condition
Seasonal toxicity
Using 3 molluscicides as examples
Matching (optimizing) seasonal sensitivity of larvae to seasonal toxicity of the molluscicide
Matching (optimizing) seasonal sensitivity of adults to seasonal toxicity of the molluscicide

5. Key Variables for Optimization
Biotic Variables
[Chlorophyll a] – can be estimated from Secchi depth or [PT]
Relationships between average summer Chlorophyll a levels and Secchi depth (left) and spring total phosphorous levels.
Secchi
depth m 2 4 6 8 5
Chlorophyll a ug/L 10 20 15 25 30
Summer Chlorophyll a ug/L 1
100
1000
Spring total phosphorous ug/L
0.1

6. Key Variables for Optimization
Abiotic Variables
“Chalk” variables
[Ca], probably the most reliable & widely used
Alkalinity (gives information on Ca availability)
pH (< 8.2, CaH2CO3; > 8.2, CaCO3)
Total hardness
Temporary hardness
Permanent hardness

7. Key Variables for Optimization
Abiotic Variables
“Trophic” variables
[PT] when P is limiting
[NT] when N is limiting
Secchi depth – easiest and cheapest to measure

8. Key Variables for Optimization
Abiotic Variables
Conductivity – useful for estimating other variables
[Ca mg/L] = x conductivity (μS/cm)– (r2 = 0.88, n=3950)
[(TDS) mg/L] = Conductivity µS/cm x 0.65
For waters with μS/cm
CF can vary between 0.54 and 0.96, depending on [TDS], with CF increasing from 500 – 25,000 TDS mg/L

9. Key Variables for Optimization
Abiotic Variables
Temperature
Temporal (e.g. seasonal) variations
Spatial variations
Vertical (e.g. depth)
Horizontal (e.g. Downstream)

10. Key Variables for Optimization
Of the biotic and abiotic factors, one of the easiest to monitor is:
Seasonal variations in surface temperature
Timing is key:
Determine when reproduction and larval development will occur (i.e. when temperatures are above 12-15oC)
Determine when settlement begins and ends

11. Biotic Factors – What do we monitor? Life Cycle

12. Planktonic stages: Larval development rate
Biotic factors
Planktonic stages: Larval development rate
Larval Density
No./m3 x 104 10 15 20 25
Apr
May
Jun
Jul
Aug
Sep
Oct
Nov
Dec
Jan
Time
Feb
Mar

13. Benthic stages: Adult Density
Biotic factors
Benthic stages: Adult Density
Density of New Recruits No./m2 x 103 10 15 20 25
Apr
May
Jun
Jul
Aug
Sep
Oct
Nov
Dec
Jan
Time
Feb
Mar

14. Benthic stages: Adult Body Condition
Biotic factors
Benthic stages: Adult Body Condition
Dry tissue weight (mg)
Apr
May
Jun
Jul
Aug
Sep
Oct
Nov
Dec
Jan
Time
Feb
Mar

15. Benthic stages: Adult Filtration Rate
Biotic factors
Benthic stages: Adult Filtration Rate
Filtration Rate
Ml/hr/indiv.
Apr
May
Jun
Jul
Aug
Sep
Oct
Nov
Dec
Jan
Time
Feb
Mar

16. Seasonal toxicity of some toxins
48h-LC50
(mg/L)
Molluscicide A
Apr
May
Jun
Jul
Aug
Sep
Oct
Nov
Dec
Jan
Time
Feb
Mar

17. Seasonal toxicity of some toxins
48h-LC50
(mg/L)
Apr
May
Jun
Jul
Aug
Sep
Oct
Nov
Dec
Jan
Time
Feb
Mar
Molluscicide B

18. Seasonal toxicity of some toxins
48h-LC50
(mg/L)
Apr
May
Jun
Jul
Aug
Sep
Oct
Nov
Dec
Jan
Time
Feb
Mar
Niclosamide
Ethanolamine salt
Molluscicide C

19. Seasonal susceptibility of some toxins
to toxins
Apr
May
Jun
Jul
Aug
Sep
Oct
Nov
Dec
Jan
Time
Feb
Mar
Molluscicide B
Molluscicide A
Molluscicide C

20. Optimizing disinfections for larvae
Susceptibility
to toxins
Temperature oC
Apr
May
Jun
Jul
Aug
Sep
Oct
Nov
Dec
Jan
Time
Feb
Mar
Northern temperate states
Warmer western states
Larval Density
Warm western states

21. Optimizing disinfections
Susceptibility
to toxins
Density of New Recruits
Time
Apr
May
Jun
Jul
Aug
Sep
Oct
Nov
Dec
Jan
Feb
Mar
Northern temperate zone
Warm western states

22. Optimizing disinfection wrt adult density
Susceptibility
to toxins
Temperature
Apr
May
Jun
Jul
Aug
Sep
Oct
Nov
Dec
Jan
Time
Feb
Mar
Northern temperate states
Warmer western states
Density of New Recruits
Northern temperate zone
Warm western states

23. Optimizing disinfection wrt adult body condition
Susceptibility
to toxins
Dry tissue weight
Warm western states
Northern temperate states
Temperature
Apr
May
Jun
Jul
Aug
Sep
Oct
Nov
Dec
Jan
Time
Feb
Mar
Warmer western states

24. Optimizing disinfection wrt adult filtration rate
Susceptibility
to toxins
Filtration Rate
Warm western states
Northern temperate
states
Temperature
Apr
May
Jun
Jul
Aug
Sep
Oct
Nov
Dec
Jan
Time
Feb
Mar
Northern temperate states
Warmer western states