Presentation is loading. Please wait.

Presentation is loading. Please wait.

Wastewater Treatment Plants & Bacteria: Strategies for Compliance Chlorination Chemistry; Considering Chloramines and Free Chlorine Harris County Wastewater.

Similar presentations


Presentation on theme: "Wastewater Treatment Plants & Bacteria: Strategies for Compliance Chlorination Chemistry; Considering Chloramines and Free Chlorine Harris County Wastewater."— Presentation transcript:

1 Wastewater Treatment Plants & Bacteria: Strategies for Compliance Chlorination Chemistry; Considering Chloramines and Free Chlorine Harris County Wastewater Symposium Wastewater Treatment Plants & Bacteria: Strategies for Compliance David Munn, PE April 26, 2011

2 Wastewater Treatment Plants & Bacteria: Strategies for Compliance Chlorination Chemistry; Considering Chloramines and Free Chlorine Purpose of this Section: – Explain how ammonia affects your wastewater disinfection capabilities – Provide another tool for reducing bacteria levels in wastewater effluent

3 Wastewater Treatment Plants & Bacteria: Strategies for Compliance Chlorination Chemistry; Considering Chloramines and Free Chlorine Goals of this Section: – Introduction of Basic Concepts & Chemical Compounds – Discuss the Formation of Chloramines – Disinfection Strength Comparison: Chloramines vs. Free Chlorine – How to Achieve a Free Chlorine Residual?

4 Wastewater Treatment Plants & Bacteria: Strategies for Compliance Introduction of the Cast Chlorine Compounds: – Chlorine = Cl 2 – Through Hydrolysis: Cl 2 + H 2 O ↔ HOCl + H + + Cl - HOCl ↔ H + + OCl - – Hyprochlorous acid = HOCl – Hypochlorite ion = OCl -

5 Wastewater Treatment Plants & Bacteria: Strategies for Compliance Introduction of the Cast Ammonia Compounds: – Ammonia = NH 3 Often referenced as ammonia-nitrogen = NH 3 -N Typical wastewater concentration: mg/l NH 3 -N – Chloramine Compounds: Monochloramine = NH 2 Cl Dichloramine = NHCl 2 Tri-chloramine = NCl 3 (aka nitrogen tri-chloride)

6 Wastewater Treatment Plants & Bacteria: Strategies for Compliance Is My WWTP Forming Chloramines? Typical Influent Ammonia Concentration = 30 mg/l NH 3 -N Simultaneous Nitrification / Denitrification > 90% removal 3.0 mg NH 3 -N requires 27 mg/l Cl 2 to achieve breakpoint Lower NH 3 -N concentrations at WWTP outfall is a result of NH 3 -N oxidation by Cl 2

7 Wastewater Treatment Plants & Bacteria: Strategies for Compliance Disinfection Performance Comparison: Free Chlorine vs. Chloramines

8 Wastewater Treatment Plants & Bacteria: Strategies for Compliance Disinfection Performance Comparison: Free Chlorine vs. Chloramines

9 Wastewater Treatment Plants & Bacteria: Strategies for Compliance How to Achieve Free Chlorine

10 Wastewater Treatment Plants & Bacteria: Strategies for Compliance Steps to Free Chlorine Step 1 – Competing Reactions – Organics, Fe 2+, Mn 2+, and H 2 S – Result = No Chlorine Residual, No Disinfection Capability

11 Wastewater Treatment Plants & Bacteria: Strategies for Compliance Steps to Free Chlorine Step 2 – Formation of Mono-chloramine – NH 3 + HOCl → NH 2 Cl (monochloramine) + H 2 – Result = Increasing Chlorine Residual, Weak Disinfection Capability

12 Wastewater Treatment Plants & Bacteria: Strategies for Compliance Steps to Free Chlorine Step 2 – Formation of Mono-chloramine – Theoretical Weight Ratio: 71 mg Cl 2 to 14 mg N = 5.1:1 – “Realworld” Weight Ratio: ≈ 6.5:1

13 Wastewater Treatment Plants & Bacteria: Strategies for Compliance Steps to Free Chlorine Step 3 – Formation of Di- and Tri-chloramines – NH 2 Cl + HOCl → NHCl 2 (dichloramine) + H 2 O – NHCl 2 + HOCl → NCl 3 (nitrogen tri-chloride ) + H 2 O – Result = Lower Chlorine Residual, Lower Disinfection Capability

14 Wastewater Treatment Plants & Bacteria: Strategies for Compliance Steps to Free Chlorine Step 4 – Breakpoint – Result= Oxidation of all ammonia and competing substances

15 Wastewater Treatment Plants & Bacteria: Strategies for Compliance Steps to Free Chlorine Step 5 – Formation of Free Chlorine – Result = Begin to Form Free Chlorine; Much Stronger Disinfection Capability

16 Wastewater Treatment Plants & Bacteria: Strategies for Compliance How Much Chlorine is Required? Reaction Review: – NH HOCl → NH 2 Cl + H 2 O + H + – NH 2 Cl + HOCl → NHCl 2 + H 2 O – 0.5NHCl H 2 O → NOH + H + + Cl - – 0.5NHCl NOH → 0.5 N HOCl + 0.5H Cl - Summary of Reactions: NH HOCL → 0.5 N H 2 O H Cl -

17 Wastewater Treatment Plants & Bacteria: Strategies for Compliance How Much Chlorine is Required? NH HOCL → 0.5 N H 2 O H Cl - Express ammonia as N; Express Chlorine as CL 2 Theoretical Weight Ratio = 7.6 mg Cl 2 to 1 mg N “Real World” Weight Ratio = 8:1 to 10:1

18 Wastewater Treatment Plants & Bacteria: Strategies for Compliance City of Munnsville Example Munnsville WWTP – Flow = 1.0 MGD – Influent Ammonia = 30 mg/l NH 3 -N – Biological Nitrification/Denitrification Capability= 95% NH 3 -N removal – Chlorination injection rate = 8 mg/l What is primary chlorine compound?

19 Wastewater Treatment Plants & Bacteria: Strategies for Compliance City of Munnsville Example Munnsville WWTP – Clarifier Effluent NH 3 -N Concentration = 30 mg/l * (1 – 95%) = 1.5 mg/l – Chlorine Injection Rate = 8 mg/l – Chlorine : Nitrogen Ratio = 8 mg Cl 2 / 1.5 mg N = 5.3 – 5.3:1 < 6.5:1 < 9:1

20 Wastewater Treatment Plants & Bacteria: Strategies for Compliance City of Munnsville Example 6.5:1 9:1 5.3:1

21 Wastewater Treatment Plants & Bacteria: Strategies for Compliance City of Munnsville Example Munnsville WWTP – Break-point Chlorination Strategy: Flow = 1.0 MGD Influent Ammonia = 30 mg/l Biological Nitrification/Denitrification Capability= 97% NH 3 removal Chlorination injection rate = 9.5 mg/l

22 Wastewater Treatment Plants & Bacteria: Strategies for Compliance City of Munnsville Example Munnsville WWTP – Clarifier Effluent NH 3 Concentration = 30 mg/l * (1 – 97%) = 0.9 mg/l N – Chlorine Injection Rate = 9.5 mg/l Cl 2 – Chlorine : Ammonia Ratio = 9.5 mg Cl 2 / 0.9 mg N = 10.6 – 6.5:1 < 9:1 < 10.6:1

23 Wastewater Treatment Plants & Bacteria: Strategies for Compliance City of Munnsville Example 6.5:1 9:1 10.6

24 Wastewater Treatment Plants & Bacteria: Strategies for Compliance City of Munnsville Example Munnsville WWTP – What is Free Chlorine Residual: – Free Chlorine = 1.4 mg/l Cl 2

25 Wastewater Treatment Plants & Bacteria: Strategies for Compliance Disinfection Performance Comparison: Free Chlorine vs. Chloramines

26 Wastewater Treatment Plants & Bacteria: Strategies for Compliance Disadvantages to Breakpoint Chlorination Higher chlorine usage and chemical costs Possibly higher chlorine residual in effluent Greater potential for creating disinfectant by- products


Download ppt "Wastewater Treatment Plants & Bacteria: Strategies for Compliance Chlorination Chemistry; Considering Chloramines and Free Chlorine Harris County Wastewater."

Similar presentations


Ads by Google