Disinfection, Safety, and Laboratory Analysis
What the candidate must know
Disinfection protects public health in both water and wastewater. Know the common disinfectants (chlorine gas, sodium hypochlorite, chloramines, UV, ozone), their advantages and hazards, and how residuals are measured. Safety topics include chemical handling, confined spaces, and personal protective equipment. Laboratory topics include sampling, proper test methods, and quality control.
Concepts to master
- Free vs. total chlorine and how to calculate combined chlorine.
- Chlorine demand and breakpoint chlorination.
- Chloramine formation and nitrification risk in distribution.
- Chemical storage and handling hazards; never mix chlorine and ammonia or acid.
- Confined space entry requirements and atmospheric testing.
- Sampling technique, chain of custody, and holding times.
- Basic lab QC: blanks, duplicates, standards.
Traps in questions
Questions often test that combined chlorine = total − free, or that chloramines are weaker disinfectants but more persistent. Safety traps include assuming a gas mask is adequate for confined spaces (it is not) or that mixing chemicals is acceptable.
Worked example / rule of thumb
Rule of thumb: if total chlorine is 1.2 mg/L and free chlorine is 0.9 mg/L, combined chlorine is 0.3 mg/L. Never enter a confined space without testing and proper procedures.