Water treatment
Water treatment is the largest technical domain on the Maine operator exam. Questions test your ability to run a conventional or alternative treatment train and to prove disinfection performance with numbers, not opinions. Expect coagulation, flocculation, sedimentation, filtration, disinfection, corrosion control, and basic process math.
Core rules
- Coagulation destabilizes particles; flocculation gently mixes to build floc; sedimentation removes settleable floc; filtration polishes; disinfection inactivates pathogens.
- For conventional filtration under the Surface Water Treatment Rule, combined filter effluent turbidity must be ≤0.30 NTU in at least 95% of monthly measurements and never exceed 1 NTU. Individual filter effluent limits and filter-to-waste rules also apply.
- Disinfection credit uses CT = disinfectant residual (mg/L) × T10 contact time (min). T10 is the time for 10% of a tracer to pass through, not the theoretical tank volume divided by flow.
- Required CT depends on disinfectant, target organism, temperature, pH, and log inactivation. Colder water and higher pH usually require more CT for free chlorine.
- Corrosion control: adjust pH, alkalinity, or add inhibitor so lead and copper action levels are met at the tap.
Worked example: CT
A clearwell has T10 = 30 min at peak flow. Free chlorine residual is 1.0 mg/L, baffling factor is 0.5, and the required CT for 3-log Giardia at 10°C, pH 7.0 is about 12 mg·min/L. Effective contact time = 30 × 0.5 = 15 min. CT = 1.0 × 15 = 15 mg·min/L. 15 ≥ 12, so the system meets the required CT, but only if peak flow and residual are maintained.
Traps
Using dose instead of residual; using theoretical detention time instead of T10; forgetting the baffling factor; mixing °C and °F in CT tables; reporting a single turbidity result as monthly compliance; assuming a higher chlorine dose always means more CT.