Water Treatment
What this domain tests
Maryland's Water Treatment domain tests process control across the treatment train: coagulation, flocculation, sedimentation, filtration, disinfection, and residuals. Expect calculations and operating judgments, not just definitions. Maryland systems range from large surface-water plants using conventional treatment to small groundwater systems using disinfection and sequestration, so know which rules apply to your plant type.
Core rules and concepts
- Multiple barriers: source protection, treatment, and distribution integrity all count. A perfect filter does not excuse a contaminated source or a dead-end main.
- Coagulation and flocculation: coagulant dose and pH drive particle destabilization. Use jar tests to set dose and confirm optimum pH; gentle flocculation must not shear floc.
- Filtration: conventional filtration must produce finished water turbidity of 0.3 NTU or less in at least 95% of monthly samples, and never exceed 1 NTU. Individual filter effluent limits and filter-to-waste decisions are operational tools, not paperwork.
- Disinfection: CT is residual concentration (mg/L) times contact time (minutes), using T10, not theoretical detention time. Required CT rises as temperature falls and, for free chlorine, as pH rises.
- Surface water rules: the Surface Water Treatment Rule requires 3-log Giardia and 4-log virus inactivation; LT2 adds Cryptosporidium control. Ground Water Rule treatment applies where fecal indicators are present.
Worked example
A plant has 1.2 mg/L free chlorine residual, 40 minutes theoretical detention time, and a baffling factor of 0.6. T10 = 40 × 0.6 = 24 minutes. CT = 1.2 × 24 = 28.8 mg·min/L. If the required CT for the target inactivation is 30, the plant does not comply. Raising residual to 1.3 mg/L gives 1.3 × 24 = 31.2 and meets the requirement; adding baffling to raise T10 would also work.
Traps that cost marks
Using theoretical detention time instead of T10; ignoring pH and temperature corrections; averaging turbidity incorrectly; confusing free and total chlorine; and assuming a filter passes because the monthly average looks good.