6.3 Taste and Odor Control & Aeration

6.3 Taste and Odor Control & Aeration

Quick Answer: Identify whether the off-flavor is volatile (H2S, some VOCs—strip with aeration), algal (geosmin/MIB—adsorb with PAC/GAC and/or oxidize), or distribution-related—then apply the matching barrier. FDEP Class C explicitly lists both Aeration and Taste and Odor Control.

Customers judge water quality with their senses long before they read a Consumer Confidence Report. Taste and odor (T&O) complaints drive phone calls, trust loss, and sometimes unnecessary boiling or bottled-water switches. Florida systems see both groundwater odors (sulfur/H2S, metallic) and surface-water or reservoir odors (musty, earthy, fishy from algae). This section ties aeration equipment to T&O strategy so you can answer Class C items that name either subject.

Causes of Taste and Odor

Geosmin and MIB

Geosmin and 2-methylisoborneol (MIB) are produced by certain cyanobacteria and actinomycetes. Humans detect them at ng/L levels—far below many analytical reporting habits of older labs. They are not efficiently removed by simple aeration because they are not highly volatile like H2S. Plants rely on:

• Watershed/reservoir management to limit blooms
• Powdered activated carbon (PAC) dosed at the plant during events
• Granular activated carbon (GAC) contactors or GAC filter caps for ongoing control
• Selected oxidants (effectiveness varies; ozone can help; free chlorine is often weak against geosmin/MIB at practical doses)

Hydrogen sulfide

H2S is common in Florida groundwater. It causes rotten-egg odor at very low concentrations and can:

• Demand chlorine (forming sulfur solids and consuming residual)
• Corrode metals and contribute to black water with iron
• Trigger immediate customer complaints even when bacteriological samples are perfect

Aeration strips H2S to the atmosphere (with odor control on the air stream as required). Chemical oxidation converts sulfide to sulfur or sulfate depending on dose and pH.

Aeration: Types and Exam Points

Aeration contacts water with air to:

1. Strip dissolved gases (CO2, H2S, some VOCs, radon in some designs)
2. Add dissolved oxygen for iron oxidation and to freshen flat-tasting water
3. Sometimes assist in mixing before chemical reaction

Design/operation concepts (no calculator required for most MCQs)

• Air-to-water ratio and contact time drive stripping efficiency.
• pH affects H2S speciation: more H2S gas form at lower pH aids stripping; higher pH favors HS− (less stripable).
• Fouled packing or trays cut efficiency—inspect and clean on a schedule.
• Off-gas may need treatment so neighbors do not smell what you stripped from the water.
• After aeration, water may need pH adjustment (CO2 removal raises pH) and disinfection residual restoration if gases or detention changed chlorine demand.

Aeration is listed as its own Class C subject—expect questions that name cascade vs packed tower vs diffused systems and the purpose of each (strip vs oxygenate).

Oxidation for Taste and Odor

Oxidants attack reduced sulfur, some organic T&O compounds, and color:

Oxidation alone does not fix every musty event—adsorption is often required for geosmin/MIB.

PAC and GAC

Powdered activated carbon (PAC)

• Dosed as a slurry during T&O events or continuously at low rates
• Needs contact time before sedimentation/filtration removes the spent carbon
• Dose increases with geosmin/MIB concentration and competing TOC
• Early addition (before coagulant) vs later addition is a plant-specific optimization—exams stress that PAC must be removed by clarification/filtration and that under-dosing fails during blooms

Granular activated carbon (GAC)

• Contactors or GAC-capped filters provide ongoing adsorption
• Capacity exhausts; monitor breakthrough of target compounds or surrogates
• Reactivation/replacement is a major O&M cost
• Can also support biological activity that helps some biodegradable T&O compounds after ozonation (advanced trains)

Copper Sulfate and Algaecide Caution

Copper sulfate and other algaecides are sometimes applied to reservoirs to suppress algae that produce geosmin/MIB or cause filter clogging. Exam-level cautions:

• Follow label, permit, and environmental constraints—copper is toxic to many aquatic organisms
• Killing a bloom can release intracellular metabolites and temporarily worsen T&O
• Dead biomass increases chlorine demand and DBP precursors
• Prefer integrated reservoir management (nutrient control, destratification, intake depth selection) over repeated copper as the only tool
• Drinking-water plants must still treat whatever metabolites reach the intake

Algaecide is not a substitute for plant-side PAC/GAC readiness during Florida’s warm, productive surface-water seasons.

Customer Complaint Response

Professional T&O response is a process, not a shrug:

1. Log the complaint: location, time, descriptors (rotten egg, musty, metallic, petroleum), hot vs cold water, first draw vs flushed.
2. Map the pattern: one street (distribution) vs system-wide (source/plant) vs single building (premise).
3. Sample and smell/taste systematically (trained staff, not random public tasting of unknown contaminants): plant finished water, distribution, customer tap after controlled flush.
4. Check plant data: raw H2S/Fe/Mn, oxidant doses, PAC feed rates, aeration performance, recent well changes, reservoir algae observations.
5. Correct the cause: adjust aeration/oxidant/carbon; repair main; flush with a plan; communicate timelines honestly.
6. Document for regulators and for the next event—T&O seasons repeat.

Do not assume every odor is “just chlorine.” Chlorinous complaints may mean true overfeed, or they may mean the customer is detecting a different compound and blaming the familiar disinfectant smell.

Florida Operating Picture

• Groundwater systems: prioritize H2S and Fe/Mn metallic tastes; aeration + oxidation/filtration is classic.
• Surface water / reservoir supplies: watch seasonal algae; keep PAC inventory and feed equipment ready before bloom season.
• Coastal RO systems: product water can taste “flat” (low TDS); remineralization and corrosion control affect mouthfeel as much as odor.
• Hurricane and flood periods: organic loading and distribution disturbances spike both true contamination risk and aesthetic complaints—pair T&O response with bacteriological vigilance.

How This Maps to the Class C Outline

FDEP’s Class C drinking-water subject list includes, among others:

• Aeration — equipment types, purposes (gas transfer, stripping, oxygenation), operation/maintenance
• Taste and Odor Control — causes (algae, H2S, organics), PAC/GAC, oxidation, source management, complaint handling
• Related neighbors: Iron and Manganese Control, Characteristics of Source Water, Reservoir and Well Field Management, Disinfection, Filtration

Study them as one storyline: source produces the compound → aeration or oxidant or carbon removes it → filters capture solids → residual disinfection does not recreate a worse odor → distribution does not recontaminate the aesthetic quality.

Integrated Control Strategy Checklist

If you can pick the right barrier for H2S versus geosmin, name three aerator types and their purpose, and walk through a complaint investigation, you have the T&O and Aeration subjects under control for the Florida water operator exams.