OH Water/Wastewater Operator flashcards

33 cards. Read the term and the definition here. The deck at the top of this page is optional.

CT calculation

CT is disinfectant residual concentration in mg/L multiplied by contact time in minutes. Required CT depends on disinfectant, pH, temperature, and target pathogen log inactivation.

Turbidity limit filtered water

Filtered water turbidity must be ≤0.3 NTU in at least 95% of monthly measurements and never exceed 1 NTU. Individual filter effluent must be ≤0.3 NTU in 95% of samples.

Jar test purpose

A jar test simulates coagulation and flocculation to determine optimum coagulant dose and pH by comparing settled turbidity across varying chemical doses.

Chlorine demand

Chlorine demand is the difference between applied chlorine dose and free chlorine residual after a specified contact time. It represents chlorine consumed by oxidizable substances in water.

Filter backwash expansion

Backwash must expand the filter bed at least 20% to release captured particles. Typical backwash rate is 15–20 gpm/ft² for anthracite-over-sand filters.

Lead action level

The 90th percentile lead action level is 0.015 mg/L. Exceeding it triggers corrosion control treatment, public education, and source water monitoring requirements.

Log removal credits

Conventional filtration provides 2.5-log Giardia and 2-log virus credit. Disinfection must provide the remaining credit to achieve required 3-log Giardia and 4-log virus inactivation.

Distribution chlorine residual

Minimum free chlorine residual in distribution is 0.2 mg/L; total chlorine minimum is 0.5 mg/L. Maximum residual disinfectant level is 4.0 mg/L as Cl₂.

Total coliform rule

No more than 5% of monthly samples may be total coliform-positive for systems collecting 40 or more samples. Any positive requires repeat sampling within 24 hours.

Minimum distribution pressure

Distribution systems must maintain at least 20 psi under all conditions. Normal operating pressure is typically 50–80 psi, with maximum around 100–125 psi to avoid damage.

Hydrant flow test

A hydrant flow test measures static pressure, residual pressure, and pitot pressure to calculate flow. Results determine available fire flow and system capacity.

Backflow prevention assembly

Reduced-pressure zone (RPZ) and double-check valve assemblies prevent backflow. RPZ assemblies must be tested annually by a certified tester; air gap is the most reliable method.

Water main disinfection

After repair or installation, chlorinate main to 25–50 mg/L for 24 hours or 100 mg/L for 2 hours, then flush and collect bacteriological samples before service.

Storage tank turnover

Storage tanks should turn over every 1–3 days to prevent water age and disinfectant loss. Poor turnover requires mixing or operational cycling to maintain quality.

BOD₅ calculation

BOD₅ = (initial DO − final DO) × dilution factor, where dilution factor equals (sample volume + dilution water volume) divided by sample volume.

F/M ratio

Food-to-microorganism ratio equals BOD or COD loading in lb/day divided by MLVSS in lb. Typical conventional activated sludge F/M is 0.2–0.5 day⁻¹.

Mean cell residence time

MCRT equals MLSS in aeration tank in lb divided by solids leaving the system per day in lb/day. Typical conventional activated sludge MCRT is 5–15 days.

Sludge volume index

SVI = (settled sludge volume in mL/L after 30 minutes × 1000) / MLSS in mg/L. SVI 80–150 mL/g indicates good settling; above 200 indicates filamentous bulking.

Nitrification oxygen demand

Nitrification consumes 4.57 lb O₂ per lb NH₃-N oxidized and destroys 7.14 lb alkalinity as CaCO₃ per lb NH₃-N oxidized.

Aeration tank dissolved oxygen

Maintain 1.5–3.0 mg/L dissolved oxygen in aeration tank for nitrification. Below 1.0 mg/L nitrification slows and filamentous bacteria may proliferate.

Anaerobic digester operation

Mesophilic anaerobic digestion operates at 35°C with 15–30 day detention, achieving 40–50% volatile solids reduction. Maintain pH 6.8–7.4 and volatile acid/alkalinity ratio below 0.3.

Wastewater chlorine CT

Disinfection CT is residual chlorine in mg/L multiplied by contact time in minutes. Required CT varies with pH, temperature, and target coliform reduction.

Minimum sewer slope

Minimum slope is 0.005 ft/ft for 8-inch pipe, 0.0033 ft/ft for 10-inch, and 0.0025 ft/ft for 12-inch. Manning equation determines design velocity.

Manning equation

Q = (1.486/n) A R^(2/3) S^(1/2) in English units. Manning n is 0.013 for concrete pipe and 0.009 for PVC pipe.

Self-cleaning velocity

Minimum velocity to prevent solids deposition is 2 ft/s at design flow. Maximum velocity is 10 ft/s to prevent pipe scour.

Infiltration and inflow

Infiltration is groundwater entering through pipe defects. Inflow is direct stormwater entering through connections. Both increase treatment costs and must be reduced.

Lift station cycle time

Cycle time equals wet well volume between pump-on and pump-off divided by inflow rate. Pump capacity must exceed peak inflow to prevent overflow.

Force main velocity

Minimum velocity in force mains is 2 ft/s to prevent solids deposition. Air release valves at high points and check valves at pump discharge are required.

Manhole spacing

Manholes are typically spaced 300–500 ft on straight runs. A drop manhole is required when invert difference exceeds 2 ft.

Sewer air test

Low-pressure air test pressurizes sewer to 4 psi for 5 minutes to verify tightness. Water exfiltration test uses 2 ft of head above pipe.

Confined space entry

Test atmosphere for oxygen 19.5–23.5%, flammable gas below 10% LEL, and hydrogen sulfide below 10 ppm before entry. Use forced ventilation and supplied-air respirator as needed.

Sewer design velocity

Design velocity should be at least 2 ft/s at average daily flow to keep solids moving. Velocity at peak flow should not exceed 10 ft/s to avoid scour.

Wet well pumping

Wet well storage volume must accommodate pump cycling without excessive starts. Pump capacity must exceed peak inflow, and standby pumps are required for reliability.