ABC Wastewater Treatment Class II flashcards

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

Confined space oxygen range

Acceptable entry atmosphere is 19.5 to 23.5 percent oxygen. Below 19.5 percent is oxygen deficient; above 23.5 percent is oxygen enriched and raises fire risk.

H2S warning limit

Hydrogen sulfide at 10 ppm or higher is a prohibited entry atmosphere. Above roughly 100 ppm it deadens the sense of smell, so odor cannot be trusted as a warning.

Lockout/tagout verification

After isolating all energy sources and applying a personal lock, the authorized employee must attempt startup or test the circuit to confirm a zero energy state before work begins.

Chlorine and acid mixing hazard

Mixing sodium hypochlorite with sulfuric or other acid releases chlorine gas. These chemicals must be stored and fed separately with no cross-connection between lines.

Primary clarifier overflow rate

Surface overflow rate equals flow divided by clarifier surface area, in gallons per day per square foot. Typical primary clarifier design falls near 600 to 1200 gpd per square foot.

Grit specific gravity target

Grit removal is designed around discrete inorganic particles with specific gravity near 2.65. The goal is to capture grit while returning organic, putrescible solids to the flow.

Primary sludge solids content

Primary clarifier sludge typically ranges from 3 to 7 percent solids. It is more readily digestible than secondary sludge because it is largely fresh organic matter.

Screen head loss meaning

Rising head loss across a bar screen indicates the screen is blinding with debris. Cleaning restores flow and prevents upstream flooding and grit carryover.

F/M ratio formula

Food-to-microorganism ratio equals pounds of BOD applied per day divided by pounds of MLVSS in the aeration tank. Conventional activated sludge operates near 0.2 to 0.4 per day.

Sludge volume index

SVI equals the 30-minute settled sludge volume in mL/L divided by MLSS in g/L, times 1000. Values of 100 to 150 mL/g indicate good settling.

Mean cell residence time

MCRT equals pounds of solids in the system divided by pounds of solids leaving per day in waste sludge and effluent. It is the sludge age control parameter.

Nitrification oxygen demand

Oxidizing ammonia to nitrate consumes about 4.57 mg of oxygen per mg of ammonia nitrogen and destroys roughly 7.14 mg/L of alkalinity as CaCO3 per mg/L of ammonia nitrogen.

Aeration basin dissolved oxygen

Dissolved oxygen is normally held at 1.5 to 3 mg/L. Low DO favors filamentous organisms and slows nitrification, while excessive DO wastes blower energy.

Return sludge rate purpose

Return activated sludge flow, typically 0.5 to 1.5 times influent flow, is set to keep the clarifier sludge blanket low and maintain the desired MLSS in the aeration tank.

CT disinfection concept

CT equals disinfectant residual concentration in mg/L multiplied by contact time in minutes. The product is the design basis for inactivating pathogens in the contact chamber.

Chlorine breakpoint

The breakpoint is the dose at which chlorine demand is satisfied and combined chloramines are oxidized. Beyond it, free chlorine residual rises in proportion to added dose.

HOCl versus OCl-

Free chlorine exists as hypochlorous acid and hypochlorite ion. Lower pH shifts the balance toward HOCl, which is the far stronger disinfectant form.

Dechlorination dose rule

Roughly 1 mg/L of sulfur dioxide destroys about 1 mg/L of chlorine residual. Sodium bisulfite is used similarly to protect the receiving stream from chlorine toxicity.

UV disinfection interference

UV effectiveness depends on light transmittance. Suspended solids shield organisms and iron, hardness scale, or fouling on lamp sleeves reduces the delivered dose.

Mesophilic digestion temperature

Anaerobic digesters are commonly held at 95 to 98 degrees F in the mesophilic range. Temperature stability matters more than the exact setpoint for stable gas production.

Volatile acid to alkalinity ratio

A ratio above about 0.3 signals an unstable digester heading toward souring. Healthy digesters typically run 0.1 to 0.2 with pH near 7.0.

Digester gas yield

Anaerobic digestion produces roughly 12 to 18 cubic feet of gas per pound of volatile solids destroyed, with methane content near 60 to 65 percent.

Solids capture percent

Capture equals solids in the cake divided by solids in the feed, times 100. It measures how much feed solids the dewatering device retains rather than recycles.

Gravity thickener loading rate

Thickener performance is set by solids loading rate in pounds per day per square foot. Diluting secondary sludge with water can improve thickening efficiency.

Pump affinity laws

For a centrifugal pump, flow varies with speed, head varies with the square of speed, and power varies with the cube of speed. Small speed changes move power sharply.

Cavitation cause

Cavitation is vapor bubble collapse at the impeller from insufficient net positive suction head. Causes include a clogged suction line, low wet well level, or warm fluid.

Motor current unbalance limit

Current unbalance between phases should stay under about 10 percent. Higher unbalance causes overheating, and single-phasing shows as high current on the remaining phases.

Short cycling pump damage

Pumps started and stopped too frequently overheat motors and stress seals. Level control setpoints need enough differential, or a minimum run timer, to prevent short cycling.

Filamentous bulking indicators

Bulking shows as elevated SVI, a poor settling blanket, and turbid effluent. Common causes are low DO, low F/M, nutrient deficiency, or septic influent.

Denitrification floating sludge

Nitrogen gas bubbles trapped in sludge can float clumps to the clarifier surface. It is distinguished from bulking by the clumped, gas-lifted appearance rather than a diffuse blanket.

BOD test validity

A BOD result is valid only when the sample depletes at least 2 mg/L of oxygen and leaves at least 1 mg/L residual DO after 5 days at 20 degrees C.

Flow-paced composite sampling

Flow-paced compositing ties sample volume to flow at the moment of collection. It is preferred over time-paced sampling when the goal is characterizing mass loading.