Wastewater Treatment Operator Class I cheat sheet

A permit-required confined space has limited entry/exit, is not meant for continuous occupancy, and contains a serious hazard; entry requires a permit, entrant, attendant, and entry supervisor.

Acceptable entry atmosphere: oxygen 19.5-23.5%, flammable gas below 10% of the LEL, hydrogen sulfide below 10 ppm, carbon monoxide below 35 ppm; test before entry and continuously while inside.

Hydrogen sulfide is heavier than air, has a rotten-egg odor at low concentrations, deadens the sense of smell quickly, and is immediately dangerous to life at 100 ppm; odor is never a valid warning.

Methane has a lower explosive limit of 5% and an upper explosive limit of 15% in air; chlorine gas is about 2.5 times heavier than air and settles in low areas.

Lockout/tagout: isolate every energy source, apply personal locks and tags, release stored energy, and verify a zero-energy state before maintenance begins.

Excavations 5 ft (1.5 m) deep or more require a protective system; spoil piles and equipment are kept back at least 2 ft from the trench edge.

Mixing sodium hypochlorite with acid releases chlorine gas; adding ammonia-based chemicals to chlorine forms chloramines; never store oxidizers next to fuels or solvents.

Fall protection is required at 4 ft in general industry; ladders, guards, and grating must be maintained around tanks, clarifiers, and wet wells.

The Clean Water Act (1972) created the NPDES permit program; 40 CFR Part 122 contains the NPDES regulations and Part 123 covers state program approval.

Secondary treatment standards: 30-day average BOD5 30 mg/L and TSS 30 mg/L, 7-day average 45 mg/L for each, with pH held between 6 and 9.

Discharge Monitoring Reports (DMRs) are submitted monthly, are signed by a responsible official, and must include calculated averages, geometric means, and any violations.

40 CFR Part 503 governs sludge: ceiling and exceptional-quality pollutant limits, Class A and Class B pathogen reduction, vector attraction reduction, and management practices.

The national pretreatment program (40 CFR Part 403) requires industrial users to meet local limits and reporting through a publicly owned treatment works control authority.

Bypass, upset, and sanitary sewer overflow events must be reported to the regulatory agency within the time frame stated in the permit, usually by phone followed by written notice.

Operator certification is required by state rule; the Class I operator must complete required continuing education hours to renew.

Permit limits, monitoring points, and sampling frequencies can only be changed through a formal permit modification, not by plant decision.

Infiltration is groundwater entering through defective pipe, joints, and manholes; inflow is storm water or drainage entering through direct connections, roof leaders, and manhole covers.

Self-cleansing velocity is about 2 ft/s at design flow; velocities above roughly 10 ft/s can scour and damage pipe.

Average residential wastewater flow is commonly estimated near 100 gallons per capita per day for dry-weather design.

Diurnal peaking factor (peak hourly to average daily flow) is typically 2 to 4, and must be used when sizing pumps, wet wells, and headworks.

Slow, septic flow in flat sewers generates hydrogen sulfide, which oxidizes to sulfuric acid and corrodes the concrete crown of the pipe.

Lift station wet wells should have enough working volume between pump-on and pump-off to limit motor starts, commonly 6 to 10 starts per hour.

Area-velocity flow meters measure both depth and velocity in a pipe; weirs and flumes are used where free-surface measurement is practical.

Manholes are placed at changes in pipe size, slope, or direction and at intervals set by state design standards.

Grit accumulates at roughly 2 to 12 cubic feet per million gallons treated; screenings average about 0.5 to 2 cubic feet per million gallons.

Grit channel velocity is held near 1 ft/s so dense inorganic grit settles while lighter organic solids stay suspended and move on to the clarifiers.

A Parshall flume measures depth at one point in the upstream converging section; flow is computed from head, and free flow requires the downstream submergence ratio to stay below about 70%.

Weir flow varies with head to the 1.5 power, so small upstream depth errors cause large flow errors; the weir crest must be level and the approach channel quiet.

Conversions: 1 MGD = 1.547 cubic feet per second = 694 gallons per minute; 1 cubic foot per second = 0.646 MGD.

A rising head differential across a bar screen indicates blinding; the screen is cleaned mechanically or manually before flow backs up into the channel.

Aerated grit chambers use air to roll the flow and separate organics from grit; vortex-type units use a gentle spiral with low headloss.

Comminutors and grinders shred screenings in the flow stream, reducing handling but returning solids to downstream processes.

Detention time = basin volume divided by flow; primary clarifiers are normally designed for 1.5 to 2.5 hours at average flow.

Surface overflow rate = flow divided by surface area, typically 600 to 1,000 gpd/ft2 at average flow; it sets the settling velocity required for removal.

Weir loading rate = effluent flow divided by total weir length, typically 10,000 to 20,000 gpd/ft; high weir loading pulls solids over the weirs.

Well-operated primary clarifiers remove about 50 to 65% of influent TSS and 25 to 40% of influent BOD5.

Percent removal = [(influent - effluent) / influent] x 100; hydraulic overload shows first as a rising effluent TSS and sludge blanket.

Sludge is removed frequently enough to prevent septic conditions; a rising sludge blanket or gas bubbles indicate too long a sludge detention time.

Inlet baffles and energy dissipaters prevent short-circuiting; density currents carry flow directly to the weirs and cut actual detention time.

Scum is collected at the surface and wasted to digesters, incineration, or landfill; a failing scum trough returns grease to the effluent.

F/M = pounds of BOD5 applied per day divided by pounds of MLVSS under aeration; conventional systems run about 0.2 to 0.4, extended aeration below 0.15.

MCRT (sludge age) = pounds of solids in the aeration system divided by pounds of solids leaving per day in waste sludge plus effluent; wasting rate is the main control.

Typical mixed liquor suspended solids are 2,000 to 3,000 mg/L and dissolved oxygen in the aeration tank is held near 1.5 to 2.5 mg/L.

SVI = 30-minute settled sludge volume (mL/L) x 1,000 / MLSS (mg/L); 80 to 150 is good settling, above about 200 indicates filamentous bulking.

RAS is normally 50 to 150% of influent flow; a rising blanket with a low SVI means the return rate should be increased.

Trickling filter loading is expressed as lb BOD5 per 1,000 ft3 of media per day and as hydraulic loading in gpd/ft2; sloughing is normal periodic media unloading.

Nitrification needs solids retention time above about 8 to 10 days at 20 degrees C, DO above 2 mg/L, and about 7.14 mg of alkalinity per mg of ammonia nitrogen oxidized.

Facultative ponds are typically 4 to 8 ft deep with 30 to 180 days detention; algae supply oxygen by day, and bacterial die-off plus sunlight reduce coliforms.

CT = disinfectant residual (mg/L) x contact time (minutes); colder water, higher pH, and higher ammonia all require a larger CT for the same kill.

Chlorine demand = applied dose minus measured residual; demand must be satisfied before any free residual appears.

Breakpoint chlorination requires roughly 7.6 mg of chlorine per mg of ammonia nitrogen; past the breakpoint, added chlorine shows up almost entirely as free residual.

Dechlorination with sulfur dioxide uses about 1 mg/L of SO2 per 1 mg/L of chlorine residual, adjusted by actual residual testing.

Typical fecal coliform limits are a monthly geometric mean near 200 CFU/100 mL with a higher 7-day limit; the actual values are set in the individual permit.

UV disinfection is dosed in millijoules per square centimeter, with about 30 mJ/cm2 typical; turbidity, iron, and fouled lamp sleeves shield organisms and reduce dose.

Free chlorine is a stronger disinfectant than combined chloramine but dissipates faster and forms disinfection byproducts with organics.

Effluent monitoring must use permit-specified methods and frequencies; results are reported as geometric means for bacterial data, never simple arithmetic averages.

Typical solids content: primary sludge 2 to 6%, waste activated sludge 0.5 to 1.5%, gravity-thickened sludge 4 to 6%, dewatered cake 15 to 30%.

Anaerobic digesters are usually mesophilic at about 35 degrees C (95 degrees F) with a solids retention time of 15 to 30 days and 40 to 55% volatile solids destruction.

Digester stability is judged by the volatile acids to alkalinity ratio: below 0.1 is stable, 0.1 to 0.3 needs watching, and above about 0.35 signals souring.

Digester gas is roughly 60 to 65% methane and 30 to 35% carbon dioxide, with about 15 to 18 ft3 of gas produced per pound of volatile solids fed.

Percent solids = (dry weight / wet weight) x 100; pounds of solids = concentration in mg/L x volume in MG x 8.34.

40 CFR Part 503 Class B sludge requires fecal coliform below 2,000,000 MPN or CFU per gram of total solids plus a vector attraction reduction option.

Gravity thickening is cheapest for waste activated sludge but can turn septic; dissolved air flotation and centrifuges handle light sludges better.

Polymer conditioning agglomerates fines so belt presses, filter presses, and centrifuges can capture solids and release free water.

Pounds formula: lb/day = concentration (mg/L) x flow (MGD) x 8.34; use the same formula to convert any dose to pounds.

SVI = settled sludge volume in mL/L after 30 minutes x 1,000 / MLSS in mg/L; low SVI means dense, fast-settling sludge.

BOD5 is measured at 20 degrees C over 5 days; a nitrification inhibitor gives CBOD5, and seeded dilution water is required when the sample lacks adequate organisms.

TSS is determined by filtering a measured sample through a glass fiber filter, drying at 103 to 105 degrees C, and weighing the residue.

Volatile solids are the portion lost on ignition at about 550 degrees C, a measure of the organic fraction of sludge or solids.

Bacterial results are averaged as a geometric mean (the nth root of the product of n counts) so a single high count does not distort compliance.

Percent removal = [(influent - effluent) / influent] x 100; percent volatile solids reduction is calculated between feed and digested sludge.

MCRT = total solids in the system divided by solids leaving per day; raising MCRT means wasting less sludge, lowering it means wasting more.

Predictive maintenance uses vibration analysis, thermography, and oil analysis to find bearing wear, imbalance, misalignment, and looseness before failure.

Cavitation occurs when suction pressure drops below the liquid vapor pressure; symptoms are noise, vibration, and impeller pitting, corrected by lowering suction lift or clearing blockage.

NPSH available must exceed NPSH required by the pump; low NPSH margin is the most common cause of cavitation in suction-lift stations.

A properly packed stuffing box should leak a slow, steady drip (roughly 40 to 60 drops per minute) for lubrication and cooling; mechanical seals need clean flush water.

Blower and pump capacity drops with a clogged air filter, worn wear rings, or a partially closed valve; check these before assuming motor failure.

Preventive maintenance intervals come from the manufacturer's manual and are tracked in a work-order system with equipment history for each asset.

All maintenance on pumps, blowers, and mixers requires lockout/tagout; work inside tanks, wet wells, or digesters also requires confined space procedures.

Spare parts inventory should cover critical long-lead items such as seals, bearings, check valves, and blower belts to avoid extended bypass or permit violations.