Physical/Chemical Industrial Waste Treatment Operator cheat sheet

H2S is heavier than air, deadens smell above roughly 100 ppm, and is immediately dangerous to life or health (IDLH) at 100 ppm; confined-space entry requires atmospheric testing before and during entry.

Oxygen-deficient atmosphere is below 19.5% O2; oxygen-enriched is above 23.5% O2 - both prohibit entry without supplied air controls.

Lower explosive limit (LEL) for methane is 5% by volume in air; combustible-gas meters read 0-100% LEL, and entry is barred above 10% LEL without ventilation.

Chlorine gas is heavier than air and corrosive to airways; the OSHA permissible exposure limit is 1 ppm as a ceiling value, so leak response uses SCBA and upwind approach.

Sodium hypochlorite and acid must never be mixed - mixing releases chlorine gas; store oxidizers separately from acids and reducing agents.

Caustic (NaOH) and acid spills are neutralized only after identifying the chemical; always add reagent slowly to water, never water to concentrated acid or caustic.

Emergency eyewash and safety showers must be within 10 seconds' travel (about 16 m / 55 ft) of acid or caustic handling points and flushed weekly.

A 4-gas meter typically measures O2, LEL, H2S, and CO simultaneously; calibrate with span gas before each shift or per manufacturer interval.

BOD5 measures oxygen consumed by microbes over 5 days at 20 °C; COD measures oxygen demand of both biodegradable and non-biodegradable matter using dichromate digestion.

Typical domestic wastewater BOD5/COD ratio is about 0.4-0.6; a ratio below ~0.3 indicates poor biodegradability and limited biological treatability.

TSS is measured by filtering a sample through a glass-fiber filter and drying at 103-105 °C; volatile suspended solids (VSS) are the fraction burned off at 550 °C.

FOG (fats, oils, grease) and pH, cyanide, and heavy metals are common industrial pretreatment limits; categorical standards derive from 40 CFR Parts 405-471.

The Clean Water Act NPDES permit sets effluent limits; the general pretreatment regulations are 40 CFR Part 403, and local limits are set by the POTW.

pH is a logarithmic scale: a drop of one unit means a tenfold increase in hydrogen ion concentration; most POTWs prohibit discharge below 5.0 or above 12.5 standard units.

Flow-proportional composite sampling is required when flow varies; grab samples are used for pH, temperature, cyanide, and other unstable parameters.

Equalization tanks damp flow and concentration swings; required volume scales with the variability period and the desired damping factor.

Gravity clarification design uses overflow rate (m3/m2·d) and solids loading rate (kg/m2·d); overflow rate governs particle removal, solids loading governs thickening.

Stokes' law settling velocity rises with the square of particle diameter and the density difference, and falls with increasing viscosity.

Dissolved air flotation (DAF) removes low-density solids and FOG using microbubbles; a recycle ratio of 20-50% is typical.

Filtration (sand, multimedia, membrane) removes residual TSS; membrane flux is expressed in L/m2·h (LMH) and declines as fouling accumulates.

Air stripping removes volatile organics such as benzene; removal depends on Henry's law constant, air-to-water ratio, and temperature.

Activated carbon adsorption follows an isotherm (Freundlich or Langmuir); breakthrough occurs when effluent concentration rises sharply, triggering carbon replacement.

Coagulation destabilizes colloids with alum, ferric chloride, or polymers; flocculation gently agitates to grow flocs large enough to settle.

Optimal coagulant dose is found by jar testing; overdosing can reverse charge and re-stabilize particles, raising turbidity.

Lime softening raises pH to precipitate CaCO3 and Mg(OH)2; pH above about 10.5 is needed for magnesium removal.

Hexavalent chromium is reduced to trivalent chromium at pH 2-3 with bisulfite or ferrous sulfate, then precipitated as Cr(OH)3 near pH 8-9.

Hydroxide precipitation of most heavy metals is optimal near pH 8-10; amphoteric metals such as zinc and lead redissolve at high pH.

Sulfide precipitation can achieve lower metal residuals than hydroxide precipitation, but carries H2S exposure risk.

Chlorination CT (concentration × contact time) governs disinfection; free chlorine residual and pH determine the ratio of HOCl to OCl-.

SVI (sludge volume index) = settled sludge volume (mL/L) × 1000 / MLSS (mg/L); a range of 80-150 mL/g indicates good settling.

F/M ratio = food (BOD or COD mass per day) / microorganism mass; low F/M favors nitrification and low sludge production, high F/M risks bulking.

Mean cell residence time (MCRT, SRT) = mass of solids in the system / mass wasted plus lost per day.

pH meters need two-point calibration with fresh buffer (typically pH 4 and 7 or 7 and 10) and storage in KCl solution, never distilled water.

Dissolved oxygen below about 1-2 mg/L limits aerobic treatment and promotes filamentous bulking; typical aeration targets are 2-4 mg/L.

Jar tests and bench-scale trials precede full-scale chemical dose changes; record dose, pH, turbidity, and settling in the log.

Turbidity (NTU) and residual chlorine (mg/L) are common continuous online parameters used for real-time process control.

Pumps lose prime from air leaks or a worn seal; cavitation sounds like gravel and is caused by low NPSH available versus required.

Centrifugal pump flow is throttled with a discharge valve, never a suction valve; suction throttling risks cavitation.

Airlocks and clogged impellers cause reduced pump flow; check suction strainers and vent the casing before assuming mechanical failure.

Blower and aeration diffuser fouling raises backpressure and lowers oxygen transfer; monitor discharge pressure trends and clean diffusers.

Lockout/tagout (LOTO) precedes maintenance on rotating equipment; verify zero energy and confirm de-energization before work.

Vibration and bearing temperature trending predict pump and blower failure; rising trends trigger inspection before catastrophic failure.

Sensor drift is detected by comparing online readings to grab-sample lab results; calibrate or replace probes when the offset exceeds tolerance.

Sludge thickening (gravity, DAF, centrifuge) reduces volume before digestion or dewatering; solids capture efficiency determines recycle load.

Anaerobic digestion stabilizes sludge and produces methane; mesophilic digestion runs near 35 °C and requires stable temperature and feed to avoid souring.

Dewatering performance is judged by cake solids percent and solids capture; polymer dose is optimized by jar or bench tests.

Sludge volume to be hauled = dry solids mass / (cake solids fraction); a higher cake percent directly reduces hauling cost.

Biosolids land application is governed by 40 CFR Part 503, which sets pathogen and vector attraction reduction requirements.

Volatile solids reduction (VSR) is a common digestion performance metric; typical well-run digesters achieve 40-60% VSR.

Dewatered cake and grit are characterized (TCLP, metals) before disposal to determine landfill acceptability.

Open-channel flow is measured with a weir or Parshall flume; flow rate is computed from measured head using the structure's rating equation.

Manning's equation estimates gravity sewer velocity: v = (1.486/n) R^(2/3) S^(1/2) in US units; self-cleansing velocity is about 0.6 m/s (2 ft/s).

Surcharging and backups occur when inflow exceeds capacity; inflow and infiltration (I/I) from stormwater and groundwater is a common cause.

Storage tanks require secondary containment sized to hold the largest tank volume plus precipitation allowance.

Incompatible wastes must be segregated in storage; acid and caustic, oxidizers and organics, and cyanide and acid must never share containment.

Level and flow instrumentation (ultrasonic, bubbler, radar) needs periodic calibration; a stuck level sensor can cause overflow or pump damage.

Equalization and holding tanks smooth batch discharges to the treatment plant and prevent shock loads on biological processes.

NPDES discharge monitoring reports (DMRs) are typically submitted monthly; violations must be reported to the permitting authority within the time specified in the permit.

Chain-of-custody forms track sample identity, collection time, and handling; missing or altered entries can invalidate analytical results.

Records must be retained per permit and 40 CFR Part 403 requirements, commonly three years, and made available to inspectors on request.

Upset, bypass, and exceedance events require documented notice, cause, corrective action, and follow-up - not just a number in the log.

Calibration and maintenance logs for monitoring instruments support data defensibility; record date, standard used, and result.

Noncompliance reports must state the parameter, magnitude, duration, and cause, plus steps taken to restore compliance.

Signatory requirements (40 CFR 122.22) designate who may certify reports; unauthorized signatures invalidate submittals.