ABC Biological Industrial Waste Treatment Operator cheat sheet

BOD5: oxygen consumed by microorganisms over 5 days at 20°C; measures biodegradable organic matter.

COD: oxygen equivalent of organic matter oxidized by dichromate; includes non-biodegradable organics.

BOD5/COD ratio >0.5 indicates readily biodegradable wastewater; <0.3 indicates poor biodegradability.

TSS: solids retained on 0.45 µm filter; VSS: volatile portion of TSS, approximates biomass.

F/M ratio = (influent BOD × flow) / (MLVSS × aeration volume); typical range 0.2–0.5 day⁻¹ for conventional activated sludge.

Nitrifying bacteria (Nitrosomonas, Nitrobacter) are autotrophs; require aerobic conditions, alkalinity, and temperatures 15–35°C.

Filamentous bacteria (e.g., Microthrix parvicella) cause bulking; low F/M, low DO, or nutrient deficiency promote their growth.

Indicator organisms: fecal coliforms (e.g., E. coli) signal fecal contamination; typical effluent limit 200 CFU/100 mL.

Coarse bar screens: openings >6 mm; remove large debris; headloss increase signals cleaning needed.

Grit removal: designed to remove particles >0.2 mm with specific gravity >2.65; prevents abrasion and accumulation.

Primary clarifier overflow rate: 30–60 m³/m²·d for domestic wastewater; industrial flows may require lower rates.

Hydraulic retention time (HRT) = volume / flow; typical primary clarifier HRT is 1.5–2.5 hours.

Weir loading rate: 125–250 m³/m·d; high rates can cause short-circuiting and solids carryover.

Primary sludge solids: 2–6% for domestic; industrial sludges vary widely; VSS/SS ratio indicates organic content.

BOD and TSS removal in primary clarifiers: typically 25–40% BOD and 50–70% TSS.

Equalization basin: reduces flow and load variations; HRT typically 4–24 hours; mixing prevents solids deposition.

Aerobic respiration: organic matter + O2 → CO2 + H2O + new cells; oxygen demand ≈ 1.42 g O2 per g VSS produced.

Anoxic denitrification: nitrate → nitrogen gas; requires carbon source (BOD) and ORP typically -50 to +50 mV.

Anaerobic digestion: complex organics → methane (60–65%) + CO2; optimal pH 6.8–7.4, temperature 35°C (mesophilic).

Sludge age (SRT) = mass of solids in system / mass wasted per day; controls nitrification and biomass composition.

Yield coefficient (Y): g VSS produced per g BOD removed; typically 0.4–0.6 for heterotrophs.

Endogenous decay coefficient (kd): 0.05–0.15 day⁻¹; increases with temperature.

Alkalinity destruction: 7.14 mg alkalinity as CaCO3 consumed per mg NH4-N oxidized to nitrate.

ORP ranges: anaerobic < -200 mV; anoxic -50 to +50 mV; aerobic > +50 mV.

MLSS: mixed liquor suspended solids; typical 2000–4000 mg/L for conventional systems; MLVSS ≈ 0.7–0.8 × MLSS.

Sludge volume index (SVI) = (settled sludge volume after 30 min, mL/L × 1000) / MLSS (mg/L); SVI 80–150 mL/g indicates good settling.

Return activated sludge (RAS) rate: 0.5–1.5 × influent flow; controls MLSS and sludge blanket in clarifier.

Waste activated sludge (WAS) rate: determined by SRT target; SRT = (MLSS × aeration volume) / (WAS solids per day).

F/M ratio low (<0.2) can cause filamentous bulking; high (>0.5) may cause poor floc formation.

Dissolved oxygen: maintain 1.5–3.0 mg/L in aeration tank; <1 mg/L favors filamentous bacteria and denitrification.

Sludge blanket in secondary clarifier: keep <0.3 m below effluent weir; rising blanket indicates solids overload.

Foaming: caused by Nocardia or Microthrix; control by reducing SRT, adding antifoam, or chlorination.

Trickling filter: organic loading rate 0.3–1.0 kg BOD/m³·d for low-rate; 1.0–2.5 kg BOD/m³·d for high-rate.

Rotating biological contactor (RBC): hydraulic loading 0.08–0.16 m³/m²·d; staging improves nitrification.

Moving bed biofilm reactor (MBBR): fill fraction 30–70%; biofilm carriers provide protected surface area.

Aerated lagoon: HRT 5–10 days; power density 1–3 W/m³ for mixing and oxygen transfer.

Facultative lagoon: aerobic surface layer, anaerobic bottom; depth 1.5–2.5 m; organic loading 20–50 kg BOD/ha·d.

Lagoon algae produce oxygen via photosynthesis; diurnal DO swings can cause effluent TSS violations.

Fixed-film systems are less sensitive to shock loads but can suffer from media clogging or biofilm sloughing.

Nitrification in fixed-film: low organic loading and high SRT favor nitrifiers; temperature >15°C required.

Pretreatment standards (e.g., 40 CFR 403) limit pollutants like metals, cyanide, and organics before discharge to POTW.

Flow equalization: reduces hydraulic and organic shock loads; design HRT 8–24 hours with mixing.

pH neutralization: required before biological treatment; optimum 6.5–8.5 for biomass; use acid/base addition with mixing.

Heavy metals (e.g., Cu, Zn, Ni) are toxic to biomass; typical inhibitory concentrations: Cu >1 mg/L, Zn >5 mg/L.

Oil and grease (O&G) removal: API separator or DAF; influent O&G >100 mg/L can coat biomass and reduce oxygen transfer.

Shock load response: increase MLSS, reduce F/M, or use equalization; monitor OUR and DO for early warning.

Toxic organics (e.g., phenols, solvents) may require pretreatment (e.g., carbon adsorption, chemical oxidation) before biological treatment.

Nutrient addition: industrial wastewaters often lack N and P; add ammonium and phosphate to maintain BOD:N:P ≈ 100:5:1.

Sludge thickening: gravity thickener increases solids from 1–2% to 3–6%; DAF achieves 4–8% for waste activated sludge.

Anaerobic digestion: volatile solids reduction 40–60%; biogas production ≈ 0.8–1.2 m³/kg VS destroyed.

Dewatering: belt filter press or centrifuge produces cake 15–30% solids; polymer conditioning improves performance.

Sludge volume index (SVI) also indicates dewaterability; high SVI sludge is harder to dewater.

Solids loading rate to digesters: 0.5–2.0 kg VS/m³·d for mesophilic anaerobic digestion.

Composting: windrow or aerated static pile; C:N ratio 25–35:1; temperature 55–65°C for pathogen reduction.

Drying beds: sand beds with underdrains; loading rate 100–200 kg/m²·yr; requires favorable climate.

Incineration: multiple hearth or fluidized bed; requires auxiliary fuel if solids <30%; air pollution control mandatory.

Chlorine disinfection: CT concept (concentration × contact time); typical CT 15–30 mg·min/L for fecal coliform reduction.

Chlorine residual: free chlorine more effective than combined; maintain 0.5–2.0 mg/L after contact.

Dechlorination: sulfur dioxide or sodium bisulfite; dose ≈ 1.0 mg/L per 1.0 mg/L chlorine residual.

UV disinfection: dose 30–40 mJ/cm² for secondary effluent; requires low TSS and UV transmittance >65%.

Ozone disinfection: dose 1–5 mg/L; contact time 5–15 minutes; produces no residual but can form bromate.

Effluent limits: typical secondary treatment: BOD5 30 mg/L, TSS 30 mg/L; advanced limits may be 10/10 or lower.

Residuals: disinfection byproducts (trihalomethanes) form from chlorine reacting with organics; monitor and control.

Biosolids classification: Class A (pathogen-free) vs Class B; vector attraction reduction required.

Confined space entry: permit required; test for oxygen (19.5–23.5%), flammables (<10% LEL), and toxics (H2S <10 ppm) before entry.

H2S: colorless, toxic gas; immediately dangerous to life at >100 ppm; odor threshold 0.01 ppm but olfactory fatigue occurs.

Methane: flammable at 5–15% in air; explosive; monitor with LEL meter in digester areas.

Chlorine gas: toxic; use respiratory protection; store cylinders in well-ventilated area; leak detection at 1 ppm.

Lockout/tagout (LOTO): required for maintenance on electrical and mechanical equipment; verify zero energy.

Personal protective equipment: gloves, goggles, and face shield when handling chemicals; safety showers and eyewash stations accessible.

Spill response: contain, report, and clean up; notify regulatory agencies if reportable quantity exceeded.

Recordkeeping: discharge monitoring reports (DMRs) must be submitted per permit; keep records for at least 3 years.

Composite sampling: flow-proportioned or time-proportioned; preferred for variable flows; refrigerate at 4°C.

Grab samples: used for pH, DO, chlorine, and other unstable parameters; analyze immediately.

BOD5 analysis: seed, dilution water, 5-day incubation at 20°C; dissolved oxygen depletion measured; nitrification inhibitor may be added.

COD analysis: dichromate digestion at 150°C for 2 hours; read absorbance at 600 nm; mercury sulfate masks chloride interference.

TSS: filter 100 mL sample through glass fiber filter, dry at 103–105°C, weigh; VSS: ignite at 550°C.

pH and DO meters: calibrate daily with standard buffers and zero-oxygen solution; record calibration in logbook.

Microscopic examination: identify filamentous bacteria and protozoa; evaluate floc size and density for process control.

Quality control: run duplicates, blanks, and standards; acceptable relative percent difference (RPD) typically <20% for duplicates.