ABC Wastewater Treatment Class IV cheat sheet

SVI = (30-minute settled sludge volume, mL/L × 1,000) ÷ MLSS, mg/L. 80–150 indicates good settling; 150–250 indicates bulking; above 250 indicates severe bulking or denitrification in the clarifier.

F/M (lb BOD per lb MLVSS per day) = lb BOD entering the aeration basin per day ÷ lb MLVSS under aeration. Conventional 0.2–0.4, extended aeration 0.05–0.15, high-rate 0.4–1.5.

MCRT (days) = lb of solids in the system ÷ lb of solids leaving per day in waste sludge plus effluent. Nitrification typically needs 8–15 days at 20°C and 15–20 days at 10°C.

Hold DO near 2.0 mg/L in the nitrifying zone. If DO falls below 1.0 mg/L, check blower output, diffuser fouling, and RAS/WAS rates before changing wasting - raising wasting cannot fix an air delivery problem.

Alkalinity destroyed is about 7.14 mg/L as CaCO3 per mg/L of ammonia nitrogen nitrified. Effluent pH below 6.5 with alkalinity below 50 mg/L means nitrification is consuming the buffer.

Rising blanket with clear supernatant and gas bubbles = denitrification in the clarifier (increase RAS rate, lower SRT, cut clarifier detention). Rising blanket with cloudy supernatant = solids overload (increase wasting, check SVI and surface overflow rate).

Percent removal = [(influent − effluent) ÷ influent] × 100, with both values in the same units.

SVI below 80 with a dense blanket points to over-wasting, pin floc, or polymer carryover; SVI above 150 at low F/M points to filamentous growth - check DO, nutrient ratio (BOD:N:P ≈ 100:5:1), and septic or high-sulfide influent.

Primary clarifier design: detention 1.5–2.5 h, surface overflow rate 600–1,000 gpd/ft² at average flow, weir loading below 10,000 gpd/ft.

Aerated grit chambers: 2–5 minutes detention at peak flow; adjust air so grit settles while organic solids stay in suspension.

Oxygen demand: roughly 1.0–1.5 lb O2 per lb BOD removed, plus 4.57 lb O2 per lb of ammonia nitrogen oxidized.

Chlorine disinfection: CT = residual (mg/L) × contact time (min). Required CT rises as pH rises above 7.5 (hypochlorous acid dissociates to the weaker hypochlorite ion), as temperature falls, and as turbidity rises.

UV disinfection: design dose 30–40 mJ/cm²; needs UV transmittance typically above 65% and low TSS. Fouled sleeves and high suspended solids cut delivered dose without changing lamp power.

Trickling filter organic loading = lb BOD/day ÷ 1,000 ft³ of media. Recirculation raises hydraulic loading and dilutes influent strength; surface ponding signals media clogging or incomplete sloughing.

Anaerobic digestion (mesophilic): 35–38°C, SRT 15–20 days, volatile solids loading 0.1–0.2 lb VS/ft³·day. VFA-to-alkalinity ratio of 0.1–0.35 is stable; above 0.8 indicates souring.

Chemical precipitation: 1 mg/L of alum consumes roughly 0.45 mg/L of alkalinity as CaCO3; ferric chloride is more corrosive and depresses pH more per mg/L added. Equalization volume is sized from the flow mass diagram as the largest cumulative difference between inflow and average outflow.

Solids load (lb/day) = flow (MGD) × 8.34 × concentration (mg/L). Multiply by 0.001 to convert to tons per day when the concentration is in percent solids.

Gravity thickener solids loading: about 20–30 lb/ft²·day for primary sludge and 4–8 lb/ft²·day for waste activated sludge; overflow rate 200–400 gpd/ft² for primary and 100–200 gpd/ft² for WAS.

Dewatering performance is judged by three numbers together: cake solids percent, solids capture (target above 90%), and polymer dose in lb per dry ton.

Lime stabilization: raise pH to 12.0 and hold for 2 hours, then keep pH above 11.5 for 24 hours to satisfy vector attraction reduction.

Class A composting PFRP: 55°C for 3 days in-vessel or aerated static pile followed by curing at 40°C for 14 days; windrow systems need 55°C for at least 15 days with five or more turnings.

40 CFR 503 Class B alternatives: fecal coliform below 2,000,000 MPN/g total solids, or Salmonella below 3 MPN/4 g total solids, plus a vector attraction reduction option.

Belt filter press troubleshooting order: floc quality and polymer mixing energy, then belt tracking, then wash water pressure and spray coverage, then belt tension and speed. Over-shearing the floc destroys dewaterability.

Anaerobic digester upset response: stop or reduce feed, stabilize temperature, verify mixing, and check for foaming; adding alkalinity raises pH but does not remove the volatile acids causing the drop.

Q = A × V. A 1 ft² cross-section flowing at 2 ft/s carries 2 cfs, about 1.29 MGD. Conversions: 1 MGD = 1.55 cfs = 694 gpm.

Affinity laws for centrifugal pumps: Q ∝ N, H ∝ N², P ∝ N³. A 10% speed reduction cuts power roughly 27%.

The operating point is the intersection of the pump curve and the system curve (static head plus friction). Throttling moves the operating point along the pump curve; changing speed or impeller diameter changes the curve itself.

NPSH available must exceed NPSH required. Cavitation appears as noise, vibration, and falling head/flow - check suction lift, plugged strainers, and vapor pressure at the water temperature.

Minimum wet well volume for pump cycling (gal) = pump capacity (gpm) × minimum cycle time (min) ÷ 4, assuming inflow near half of pump capacity. Excessive cycling is corrected with larger storage or VFD control.

Parshall flume free flow requires submergence (downstream depth ÷ upstream depth) below about 70% for throats up to 1 ft and about 60% for larger throats; beyond that a submerged-flow correction is applied and accuracy falls.

Weir formulas: suppressed rectangular weir, Q (cfs) = 3.33 × L (ft) × H (ft)^1.5; 90° V-notch weir, Q (cfs) = 2.5 × H (ft)^2.5.

Sanitary sewers: 2 ft/s minimum self-cleansing velocity at design flow and about 10 ft/s maximum to limit abrasion and sulfide generation. Rising pump run-hours at steady flow indicate infiltration; wet-weather spikes indicate inflow.

BOD5: incubate at 20°C ± 1°C for 5 days. The test is valid when depletion is at least 2 mg/L and residual DO is at least 1 mg/L; otherwise dilute further and apply the seed correction.

TSS: filter through a glass fiber filter and dry at 103–105°C. VSS: ignite the dried filter at 550°C; the loss on ignition is the volatile fraction.

Settleable solids are measured in an Imhoff cone for 60 minutes and reported in mL/L. The 30-minute settled volume in a 1,000 mL graduated cylinder is the numerator of the SVI calculation.

Calibrate pH with 4.0, 7.0, and 10.0 buffers; a slope outside 95–105% means the electrode needs cleaning, rehydration, or replacement.

BOD5/COD for domestic wastewater is roughly 0.5–0.7. A sharp drop in the ratio signals an industrial discharge of poorly biodegradable organics.

Percent removal = [(influent − effluent) ÷ influent] × 100. Duplicate analyses should agree within the method's control limit before results are used for process decisions.

Residual chlorine by DPD colorimetry at 515 nm; switch to amperometric titration when color, turbidity, or combined chlorine interferes with the colorimetric reading.

Membrane filtration uses a 0.45 µm filter: fecal coliform incubated at 44.5°C, total coliform at 35°C, reported as colonies per 100 mL. Grab samples are required for pH, chlorine, and dissolved oxygen because those values change in the bottle; flow-proportioned composites are used for loading-based permit limits.

Permit-required confined space entry: test before entry and continuously during entry - oxygen 19.5–23.5%, combustible gas below 10% LEL, hydrogen sulfide below 10 ppm, carbon monoxide below 35 ppm.

Hydrogen sulfide: OSHA ceiling 20 ppm, IDLH 100 ppm. The sense of smell is deadened at high concentrations, so odor is never a valid warning of a dangerous atmosphere.

Chlorine gas: OSHA ceiling 1 ppm, IDLH 10 ppm. Open cylinder valves slowly, never apply heat or water to a leaking container, and evacuate upwind.

NPDES permits are issued for terms up to 5 years. Discharge Monitoring Reports are submitted on the permit schedule and supporting records are retained at least 3 years under 40 CFR 122.41.

40 CFR 503 Class B: fecal coliform below 2,000,000 MPN/g total solids, or Salmonella below 3 MPN/4 g total solids, at the time of use or disposal, plus a vector attraction reduction practice.

Lockout/tagout (29 CFR 1910.147): isolate every energy source, release stored energy, verify isolation by attempting startup, and allow only the person who applied the lock to remove it.

Hazard communication (29 CFR 1910.1200): a current safety data sheet must be accessible for every chemical on site, and every container must be labeled with its identity and hazard warnings.

Sanitary sewer overflows and significant noncompliance are reported to the primacy agency within the time stated in the permit or state rule - commonly 24 hours by phone with written follow-up within 5 days.

MTBF = operating hours ÷ number of failures; MTTR = total repair hours ÷ number of repairs; availability = MTBF ÷ (MTBF + MTTR).

Predictive tools map to failure modes: vibration analysis for bearings and imbalance, infrared thermography for electrical and insulation faults, oil analysis for wear metals and contamination, ultrasound for leaks and early bearing faults.

Criticality ranking = consequence of failure × likelihood of failure. It sets spare-parts stocking levels, PM frequency, and rebuild-versus-replace decisions.

Energy benchmark: kWh/MG = (kW × 24) ÷ MGD. A rising trend at constant flow points to fouled diffusers, worn impellers, or partially plugged piping.

Work order backlog measured in crew-weeks: sustained backlog above 4–6 weeks signals understaffing, while scheduled-task compliance below 80% usually signals planning and parts problems rather than labor shortage.

A preventive task is interval-based (change oil at 2,000 hours); a predictive task is condition-based (change oil when analysis shows it). Do not schedule both for the same failure mode.

Root cause analysis separates the physical cause, the human cause, and the latent system cause; corrective action targets the system, not just the failed part.

Certification and training records must be retained, operator grade must match the plant classification, and shift coverage must satisfy the permit's staffing requirement.