ABC Wastewater Treatment Class IV flashcards

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

Sludge Volume Index

The volume in milliliters occupied by one gram of mixed liquor solids after 30 minutes of settling, calculated as settled volume in mL/L times 1,000 divided by MLSS in mg/L. Values of 80 to 150 indicate good settling.

Food-to-Microorganism Ratio

Pounds of BOD entering the aeration basin per day divided by pounds of mixed liquor volatile suspended solids under aeration. Conventional activated sludge runs 0.2 to 0.4; extended aeration runs 0.05 to 0.15.

Mean Cell Residence Time

The total solids inventory in the activated sludge system divided by the solids leaving each day in waste sludge and effluent. It sets sludge age, which controls nitrification, oxygen demand, and bulking tendency.

Filamentous Bulking

Poor sludge settling caused by filamentous bacteria overgrowth, producing an SVI above 150 with a low, diffuse blanket. Common triggers are low dissolved oxygen, low food-to-microorganism ratio, nutrient deficiency, and septic influent.

Rising Sludge

A clarifier sludge blanket that rises with entrapped gas because denitrification releases nitrogen in the sludge. Correct it by increasing return sludge rate, lowering sludge age, or reducing clarifier detention time.

Chlorine CT Value

Disinfectant residual concentration in mg/L multiplied by contact time in minutes. The CT required for a given kill increases as pH rises above 7.5, as temperature drops, and as turbidity increases.

Aerated Grit Chamber

A tank using diffused air to keep lighter organic solids in suspension while heavier grit settles for removal. Typical detention is two to five minutes at peak flow, with air adjusted to separate grit from organics.

Nitrification Oxygen Demand

Oxidizing one pound of ammonia nitrogen to nitrate consumes about 4.57 pounds of oxygen and destroys about 7.14 pounds of alkalinity as calcium carbonate, so nitrifying plants need extra air and buffer.

Primary Clarifier Overflow Rate

Flow divided by clarifier surface area, expressed as gallons per day per square foot. Typical design values are 600 to 1,000 gpd per square foot at average flow, with weir loading below 10,000 gpd per foot.

Trickling Filter Organic Loading

Pounds of BOD applied per day per 1,000 cubic feet of filter media. Recirculation dilutes influent strength and maintains wetting and sloughing, while loadings above design cause ponding, odors, and poor nitrification.

Thickener Solids Loading Rate

Dry pounds of solids applied per day divided by thickener surface area in square feet. Primary sludge thickens at roughly 20 to 30 pounds per square foot per day; waste activated sludge is limited to about 4 to 8.

Volatile Solids Reduction

The percentage of volatile solids destroyed across digestion, computed from feed and digested solids concentrations. A reduction of at least 38 percent demonstrates adequate stabilization under common Class B treatment requirements.

Cake Solids

The dry solids concentration of dewatered biosolids, reported as a percentage. Belt filter presses typically produce 18 to 25 percent cake from digested sludge, and solids capture should exceed 90 percent.

Class B Pathogen Standard

Fecal coliform density must stay below 2,000,000 most probable number per gram of total solids, or Salmonella below 3 MPN per 4 grams, at the time of use or disposal.

Pump Affinity Laws

For a centrifugal pump, flow varies directly with impeller speed, head with speed squared, and power with speed cubed. Trimming the impeller diameter follows similar relationships and reduces energy use.

Minimum Scour Velocity

Gravity sewers should carry at least two feet per second at design flow to keep solids moving and prevent deposition. Velocities above about ten feet per second accelerate abrasion and hydrogen sulfide corrosion.

Parshall Flume Submergence

A Parshall flume measures free flow only when downstream depth stays below about 70 percent of upstream depth for small throats. Beyond that limit a submerged-flow correction is required and accuracy declines.

NPSH Available

The absolute pressure head at a pump suction above the liquid vapor pressure. It must exceed the pump's required NPSH or cavitation will damage the impeller and reduce discharge flow and head.

System Curve

A plot of total head required versus flow, made up of static head plus friction losses that rise roughly with the square of flow. The pump operates where its performance curve crosses this curve.

Five-Day BOD Test

A sample is incubated at 20 degrees Celsius for five days. Dissolved oxygen depletion must be at least 2 mg/L with at least 1 mg/L remaining, or the sample must be diluted and the seed correction applied.

Total Suspended Solids

Residue retained on a glass fiber filter after drying at 103 to 105 degrees Celsius. Volatile suspended solids are the portion of that residue lost on ignition at 550 degrees Celsius.

Flow-Proportioned Composite Sample

Aliquots collected in proportion to flow over the sampling period, producing a flow-weighted average. It is required for permit compliance when discharge quality varies with flow or production schedule.

DPD Method

A colorimetric test for residual chlorine using DPD indicator read at 515 nanometers. Reagents added determine whether free or total chlorine is measured, and it is the standard field method.

Membrane Filtration Coliform Test

A measured sample is filtered through a 0.45 micron membrane, incubated on selective medium, and colonies are counted. Fecal coliform plates are incubated at 44.5 degrees Celsius to select thermotolerant organisms.

Permit-Required Confined Space

A space with limited entry and exit, not designed for continuous occupancy, that may contain a hazardous atmosphere, engulfment hazard, or entrapment risk. Entry requires a permit, atmospheric testing, an attendant, and a rescue plan.

Discharge Monitoring Report

The periodic report of self-monitoring results submitted to the permitting agency under the NPDES program. Supporting records are kept at least three years and the report is signed by a responsible official.

Hydrogen Sulfide Exposure Limit

OSHA sets a 20 ppm ceiling and the immediately dangerous to life or health level is 100 ppm. The gas deadens the sense of smell at high concentrations, so odor is never a safe indicator.

Lockout Tagout

Placing a personal lock and tag on an energy-isolating device before servicing equipment. Stored energy must be released and verified, and only the person who applied the lock may remove it.

Mean Time Between Failures

Total operating hours divided by the number of failures in the period. It measures equipment reliability and supports decisions to rebuild, replace, or change the maintenance strategy for an asset.

Predictive Maintenance

Condition-based tasks such as vibration analysis, thermography, oil analysis, and ultrasound that forecast failure and schedule repair before breakdown. It usually costs less than reactive repair and cuts unplanned downtime.

Criticality Ranking

Ordering assets by the consequence of failure multiplied by the likelihood of failure, so limited maintenance resources go first to equipment whose failure most threatens permit compliance, safety, or service.

Specific Energy per Million Gallons

Kilowatt-hours consumed per million gallons pumped, calculated as kilowatts times 24 divided by daily million gallons. It is the standard benchmark for tracking pumping efficiency over time.