Glossary and unit equivalence

Notation must retain its meaning across the book, simulator and laboratory data. Spanish and English terms are paired here so translation does not change the quantity. Concentrations require both a unit and a chemical basis.

Water and load

COD / DQO. Chemical oxygen demand, commonly mg O2/L. It describes response under an analytical oxidation method. It is neither carbon mass nor direct identification of individual compounds.

BOD5 / DBO5. Biochemical oxygen demand measured under the method's five-day conditions. Its ratio to COD is an aggregate descriptor rather than an inventory of each compound's biodegradability.

TSS / SST. Total suspended solids. Sampling and prior separation determine what is quantified. A settled sample differs from a mixed-tank sample.

TOC / COT. Total organic carbon under the selected method. It differs from COD; discussing mineralisation requires the included phases and carbon forms to be known.

Total N. Concentration expressed as elemental nitrogen. It cannot be exchanged for ammonium-ion mass without conversion. Kjeldahl nitrogen is not automatically total N when oxidised species occur.

Total P. Concentration expressed as elemental phosphorus. Phosphate reported as ion mass retains a different basis and must be explicitly converted before comparison.

Load. Quantity per period or batch. For m3 and mg/L, kg=V*C/1000. Using m3/day gives kg/day. Concentration and load answer different questions.

Hydraulics and exposure

Qr. Recirculation flow through the circuit, normally m3/h. Measure it at the operating point rather than inferring it solely from a pump rating.

Qf. Net feed flow. At steady state without volume change or other flows it equals net effluent, not circulation.

Vb and Vd. Useful tank volume and daily treated volume. Both have volume dimensions but different meanings.

c. Dimensionless exposure ratio: Qr*t/Vb for a closed batch and sum(q*h)/Vd for the daily index. Declare the definition used.

Pass. Exposure of a portion to a unit, not necessarily one mean tank turnover. This book preferably reserves turnover for the hydraulic ratio.

RTD. Residence-time distribution. It describes distributed retention and helps investigate short-circuiting and slowly exchanging regions.

Model and measurement

theta. Effective ceiling of the branch being analysed. It remains constant for inverse calculation only while rules and conditions remain unchanged.

phi. Fraction removed per physical visit in a specified balance. An effective exponential coefficient must not receive the same value merely because notation looks similar.

Floor. Numerical lower bound in software, not a laboratory quantification limit or demonstrated residual concentration.

Calibration. Selecting parameters using data. Independent validation. Comparing with results not used to select them, under a defined question and domain.

Sensitivity. Output variation under changing inputs or parameters. It is not probabilistic unless an explicit probability model describes those changes.

Uncertainty. Limited knowledge of a quantity or prediction. It can involve sampling, analysis, parameters and model structure; decimal places do not automatically summarise it.

Energy and materials

Electrical P. Power in kW. Distinguish it from P for phosphorus through context and subscripts. Energy is integrated power, in kWh.

Electrical charge. I*t, in coulombs when time is seconds. One hour is 3600 seconds. This differs from pollutant load.

Specific energy. kWh/m3 or kWh/kg removed, stating pollutant and boundary. The denominators differ and concentration is needed for conversion.

Faradaic efficiency. Charge associated with the reaction of interest relative to supplied charge under the stated definition. Electrode loss may include chemical corrosion and cannot automatically replace this ratio.

kLa. Volumetric transfer coefficient, normally h-1 or s-1. Convert units before comparison. It is neither air flow nor oxygen concentration.

OTR and OUR. Oxygen transfer and oxygen uptake rates. Dissolved-oxygen increase follows their balance together with other inputs and outputs.

Common conversions

Hourly-flow conversion to daily volume applies only to the stated operating period. A plant operating for twenty hours uses twenty in its volume calculation. An interface multiplying by 24 must be checked against the original data definition.