Blog
Wahlbergisms
- September 10, 2013
- Posted by: Eric & Patti Wahlberg
- Category: From the Mind of Eric Wahlberg
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- M∙mg/L: used to cancel mg, L and M (in Mgal) in pounds and pounds/day calculations
- Mgal/106 gal: used to insert M into the pounds and pounds/day calculations when volume or flow is given in units of gal (106 gal = 1,000,000 gal) or other volume units converted to gal
- %TS: (usually in sludge or sludge cake) expressed as lb/100 lb of sludge or cake; for example, primary sludge is given as containing 4.8% TS is expressed as 4.8 lb TS/100 lb sludge; for example, centrifuge cake is given as containing 22% TS is expressed as 22 lb TS/100 lb cake
- %VS: always expressed as lb VS/100 lb of TS; for example, primary sludge is given as containing 76.8% VS is expressed as 76.8 lb VS/100 lb TS (in digester gas calculations, expressed as 76.8 lb VSapplied/100 lb TS)
- VSR: given as a percent and expressed as lb of VS destroyed in a digester per 100 lb of VS applied, or fed, to the digester (lb VSdestroyed/100 lb VSapplied); for example, a VSR of 59.8% is expressed as 59.8 lb VSdestroyed/100 lb VSapplied
- Percent solids recovery (%SR): given as a percent and expressed as lb of TS in output from per 100 lb of TS in input to the thickening or dewatering unit; for example, a belt filter press is given as having a %SR of 96.6% is expressed as 96.6 lb TSc (TS in cake, output from the press)/100 lb TSs (TS in sludge feed, input to the press)
- Percent CH4 (methane): in digester gas; expressed as ft3 CH4 per 100 ft3 gas; for example, 66% methane is expressed as 66 ft3 CH4/100 ft3 gas (this is the only instance in wastewater math where percent is on a volumetric rather than a weight (mass) basis)
- Holy grail of pond math-3.069 ac∙ft/Mgal: if ac and Mgal are on opposite sides of the equals sign or on opposite sides of the railroad track, this conversion factor greatly simplifies the math
- F/M: almost always given without units but is not unitless; for example, given an F/M ratio of 0.35, it is expressed as 0.35 lb BOD/d∙lb MLVSS
- %AI (active ingredient): when used in chemical dosing problems, expressed as pounds of AI per 100 pounds of solution(or however the solution is labeled); for example, 0.35% polymer solution is expressed as 0.35 lb/100 lb soln; for example, sodium hypochlorite (hypo) is given as 12.5% chlorine is expressed as 12.5 lb Cl2/100 lb hypo; for example, liquid alum (LA) is given as 49% dry alum (DA) is expressed as 49 lb DA/100 lb LA
- Density: used constantly in wastewater math to convert back and forth between gallons and pounds (density of water, 8.34 lb/gal, most common), but when concentration is given in percent (%), proper labeling is key; for example, 8.34 lb soln/gal soln; for example, 10.0 lb hypo/gal hypo; for example, 6.21 lb AqA (aqueous ammonia)/gal AqA; for example, 11.0 lb liquid alum/gal liquid alum (or, using an abbreviation, 11.0 lb LA/gal LA)
- Remember: no matter what “method” you use in your calculations (using formulas, using algebra, using dimensional analysis (the railroad track)), if we get the same answer, we are doing it the same way
- When using the railroad track, the units tell you what the equation is and they do the algebra for you! Practice making your drawings and labeling them like we did in class!