Targeting Maximum Water Reuse for Single Contaminants

A number of points need to be noted regarding the data in Table 26.4. First, the concentration is specified on the basis of the mass flowrate of water and not the mass flowrate of the mixture. 

In most problems, the concentration of contaminant is so small that there is virtually no difference between the concentration based on the mass flowrate of water and the mass flowrate of the mixture. However, it is important to be consistent and follow the convention given in Equation 26.1. The other point to note is regarding the units. It is convenient to define the flowrate in terms of metric tons (typically tons per hour or tons per day). It is also convenient to define the concentration in terms of parts per million (ppm). If the basic unit of flowrate is taken to be tons and concentration to be parts per million, then the mass load is measured in grams (typically grams per hour or grams per day). 

The flowrate in Table 26.4 refers to the limiting water flowrate. The limiting water flowrate is the flowrate required if the specified mass of contaminant is picked up by the water between the maximum inlet and outlet concentrations. If an operation has a maximum inlet contaminant concentration greater than zero and it is fed by water with zero concentration, then for the specified mass load, a lower flowrate than the limiting water flowrate could be used. 

Operation number Contaminant mass (g-tr1) r - in (ppm) Cout (ppm) Limiting water flowrate (t-h 1) 

Analysis of the data in Table 26.4 can be started by calculating the flowrate that would be required for each of these operations, if each operation was fed by freshwater with zero concentration. The relationship between mass pickup of contaminant, mass flowrate of water and concentration change is given by  

---