A stream containing 5.15 wt % chromium (Cr) is contained in the waste water from

Question

A stream containing 5.15 wt % chromium (Cr) is contained in the waste water from a metal finishing plant. The waste water stream is fed to a treatment unit that removes 95% of the chromium in the feed to recycle it(no water content) to the plant. The residual liquid stream leaving the treatment unit is sent to a waste lagoon. The treatment unit has a maximum capacity of 4500 kg wastewater/h. If waste water leaves the finishing plant at a rate of 6000 kg/h, which is higher than the maximum capacity of the treatment unit, so that the excess of waste water bypasses the treatment unit and combines with the residual liquid leaving the unit, and combined stream goes to the waste lagoon. The schematic flowchart of the treatment process is shown in Figure 1. Based on 6000 kg/h of waste water from the metal finishing, calculate; (a) The flow rate of liquid (kg/h) to the waste lagoon, and the mass fraction of chromium in this liquid (b) The mass fraction of chromium and flow rate of liquid (kg/h) leaving the treatment unit if the process is scaled to 75% of its outlet flow rate of treatment unit.

Explanation / Answer

Solution:

a) Calculate the flow rate of liquid to the waste lagoon and the mass fraction of Cr in this liquid

5779.8 Kg/h

0.0154 kg cr/kg

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