chromium is one of the heavy metal .It may harm human's health when people take the creature which absorb it as nutrition.ALso a heavy metal ion may cause the fish in the water die.All in a word it was harmful so factory must remove it before the waste water is emissioned.
use a CaO to adjust the PH of the water.Cr may be precipated at the pH of 6
Cr2O72-+14H++6e===2Cr3++7H2O
In factory we may use such electronating agent like FeSO4,SO32- to act as the e-
I was too tired to continue the answer last night.But I like these kind of questions which needs us to answer in English.I am Junior .though I have past the cet6 but my spoken english is very poor.I cant express what I want to tell clearly especially when it comes to my major english.I need excises.And thank you for providing such a good stage for me and other students with similiar thoughts.