Once again---the oxidation ...
Published by Joseph Cotruvo, President at Joseph Cotruvo & Associates, Water , Environment and Public Health
Once again---the oxidation reduction chemistry of SO2 and bisulfite with chlorine is very complete, so you would not need GAC for chlorine removal. Who told you that you need it? Maybe you need a different consulting engineer? Also, adding ammonia to produce a small amount of chloramine is probably your best choice, because it will eliminate the free chlorine and also protect your downstream membranes. This is normal practice with membranes to reduce microbial biofouling.