Dear Mr.Liang After I check MSDS of surfactant RM about COD and calculate data for compare COD between YC0 and YC2 that the result should not be different.So I think, Tycoons waste water problem is foam more than COD.Today, I tell Ms.Ae set up our lab able to check COD which can done soon.This week, we go to Tycoons to talk and solve this problem. Best Regards,Sukit T.