For 1, the results can be calculated through the chemical reaction equation. And for 2 is often through the small test, with a suitable concentration, can not blindly specify a quantity of a concentration for dosage. Because often the flow of sewage is much higher than the dosage, so in the configuration of 2 can try to configure some dilute, and then mentioned a relatively large concentration, when the chemicals and sewage fully mixed. According to my experience, the actual dosage is often higher than the results of the small test, but not too high, too much will cause the water to be more mixed, this problem should also take into account some of the parameters of the sedimentation tank.