What will happen to antiscalants when we discharge them to the enviroment ? Are they toxic? Are they biodegradable? If so how long will they take to decay?

There are different types of antiscalants. Some are phosphonate based,and some are polymer based. Many are blends to provide synergistic effects of the two chemistries. Antiscalants have to be non-toxic, or they would not be approved by NSF for potable water applications. Both phosphonate and polymer based antiscalants are biodegradable over time. Ultraviolet light increases the rate of degradation as the chemical bonds are broken, and certain types of bacteria produce enzymes that cleave the bonds.

Recently some “green” antiscalants have been introduced into the market, with the claim that they biodegrade at a faster rate. In reverse osmosis membrane systems, anything that biodegrades too quickly will be a carbon source for bacteria and contribute to biofouling. It is best to avoid such chemistries from an operational standpoint.