IMHO, the biodegradable ...

IMHO, the biodegradable material is one which is amenable to degrading through enzymatic biochemical reactions, which is primarily brought about by the action of bacteria.

Normally, a 5-day period is desirable as based on the initial experiments, they specified 5-day Biochemical Oxygen Demand. In a treatment plant, however, it is desirable to reduce this time to less that one day by increasing the concentration of bacteria and other parameters fine tuNing. WWTP are designed to enhanced the natural process of bydegradable, which is generally slow process. All ETP does is increase the speed of process.

Some chemicals ss mentioned by you may be amenable to oxidation by enzymatic biochemical processes. WHO is better equipped to answer that question as to why these are biodegradable.

Looking at it, given enough time water dissolves material, and that is why it is called a Universal Solvent. 

Based on my little experience with Water and Wastewater Management issues.

Regard and Best.

Jagdish Kumar Bassin

Former Chief Scientist & Head

CSIR-NEERI Delhi Center

New Delhi

Chief Advisor, India Water Foundation.

Freelance Consultant for Air and Water quality Modelling and Design of wastewater treatment plant.