why do biodegradable subatance do not harm environment?

Dear student, 
​Please find below the link to the asked query        

Mostly biodegradable wastes do not cause harm to environment as these are easily degradable and do not remain in the environment for long. But there are some biodegradable substances that cause pollution.
https://www.meritnation.com/ask-answer/question/does-biodegradable-waste-harm-the-environment/our-environment/6900619

Regards