सीवेज बहिःस्राव (sewage effluent) का द्वितीयक वायवीय जैव रासायनिक उपचार मुख्य रूप से किसकी एक प्रक्रिया है?

Turbidity in water is measured on which standard scale?

Mudball formation in rapid sand filters is the result of:

In a water sample, if 2 mg of platinum cobalt salt is dissolved in 1 litre of distilled water, then the colour produced is equal to: