एक अच्छी तरह से ऑक्सीकृत सीवेज (मलजल) में नाइट्रोजन मुख्य रूप से किस रूप में होती है?

Which of the following flows is also known as sanitary sewage?

In the very first stage of decomposition of the organic matter in sewage:

The secondary treatment of sewage is primarily caused by: