*PYQs Section:* *Essay Question* *Primary and Secondary Sewage Treatment:* • Draw a flowchart: https://link.marrow.com/pearl/5a03f1e64f25447d0916fceb • Write a few lines about each method as given in the Pearl *Short Answers* Septic tank: PM1661 https://link.marrow.com/pearl/5a03e5524f25447d0916fc38 *Very Short Answers:* • Oxidation ponds: https://link.marrow.com/pearl/5a03f5094f25447d0916fcee • BOD, COD: https://link.marrow.com/pearl/5a03ef074f25447d0916fc3c