Chapter 26, Problem 9MC

Summary Introduction

Introduction:

Water treatment is the process by which the quality of water is improved and makes it suitable for use. Wastewater treatment consists of four phases namely, primary treatment, secondary treatment, chemical treatment, and sludge treatment.

Primary treatment: This is the first phase of wastewater treatment. In this process, heavy materials which settle at the bottom as sludge are removed and light materials which float on the water surface are skimmed off. Alum is added in this process which acts as a flocculating agent.

Secondary treatment: This is the second phase of water treatment. Water after primary treatment is aerated to increase the growth of microbes in it. This facilitates the microbes to oxidize the dissolved organic chemicals and convert them into water and carbon dioxide. Most of the organic compounds are removed in this phase.

Chemical treatment: After secondary treatment, water is sent for chemical treatment. In this process, chemicals such as oxidizing agents, iodine, and chlorine are used. Addition of these compounds helps in reducing the growth of microbes and kills them. It is a form of disinfection.

Sludge treatment: In this process, sludge undergoes anaerobic treatment. It is fermented by anaerobic microbes to produce organic acids and carbon dioxide. These organic acids are then treated again by microbes so as to produce simpler organic acids. These simpler organic acids are then converted to methane gas by microbes. Leftover sludge is then dried and sent to landfill.