MEV 015: Unit 10 - Water Pollution and Its Control

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Unit 10: Water Pollution and Its Control

10.1 Introduction

Water pollution happens when harmful substances like chemicals, waste, and microorganisms enter water bodies, making them unsafe for drinking, agriculture, and aquatic life. Treating polluted water is essential to protect health, the environment, and water resources. This unit explains the various physical, chemical, and biological methods used to clean wastewater, along with advanced treatment techniques.

10.2 Objectives

This unit aims to:

·         Explain the different types of water treatment processes

·         Understand the role of physical, chemical, and biological methods in water purification

·         Learn how wastewater treatment plants are designed

·         Explore modern water treatment technologies like reverse osmosis and carbon adsorption

10.3 Physical Unit Processes

These processes remove solid materials from water using physical methods.

·         Screening: Removes large particles like sticks, plastic, or cloth using metal bars or screens at the beginning of the treatment.

·         Flocculation: Small particles in water are gathered into larger clumps (called flocs) by adding chemicals and slowly mixing the water.

·         Sedimentation: The flocs settle at the bottom of a tank due to gravity, leaving the clear water on top.

·         Filtration: The clear water passes through filters made of sand or gravel, which trap any remaining particles.

10.4 Chemical Unit Processes

These methods use chemicals to remove impurities or kill harmful microorganisms.

·         Chemical Precipitation: Certain chemicals are added to react with pollutants and form solid particles that can be removed by settling or filtration.

·         Adsorption Process: Polluted water is passed over a solid material (like activated carbon), which traps pollutants on its surface.

·         Disinfection Process: Chlorine, ozone, or UV rays are used to kill bacteria, viruses, and other pathogens, making the water safe for use.

10.5 Biological Unit Processes

These processes use microorganisms to break down organic waste in water.

·         Role of Micro-organisms: Bacteria and other microbes feed on organic pollutants and convert them into simpler, harmless substances.

·         Activated Sludge Process: Air is pumped into a tank containing wastewater and microbes. The microbes consume the waste, and the clean water is separated out.

·         Aerated Lagoons: Large ponds where air is added to support microbial activity and break down pollutants.

·         Stabilization Ponds: Natural or artificial ponds where sunlight, algae, and bacteria work together to purify water over time.

o    Aerobic Ponds: Use oxygen-using microbes

o    Anaerobic Ponds: Use microbes that work without oxygen

o    Facultative Ponds: Support both aerobic and anaerobic microbes

·         Trickling Filters: Wastewater is trickled over a bed of stones or plastic. Microbes living on the surface of the material eat the waste and clean the water.

·         Sludge Management: After treatment, the leftover solid waste (sludge) is treated, dried, and either disposed of safely or reused as fertilizer.

10.6 Design of a Wastewater Treatment Plant

A wastewater treatment plant is designed by combining physical, chemical, and biological processes in a step-by-step manner. The goal is to clean the water to meet environmental standards before discharging it into rivers or reusing it. The design includes proper flow of water, selection of treatment units, energy use, and safe sludge handling.

10.7 Advanced Water Treatment Processes

Advanced methods are used when high purity water is needed or when regular treatment methods are not enough.

·         Ion Exchange Process: This method removes unwanted ions like calcium and magnesium (which cause hardness) by exchanging them with harmless ions.

·         Reverse Osmosis (RO): Water is forced through a semi-permeable membrane that blocks salts, bacteria, and other pollutants. RO is widely used for drinking water purification.

·         Electro-dialysis: An electric current is used to move dissolved salts across membranes, separating them from clean water.

·         Carbon Adsorption: Activated carbon is used to trap and remove harmful organic compounds, bad tastes, and odors from water.

10.8 Let Us Sum Up

Water pollution is a major environmental problem, but it can be controlled using a combination of physical, chemical, and biological treatment methods. Physical processes remove solids, chemical processes remove or neutralize pollutants, and biological processes break down organic waste. Advanced methods like reverse osmosis and carbon adsorption provide high-quality water when needed. Proper design and management of treatment plants are essential to protect public health and the environment.

 

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