Water Treatment in Environmental Engineering – Complete Guide for JKSSB, SSC JE & RRB JE

📅 Updated: July 2025
🔍 Subject: Environmental Engineering – Civil
🎯 Exam Focus: JKSSB JE Civil, SSC JE, RRB JE, State AE/JE

🧱 Introduction

Water treatment is the systematic process of enhancing the quality of raw water to make it appropriate for a specific purpose such as domestic consumption, industrial use, or agricultural irrigation. The process involves removing physical, chemical, and biological contaminants that pose health or operational risks.

In civil engineering, especially in the domain of environmental engineering, water treatment is a critical component for achieving safe water supply, reducing environmental pollution, and promoting sustainable development. It includes scientific knowledge of water chemistry, process engineering, and public health standards, all of which are essential for designing efficient water treatment plants (WTPs).

Understanding each stage of water treatment—from screening to disinfection—enables civil engineers to construct reliable and cost-effective systems that ensure the supply of clean, potable water in both urban and rural areas. For JKSSB and other competitive exams, mastering this topic helps answer both theoretical and formula-based questions accurately.

🌊 Sources of Water

📝 JKSSB Tip: Questions may ask about the most contaminated or most reliable water sources.

⚠️ Objectives of Water Treatment

1. Remove physical impurities like suspended solids and turbidity.
2. Eliminate chemical pollutants such as hardness, iron, fluoride, and heavy metals.
3. Kill or remove biological contaminants like bacteria, viruses, protozoa.
4. Improve taste, odor, and appearance.
5. Ensure compliance with IS 10500 and WHO drinking water standards.

🔀 Complete Process of Water Treatment

Source Water → Screening → Aeration → Coagulation → Flocculation → Sedimentation → Filtration → Disinfection → Storage & Distribution

🧱 1. Screening

• Purpose: To remove large-sized floating and suspended matter such as plastics, rags, wood pieces, twigs, leaves, and other debris that could damage or clog pumps and pipes in the treatment plant. Screening is the first and essential barrier that ensures only manageable-sized particles enter subsequent treatment stages. It enhances the operational efficiency and longevity of downstream equipment like aerators and sedimentation tanks.
• Types of screens:
  • Coarse Screens: Bar spacing ≥ 25 mm
  • Fine Screens: Bar spacing < 25 mm

📌 JKSSB Fact: Screening is a mechanical process and doesn’t affect water chemistry.

🌳 2. Aeration

• Goal: Enhance the oxygen content of raw water and effectively strip out dissolved gases such as carbon dioxide (CO₂), hydrogen sulfide (H₂S), methane (CH₄), and volatile organic compounds (VOCs). Aeration also aids in the oxidation of soluble iron (Fe²⁺) and manganese (Mn²⁺) to form insoluble oxides, which can be removed in subsequent processes. This step improves water aesthetics by reducing unpleasant taste and odor and supports the efficiency of downstream treatments like coagulation and filtration.
• Techniques Used:
  • Waterfalls
  • Cascade aerators
  • Spray aerators

💡 Improves taste/odor and oxidizes iron and manganese.

🤫 3. Coagulation

• Removes colloidal particles that can’t settle naturally, as these particles are too small to settle by gravity alone. They remain suspended due to their surface charge and size, causing turbidity. Coagulation neutralizes these charges and destabilizes the particles, allowing them to clump together into larger flocs that can be removed by sedimentation or filtration.
• Common coagulants used include chemical agents like alum and ferric chloride, which are cost-effective and efficient for large-scale operations. These coagulants react with natural alkalinity in water to form flocs.
• Commonly used coagulants:
  • Alum (Al₂(SO₄)₃·18H₂O)
  • Ferric chloride (FeCl₃)
  • Polyelectrolytes

Alum Dose Formula (Unicode):
𝟯 (mg/L) = ( Alum used (mg) ) ÷ Volume of water treated (L)

🛠️ 4. Flocculation

• Gentle mixing after coagulation to form flocs.
• Performed using paddles or hydraulic mixing.
• Retention Time: 20–30 minutes

Velocity Gradient (Unicode):
𝐂 = √(𝗅 ÷ μ × 𝗴)

Where:
𝗅 = Power input (W), μ = Viscosity, 𝗴 = Volume

🏠 5. Sedimentation

• Gravity-based removal of flocs and heavier suspended particles.
• Sedimentation tanks are designed for optimal retention time and flow rate, often rectangular or circular in design.
• Sludge is collected at the bottom and removed periodically.

Settling Velocity Formula (Unicode):
𝐛ₛ = (𝐋 × (𝔾ₛ − 𝔾) × 𝑛²) ÷ 18𝐒

Where:
𝐋 = 9.81 m/s², 𝑛 = Diameter of particle (m), 𝔾 = Water density, 𝔾ₛ = Particle density, 𝐒 = Dynamic viscosity

🛁 6. Filtration

• Removes fine suspended solids and bacteria.
• Consists of a filter bed (sand/gravel/anthracite) and underdrain system.
• Requires regular backwashing (especially for RSF).

Types:

• Slow Sand Filter: Rate = 0.1 to 0.3 m³/m²/hr
• Rapid Sand Filter: Rate = 5 to 15 m³/m²/hr

Filtration Rate Formula (Unicode):
𝐒 = 𝐆 × 𝐛

Where:
𝐒 = Discharge, 𝐆 = Area, 𝐛 = Rate

💊 7. Disinfection

• Final stage to kill pathogenic microorganisms.
• Must ensure residual chlorine to prevent post-contamination.

Chlorine Dose Formula (Unicode):
𝐎 = 𝐋 + 𝐝

Where:
𝐎 = Applied dose, 𝐋 = Demand, 𝐝 = Residual chlorine

Common Methods:

• Chlorination (most used)
• UV radiation
• Ozonation

📊 WHO & IS 10500 Drinking Water Standards

🧠 Memory Aids

• SC-AF-SFD = Screening → Coagulation → Aeration → Flocculation → Sedimentation → Filtration → Disinfection
• SSF vs RSF: SSF = Slow & Simple, RSF = Rapid & Reversible

📝 JKSSB PYQs

1. Most used coagulant? ✔️ Alum
2. Filtration rate in RSF? ✔️ 5–15 m³/m²/hr
3. Purpose of chlorination? ✔️ Disinfection

📓 Conclusion

Water treatment is a key topic in JKSSB, SSC JE, and RRB JE exams. Focus on:

• Sequence of treatment stages
• Coagulation & filtration design
• Formulas and standard values

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Sahil Digra

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