This article on Environmental Engineering has been written by Rohit Sachdeva. He graduated from Delhi College of Engineering (now DTU) in 2012 (a gold medalist in his batch) in Civil Engineering branch. Then he appeared in Civil Engineering (CE) paper in GATE 2017 and secured an All India Rank (AIR) of 93.

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A rough breakup of questions of various topics in last 30 years in GATE is as follows:

An analysis of last 5 years of GATE papers reflect that Environmental Engineering carries 10-12 marks, which is huge, and hence needs thorough preparation.

Time required for preparation

28-30 days (if you have 8-10 month of preparation) with 3-4 hours daily
14 days (if you have 4-5 months of preparation) with 6-8 hours daily

Equal weightage of 1-mark and 2 mark questions can be expected, with a fewer number of NAT questions. There is lesser to practice than to remember, so 2 rounds of revision are suggested. There are some formulas which you should remember, which I will specifically mention; and it is better to make a formula sheet for future revision. The textbook(s) to be referred are mentioned in a separate comprehensive blog which you should refer.

Let’s start our topic-wise discussion (most important concepts are bold & italics):

WATER SUPPLY ENGINEERING

1. WATER DEMAND (1 DAY)

Population forecasting (Arithmetic, Geometric, Incremental & Decrease in Growth Rate, Logarithmic), Variations in water demands (hourly, daily, weekly, monthly, etc), coincidental draft. Practice 1 numerical each for population forecasting.

2. WATER QUALITY CONTROL (4 DAYS)

This is the most important topic in water supply and there will be one sure question. There are 3 parts:

• Physical: Temperature, color, turbidity, odour and taste. You should know the measurement methods/equipment and permissible values/ranges.
• Chemical: This is the most important section. Solids (Total, dissolved, volatile, etc), pH (& pOH), Acidity, Alkalinity, Hardness, Chlorides, Sulphates, Dissolved Oxygen, Flourides, Nitrogen compounds, toxic chemicals.

lot of numericals relating alkalinity and hardness as there will be 1 sure question from this concept. Also practice numericals on pH & pOH.

Limits/ranges of different metals in water are important and should be learnt (make short notes), most important being nitrogen compounds.

• Biological: Qualitative and quantitative test for E.Coli, MPN and E.Coli index. From theory point of view, just read different water borne diseases.

3. PLAIN SEDIMENTATION (1 DAY)

This is another very important topic from point of view of 2 mark & NAT questions.

Type-1 settling, terminal velocity (Stoke’s law), sedimentation tank (types and design), design parameters (surface overflow rate, detention time, loading rate and flow-through velocity), particle removal efficiency (Vs > Vo). Practice numericals!!

4. COAGULATION (1 DAY)

This is a more of theoretical topic. Different types of coagulants (alum, copperas, chlorinated copperas, sodium-aluminate, remember chemical equation & note in formula sheet) and their application can be asked as a match the following type. You should also know the dosage and action (alkalinity) of alum (and lime); optimum dosage of coagulant.

Clariflocculator design (detention time, velocity gradient), relation b/w turbidity, alkalinity and coagulant dosage.

5. FILTERATION (1 DAY)

Mechanism of filtration, classification of filters, comparison and design of slow sand & rapid sand filters, filter kinetics, operational troubles in rapid sand filters, pressure filters & multi-media filters (theoretical reading).

6. DISINFECTION (2-3 DAYS)

Mechanism of disinfection, methods of disinfection (physical and chemical). Chlorination is the most important method. Understand in detail the action of Chlorine (chemical equation, different forms, their % and pH range of their formation); chlorine demand of water, physical forms in which Chlorine is available (hypochlorite, chloramines, chlorine gas & chlorine dioxide). Practice 2-3 numericals from kinetics of chlorination.

Types of chlorination is important; understand the concept of residual chlorine (its graph) and break-point chlorination. Practice numericals to calculate chlorine demand based on this. Read through the test to find residual chlorine.

7. MISC. WATER TREATMENT (1 DAY)

This is more of a theoretical topic covering aeration, softening (chemical requirements, Zeolite process, remember chemical equation & note in formula sheet), desalination of water (reverse osmosis, electro-dialysis, distillation), fluoridation & defluoridation (Nalgonda method), color removal.

8. DISTRIBUTION SYSTEMS (1 DAY)

An in-depth study is not required for this topic. Type of water distribution system (gravity, pumping, combined, their advantages/disadvantages), storage capacity of reservoir, layouts of water distribution, types of valves.

WASTEWATER ENGINEERING

9. DESIGN OF SEWERS & CONSTRUCTION (1-2 DAY)

Types of wastes (sewage, refuse, sullage, etc), Dry weather flow & wet weather flow (estimation, rational formula, time of concentration), design of sewers (self cleansing & non-scouring velocities, Manning’s formula, different conditions of flow through sewers), sewer appurtenances (not in details).

10. QUALITY CHARACTERISTICS OF SEWAGE (2-3 DAYS)

This is the most important topic in wastewater and numericals should be practised. There are 3 parts:

• Physical: Temperature, color, turbidity and odour. Comparison b/w old & fresh sewage based on these parameters.
• Chemical: This is the most important section. Organic content (oxygen demand test to measure organic strength: BOD, COD, TOD, ThOD), Inorganic content and dissolved gases. Understanding BOD is most important (test, formulae, concept of dilution factor, temperature dependence, population equivalent, relative stability); most numericals will include it. Practice lot of numericals of BOD as it has variety.

COD includes chemical reagents & sewage classification based on BOD/COD ratio. Read through TOD & ThOD (chemical equation).

11. TREATMENT OF SEWAGE (1 DAY)

Classification of treatment methods (physico-chemical vs biological, aerobic vs anaerobic), stages of treatment of wastewater; this chapter covers preliminary & primary treatment. Screening, grit chamber, skimming tank & primary clarifier should be read. There can be direct theoretical/conceptual questions. Read through once.

12. ACTIVATED SLUDGE PROCESS (1 DAY)

This is the aerobic method of waste treatment and is important for numericals; design parameters (F/M ratio, mean cell residence time, BOD loading rate, SVI, recycling ratio). Write these formulae in formula sheet. Read through conventional & modified ASP, operational problems related to ASP.

13. TRICKLING FILTER (1 DAY)

This is again aerobic method of treatment. Read through the mechanism & operational problems of trickling filter; and practice problems related to design (NRC equation, recirculation; write them in formula sheet).

14. SLUDGE TREATMENT (2 DAYS)

This contains anaerobic type of treatment which contains Mass-volume relation of sludge, volume reduction (formula sheet), design of sludge digester. Practice lot of numericals from this topic.

Next topic is Septic tank and Imhoff tank, which contains design numericals. Practice 2 numericals of each.

15. OXIDATION PONDS (1 DAY)

They are aerobic waster stabilization ponds. This topic contains the design of ponds; practice 1-2 numericals.

16. DISPOSAL OF SEWAGE EFFLUENTS (2 DAYS)

Disposal by dilution and land treatment, disposal limits, self-purification of water bodies (mixing of sewage into rivers, Streeter-Phelps equation-deoxygenation & reoxygenation), zones of pollution. Streeter-Phelps equation contains big formulae which you should write in a formula sheet & practice numericals.

17. SOLID WASTE MANAGEMENT (2 DAYS)

Classification of solid waste, characteristics of solid waste & disposal methods are the topics in this chapter. Numericals are asked from moisture content, equivalent specific gravity, energy content, ash content and organic content of solid waste. Disposal methods should be read through, particularly difference b/w Indore & Bangalore methods.

18. AIR POLLUTION & CONTROL (2 DAYS)

Read through composition of atmosphere, sources of air pollution, classification of air pollutants & major air pollutants. Thorough understanding of lapse rate & plume-rise models is required, both from theory & numerical point of view. Holland’s formula (effective stack height) should be read once.

Air pollution control is theoretical topic & in-depth study in not required. Read through air pollution preventive measures. Air pollution control techniques contains particulate control technologies & Gaseous control technologies; in which particulate control is important. It further includes dry control devices (gravity settling chambers, cyclone separators, electrostatic precipitator, fabric filters) & wet control devices (spray tower cyclone scrubber, venture scrubber). The diameter of particles that can be removed and efficiency of these methods are only needed.

19. NOISE POLLUTION (1 DAY)

Definition & formula of Sound Pressure level (SPL), standard reference pressure (20 µPa), decibels, Total SPL (2 methods to calculate), Average SPL & Equivalent SPL (when different sounds are heard for different times) should be studied. Practice numericals.

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