This blog is the 7th article in a series of GATE preparation tips blog articles for Civil Engineering Students. The blog author, Rohit Sachdeva has secured AIR 93 in GATE 2017 and is currently studying at IISc Bangalore. You can read the rest of the articles under the CE section for GATE blogs at http://gate.vidyalankar.org/category/civil-engineering/.
Environmental Engineering is a very vast and important subject in Civil Engineering. In this blog, I will be discussing how to prepare for the PART 2 of Environmental Engineering: Waste Water Engineering. It carries a high weightage in GATE exam. This subject should be studied thoroughly and should not be skipped at any cost. It includes theory & numericals, but, we can observe that questions have been following a similar trend through years. Since there are many topics to be covered & formulas to be memorized, try to revise this subject maximum time.
A rough breakup of questions of various topics in last 30 years in GATE is as follows:
||No. of Questions
||Design of Sewers & Construction
||Quality Characteristics of Sewage
||Treatment of Sewage
||Activated Sludge Process
||Disposal of Sewage Effluents
An analysis of last 5 years of GATE papers shows that Environmental Engineering (all parts together) carries 10-12 marks.
Time required for preparation (Part 2)
11-13 days (if you have 8-10 month of preparation) with 3-4 hours daily
5-7 days (if you have 4-5 months of preparation) with 6-8 hours daily
Equal weightage of 1-mark and 2 marks questions can be expected, with fewer number of NAT questions. There is lesser to practice than to remember, so 2 rounds of revision are suggested. The textbook(s) to be referred are mentioned in BLOG-3 which you can utilize.
Let’s start our topic-wise discussion (most important concepts are bold & italics):
1. 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, different sewer appurtenances.
2. QUALITY CHARACTERISTICS OF SEWAGE (2-3 DAYS)
This is the most important chapter in wastewater and numericals should be practiced. This chapter has following three parts:
- Physical characteristics: Temperature, color, turbidity and odour. Study the comparison b/w old & fresh sewage based on these parameters.
- Chemical characteristics: This is the most important part in this chapter. Organic content (oxygen demand test to measure organic strength: BOD, COD, TOD, ThOD), Inorganic content and dissolved gases. Understanding concept of BOD is very important (test, formulas, concept of dilution factor, dependence on temperature, 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).
3. 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 questions (theoretical).
ACTIVATED SLUDGE PROCESS (1 DAY)
Aerobic method of waste treatment; design parameters (F/M ratio, mean cell residence time, BOD loading rate, SVI, recycling ratio). Prepare formula sheet. Read through conventional & modified ASP, operational problems related to ASP. Also practice numericals on design parameters.
4. TRICKLING FILTER (1 DAY)
Read through the mechanism & operational problems of trickling filter; and practice problems related to design (NRC equation, recirculation; write them in formula sheet).
5. SLUDGE TREATMENT (2 DAYS)
This chapter contains anaerobic treatment which includes Mass-volume relation of sludge, volume reduction (formula sheet), design of sludge digester. Practice lot of numericals from this topic.
Design and processes in septic tank and Imhoff tank. Practice 1-2 numericals of each.
6. OXIDATION PONDS (1 DAY)
They are aerobic waster stabilization ponds. This topic contains design of ponds; practice 1-2 numericals.
7. 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 should be included in formula sheet. Also practice numericals.