List of top Questions asked in GATE Environmental Science and Engineering

A saturated \(CaCO_3 \)stock solution is existing at 25°C. In one experiment (i) 25 g \(Na_2CO_3 \)is added to the stock solution. In another experiment (ii) 25 g \(Na_2SO_4\) is added to the stock solution. Select the correct statement from the following.

In a region, total annual consumption of gasoline is 30.6 million tons. The land required for growing sugarcane to produce enough bioethanol to replace the gasoline completely is ___________ \(km^2\) (an integer value). 
Ethanol energy equivalent is 67% of gasoline, gasoline density is 850 \(kg/m^3\), yield of bioethanol produced from sugarcane per hectare of land is 3750 L, and 1 \(km^2\) = 100 hectares

Food waste, paper waste and plastic waste have typical densities of \(280 kg/m^3\), \(80 kg/m^3\), and \(50 kg/m^3\), respectively. The mixed waste is composed of 70% food waste, 20% paper waste and 10% plastic waste. The density of the mixed waste is ______ \(kg/m^3\). (rounded off to 2 decimal places). Neglect compaction effect.

A person consumes 2.5 liters of water per day. The water quality test indicated that the supplied water has a Pb concentration of 0.6 mg/L. If the weight of the person is 75 kg, the exposure level for Pb for this person from this drinking water source is _________mg/kg/day (rounded off to 2 decimal places).

For a biodegradable waste with a chemical formula $C_{50}H_{100}O_{40}N$, the maximum theoretical methane production per ton of waste is __________kg (rounded off to 2 decimal places).
Assume 100% anaerobic conversion. Atomic weights of C-12; H-1; O-16; N-14

Initially a bottle contained 400 g of ethanol. Half of ethanol was used by a student for preparing the stock solution in an environmental chemistry laboratory just before summer vacation of 90 days. After completing the procedure, the student left the bottle uncorked. If the unsealed bottle losses ethanol at a rate of 0.5 g/day, the ethanol that will be left in the bottle at the end of the summer vacation is __________ g (an integer value).

An industry discharges 2 million liters per day (MLD) of wastewater with a temperature of 45°C and a pH of 2, whereas the neighboring industry produces 3 MLD of wastewater with a temperature of 30°C and pH of 8. If both the wastewaters are mixed and carried through a pipeline, then the resultant pH of mixed wastewater is ___________ (rounded off to 2 decimal places).
Neglect buffering capacity of the system and the temperature effect on pH.

One million liters per day (MLD) of wastewater with a soluble BOD of 200 mg/L is treated in an activated sludge process. The BOD of treated wastewater is 20 mg/L. The observed yield coefficient of the biological system is 0.35.
The daily biomass generation in the system is _____________kg (an integer value).

Consider a watershed and isohyets as shown in the figure. The average rainfall in the watershed is __________ mm (an integer value).

In a cyclone separator of radius 25 cm, a particle is travelling with a gas stream at velocity of 18 m/s. The ratio of centrifugal force to the gravitational force acting on the particle is ________(rounded off to 2 decimal places).
Consider acceleration due to gravity (g) as 9.8 m/s2.

With reference to the gate shown in the figure, the gate will start opening automatically when the water level 'h' above the hinge is ________ m (rounded off to 2 decimal places).

Two hypothetical organic waste streams A and B are mixed prior to the composting process. Waste-A has 2.16% of C and 1.20% of N. Waste-B has 19.10% of C and 0.14% of N. The quantity of Waste-B that should be mixed with per kg of Waste-A to achieve the desired C:N ratio of 25 is ________ kg (rounded off to 2 decimal places). Assume both the waste streams are completely dry.

Two sources of noise, adjacent to each other in a room, have sound pressure levels of 30 and 40 decibel (dB). The combined sound pressure level in the room is _________ dB(rounded off to 2 decimal places).
Use reference sound pressure as $20 \mu Pa$.

An industrial stack emits 100 g/s of CO at an effective height of 'H', where the wind speed is 5 m/s. At 3 km distance downwind, the values of dispersion coefficient in y- direction and z-direction are 50 m and 25 m, respectively. The CO concentration at the centerline of the plume at 3 km distance downwind is ________ \(mg/m^3\) (rounded off to 2 decimal places)?  Use Gaussian plume model and value of \(\pi\) = 3.14. Neglect reactions and the ground effect of plume in the calculations.

The Streeter-Phelp's oxygen sag equation for a river is based on a few assumptions. The correct assumption(s) is/are

Consider the equation for a curve, $y = f(x) = x^2 + x$. The area enclosed by the curve, the x-axis (y = 0 line); the vertical lines passing through x = 1 and x = 2 is ______(rounded off to 2 decimal places)

The ionic strength of a solution containing 0.01M of $CaCl_2$ and 0.001M of $Na_2SO_4$ is _____ M (rounded off to 3 decimal places)

Based on the ISO 14040 methodology for Life Cycle Assessment, match the terms with the descriptions in the table.

Term	Description
(a) Goal and Scope	(i) Based on the product or system, the comparative unit must be carefully defined and be same for all scenarios
(b) Functional Unit	(ii) The problem is described, and the objective of the study are defined
(c) Life Cycle Inventory	(iii) Evaluates the environmental implications due to the inventorized emissions
(d) Impact Assessment	(iii)  Process based approach and input-output approach

The correct match(es) is/are

Water is flowing FULL through a rectangular tunnel of size 3 m (width) × 2 m (height). The average velocity of flow is 1 m/s. The frictional head loss is observed to be 1 m per km. Consider acceleration due to gravity (g) as 10 \(m/s^2\). The correct statement(s) is/are

The concentration of Ozone corresponding to a mixing ratio of 120 ppbv at pressure of 1 atmosphere and temperature of 25°C is ________ \(μg/m^3\) (rounded off to 1 decimal place).
Atomic weight of oxygen = 16; R= 8.314 J/K-g.mole.

The pH of a solution containing 0.1M of acetic acid and 0.05 M of sodium acetate is ________ (rounded off to 2 decimal places).
The $pK_a$ value of ionization of acetic acid is 4.76.

Consider the function f(x) = ln(sin(x)). Expand f(x+h) using Taylor's series. In this context, the correct statement(s) is/are

Consider two horizontal layers of an aquifer as shown in figure. Each layer is isotropic and homogeneous. Flow is parallel to the stratification. Thickness and horizontal hydraulic conductivity of layer-1 are $h_1$i and $K_1$, respectively. Thickness and horizontal hydraulic conductivity of layer-2 are $h_2$ and $K_2$, respectively, where $h_1$ is not equal to $h_2$. The equivalent horizontal conductivity $K_x$ for the aquifer system is given by _____

Enzymes with the class of enzymes are listed in the table. Enzyme Class of Enzyme

Enzymes	class of enzymes
(a) Lactate dehydrogenase	(i) Isomerases
(b) Alanine racemase	(ii) Transferases
(c) Lipase	(iii) Oxidoreductases
(d) Hexokinase	(iv) Hydrolases

Select the correct match(es)

A gravity settling chamber of height ‘H' and length ‘L' is designed to control particulate air pollution. In the chamber, the horizontal velocity of air flow is $'V_h'$ and terminal settling velocity of the target particle is $'V_ť$. Which one of the following expressions is the correct concept used to calculate the minimum size of the target particle that will be removed with 100% efficiency?