GATE ES year:2021 PYQs & Answers — Page 7 — Exam Papers

Questions 61–65 of 65. Imported answers require independent review unless marked reviewed.

Topic practice 65 questionsPage 7 of 7

The municipal solid waste (MSW) generated in a community (population = 10000) is disposed on a 12×10⁴ m² landfill site, which can be filled to a total depth of 25 m (including soil cover). Assume that MSW is generated at a rate of 2.5 kg per person per day and its compacted density is 800 kg/m³. If the volumetric ratio of MSW and soil cover is 5:1, the useful life of the landfill site is ______ years (rounded off to the nearest integer).

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A mechanized stationary container system is proposed for waste collection from a commercial area. The container unloading time is 0.1 hours per container. There are two containers at each location and the drive time between the two locations is 0.2 hours. The maximum waste ‘pick-up time’ is 2.4 hours per trip. The ‘pick-up time’ starts at the instant the truck arrives at the first pick-up location and ends when the last container on the route is emptied. The maximum number of locations which can be covered in a trip by the collection vehicle are ______ (answer in integer).

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The molar concentrations (M, i.e. mol/L) of some ionic species in a water sample were estimated as follows: Na⁺ = 0.25 M; Ca²⁺ = 0.12 M; Cl⁻ = 0.32 M; HCO₃⁻ = 0.05 M. The ionic strength of this water sample is ______ M (correct up to two decimal places).

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Excess amount of solid calcium sulfate (CaSO₄) was added to a pure water sample (pH = 7) so that some solids remain undissolved at the equilibrium. The solubility product of CaSO₄ is 2×10⁻⁵ mol²/L². The molar concentration of SO₄²⁻ in this water sample at equilibrium will be ______ mol/L (rounded off to three decimal places).

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A facultative pond system for sewage treatment consists of two ponds in series. The hydraulic retention time (HRT) of each pond is 6 days. The total BOD₅ reduction through the entire pond system is 90 %. If the ponds are considered to be completely mixed, then the rate constant describing the BOD₅ removal is ______ day⁻¹ (rounded off to two decimal points). Assume that the rate constant is same for both the ponds.

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