Q1. [4] medium exam-ready
Read the following passage and answer the questions that follow:
Every litre of waste water discharged by industry pollutes eight times the quantity of freshwater. Industrial effluents can be treated in three phases: primary treatment involves mechanical means such as screening, grinding, flocculation and sedimentation; secondary treatment uses biological processes; and tertiary treatment involves recycling of wastewater through biological, chemical and physical processes. In addition, particulate matter in the air can be reduced by fitting smoke stacks with electrostatic precipitators, fabric filters, scrubbers and inertial separators.
(i) What is the purpose of tertiary treatment of industrial effluents? (1)
(ii) Name any two devices, other than electrostatic precipitators, that can be fitted to smoke stacks to reduce air pollution. (1)
(iii) Apart from treating effluents, suggest two other strategies industries can adopt to reduce water pollution. (2)
Generated by claude-sonnet-4-6 · 2026-06-26 13:34 · grounding rag
Model Answer
(i) Tertiary treatment involves recycling of wastewater through biological, chemical and physical processes. Its purpose is to further purify water so it can be reused or safely discharged.
(ii) Two devices (other than electrostatic precipitators) that can be fitted to smoke stacks to reduce air pollution are:
- Fabric filters
- Scrubbers (or inertial separators)
(iii) Two other strategies industries can adopt to reduce water pollution:
- Minimising use of water for processing by reusing and recycling it in two or more successive stages.
- Harvesting rainwater to meet water requirements, reducing dependence on freshwater sources.
Source: Control of Environmental Degradation, Chapter 6
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Explanation
- (i) The answer is directly stated in the passage — "tertiary treatment by biological, chemical and physical processes...involves recycling of wastewater." Mention recycling explicitly.
- (ii) The passage lists four devices; the question excludes electrostatic precipitators, so pick any two from the remaining three: fabric filters, scrubbers, inertial separators.
- (iii) The passage lists three strategies to reduce water pollution. The question asks for strategies apart from treating effluents, so avoid mentioning effluent treatment — pick minimising/recycling water use and rainwater harvesting. Each point earns 1 mark.