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Question 1
ప్రశ్న 1
Which statement best describes the basic operating principle of a conventional slow sand filter?
Select an option first. || ముందుగా ఒక సమాధానాన్ని ఎంచుకోండి.
Explanation:
A conventional slow sand filter normally operates as a gravity downflow granular-media filter. Water passes through a relatively fine sand bed at a low hydraulic loading rate. Removal occurs through a combination of physical, biochemical and biological mechanisms. The biologically active surface layer becomes particularly important after the filter has ripened. Therefore Option A is correct.
వివరణ:
Question 2
ప్రశ్న 2
Which sequence correctly represents the principal layers of a slow sand filter from top to bottom?
Select an option first. || ముందుగా ఒక సమాధానాన్ని ఎంచుకోండి.
Explanation:
Raw water first occupies the supernatant-water zone above the sand surface. The schmutzdecke develops at or near the upper surface of the fine sand bed. Graded gravel beneath the sand prevents the filter medium from entering the drainage system and supports uniform collection. The underdrainage system at the bottom conveys filtered water away from the bed. Therefore Option A is correct.
వివరణ:
Question 3
ప్రశ్న 3
What is the principal hydraulic function of the supernatant water above the sand bed in a slow sand filter?
Select an option first. || ముందుగా ఒక సమాధానాన్ని ఎంచుకోండి.
Explanation:
The supernatant water provides hydraulic head above the sand surface. This head supplies the driving force necessary for water to pass through the increasingly resistant filter bed. It also provides some short-term storage before water reaches the sand surface. As the filter clogs, a greater portion of the available head is consumed in overcoming resistance. Therefore Option A is correct.
వివరణ:
Question 4
ప్రశ్న 4
According to current CPHEEO engineering guidance, which sand-media characteristics are appropriate for a slow sand filter?
Select an option first. || ముందుగా ఒక సమాధానాన్ని ఎంచుకోండి.
Explanation:
Current CPHEEO engineering guidance describes natural sand with an effective size of approximately 0.25 to 0.35 mm for slow sand filtration. The corresponding uniformity coefficient is indicated in the approximate range of 3 to 5. Fine sand and the low filtration rate together promote effective removal near the upper portion of the bed. These values should not be confused with the coarser media generally associated with rapid sand filtration. Therefore Option A is correct.
వివరణ:
Question 5
ప్రశ్న 5
What is the principal purpose of the graded gravel layer beneath the sand in a slow sand filter?
Select an option first. || ముందుగా ఒక సమాధానాన్ని ఎంచుకోండి.
Explanation:
The fine filtering sand cannot be placed directly over relatively large drainage openings without suitable support. Graded gravel supports the sand and prevents filter media from entering the underdrainage system. It also assists in obtaining relatively uniform hydraulic abstraction from the bed. Current CPHEEO guidance indicates a gravel depth of roughly 0.2 to 0.3 m. Therefore Option A is correct.
వివరణ:
Question 6
ప్రశ్న 6
What is the primary function of the underdrainage system in a slow sand filter?
Select an option first. || ముందుగా ఒక సమాధానాన్ని ఎంచుకోండి.
Explanation:
Filtered water reaches the lower part of the filter after passing through the sand and gravel. The underdrainage system collects this water across the bed and conveys it toward the outlet. Suitable underdrains may be formed using channels, perforated pipes or other appropriate arrangements. Unlike rapid sand filters, conventional slow sand filters are normally cleaned by surface scraping rather than routine hydraulic backwashing. Therefore Option A is correct.
వివరణ:
Question 7
ప్రశ్న 7
What is the schmutzdecke in a slow sand filter?
Select an option first. || ముందుగా ఒక సమాధానాన్ని ఎంచుకోండి.
Explanation:
The schmutzdecke is a thin biologically active layer that develops on the surface of a functioning slow sand filter. It contains microorganisms and accumulated organic and particulate matter. Biological activity within this layer contributes substantially to removal and transformation of contaminants. Its development distinguishes mature slow sand filtration from simple mechanical straining through clean sand. Therefore Option A is correct.
వివరణ:
Question 8
ప్రశ్న 8
Which group best represents the important purification mechanisms operating in a slow sand filter?
Select an option first. || ముందుగా ఒక సమాధానాన్ని ఎంచుకోండి.
Explanation:
Slow sand filtration is not based on a single removal mechanism. Physical processes such as straining and deposition within the upper bed contribute to particle removal. Sedimentation and interception within pore spaces also assist in retaining impurities. Biological and biochemical activity in the schmutzdecke and upper sand layers contributes strongly to organic and microbiological purification. Therefore Option A is correct.
వివరణ:
Question 9
ప్రశ్న 9
Why is a newly cleaned or newly commissioned slow sand filter normally allowed to ripen before its filtrate is sent directly to supply?
Select an option first. || ముందుగా ఒక సమాధానాన్ని ఎంచుకోండి.
Explanation:
The biological surface layer does not instantly possess its mature purification capability after a new filter is commissioned or heavily cleaned. A period of biological development and stabilization is required. CPHEEO guidance describes operating the filter during this period and sending the initial filtrate to waste until satisfactory quality is demonstrated. Bacteriological performance is particularly important in deciding whether ripening is complete. Therefore Option A is correct.
వివరణ:
Question 10
ప్రశ్న 10
What normal filtration rate is recommended in CPHEEO design guidance for slow sand filters?
Select an option first. || ముందుగా ఒక సమాధానాన్ని ఎంచుకోండి.
Explanation:
CPHEEO design guidance recommends approximately 0.1 m/h as the normal design filtration rate for slow sand filters. This low hydraulic loading is a defining feature of the process. It allows effective purification in the upper sand and biologically active layer but results in comparatively large required filter areas. An overload rate of about 0.2 m/h is separately identified for appropriate temporary conditions. Therefore Option B is correct.
వివరణ:
Question 11
ప్రశ్న 11
Why does CPHEEO guidance recommend providing at least two slow sand filter units?
Select an option first. || ముందుగా ఒక సమాధానాన్ని ఎంచుకోండి.
Explanation:
Slow sand filters must periodically be taken out of service for surface cleaning and subsequent return to operation. Multiple units provide operational continuity during this maintenance period. CPHEEO therefore recommends a minimum of two filter units. Its traditional design guidance identifies approximately 0.2 m/h as the maximum overload rate associated with maintaining production when a unit is unavailable. Therefore Option A is correct.
వివరణ:
Question 12
ప్రశ్న 12
A normal slow-sand filtration rate of 0.10 m/h is equivalent to what daily hydraulic loading?
Select an option first. || ముందుగా ఒక సమాధానాన్ని ఎంచుకోండి.
Explanation:
A filtration rate expressed in m/h is numerically equivalent to m³ per m² of filter area per hour. Multiplying 0.10 m/h by 24 hours gives 2.4 m/day. Thus each square metre of operating filter area produces 2.4 m³/day at the stated constant rate. This conversion is useful when filter area is calculated from a plant capacity expressed in MLD. Therefore Option C is correct.
వివరణ:
Question 13
ప్రశ్న 13
A slow sand filtration plant must treat 2.4 MLD continuously at a normal filtration rate of 0.10 m/h. What total operating filter area is required?
Select an option first. || ముందుగా ఒక సమాధానాన్ని ఎంచుకోండి.
Explanation:
A flow of 2.4 MLD equals 2,400 m³/day or 100 m³/h. Required filter area equals flow divided by filtration rate. Therefore A = 100/0.10 = 1,000 m². The same result follows from 2,400 m³/day divided by 2.4 m³/m²·d. Therefore Option C is correct.
వివరణ:
Question 14
ప్రశ్న 14
Using the CPHEEO recommended-number table for slow sand filters, how many beds are recommended for a total filter area of 1,000 m²?
Select an option first. || ముందుగా ఒక సమాధానాన్ని ఎంచుకోండి.
Explanation:
The CPHEEO recommended-number table places total filter areas from 650 to 1200 m² in the five-bed category. A total area of 1,000 m² lies within this range. Dividing the plant into several beds improves operational flexibility during cleaning and maintenance. This question uses the explicit CPHEEO planning table rather than assuming that every slow-sand plant must have exactly two beds. Therefore Option D is correct.
వివరణ:
Question 15
ప్రశ్న 15
If the 1,000 m² total area in the previous case is divided into five equal slow sand filter beds, what is the area of each bed?
Select an option first. || ముందుగా ఒక సమాధానాన్ని ఎంచుకోండి.
Explanation:
The total filter area is 1,000 m² and there are five equal units. Area per unit is therefore 1,000/5. This gives 200 m² for each slow sand filter bed. Equal division is assumed explicitly in the question, although actual layouts may be adjusted to suit site geometry and hydraulic arrangements. Therefore Option B is correct.
వివరణ:
Question 16
ప్రశ్న 16
The five equal 200 m² filters described above treat 2.4 MLD. If one filter is taken out of service and the remaining four must carry the same total flow, what filtration rate is required in each operating bed?
Select an option first. || ముందుగా ఒక సమాధానాన్ని ఎంచుకోండి.
Explanation:
The total plant flow is 2.4 MLD, which equals 100 m³/h. With one unit out, four beds remain in service and their combined area is 4 × 200 = 800 m². The required filtration rate is therefore 100/800 = 0.125 m/h. This exceeds the normal 0.1 m/h rate but remains below the 0.2 m/h overload value cited in CPHEEO guidance. Therefore Option C is correct.
వివరణ:
Question 17
ప్రశ్న 17
A slow sand plant must treat 3.6 MLD continuously at the normal rate of 0.10 m/h. What total filter area is required?
Select an option first. || ముందుగా ఒక సమాధానాన్ని ఎంచుకోండి.
Explanation:
A flow of 3.6 MLD equals 3,600 m³/day or 150 m³/h. At a filtration rate of 0.10 m/h, the required area is 150/0.10. This gives a total filter area of 1,500 m². Alternatively, dividing 3,600 m³/day by 2.4 m³/m²·d gives the same result. Therefore Option C is correct.
వివరణ:
Question 18
ప్రశ్న 18
Which statement correctly describes the sand-bed depth recommended for a slow sand filter in current CPHEEO engineering guidance?
Select an option first. || ముందుగా ఒక సమాధానాన్ని ఎంచుకోండి.
Explanation:
CPHEEO guidance provides an initial slow-sand filter-bed depth of about 1.0 m. Periodic cleaning removes a thin layer from the upper surface and therefore gradually reduces the sand depth. The current engineering guidance indicates that the effective bed thickness should not fall below roughly 0.4 to 0.5 m for best efficiency. Re-sanding becomes necessary after repeated cleanings have significantly reduced the bed depth. Therefore Option A is correct.
వివరణ:
Question 19
ప్రశ్న 19
How is a conventional slow sand filter normally cleaned when accumulated material and head loss become excessive?
Select an option first. || ముందుగా ఒక సమాధానాన్ని ఎంచుకోండి.
Explanation:
Most of the clogging material in a slow sand filter accumulates near the sand surface and within the biological layer. CPHEEO guidance describes lowering the water level and scraping approximately the upper 10 to 20 mm of sand during cleaning. This removes the clogged surface material without disturbing the entire filter bed. The process differs fundamentally from the frequent hydraulic backwashing used for rapid gravity filters. Therefore Option A is correct.
వివరణ:
Question 20
ప్రశ్న 20
A slow sand filter starts with 1.00 m of sand. If 20 cleanings each remove an average of 15 mm of sand and no re-sanding occurs, what sand depth remains?
Select an option first. || ముందుగా ఒక సమాధానాన్ని ఎంచుకోండి.
Explanation:
Each cleaning removes 15 mm, which is 0.015 m of sand. Twenty such cleanings remove 20 × 0.015 = 0.30 m. The remaining depth is therefore 1.00 - 0.30 = 0.70 m. This remains above the approximate 0.4 to 0.5 m minimum-effective-depth range cited in CPHEEO guidance, although continued scraping will eventually require re-sanding. Therefore Option C is correct.
వివరణ:
Question 21
ప్రశ్న 21
A raw surface water reaching a slow sand filter develops persistently high turbidity that would cause rapid clogging. Which response is most consistent with current CPHEEO guidance?
Select an option first. || ముందుగా ఒక సమాధానాన్ని ఎంచుకోండి.
Explanation:
Slow sand filtration performs best when the incoming particulate load is reasonably low. Persistently high turbidity can clog the biologically active surface and shorten filter runs severely. Current CPHEEO guidance identifies storage, sedimentation or primary filtration as possible pretreatment where raw-water turbidity is high. It also cautions that conventional coagulation and flocculation can produce gelatinous floc that may rapidly clog slow-sand media. Therefore Option A is correct.
వివరణ:
Question 22
ప్రశ్న 22
Which combination best describes a practical advantage and a practical limitation of slow sand filtration?
Select an option first. || ముందుగా ఒక సమాధానాన్ని ఎంచుకోండి.
Explanation:
Slow sand filters are mechanically simple and can provide excellent particulate and microbiological improvement under suitable raw-water conditions. They require relatively little sophisticated mechanical equipment compared with high-rate filtration systems. Their low filtration rate, however, produces a large required plan area for a given plant capacity. They are also unsuitable for persistently high particulate loads unless suitable pretreatment is provided. Therefore Option A is correct.
వివరణ:
Question 23
ప్రశ్న 23
Why does head loss through a slow sand filter generally increase as a filter run progresses?
Select an option first. || ముందుగా ఒక సమాధానాన్ని ఎంచుకోండి.
Explanation:
Particles and biological material progressively accumulate near the upper portion of the slow sand bed. This increases resistance to passage of water through the filter. A greater hydraulic head is consequently required to maintain the selected filtration rate. When resistance becomes excessive or the available head is exhausted, the unit must be taken out for cleaning. Therefore Option A is correct.
వివరణ:
Question 24
ప్రశ్న 24
A slow sand filter has 500 m² of operating area and runs continuously at 0.10 m/h. What is its theoretical daily filtrate production?
Select an option first. || ముందుగా ఒక సమాధానాన్ని ఎంచుకోండి.
Explanation:
At 0.10 m/h, each square metre of filter produces 0.10 m³/h. For 500 m², the hourly output is 500 × 0.10 = 50 m³/h. Over 24 hours, production is 50 × 24 = 1,200 m³/day. This is equal to 1.20 MLD. Therefore Option C is correct.
వివరణ:
Question 25
ప్రశ్న 25
Which statement about microbiological treatment by a slow sand filter is most appropriate?
Select an option first. || ముందుగా ఒక సమాధానాన్ని ఎంచుకోండి.
Explanation:
A mature slow sand filter can provide substantial microbiological improvement because of biological predation, adsorption and other processes in the upper bed. CPHEEO describes slow sand filtration as capable of removing most pathogens under suitable conditions. Nevertheless, drinking-water safety should rely on a multiple-barrier treatment approach rather than assuming that one filter alone guarantees absolute pathogen absence. Disinfection and distribution-system protection remain important components of safe public water supply. Therefore Option A is correct.
వివరణ:
Question 26
ప్రశ్న 26
Consider the following statements about slow sand filters: I. Their normal design filtration rate is about 0.1 m/h. II. The schmutzdecke contributes significantly to purification. III. Cleaning is normally performed by scraping the clogged upper sand layer rather than routine rapid backwashing. IV. High raw-water turbidity may require pretreatment to prevent excessive filter loading. Which option is correct?
Select an option first. || ముందుగా ఒక సమాధానాన్ని ఎంచుకోండి.
Explanation:
Statement I is correct because CPHEEO guidance identifies approximately 0.1 m/h as the normal slow-sand filtration rate. Statement II is correct because the biologically active schmutzdecke is a defining purification feature of the process. Statement III is correct because conventional slow sand filters are cleaned primarily by surface scraping rather than by routine high-rate backwashing. Statement IV is correct because excessive raw-water turbidity shortens filter runs and may require storage, sedimentation or primary filtration ahead of the filters. Therefore all four statements are correct and Option D is the valid answer.
వివరణ:
Answer Key సమాధానాల పట్టిక
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Question 1 ప్రశ్న 1Answer: A. Water passes slowly downward through fine sand, where physical and biological processes remove impurities సమాధానం: A.
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Question 2 ప్రశ్న 2Answer: A. Supernatant water → schmutzdecke and sand bed → graded gravel → underdrainage system సమాధానం: A.
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Question 3 ప్రశ్న 3Answer: A. To provide the driving head required to overcome resistance through the filter and associated hydraulic system సమాధానం: A.
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Question 4 ప్రశ్న 4Answer: A. Effective size about 0.25–0.35 mm with uniformity coefficient about 3–5 సమాధానం: A.
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Question 5 ప్రశ్న 5Answer: A. To support the sand, prevent its entry into the underdrains and help distribute collection of filtered water సమాధానం: A.
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Question 6 ప్రశ్న 6Answer: A. To support the overlying media arrangement and provide an unobstructed path for collecting filtered water సమాధానం: A.
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Question 7 ప్రశ్న 7Answer: A. A biologically active surface layer that develops on the upper sand bed and contributes strongly to purification సమాధానం: A.
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Question 8 ప్రశ్న 8Answer: A. Straining, sedimentation or interception, and biochemical or biological action సమాధానం: A.
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Question 9 ప్రశ్న 9Answer: A. Because the biologically active filter skin must develop or re-establish and satisfactory effluent quality should be confirmed సమాధానం: A.
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Question 10 ప్రశ్న 10Answer: B. 0.10 m/h సమాధానం: B.
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Question 11 ప్రశ్న 11Answer: A. So that filtration can continue when one unit is taken out for cleaning సమాధానం: A.
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Question 12 ప్రశ్న 12Answer: C. 2.4 m³/m²·d సమాధానం: C.
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Question 13 ప్రశ్న 13Answer: C. 1,000 m² సమాధానం: C.
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Question 14 ప్రశ్న 14Answer: D. 5 సమాధానం: D.
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Question 15 ప్రశ్న 15Answer: B. 200 m² సమాధానం: B.
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Question 16 ప్రశ్న 16Answer: C. 0.125 m/h సమాధానం: C.
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Question 17 ప్రశ్న 17Answer: C. 1,500 m² సమాధానం: C.
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Question 18 ప్రశ్న 18Answer: A. A new filter is provided with about 1.0 m of sand, and effective bed thickness should not be allowed to fall below roughly 0.4–0.5 m before re-sanding సమాధానం: A.
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Question 19 ప్రశ్న 19Answer: A. By draining the water level appropriately and scraping approximately the upper 10–20 mm of dirty sand సమాధానం: A.
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Question 20 ప్రశ్న 20Answer: C. 0.70 m సమాధానం: C.
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Question 21 ప్రశ్న 21Answer: A. Provide suitable pretreatment such as storage, sedimentation or primary filtration before the slow sand filter సమాధానం: A.
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Question 22 ప్రశ్న 22Answer: A. Simple operation and strong biological purification, but comparatively large land area is required because of the low filtration rate సమాధానం: A.
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Question 23 ప్రశ్న 23Answer: A. Accumulated material and growth of the surface layer increase hydraulic resistance to flow సమాధానం: A.
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Question 24 ప్రశ్న 24Answer: C. 1.20 MLD సమాధానం: C.
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Question 25 ప్రశ్న 25Answer: A. The biological layer can remove a large proportion of pathogens, but filtered water should still be managed within the overall drinking-water treatment and disinfection strategy సమాధానం: A.
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Question 26 ప్రశ్న 26Answer: D. I, II, III and IV సమాధానం: D.