Environmental Engineering — Part 1 MCQs with Explanations

Slow sand filters operate at a very low filtration rate because the purification mainly occurs through biological action in the schmutzdecke layer formed on top of the sand. The typical rate of filtration for slow sand filters is 0.1 to 0.2 m³/m²/hr, which when converted equals approximately 50 to 60 million litres per day per hectare (MLD/ha). Thus, the correct filtration rate range matches Option A.

Residual chlorine in water can be determined using both the Starch iodide method and the Orthotolidine method . The Starch iodide method involves adding a solution of starch and potassium iodide to the water sample containing residual chlorine. The residual chlorine oxidizes iodide ions to iodine, which then reacts with starch to form a blue complex, indicating the presence of residual chlorine. The Orthotolidine method is another commonly used method for determining residual chlorine in water. In this method, orthotolidine (OT) reacts with residual chlorine to form a yellowish-brown color, which is then quantified spectrophotometrically. Therefore, Option C: Both (A) and (B) is the correct choice, as both the Starch iodide method and the Orthotolidine method can be used to determine residual chlorine in water.

The gas from a sludge digestion tank is primarily composed of Methane . Sludge digestion is a process in environmental engineering where organic matter in sewage sludge is decomposed by microorganisms in an anaerobic environment, producing biogas as a byproduct. Biogas is mainly composed of methane, along with smaller amounts of carbon dioxide and traces of other gases such as hydrogen sulfide and nitrogen.

The correct answer is Option A: Maximum at noon Let's break down why: * Dissolved Oxygen (DO): This refers to the amount of oxygen gas that is present in the water. * Photosynthesis: Aquatic plants (like algae) and phytoplankton in streams perform photosynthesis. This process uses sunlight to convert carbon dioxide and water into glucose (food) and, importantly, oxygen . This oxygen is released into the water, increasing the DO. * Sunlight and Photosynthesis: Photosynthesis is dependent on sunlight . * Noon: Around noon, sunlight is typically at its strongest intensity. * Therefore, maximum photosynthesis occurs around noon , leading to a maximum level of dissolved oxygen in the stream. * Midnight: At midnight, there is no sunlight, so photosynthesis stops. Respiration by aquatic organisms (which *consumes* oxygen) continues. Therefore, DO is typically *lowest* at night. * So, the dissolved oxygen is not the same throughout the day.

Chlorination is the suitable method for disinfection of swimming pool water . Chlorine is commonly used to disinfect swimming pool water because it is effective in killing bacteria, viruses, and other microorganisms that can thrive in water. It helps maintain safe and sanitary swimming conditions by preventing the spread of waterborne diseases. The other options are not typically used for disinfecting swimming pool water: Option A: Ultra violet rays treatment is a method for disinfection, but it is less commonly used in swimming pools. Option B: Lime treatment is not primarily used for disinfection but may be used for water conditioning and pH adjustment. Option C: By using potassium permanganate is not a common method for swimming pool disinfection. So, the correct answer is Option D: Chlorination , which is the standard and effective method for disinfecting swimming pool water.

Understanding the Question: This question is about water supply in a city. We know the average daily water use (1,00,000 m³). But, water demand isn't constant throughout the day. There's always a peak time when consumption is much higher. Finding the Peak Demand: The question asks for the maximum amount of water used during the highest demand hour of the day. This peak hourly demand is always higher than the average daily consumption because people tend to use more water during certain hours (like mornings and evenings). Typical Peak Factors: To calculate peak hourly demand, we use a peak factor . This factor tells us how much higher the peak hourly demand is compared to the average daily demand. This peak factor varies depending on factors like the city's size and water distribution system. Commonly, it falls within the range of 1.5 to 2.7. Applying the Peak Factor: Let's consider a peak factor of 1.5 (or 1.5 times the average daily demand). Then, the peak hourly demand would be 1,00,000 m³ * 1.5 = 1,50,000 m³. If we used a peak factor of 2.7, the peak hourly demand would be 1,00,000 m³ * 2.7 = 2,70,000 m³. Choosing the Right Answer: Considering common peak factors, option B (1,50,000 m³) and option D (2,70,000 m³) are both plausible. The exact answer would depend on the specific peak factor used for that city. The question may require you to assume a typical peak factor or provide one in the problem itself.

A sewerage system needs to handle varying amounts of wastewater. It's not enough to design it for just one flow rate. Maximum Flow: The system must be able to handle the peak flow , which occurs during times of high water usage (like after heavy rain or during certain times of the day). If the system isn't designed for maximum flow, it could overflow, causing pollution and other problems. Minimum Flow: The system also needs to function properly during times of low flow . If the flow is too low, solids can settle in the pipes, leading to blockages and the production of unwanted gases. Minimum flow is important for maintaining a self-cleansing velocity. Options A, B, and C are incorrect because they only consider one extreme of flow, which is not sufficient for a well-functioning sewerage system. A good design considers both extremes to ensure reliable and efficient operation.

Self-cleansing velocity is the minimum velocity required to prevent the deposition of solids and keep the sewer clean. It depends on the diameter of the grain (particle size) rather than the diameter of the sewer. The self-cleansing velocity in a sewer is typically given by the formula: v = k * sqrt(g * d * (G - 1) / f) Where, v = Self-cleansing velocity k = Sediment coefficient g = Acceleration due to gravity d = Particle diameter G = Specific gravity of the particle f = Friction factor From this equation, it is evident that self-cleansing velocity is independent of the sewer diameter . Thus, increasing the sewer diameter has no effect on the self-cleansing velocity .

The correct answer is Option B: Sludge disposal . First, what is sludge ? In simple terms, when we treat dirty wastewater (like from homes or factories) to make it clean, a lot of solid waste settles down. This concentrated solid waste is called sludge . It's thick, full of organic material, and needs to be managed carefully. Now let's look at the methods mentioned: 1. Composting : Imagine making compost for your garden from kitchen scraps. Composting for sludge is a very similar process! It's a natural biological process where tiny living things (microorganisms) break down the organic matter in the sludge. This happens under controlled conditions, usually with good air supply. The goal is to turn the harmful sludge into a stable, soil-like material called compost, which can then be safely used, for example, as a soil conditioner in farming. 2. Lagooning : This method involves putting sludge into large, shallow ponds or basins called lagoons. The sludge stays there for a long time, sometimes for months or even years. During this time, natural processes like gravity settling (solids sinking), evaporation (water disappearing into the air), and biological breakdown (by bacteria) occur. These processes help to reduce the volume of the sludge and make it less harmful, stabilizing it over time. Both composting and lagooning are methods specifically designed to handle the sludge after it's produced during wastewater treatment. They aim to reduce its volume, stabilize it, and prepare it for its final destination or use. Therefore, these methods are used for the final management or ultimate fate of sludge , which is commonly referred to as sludge disposal . Why not the other options? * Sludge digestion (Option A): Digestion is actually a part of what happens *inside* composting and lagooning, where microorganisms break down organic matter. But composting and lagooning are the broader methods that lead to the sludge's final management or disposal. * Sedimentation (Option C): This is a process where solid particles settle out of water due to gravity, which *produces* sludge in the first place during wastewater treatment. It's not a method for treating or managing the sludge itself. * Filtration (Option D): This is a process to separate solids from liquids by passing them through a filter. While filtration can be used to remove water from sludge (dewatering), it's not the main mechanism behind composting or lagooning. So, composting and lagooning are effective ways to manage and dispose of sludge safely, and sometimes beneficially, after it's collected from wastewater treatment.

In environmental engineering, the detention period for oxidation ponds is typically kept as 10 to 15 days (Option C). Oxidation ponds, also known as stabilization ponds, are wastewater treatment systems that use natural processes such as sunlight, algae growth, and bacterial action to treat wastewater. The detention period refers to the average time that wastewater remains in the pond before being discharged. A detention period of 10 to 15 days allows sufficient time for the biological and chemical processes in the oxidation pond to effectively treat the wastewater, reducing its pollutant levels and improving its quality before discharge. Therefore, the correct option is Option C: 10 to 15 days .

Slow sand filters are a type of water treatment system. They use layers of sand to remove impurities from water. The size of the sand particles is important for how well the filter works. If the sand is too fine, the water will flow too slowly. If the sand is too coarse, it won't trap enough impurities. The effective size refers to the size of the particles where 10% of the sand is finer. For slow sand filters, the effective size needs to be just right for optimal performance. The correct range for effective sand particle size in slow sand filters is 0.25 to 0.35 mm . Therefore, the best option is A .

2 is the correct answer to “Which of the following values of pH represents a stronger acid”. This question is standard in competitive examination syllabi for Environmental Engineering.

Maximum hourly demand on maximum day is the correct answer to “The distribution mains are designed for”. This question is standard in competitive examination syllabi for Environmental Engineering.

Average flow only is the correct answer to “Sewage treatment units are designed for”. This question is standard in competitive examination syllabi for Environmental Engineering.

6.5 to 8.0 is the correct answer to “For satisfactory working of a sludge digestion unit, the pH range of digested sludge should be maintained as”. This question is standard in competitive examination syllabi for Environmental Engineering.

Chlorination is the correct answer to “The pathogens can be killed by”. This question is standard in competitive examination syllabi for Environmental Engineering.

Residual chlorine is the correct answer to “Orthotolidine test is used for determination of”. This question is standard in competitive examination syllabi for Environmental Engineering.

2 - 3 months is the correct answer to “Period of cleaning of slow sand filters is about”. This question is standard in competitive examination syllabi for Environmental Engineering.

Anaerobic in lower compartment and aerobic in upper compartment is the correct answer to “The working conditions in imhoff tanks are”. This question is standard in competitive examination syllabi for Environmental Engineering.

1.0 m/sec to 1.2 m/sec is the correct answer to “The self cleansing velocity for all sewers in India is usually”. This question is standard in competitive examination syllabi for Environmental Engineering.

Circle method is the correct answer to “The method of analysis of distribution system in which the domestic supply is neglected and fire demand is considered is”. This question is standard in competitive examination syllabi for Environmental Engineering.

Manhole is the correct answer to “The means of access for inspection and cleaning of sewer line is known as”. This question is standard in competitive examination syllabi for Environmental Engineering.

0.001 ppm is the correct answer to “The phenolic compounds in public water supply should not be more than”. This question is standard in competitive examination syllabi for Environmental Engineering.

Requires treatment before disposal is the correct answer to “The water carriage system of collection of waste product”. This question is standard in competitive examination syllabi for Environmental Engineering.

Increases is the correct answer to “In chlorination, with the rise in temperature of water, death rate of bacteria”. This question is standard in competitive examination syllabi for Environmental Engineering.

Alkaline and acidic is the correct answer to “The characteristics of fresh and septic sewage respectively are”. This question is standard in competitive examination syllabi for Environmental Engineering.

Provides self cleansing velocity at low discharges is the correct answer to “An egg shaped section of sewer”. This question is standard in competitive examination syllabi for Environmental Engineering.

Circular section is the correct answer to “Most suitable section of sewer in separate sewage system is”. This question is standard in competitive examination syllabi for Environmental Engineering.

Lateral sewer is the correct answer to “A sewer that receives the discharge of a number of house sewers is called”. This question is standard in competitive examination syllabi for Environmental Engineering.

Hardness in water is the correct answer to “Standard EDTA (ethylene diamine tetra acetic acid) solution is used to determine the”. This question is standard in competitive examination syllabi for Environmental Engineering.

1.5 is the correct answer to “The hourly variation factor is usually taken as”. This question is standard in competitive examination syllabi for Environmental Engineering.

Killing of disease bacteria is the correct answer to “Disinfection of water results in”. This question is standard in competitive examination syllabi for Environmental Engineering.

Total alkalinity is the correct answer to “If the total hardness of water is greater than its total alkalinity, the carbonate hardness will be equal to”. This question is standard in competitive examination syllabi for Environmental Engineering.

Sight rails and boning rods is the correct answer to “Laying of sewers is usually done with the help of”. This question is standard in competitive examination syllabi for Environmental Engineering.

TOD > COD > BOD is the correct answer to “The correct relation between theoretical oxygen demand (TOD), Biochemical oxygen demand (BOD) and Chemical oxygen demand (COD) is given by”. This question is standard in competitive examination syllabi for Environmental Engineering.

More discharge is the correct answer to “As compared to shallow wells, deep wells have”. This question is standard in competitive examination syllabi for Environmental Engineering.

Stronger is the correct answer to “As compared to cast iron pipes, steel pipes are”. This question is standard in competitive examination syllabi for Environmental Engineering.

Bacteria and colloidal solids is the correct answer to “In water treatment, rapid gravity filters are adopted to remove”. This question is standard in competitive examination syllabi for Environmental Engineering.

Dual action of aerobic bacteria and anaerobic bacteria is the correct answer to “In facultative stabilization pond, the sewage is treated by”. This question is standard in competitive examination syllabi for Environmental Engineering.

Oxidation ditch is the correct answer to “The maximum efficiency of BOD removal is achieved in”. This question is standard in competitive examination syllabi for Environmental Engineering.