Test: Environmental Engineering- 2 - Civil Engineering (CE) MCQ

The amount of nitrites or nitrates present in sewage sample can be measured by colour matching methods.

For nitrites, the colour is developed by adding Sulphonilic acid and naphthamine whereas for nitrates, the colour is developed by adding phenol-di-sulphonic acid and potassium hydroxide. The colour developed in waste water is finally compared with the standard colours of known concentrations.

At lower temperatures, bacterial kill tends to be slower and higher doses are needed. The effect of low temperatures is greater with combined chlorine than with free available chlorine.

Contact time is as important as the chlorine dose in determining the efficiency of water treatment chlorination. Contact time is the amount of time which the chlorine has to react with the microorganisms in the water, which will equal the time between the moment when chlorine is added to the water and the moment when that water is used by the consumer. The longer the contact time, the more efficient the disinfection process is. When using chlorine for disinfection a minimum contact time of 30 minutes is required for adequate disinfection.

The period after which the entire catchment area will start contributing to the runoff is called as the time of concentration. Time of concentration (T_c) is the time required for runoff to travel from the hydraulically most distant point in the watershed to the outlet. The time of concentration is equal to sum of inlet time and time of travel.

In sewers,

Inlet time = The time taken by rainfall water to run from most distant point of water shed to the inlet of sewer.

Time of travel = The time required for flow of water in sewer to the point under consideration.

Advantages of Activated carbon:

i) Due to its adsorption property it removes taste, colour and odour

ii) It removes phenol type impurity

iii) When used in coagulants, it aids in coagulation

iv) It reduces the chlorine demand of water because some amount of chlorine is used to oxidise organic matter which is removed by activated carbon

v) Its overdose is not harmful

Filters are basically classified as Gravity filters and Pressure filters:

In gravity filters, the head required to flow through sand will be provided by the head of water over the sand medium, but in pressure filtration, the necessary head would be provided by pressure applied from outside.

Slow sand filters and Rapid sand filters are example of gravity filters.

Note: Slow sand filter removes larger percentage of impurities as compared to rapid sand filters, but the rate of filtration is more in rapid sand filters as compared to slow sand filters.

Deoxygenation constant (K_D) is given by:

T= Temperature of waste water in ^oC

The alkalinity of fresh waste water sample is alkaline but as time passes it becomes acidic because of the bacterial action in anaerobic or nitrification process. As the time passes away, the biological activity increases which in turn increases the H⁺ ions (main cause of acidity) leading to decrease in alkalinity of waste water.

Standards of Dilution for discharge of wastewaters into rivers:

Population equivalent is given by:

Total BOD₅

Testing of leakage in the pipe joints or at any point in the pipeline is done by two methods:

1) Water Test: This test is carried out between two manholes. In this method the water is allowed to flow in the sewer line from upper manhole until the sewer is completely filled up.

Then, the depth of water in the upper manhole is raised up to 1 m above the sewer line and is inspected to detect the leakage by observing any sweating.

2) Air Test: This test is carried out for large diameter sewer. In this method pressure gauge is used to measure the pressure drop with its permissible value, If the pressure drop in the pipe line is below the permissible value, then it is an indication of leakage. The exact point of leakage is found out by applying soap solution which will show bubbles at the point of leakage.

Decomposers are organisms that break down dead or decaying organisms, and in doing so, they carry out the natural process of decomposition. Like herbivores and predators, decomposers are heterotrophic, meaning that they use organic substrates to get their energy, carbon and nutrients for growth and development.

Reservoirs are of two main categories: (a) Impounding reservoirs into which a river flows naturally, and (b) Service or balancing reservoirs receiving supplies that are pumped or channeled into them artificially.

In general, service or balancing reservoirs are required to balance supply with demand. These reservoirs are relatively small in volume because the storage required by them is to balance flows for a few hours or a few days at the most. Impounding or storage reservoirs are intended to accumulate a part of the flood flow of the river for use during the non-flood months.

pOH = -log [OH^-]

pOH = -log (10^-5.6 × 10^-3)

pOH = -log (10^-8.6)

pOH = 8.6

But, pH + pOH = 14

pH =14 – 8.6

pH = 5.4

Carbonate hardness is lesser of alkalinity and total hardness.

Hence carbonate hardness= 250 mg/l and Non-Carbonate Hardness= 400-250= 150 mg/l.

1.Tube well water is free from solids.

2. Water in deep tube well reaches after seepage passing through pores. Hence it contains less suspended particles, but it may contain pathogens therefore disinfection is required.

Ozone and PAN

Photochemical smog is produced when pollutants from the combustion of fossil fuels react with sunlight. The energy in the sunlight converts the pollutants into other toxic chemicals. In order for photochemical smog to form, there must be other pollutants in the air, specifically nitrous oxides and other volatile organic compounds (VOCs). When nitrous oxides and VOCs interact with sunlight, secondary pollutants are formed, such as ozone and peroxyacetyl nitrate.

Pyrolysis is a thermochemical decomposition of organic material at elevated temperatures in the absence of oxygen. Anhydrous pyrolysis can also be used to produce liquid fuel similar to diesel from plastic waste, with a higher cetane value and lower sulphur content than traditional diesel.

Composting is a natural biological process, carried out under controlled aerobic conditions (requires oxygen). In this process, various microorganisms, including bacteria and fungi, break down organic matter into simpler substances. The effectiveness of the composting process is dependent upon the environmental conditions present within the composting system i.e. oxygen, temperature, moisture, material disturbance, organic matter and the size and activity of microbial populations.

Incineration is a waste treatment process that involves the combustion of organic substances contained in waste materials. incineration of waste materials converts the waste into ash, flue gas and heat.

Sanitary landfills are sites where waste is isolated from the environment until it is safe. It is considered safe when it has completely degraded biologically, chemically and physically.

The clogging of a filter due to the presence of air released from water. Air entering the filter media is harmful to both the filtration and backwash processes. This occurs when negative head due to resistance provided by filter media becomes high and vacuum created release dissolved gases.

Zeolite process for water softening has become a commercial success for the reason that zeolite can be easily regenerated. When Ca²⁺ and Mg²⁺ ions containing hard water is passes through a bed of sodium zeolite, the sodium ions are replace by the calcium and magnesium ions. Zeolite process is the best process to remove permanent hardness from the water.

Note: Temporary hardness can be removed by simply boiling