Power Plant : Practice Questions and Answers

Sedimentation using chemical coagulation has been implied mainly to pre-treatment of industrial or process waste waters and removal of phosphorus from domestic waste waters. Alum is mostly used as it is cheap and easily available.

Pumping facilities may be employed to gain sufficient head for the waste water to flow through the treatment works to the point of final disposal. Pumping is also generally required for recirculation of all or part of the flow around certain units within the plant. Pumping facilities are classified as influent, effluent, or recirculation stations and perform a critical function.

Grit represents the heavier inert matter in waste water which will not decompose in treatment processes. It is identified with matter having a specific gravity of about 2.65 and design of grit chambers is based on the removal of all particles of about 0.011 inches or larger (65 mesh).

Chemical immobilization is a process consisting of precipitation and adsorption. Phosphorus is removed by chemical immobilization and it is also removed by plant uptake. The plant utilizes phosphorus for various purposes.

Refractory organics tend to resist conventional methods of waste water treatment. Typical examples include surfactants, phenols, and agricultural pesticides.

The concentration of total solids present in weak waste water is 350 mg/ L. The concentration of total solids present in strong waste water is 1200 mg/ L. The medium range consists of 720 mg/ L.

The advanced waste water sludge constitutes biological sludge. This also constitutes chemical sludge. The advanced waste water sludge is sent to the primary clarifier, where mixing is carried out in order to provide an uniformity to the mixture.

The controlled application of waste water onto the land surface to achieve a specified level of treatment through natural physical, chemical, and biological processes within the plant soil-water matrix is called land treatment.

The amount of TSS removed is 132 kg/d. The mass of the TSS removed = 220kg/1000/m3 x 0.6×1000 m3/d =132 kg/d. 220 mg/L is converted into Kg/L.

Urban cities have a large area and high population, therefore water usage is more and sewage generated will also be more. Hence, a separate system to carry sewage and stormwater is necessary. Whereas in rural areas, precipitation will be absorbed by the ground and infiltered. Therefore only a little amount of precipitation forms storm. Hence the combined system is preferred.

There are different types of nitrogen present in waste water. Basically, our types of nitrogen are present. They are organic nitrogen, ammonia nitrogen, nitrate nitrogen and nitrite nitrogen.

The unit lpcd stands for litres per capita per day and gpcd stands for gallons per capita per day. 40 lpcd indicates the minimum water usage for places like kids play home and schools. 700 lpcd is for hospitals.

When alum is added to a waste water containing calcium salts Al (OH)3 is precipitated. This is a gelatinous floc. This reaction sweeps out suspended particles.

Summers are usually dry. Hence the rainfall is minimum and is called as dry weather flow in sewers. During the rainy season or periods of high rainfall or storm, the sewers will be full and are called wet weather flow.

Dry wastes such as dry leaves, paper and grass are called garbage. Discharge is the outflow of water or waste water. Sewage is the waste water from various houses. Sullage is the waste water from bathroom, kitchen, wash basins, etc.

One of the sewer waste water treatment processes is a biological treatment known as activated-sludge process. Waste water is agitated and aerated to remove solids and oxidation methods are introduced to activate decomposition.

Waste water is from showers, basins, kitchen sinks, washing machines and the like. This is also called grey water. Normally a minimum of 75 mm diameter pipes is used for drainage of waste water.

Slow Rate (SR) systems are the predominant form of land treatment for municipal and industrial waste-water. Such a technology incorporates waste-water treatment, water reuse, crop utilization of nutrients and waste-water disposal.

Treatment is the next step after water abstraction in the waste water treatment process. The abstracted water undergoes various treatment stages including physical, chemical, and biological processes before being supplied to consumers.

Waste water is oxidised chemically using dichromate in acid solutions. High COD value indicates that the presence of inorganic compounds is high. Inorganic compounds get chemically oxidised and this results in the increase of organic compounds in the sample.