Part I (60 Points) 1. Describe the mechanism though which sediment is removed fr

Question

Part I (60 Points) 1. Describe the mechanism though which sediment is removed from a waste stream in "slow" sand filtration. 2. Define adsorption, how does it differ from absorption? 3. What does an Isotherm indicate in the process of carbon adsorption 4. What are the three mechanisms that result in a particle coming into contact with a collector (filter media particle)? Describe the mechanism though which sediment is removed from a waste stream in "fast" filtration. 5. 6. The Langmuir Isotherm reaches a maximum value, describe physically what has happened when this value is reached (on an individual particle scale).

Explanation / Answer

1. It is a water purification and filtration system that uses Fine sand particles and micro-organisms.Slow sand filtration is a Physical, biological process. It removes the turbidity and pathogens in wastewater in a single step.The sand particles are arranged in terms of the size. The coarse particles on the top and the fine particles at the bottom of the bed. The sediments are clogged in between the sand particles having a size of approx 0.2mm. In addition to this, the microorganisms present at the sand-water interface kills the pathogens. Thus, it is an effective way of water purification without involving any chemicals.

2. Adsorption: It refers to a surface phenomenon where a large number of molecules (Either in solid or liquid or gaseous phase) accumulates as a thin layer on the surface of another body.

3. Isotherm refers to a line or curve representing a given process occurring at a constant temperature.

   Carbon adsorption is a process of adsorbing many organic, synthetic chemicals from water during drinking water treatment.The Isotherm here indicates the equilibrium relationship between Adsorbent, Adsorbate and the equilibrium concentration of Adsorbate in water. The plot is a straight line and helps us to understand the adsorbing capacity of a particular carbon compound. The adsorbing capacity of the carbon decreases as the steepness of the isotherm increases.

4. The three predominant mechanisms that result in a particle coming into a filter media particle are

a) Interception: When a particle following a given streamline comes within one particle radius to the filter media then the capturing of the particle by filter media is called Interception.

b) Inertial Impaction: The streamline of a given particle changes when there is any obstruction in its path.When a large particle is unable to change its direction due to its inertia and gets attached to the filter media present in its path.It is called Inertial Impaction.

c) Diffusion: All the gas molecules tend to move randomly which is referred to as Brownian Motion. When the size of the particles is very low i.e., in the order of microns, they move randomly due to their collisions with gas molecules. This process, when continued, increases the chances of a particle hitting the filter media. Thus, the process of random motion of small particles resulting in interaction with filter media is called diffusion.

5)The Rapid sand filter or Fast filtration uses a bed of silica having particles ranging from 0.5 -1 mm size. It doesn't have a biological mat and the large size of particles results in larger filtration values.Mechanical straining and physical adsorption are the two important principles of the rapid sand filter. The larger particles get stuck in between the sand grains as they pass the filter which is called mechanical straining. And the smaller particles get adsorbed to the surface of sand particles due to vander waal forces, which is called physical adsorption. The principle of hydraulic backwashing is done to remove the clogged particles frequently to ensure proper working.

6.

Adsorption Absorption 1. It is a surface phenomenon where the accumulation of molecules is more on the surface as compared to the bulk of the body 1. It is a bulk phenomenon where accumulation is more into the bulk of the body 2.It is same throughout the material 2. Most of the accumulation is limited to the surface only 3. Heat is absorbed during the process making it an endothermic process 3. Heat is released out making it an exothermic process

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