Propose a drinking-water treatment scheme for a community that can effectively r

Question

Propose a drinking-water treatment scheme for a community that can effectively remove turbidity particles, natural organic matter, pathogens, and herbicides from water. Please note that the community cannot afford to use membrane filtration and reverse osmosis. For the proposed treatment system, please name the chemicals to be used and comment on how to determine the doses of the chemicals. Please discuss the general mechanisms of each treatment unit you have proposed, (one sentence for each treatment unit;) Define break-point disinfection in one sentence. The disinfection byproducts (DBPs) of drinking water of another community is elevated. Please propose three solutions for the community to lower the concentrations of DBPs. In addition to the disinfection unit within the water treatment plant, can DBPs also be formed in the distribution system?

Explanation / Answer

Water treatment scheme for the given condition:-

Treatment of water is based upon both quaality of raw water and desited quality of water.

(1)Treatment of water for the given condition can be done in the following methods:-

A)Screening:-By coarse screen or fine screen.

B)Aeration:-By spray nozzle, tray tower, cascade aerattion or defused air method.

C)Sedimentation: can be done along with coagulation and flocculation if needed.

D)Filtration: better to use slow sand filter technique.

E)Disinfection: better to use chlorine as it will be more economical

(2)The chemical used in the above treatment plant is chlorine(for pathogen)

Its dose can be determined by first determining the amount of bacteria or pathogens, and its dose also depends on the amount of residual chlorine which we want to as residual chlorine.

Others chemical are alum (quick lime)

Its dose depends on the amount of suspended solids present in the water.

First we have to detrmine the amount of suspended solids in 1 litre of water and the amount of alum required to remove the suspended solids present in 1 litre of water then we can multiply the result with the total amount of water which have to be treated.

(3)

A)Screening:-It is the process of removal of heavy suspended solids from the water like organic matter (small plants, trees, animals).

B)Aeration:-It is the process in which water is brought in contact with air in order to allow the absorption of oxygen in it. It helps in the removal of various dissolve impurities specially unwanted dissolve gases like CO2, H2S

C)Sedimentation:-In this we use either quiscent type or continuous type tank.

In quiscent type tank detention time is generally kept 24 hrs. cleaning period is 6-8 hrs.

In this flow of water is completely stopped for 24 hrsduring which suspended solids gets settled in the tank leading to the formation of sludge.

D)Filtration:-It removes unsedimented solids which are not removed by screening and sedimentation.

It can also removes dissolve organic matter, dissolve minerals and micro-organism.

E)Disinfection:-It may be defined as the process of distruction of harmful micro-organism inwater. It is the most important part in the treatment of water as micro-organism are capable of spreading diseases.

(4)Breakpoint disinfection or the breakpoint chlorination are the point or event during chlorination after which chlorine demands become constant.

(5)To reduce DBPs:-

a)reduce NOM(Natural Organic Matter)

b)use alternate disinfectant (other than chlorine)

c)use double filtration technique.

(6)Yes, DBPs can also be formed in the distribution sustem

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