الفهرس 
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Abstract
SUMMARY
This study was performed to find accessible solutions that can be employed for water treatment aspiring for more safe and applicable techniques. Water contamination appears as a serious problem behind which many reasons lie. Fecal contamination of raw water introduces coliform bacteria, which includes E.coli as the most outstanding member, into water that can sometimes result in health problems. Although most coliform bacteria do not cause disease, some rare strains of E. coli, particularly the strain 0157:H7 can cause serious illness.
As reported in previous studies, chitosan is a natural biopolymer that is well known for its antimicrobial activity. It is thought that the mechanism of that activity (action) includes interaction between positively charged chitosan molecules and negatively charged microbial cell membrane leading to leakage of intracellular contents and it also acts as a chelating agent for metals necessary to bacterial vitality. Restrictions due to poor solubility resulted in a need for quaternary ammonium salts (QAS) and other forms that bring in more positive charge and better activity. Due to its antimicrobial activity, chitosan was investigated here as a disinfectant in water treatment through the usage of the prepared solutions.
This thesis is presented in 3 main parts;
1- Introduction:
This part clarifies the nature of water and its critical importance to human body and his survival besides the problems that man can be subjected to in case of the presence of contaminated water.
Literarure review:
This part presents ascientific and a historical review concerned with discussing waterborne diseases and their routes of transmition, microbial indicators resembling drinking water quality including total coliform bacteria and fecal coliform bacteria (gram –ve E.coli), composition of the cell wall of gram –ve bacteria, history of water disinfection and and today disinfection, chitosan and its properties, in usage applications of chitosan in different fields, the antimicrobial activity of chitosan and the mechanism proposed of it.
This part also deals with chemical modifications on chitosan and their effect on antimicrobial activity, the action of chitosan against E.coli through changes of cell membrane and the possible applications of chitosan that candidate it as a solution of water treatment.
2- Materials and Methods:
In this part, chitosan was prepared by the chemical method from the crab, shrimp and other crustaceans shells via the deacetylation of the prepared chitin. Prepared chitosan was characterized by FTIR, 1HNMR and elemental analysis. The results confirmed the structure of the product.
In this study, solvents were the main players according to whom the activity of chitosan witnessed a clear variation so acetic acid, N-(carboxymethyl)-N,N-diethyl benzene ammonium chloride and malonic acid were used as solvents in which chitosan solutions with a concentration of 2.5% was prepared forming solution 1, solution 2 and solution 3 respectively.
The MIC (minimum inhibitory concentration) values of the prepared solutions against total coliform bacteria and E.coli were investigated according to Kirby-Bauer disk-diffusion method but in case of total coliform bacteria, the method was modified as raw water samples were used as a source of that bacteria so they were first filterated through a membrane filter system.
Collected raw water samples were characterized physically, chemically and bacteriologically according to standard methods of APHA (2005).
The study discussed the effect of chitosan solutions on the activity of coliform bacteria that are considered worldwide as a water quality indicator. In each time, 1 liter of raw water was treated with an independent consequent volume of each solution to figure out which volume added could inhibit the growth of coliform bacteria.
3- Results and discussion:
This part reveals that MIC values of the three solutions of chitosan against total coliform bacteria were 2.75, 0.2 and 2 µ/ml respectively which were also the same values against E.coli.
As for raw water treatment for 30 min as a contact time, 300 ml of solution 1 were able to completely inhibit the growth of total coliform bacteria in 1 litre where 50 ml of solution 2 and 200 ml of solution 3 were able to do the same.
Contact time was proved to have an effect on the results as increasing it to 1 hr showed a better effect through achieving inhibition by the addition of 260, 46 and 200mls respectively, while after 2 hrs much better effect was noticed as 200, 30 and 150 ml succeeded in achieving unnoticeable growth.
The results showed that the solution of chitosan in N-(carboxymethyl)-N,N-diethyl benzene ammonium chloride had the most powerful activity against the tested group followed by malonic then acetic acid. N-(carboxymethyl)-N,N-diethyl benzene ammonium chloride having a benzene ring, chloride ion, +ve N and the highest molecular weight assuring that the antimicrobial activity of chitosan increased with longer side chain adding more sites enhancing antimicrobial activity while malonic acid is quite strongly dissociated and appear to exert its disinfectant action in the manner of the mineral acids, mostly through the hydrogen ion. The toxic action of this group against bacteria, appears to parallel the degree of dissociation, the more dissociated acids having a greater bactericidal effect.
Recommendation:
This study recommends with using chitosan as an antibacterial agent in water treatment against microbial contamination. This study also recommends with increasing contact time in treatment. Those recommendations shoud be taken into consideration by those concerned with water trratment in order to get a better access to a clean cup of water.