Application of chitosan as an alternative coagulant in drinking water treatment

Stipendiatin/Stipendiat: Marcela Krenkova

The reason, why to study the usage of biopolymers in drinking water treatment, is mainly the lasting pollution of surface water, which necessarly leads to the consumption of a high level of destabilization agents. There is a certain amount of organic and inorganic particles suspended in natural raw water. To remove these particles, processes such as coagulation-floculation and sedimentation have to be applied. The treatment procedure included destabilization of colloidal particles following agregation into bigger clusters, which can be removed by sedimentation, filtration or centrifugation. To destabilize the colloids when treating raw surface water, the ferric and aluminium salts are usually used. The advantages of this conventional treatment are proven performance, cost-effectiveness, relative ease of handling, and availability. Besides the usage of ferric salt and alum leads to some problems such as a large amount of produced sludge, with high level of residual metals in it and increased concentration of iron and aluminium in drinking water, which has raised concern to public health. It is proven, that metal such as those mentioned above, weakens the cellular immunity and there is as well a connection between high quantity of consumed alum salt and the onset of Alzheimer desease. Therefore a synthetic organic polymers have been used as an aid coagulants to improve the effectivenes of primary coagulants. Another advantage was that the amount of produced sludge was lowered. However, there are some limitation. Polymer formulations contain contaminants from the manufactoring process such as residual monomers, other reactants and reaction by-products that could potentially negatively impact human health. In addition polymers and product contaminants can react with other chemicals added to the water treatment process to form undesirable secondary products.Thus natural polyelectrolytes, particularly biopolymers, are promising alternatives, which could replace the conventional coagulants and synthetic polymers, because of they are derivate from certain kinds of plants and animals. Present studies manifest, that when using them, biodegradable, nontoxic sludge is formed, the treated water is safe to human health and there is a wider effective dose range of flocculation for various colloid suspension.The project would be focused on the treatment of surface raw water, because there is the main problem of treating water by coagulation. Most of the published results are related to synthetic water, in which the turbidity is made up by precise agents such as bentonit, clay etc. For practical use in the water treatment plants is needed to work with raw water, which contrary contains lots of heterogeneous particles. The project would be based on research of chitosan as a primary coagulant when raw surface water would be used. Practically the basic fulfilment of the work would be to optimise the dose of chitosan, which means to study the influence of pH, velocity gradients and time of reaction on the efficiency of destabilization and also the comparision with the traditional deatabilization agents (Al2(SO4)3* 18H2O and FeCl3* 6H2O) in the laboratory conditions.

01.03.2009 - 31.01.2010

Technische Universität Dresden
Institut für Siedlungs- und Industriewasserwirtschaft

Prof. Dr. Wolfgang Uhl

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