A Study On Improved Biological Treatment Of Wastewater By Chitosan

Chitin is the most abundant natural polymer except cellulose all over the world, which can be found not only in the organic exoskeleta of crustacean such as crabs, shrimps, prawns and lobsters, but also from fungi and elsewhere. Chitosan, the deacetylated product of chitin, is a positively-charged polysaccharide, composed of poly-N-acetyl-glucoamine units, linked by beta 1-4 bonds into a linear polymer. It is a liner polyamine whose amino groups are readily available for chemical reaction and salt formation with acids. Since the positive charge of chitosan interacts strongly with the negative charges in water, chitosan has become a kind of promising natural macromolecule flocculant which has been applied broadly on water treatment. However, most of the research work on chitosan is concerned on being used as a flocculant.It is unreported that chitosan can be used in wastewater treatment by activated sludge process to enhance effect as a bioaugmentation agent, so that it is necessary to have exploring research hi this field. Two aspects of research were mainly involved in this thesis. One was the comparison on their removal effect between chitosan sludge and conventional activated sludge in treating synthetic municipal wastewater, and the other was study on the mechanism of bioaugmentation from the view of biodegradable possibility of chitosan and microbiology. Following results was obtained:Firstly, the comparison on removal effect of CODcr, BODs, NHs-N between chitosan sludge and conventional activated sludge in treating synthetic municipal wastewater were studied, and the results showed that chitosan could enhance the biological treatment of the activated sludge and could be used as a bioaugmentation agent. It was obtained that chitosan with bigger of molecular weight ,showed the stronger ability of enhancing the bilogical treatment.Secondly, the mechanism research of bioaugmentation of chitosan hi activatedsludge process was carried out. Based on experimental values BODs/CODcr on chitosan with different molecular weight and different degree of deacetylation and microbial activities of activated sludge by adding chitosan, it showed that chitosan was not biodegradable by activated sludge. Furthermore, the effect of molecular weight and degree of deacetylation of chitosan on antibacterial activity to activated sludge was investigated in detailed, which found that chitosan with smaller of the molecular weight and the larger of degree of deacetylation, showed the much antibacterial activity.In order to put insight into why chitosan could be used as a bioaugmentation agent, the mechanism from the view of microbiology was studied, such as microbial activities, sludge volume index, sludge settling property and the structure of activated sludge. The results demonstrated that although chitosan has bacteriostasis to activated sludge, it could improve settling property and structure of activated sludge. Owing to the dense structure of chitosan sludge, it proved in the experiment that activated sludge with chitosan could treat much more wastewater by lengthening SRT, enhancing sludge concentration, increasing volumetric loading and shortening HRT.As a natural biodegradable organic macromolecule, chitosan has no poison and no harm to human body, and furthermore no re-pollution to environment. Form the viewpoint of the sustained development, the exploitation and application of chitosan will be endued with practical significance.