STABILITY OF CHITOSAN GEL AS ENTRAPMENT MATRIX OF VIABLE SCENEDESMUS-BICELLULARIS CELLS IMMOBILIZED ON SCREENS FOR TERTIARY-TREATMENT OF WASTE-WATER

An experiment with immobilized microalgal cells was carried out using high and low viscosity chitosan and konjac flour to enhance the stabil ity of hardened gels during tertiary treatment of wastewaters containi ng a high concentration of phosphate salts (1 M Na3PO4). Mechanical pr operties as well as compression testing, moisture retention in gels an d the uptake of nutrients, such as nitrogen and phosphorus, from artif icial wastewater were studied in the immobilized gel state. The disrup tion due to chemical interactions of pure high and low viscosity chito san or mixed gels with konjac flour was examined daily by microscopic counting of the total cells released in the medium during seven weeks. The removal of NH4+-N and PO43--P was monitored during four nutrient starvation-removal cycles. A complete cycle consisted of starving immo bilized cells for 48 h in air saturated at 100% relative humidity, fol lowed by removal of nutrients from wastewater The immobilization obtai ned from 2% (m/v) high viscosity chitosan gels showed a more significa nt chemical stability (P less than or equal to 0.05) in medium with I M Na3PO4 that contained viable cells than low viscosity chitosan or mi red gels. Sodium pyrophosphate was the best chelating agent used for c ross-linking and did not affect the diffusion of inorganic nutrients t hrough the hardened gels or the microalgal growth inside the network o f chitosan immobilized cells. After the second uptake, the elimination of NH4+-N and PO43--P was 100% within 3 h, whereas after the fourth u ptake, the nitrogen disappearance was 99% within 2 h and 100% for phos phorus with the same incubation time. After more than one month incuba tion of chitosan gel beads containing Scenedesmus bicellularis cells t hat had been soaked daily in a fresh I M Na3PO4 solution, the stabilit y of hardened gels was not affected and no significant release (P grea ter than or equal to 0.05) of entrapped cells was observed in the medi um. Copyright (C) 1996 Elsevier Science Ltd.