Study On The Conditions Of PVA-degrading Enzyme Fermentation By Mixed Culture Bacteria

Polyvinyl alcohol (PVA) is a kind of water-soluble synthetic macromolecular polymer. It was widely used in the textile as a sizing reagent. But the cotton fabrics treated by PVA must be desized to enhance their water absorbency. In conventional desizing method, cotton fabrics were washed with hot-water (70～90℃) to remove PVA. Thus, the wastewater from the textile plant contains abundant PVA, which caused environmental pollution due to the low biodegradability of PVA. If PVA-degrading enzymes were used, the PVA could be partially degraded during the enzymatic desizing process. The potential advantage of enzymatic desizing process included less wastewater treatment cost, more energy and water savings and the quality improvement of textile products. In this study, on the base of previous study team, the fermentation conditions of PVA-degrading enzymes were also studied. The effects of metal ions, yeast extract addition strategies and two-stage nutrition control on mixed culture bacteria growth and PVA-degrading enzyme production were investigated. The major results are summarized as follows:(1) The single factor experiments of metal ions show that magnesium and iron ions have a great effect on mixed culture bacteria growth and PVA-degrading enzyme production. The enzyme activities were 449.0 % and 1766.3 % higher than before respectively. But the copper and zinc ions have inhibitory effect. The enzyme activities were only71.5 % and 20.1 % of the control. The manganese and calcium ions have little effect on enzyme activity.(2) The effects of individual addition of magnesium and manganese on PVA-degrading enzyme production were not obvious, but the combined addition of these metal ions with calcium could promote enzyme production. The enzyme activities were 1.461 U·ml-1 and 1.453 U·ml-1 respectively. The combined addition of iron, calcium, magnesium and manganese played an important role on PVA-degrading enzyme activity, and promote the enzyme production.(3) The batch cultivation processes of mixed culture for PVA-degrading enzyme production under diverse initial PVA concentrations were investigated. It was concluded that the yeast extract was the most restrictive factor. The effects of different cultivation modes such as one-time feeding, batch feeding, constant-rate feeding on enzyme production were also studied. High production of enzyme activity was all realized in these cultivation modes of yeast extract feeding. As a whole, batch feeding culture was the most suitable approach to attain high enzyme activity, in which the maximum enzyme activity was 3.318 U·mL-1.(4) The constant-rate feeding of glucose and yeast extract could accelerate the mixed culture growth obviously. The maximum DCW was 27.18 g·L-1 at feeding rate of 2.4 g·L-1·h-1. Effect of different PVA concentration on PVAase production was investigated. It was show that with the initial PVA concentration of 1 g·L-1 and 4 g·L-1 of PVA feeding, the enzyme activity was 8.020 U·mL-1. It was 6.22 times higher than the control.