Design And Preparation Of Novel Polyvinyl Alcohol Carriers And Application For Wastewater Treatment

The preparations of poly(vinyl alcohol) (PVA) carrier for microorganism immobilization and their improved methods are introduced. The processes on immobilized microorganism by PVA carrier for wastewater treatment is reviewed. The research orientation of PVA carrier preparation and development prospects in wastewater treatment are pointed out. Nanoscale Fe0 was immobilized in and on PVA microspheres by the inverse suspension crosslinked method. Two different sizes of Fe0/PVA microspheres were synthesized in the presence and absence of dispersant. The nitrobenzene (NB) reduction reactions followed pseudo-first-order kinetics. The normalized surface rate constants (kSA) values were determined to be 0.162 L h-1m-2 for L-Fe0/PVA microspheres,0.098 L h-1m-2 for S-Fe0/PVA microspheres, and 0.023 L h-1m-2 for nanoscale Fe0 particles. Furthermore, with the analysis of the products by GC-MS, possible reductive pathways of NB by Fe0/PVA microspheres were suggested. The recovery rates of iron in microspheres were determined to be 81.17% for large Fe0/PVA and 60.31% for small Fe0/PVA。Macroporous PVA foam using epichlorohydrin as crosslinking agent was investigated. The average molecular weight among crosslinks, crosslinking density, and mesh size was determined through the equilibrium swelling theory. The characterization of foams with different crosslinking ratios was also investigated by testing thermal properties, specific surface areas, and diffusion coefficients. The biomass densities and activity yields were measured by detecting protein concentration and oxygen uptake rate. TG and DSC tests showed an increase in thermal stability and a decrease in polymeric crystallinity with increasing crosslinking ratio. The biomass densities increase along with the increase in the crosslinking ratio,with the highest value shown at 0.0638±0.0093 g VSS g-1 carrier. However, the activity yields decrease with the increase in the crosslinking ratio, showing the highest value at 69.38%.The crosslinked PVA foam (CPVAF) carrier demonstrated better chemical and thermal stability, as well as larger specific surface area and diffusion coefficients than the traditional PVA (TPVA) carrier. Nitrifying bacteria were used to test the suitability of CPVAF and TPVA carriers for immobilized microorganisms. CPVAF carriers supported higher biomass density and microbial activity than TPVA carriers. At the same biomass density, the higher nitrification rate of CPVAF carriers was attributed to excellent mass transfer of the substrate (and oxygen) between the bulk solution and the immobilized microorganisms.The traditional PVA-boric acid method was modified using calcium carbonate as a pore-forming agent to form the macroporous structure and formulated macroporous carrier (MPC) post crosslinked with glutaraldehyde. The pore volumes, pore structure, porosity, and swelling behavior of MPCs were evaluated. The crosslinking density of MPCs with four different crosslinker dosages was calculated from their swelling properties using the modified Flory equation. MPCs demonstrated high swelling capacity, large specific surface area, high diffusion coefficient, as well as chemical and mechanical strength. The high crosslinking degree MPCs resulted in high biomass densities and low activity yield and vice versa. The characterizations of MPC suggest significant potential of its use for microbial immobilization and provide a scientific basis for immobilized carrier design and optimization.