A Preliminary Study On The Preparation Of Chitosan Ulfiltration Membrane And Its Application On The Treatment Of Aquatic Product Processing Wastewater

In this research, the effects of main processing parameters involved in the preparation of chitosan(CS) membrane, including concentration of chitosan in membrane casting solution(A), molecular weight of PEG as an additive(B), dosage of acetone in solvent(C), torrefaction temperature(D) as well as the concentration of NaOH solution as coagulation bath(E), on the permeation flux of membrane were evaluated by orthogonal experiments. The results showed that, the degree order that the five factors influence permeation flux(F) of membrane was listed as follows: B>A>D>E>C. Among them, molecular weight of PEG has the most significant effect on F value. The CS membrane had a maximum F value at the following conditions: A was 2.0%, B was 800, C was 40% (V/V), D was 50℃, E was 0.25 mol·L-1.Then, the effect of molecular weight(M)and dosage(C) of PEG on the microcosmic surface texture and properties of CS membranes were studied specially. A series of CS membranes were prepared by changing the values of M and C of PEG in membrane casting solution. The permeate flux(F) and rejection ratio(R) of these membranes were tested under a pressure of 0.2MPa, the microcosmic surface texture of CS membranes was also observed with scanning electron microscope(SEM). It showed that, the microcosmic texture of membrane surface was evidently affected by M and C. With the increase of M or C, microcosmic surface texture became more and more rough, granulation degree of membrane became larger, size of micropore increased unceasingly as granule radius became larger, which resulted in that F ascend and R descend. It had been observed that granule on the membrane surface became patch when the dosage of PEG800 and PEG1000 were 10% and 8% respectively, at the same time, slot appeared as pores connected. With the further increase in dosage of PEG800 and PEG1000, CS membrane cannot be obtained for water swelling augmenting.For the properties of CS membranes, water permeate flux (F) raised gradually with the increase of M and C, while rejection ratio (R) became smaller and smaller. There was a better linear relationship statistically between M and R, but F value had non-linear relationship with C growth. For PEG200, PEG400 and PEG600, the maximum value of F were obtained when their dosage reached 10%, 8% and 10% respectively. In comparison with PEG800, the addition of PEG1000 lead to a distinct change in membrane micro-surface, accompanied by a sharp rise in F and a rapid decrease in R. It is concluded that PEG was not only a sort of pore-causing reagent, but also influence the structure and performance of membrane through interfering the aggregation state of polymer, thermodynamics action of solution and dynamic behaviors of coagulation.Generally, the additive PEG200 of 10% or PEG400 of 8% in membrane casting solution may obtained the better performance of CS membrane, with a R value aboved 90% and a F value of 12~13ml·h-1·cm-2. When PEG400 of 8% was added, the CS membrane had a retention range from 60000 to 70000 in molecular weight, and a smaller range in pore size of membrane.In recent years, wastewater from aquatic product processing has become a new pollution source in the coastal areas. Therefore, serial processes consisted of rough filtration with filter paper and ultrafiltration with CS membrane was designed to deal with three kinds of aquatic product processing wastewater. The removal rate of CODcr reached to 82.6%, 89.3% and 90.0% respectively.The CODcr of outflow could fit for the Intergrated Wastewater Discharge Standard of China (100mg·L-1). For two kinds of wastewater from fish slice production containing protein of 111.32 mg·L-1 and 84.55 mg·L-1 respectively, the total protein rejection of 85.8% and 84.2% were obtained respectively during the whole process, in which protein(granulated) of 32.9% and 39.4% were rejected by rough filtration, and deliquescent protein of 52.9% and 44.8%(relate to concentration of protein in raw wastewater)was rejected by CS membrane ultrafiltration. Optimization of pH value in wastewater raised the removal of CODcr and protein by rough filtration through the formation of organic detritus, but the total rejection ratio was not improved clearly in the whole treatment process.In comparison with biological treatment, ultrafiltration with CS membrane not only had a better purification to wastewater from aquatic product processing, but also create suitable conditions for the reuse of nutrimental components in wastewater.