CN1039655C

CN1039655C - Manufacturing method of polyvinyl alcohol solid support with good air permeability and inclusion sludge microbe or biological catalyst

Info

Publication number: CN1039655C
Application number: CN92114195A
Authority: CN
Inventors: 陈国诚
Original assignee: Individual
Current assignee: Individual
Priority date: 1992-12-01
Filing date: 1992-12-01
Publication date: 1998-09-02
Anticipated expiration: 2007-12-01
Also published as: CN1087680A

Abstract

Sludge microorganisms or biocatalysts are mixed with a water solution of polyvinyl alcohol (the alkalization degree is higher than 70%, and the polymerization degree is from 1000 to 3000) with 5 to 30 wt% of concentration, the mixture is placed in 3 wt% saturated water solution of boric acid to form spheres by gelatinization in a short time, the spheres come in contact with a phosphate solution (higher than 5 wt%) for sufficient hardening, and immobilized supporters of the sludge microorganisms or the biocatalysts are prepared. According to a proportion that 5 to 55 grams of polyethyleneglycol is used for 100 grams of polyvinyl alcohol, the polyethyleneglycol with average molecular weight from 500 to 8000 is mixed with the sludge microorganisms or the biocatalysts in advance so as to make the immobilized supporters have good ventilation performance. The immobilized supporters are suitable for the denitrification and the removal of BOD, etc. in the process of waste water organism treatment, are suitable for the production of microorganism fermentation products, and are particularly suitable for an anaerobic sludge program.

Description

Method for producing polyvinyl alcohol carrier embedded with sludge microorganisms with good air permeability

The present invention relates to a technique for immobilizing sludge microorganisms on a support, and more particularly, to a method for immobilizing sludge microorganisms on a support using polyvinyl alcohol (PVA) as an immobilizing support to provide the support with good air permeability.

Polyvinyl Alcohol (PVA) is a water-soluble resin obtained by polymerizing vinyl acetate monomer and then alcoholizing the polymerized product. PVA is nontoxic, easy to prepare, excellent in mechanical strength, and is a commercially available low-cost polymer material. Therefore, it is very suitable as an immobilized carrier for sludge microorganisms.

Japanese patent laid-open No. 61-100193 discloses a method for immobilizing microorganisms or enzymes using PVA as an immobilized carrier, which comprises mixing an aqueous PVA solution with a microorganism or enzyme, and immersing in a saturated aqueous boric acid solution for 12-24 hours to form a gel sphere. This is detrimental to the biological activity of the microorganism or enzyme because the boric acid used is toxic and requires a long time for boric acid treatment.

Japanese patent laid-open Nos. 64-5490 and 64-5491 disclose a method of immobilizing PVA-supported microorganisms or enzymes by using an aqueous solution of a sulfate salt instead of the aqueous solution of saturated boric acid in Japanese patent laid-open No. 61-100193, which shortens the gelation time, but the aqueous solution of the sulfate salt used is an aqueous solution of 30% sodium sulfate or 70% ammonium sulfate at a high concentration, and also exerts a considerably adverse effect on the biological activity of the microorganisms or enzymes.

The above-described PVA supports immobilized with microorganisms or enzymes disclosed in the prior art are not too high in concentration because the aqueous boric acid or sulfate solution used has an adverse effect on the activity of the microorganisms or enzymes, but when the concentration is low, not only a relatively long gelling time is required but also the mechanical strength of the gelled support is not good.

Japanese patent laid-open No. 1-281195 discloses a PVA high-water-content gel having a fine mesh structure and a PVA high-water-content gel in which microorganisms are embedded in the gaps between fine meshes, wherein the PVA high-water-content gel is prepared by adding a polysaccharide or protein material such as agar (agar) or carrageenans (K-carrageenans) to the PVA before the PVA gel is frozen and returned to a temperature to achieve the purpose of the fine mesh structure.

The present inventors have used an aqueous solution of boric acid to perform a short-time gel impregnation and then hardened with an aqueous solution of phosphoric acid or phosphate, thereby obtaining a PVA carrier embedded with sludge microorganisms having excellent bioactivity and mechanical strength (Taiwan application No. 80108792). However, the gel support prepared from such PVA materials is not very suitable for generating methane, nitrogen and CO because the gel structure is very compact, so the permeability of gas molecules in the gel is not very good₂And the like, for example, a denitrification reaction.

Because the generated nitrogen gas is accumulated in the carrier, the gel sphere is expanded and floats to the upper part of the reactor, which causes troubles in practical operation.

In order to solve the above problems, the present invention provides a PVA carrier embedded with sludge microorganisms, which has excellent air permeability.

Another object of the present invention is to provide a PVA carrier immobilized with sludge microorganisms suitable for use in an anaerobic wastewater treatment process.

A preparation method of PVA carrier embedded with sludge microorganism comprises mixing sludge microorganism, 5-30 wt% polyvinyl alcohol aqueous solution and water-soluble polyethylene glycol, placing the mixture in 3 wt% to saturated boric acid aqueous solution for gelation treatment for 10 minutes to 2 hours to generate gel spheres, taking out the gel spheres, and soaking in 3-20 wt% phosphoric acid or phosphate aqueous solutionfor more than 30 minutes to harden the gel spheres, thus obtaining the PVA carrier embedded with sludge microorganism with good air permeability, wherein the polyvinyl alcohol has the alkalization degree of more than 70% and the polymerization degree of 1000-3000, and the polyethylene glycol has the average molecular weight of 500-8000, and 5-55 g of polyethylene glycol is used per 100 g of polyvinyl alcohol.

The polyethylene glycol used in the method of the present invention has the effect of relaxing the internal structure of the PVA gel during the process of PVA gelation and hardening, and making it more uniform, thereby improving the air permeability of the PVA gel.

The polyvinyl alcohol used in the process of the invention is preferably one having a degree of basification of from 90 to 99.9% and a degree of polymerization of from 1500-2000, and the concentration of the aqueous polyvinyl alcohol solution used in the process of the invention is preferably from 10 to 20% by weight.

The polyethylene glycol is preferably used in an amount of 10 to 35 g per 100 g of polyvinyl alcohol.

The gelation treatment time of the aqueous boric acid solution in the method of the present invention is preferably 30 to 60 minutes.

The concentration of the phosphoric acid or aqueous solution of phosphoric acid salt used in the process of the present invention is preferably 5 to 15% by weight, and the immersion time is preferably 30 to 60 minutes. The phosphate is preferably sodium phosphate, potassium phosphate, ammonium phosphate or an acid salt thereof.

The process of the invention also makes it possible to mix the aqueous boric acid solution and the aqueous phosphoric acid or phosphate solution, while simultaneously curing the gel and the gel spheres, within a time of from 30 minutes to 3 hours, preferably from 1 to 2 hours.

The PVA carrier embedded with sludge microorganisms prepared by the method of the invention not only reduces the adverse effect of boric acid on microorganisms or enzymes because of the short contact time of boric acid, but also enhances the mechanical strength because of hardening by using phosphoric acid or phosphate aqueous solution.

The water-soluble polyethylene glycol used in the method is a substance harmless to the biochemical activity of organisms, and can effectively improve the air permeability of the PVA carrier, so that the PVA carrier embedded with the sludge microorganisms can be suitable for anaerobic wastewater treatment procedures or aerogenic microorganism fermentation production procedures in wastewater treatment.

The sludge microorganisms used in the method of the present invention basically include microorganisms or enzymes commonly used in microbial fermentation of biochemical products and biological treatment of wastewater, such as cellulase, protease and starch hydrolase; examples of commonly used microorganisms include anaerobic sludge microorganisms, denitrified sludge microorganisms, BOD-removed activated sludge microorganisms, decolorized sludge microorganisms, deodorized sludge microorganisms, detoxified sludge microorganisms, alcohol fermentation yeasts, enzyme-producing bacteria, microorganism organs, animal and plant cells, and the like.

The present invention is further illustrated by the following examples, which are intended to be illustrative only and are not intended to be limiting in scope.

Example 1:

in this example, different concentrations of polyethylene glycol (PEG) were used in the PVA gelling process, and the obtained PVA support has significantly improved air permeability compared to the PVA support without PEG.

Polyethylene glycol (type PEG-4000, average molecular weight 3000, available from Japan and Wako pure chemical industries, Ltd.) was added in an amount of 1, 2, 3 and 4 g, respectively, and dissolved in 50ml of a suspension (30.9g MLSS/l) of denitrified sludge (domestic sludge containing denitrifying bacteria). Mixing 18 wt% PVA (with alkalization degree of more than 99% and polymerization degree of 2000) water solution with the denitration sludge suspension containing polyethylene glycol with different concentrations in a volume ratio of 1: 1, and stirring uniformly. Then slowly dripping the mixed solution into saturated boric acid solution with a syringe, and stirring for 30-60 min. Then, the residue was taken out through a screen, washed with water to remove boric acid, and then immersed in a 0.5M to 1.0M phosphate solution. Taking out with a screen after 30-50min to obtain granules with average particle diameter of about 3 mm.

The PVA grains obtained were distributed in 100ml aluminum-capped glass bottles containing 80ml of nitrate-containing synthetic wastewater (the composition of which is shown in Table 1), aerated with nitrogen (or helium) for 5-10min to remove oxygen in the bottles, sealed with rubber stoppers and aluminum caps, placed in a shaker at 30 ℃ and 130rpm for shaking culture, after 3 hours of culture, about 1ml of liquid sample was taken, the nitrate concentration was analyzed by an Ion Chromatograph (Ion Chromatograph), and the biochemical activity (denitration rate, in mgNO) of the immobilized denitration sludge on the day was calculated from the amount of change in the nitrate concentration₃ ^--N/h/g-gel). The synthetic wastewater is updated every day, the experiment is repeated, and the change conditions of the denitration speed and the air permeability of the supporter are observed.

TABLE 1 concentration of ingredients (g/l) KNO₃0.722 CH₂OH 0.5 Na₂HPO₄·2H₂O 0.418 KH₂PO₄0.202 MgSO₄·7H₂O0.02 minor constituent CaCl₂·2H₂O 0.01 FeSO₄·7H₂O 0.005 MnSO₄·nH₂O 0.0025 Na₂MoO₄·2H₂O 0.0025 pH7.0

The method for expressing the air permeability comprises the following steps:

before the synthetic wastewater is updated every time, the number of the floating particles and the number of the sinking particles are calculated, the situation that the number of the floating particles increases along with the number of culture days is observed, and the air permeability of the PVA carrier is judged according to the percentage of the number of the floating particles to all the particles at the end of the 7 th day experiment.

FIG. 1 shows N, an embodiment of the invention₂The penetration from the surface of the PVA carrier; FIGS. 2 and 3 show the floating of PVA grains with and without polyethylene glycol (air permeability comparison).

The results of the experiment are shown in Table 2. In Table 2, there are listed control experiments without polyethylene glycol, which were performed under the same conditions except that polyethylene glycol was not used.

Table 2 different PEG-4000 additions, regarding improvements in comfort PEG addition degree 1% 2% 3% 4% not added test site, comfort PEG addition, comfort in day 1, day 7, comfort in 5.5512.276.1611.823.4710.3711.9518.2131.6351.52

(1.19)% of (2.14) (1.02) (2.61) (1.07) (1.23) (0.81) (1.61) (5.36) (2.69) denitration rate, 0.0610.1680.0480.1720.0560.1750.0450.1680.0510.172 mgNO₃ ^-The/h/g-gel (0.009) × (0.009) (0.004) (0.001) (0.006) (0.006) (0.005) (0.002) (0.008) (0) × brackets inner digit reservoir repeats 5 times of the standard deviation value from experimentsAs is evident from the data in Table 2, the number of floating PVA particles is significantly reduced in the case of adding an appropriate amount of polyethylene glycol to the PVA gel, and this result confirms that the air permeability of the PVA support is indeed greatly improved by the addition of PEG.

Example 2:

this example demonstrates the effect of using polyethylene glycols of different average molecular weights in the gelation process of PVA to enhance the breathability of the PVA support.

The procedure of example 1 was repeated except that polyethylene glycols (type PGE-1000 and PEG-6000, manufactured by Nippon and Wako pure chemical industries, having average molecular weights of 1000 and 7500, respectively) having different average molecular weights and a fixed amount (2 g) of polyethylene glycol were added and dissolved in a denitrified sludge suspension (30.46g MLSS/l). The results of the experiment are shown in Table 3.

TABLE 3

Effect of different PEG molecular weights on improvement of air Permeability PEG molecular weight 10007500 No test time was added, air Permeability on day 1 day 7, 01.380.071.50.1319.28

Denitration rate of (0) × (0.28) (0.08) (0.38) (0.10) (8.91), 0.0880.1010.040.0870.040.065 mgNO₃/h/g-gel (0.026)*(0.003)(0.005)(0.009)(0.016)(0.019)

Number in parentheses is the standard deviation value of 5 replicates

The experimental results in Table 3 also clearly show that the PVA particles prepared by the method of the present invention using PEG of different average molecular weights have significantly improved colloidal gas permeability characteristics.

Example 3:

this example demonstrates the continuous denitrification of wastewater using the immobilized denitrified sludge prepared by the present invention.

A closed CSTR reaction tank (packed volume 1.51) having a volume of 2.01 was filled with PVA grains using 2 g of polyethylene glycol prepared in example 1 at a packing ratio (packing ratio) of 40 vol%, and oxygen present in the reaction tank was removed by aeration with nitrogen gas before introduction of nitrate-containing synthetic wastewater. Then, a continuous feed containing 100ppmKNO was fed at room temperature₃The synthetic wastewater contains 0.5M H₃PO₄The pH of the aqueous solution was maintained at about 7, and an appropriate amount of methanol was added as a carbon source for denitration reaction (carbon: nitrogen: 2.7 or more). The CSTR reactor has an operating load (loading) of about 0.6g NO₃ ^--N/1 day, the residence time of the synthesis wastewater in the reactor being about 4 hours.

At the beginning of the operationThen, monitoring NO₃ ^-The concentration of the organic compound is changed. NO from the effluent₃ ^-Concentration measurements of NO in the effluent water 2 days after the start-up of the denitrification reactor₃ ^-The concentration is close to zero ppm, and NO in the effluent is detected after continuously operating the denitration reactor for four months₃ ^-The concentration was maintained around zero ppm.

Claims

1. A process for preparing polyvinyl alcohol carrier embedded with sludge microbes and having good air permeability includes such steps as mixing the sludge microbes,5-30 wt% of polyvinyl alcohol solution and water-soluble polyethanediol, gelifying the mixture in 50-15 wt% of saturated boric acid solution for 30-60min to generate gel spheres, taking out the gel spheres, immersing in 5-15 wt% of phosphoric acid or phosphate solution for more than 30 min, and hardening, and features high alkalization degree of 90-99.9, polymerization degree of 1000-3000, average molecular weight of 1000-7500 and 10-35 g of polyethanediol per 100 g of polyethanediol.

2. The method of claim 1, wherein the sludge microorganism is selected from the group consisting of anaerobic sludge microorganisms, denitrified sludge microorganisms, BOD-depleted activated sludge microorganisms, decolourized sludge microorganisms, deodorized sludge microorganisms, detoxified material sludge microorganisms, alcohol fermentation yeast, enzyme producing bacteria, biological organ bodies, and animal and plant cells.