KR100330687B1 - Biological Removal of Heavy Metals in Wastewater Using Packed-bed Reactor Containing Organic Substrates - Google Patents

Abstract

The present invention relates to a wastewater treatment method using a packed bed reactor filled with an insoluble solid organic matter (organic carrier) in a method for treating heavy metal-containing wastewater such as hexavalent chromium using sulfate reducing bacteria. In addition, in order to enhance the treatment effect of heavy metals, the organic water-soluble wastewater may be mixed with the organic carrier or separately supplied at the same time. At this time, by treating the organic matter derived from the organic wastewater to not be discharged to the treated water, treatment of the two wastewaters at the same time It is possible. The method of the present invention is also applicable to wastewater containing other heavy metals.

Description

Biological Removal of Heavy Metals in Wastewater Using Packed-bed Reactor Containing Organic Substrates

The present invention relates to a method for simultaneously removing chromium and other heavy metals from wastewater containing heavy metals such as water-soluble hexavalent chromium (Cr (VI)) at low cost using a packed bed reactor packed with an organic carrier.

Plating wastewater can be classified into chromium-based, acid-alkali, cyan-based and complex salt-based according to their properties (cf. Plating Industry Association Manual, 1994). These commonly contain heavy metals such as copper, nickel, zinc and tin, chromium waste water contains high concentrations of hexavalent chromium, and cyan waste water contains cyan. To remove heavy metals from these wastewaters, the wastewater is neutralized and reduced to sodium sulfite (Na ₂ SO ₃ ) to precipitate as metal hydrate, or precipitated with metal sulfide salt using sodium sulfide (Na ₂ S) to remove it. Treatment methods are used (see Plating Industry Association Manual, 1994). However, this chemical treatment uses a large amount of precipitant to promote precipitation, so a large amount of malignant sludge occurs after treatment. In addition, since the composition of the waste water changes frequently, it is difficult to properly control the amount of the drug used, which may result in insufficient treatment or damage due to the excessive input of the drug. Therefore, there is a need to develop a process that can replace the chemical plating wastewater treatment process.

Hexavalent chromium is not known in nature and is a heavy metal produced by human industrial activities. It is harmful to animals and plants, including humans, and is present in high concentrations in metal industry wastewater, especially in the plating industry. Hexavalent chromium is also water soluble and thus easily causes environmental pollution. While heavy metals such as iron, nickel, copper, manganese, zinc and lead are precipitated and removed as sulfides, hexavalent chromium is reduced by hydrogen sulfide generated by the action of sulfate reducing bacteria, thereby insoluble trivalent chromium (Cr (III)). Easily precipitated (Smillie et al., 1981, Water Research. 15, 1351-1354).

Recently, many anaerobic bacteria (hexavalent chromium reducing bacteria) using hexavalent chromium as electron acceptors instead of oxygen have been reported (see Schmeiman et al., 1997, Applied and Biochemistry and Biotechnology. 63, 855-864; Tebo et al., 1998). , FEMS Microbiology Letters.162, 193-198; Wang et al., 1989, Applied and Environmental Microbiology 55, 1665-1669)

Techniques have been developed to remove hexavalent chromium from wastewater using sulfate-reducing bacteria or hexavalent chromium-reducing bacteria, but these are primarily continuous stirred tank reactors (CSTRs) operated by mixing water-soluble electron donors. : Chen and Hao, 1997 Journal of Chemical Technology and Biotechnology, 69, 70-76, and packed-bed reactors using inorganic carriers such as ceramics (see Turick et al., 1997, Applied Biochemistry and Biotechnology, 63-65, 871-877).

The carrier used in the packed bed reactor of Turick et al. Is a spherical support composed of activated carbon powder in a fibrous polyarimid matrix. Inorganic carriers of this kind are materials commonly used in biological wastewater treatment and are porous and adsorbent so that the microorganisms in the reactor are not lost by the continuous flow of wastewater and other water-soluble substances. However, the inorganic carrier only serves to fix the microorganism in the packed bed reactor, and cannot serve as a nutrient source of the microorganism. In addition, there is a disadvantage in that an expensive organic material is used as a nutrient source and a separate high pressure nitrogen bottle is attached to maintain the reactor in an anaerobic state.

In addition to plating wastewater, most heavy metal-containing wastewater, such as mine acidic wastewater, has a very low concentration of organic matter in the process of generation. Therefore, in a packed bed reactor filled with an inorganic carrier, an organic material to be used as a nutrient source for microorganisms must be supplied. At this time, the rate at which organic matter enters the reactor and the concentration of organic matter should be determined in consideration of the growth rate and nutritional requirements of microorganisms in the reactor. This is because a limited amount of organic matter does not meet the nutritional requirements necessary for the growth of microorganisms and thus does not become an effective wastewater treatment system, and excess organic matter remains in the treated water and is discharged into the environment, causing secondary pollution. In addition, when the concentration of heavy metals in the wastewater to be treated is variable, it is difficult to adjust the concentration of microbial nutrients to an appropriate level.

On the other hand, normal bacteria are inhibited by 1-2 mmol of hexavalent chromium, whereas enterobacter cloacae, which are permeable anaerobic bacteria and use hexavalent chromium as the final electron acceptor in the anaerobic state, are resistant to 10 mmol. (See Komori et al., 1990, Applied and Microbiology and Biotechnology, 33, 117-119), and 40 millimolar of hexavalent in an anaerobic consortium containing sulfate-reducing bacteria isolated from wastewater contaminated with hexavalent chromium. It has been reported to reduce chromium (Fude et al., 1994, Applied and Environmental Microbiology. 60, 1525-1531).

However, methods for treating wastewater containing hexavalent chromium using the known sulfate reducing bacterium or hexavalent chromium reducing bacterium have been studied only for continuous stirred tank reactors and packed bed reactors using inorganic carriers. There has been no study of packed bed reactors using solid organics, which may also be used as carriers.

Accordingly, it is an object of the present invention to provide a method for treating heavy metal-containing wastewater using sulfate reducing bacteria in a packed bed reactor packed with an organic carrier.

Another object of the present invention is to provide a method for mixing organic water-soluble wastewater with an organic carrier or separately and simultaneously supplying a method for treating heavy metal-containing wastewater using sulfate reducing bacteria in a packed bed reactor filled with an organic carrier.

1 is a structure of a reactor used to incubate sulfate reducing bacteria to remove heavy metals in wastewater.

<Explanation of symbols for main parts of the drawings>

1. Wastewater Storage Container

2, 4, 7. Flow Control Pump

3. China

5. Packed bed reactor

6. Recovery Container

8. Wastewater

The object of the present invention is achieved by a wastewater treatment method characterized by using a packed bed reactor packed with solid organics in a wastewater treatment method for removing heavy metals from heavy metal-containing wastewater using sulfate reducing bacteria.

That is, the present invention treats heavy metal-containing wastewater using a packed bed reactor filled with insoluble solid organics (hereinafter referred to as 'organic carriers') that can act as a carrier for immobilizing microorganisms as well as as a nutrient source of microorganisms. It has its features.

According to the process of the invention, in particular, chromium and other heavy metals can be removed simultaneously from wastewater containing water-soluble hexavalent chromium (Cr (VI)).

More specifically, according to the present invention, chromium and other heavy metals can be simultaneously removed from wastewater generated in plating plants containing water-soluble hexavalent chromium.

Like hexavalent chromium, hexavalent uranium (U (VI)) (Love et al., 1992, Applied and Environmental Microbiology, 58, 850-856; Lovely et al., 1992, Applied and Environmental Microbiology, 59, 3572-3576) , Hexavalent selenium (Se (VI)) (Tomei et al., 1995, Journal of Industrial Microbiology, 14, 329-336), Hexavalent technicium (Tc (VII)) (Lloyd et al., 1996, Applied and Environmental microbiology, 62, 578-582) has also been reported that heavy metals can be removed in a stable form by the action of sulfate reducing bacteria or metal salt reducing bacteria. Therefore, the present invention is not only used for plating wastewater containing hexavalent chromium, but also for wastewater containing metals such as hexavalent uranium, hexavalent selenium, and valent technetium, which can be reduced to sulfate reducing bacteria. It can also be applied.

In addition, according to the method of the present invention, in order to enhance the treatment effect of heavy metals, two wastewaters can be treated at the same time by mixing the organic water-soluble wastewater with a solid organic material or supplying them separately at the same time. Drive carefully to avoid pollution.

The wastewater treatment method using the packed bed reactor packed with the organic carrier of the present invention is a method of supplying organic water-soluble wastewater as a nutrient source of microorganisms and at the same time supplying some nutritional requirements from the organic carrier. At this time, if a nutrient source readily available due to the physiological characteristics of the microorganism (also called a substrate or electron donor), that is, an organic water-soluble wastewater and a nutrient source that is not easily decomposed (insoluble organic carrier or filler) is present at the same time, There is selectivity for available nutrient sources. Therefore, in the present invention, the use of organic water-soluble wastewater is first induced as a nutrient source required for the growth of microorganisms required for the treatment of heavy metals in the wastewater, and the remaining needs are supplied from the organic carrier. Thus, for varying concentrations of wastewater, organic carriers have the ability to variably cope with concentrations of organic water-soluble wastewater.

In the present invention, an organic solid, which is a carrier used to immobilize sulfate reducing bacteria in a packed bed reactor, is a material that is inexpensive and abundantly present in nature, and may be organic material for growth of sulfate reducing bacteria, and other microorganisms may be used as a substrate. The product obtained can also be used as a substrate for sulfate reducing bacteria. Therefore, substrates used for the purification of mine acid wastewater, for example, waste wood remaining after cultivation of shiitake mushrooms, and paper sludge produced from by-products obtained from paper production and recycling processes (see, Kim, Byung-Hong et al., 1997, Korean Patent Application No. 1997- 3042) can be used as the microbial carrier of the present invention, in which anaerobic digester sludge is added to make the concentration of a series of anaerobic microorganisms including sulfate reducing bacteria high in a short time. In addition to increasing the concentration of microorganisms, the addition of anaerobic digester sludge also has the side effect of increasing the concentration of cells by supplying water-soluble organic substances readily available to microorganisms (see, Kim, Byung-hong et al., 1997, Korean Patent Application No. , 97-3042). Therefore, the wastewater generated in the starch production plant can be used as such organic water-soluble wastewater.

In the present invention, the sulfate reducing bacterium refers to an anaerobic bacterium that uses sulfate as a final electron acceptor in order to consume electrons generated by oxidizing an organic material. In addition, hexavalent chromium reducing bacteria means anaerobic bacteria that use hexavalent chromium as the final electron acceptor in order to consume electrons generated by oxidizing organic matter. Sulfate reducing bacteria or hexavalent chromium reducing bacteria that can be used in the present invention include, but are not limited to, Dissulfovibrio and Enterobacter. Representative strains include, for example, Desulfovibrio sp .: KCTC 2484; ATCC 27882, Desulfovibrio desulfuricans: KCTC 2360; ATCC 7757, 13541, 27774, 29775, and Disulfo Vibrio. Desulfovibrio vulgaris: KCTC 1910, ATCC 29579, 35115, Desulfotomaculum ruminis and Enterobacter cloacae: KCTC 1684, 1685, 1943, 2361, 2519; ATCC 222, 529, 961 , 962, 7256, etc.), and can be easily obtained from each strain bank.

The method of the present invention increases the activity of the microorganisms by pretreating the wastewater in accordance with the optimum growth conditions of the microorganisms used. For example, for the growth of microorganisms, including sulphate reducing bacteria that have optimal growth conditions at neutral, the pH of the wastewater to be treated may be neutralized and then treated.

The process of the present invention is preferably carried out under an inert atmosphere (eg nitrogen) in order to maximize contact with oxygen.

In the present invention, it is preferable that the cultivation of the sulfate reducing bacterium is carried out in a batch culture and then converted to a continuous culture and a wastewater treatment process in order to sufficiently reduce the sulfate.

Plating wastewater treatment method in the present invention can be carried out using the apparatus shown in FIG. According to FIG. 1, the wastewater of the wastewater storage container 1 flows into the neutralization tank 3 filled with limestone first through the flow regulating pump 2, and then the neutralized wastewater is returned to the organic carrier through the flow regulating pump 4. After the wastewater is introduced into the lower portion of the packed bed reactor 5 filled with the wastewater, the wastewater is recovered to the recovery vessel 6 after being treated in an upflow manner. At this time, the organic water-soluble wastewater 8 may be introduced in the same manner as the heavy metal wastewater inflow through the flow control pump 7 to maximize the treatment effect.

Hereinafter, although an Example demonstrates this invention more concretely, this invention is not limited to these Examples.

<Example 1>

The chromium wastewater with the highest concentration of hexavalent chromium among the four wastewaters (chromium, acid alkali, complex salt, and cyanide) brought into the plating factory through the Banwol Central Plating Association was mainly targeted. In the laminar bed reactor, cellulose-based waste was used as an organic substance, and oak remaining after cultivation of paper sludge and shiitake mushroom, which was considered to be a substrate for complex microorganisms in the preceding patent (see Kim Byung-hong et al., 1997, application number 97-3042). 65.6 g of organic matter was filled with the waste wood mixed. The wastewater was neutralized at an initial pH of 2.4 to 6.2, mixed 1: 1 with anaerobic digester sludge, and then 360 milliliters were added to the reactor already filled with solid organics and the total reactor volume was 500 milliliters. Operation was batch cultured for about 9 days.

By culturing such sulfate reducing bacteria, the heavy metal concentration and sulfate concentration were measured for the treated wastewater.

Heavy metal concentration was analyzed using atomic absorbance spectrophotometer (Hitachi Z-8200), and neutralized water and final effluent concentration were measured by comparing with titration curve. Wastewater pretreatment methods, sulfate concentration analysis, and chemical oxygen demand (COD) were all based on standard methods (see Standard Methods for the Examination of Water and Wastewater, 1992).

Table 1 shows the properties of three types of plating wastewater except cyanide, and it can be seen that the chromium-based wastewater has the highest chromium concentration.

The heavy metals contained in the wastewater were removed after about 6 weeks, except for 1 ppm of chromium. After 9 weeks, no residual heavy metals were measured. Along with this, sulphate was removed over 1000 piem.

Properties of Plating Wastewater Wastewater type pH sulfate chrome Copper nickel iron zinc manganese cadmium PPM Chrome 2.38 1564.0 224.5 36.5 54.5 13.0 - - - Acid alkali system 2.22 1028.9 3.75 84.0 25.7 5.0 - - - Complex system 6.65 593.3 4.25 0.75 78.0 3.25 - - - -: Analytical concentration or less (typically 0.01 pim or less)

Primary batch culture results of chromium-based wastewater Hours (days) pH sulfate chrome Copper nickel iron PPM 0 6.42 1507.9 37.0 1.0 1.0 5.0 3 5.94 1133.2 3.0 - - 17.0 6 5.74 97.0 1.0 - - - 9 5.82 319.8 - - - - -: Analytical concentration or less (typically 0.01 pim or less)

<Example 2>

Reactors showing that heavy metals including chromium may be removed by batch culture were operated continuously in the manner shown in FIG. 1. At this time, the water retention time was set to 20 days and a total of 5 weeks of operation allowed the entire reactor to be converted to new wastewater more than once. Table 3 shows the pH and heavy metal concentrations of raw wastewater, neutralized wastewater and final treated effluent during continuous operation.

The concentration of sulfate-reducing bacteria in the culture tank was analyzed by anaerobic bacterial culture in vitro and by the most probable number (MPN) test. Culture substrates were Postgate C (Postgate C, KH ₂ PO ₄ 0.5 g / L, Na ₂ SO ₄ 4.5 g / L, NH ₄ CL 1.0 g / L, CaCl ₂ 0.06 g / L, MgCl ₂ 0.06 g / L, sodium citrate 0.3 g / L, sodium lactate (50%) 7 ml, yeast extract 1.0 g / L, 0.2% resazurin solution 1 ml) medium was filled with nitrogen as a basal medium. In the middle of the reactor after 5 weeks of continuous culture, the sulfate reducing bacteria measured about 1.0 x 10 ⁸ MPNs / ml. This indicates that the concentration of sulfate reducing bacteria in the reactor is very high.

<Example 3>

In order to increase the treatment effect in continuous operation, it should be operated under the optimum operating conditions. The treatment effect of the reactor should be heavy metals including chromium. Solid organic matter has the advantage of increasing the cell concentration by immobilizing microorganisms as well as organic matter in the packed bed reactor. However, the solid organic material is limited in the organic supply rate as the concentration of the microorganism increases, so the treatment effect may no longer increase. In order to overcome this problem, the present invention was intended to maximize the effect of the invention by adding an organic water-soluble wastewater in a water-soluble form that can be easily used by microorganisms in the treatment tank.

Wastewater from the starch production process includes organic acids and alcohols converted from some glucose by glucose and microorganisms. Therefore, these components are organic materials that can be easily used in biological reactors. A separate inlet device was attached to add 30 milliliters per day to a continuous reactor that reduced the hydraulic retention time from 20 days to 10, 5 days to increase the load of heavy metal wastewater by two or four times. The chemical oxygen demand of organic starch wastewater was 1,500 ppm and the chemical oxygen demand of the effluent was analyzed along with the heavy metal concentration.

Tables 4 and 5 show the results and show a decrease in chemical oxygen demand with heavy metal concentrations.

<Example 4>

The heavy metal concentration and chemical oxygen demand of the effluent were measured while reducing the water treatment residence time of the heavy metal wastewater (plating wastewater) in 5 days and increasing the inflow of organic wastewater (starch wastewater). First, the organic wastewater was fixed in the reactor so that 120 ml was added per day, and the heavy metal wastewater was shortened to 2.5 days and 1.25 days of water treatment, thereby increasing the load of heavy metal wastewater by 8 and 16 times. As a result, when the heavy metal wastewater load was 8 times, heavy metal was not leaked, but 39.5 ppm of chromium was leaked 4 days after increasing to 16 times. In subsequent experiments, the amount of organic wastewater was increased to 180 ml per day, and the heavy metals in the effluent were completely removed after 6 days. . This condition is 1 day for water treatment of heavy metal wastewater, and 0.73 days when calculated with organic wastewater. It is also shown that the proper addition ratio of heavy metal wastewater and organic wastewater is 2.78: 1. However, this ratio can vary depending on the concentrations of organic matter and heavy metals in the two wastewaters.

According to the present invention, by using an insoluble solid organic material (organic carrier) in a packed bed reactor as a carrier capable of immobilizing microorganisms in the reactor, the filled organic carrier can also act as a nutrient source of the microorganisms, so that the metal in the wastewater It is possible to treat heavy metals in the wastewater within a short time by adjusting the hydraulic retention time (HRT) according to the concentration, so that it can be operated with less manpower, and it is a concern in chemical treatment method or continuous stirred tank reactor. It is possible to reduce the chemical consumption and sludge generation without problems due to incomplete treatment or excessive use of chemicals or electron donors, which can reduce environmental pollution caused by heavy metals, and can be applied to any heavy metal-containing wastewater.

Claims (4)

In the method for treating heavy metal-containing wastewater using sulfate reducing bacteria, the wastewater is neutralized with limestone, mixed with anaerobic digester sludge, and then charged into a packed bed reactor filled with a solid organic material for reduction. Heavy metal containing wastewater treatment method. The process of claim 1, wherein the organic aqueous wastewater is further mixed with the solid organics or fed separately simultaneously to the reactor. The method of claim 1, wherein the wastewater is a plating wastewater and the heavy metal is selected from the group consisting of hexavalent chromium, hexavalent uranium, hexavalent selenium, and hexavalent calcium. The method according to any one of claims 1 to 3, wherein the solid organic material is a mixture of papermaking slurry and oak waste wood remaining after shiitake cultivation.