DD255153A1 - PROCESS FOR THE BIOLOGICAL CLEANING OF NITRATE AND HEAVY METAL CONTAINERS - Google Patents

Abstract

The invention relates to a process for the purification of nitrate-containing effluents, as obtained in pickling and in the inorganic pigment production and make difficult by their content of heavy metals, the biological treatment or make impossible. The invention is therefore based on the object, by suitable measures and using the specific, chemically treated carrier material to eliminate the wastewater microbial contents. The object is achieved by the invention that nitrate and heavy metal-containing waste water in the presence of oxidizable carbon compounds are passed once or several times through a fixed-bed or fluidized bed biofilm reactor in which the denitrification microorganisms are on solid waste products of lignite coke as a carrier medium.

Description

Field of application of the invention

The invention relates to a process for cleaning nitrate-containing effluents, as obtained in pickling and in the inorganic pigment production and which make difficult by their content of heavy metals, the biological treatment or impossible.

Characteristic of the known technical solutions

The biological treatment of nitrated wastewaters is well known and state of the art. Effective methods work with fixed-bed or fluidized-bed biofilm reactors, wherein as carrier materials of the fluidized bed or the fixed bed and as a growth medium of the microorganisms sand (DE-AS 2924465), silicates (DE-OS 2930812), organic polymers with open macropores ( DE-OS 3062869), activated carbon (DE-OS 2331192), anion resins, loam, activated carbon (DE-OS 3046686), expanded clay (DE-OS 3324073), buoyant plastic (DE 3032899 and EP 0058247), with molybdenum salts impregnated clay (US 4253966), straw bales (DD-PS 140031), hydrophobic inorganic substances in tabletted or pelleted form (DD-WP 254051-8) are used. Also by-products of lignite coke gasification, so-called Winklergeneratoraschen or dusts have been proposed (DD-WP 277526-2).

However, the known support materials fail when the heavy metals introduced into the biological denitrification step develop their toxic effect, i. H. The elimination of nitrogen or nitrate-containing ingredients is impaired or prevented.

(Lewandowski, Z., Water Research 19 [1985] 589; Slater, J. and DC Capone, Mar. Ecol Progr. Ser. 18 [1984] 89) For the removal of the interfering heavy metals, therefore, the known methods of hydroxide or Sulfide precipitation applied, which have the disadvantage of difficult to filterable and drainable rainfall. They also require an additional process stage and appropriate expense for the precipitation chemicals (Hartinger, C, Taschenbuch der Abwasserbehandlung for the metalworking industry, Carl Hanser Verlag, Munich-Vienna 1976).

In the galvanic industry, the use of ion exchange systems for the recovery of heavy metals is common.

Ion exchange processes are complicated and u. a.- only acceptable where appropriate heavy metal contents are to be removed, which allow a return of the eluates in upstream stages (Knothe, M. and S. Ziegenbalg, Z. Chem. 221982]

Redox, extraction and membrane separation methods are also proposed, which are currently available. cause considerable capital and operating costs and are thus only appropriate where the recovered concentrates beneficially recirculate (Kümmel, R., F. Winkler and R. Beck, Acta hydrochim., hydrobiol., 12 [1984] 227).

Object of the invention

The object of the invention is to develop a wastewater treatment process, with the effort for the separate heavy metal removal is significantly reduced without affecting the denitrification.

Explanation of the essence of the invention

Through lengthy and complicated experiments and studies, it has surprisingly been found that microorganisms which process heavy metal and nitrate-containing wastewater complex and permanently on a certain chemically treated support material and under certain conditions. The invention is therefore based on the object to eliminate microbial wastewater ingredients by appropriate measures and using the specific, chemically treated carrier material.

The object is achieved in that nitrate and heavy metal-containing wastewater in the presence of oxidizable carbon compounds one or more times by a fixed bed or. Fluid bed biofilm reactor in which the denitrification-effective microorganisms are on solid waste products of brown coal coke gasification as the carrier medium, which is characterized by their content of surface carboxyl groups of 0.5 to 1.0% and surface ether groups of 0.4 up to 0.6%. The surface active groups are exposed by a hydrochloric acid wash. Due to the pore system, the denitrification-active biofilm can anchor firmly, is partially protected from the acting shear forces and thus particularly efficient. It shows on the one hand that the microorganisms can not be contaminated on all sides by the toxic heavy metals, while on the other hand, the carboxyl groups present in the support material heavy metals bind mainly chemisorptive.

The support materials were used in the particle size range from 0.1 to 0.4 mm for the fluidized bed and from 0.8 to 2.5 mm for the fixed bed method. Before use, they have to be mixed with 5 to 30% strength, preferably 10% strength hydrochloric acid in a mass ratio of 1: 4, separated from the solution after about one hour and washed neutral.

The necessary for microbial Denitrifaktion carbon can be provided in a known manner by addition of alcohols, ketones, etc., as well as BOD ₅ -containing water.

The separation of the excess biomass is carried out in a known manner due to the density difference between overgrown and unvegetated particles, whereby particles with large biofilm thickness are drawn off and deposited via an overflow. A regeneration of the fluidized bed carrier material is not required. It is only replaced with the biomass discharged carrier material. The reactor is operated with pH values of the aqueous phases of 6.5 to 9.5 and temperatures of 10 ^c C to 45 ⁰ C. The flow rate in the microbiological reaction zone should be in the range of 0.0001 to 0.1 m / s.

In the following the invention with reference to 4 embodiments will be explained in more detail.

Embodiment 1

In Embodiment 1, nitrate and lead-containing water were denitrified semicontinuously in round bottom flasks under anoxic conditions. As denitrifying microorganisms mixed populations were used, which were obtained from comunal anaerobic sludge and adapted over a period of 4 months to lead concentrations of 2 mg / l Pb ²⁺ .

The flasks were inoculated 1:10 with the microorganism suspension. The model water used contained:

1000mg / INO'3 1 500 mg / l CH ₃ OH 180mg / IP (C / N / P = 2.5 / 1 / 0.8)

Trace salts and Pb ²⁺ ions in concentrations of 0 ... 8mg / l. Parallel investigations were carried out with and without the addition of 5 g / l HCL-washed Winkler generator ash. The measurement of the nitrate concentrations and the pH value were used to determine the denitrification rate and for process control. At intervals of 3 or 4 days, the contents of the flask were renewed to 50%.

The following table shows the mean nitrate reduction rates A obtained during the study period of 2 months:

Lead input A ₁ A ₂

Concentration without

Winkler generator pocket Winkler generator pocket

-3 -3

mg / l 10g / m ³ -s 10g / m ³ -s

0 3.78 3.79 0.5 3.69 4.07 0.75 3.57. 3.65

1 3.09 3.23 1.5 1.98 2.35

2 0.59 2.30 4 "0.39 2.35 8 0.28 2.50

It can be seen that denitrification is not disturbed by Pb ²⁺ ions in the presence of Winkler's genome ore pocket. The ⁷ measurement of the Pb ²⁺ content in the solution showed that even after two months since the beginning of a rapid removal of Pb ²⁺ from the aqueous phase solid-state, which indicates the adsoptiove binding of the heavy metal to the Winkler generator ash.

Embodiment 2

The influence of CrOj'-ions on the denitrification was examined similarly to the semicontinuous procedure described in Example 1. After an 8-week adaptation period of mixed population were treated with a model solution composed of 1,000 mg / l NO3,1 500 mg / l CH ₃ OH, 180 mg / l P and trace salts, the following nitrate reduction rates A determined depending on the Cr (VI) content:

Cr (VI) A ₁ A ₂

without with

Winkler generator pocket Winkler generator pocket

mg / l 1 (T ³ g / m ³ -s 1 (T ³ g / m ³ -s

0 1.33 1.46

0.1 0.92 1.39

0.2 0.32 1.62

0.3 0.20 1.59

As in Embodiment 1, here too, the addition of Cr (VI) to the batches with Winkler generator ash causes no repression of the denitrification. However, a significant inhibition occurred in the flask without Winkler generator ash addition.

Embodiment 3

In Embodiment 3, the microbial denitrification was carried out continuously in the fluidized bed biofilm reactor. The heavy metal-containing water to be denitrified, which may have nitrate concentrations of 100 to 5000 mg / l, is passed from a raw water reservoir to a make-up tank containing the optimum parameters for the denitrification process (pH, nutrient salt and trace salt content, organic carbon compound). be set. In the present example, the denitrification of a partial water composed as follows was investigated:

100mg / INO5 200 mg / l CH ₃ COOH 6.5 mg / l Cu ²⁺ pH = 7.0 ... 7.4

From the batch tank, the water passes through a metering pump, with a constant flow of 0.8 h ^{1 was} set in the fluidized bed biofilm reactor. With a thermostatically controlled circulation pump, the flow velocities required for the generation of the fluidized bed are realized by means of a throttling and obturator and pumped to be denitrified water in the circulation.

The fluidized bed carrier used was 25 g of HCI-washed waste product from lignite coke gasification with a particle diameter of 0.2 to 0.4 mm.

The mixed population used was obtained from municipal anerubbio sludge. The immobilization of the microorganisms was initially semicontinuous under fixed bed conditions and then in the fluidized bed of the reactor at high biomass concentrations in the circulating solution. In the process, the microorganisms settled on the carrier particles and formed a denitrification-active biofilm.

The denitrified water is removed from the reactor via the top outlet.

Via an overflow weir, the particles with large biofilms, which accumulate in the upper part of the fluidized bed due to the density differences between the biomass and the carrier medium, can be removed from the reactor and thus the excess biomass formed can be withdrawn. The eliminated bioparticles have a good settling ability.

With the carrier according to the invention and under the conditions described, constant denitrification rates of 74.1 mg / l h NO3 were achieved over a period of 8 days. This corresponds to a 92% reduction of the input nitrate. The nitrate residual concentration in the reactor effluent was 7.4 mg / l. A disturbance of the denitrification process by the continuous copper addition could not be observed.

No copper was detectable in the reactor effluent.

Embodiment 4

In the embodiment 4, the continuous denitrification of lead-containing waters took place. 25 g of overgrown waste product from lignite coke gasification were used as fluidized bed carriers. The immobilized microorganisms were not adapted to Pb ²⁺ ions.

To the denitrifying raw water with 200mg / l NOJ and 4mg / l Pb ²⁺ 250mg / l CH ₃ OH, 22mg / l P and trace salts were added and adjusted to a pH of 7.0. The flow rate was 1.0h " ¹ .

During the study period of 6 weeks, no inhibition of denitrification could be detected. No lead was detectable in the reactor effluent. The denitrification rate was 185 mg / L NO ₃ NO ₃ content averaged 14.5 mg / L was measured in the reactor effluent. This corresponds to a denitrification performance of 93%.

Claims (5)

1. A process for the biological purification of nitrate and heavy metal-containing wastewaters with conventional denitrifying microorganisms on growth medium in fixed bed or fluidized bed biofilm reactors optionally with the addition of C source and trace salts, characterized in that the growth medium treated with aqueous hydrochloric acid ashes of lignite coke in a grain size of 0.2 to 2.5 mm and a content of surface carboxyl groups of 0.2 to 1.0%, preferably 0.5%, and surface ether groups of O, 1 to 0.9%, preferably 0.4% , 2. The method according to claim 1, characterized in that the grain size of the growth medium in the fixed bed reactor preferably 0.8 to 2.5 mm and in the fluidized bed reactor is preferably 0.2 to 0.4 mm. 3. The method according to claim 1 and 2, characterized in that the ashes of brown coal coke gasification for one hour with 5 to 30% strength, preferably 10%, treated aqueous hydrochloric acid and then washed with water. 4. The method according to claim 1 to 3, characterized in that the biological purification in the biofilm - reactor at pH values of the aqueous phase of 6.5 to 9.5, at flow rates of 0.0001 to 0.1 m / s and takes place at temperatures of from 1O ⁰ C to 45 ° C. 5. The method according to claim 1 to 4, characterized in that the excess biomass formed is eliminated by particles are removed with large biofilm thickness due to their low density via an overflow from the reactor.