Liquid purification or separation – Processes – Treatment by living organism
Patent
1996-07-01
1998-10-13
Woo, Jay H.
Liquid purification or separation
Processes
Treatment by living organism
210750, 210762, 210903, 423235, C02F 312
Patent
active
058207619
DESCRIPTION:
BRIEF SUMMARY
This invention relates to a process for the degradation of organic pollutants in wastewaters by wet oxidation in which pure oxygen or an oxygen-containing gas is added at temperatures of 80.degree. to 330.degree. C. and under pressures of 1 bar to 200 bar.
To reduce the temperatures (and hence the pressures) required for oxidation, it has already been proposed to treat the organically polluted wastewaters with oxygen or oxygen-containing gases at a redox potential of 300 to 600 mV, the redox potential being adjusted by addition of redox systems, preferably Fe.sup.++ or Fe.sup.+++ ions. It is possible in this way to reduce the reaction temperature to well below 250.degree. C. It is also known that the reaction temperature can be further reduced by adding benzoquinones or naphthoquinones as co-catalysts to the wastewater during the wet oxidation process. This process is described in DE 33 16 265 and in the Article by O. Horak in Chem. Ing. Techn. 62 (1990), No. 7, pages 555-557.
It has now been found that treated sludge can be used as co-catalyst instead of the quinones mentioned in DE 33 16 265. The treated sludge may be either surplus sludge from an industrial sewage treatment plant or digested sludge from a communal sewage treatment plant. There is thus no longer any need for the expensive quinoidal chemicals or for the elaborate pretreatment measures described in DE 33 16 265. At the same time, a large part of the biological surplus sludge can be oxidatively eliminated in this way.
Accordingly, the present invention relates to a process for the degradation of organic pollutants in wastewaters by wet oxidation in which pure oxygen or an oxygen-containing gas is added at temperatures of 80.degree. to 330.degree. C. and preferably 120.degree. to 200.degree. C., under a pressure of 1 bar to 200 bar and preferably 3 bar to 50 bar and at a pH value below 7 and preferably below 4, characterized in that the wet-oxidative degradation is carried out in the presence of iron and digested sludge or surplus sludge from a biological sewage treatment plant.
The digested sludge or the surplus sludge is preferably added to the wastewater in a quantity of 1 g to 150 g and more preferably in a quantity of 3 g to 30 g sludge dry matter per liter of wastewater.
After the wet oxidation, the acidic wastewater is best neutralized or alkalized by addition of alkali.
Another embodiment of the invention is characterized in that the basic wastewater is passed through a stripping column to remove the ammonium formed during the wet oxidation of organic nitrogen compounds and to recover it in the form of ammonia solution. The ammonia solution recovered may then advantageously be used as reducing agent in the catalytic removal of nitrogen oxides from waste gases.
Heavy metal hydroxides may be precipitated during the alkalization of the acidic wastewater coming from the wet oxidation process. They are best filtered off in a separate step and separately disposed of. The basic wastewater freed from heavy metal hydroxides is then advantageously delivered to a biological sewage treatment plant.
A further improvement is obtained by delivering the wastewater free from the ammonium to the denitrification stage of a biological sewage treatment plant.
The following advantages are afforded by the invention: the expensive production of quinones in a preliminary stage of the wastewater treatment. eliminated. .
BRIEF DESCRIPTION OF THE DRAWING
The FIGURE is a flowchart showing the process of the invention.
The invention is described in more detail in the following with the aid of Comparison Examples and a flow chart.
Treated sludge with a concentration of around 10 to 20 g dry matter per liter wastewater and iron ions in the form of iron salts with a concentration of around 0.3 to 0.5 g Fe.sup.++ /1 are added to an untreated wastewater with a COD content of 1 to 200 g/l and the mixture is acidified with H.sub.2 SO.sub.4 to a pH value of 1.5 to 2. The acidic wastewater sludge mixture is brought by a pump 1 to a process pressure of around 20 bar, he
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Holzer Klaus
Horak Otto
Melin Thomas
Bayer Aktiengesellschaft
Morrison Betsey J.
Woo Jay H.
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