Biological filter and process

A continuous methanogenic, anaerobic biological degradation process wherein denitrification is not accomplished and wherein a liquid waste water stream containing organic pollutants amenable to biological degradation is contacted with a biomass of anaerobic microorganisms located on the surface of a support packing so as to effect the biological degradation of said organic pollutants to carbon dioxide, methane and other products, said microorganisms being capable of degrading said organic pollutants to carbon dioxide, methane and other products, said process being conducted in the absence of molecular oxygen, which process comprises:

• (a) continuously passing a liquid mixture comprised of said waste water stream and the hereafter defined recycle stream downwardly through a packed section confined within a sealed vessel, said packed section being filled with the said support packing on the surface of which is a said biomass of said microorganisms, said sealed vessel being sealed whereby air and other sources of molecular oxygen cannot enter said sealed vessel, such that said liquid mixture intimately contacts said biomass as it descends through said packed section under conditions whereby at least a portion of the organic pollutants from said waste water stream are biologically degraded and converted to carbon dioxide, methane, and other products and resulting in a liquid effluent from the lower end of said packed section containing a lower concentration of said organic pollutants than in said liquid mixture, and whereby liquid descends through said packed section while carbon dioxide, methane and other gases generated in the biological degradation ascend through said packed section countercurrently to the descending liquid, the contacting of said liquid mixture with said biomass being accomplished at a temperature within the range of about 10.degree. to 60.degree. C. which is suitable for said biological degradation and at substantially atmospheric pressure;
• (b) continuously withdrawing from the upper end of said sealed vessel at a point above said packed section the said carbon dioxide, methane and other gases generated in the said biological degradation;
• (c) continuously withdrawing said liquid effluent from the lower end of said sealed vessel at a point below said packed section, the rate of withdrawal of said liquid effluent being such as to maintain the liquid level of any said liquid effluent accumulating in the bottom of said sealed vessel below said packed section, a portion of said liquid effluent being withdrawn as a treated waste water outfall stream;
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• (d) continuously recycling as a said recycle stream a portion of said liquid effluent withdrawn from the lower end of said sealed vessel and mixing said recycle stream with said waste water stream prior to passing the resulting said liquid mixture downwardly through said packed section in accordance with the preceding step (a), the portion of said liquid effluent so recycled as said recycle stream being at least 60% thereof and an amount that, when mixed with said waste water stream, will cause the said liquid mixture to have a concentration of said organic pollutants and of any biostatic or biocidal species to be below that concentration which would inhibit the growth processes of said microorganisms.

A continuous biological degradation process wherein a liquid waste water stream containing organic pollutants amenable to biological degradation, and also containing nitrogen compounds wherein combined nitrogen is present as a nitrate, a nitrite or a nitrogen oxide, is contacted with a biomass of microorganisms located on the surface of a support packing so as to effect the biological degradation or conversion of said organic pollutants to carbon dioxide and other products, and to effect the biological degradation or conversion of said combined nitrogen to molecular nitrogen, said microorganisms being capable of degrading said organic pollutants to carbon dioxide and other products and of degrading or converting said combined nitrogen to molecular nitrogen, said process being conducted in the absence of added molecular oxygen, which process comprises:

• (a) continuously passing a liquid mixture comprised of said waste water stream and the hereafter defined recycle stream downwardly through a packed section confined within a sealed vessel, said packed section being filled with the said support packing on the surface of which is a said biomass of said microorganisms, said sealed vessel being sealed whereby air and other sources of molecular oxygen cannot enter said sealed vessel, such that said liquid mixture intimately contacts said biomass as it descends through said packed section under conditions whereby at least a portion of the organic pollutants from said waste water stream are biologically degraded and converted to carbon dioxide and other products and at least a portion of the combined nitrogen from said waste water stream is converted to molecular nitrogen and resulting in a liquid effluent from the lower end of said packed section containing a lower concentration of said organic pollutants and a lower concentration of said nitrogen compounds than in said liquid mixture, and whereby liquid descends through said packed section while carbon dioxide, molecular nitrogen and other gases generated in the biological degradation ascend through said packed section countercurrently to the descending liquid, the contacting of said liquid mixture with said biomass being accomplished at a temperature within the range of about 10.degree. to 60.degree. C. which is suitable for said biological degradation and at substantially atmospheric pressure;
• (b) continuously withdrawing from the upper end of said sealed vessel at a point above said packed section the said carbon dioxide, molecular nitrogen and other gases generated in the said biological degradation;
• (c) continuously withdrawing said liquid effluent from the lower end of said sealed vessel at a point below said packed section, the rate of withdrawal of said liquid effluent being such as to maintain the liquid level of any said liquid effluent accumulating in the bottom of said sealed vessel below said packed section, a portion of said liquid effluent being withdrawn as a treated waste water outfall stream;
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• (d) continuously recycling as a said recycle stream a portion of said liquid effluent withdrawn from the lower end of said sealed vessel and mixing said recycle stream with said waste water stream prior to passing the resulting said liquid mixture downwardly through said packed section in accordance with the preceding step (a), the portion of said liquid effluent so recycled as said recycle stream being at least 60% thereof and an amount that, when mixed with said waste water stream, will cause the said liquid mixture to have a concentration of said organic pollutants, and of any said nitrogen compounds, and of any biostatic or biocidal species to be below that concentration which would inhibit the growth processes of said microorganisms.