GB2281306A - Method and apparatus for treating sewage - Google Patents

Method and apparatus for treating sewage Download PDF

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Publication number
GB2281306A
GB2281306A GB9414468A GB9414468A GB2281306A GB 2281306 A GB2281306 A GB 2281306A GB 9414468 A GB9414468 A GB 9414468A GB 9414468 A GB9414468 A GB 9414468A GB 2281306 A GB2281306 A GB 2281306A
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Prior art keywords
water
hydrogen sulphide
scrubber
sewage
liquid phase
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GB9414468A
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GB9414468D0 (en
Inventor
Gerald Victor Horner
Matthew Charles Dami Griffiths
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ETA Process Plant Ltd
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ETA Process Plant Ltd
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Filing date
Publication date
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Publication of GB9414468D0 publication Critical patent/GB9414468D0/en
Publication of GB2281306A publication Critical patent/GB2281306A/en
Withdrawn legal-status Critical Current

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    • C—CHEMISTRY; METALLURGY
    • C12—BIOCHEMISTRY; BEER; SPIRITS; WINE; VINEGAR; MICROBIOLOGY; ENZYMOLOGY; MUTATION OR GENETIC ENGINEERING
    • C12M—APPARATUS FOR ENZYMOLOGY OR MICROBIOLOGY; APPARATUS FOR CULTURING MICROORGANISMS FOR PRODUCING BIOMASS, FOR GROWING CELLS OR FOR OBTAINING FERMENTATION OR METABOLIC PRODUCTS, i.e. BIOREACTORS OR FERMENTERS
    • C12M47/00—Means for after-treatment of the produced biomass or of the fermentation or metabolic products, e.g. storage of biomass
    • C12M47/18—Gas cleaning, e.g. scrubbers; Separation of different gases
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D53/00—Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols
    • B01D53/14—Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols by absorption
    • B01D53/1456—Removing acid components
    • B01D53/1468—Removing hydrogen sulfide
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D53/00—Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols
    • B01D53/34—Chemical or biological purification of waste gases
    • B01D53/46—Removing components of defined structure
    • B01D53/48—Sulfur compounds
    • B01D53/52—Hydrogen sulfide
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D53/00—Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols
    • B01D53/34—Chemical or biological purification of waste gases
    • B01D53/74—General processes for purification of waste gases; Apparatus or devices specially adapted therefor
    • B01D53/84—Biological processes
    • C—CHEMISTRY; METALLURGY
    • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F1/00—Treatment of water, waste water, or sewage
    • C02F1/20—Treatment of water, waste water, or sewage by degassing, i.e. liberation of dissolved gases
    • C—CHEMISTRY; METALLURGY
    • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F11/00—Treatment of sludge; Devices therefor
    • C02F11/02—Biological treatment
    • C02F11/04—Anaerobic treatment; Production of methane by such processes
    • C—CHEMISTRY; METALLURGY
    • C12—BIOCHEMISTRY; BEER; SPIRITS; WINE; VINEGAR; MICROBIOLOGY; ENZYMOLOGY; MUTATION OR GENETIC ENGINEERING
    • C12M—APPARATUS FOR ENZYMOLOGY OR MICROBIOLOGY; APPARATUS FOR CULTURING MICROORGANISMS FOR PRODUCING BIOMASS, FOR GROWING CELLS OR FOR OBTAINING FERMENTATION OR METABOLIC PRODUCTS, i.e. BIOREACTORS OR FERMENTERS
    • C12M21/00—Bioreactors or fermenters specially adapted for specific uses
    • C12M21/04—Bioreactors or fermenters specially adapted for specific uses for producing gas, e.g. biogas
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02A—TECHNOLOGIES FOR ADAPTATION TO CLIMATE CHANGE
    • Y02A50/00—TECHNOLOGIES FOR ADAPTATION TO CLIMATE CHANGE in human health protection, e.g. against extreme weather
    • Y02A50/20—Air quality improvement or preservation, e.g. vehicle emission control or emission reduction by using catalytic converters
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E50/00—Technologies for the production of fuel of non-fossil origin
    • Y02E50/30—Fuel from waste, e.g. synthetic alcohol or diesel
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
    • Y02P20/00—Technologies relating to chemical industry
    • Y02P20/50—Improvements relating to the production of bulk chemicals
    • Y02P20/59—Biological synthesis; Biological purification
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02W—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO WASTEWATER TREATMENT OR WASTE MANAGEMENT
    • Y02W10/00—Technologies for wastewater treatment
    • Y02W10/20—Sludge processing

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  • Engineering & Computer Science (AREA)
  • Chemical & Material Sciences (AREA)
  • Life Sciences & Earth Sciences (AREA)
  • Health & Medical Sciences (AREA)
  • Organic Chemistry (AREA)
  • Oil, Petroleum & Natural Gas (AREA)
  • Biomedical Technology (AREA)
  • Environmental & Geological Engineering (AREA)
  • General Chemical & Material Sciences (AREA)
  • Wood Science & Technology (AREA)
  • Zoology (AREA)
  • Molecular Biology (AREA)
  • Bioinformatics & Cheminformatics (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • Analytical Chemistry (AREA)
  • Genetics & Genomics (AREA)
  • Biotechnology (AREA)
  • Microbiology (AREA)
  • General Health & Medical Sciences (AREA)
  • General Engineering & Computer Science (AREA)
  • Hydrology & Water Resources (AREA)
  • Biochemistry (AREA)
  • Water Supply & Treatment (AREA)
  • Sustainable Development (AREA)
  • Purification Treatments By Anaerobic Or Anaerobic And Aerobic Bacteria Or Animals (AREA)
  • Treating Waste Gases (AREA)
  • Gas Separation By Absorption (AREA)

Abstract

In the treatment of sewage sludge by anaerobic digestion 10, contaminants eg H2S are removed from the resulting methane by scrubbing at 16 the methane with water 13 which has been separated from other constituents of the sewage and is to be discharged. The H2S-bearing water may be passed to an air stripper before discharge and the H2S so obtained passed to a tower for biological conversion to H2SO4. <IMAGE>

Description

Title: "Method of Treating Sewage and Apparatus for use in the Method" Description of invention The present invention relates to the treatment of sewage by anaerobic digestion which results in the formation of methane from organic constituents of the sewage. It has been proposed that methane obtained in this way should be used as a fuel. However, the methane generated by anaerobic digestion of sewage is contaminated, usually by a variety of contaminants. These contaminants include hydrogen sulphide, ammonia and sulphur dioxide.
The methane also contains other gases, for example carbon dioxide and nitrogen, which may be considered not to be contaminants. However, hydrogen sulphide and sulphur dioxide are corrosive and it is generally desirable that they should be removed from the methane, before the methane is used in combustion equipment. If these contaminants are not substantially removed, the life of the combustion equipment will be impaired significantly.
Various techniques have been proposed for removing the corrosive contaminants from methane produced by anaerobic digestion. These techniques include the use of activated carbon, chemical scrubbing and the use of catalysts.
However, use of these techniques leads to unacceptably high capital and running costs and also results in the production of non-biodegradable waste products, with consequent disposal problems.
The solubility of hydrogen sulphide in water at ambient temperature is low.
In order to achieve satisfactory transfer of hydrogen sulphide from a gaseous phase to an aqueous liquid phase, it is necessary either to maintain the liquid phase at a temperature well below the ambient temperature, or to subject the gaseous phase to a high pressure or to use a large volume of water or to use two or all of these conditions in combination.
In view of this requirement, the use of an aqueous liquid phase to scrub hydrogen sulphide from methane derived from anaerobic digestion has not been used commercially, for reasons of cost.
The present invention provides a relatively low-cost way of achieving the required reduction in the concentration of hydrogen sulphide in methane.
According to the present invention, there is provided a method of treating sewage wherein (a) sludge comprising organic constituents is separated from the sewage, (b) the sludge is subjected to anaerobic digestion to form methane in admixture with contaminants, and (c) water which has been separated from other constituents of the sewage is discharged, characterised in that, prior to discharge, at least some of the water to be discharged is brought, as a liquid phase, into contact with the contaminated methane, in a gaseous phase, to promote the transfer of contaminants from the gaseous phase to the liquid phase, the gaseous phase after having been in contact with the liquid phase is removed for use and the liquid phase is discharged.
The liquid phase which has been in contact with the gaseous phase can be mixed with the remainder of the water to be discharged and the resulting mixture can be discharged, for example into a water course, with little or no adverse environmental impact. Such discharge may be direct, or may involve an intermediate treatment operation to reduce the toxicity of the contaminated water. For example, where the contaminant is removed from the methane by the use of a water scrubber, the liquid from the scrubber may be ducted to a plant at which the concentration of hydrogen sulphide is reduced. Such a plant may involve the use of an oxidising agent, particularly advantageously a biodegradable oxidising agent such as hydrogen peroxide, but preferably, and particularly where the invention is to be practised in a locality where the delivery of chemical reactants or the removal of chemical byproducts is difficult, a biological agent is utilised. For example, the hydrogen sulphide may be delivered, conveniently in gaseous phase, to a biological scrubbing tower containing a bacteria which "digests" hydrogen sulphide, converting it to a very small quantity of dilute sulphuric acid.
Preferably the water containing hydrogen sulphide in solution delivered from the scrubber is first passed through an air stripper, in which at least some of the hydrogen sulphide is removed from the water prior to its discharge, in gaseous phase. Preferably the hydrogen sulphide so removed is carried in gaseous phase into the biological scrubber, in which the bacteria is present on the surfaces of packing elements in a scrubbing tower.
Preferably the water for the biological scrubber is obtained from the discharge water from the separator.
According to a second aspect of the invention, there is provided apparatus for treating sewage and comprising an anaerobic digestion tank, separating means for separating water from incoming sewage, means for delivery of sludge from the separator to the digestion tank, a scrubber for promoting contact between a liquid phase and a gaseous phase, means for delivery of a gaseous mixture from the digestion tank to the scrubber and means for delivery of water from the separating means to the scrubber.
There will now be given descriptions, to be read with reference to the accompanying drawings, of two apparatus which are embodiments of the invention, and which may be utilised in the practice of the invention, the apparatus being descriptive of the invention by way of example.
In the accompanying drawings: Figure 1 is a diagrammatic representation of part only of the apparatus which is the first embodiment of this invention; and Figure 2 is a diagrammatic representation of part only of the apparatus which is the second embodiment of this invention.
The apparatus which is the first embodiment of this invention, a part of which only is shown in Figure 1, comprises a number of settlement or clarification tanks 11, into which sewage is fed, and from which water is fed along conduit 12, and sewage sludge along conduit 14. In practice, a series of clarification tanks 11 will be utilised, successively clarifying the water and reducing the concentration of suspended solids by a settlement process, until the stage 11a, at which the water is sufficiently clear for discharge into a water course 20 to be effected.
The sludge is fed to a digestion tank 10 in which the sludge is subjected to anaerobic digestion, producing (inter alia) methane gas, having a relatively high concentration of hydrogen sulphide.
The gaseous mixture is fed to a scrubber 16. At least a proportion of the water flowing from the clarification tank 11 is pumped along conduit 13 to the scrubber 16 and the scrubber is arranged to establish counter current flow of the gaseous and liquid phases and to promote good contact between these phases.
The gaseous and liquid phases are then permitted to separate. The separated gaseous phase is directed to suitable storage or to combustion apparatus, for example a boiler, indicated by the number 19.
The liquid phase is pumped from the scrubber along conduit 17 to the discharge path 12, along which water is discharged from the clarification tank 11 to the water course. In this way, the liquid phase from the scrubber 16 is diluted by the remainder of the water flowing from the clarification means to the water course and the concentration of contaminants in the water discharged to the water course may be acceptable.
If required, the concentration of contaminants in the liquid phase from the scrubber 16 may be reduced by treatment of this liquid phase before it is directed into the flow of water from the clarification means to the water course. Such treatment may comprise, for example, treatment with a biodegradable oxidising agent in a plant 18, utilising (e.g.) hydrogen peroxide as oxidising agent.
The volume of water flowing through the scrubber 16 per hour may be in the region of one half of the volume (measured at ambient pressure and ambient temperature) of the gaseous phase flowing through the scrubber. For example, in order to treat gaseous phase which is produced at approximately 800m3/hr (measured at ambient pressure and at a temperature within the range 100 to 20"C), a flow of water at a rate of 300-400m3/hr may be diverted from the water flow to the water course from the clarification tank 11, the diverted water being directed to the scrubber and into intimate contact with the gaseous phase. A suitable scrubber would have a height in the region of 6m to 7m and a diameter in the region of 1m to 2m. In this way, a gaseous phase produced in the digestion tanks and containing up to 4000 p.p.m of hydrogen sulphide can be treated to reduce the concentration of hydrogen sulphide in the gaseous phase to less than 300 p.p.m. The liquid phase from the scrubber may have a concentration of hydrogen sulphide in the range 8mg to 20mg/l. Dilution of this liquid phase with water flowing directly from the clarification means reduces the concentration of hydrogen sulphide in the discharge to the water course to an acceptable level.
The apparatus which is the second embodiment of this invention is similar to the apparatus above described, and will be described herein primarily insofar as it differs from the first embodiment. Similar numerals have been utilised in the second embodiment as have been used in relation to the first embodiment, together with the suffix b.
In the second embodiment sewage is separated in a sequence of separator tanks (not shown) similar to the separator tank illustrated schematically in Figure 1, solid material being ducted to a digester (not shown), and water having a low level of suspended solids being discharged. Gases produced in the digester, including contaminated methane, is fed to a scrubber 16a, and as with the first embodiment, is scrubbed with water obtained from the separator tank, being pumped from conduit 12~by pipe 13a.
On conclusion of scrubbing, the methane, having a concentration of hydrogen sulphide at an acceptable level of no greater than 500ppm, is discharged through conduit 26 to an appropriate storage tank 19a or user of the gas, whilst the water utilised in the scrubbing operation, having a relatively high concentration of hydrogen sulphide, is ducted by conduit 28 to an air stripper 30.
Air is ducted into the stripper 30 through conduit 32, and the water, from which a large proportion of the hydrogen sulphide has been stripped, is discharged into a water course or the like, indicated by the numeral 20a.
Contaminated gas from the air stripper 30 is pumped through conduit 34 by pump 36 into a scrubber, having at this stage a concentration of hydrogen sulphide of approximately 500ppm. The gas is passed repeatedly through a packing tower 38 containing packing elements having on the surface thereof bacteria for the "digestion" of hydrogen sulphide, specifically converting hydrogen sulphide in an aqueous phase into dilute sulphuric acid. The carrier gas treated in this way is subsequently vented through vent 40 to atmosphere, having an acceptably low hydrogen sulphide concentration of no more than Sppm. The water carrier, similarly obtained from the water delivered from the settlement tank 11, 1 lea via conduit 37, is ducted from the bioscrubber 38 in conduit 39, having a low concentration of dilute sulphuric acid, is mixed with water emanating from the air stripper 30, and is mixed with the remainder of the water emanating from the separator tank 11, and is discharged at 20 having a ph value of between 6.5 and 7.
The features disclosed in the foregoing description, or the following claims, or the accompanying drawings, expressed in their specific forms or in terms of means for performing the desired function, or a method or process for attaining the disclosed result, may, separately or in any combination of such features, be utilised for realising the invention in diverse forms thereof.

Claims (18)

CLAIMS:
1. A method of treating sewage wherein sludge comprising organic constituents is separated from the sewage, the sludge is subjected to anaerobic digestion to form methane in admixture with contaminants and water which has been separated from other constituents of the sewage is discharged, characterised in that, prior to discharge, at least some of the water to be discharged is brought, as a liquid phase, into contact with the contaminated methane in the gaseous phase, to promote the transfer of contaminants from the gaseous phase to the liquid phase, the gaseous phase, after having been in contact with the liquid phase is removed for use and the liquid phase is discharged to the water discharge.
2. A method according to Claim 1 wherein a minor proportion of the water to be discharged is directed through a packed column in counter-current flow to the gaseous phase.
3. A method according to Claim 1 or Claim 2 wherein the water separated from the gaseous phase after contact with the contaminated methane is treated to reduce the contamination of this water.
4. A method according to Claim 3 wherein the water is treated with an oxidising agent.
5. A method according to Claim 3 wherein the water is treated with an air stripper to remove hydrogen sulphide from solution.
6. Apparatus according to one of Claims 4 and 5 wherein hydrogen sulphide is converted to sulphuric acid prior to discharge with the effluent water.
7. A method according to Claim 6 wherein the hydrogen sulphide is converted to sulphuric acid by a biological agent.
8. Apparatus for treatment of sewage and comprising separating means for separating water from incoming sewage, an anaerobic digestion tank, a scrubber for promoting contact between a liquid phase and a gaseous phase, means for feeding sewage sludge from the separating means to the digestion tank, means for feeding a gaseous mixture from the digestion tank to the scrubber and means for feeding water from the separating means to the scrubber.
9. Apparatus according to Claim 5 further comprising mixing means for mixing an agent with the liquid phase which leaves the scrubber.
10. Apparatus according to Claim 8 wherein the hydrogen sulphide conveyed from the scrubber is subjected to a further treatment operation for conversation to sulphuric acid.
11. Apparatus according to Claim 8 wherein the treatment to which the hydrogen sulphide is subject is a biological treatment.
12. Apparatus according to any one of Claims 8, 10 and 11 wherein the water from the scrubber is subject to an operation in which hydrogen sulphide is removed therefrom, such hydrogen sulphide being fed to a biological tower within which some at least is converted to a small volume of sulphuric acid.
13. Apparatus according to Claim 12 wherein the hydrogen sulphide is so converted in a gaseous phase.
14. Apparatus according to one of Claims 12 and 13 comprising an air stripper for removing hydrogen sulphide from the water by the use of air.
15. Apparatus according to Claim 14 in which the hydrogen sulphide so removed is mixed with water obtained from the separating means.
16. Apparatus according to any one of Claims 10 to 15 in which the water from which hydrogen sulphide has been stripped is returned to the water discharge.
17. Any novel feature or novel combination of features disclosed herein and/or shown in the accompanying drawing.
18. A method of treating sewage substantially as herein described with reference to the accompanying drawing.
GB9414468A 1993-08-26 1994-07-18 Method and apparatus for treating sewage Withdrawn GB2281306A (en)

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
GB939317734A GB9317734D0 (en) 1993-08-26 1993-08-26 Method of treating sewage and apparatus for use in the method

Publications (2)

Publication Number Publication Date
GB9414468D0 GB9414468D0 (en) 1994-09-07
GB2281306A true GB2281306A (en) 1995-03-01

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GB939317734A Pending GB9317734D0 (en) 1993-08-26 1993-08-26 Method of treating sewage and apparatus for use in the method
GB9414468A Withdrawn GB2281306A (en) 1993-08-26 1994-07-18 Method and apparatus for treating sewage

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Application Number Title Priority Date Filing Date
GB939317734A Pending GB9317734D0 (en) 1993-08-26 1993-08-26 Method of treating sewage and apparatus for use in the method

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Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4354936A (en) * 1980-05-20 1982-10-19 The Agency Of Industrial Science And Technology Anaerobic digestion process
GB2190682A (en) * 1986-04-18 1987-11-25 Wessex Water Authority Treatment of bio-gas
WO1991019558A1 (en) * 1990-06-15 1991-12-26 Paques B.V. Process for the removal of hydrogensulphide (h2s) from biogas

Patent Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4354936A (en) * 1980-05-20 1982-10-19 The Agency Of Industrial Science And Technology Anaerobic digestion process
GB2190682A (en) * 1986-04-18 1987-11-25 Wessex Water Authority Treatment of bio-gas
WO1991019558A1 (en) * 1990-06-15 1991-12-26 Paques B.V. Process for the removal of hydrogensulphide (h2s) from biogas

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Publication number Publication date
GB9317734D0 (en) 1993-10-13
GB9414468D0 (en) 1994-09-07

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