CA2892390A1

CA2892390A1 - Advanced waste treatment for forestry product sludges

Info

Publication number: CA2892390A1
Application number: CA2892390A
Authority: CA
Inventors: Ian W. Wylle; Graham Illingworth; Tony Illingworth; David Young; Mark Maertens-Poole
Original assignee: Axsiom Management Inc
Current assignee: Axsiom Management Inc
Priority date: 2015-06-25
Filing date: 2015-06-25
Publication date: 2016-12-25

Abstract

The invention described herein is a method of treating sludges or other wastes containing organic compounds to generate biogas and to recover useful products from those wastes including sulfur compounds. The Kraft pulp process which utilizes sulfide ions (S2-) as a feedstock to strengthen paper through lignin or other non-cellulose material removal is a particular but non-exclusive application for this invention. The generation of biogas from forestry product wastes is indicated in part because of the large concentration of carbon-compounds in the waste which produces a high yield of biogas containing methane, carbon dioxide, and hydrogen sulfide. The hydrogen sulfide in the biogas is undesirable because of its toxicity and the regulatory barriers to its presence and use in natural gas streams.
Preferential removal of the hydrogen sulfide (H2S) Is performed with a gas-liquid Interaction (scrubber) of the biogas with an alkaline solution, preferably containing caustic (NaoH). The configuration and parameters of the scrubber is described herein, Optionally, the capture of H2S Is performed with a "white liquor" solution from a Kraft pulp and paper process and optionally recycled for further use In the Kraft paper process. Other Kraft process gases, such as methyl mercaptan (CH4S), can also be captured in an alkaline solution for similar purposes. An additional method of producing and treating biogas contaminated with sulfur compounds is described. This method describes a preferential treatment of the organic waste at a lower temperature (below 35°C) to enhance the production of these sulfur gases by sulfur reducing bacteria (SRB) followed by a higher temperature (above 35°C) methanogenic biogas formation step to produce Wages essentially free of reduced sulfur compounds. A method of capturing less water soluble reduced sulfur gases, such as dimethyl sulfide (C2H6S) and dimethyl disulfide (C2H6S2), using a solution containing methanol is also disclosed with an optional method of electrochemical treatment of the dissolved gases. Finally, the biogas process may also constitute one step of a combined treatment process for forestry product wastes which may include a step of recycling other nutrients for enhanced waste digestion including nitrogen and phosphorus.

Description

Statement of the Problem and Background of the Prior Art:
Many organic wastes, such as sludges, wastewater or other mixtures or solutions containing organic compounds are subject to conversion to blogas through the action of anaerobic bacteria.
Biogas is usually composed of a mixture of methane (CH4) and carbon dioxide (CO2) and often contains significant quantities of gaseous sulfur compounds and In particular hydrogen sulfide (H2S) which Is the simplest reduced sulfur compound, H2S and other reduced sulfur compounds are noxious, odourous, toxic chemicals which if burned can produce acidic by-products including sulfurous (H2S03) and sulfuric acid (H2SO4) as well as regulated pollutants such as sulfur dioxide (SO2) and sulfur trioxide (503). Such acid by-products are known to rapidly degrade common materials used in combustion systems, such as steel. This Is one of the reasons why the presence of reduced sulfur compounds In fuels, Including gaseous fuels such as natural gas, is regulated within tight limits. Many methods have been used in the past to reduce or eliminate the presence of sulfur compounds in fuels, including the Claus process (REF 1: for example, US patent number 5,021,232, Hise).
A mixture of reduced sulfur compounds Is often measured In terms of Total Reduced Sulfur (IRS) and It often Includes a number of such compounds in a mixture. Common industrial sources of TRS compounds Include emissions from of VI Kelowna I www.axsiomgroup.com I Calgary Revision Date: 12/1242014 A Y.4 IQ I in mahaaement Inc.
Canadian Provisional Patent Application pulp and paper manufacturing, and in particular the Kraft pulp process (REF 2:
for example, US patent number 8,246,779, Foan). The Kraft process typically produces a TRS mixture including various quantities of H2S, methyl mercaptan (CH4S), dirrethyl sulfide (C2H4S)(DMS), and diMethyl disulfide (C21-14S2)(DDMS) (REF
3: for example, Z. Zhang et al, "Scrubbing NCG
with White Liquor to remove reduced Sulfur gases", Pulp and Paper Canada, 107:12 (2006), 74-79). Such TRS compounds have been captured or scrubbed using various prior art methods. For example, US patent number 6579506 (Spink), describes a method of contacting a gaseous TRS mixture with a spray of mean droplet size of 5-250 microns, containing a solution of the potent oxidizer chlorine dioxide (d02) and the oxidative destruction of the TRS compounds through reaction with the C102. Other prior art describes the capture or reuse of some portion of these TRS gases from the Kraft process. For example, US patent number 5820830 (vicliiroy), describes the condensation of these TRS gases and their reuse in the Kraft process. However, the water solubility of these TRS
compounds Is relevant in determining the capture efficiency of these gases for reuse or destruction. Some of the prior art, including Spink, describes the use of Kraft "White Liquor" (an aqueous solution comprising sodium hydroxide, Na0H, and sodium sulfide, Na2S) to capture at least a portion of these TRS gases. However, the water solubility of DMS (7.28 g/L at 20 C, ref 3: http://www.cochem.com/
msds/1.00000Q13158 _SDS USEN.P_p_E) and DDMS (2.5g/L¨ref4:
hltie:/hzestis-enarust.denxt/eateway.a/gestis en/0,1051P.xmln=templates5fn=defaulthtm$3.0) is quite limited. This low water solubility limits the capture efficiency for DMS and DDMS using aqueous media.
Conventional alkane analogues of these compounds such as diethyl sulfide (C4H20S) and methyl-ethyl sulfide (C31-laS) and their disulfide equivalents are also similarly difficult to capture with aqueous media since their water solubility is similar or even lower. A more efficient method of capturing these less water soluble toxic sulfur gases Is therefore a useful advance in the art.
The Kraft pulp process utilizes a feedstock containing sulfide ions (52.) and bisuifide Ions (H5-) in order to de-polymerize lignin and separate it from cellulose in an alkaline solution (OH-) and thus to strengthen the resulting paper.
These sulfide ions can be produced directly by adding sodium sulfide (Na2S) into a solution of sodium hydroxide, or "caustic" (NaOH), also called "white liquor". Alternatively, the carbon in the wood fiber may be used to chemically reduce oxidized sulfur compounds which result from combustion of reduced sulfur compounds according to the following reaction (ref 5: Biermann, Christopher J. (1993). Essentials of Pulping aria Papermaking. San Diego: Academic Press, Inc. Oa 0-12-097360-)c):
Reaction 1: N82504 2C Na2S 2CO2 The production of biogas from wastes and sludges from Kraft and other paper processes (such as the sulfite paper process), can produce large volumes of biogas because of the high proportion of carbon from lignin, cellulose and hemicellulose typically present in these wastes. However, given the use of sulfur compounds in these paper-making processes as exemplified above, the production of biogas from sludges produced by these pulp processes will usually be heavily contaminated with reduced sulfur compounds. These compounds are especially odourous due to the very low threshold for their detection, i.e. less than 1 ppb (ref 6: Ministry of the Environment, "Ontario Air Standards for Total Reduced Sulfur", Standards Development Branch, 2007.) Therefore, the disposal of these wastes through conventional lagoon and other open air treatment ponds can therefore introduce a large quantity of toxic and odourous compounds to the environment. An improved method of capturing and preventing the emission of these toxic and adourous compounds is thus a desirable and necessary advance In the art.
Summary of the Invention A method for the separation and reuse of reduced sulfur-containing gases produced from biogas and other sources is described herein. The method comprises a series of steps Including optional steps to efficiently perform the MEMKelowna I www.axslorngroup.com j Calgary Revision Date: 12/1212014 A!t:9siom Canadian Provisional Patent Application , Management Inc.
recapture and reuse of these reduced sulfur compounds. The following embodiments will highlight the key features of the Invention.
I) The first embodiment of the invention utilizes a method for the recovery and reuse of reduced sulfur compounds from brogas as follows;
1) Anaerobic digestion of organic wastes producing high levels of reduced sulfur compounds, e.g. >0,5 v% H2S

2) Directing a gaseous stream from the anaerobic digestion into an alkaline aqueous solution preferably comprising NaOH

3) Salvation of the sulfur compounds into ionic forms of the sulfur compounds including sulfide (52-) and/or bisuIfide (H5-) Ions

4) Directing the V or HS- Ions to further chemical processing, optionally including the use of such ions In a Kraft paper process

5) Production of biogas comprising CH4 and CO2 from the alkaline solution A clearer view of the essential elements of the invention can be gained by reference to the attached figures. in figure 1 is shown a sludge and wastewater, exemplified by a forestry product sludge, or organic waste containing elevated levels of sulfur compounds. Said waste is first Introduced into an anaerobic digester where biogas is generated comprising Cl-i4 and CO2 and also comprising an elevated level of gaseous reduced sulfur compounds typically produced by the action of SRBs, typically comprising a majority concentration of HS. Said biogas contaminated with reduced sulfur compounds is then directed into en alkaline aqueous solution comprising NaOH and thus forming a solution containing dissolved sulfur compounds comprising at least a portion of S2' and/or HS- Ions. The biogas directed to the alkaline solution Is thus stripped of its sulfur compounds and Itself does not significantly dissolve In the aqueous solution. The biogas therefore can realistically be considered to have been desulfurized (typical concentration of remaining gaseous sulfur compounds 40.1 v% and more preferably less than 0.01 v%) and available for low-pollution (low sulfur) combustion. The dissolved sulfur compounds present In the aqueous solution can then be directed to another process step where they can be consumed or used for other purposes. Said other process can preferably be a Kraft pulp process where the sulfide or bisulfide Ions are utilized for delignifIcation of pulp.
Ii) A second embodiment of the invention utilizes many of the same steps as the first embodiment of the invention above except that it includes an additional source of reduced sulfur gases. Said additional source can optionally be the Non-Condensable Gases (NCGs) from a Kraft pulp process, comprising at least some Has and CH4S. The sequence of steps for this method Is as follows, and it can also be seen in Figure 2 below:
1) Anaerobic digestion of organic wastes producing relatively high levels (>0.5 v%) of reduced sulfur compounds 2) A stream of NCGs gases comprising a significant quantity (>10 v%) I-12S
and/or CH4S
3) Directing a gaseous stream from the anaerobic digestion and the NCGs Into an alkaline aqueous solution preferably comprising NaOH
4) Salvation of the sulfur compounds into ionic forms of the sulfur compounds including sulfide (V-) and/or blsulfide (H5-) Ion 5) Directing the solvated S2' or HS- ions to further chemical processing, optionally including the use of such ions In a Kraft paper process

6) Production of biogas comprising CH4 and CO2 from the alkaline solution A clearer view of the essential elements of the invention can be gained by reference to the attached figures. In figure 2 Is shown a sludge and wastewater, optionally exemplified by a forestry product sludge, or organic waste containing elevated levels of sulfur compounds. However, In this embodiment there are two sources of the gaseous sulfur compounds: the anaerobic digester and the Non-Condensable Gases from the mill.
As In the first embodiment, the biogas from the anaerobic digester contains an elevated concentration of reduced sulfur gases including H25, however, In 1=111 Kelowna I www.axslorngroup.corn Calgary Revision Date: 12/1212014 -=

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= anageMent Canadian Provisional Patent Application addition, a second source of reduced sulfur gases is introduced from the mill or other industrial process producing elevated levels of reduced sulfur compounds (which may optionally be a Kraft pulp mill) comprising at least a significant quantity (>10 v%) of H2S and/or CH4S. Both of these sources of reduced sulfur gases are directed to the alkaline solution preferably comprising NaOH, In the alkaline solution, as In the first embodiment, the reduced sulfur compounds are solvated into soluble forms of the compounds comprising at least a portion of S2- and/or I-IS- and/or CH3S- ions. The solvated solution of those reduced sulfur Ions are then directed for a further chemical process. Said further chemical process can preferably be a Kraft pulp process where the sulfide or blsulfide ions are utilized for delignification of pulp.
III) A third embodiment of the Invention utilizes some of the same method steps as the first and second embodiment of the invention above except that the anaerobic digestion process comprises a two-step process. The first anaerobic digestion process produces relatively high levels of reduced sulfur gases while the second anaerobic digestion process produces biogas relatively free of reduced sulfur gases. The sequence of steps for this method is as follows, and it can also be seen in Figure 3 below:
1) A first anaerobic digestion step of organic wastes at a reduced temperature (<35 C) preferably to produce high levels of reduced sulfur compounds (>2 v%), preferably using two groups of SRBs ¨ incomplete and complete oxidisers 2) Directing a gaseous stream comprising relatively high levels of reduced sulfur compounds produced from the anaerobic digestion at a reduced temperature to an alkaline aqueous solution comprising NaOH
3) Solvation of the sulfur compounds into ionic forms of the sulfur compounds including sulfide (52') and/or bisuificie (HS-) ion 4) A second anaerobic digestion step of the organic waste previously treated in the first anaerobic digestion step to deplete the concentration of sulfur in the waste, at a somewhat elevated temperature (>35 C) preferably producing relatively pure biogas (CH4+ CO2) with very low levels of reduced sulfur compounds (<0.1%) 5) Directing the solvated S2- or HS- Ions to further chemical processing, optionally Including the use of such ions in a Kraft paper process 6) Production of Wages comprising CH4 and CO2 from the alkaline solution A clearer view of the essential elements of the invention can be gained by reference to the attached figures.
Figure 3 Illustrates sludge and wastewater, optionally exemplified by a forestry product sludge, or organic waste containing elevated levels of sulfur compounds, However, in this embodiment the waste is first directed to a first anaerobic digestion step at a relatively reduced temperature (<3.5 C or more preferably in a range from 20-30 C). In this digestion process SRBs preferably deplete the waste of sulfur compounds producing relatively high levels of reduced sulfur gases, comprising H2S, typically at a concentration above 2 v it is important to ensure the H2S Is vented from the digestion tank regularly to ensure that the H25 concentrations do not exceed 0.002-0.003 mole/H25 as even at these low levels, this may be toxic to the micro-organisms, causing the SRB's to become Inactive. SRFis are known in the art to metabolize sulfur compounds most rapidly at a temperature between 28-29 C. The specific species of SRBs will be dependent upon the chemical and physical properties of the sludge;
Desulfovlbrlo and Desulfobulbus spp. are the dominant species in municipal sludge. As In the first and second embodiments, the gases produced from digestion of the waste at a temperature below 35 C from the anaerobic digester contains an elevated concentration of reduced sulfur gases Including H25. Once the concentration of sulfur compounds In the waste is depleted of sulfur and/or when the concentration of H2S in the gases being produced by the anaerobic digestion has been reduced to a certain level (e.g. <0.2 v%), the waste is either heated to a higher temperature (>35 C) and methanogenic bacteria can optionally be added to the digester or the waste can be directed into a second anaerobic digester which is maintained at a higher temperature (preferably above as.c). i.e, the process can be either a "batch mode" Or a "continuous mode" process where two separate steps are conducted sequentially in time or space. This means that the first anaerobic digestion process to deplete the sulfur concentration of the waste conducted at a reduced temperature can be conducted on a batch of waste and completed (attaining a desired lower level of reduced sulfur off gases) before the waste is directed to the second anaerobic digestion step OR a continuous flow of waste can be directed from a first anaerobic digester to a second 4 of 14 Kelowna www.axsiorngroup.com j Calgary Revision Date: 12/12/2014 Artk"
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Management Inc. Canadian Provisional Patent Application anaerobic digester where biogas is produced at a somewhat elevated temperature. The off-gases from the first anaerobic digestion are directed to an alkaline solution preferably comprising NaOH
where the reduced sulfur compounds are solvated to form at least some sulfide (52) ions. These sulfide Ions are directed into another step for further chemical processing preferably comprising a Kraft delignifIcation process.
A preferred outcome of the first anaerobic digestion step Is that the sulfur concentration of the waste is depleted, The depletion of the sulfur from the first anaerobic digestion will lead to improved (typically more rapid and/or more complete) digestion of the sludge by the methanogenic bacteria. After the first anaerobic digestion step, the second anaerobic digestion step conducted at a somewhat elevated temperature (>35T), and more preferably in the range of 40-45T, and preferably conducted using a "seeded" concentration of rnethanogenic bacteria, is conducted In order to generate blow relatively free of reduced sulfur compounds (preferably less than 0.1 v% and more preferably less than 0.01 v%). A seeded concentration of methanogenic bacteria can be produced by adding dried or wet mixtures of appropriate bacterial cultures of these methanogenic species according to prior art methods. Given that the concentration of reduced sulfur gaseous products off-gasing from the second anaerobic digestion step is relatively free of reduced sulfur compounds (in a second digester adjusted for a somewhat elevated temperature or in the first digester adjusted to a higher temperature >35T), the biogas produced from said second digester can be used for low-sulfur (low S02/503 emission) combustion.
IV) A fourth embodiment of the invention utilizes many of the same steps as the first embodiment of the Invention above except that it includes additional steps to recapture nutrients from digestion to aid In aerobic digestion. The sequence of steps for this method is as follows, and it can also be seen In Figure 4 below:
1) Polymer addition to a wastewater or sludge to help separate solids from liquids (centrate) 2) Directing the solids from polymer thickening to a steam hydrolysis step 3) Directing centrate from polymer thickening to an aerobic digestion step 4) After steam hydrolysis, directing the product of the steam hydrolysis to an anaerobic digestion step where a gas stream is produced which contains relatively high levels (>0.5 v%) of reduced sulfur compounds 5) The solids produced from the anaerobic digestion (digestate) is directed hack to the aerobic digestion step 6) Directing the gaseous stream from anaerobic digestion into an alkaline aqueous solution preferably comprising NaOH

7) Solvation of the sulfur compounds into ionic forms of the sulfur compounds including sulfide (S2) and/or bisulflde (HS-) ion

8) Directing the solvated 52' or HS- ions to further chemical processing, optionally including the use of such ions In a Kraft paper process

9) Production of biogas comprising CH4 and CO2 from the alkaline solution A clearer view of the essential elements of the invention can be gained by reference to the attached figures. In figure 4 Is shown a sludge and wastewater, optionally exemplified by a forestry product sludge, or organic waste containing elevated levels of sulfur compounds. In this embodiment, the sludge is first directed to polymer thickening step where a coagulant polymer Is added to the solution to increase the propensity of the solids in the solution to separate from the liquid portion (centrate). As is common in the prior art, the step may optionally Include a centrifugation step to encourage further separation of the solids and liquids. Alternatively a settling tank, clarifier or Dissolved Air Flotation (OAF) device may be the used to encourage separation of the solids from the liquids as is common in the art. The centrate typically contains a portion of the dissolved nutrients, typically including nitrogen compounds such as urea, and phosphorus, typically including phosphate ions or similar. This centrate can be directed to a steam hydrolysis step where the microbial cells, e.g. bacterial cells, contained in the sludge or wastewater can be destroyed or "activated" by the action of the steam. Typical steam conditions are in the range of 150C-250 C.
Pressure can optionally be applied to further accelerate and increase the efficacy of the cell rupture or "activation". As In the prior art, the cell contents are liberated or 'activated' by boiling of the internal cell water. An alternative method of activating the sludge through the destruction of the cell walls involves the chemical oxidation of the solution through commonly known prior art oxidants such as ol 14 Kelowna I www.axsiomgroup.com j Calgary Revision Date: 12/12/2014 AOM
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BI% Canadian Provisional Patent Application 4 Management Inc.
hydrogen peroxide (H202), and/or peroxodisulfate (S2082-) and/or peroxodicarbonate (C2062-). Said oxidants can be further catalyzed or encouraged to oxidize more rapidly and/or more effectively through the action of UV light (e.g. 251 nm), electrochemical acceleration, ultrasound or thermal activation, eg. S0-80 C. Peroxodisulfate After the steam hydrolysls/activation step, or chemical activation step, the waste or sludge Is directed to an anaerobic digestion.
As in the first embodiment, the solids are digested further in an anaerobic digester to produce a [slops containing an elevated concentration (e.g. >5%) of reduced sulfur gases Including H25.
The solids remaining after digestion (digestate) which will also contain "activated" forms of nitrogen or phosphorus and other nutrients whose cells have been previously destroyed by the action of the steam In the previous step, can also be directed to aerobic digestion where the nitrogen and/or phosphorus aid in the further digestion of the sludge or organic waste.
The biceps containing elevated levels of reduced sulfur gases are directed to the alkaline solution preferably comprising NaOH. In the alkaline solution, as In the first embodiment, the reduced sulfur compounds are solvated into soluble forms of the compounds comprising at least a portion of 52' and/or HS-Ions. The solvated solution of those reduced sulfur ions are then directed for a further chemical process, said further chemical process can preferably be a Kraft pulp process where the sulfide or bisulfide ions are utilized for delignification of pulp.
V) A fifth embodiment of the invention utilizes many of the same steps as the second embodiment of the invention above except that it Includes an additional step of capturing less water soluble sulfur-containing gases such as DNIS (C2HGS) and DDMS (C21-1652) and further processing these gases to allow them to be reused or discharged more safely to the environment. The sequence of steps for this method is as follows, and it can also be seen In Figure 5 below;
1) Anaerobic digestion of organic wastes producing relatively high levels (>0.5 v%) of reduced sulfur compounds 2) A stream of NCGs gases comprising a significant quantity (>10 v%) Fi2S
and/or CH45 3) Directing a gaseous stream from the anaerobic digestion and the NCGs Into an alkaline aqueous solution preferably comprising NaOH
4) SolvatIon of the more water soluble sulfur compounds (H2S, CH45) Into ionic forms of the sulfur compounds including sulfide (S2-) and/or bisulftde (HS-) Ion with a significant fraction of the less water soluble sulfur compounds e.g. DMS, DDMS, not being captured significantly In the alkaline solution 5) Directing the solvated V- or HS- ions to further chemical processing, optionally including the use of such ions in a Kraft paper process 6) Directing the less water soluble S compounds, e.g. DMS, DDMS, and the blogas to a solution comprising an organic alcohol (preferably comprising methyl alcohol, Clis0H) 7) Solvating a significant fraction (e,g. >50%) of the less water soluble 5 compounds in the organic alcohol solution 8) Production of biogas comprising CH4 and CO2 from the alcohol solution 9) Optionally directing the solution comprising the solvated less water soluble S compounds, e.g. DMS and/or MINAS, to an electrochemical cell and applying a current using prior art methods to oxidize the S compounds.
A clearer view of the essential elements of the invention can be gained by reference to the attached figures. In figure 5 is shown a sludge and wastewater, optionally exemplified by a forestry product sludge, or organic waste containing elevated levels of sulfur compounds. However, in this embodiment there are two sources of the gaseous sulfur compounds: the anaerobic digester and the Non-Condensable Gases from the mill.
As In the first embodiment, the Wages from the anaerobic digester contains an elevated concentration of reduced sulfur gases including H25, however, in addition, a second source of reduced sulfur gases is introduced from the mill or other industrial process producing elevated levels of reduced sulfur compounds (which may optionally be a Kraft pulp mill) comprising at least a significant quantity (>10 v%) of HS and/or CH4S, Both of these sources of reduced sulfur gases are directed to the alkaline solution preferably comprising NaOH. In the alkaline solution, as in the first embodiment, the reduced sulfur compounds and In particular the more water soluble 5 compounds, e.g. I-12S, CH45, are solvated into soluble forms of the compounds comprising at least a portion of 52- and/or HS- and/or Ci-is5- ions. The solvated solution of those reduced sulfur Ions are E, of Kelowna I www.axsiomgroup.corn Calgary Revision Date: 12/12/2014 /
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then directed for a further chemical process. Said further chemical process can preferably be a Kraft pulp process where the sulfide or brsuifide ions are utilized for delignification of pulp.
After directing the gaseous stream to the alkaline solution, the biogas components (CH4, CO2) and the less water soluble reduced S gases, e.g. DMS and/or DDMS, are directed to an organic alcohol containing solution preferably comprising methanol (CH3011), where the less water soluble reduced S gaseous compounds, e.g. DMS and/or DDMS and their alkane analogs, such as Methyl-Ethyl Sulfide are preferentially solvated. In addition to or in place the methanol, ethanol or other organic alcohols may be used to enhance the solubility of the less water soluble reduced sulfur gases.
The blogas (CI-14, CO2) does not tend to dissolve In organic alcohols and will not tend to be solvated by the solution, However, the now soivated reduced sulfur gases which have now been captured from the gas stream can be disposed or more easily and directly. Optionally, after the selective capture of these reduced sulfur gases, the solution can be directed to an electrochemical cell where a prior art electrochemical oxidation may be conducted to oxidize the sulfur compounds.
Said reduced sulfur compounds are readily oxidized in readily available electrochemical cells such as those sold by Electrocell, Inc. with several optional choices for the anodes and the cathodes. A commonly available anode material, "DSA" (Dimensionally Stable Anode), which is a titanium substrate coated with a mixed metal oxide of iridium and ruthenium, will readily oxidize these sulfur compounds without significant oxidation of the organic alcohol since the oxidation potential of the sulfur compounds Is significantly lower than the oxidation potential of the alcohols. The cathodic reactions of these solutions will tend to emphasize the reduction of hycironium (H30+) ions to form gaseous hydrogen. Further reduction of the sulfur compounds, while possible, will occur at a much lower rate than the reduction of hydroniurn ions, Said electrochemical reaction will preferably be facilitated by the addition of an electrolyte, such as sulfuric acid (I-12SO4) to reduce parasitic resistance In the electrochemical cell. Typical oxidation by products of the oxidation of DMS and/or DEWS include sulfite (S032-) and sulfate ions (SO4) and methanol among others. It may be preferable to reintroduce the sulfite and/or the sulfate ions back into solution with white liquor to allow these sulfur ions to be reprocessed by the Kraft reduction process for further delignification, A method of efficiently capturing the reduced sulfur gases in a liquid solution, i.e. a gas to liquid columnar contactor utilizes mostly prior art methods including [reference:
http;//www.kch-litsch,com/Document%2QLibray/KGPP1.pf]. However, in this case, the system will be optimized for white liquor (mostly water with dissolved NaOH and Na2S), dissolving sulfur gases of various solubilities In water. See Figure 6 for a schematics of the overall (conical-shaped) system to perform this function. The gas enters at the bottom with liquid entering at the top.
After entering the column through an Inlet liquid ciistributor device that provides initial distribution of the liquid across the cross-sectional area of the column. The liquid then descends to the bottom of the tank under the influence of gravity through an anti-fouling liquid distributor to spread out the liquid across the whole cross-sectional area of the system. Such a liquid distributor device will typically require at least 80 distribution points per meter squared of area. The system will also typically exhibit a high turn-down ratio to further optimize the effectiveness of interaction between the liquid and the gas.
To maximize the surface area and the wettability of the surface area and the residence time or "hold-up time" for interaction between the gas and the liquid, a large volume of "packing beads"
(or other appropriately shaped objects) are compressed with a hold-down mechanism to allow passage of the liquid with a certain delay time through the complex internal structure of the packing bead material. The gas inlet is below the packing bead material and moves upward through the column under an appropriate negative pressure applied through the gas outlet. The upward movement of the gas includes Interaction with the liquid on the surface of the beads to optimize dissolution of the gas In the white liquor. given that the objective of this gas-liquid Interaction is designed to absorb sulfur gases of reasonably high solubility and rapid dissolution time but not carbon dioxide with a relatively longer dissolution time, the surface area and residence time of the system will need to be adjusted to optimize the sulfur gas solubility and to minimize the carbon dioxide solubility.
Before exiting the column, the residual gases (in this case blogas comprising methane and carbon dioxide) will pass through a mist eliminator with relatively small pores to remove mist particles. Typical mist eliminators will remove more than 90% of the mist particles of 5 microns or larger. They will also tend to be anti-fouling as in the prior art. The liquid distributor, the gas inlet device and the packing beads vvill be optimized for the sulfur gas removal (dissolution) process.
111= Kelowna I www.axslomgroup.com I Calgary Re,visin Nit:: 12/12/2014

Claims

Sample patent claims (illustrative of Invention). We claim:

1) A method of treating organic matter waste comprising the steps of: a) anaerobically digesting the waste, b) obtaining a gaseous product from the waste comprising a gaseous sulfur compound, c) directing a portion of the gaseous product as a gas stream Into an alkaline solution thereby increasing the concentration of sulfur-containing compounds in the solution, d) using the alkaline solution containing the sulfur-containing compounds for a specified process.

2) The method of claim 1, whereby the organic waste comprises forestry product sludges and the specified process comprises a delignification step In the treatment of forestry pulp.

3) The method of claim 2, whereby the organic waste comprises a sludge from a Kraft pulp process.

4) The method of claim 1, whereby the alkaline solution comprises sodium hydroxide or "caustic".

5) The method of claim 1, whereby the gaseous sulfur-containing compounds comprises one or more of hydrogen sulfide, or methyl mercaptan.

6) The method of claim 1, whereby the method additionally comprises the step of directing other sulfur containing gases into the alkaline solution.

7) The method of claim 6, whereby the other sulfur containing gases comprise one or more of hydrogen sulfide, methyl mercaptan, dimethyl sulfide, and/or dimethyl disulfide.

8) The method of claim 6, whereby the hydrogen sulfide or methyl mercaptan are selectively removed from the gas stream.

9) The method of claim 7, whereby less water soluble gases comprising dimethyl disulfide and/or dimethyl disulfide form a gas stream which is direct through a solution containing an alcohol, preferably comprising methanol, which dissolves the less water soluble gases forming a solution of the sulfur compounds.

10) The method of claim 8, whereby the solution of less water soluble sulfur compounds is oxidized with an electrochemical process.

11) The method of claim 1, comprising an additional step of first activating the waste with steam or chemical activation.

12) The method of claim 11, whereby the chemical activation is conducted with a solution comprising peroxodisulfate ions and/or peroxodlcarbonate ions.

13) The method of claim 12, whereby a solution comprising peroxodlsulfate is formed from a feedstock derived from hydrogen sulfide gases.

14) The method of claim 13, whereby the solution comprising peroxodisulfate is formed by electrochemical oxidation of solution Initial comprising hydrosulfide or sulfide Ions.

15) The method of claim 1, whereby the anaerobic process is conducted at a first temperature below 35 degrees C to preferentially encourage the generation of sulfur gases

16) The method of claim 15, whereby the anaerobic process is conducted at a second temperate above 35 C.

17) The method of claim 15, whereby the anaerobic process generates a gaseous mixture comprising a proportion of reduced sulfur gases of greater than 1% by volume.

18) The method of claim 15, whereby the anaerobic process generates a gaseous mixture comprising a proportion of reduced sulfur gases of greater than 5% by volume.

19) The method of claim 15, whereby sulfate reducing bacteria generate the sulfur-containing gaseous mixture.

20) The method of claim 15, whereby a batch process first utilizes a low temperature step below 35C and the batch process subsequently utilizes a higher temperature step above 35C

21) The method of claim 15, whereby the first temperature is between 20 and 30 degrees C.

22) The method of claim 1, whereby the gas stream is Introduced Into a scrubber with a gas pressure between 1 atmosphere and 10 atmosphere.

23) The method of claim 1, whereby the gas stream is introduced through a flush nozzle or feed device comprising vanes, or a header with orifices sized to provide a specific pressure drop and distribution pattern.

24) The method of claim 1, whereby the gas stream in introduced into an alkaline-containing solution with a flow velocity of between 1 meter per second and 100 meters per second.

25) The method of claim 1, additional comprising a step of separating nitrogen and/or phosphorus compounds from the organic waste after anaerobic digestion and utilizing that nitrogen and/or phosphorus for microbial digestion of sludge or organic waste.

26) A method of removing less water soluble gaseous sulfur compounds comprising dimethyl sulfide and/or dimethyl disulfide from a gas stream, comprising the steps of: a) directing the gas stream through a solution comprising an alcohol, preferably methanol, b) removing a portion of the gaseous sulfur compounds from the gas stream and thereby forming a solution of the sulfur compounds, c) chemically treating the solution to modify the chemical nature of the sulfur compounds in solution.

27) The method of claim 22, whereby the chemical treatment comprises an electrochemical oxidation process.

28) The method of claim 27, whereby the electrochemical oxidation process converts reduced sulfur compounds into oxidized sulfur compounds comprising sulfite and/or sulfate ions.

29) The method of claim 27, whereby the electrochemical oxidation process converts reduced sulfur compounds into peroxodisulfate.
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