CA2884187A1

CA2884187A1 - On-site activation of sludges, organic compounds and wastewater for microbial digestion using peroxodisulphate derived from toxic sulfur compounds

Info

Publication number: CA2884187A1
Application number: CA2884187A
Authority: CA
Inventors: Ian W. Wylie; Toni Illingworth
Original assignee: Axsiom Management Inc
Current assignee: Axsiom Management Inc
Priority date: 2015-03-10
Filing date: 2015-03-10
Publication date: 2016-09-10

Abstract

The Invention described herein is a method of chemically activating sludges, wastewater containing organic compounds, and other organic matter (generally referred to herein as "organics" unless it is necessary to distinguish between them) using a potent chemical oxidizer, peroxodisulfate ("persulfate", S2O8 2-), typically derived from toxic sulfur-containing gases, e.g. hydrogen sulfide or methyl mercaptan, or other sulfur compounds, preferably on-site. The activation of organics with persulfate can be accelerated through the use of heat, catalysts (such a ferrous ion, Fe2+), radiation, or ultraviolet light. The chemical activation Is controlled to limit the amount of oxidation of the organics to a level sufficient to accelerate subsequent microbial digestion, presumably Including chemical disruption of cell walls, but significantly less than the amount required to completely oxidize (mineralize) the organics present. This moderate but sufficient level of oxidation, will facilitate digestion of the remaining organics present but limit the oxidation to less than the amount that would eliminate or nearly eliminate the organics present, thus preventing them being available for digestion. After oxidative treatment with persulfate, the said organic compounds will contain a greater proportion of oxidized groups, such as carboxylic acids or alcohols, which will increase the water solubility of the organic matter, rendering it more readily digestible by microbial activity for subsequent biofuel production or other useful processing. Sulfur-containing gases, such as hydrogen sulfide and methyl mercaptan, can be converted to persulfate directly at an organics processing site through a variety of processes including combustion and electrochemical oxidation together, or by electrochemistry alone, preferably on a boron-doped diamond anode. The process can be applied to many types of organic matter and wastes Including cellulosic, lignocellulosic, and cellular residues for the production of many types of biofuels, Including biogas (mostly methane and CO2), and ethanol. Such activated (oxidized) organic matter may also be used as a feedstock for other chemical and biological processing.

Description

Statement of the Problem:
Many organic wastes, such as municipal sludges from wastewater treatment plants (WWTP), forestry product processing, agricultural and fishery wastes, refinery and chemical wastes, and organic wastes from resource extraction, e.g. oil and gas, contain large quantities of organic matter which are uneconomic or otherwise difficult to reuse or reprocess for other purposes. Much of this potentially useful waste Is released into the environment in landfills, or into the ocean or other bodies of water, in deep wells or even abandoned mine sites. Water contamination, including drinking water contamination, resulting from such dumping or leakage is a significant issue nearly everywhere in the world.
Production of biases and other blofuels (such as ethanol or butanol) are known processes to convert organic wastes, including toxic organic wastes, Into useful fuels or chemical feedstock for subsequent processing. However, many organic wastes are relatively insoluble In water or contain refractory chemical compounds, e.g. polyaromatIc hydrocarbons¨ PAHs such as anthracene, phenols, naphthenic acids, or other "difficult to digest' by microbial action, polymeric or high molecular weight compounds such as cellulose, lignocellulose, or other such polymers, which are very slow to or do not metabolize by readily available (inexpensive) biological means. Previous methods of activation of such wastes are found In the art; for example, US patent # 8449773, "Method for pre-treatment of Cellulosic and LIgnocelluloslc materials for conversion to Bio Energy", in which ozone is used to oxidize such "woody"
wastes prior to digestion by anaerobic bacteria.
However, the generation of ozone Is both expensive and relatively dangerous due to the poor aqueous solubility of ozone and Its gaseous toxicity. The US Environmental Protection Agency regulates airborne ozone to less than 70 parts per billion. Concentrations of higher than 70 parts per billion are required in order to raise the concentration of ozone in Kelowna www.axsiomgroup.com Calgary _______________________________________________________________________________ ___ 1 Revision Dare: 12/12/2014 Management Ina. Canadian Provisional Patent Application aqueous solution to a sufficient level to oxidize a reasonable quantity of organic material. Ozone generating equipment, typically a corona discharge, requires a power supply to generate 20,000V in the presence of relatively pure oxygen and the subsequent dissolution of the resulting ozone into water. AS much as 60-80% of the ozone generated by corona discharge does not dissolve in the water and remains in the ambient air, requiring air handling to avoid a hazardous or toxic concentration of ozone from accumulating or being discharged to the environment. As a result, although ozone generation is a mature technology, an inexpensive and safer method of processing these difficult to use, or uneconomic wastes, for subsequent blofuel or biological material feedstock is highly desirable to Improve the economics of the waste to energy and the waste to chemical industries.
A related set of toxic by-products of many industries including: oil and gas refining and processing, pulp and paper production, chemical and biofuel production Is hydrogen sulfide (HA, methyl mercaptan (CH4S), and many other related small (typically gaseous) sulfur-containing compounds. Such toxic sulfur compounds typically require expensive methods to detoxify or treat them, such as the Claus process. The Claus process Is well known In the art, for example, US patent #4012486, "Process for reducing the total sulfur content of Claus off-gases", describes the conversion of H2S often from "sour gas" or other chemical or biological processing to elemental sulfur (Se) and water (H20). Elemental sulfur may be used for various purposes, such as sulfuric acid production or as a pesticide for organic farming. However, the volume of elemental sulfur production from the Claus process currently Is very large, especially in Western Canada, and the ability to transport large volumes of such material is limited and/or uneconomic. One consequence of this situation is that elemental sulfur is often "stranded (dumped) or simply burned, which creates other toxic acid-producing gases, such as sulfur-dioxide (SO2) and sulfur-trioxide (503). Another source of sulfur-containing gases Is the formation of H2S during the biogas generation process. The presence of sulfur containing amino acids such as methionine, cysteine, and homocystelne, is another source of elemental sulfur. Typical concentrations of HIS in biases can average around 1.5 (mole %). The presence of high concentrations of sulfur is one reason that biogas must be upgraded or cleaned before it can be said to be "pipeline grade", which has a limit on sulfur content of roughly 50 ppm, he. 0.005%. A method of re-use or a method of reducing the quantity of H2S or other sulfur compounds on-site derived from biogas production, refining of oil and gas and other industrial or natural sources of sulfur gases, without the requirement to transport the material from the site, Is highly desirable to improve the economics of sulfur processing and reduce emissions of toxic sulfur-containing gases to the environment and work site.
Detailed Description of the Invention: The invention described herein includes the conversion of H2S and other related sulfur compounds to sulfate ions (S042-) either by combustion, chemical means, or electrochemical means, and subsequent electrochemical conversion to peroxodlsulfate (52082" "persuifate", or "PS"), preferably on a boron-doped diamond anode. The persulfate is then used to process (oxidize) organic wastes, including sludge from WVvTPs, pulp and paper waste, or other sources of organic waste into more soluble, more treatable, or more useful forms. After oxidation of the organic compounds, PS is chemically reduced back to harmless sulfate Ions. The oxidation of the organic waste with PS is performed at a sufficiently high mass ratio of PS to dry sludge mass that the sludge or organic waste In question Is rendered more available for subsequent processing, including for the production of biofuels such as biogas (CH4, CO2, and H25) and alcohols. Typical mass ratios that have been used to completely oxidize organic material (mineralization) are in the range of 6:1 up to as high as 20:1(mass of PS to mass of organic matter), depending upon the time frame available and the potential presence of catalysts or heat. The mass ratio for activation of sludges and other organics must, of necessity, be a much lower ratio. For example, mass ratios of 0.03. PS: 1.0 organic up to 1:1 could be useful and more preferably from a mass ratio of 0.05:1 up to 0.5:1(PS: organic).
Catalysts for the reaction of PS with organic material include ferrous Ions (Fe2), heat, hard radiation such as X-rays or microwaves, and ultraviolet light, typically in a wavelength range from 190 nm to 350 nm. A mercury UV lamp with a strong emission at 254 nm is an effective wavelength for the breakage of the single bond oxygen peroxy bond -0-0-.
Coupling of the light with the solution being irradiated is important since the opacity of the persulfate/organIc solution, the absorbance of "brown" organics or even bubbles, can interfere with the penetration of short wavelength UV.
111121L._ Kelowna I www.axsiomgroup.com Calgary Revision Date: 12/12/2014 A.ivwsionn Management Ina. Canadian Provisional Patent Application The key illustrative chemical reactions to convert 1-125 to persulfate with other contextual reactions are listed below:
1) Combustion of Hydrogen sulfide In air H2S (g) + 3/2 02 (g) 4 SO2 (g) + H20 (g) Enthalpy of Combustion -519 ki/mol

2) Combustion of Methane (principle component of natural gas) in air CH4 (g) + 202 (g) 4 CO2 (g) + 2 I-40 (g) Enthalpy of Combustion = -882 k)/mal

3) Combustion of Sulfur Dioxide in air to form sulfur trioxide So a (g) 1/2 02 (g) 4 SO3 (g) Enthalpy of Combustion = -198 kl/mol

4) Reaction of sulfur trioxide and water to form sulfuric acid in solution SO z (g) + I-I20 4 H2s04 (aq) Enthalpy of Reaction e -88 kJ/mol

5) Electrochemical conversion of sulfate from sulfuric acid or other sulfate source to persulfate (anode reaction) 2S042' (aq) -2e' i+ S2082' (aq) Standard Half Cell Potential, Eo = +2.6V

6) Oxidation of Organics by persulfate (Illustrative reaction) S2081- (aq) + organic (e.g. CxHy) + H20 = S041 + 2H+ (aq) + oxidized organic (e.g. R-COOH) The reactions shown above for the oxidation of HS all the way to sulfate (#1, #3, and #4) are all very exothermic.
Combined, they produce 805 kgmol which Is almost as much enthalphy as the oxidation of methane (882 kl/mol), shown in reaction #2. Therefore, there is an advantage to combusting H25 in oxygen lithe resultant energy can be harnessed to perform useful work, such as the generation of electricity. Certainly, it is possible to perform ALL the synthesis reactions on an anode of an electrochemical cell. However, that "wastes" all the exothermic energy for the combustion reactions involved. This result may be advantageous if a suitable combustion system is unavailable or undesirable for other reasons, e.g. the generation of PS from H2S directly in an electrochemical cell is necessary to avoid loss of the sulfur-containing chemicals. The synthesis of peroxodisulfate from sulfate In various electrochemical cells is well known In the art. In particular, platinum and boron-doped diamond electrodes have been used extensively in the past to convert sulfate Ir to persulfate for example in US patent #6503386, "Process for the production of alkali metal and ammonium peroxodIsulfate".
The conversion of the HIS content of biogas Into PS in order to facilitate the treatment of organics to produce more blogas Is a "virtuous circle" of the reuse of wastes and the removal of toxins from the environment. However, many refinery operations produce copious quantities of HIS and also large quantities of residues (often these residues are toxic) that are difficult to process further. Some of these residues end up as asphalt for roads. it is possible that the conversion of H2S or other gaseous sulfur compounds into persulfate and its use for treatment of difficult to oxidize wastes, such as refinery wastes, would allow conversion of at least a portion of the refinery wastes Into biogas and other biofuels useful for the operation of refinery or other processing equipment. This process could potentially reduce the quantity of low value and/or toxic by-products of such chemical and energy processing entering the environment and increase the quantity of usable feedstock for producing more valuable products, including blofuels such as biogas and binethanol.
The conversion of treated or "activated" (chemically oxidized) organics into blogas Is usually accomplished through action of anaerobic methanogenlc microbes (Archaea). Typical species include methanobacteria formicum and other similar species. Heat may be applied to anaerobic digesters to accelerate the production of biogas, Elemental nitrogen and phosphorus may also be necessary to provide nutrition to the bacteria.
However, the chemical treatment of sludges and other organic wastes may not only liberate organic molecules for reaction with the methanogens but may also liberate such nutrients (N, P) to further accelerate the metabolic process of the methanobacteria to create biogas.
________________ . Kelowna I wwW.axsiomgroup.com Calgary Revision Date: 12/12/2014 A SIOM
Management Ina.
Canadian Provisional Patent Application It is common that anaerobic sulfur reducing bacteria (SRBs) are present along with methanogenlc bacteria. Some Arc haeo are known to be able to reduce sulfur as well. SRBs and acetogenic &
methanogenic bacteria all compete for the same fermentation products. When the fermentation process is complete, if the temperature in the anaerobic digester is maintained at a lower temperature (mesophilic conditions, 30-40.C), the SRBs would be able to outcompete the other bacteria for resources which would result in a greater production of H25, provided there was an abundance of sulphate present in the sludge. Temperatures above 409C result In a decrease in SRBs as they become inhibited by the heat;
methanogenic bacteria thrive at 5O-60C. For purposes of this invention, It may be preferable to "pre-treat" the chemically activated sludges or other organics to remove a significant quantity of the sulfur compounds In the mixture and thus allow the liberation of H25 as a feedstock for the production of PS. in other words, a virtuous cycle would be created whereby sludges or other organic wastes would be activated with PS and then the activated sludges would be treated with SRBs to produce H2S, preferably at temperatures below 40 degree Celsius to favor the SRBs, which would then be converted back to PS to allow activation of additional wastes or sludges. Alternatively, an alkaline pH solution could be used to selectively capture H2S in the form of hydrosulfide ions (HS}, from either a stream of CO2, CH4 and HS from a biogas digester or a mixture of gases from which the H2S Is selectively removed with other known methods In the art.

Claims

We claim:

1) A method of chemically activating organic wastes using peroxodisulfate (PS) derived from gaseous sulfur compounds in order to allow them to be processed for biofuel production or to produce an organic feedstock.
2) The method of claim 1, whereby the gaseous sulfur compounds are first oxidized to form sulfate and then further oxidized to form peroxodisulfate.
3) The method of claim 2, whereby the oxidation of sulfate to form peroxodisulfate Is performed in an electrochemical cell, preferably with a platinum or boron-doped diamond anode.
4) The method of claim 1, whereby the organic wastes are comprised of municipal wastewater treatment plant sludges, or pulp and paper sludges, or agricultural wastes, or food/beverage processing organic wastes, or pharmaceutical wastes, or oil and gas refinery wastes.
5) The method of claim 1, whereby the gaseous sulfur compound are oxidized by combustion to form sulfur dioxide or sulfur trioxide and subsequently further oxidized to form sulfate.
6) The method of Claim 1, whereby the gaseous sulfur compounds comprise hydrogen sulfide or methyl mercaptan.
7) The method of claim 2, whereby the gaseous sulfur compounds are oxidized to form peroxodisulfate on the same site as the biofuel or other biological material conversion activities.
8) The method of claim 1, whereby the organic compound Is activated with a mass ratio of between 0.01 to 1.0 peroxodisulfate to organic.
9) The method of claim 9, whereby the chemical organic compounds is activated with a mass ratio of between 0.05 to 0.5 peroxodisulfate to organic.
10) The method of claim 1, whereby the derivation of sulfur containing compounds from a mixture of organic materials is conducted at a temperature of less than 40 degrees Celsius.
11) The method of claim 10, whereby the action of sulfate reducing bacteria generates the sulfur containing compounds.

12) The method of claim 1, whereby the organic material is first digested via microbial action at a temperature above 40 degrees Celsius, and subsequently reduced in temperature below 40 degrees Celsius to generate sulfur containing compounds.