ON-SITE ACTIVATION OF SLUDGES, ORGANIC COMPOUNDS AND WASTEWATER FOR MICROBIAL DIGESTION USING PEROXODISULPHATE DERIVED FROM TOXIC SULFUR COMPOUNDS

ACTIVATION SUR PLACE DE BOUES, COMPOSES ORGANIQUES ET EAUX USEES DESTINES A LA DIGESTION MICROBIENNE AU MOYEN DE PEROXODISULFATE DERIVE DE COMPOSES DE SOUFRE TOXIQUES

English 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.

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.

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
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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.
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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.
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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.