Patent Application
20200079670
Control of hydrogen sulfide production in wastewater, particularly sewage collection systems, has been an ongoing concern for centuries. Hydrogen sulfide is generated in wastewater when sulfate-reducing bacteria growing in the biofilm layer of wastewater consumes sulfate oxygen found in the wastewater, releasing bisulfide ions (SH−). The bisulfide ions combine with hydrogen to form hydrogen sulfide (H2S) which is released into the surrounding atmosphere as a malodorous gas. Released hydrogen sulfide gas is subsequently consumed by aerobic sulfate-oxidizing bacteria, such as Thiobacillus, growing on the moist surfaces of the various components of the wastewater collection system, converting the hydrogen sulfide to highly corrosive sulfuric acid (H2SO4). Sulfuric acid mediated corrosion of the concrete conduits and steel pipes in which organic sewage is transported costs municipalities billions of dollars annually in sewage system failure and repairs.
A time tested method for achieving hydrogen sulfide control in wastewater collection systems is the application of nitrates, such as calcium nitrate (Ca(NO3)2), to the wastewater. Nitrates are capable of both chemically reacting with existing hydrogen sulfide to form sulfate ions (SO42−) with the release of nitrogen (N2) and water (H2O), and reducing aerobic reduction of sulfate ions to hydrogen sulfide by providing nitrates as an alternative preferential source of oxygen for consumption by the bacteria growing in the biofilm layer of the wastewater.
While generally effective for suppressing hydrogen sulfide generation in wastewater collection systems, nitrate treatment is ephemeral and has several significant drawbacks for long-term hydrogen sulfide control including prohibitive capital and material costs for effecting prolonged treatment and increased nitrogen and nitrate levels in the wastewater over time.
Accordingly, a substantial need exists for a cost effective and environmentally sound technique for achieving long-term control of hydrogen sulfide production in wastewater.
I have surprisingly discovered that cost effective and environmentally sound hydrogen sulfide control in a wastewater collection systems can be achieved by the limited administration of nitrate with the coadministrating of anaerobic sulfide oxidizing bacteria. Without intending to be limited thereby, I believe that administration of anaerobic sulfide oxidizing bacteria reduces hydrogen sulfide by oxidizing hydrogen sulfide to sulfate as well as the intracellular sequestration of sulfur. This, when accompanied by an increase in the bioavailability of nitrate oxygen for use by the bacteria in the biofilm, results in excellent suppression of hydrogen sulfide production with reduced nitrate loading.
Nitrates, such as calcium nitrate, used in concert with anaerobic sulfide oxidizing bacteria provide for a more complete reduction of hydrogen sulfide gas by providing multiple modes of action for its reduction. Through the synergistic treatment methodology of the present invention, using a nitrate to biologically change the biogenic populations and reducing agents in the sewage biofilm and adding anaerobic sulfide oxidizing bacteria to oxidize any residual hydrogen sulfide that is formed from the biofilm, more complete control of hydrogen sulfide gas is achieved. The synergistic effect of employing these two additives allows less of each additive to be employed relative to the amount necessary when used alone, making the technique a more cost effective and environmentally sound solution. The process also provides for a denitrification pathway through the sulfur oxidizing bacteria to scavenge any residual nitrates that are added in the system, thus reducing the nitrogen load on the waste treatment plant. The nitrate is preferably added as an aqueous solution of an alkali or alkaline earth metal nitrate, such as a 50% active aqueous solution of a calcium and/or sodium nitrate.
An alkali metal may also be coadministered for purposes of neutralizing the pH of the wastewater. The preferred alkali metal is Mg(OH)2. It is generally desired to add sufficient alkali metal to adjust the pH of the wastewater to between 6 and 9 with a preference for a pH of between 7 and 9.
Any genus and species of anaerobic sulfide oxidizing bacteria may be employed, with selection generally guided by the particular conditions (e.g., dissolved oxygen concentration, pH, temperature, etc.) of the wastewater being treated. The anaerobic sulfide oxidizing bacteria is preferably employed as a bacterial consortium.
A listing of preferred bacteria species for inclusion in the bacterial consortium is provided below in Table One.
Chromatium
Chromatium
Rhodspirrillum
Chlorobium
Chloroflexus
Beggiatoaceae
Thiocyctis
Rhodobacter
Prosthecochloris
Chloronema
Achromatium
Thiospirillum
Rhodopseudomonas
Pelodictyon
Oscillochloris
Thiobacterium
Thiocapsa
Rhodomicrobium
Ancalochloris
Macromonma
Lamprocystis
Rhodopila
Chloroherpeton
Thiospira
Lamprobacter
Thiovulum
Thiopedia
Bilophocucus
Thiobacillus
Thiomicrospira
Thiodendron
Thiosphaera
Acidiphilium
Thermothrix
Sulfolobus
Acidianus
The consortium can include at least 1 to 10 parts by CFU purple bacteria, at least 1 to 10 parts by CFU purple non-sulfur bacteria, at least 1 to 10 parts by CFU green sulfur bacteria, at least 1 to 10 parts by CFU filamentous green bacteria, and at least 1 to 10 parts by CFU colorless sulfur bacteria.
The consortium can further include at least two different species of purple bacteria, at least two different species of purple non-sulfur bacteria, at least two different species of green sulfur bacteria, at least two different species of filamentous green bacteria, and at least two different species of colorless sulfur bacteria.
Coadministration of the nitrate and the anaerobic sulfide oxidizing bacteria may be effected in any sequence and on substantially any schedule, with a preference for commencement of nitrate administration coincidentally with or up to two weeks prior to commencement of administration of the anaerobic sulfide oxidizing bacteria, followed by coincidental administration thereafter.
Effective relative loadings of nitrate and the anaerobic sulfide oxidizing bacteria, per 100,000 gallons of wastewater, are noted in Table Two.
Generally, effective results can be achieved by inoculating the wastewater with 103 to 108 CFUs of anaerobic sulfide oxidizing bacteria per 100,000 gallons of wastewater with coadministration of between 10% and 500% of a stoichiometric amount of NO3 relative to H2S in the wastewater, with a general preference for inoculating the wastewater with 104 to 108 CFUs of anaerobic sulfide oxidizing bacteria per 100,000 gallons of wastewater with coadministration of between 20% and 500% of a stoichiometric amount of NO3 relative to H2S in the wastewater.
More many applications, excellent cost effective results can be achieved by inoculating the wastewater with 104 to 108 CFUs of anaerobic sulfide oxidizing bacteria per 100,000 gallons of wastewater with coadministration of between 50% and 300% of a stoichiometric amount of NO3 relative to H2S in the wastewater.
Administration may be made on substantially any schedule, with a preference for regularly schedule administration on a daily or weekly basis, with relatively continuous administration most preferred when automated administrations is an option.
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/US2017/064130 | 12/1/2017 | WO | 00 |
| Number | Date | Country | |
|---|---|---|---|
| 62429322 | Dec 2016 | US |
