AU2006203567A1 - Improved nitrate solutions for odour control - Google Patents

Description

Regulation 3.2

AUSTRALIA

Patents Act 1990 COMPLETE SPECIFICATION FOR A STANDARD PATENT

(ORIGINAL)

Name of Applicant: Actual Inventor(s): Address for Service: Invention Title: SULFIDE CONTROL PTY. LTD.

P.J. DACK SANDERCOCK COWIE SUITE 8C, 50-54 ROBINSON STREET DANDENONG VIC 3175 IMPROVED NITRATE SOLUTIONS FOR ODOUR

CONTROL

Details of Associated Provisional Application(s): No(s): Australian Provisional Application No. 2006900725 Filed: 1 5 th February, 2006 The following statement is a full description of this invention, including the best method of performing it known to us: 1 Fc2006-08-1 4,Z:\Fifing\sulfide.file.wpd, 1 la- TITLE: IMPROVED NITRATE SOLUTIONS FOR ODOUR CONTROL FIELD OF THE INVENTION This invention concerns a method and composition for odour control in wastewater, waste or sludge.

This invention describes a versatile series of manufactured solutions containing nitrate and nitrite which when dosed into receiving systems have been specifically devised to 2006-08-14,Z:\Specifications'sulfide.cap. wpd,I allow quicker removal of existing sulfides than if nitrates alone were present, but still provide the preventative benefits of nitrates.

BACKGROUND OF THE INVENTION There have been many methods proposed in the past for reducing and controlling odour levels from receiving systems containing wastewater, wastes and sludges. In many cases the odour problems have been caused by sulfides contained in them, and sometimes also by the levels of ammonia and other compounds present. One group of treatment methods has involved the addition of nitrate containing solutions, with or without other chemicals being present. The addition of nitrates to anaerobic wastewaters has been shown to both assist with removal of existing sulfides and help prevent the formation of more sulfide as may occur under anaerobic conditions in the presence of sulfate reducing bacteria and sulfate. One of the problems sometimes encountered with nitrate addition is that it cannot remove levels of existing sulfide quickly enough.

Another group of treatment methods used in the past involves the addition of nitrites to sulfide containing wastes. Nitrites have the ability to increase the speed of sulfide removal but due to their reactivity and biocidal properties, are not useful in providing a safe means of preventing sulfide generation in many cases.

SUMMARY OF THE INVENTION The composition aspect of the invention provides treatment compositions for odourous waste comprising an aqueous mixture of an inorganic nitrate and inorganic nitrite in a total concentration of up to 60% by weight.

The method aspect of the invention provides a method of treating odourous waste containing sulfides and sulfide generating organisms comprising dosing the wastewater with a solution of an inorganic nitrite and an inorganic nitrate.

Solutions in accordance with this invention contain one of several inorganic nitrates together with varying amounts of one of several inorganic nitrites, plus additional minor 2006-08-14,Z:\Specifications\sulfide.cap.wpd,2 components which may or may not be required. The ratio of nitrate to nitrite is variable depending on the particular wastewater, waste or sludge, the levels of sulfides and the timing required for removal of the odourous components in the receiving system being considered.

For sulfide removal sufficient nitrite is added to the solution being manufactured to ensure that existing sulfides in the receiving system are oxidised within a preferred time frame (usually within a few hours) whilst sufficient nitrate is added to then prevent regeneration of sulfides by any sulfate reducing bacteria present.

Nitrite is only added at sufficient levels to remove existing sulfides. If excess nitrite is added, this may compromise downstream treatment systems due to the biocidal effects of residual nitrite at high levels. Ifa downstream sulfide "prevention" effect is required, it is therefore achieved using nitrate in combination with appropriate levels of nitrite.

Applications of these manufactured solutions can be into receiving systems containing wastewater, waste and sludge (but is not limited to) pipelines, ponds, storages, channels, tanks, treatment plants and other treatment equipment.

The solutions made can be stored in suitable chemical storage facilities and pumped to the receiving system with suitable commonly available dosing pumps and control systems similar to those used for nitrate dosing.

If the waste is fresh with no initial sulfide present, a straight nitrate solution may be used to prevent the microorganisms in the waste from producing sulfides, and normally this will provide a practical level of protection for up to three days of retention time if enough nitrate is added. If on the other hand some sulfide already exists, and it is necessary to remove this quickly in less than a certain time, eg. within five hours travel time in a wastewater pipeline, a straight nitrate containing solution will not usually remove the sulfide quickly enough. If an appropriate amount of nitrite is added to the nitrate solution, this then becomes possible. The relative amounts of nitrate and nitrite required will depend on: 2006-08-14,Z:\Specifcations\sufide.cap.wpd,3 1. The initial sulfide level.

2. How quickly the sulfide needs to be removed.

3. The oxidation/reduction potential of the waste.

4. The temperature and pH of the waste.

5. The need or otherwise to keep the waste "fresh" and sulfide free once the nitrite has removed the initial sulfide.

6. The non-sulfide uptake of nitrite and nitrate by the waste and the microorganisms it contains.

The relative quantities of nitrate and nitrite in the particular solution to be used for a particular situation will therefore be adjusted for that situation. Customer requirements vary for the reasons discussed and the composition may contain a mixture of inorganic nitrate and nitrite in a total concentration of 5, 10, 15, 20, 25, 30, 35, 40, 45, 50, 55 or by weight.

In practice, the actual doses needed are determined by conducting laboratory dosing tests under the conditions to be found in the pipeline or other place containing the waste.

Example 1 A sample of "stale" sewage containing 6.2mg/L of dissolved sulfide was dosed in sealed bottles with a solution containing similar levels of nitrate and nitrite such that the concentration of each in the sewage was 118mg/L. The sulfide concentration was reduced to 1.6mg/L within one hour. When only nitrate was dosed into the stale sewage at the same total concentration, 4.9mg/L of sulfide still remained at one hour. An undosed sample still had 5.7mg/L of sulfide at one hour.

Example 2 A sample of mixed sewage and pulp and paper mill wastewater containing 35mg/L of sulfide was dosed in sealed bottles with a solution containing sodium nitrate and sodium nitrite and 40% respectively). The sulfide concentration was reduced to less than 0.4mg/L in less than 3.5 hours compared to an undosed sample which still had more than 2006-08-14,Z:\Specifications\sulfide.cap.wpd4 26mg/L after this time.

Example 3 A sewage sample containing 5.14mg/L of sulfide was dosed in sealed bottles with a solution containing 6.3% nitrite (sodium nitrite) and 2.5% nitrate (calcium Nitrate). After four hours, the sample had 1.68mg/L of sulfide left, whereas the undosed sample sulfide level had increased to 7.1mg/L.

Example 4 Referring to Figure 1. To treat a piped mixed sewage and industrial wastewater containing a headspace hydrogen sulfide concentration (HHSC) of 80ppm, 1000 litres of treatment solution was manufactured by adding 75kg of sodium nitrate and 475kg of sodium nitrite to water. The solution was transferred to site in a 1000L container and dosed at point A in the pipeline using a diaphragm type chemical dosing pump. At point B, after three hours travel time, the HHSC was 16ppm with no nitrite remaining. After another four hours of travel to point C, the HHSC was Oppm. When the pipeline was dosed with a straight nitrate solution with the same total nitrogen concentration, the HHBS at point B was still 80ppm and at point C was still 61ppm.

If a waste contains initial sulfide and this needs to be removed in a very short period of time of perhaps less than 30 minutes, the solutions described herein may not be appropriate. This still needs to be confirmed by pre-testing the dosing in a laboratory situation.

BRIEF DESCRIPTION OF THE DRAWINGS The single figure is a diagram of a sewage pipeline showing dosing point A, measurement point B and measurement point C.

We have found the advantages of the examples described above to be: 2006-08-14,Z:\Specifications\sulfide.cap. -6- 1. When dosed into laboratory wastewater samples or wastewater pipelines, the removal of existing sulfides is quicker than with solutions containing nitrate alone.

2. The solutions prevent re-generation of sulfides after the nitrite is depleted.

It is to be understood that the word "comprising" as used throughout the specification is to be interpreted in its inclusive form, ie. use of the word "comprising" does not exclude the addition of other elements.

It is to be understood that various modifications of and/or additions to the invention can be made without departing from the basic nature of the invention. These modifications and/or additions are therefore considered to fall within the scope of the invention.

2006-08-14,Z:\Specifications\sufide.cap. wpd,6

Claims (9)

1. A method of treating odourous waste containing sulfides and sulfide generating organisms comprising dosing the wastewater with a solution of an inorganic nitrite and a inorganic nitrate.

2. A method as claimed in Claim 1, wherein sufficient nitrite is introduced to only oxidise the existing sulfides initially.

3. A method as claimed in Claim 1 or 2, wherein sufficient nitrates are introduced to prevent re-generation of sulfides by any sulfate reducing organisms.

4. A method as claimed in any one of Claims 1-3, wherein the inorganic nitrite and nitrate are present in varying relative concentrations.

Treatment compositions for odourous waste comprising an aqueous mixture of an inorganic nitrite, an inorganic nitrate in a total concentration of up to 60% by weight.

6. Treatment compositions as claimed in Claim 5, wherein the inorganic nitrate is 0.1-60% by weight.

7. Treatment compositions as claimed in Claim 5 or 6, wherein the inorganic nitrite is 0.1-60% by weight.

8. Treatment compositions as claimed in any one of Claims 5-7, wherein the mixture contains a nitrate and nitrite of iron, an alkali metal, an alkaline earth metal, or ammonium.

9. A method of treating odourous waste substantially as described. A composition for treating odourous waste according to any one of the Examples.

2006-08-14,Z:\Specifications\suIfide.cap. wpd,7 -8- Dated this 1 5 day of August, 2006. SANDERCOCK COWIE PATENT ATTORNEYS FOR SULFIDE CONTROL PTY. LTD. 20O6-0814,Z:\Specifications'sulfide.cap. wpd, 8