MONITORED METHOD FOR IMPROVED IMPAIRED-WATER REMEDIATION

Abstract

The invention is a method of remediating water by adding to a quantity of water to be treated a compound or composition that generates hypohalous acid in situ, followed by addition or generation of ammonia to create an excess of ammonia and in turn to accomplish heretofore unachievable benefits and efficiencies.

Claims

1. A method of remediating water, comprising adding to a quantity of water to be treated a compound or composition that generates hypohalous acid in situ upon addition to water, followed by addition or generation of ammonia to create an excess of ammonia in the amount of at least 1 ppm in said quantity of water to be treated.

2. The method according to claim 1, wherein said compound or composition that generates hypohalous acid is sodium hypochlorite and said hypohalous acid is hypochlorous acid.

3. The method according to claim 2 wherein said ammonia excess is monitored by an ammonia sensor.

4. The method according to claim 3 wherein ammonia monitoring takes place over time.

5. The method according to claim 4 wherein said compound or composition that generates hypohalous acid is added to achieve free residual halogen and further wherein ammonia added thereafter causes the water to reach a free residual halogen/ammonia ratio of about 3:1 to 10:1.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0006] Chemistry from municipal, or even pool-and-spa, traditions of water purification amounts to de facto misdirection when it comes to very impaired water, whether the impaired water is from flowback or produced water or some other polluted source. The real challenge in addressing seriously compromised water lies in part in determining the actual composition of the watersuch as the presence of Naturally Occurring Materials (NOMs) that inevitably include colloidal metals including iron and other metals, and alkane residues of various length and substitution, such as methane, ethane, etc. In other words, when one is cleaning up really nasty water, one has to take a different approach to remediation than one might in more typical municipal or recreational water management scenario.

[0007] The present invention is a sequential water treatment method in which hypohalous acid is first generated in the water, and then that hypohalous acid generation is followed in rapid succession by a monitored titration to at least a 1 ppm excess of ammonia in the water, by adding ammonia or ammonia generating compositions (after adding the ingredient responsible for the hypohalous acid generation and by periodically or constantly monitoring the ammonia levels). The amount of hypohalous acid needed to resolve a given microbial load is known in the art and is not central to the present invention; the invention inheres in the sequential treatment of the water with hypohalous acid, and ammonia, in that order, leaving an excess of ammonia of at least about 1 ppm.

[0008] One good way of generating a hypohalous acid in situ, namely, hypochlorous acid, is by the addition of sodium hypochlorite to the water to be treated. Sodium hypochlorite can be purchased commercially as chlorine bleach and is also available as a readily available industrial supply composition. However, any hypohalous acid in the water will perform the same biocidal function, so addition of an appropriate amount of a composition which generates the necessary biocidal function of any hypohalous acid is contemplated by the present invention. The inorganic chemistry of hypohalous acid generation is well known and therefore need not be repeated here. The important thing is that the present invention inheres in the sequential water treatment steps of adding something to the water that will generate adequate hypohalous acid to neutralize the biological load (microbial contents) followed by addition of ammoniaor something that will generate ammoniato yield excess ammonia of at least 1 ppm to generate halamine species. The remainder of the invention can be practiced with variation as to choice of starting constituents or reactants, as long as the above-described parameters are observed.

[0009] For example, water additives that generate ammonia, other than ammonia itself, include ammonia salts such as NH.sub.4Cl, NH.sub.4SO.sub.4, NH.sub.4OH, NH.sub.4Br and any other ammonia salts that generate ammonia upon addition to water. Generation of hypobromous acid, rather than hypochlorous acid, is also well known in aqueous systems and therefore need not be repeated here. Generation of other hypohalous acids is within the skill of the art at this writing.

[0010] Optimally, and as a preferred embodiment of the invention, sufficient oxidizer (hypohalous acid generator) is added to achieve free residual halogen, and therefore the supplemental ammonia ideally reaches an optimal level in which a free residual halogen/ammonia ratio of about 3:1 to 10:1 is achieved.

[0011] Surprisingly, the practice of this invention proved to be surprisingly compatible with friction reducers and scalants already in use in hydraulic fracturing applications. This compatibility is believed to be attributable to the ability of the oxidizer to sequester colloidal ferric iron and other colloidal metals from the water thereby enhancing the ability of the metals and microorganism solids to flocculate readily, while at the same time the ammonia excess prevents the formation of unwanted compounds (trihalomethanes) which are not only carcinogenic or otherwise unwanted in and of themselves, but which are potentially reactive with the scalants and friction reducers of the prior art due to their nonpolar, cosolvent natures. In other wordsit is believed that a side benefit of preventing the formation of trihalomethanes is the preservation of initial alkane residues in the water in their initial unhalogenated statewhich are usually if not always free unsubstituted short- chain alkanes susceptible of quick removal from the treated water by simple volatilization upon exposure of the water to the air.

EXAMPLE

[0012] As a real world test, the inventor collected water for analysis from an active hydraulic fracturing well. Directly on the well pad was a tank which stored impaired water (flowback/produced water) only. Isolated in the area was an off-site fresh water only impoundment. Fresh water and impaired water were then blended as 50% fresh water and 50% impaired water in work tanks adjacent to the well head. To each 1000 barrels of water were added about 5 gallons of a known concentration of sodium hypochorite, with mixing, which not only killed the entire microbial load of the specific water being treated but which also precipitated out all cloudiness, presumably due to the generated hypochlorous acid's sequestering the colloidal ferric iron from the water and allowing it to precipitate along with the no-longer-viable microorganism solids. Immediately after the addition of the sodium hypochlorite, ammonia was added to achieve a 5:1 molar concentration, respectively. At the work tank an ammonia sensor was placed to monitor ammonia levels in the water. As needed, additional ammonia was added to keep the excess ammonia level in the water at 1 ppm.

[0013] Although the invention has been described with respect to particular methods and constituents, above, the scope of the invention is only to be limited insofar as is set forth in the accompanying claims.