DESALINATION PROCESSES AND FERTILIZER PRODUCTION METHODS
A multistage desalination process for treatment of seawater or salt wastewater. During initially processing the seawater or salt wastewater is treated to precipitate scaling minerals as phosphates including magnesium ammonium phosphate useful as a fertilizer. During the initial phase, ammonium phosphate and sodium phosphate are added to the seawater or salt wastewater followed by an addition of ammonia and a water-based charged solvent. After separating the precipitated solids, the cleaned seawater or salt wastewater is aerated and filtered to produce potable or otherwise usable water.
This application claims priority from U.S. application 62/216,163, filed Sep. 9, 2015, which is incorporated by reference herein.
BACKGROUND OF THE INVENTION Field of the InventionThe present invention relates to multistage desalination processes having ordered impurity removal without addition of harsh chemicals. Further, the invention includes production of a useful byproduct (fertilizer) during descaling of seawater.
Brief Description of the Prior ArtDesalination of seawater is increasingly important for production of potable water in many areas of the world. Disposal of salt wastewater is also a problem. Typically, desalination processes and desalination plants utilize reverse osmosis technologies (seawater reverse osmosis, SWRO). However, since the mineral content, organic material content and pollutant content of seawater varies by location, it can be difficult to adjust any particular process for alternative locations or to utilize a single method in multiple areas having varied organic and mineral components. In some instances, high impurity content can cause plugging or scaling of the membranes utilized during reverse osmosis processing and can result in the need to use high pressure for the reverse osmosis process. Further, descaling during conventional desalination processing often utilizes harsh chemical treatment that can result in chemical waste material that must be disposed of. With salt wastewater disposal the most common disposal method is to transport the wastewater to facilities that treat and dispose of water, frequently by injection into the subsurface which can lead to serious environmental consequences. It would be desirable to develop alterative desalination processes to address the problems discussed above.
BRIEF SUMMARY OF THE INVENTIONThe invention encompasses seawater and salt wastewater treatment processes that produce potable or otherwise usable water and additionally produce fertilizer material. In accordance with the invention, a desalination process includes four major stages wherein:
A first stage involves performing a phosphate precipitation process, the phosphate precipitation process including adding a first mixture comprising ammonium phosphate and sodium phosphate to seawater or salt wastewater and mixing the first mixture and the seawater or salt wastewater. After mixing the first mixture and the seawater or salt wastewater, adding a second mixture comprising ammonia and a water-based charged solvent to the seawater or salt wastewater and mixing to produce a seawater or salt wastewater mixture having a pH of greater than or equal to about 8.5.
In a second stage, the precipitated solids are collected from the seawater or salt wastewater mixture. In an embodiment the solids collection process comprises centrifugal flow. The collected solids include one or more of divalent mineral oxides, monovalent mineral oxides and magnesium ammonium phosphate.
After performing the solids collection, a third stage involves subjecting the cleaned seawater or salt wastewater to an oxidation process comprising aeration of the cleaned seawater, followed by filtration removal of solids produced during the oxidation process.
A fourth and last stage involves performing a final filtration process comprising microfiltration followed by nano-filtration of the oxidized cleaned seawater or salt wastewater to produce potable or otherwise usable water.
In some embodiments the cleaned seawater or salt wastewater is filtered after the solids collection process before it is oxidized.
The solids collected in stage 2 containing magnesium ammonium phosphate are an excellent fertilizer. The magnesium ammonium phosphate can additionally serve as a carrier for organic matter and minor elements beneficial or essential to plant growth.
The invention summarized above comprises the methods hereinafter described, the scope of the invention being indicated by the subjoined claims.
In the accompanying drawings, in which several of various possible embodiments of the invention are illustrated, corresponding reference characters refer to corresponding parts throughout the several views of the drawings in which:
The following detailed description is merely exemplary in nature and is not intended to limit the described embodiments or the application and uses of the described embodiments. Furthermore, there is no intention to be bound by any expressed or implied theory presented in the preceding background, brief summary, drawings or the following detailed description.
The desalination processes of the invention comprise multiple process steps that can overcome many or all of the problems encountered utilizing conventional SWRO methods. In general, seawater from any location can be processed by the methodology of the invention with little or no process variation, even if the impurity content and concentrations differ between locations. Salt wastewater resulting from various industrial processes may also be processed by the methodology of the invention.
The sequential process stages are described generally with reference to the accompanying drawings (
A first mixture that is added to the seawater contains ammonium phosphate and sodium phosphate. An example amount for addition can be about 1.0 g ammonium phosphate for every 250 mg/l of magnesium present in the seawater; and about 1.0 g sodium phosphate for every 150 mg of calcium present in the seawater. The first mixture can preferably be a water solution that is added to the seawater, simultaneously with or followed by mixing of the first mixture with the seawater. The addition and mixing can be performed, for example, utilizing an inline injection system.
More particularly as shown in
After addition and mixing of the phosphate and seawater mixture, a second chemical mixture is added to produce a “seawater mixture”. The second chemical mixture comprises an ammonia and a water-based charged (electromagnetic) solvent. The water-based charged solvent can be the charged solvent as described in U.S. Pat. No. 8,475,757 which is hereby incorporated by reference. As disclosed therein the water based charged solvent comprises water, alcohol and sodium hydride. Although not limited to any particular ratio, an example seawater mixture can contain 40 ml of a 7% ammonia solution and 0.25 ml of charged solvent per liter of seawater. At that ratio, the resulting seawater mixture may have a pH of greater than 8.5.
As described in U.S. Pat. No. 8,475,757 the charged solvent is formed by adding solid NaOH to solid silicon in a reaction vessel. With vigorous mixing, a first water ammonium mix is added at a concentration of two parts water ammonium mix per one part NaOH with the ammonium mix being 5% ammonium by weight. The mixture is reacted for from about 1 hour to about 2 hours at a temperature less than or equal to about 195° F. A second water ammonium mix is then added, the second water ammonium mix being 10% ammonium by weight, to maintain the temperature at or below about 195° F. until the final water ratio is 4 parts water to 1 part sodium silicate. This second mixture is reacted for from about 6 hours to about 8 hours and water is added until the density reaches about 1.3 specific gravity and then allowed to stand for about 24 hours. Alcohol is added and mixed vigorously, the reactants allowed to settle and the uppermost fraction collected for use in the subject desalination and fertilizer production methods as the water-based charged solvent.
The formation of the seawater mixture in the second stage can utilize a second inline injection system although such inline methodology is not mandatory. As shown in
Referring to
Because of its low solubility, the “solids fertilizer” collected in stage 2 is a slow release fertilizer, the release of which can be further controlled by granular size unlike conventional water soluble fertilizers. The “solids fertilizer” does not leach from sandy or porous soils even with over watering or heavy rain. Because of this property, several years supply of fertilizer may be applied when planting reducing labor costs. Further benefits include placing the “solids fertilizer” adjacent to the bare roots of plants without danger of burning or damaging the plants. Accurate placement of the fertilizer next to the roots also encourages rapid growth of the plants without fertilizing the weeds. Past testing has also shown that there is less need for herbicides and insecticides.
Stage 3 of the desalination process involves subsequent processing of the cleaned seawater as depicted in
The cleaned seawater may then be filtered as shown in
The micro-filtered water can then be passed through a nano-filtration system. The micro-filtered water is correctly charged for ion removal during nano-filtration, has no suspended solids or scaling components that can clog the nano-filter(s), and contains no components that can chemically damage the nano-filter(s). Further, the surface tension of the micro-filtered water has been reduced (relative to the original seawater) and has no corrosive properties. Accordingly, in contrast with conventional desalination processes, the nano-filtration process of the present invention can be conducted under low pressure (less than or equal to about 250 psi.)
The nano-filtration processing can utilize one or more nano-filtration units each comprising one or more nano-filters (same or differing pore sizes, materials, etc.). The resulting nano-filtered water can be purified to total dissolved solids (TDS) content of less than or equal to 800 ppm. The resulting product is potable and the methodology is streamlined and cost effective due to the decreased pressurization relative to conventional methodology and non-utilization of expensive reverse osmosis membranes. Further, the amount of brine (waste) from the system (collected from the nano-filtration processing) is dramatically decreased relative to alternative technologies and is therefore relatively inexpensive to dispose of. Accordingly the methodology of the invention is much more efficient and cost effective than alternative systems.
The following examples illustrate the invention.
EXAMPLE 1A fertilizer was extracted from seawater from the Yellow Sea as follows:
Step 1
From 1500 ml of unfiltered seawater were 500 ml was reserved as “seawater before sample”.
Step 2
Four grams of ammonium phosphate and 2 g of sodium phosphate were mixed with 1000 ml of seawater until the phosphate salts were completely dissolved.
Step 3
A premix of 950 ml distilled water with 30 ml of 30% ammonium hydroxide was formed to which 20 ml of a water-based charged solvent as described in U.S. Pat. No. 8,475,757 was added.
Step 4
All of the mixture from step 2 was combined with 40 ml of the mixture from step 3 and stirred until completely mixed.
Step 5
The solids were allowed to settle out and were separated from the “seawater after sample”.
Step 6
The solids were rinsed with water and dried for use as a fertilizer.
The “solids fertilizer” (1402101), “seawater before sample” (1402099) and the “seawater after sample” (1402100) were subjected to inductively coupled plasma mass spectrometry (ICP-MS), the results of which are shown in Table I. A mass spectrometry analysis of the “solids fertilizer” ID 1402101 is shown in
The same procedure as described in Example 1 was done with seawater from the Pacific Ocean off the shores of southern Canada. The “seawater before sample” (4030973-01), “seawater after sample” (4030973-02) and “solids fertilizer” (4030973-03) were subjected to analysis:
- Method Reference Descriptions:
- ASTM ASTM International Test Methods
- APHA Standard Methods for the Examination of Water and Wastewater, American Public Health Association
- Carter Soil Sampling and Methods of Analysis, Carter/Gregorich
- EPA United States Environmental Protection Agency Test Methods
- Glossary of Terms:
- MRL Method Reporting Limit
- Less than the Reported Detection Limit (RDL)—the RDL may be higher than the MRL due to various factors such as dilutions, limited sample volume, high moisture, or interferences
- AO Aesthetic objective
- MAC Maximum acceptable concentration (health-related guideline)
- % Percent W/W
- % dry Percent, reported on a dry weight basis
- % wet Percent, reported on an as-received basis
- mg/kg dry Milligrams per kilogram (ppm), reported on a dry weight basis
- mg/L Milligrams per litre
- pH units pH <7=acidic, pH>7=basic
The agronomic properties of the “solids fertilizer” collected in examples 1 and 2 are remarkable. It contains an average of 8-10% magnesium or higher depending on the magnesium content of the seawater. Magnesium is involved in chlorophyll production and the extra magnesium in the fertilizer helps plants produce chlorophyll in lower light situations (both intensity and duration) which boosts plant growth. In addition the “solids fertilizer” is a carrier for other minor elements beneficial or essential to plant growth such as potassium.
As various changes could be made in the methods described above without departing from the scope of the invention, it is intended that all matter contained in the above description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.
Claims
1. A seawater or salt wastewater desalination process comprising:
- performing a phosphate precipitation process, the phosphate precipitation process including adding a first mixture comprising ammonium phosphate and sodium phosphate to seawater or salt wastewater and mixing the first mixture and the seawater or salt wastewater;
- after mixing the first mixture and the seawater or salt wastewater, adding a second mixture comprising ammonia and a water-based charged solvent to the seawater or salt wastewater and mixing to produce a seawater or salt wastewater mixture having a pH of greater than or equal to about 8.5;
- performing a solids collection process to collecting precipitated solids from the seawater or salt wastewater mixture, the solids including, magnesium ammonium phosphate;
- after performing the solids collection, performing an oxidation process comprising aeration of the seawater or salt wastewater mixture, followed by filtration removal of solids produced during the oxidation process; and
- performing a final filtration process comprising microfiltration followed by nano-filtration of the seawater or salt wastewater to produce potable or usable water.
2. The desalination process of claim 1 further comprising filtering the seawater or salt wastewater mixture after the solids collection process.
3. The desalination process of claim 2 wherein the filtration comprises filtration through sand followed by carbon filtration or the like.
4. A fertilizer production process comprising:
- providing seawater or salt wastewater;
- performing a phosphate precipitation process, the phosphate precipitation process including:
- adding a first mixture comprising ammonium phosphate and sodium phosphate to the seawater or salt wastewater and mixing the first mixture and the seawater or salt wastewater;
- after mixing the first mixture and the seawater or salt wastewater, adding a second mixture comprising ammonia and a water-based charged solvent to the seawater or salt wastewater and mixing to produce a seawater or salt wastewater mixture having a pH of greater than or equal to about 8.5; and
- performing a collection process to collect a fertilizer product comprising precipitated solids from the seawater or salt wastewater mixture, the solids including magnesium ammonium phosphate.
5. The fertilizer production process of claim 4 wherein the fertilizer product further comprises organic matter.
6. The fertilizer production process of claim 4 wherein the solids additionally contain potassium, calcium and other mineral salts.
7. The fertilizer production process of claim 4 wherein a seawater or salt wastewater is selected for processing such that the solids contain from about 8 to 20% by weight magnesium.
8. The fertilizer produced by the process of claims 4-7.
Type: Application
Filed: Mar 8, 2018
Publication Date: Mar 14, 2019
Inventor: XiaoLing Cheng (Nanjing)
Application Number: 15/915,504