AU2008100116A4 - A process for phosphorus removal - Google Patents

Description

I

APPLICANT: Rajendra G Kurup

NUMBER:

FILED:

AUSTRALIA

THE PATENTS ACT 1990 INNOVATION PATENT SPECIFICATION FOR THE INVENTION ENTITLED A PROCESS FOR PHOSPHORUS REMOVAL The present invention will be described in the following statement: 00

TITLE

A PROCESS FOR PHOSPHORUS REMOVAL 00 The present invention relates to a process for phosphorus removal.

BACKGROUND TO THE INVENTION 0 Phosphorus either as ortho-phosphate or in the form of filterable reactive Sphosphorus (FRP), is a major nutrient in natural water, wastewater (both municipal and industrial) and contained water systems spas, swimming pools and aquariums). The presence of high concentrations of P in waters causes problems such as algal blooms. There hence, chemical methods including precipitation with metal salts are commonly used to remove P during wastewater treatment.

In particular, gypsum amended red mud has been applied for P removal in modified leach drains for on-site wastewater treatment. However, this application has not been extended to river pollution abatement or other small and large scale wastewater treatment processes, possibly limited by the local availability of red mud, a residue from bauxite processing. Also, while red mud is a waste and hence cost effective material, the radioactive property and heavy metal contents of the red mud limit its application.

It is also known that materials such as activated carbon have been employed to remove contaminants including P from water systems. To obtain activated carbon, however, high temperature processes are typically required, which adds to the energy 00 0 consumption and hence cost of production of the material. While activated carbon may be obtained as a by-product of mining operations such as mineral sand Sprocessing, such by-products are likely to possess undesirable radioactive properties 00 and heavy metal contents as with the case of red mud.

The present invention attempts to overcome at least in part the aforementioned challenges associated with P removal.

SUMMARY OF THE INVENTION In accordance with one aspect of the present invention, there is provided a process for phosphorus removal from an aqueous medium containing phosphorus, comprising contacting the aqueous medium with a particulate gravel material, wherein the gravel material contains iron and/or aluminium, so as to remove phosphorus from the aqueous medium.

DETAILED DESCRIPTION OF THE INVENTION Particulate gravel material (hereinafter referred to as pea gravel), typically 14 to 16 mm in particle size, is a material naturally abundant in Western Australia and many other parts of the world. This material does not contain, and hence will not emit, any harmful by-products or persistent chemicals to the system that is in contact with the material. Also, the pea gravel does not alter the pH of the system it is contacted with.

Further, the pea gravel may be easily ground and sieved to different particle sizes if required, and conveniently transported to various locations.

00 In accordance with the process of the present invention aqueous medium such as wastewater or other water bodies polluted by P, is contacted with a particulate gravel 00 0 material to remove P. The gravel material may be added directly into a water body, INO or packed and used as an external filter where P can be removed while contaminated 0water flows through the filter.

00 SPreferably, the gravel material used in the process of the present invention contains from 100 to 300g/Kg of iron. Further, the gravel material preferably contains from 100 to 300 g/Kg of aluminium.

Preferably, the gravel material is contacted with the aqueous medium for a time sufficient to remove at least 90% by weight of the P from the aqueous medium. More preferably, the time of contact is in the range from 2 to 10 minutes.

The present invention will now be described with reference to the following examples.

In all the examples shown, the pea gravel samples are washed with deionised water and oven dried at 105 'C for 24 hrs before use. All the experimental studies in the examples shown were conducted at 25 'C.

00 0 Example 1 SThis example illustrates the capacity and efficiency of pea gravel (being a particle size Sof from 14 to 16 mm) to adsorb P from solution. 50 g of pea gravel samples were 00 placed in 250 mL glass flasks, and admixed with 50 mL of 0.01 M KC1 solution INO spiked with KH 2

PO

4 to give one of six concentrations of P 30, 50, 100, 200 and 500 mg/L). At each concentration of P, duplicate studies were carried out. The glass flasks were sealed in airtight manner and continuously shaken during the 00 experimental period. Solution samples were taken after 3hr, Id, 2d and Sd period and analysed for their equilibrium P concentrations.

Using the well known Langmuir isotherm equation, the maximum capacity of the pea gravel to adsorb P after the above mentioned time periods were determined to be: Reaction time Maximum P adsorption capacity (mg/Kg) 3hr 53.8 Id 78.7 2d 79.4 99.0 From the data, it can be seen that the capability of pea gravel to adsorb P increases with contact time. After a 5d period, a maximum adsorption capacity of 99.0 mg of P per Kg of pea gravel was reached.

00 0 Example 2 This example illustrates the effect of grinding pea gravel down to particle sizes of C 2mm and <175 pm, respectively, on the capacity and efficiency of the gravel material 00 to remove P from solution. 25 g of the 2mm fine gravel (FG) and 10 g of the <175 IND pm fine powder (FP) were admixed with respective 50 mL of 0.01 M KCl solutions Sspiked with KH 2

PO

4 to give a P concentration of 60 mg/L. The mixtures were 00 continuously shaken as in Example 1. Solution samples were taken after 1 hr, 3hr, Id, ¢CI 2d and 5d period and analysed for their equilibrium P concentrations. The percentage of P removed by FG and FP from the treatment solution as a function of time the P removal efficiency of FG and FP) is shown in the following graph.

Fine Powder Fine Gravel 99.1 100 97.6 97.6 100 100 100 88.7 98 .96 94 .1 C 1.0 30 I m 1 h 24 h 48 h 5d Reaction time It can be seen that within 5 minutes of reaction time, over 98% of P was removed from solution by pea gravel powder (<175 ipm). The 2mm fine gravel, on the other hand, took 48 hours to achieve similar results.

00 0 Example 3 This example illustrates the mineral content of the gravel material in relation to P Sadsorption. The very fine pea gravel powder (ground to <150 jtm) is used for the 00 study detailed below.

A 1 L solution of KH 2

PO

4 in 0.01 M KMnO 4 with a P concentration of- 100 mg/L 00 was placed in a 2 L glass flask. The solution was stirred with a magnetic stirrer. The Svery fine gravel powder (in an amount of 500mg, 1g, 2g, 4g, 10g, 25g, 50g, 82.5g, respectively) was added to the solution incrementally at intervals of minutes. After each addition, the mixture in the 2 L glass flask was stirred continuously for 5 minutes and left standing for another 5 minutes. After the final addition of pea gravel powder, the mixture was left undisturbed for 24 hours. The gravel powder settled as sludge at the bottom of the flask and the liquid over the sludge was clear. Then, a clear supemrnatant was collected for elemental analysis, while the sludge from the experiment was oven dried at 105 'C for 48 hours, and a sample of the dried sludge was used for examination of mineral content. In order to compare the difference, a sample of the virgin <150 jim gravel powder, i.e. have not being used for any experiment, was also analysed for mineral content.

The mineral content of the <150 jim virgin gravel powder and the dried sludge are shown below.

Sample type Al Ca Fe Mg P (g/Kg) (g/Kg) (g/Kg) (g/Kg) (g/Kg) Virgin gravel 190 5.7 150 0.22 0.06 powder Dried sludge 150 4.7 150 0.21 0.18 It can be seen that the P content of the dried sludge after exposure to the KH 2

PO

4 solution) is three times higher than the virgin gravel powder indicating adsorption of P upon exposure of the gravel powder to the KH 2

PO

4 solution. The identical Fe content between the virgin sample and the dried sludge shows that Fe did not leach during the experiment, which indicates that P would have been adsorbed to the Fe sites of the gravel.

Elemental analysis of the clear supernatant collected at the end of the study 24 hours after the final addition of the gravel powder) showed presence of Al, Ca and Mg; however, Fe was not detected as shown below.

Sample type Al Ca Fe Mg P (mg/L) (mg/L) (mg/L) (mg/L) (mg/L) Clear Below 0.032 20 0.81 0.09 supernatant detection This confirms that Fe did not leach, and adsorption reaction.

the Fe sites in the gravel contributed to P 00 SExample 4 This example illustrates a P desorption study. The study was carried out to Sinvestigate if P bound to pea gravel (being a particle size of from 14 to 16 mm) will 00 0 be leached back to solution at neutral or acidic pH environment. The 50 g pea gravel IND samples that were used for P adsorption study with 5 days retention time as disclosed in Example 1, were used for this P desorption study. The gravel samples were oven dried for 24 hours at 105 'C after the adsorption study of Example 1, and before this 00 Sdesorption study. The pea gravel samples, 100 mL deionised water and 0.01 M KC1 solution were added to 250 mL glass flasks. The 0.01 M KC1 solution was acidified with H 2 S0 4 to enable the desorption study to be carried out at a condition of pH 2.

The glass flasks were continuously shaken during the experimental period. After a reaction time of lihr, 3hr, 1d, 2d, 5d and 9d, respectively, solution samples were collected for P analysis.

The results of the analyses showed that, even after a reaction time of 5d, little or no P was found in solution solution P concentrations were below the detection limit of This indicates that P was not released from the particulate gravel material into the solution.

Modifications and variations as would be apparent to a skilled addressee are deemed to be within the scope of the present invention.

Claims (11)

1. A process for phosphorus removal from an aqueous medium containing 00 0phosphorus, comprising contacting the aqueous medium with a particulate gravel IND material, wherein the gravel material contains iron and/or aluminium, so as to remove phosphorus from the aqueous medium. oO2. A process according to claim I, wherein the gravel material has a particle size 00 of 16mm or less.

3. A process according to claim 2, wherein the gravel material has a particle size of 2mm or less.

4. A process according to claim 3, wherein the gravel material has a particle size of less than 175 lm. A process according to claim 4, wherein the gravel material has a particle size of less than 150 jim.

6. A process according to any one of the preceding claims, wherein the gravel material contains from 100 to 300 g/Kg of iron.

7. A process according to any one of the preceding claims, wherein the gravel material contains from 100 to 300 g/Kg of aluminium.

8. A process according to any one of the preceding claims, wherein the gravel material is contacted with the aqueous medium for a time sufficient to remove at least by weight of the P from the aqueous medium.

9. A process according to claim 8, wherein the time in which the aqueous medium is contacted with the gravel material is in the range from 2 to 10 minutes. 00 O 10. A process according to anyone of the preceding claims, wherein the gravel material is added directly into the aqueous medium to remove phosphorus.

11. A process according to any one of claims 1 to 9, wherein the gravel material is 00 packed and used as an external filter such that phosphorus is removed whilst the sO aqueous medium flows through the external filter.

12. A process according to any one of the preceding claims, wherein P desorption 00 analysis on the particulate gravel material after removal of P from an aqueous 0 medium shows that little or no P is found in solution even after a reaction time of days.

13. A process according to claim 12, wherein the desorption analysis is carried out at a pH of 2 or less.

14. A process for phosphorus removal from aqueous medium substantially as hereinbefore described in any one of the Examples.