Tetrakis hydroxymethyl phosphonium sulfate is a new type of quaternary phosphate salt fungicide. It has the advantages of low toxicity and environment friendly.
A series of static sterilization experiments and dynamic experiments show that THPS biocide is used in water treatment systems, with broad-spectrum, high efficiency, and fast-killing characteristics. And good compatibility with common corrosion and scale inhibitors. Tetrakis hydroxymethyl phosphonium sulfate is a biocide with good prospects for application.
In the circulating cooling water system, microorganisms will multiply in large quantities to make the cooling water black in color, bad smell, and pollute the environment. At the same time, a large amount of slime will be formed, reducing the heat transfer efficiency and causing or promoting the occurrence of corrosion.
These slimes isolate the action of the agent on the metal so that the agent can not play the proper scale and corrosion inhibition effectiveness.
Therefore, the harm of microorganisms and scale, corrosion on the cooling water system is as serious as the harm. It can even be said that, when comparing the three, the control of microbial hazards is of primary importance.
The use of biocides to control the growth of microorganisms is a common and effective method of microbial growth in circulating cooling water.
Environment-friendly biocides gradually replace the production of secondary pollution biocides to become an inevitable trend. Tetrakis hydroxymethyl phosphonium sulfate (THPS) is a new type of environmentally friendly quaternary phosphate salt biocide.
1. Experimental part
1.1 Static sterilization experiment
1.1.1 Experimental methods
For the determination of heterotrophic bacteria, the live bacteria flat dish counting method was used. The water samples were inoculated on the prepared agar medium of the flat dishes. Three dishes were repeatedly inoculated for each dilution. Then incubate at 37°C for 48 hours. Select the number of colonies between 30 and 300 for the flat dish reading and multiply by the dilution. That is, the number of heterotrophic bacteria per ml of the original water sample can be calculated.
For the determination of sulfate-reducing bacteria, the multi-tube fermentation technique was used. Incubate at 37°C for 14 days. If a black precipitate with a hydrogen sulfide odor is produced in the test tube indicating a positive reaction, the MPN technique is used to count the sulfate-reducing bacteria in the sample being tested.
For the determination of iron bacteria, the multi-tube fermentation technique was used. Incubation at 37°C for 14 days indicated a positive reaction if the brown color disappeared and a brown or black precipitate formed in the tubes. The MPN technique was used to count the iron bacteria in the samples tested. Determination of fungi: This method was determined by using a soil fungal medium and incubating at 29+1°C for 72 hours using the flat dish counting method.
1.1.2 Biocidal performance evaluation method
1.1.3 Experimental results and review
1.1.3.1 Sterilization effect on four main harmful bacteria in circulating cooling water
| Medicine concentration (mg/L) | 0 | 10 | 20 | 40 | 60 | 80 |
|---|---|---|---|---|---|---|
| Number of colonies (units/ml) | 2.4*106 | 2.5*104 | 2.2*104 | 3.7*102 | 20 | 40 |
| Sterilization rate (%) | 0 | 97.58 | 99.08 | 99.89 | 100 | 100 |
As can be seen from Table I, the bactericidal effect of THPS reached more than 97% at a concentration of 10 mg/L.
| Medicine concentration (mg/L) | 0 | 5 | 10 | 20 | 40 |
|---|---|---|---|---|---|
| Number of colonies (units/ml) | 450 | 200 | 45 | 6.5 | 0 |
| Sterilization rate (%) | 0 | 55.65 | 90 | 98.56 | 100 |
As can be seen from Table II, THPS had a good killing effect on sulfate-reducing bacteria. the bactericidal rate reached more than 98% at 20 mg/L.
| Medicine concentration (mg/L) | 0 | 5 | 10 |
|---|---|---|---|
| Number of colonies (units/ml) | 45 | 0.4 | 0 |
| Sterilization rate (%) | 0 | 99.11 | 100 |
As can be seen from Table III, THPS has a very good killing effect on iron bacteria. The bactericidal effect can reach more than 99% at the concentration of 5 mg/L.
| Medicine concentration (mg/L) | 0 | 50 | 100 | 150 | 200 |
|---|---|---|---|---|---|
| Number of colonies (units/ml) | 4.5*103 | 1.1*103 | 1.0*103 | 7.3*102 | 6.0*102 |
| Sterilization rate (%) | 0 | 76.09 | 78.26 | 84.13 | 86.96 |
Compared to the killing of heterotrophic bacteria, THPS inactivates fungi at much higher concentrations and has a significantly lower bactericidal rate.
1.1.3.2 Study of the applicable conditions of THPS
| Action time (h) | Concentration (mg/L) | Number of bacteria (units/mL) | Sterilization rate (%) |
|---|---|---|---|
| 0 | 0 | 2.1*106 | 0 |
| 2 | 20 | 5.1*104 | 97.57 |
| 8 | 20 | 3.2*103 | 99.85 |
| 24 | 20 | 1.6*105 | 92.38 |
| 48 | 20 | 1.9*105 | 90.95 |
The effect duration is long. When the concentration is 20mg/L, the bactericidal rate can still be maintained above 90% after 48 hours of action.
| ph value | 4 | 6 | 7 | 8 | 9 |
|---|---|---|---|---|---|
| Number of bacteria (units/mL) | 8.0*102 | 2.0*103 | 3.6*103 | 2.5*103 | 3.6*103 |
| Sterilization rate (%) | 99.68 | 99.20 | 98.57 | 99.00 | 98.56 |
| Annotations: concentration of THPS: 20 mg/L, bacterial species: heterotrophic bacteria, starting number of bacteria: 2.5*105 units/mL | |||||
As seen in Table VI, THPS can be used over a wide pH range.
| Temperature (°C) | 20 | 30 | 40 | 50 | |
|---|---|---|---|---|---|
| Sterilization rate (%) | 97 | 94.58 | 99.25 | 98.88 | |
| Annotations: concentration of THPS: 20 mg/L, bacterial species: heterotrophic bacteria. | |||||
From Table VII, it can be seen that THPS has a good biocidal effect at temperatures of 20°C ~ 50°C.
1.1.3.3 Comparison of the biocidal effect of THPS and commonly used biocides
| fungicides | concentration: 40 mg/L | concentration: 80 mg/L | ||
|---|---|---|---|---|
| Number of bacteria (units/mL) | Sterilization rate (%) | Number of bacteria (units/mL) | Sterilization rate (%) | |
| blank | 7.4*107 | — | 7.4*107 | — |
| THPS | 3.4*105 | 99.54 | 1.5*105 | 99.80 |
| Kathon 886 | 7.3*106 | 90.14 | 5.5*106 | 92.57 |
| 1227 | 7.4*105 | 99.00 | 3.3*105 | 99.55 |
| Glutaric dialdehyde | 2.0*105 | 99.72 | 1.7*105 | 99.77 |
| Annotations: 1227, Glutaric dialdehyde and Kathon 886 manufactured by Haili, Wuhan science and technology chemical Ltd; Action time: 6h. | ||||
The biocidal effect of THPS is better than that of isothiazolinone and 1227, which are widely used in the market today. And glutaraldehyde is similar.
1.2 Experiments on the compatibility of tetrahydroxymethyl phosphonium sulfate with common corrosion and scale inhibitors
In circulating cooling water, biocides are usually used together with other water stabilizers such as corrosion inhibitors and scale inhibitors. Therefore, the choice of biocides should also consider whether the biocides and corrosion inhibitors match compatibility.
Experiment using the empirical method of measuring corrosion and scale inhibition rate. The copper ring was hung in a beaker, and the copper ring was removed after the water in the beaker reached a certain concentration multiplier at 50°C in a water bath. By calculating the corrosion and scaling of the copper ring in different water samples to evaluate the effect of corrosion and scale inhibition performance of commonly used corrosion inhibitors.
| Sample | surface area of copper (*10-6m2) | Original weights (g) | weights after the experiment (g) | Weights after removing corrosion or scaling (g) | Enrichment magnification | scaling (g) | corrosion (g) |
|---|---|---|---|---|---|---|---|
| PAA | 1718.11 | 6.2109 | 6.1491 | 6.1427 | 5.51 | 0.0064 | 0.0682 |
| PAA +60mg/L THPS | 1647.90 | 6.0039 | 5.9437 | 5.9338 | 5.42 | 0.0099 | 0.0701 |
| BTA | 1657.19 | 6.0337 | 6.0384 | 6.0331 | 5.79 | 0.0053 | 0.0006 |
| BTA +60mg/L THPS | 1697.13 | 6.1437 | 6.1472 | 6.1430 | 5.45 | 0.0042 | 0.0007 |
| PBTCA | 1683.98 | 5.9098 | 5.8195 | 5.8163 | 5.94 | 0.0032 | 0.0935 |
| PBTCA +60mg/L THPS | 1667.62 | 6.3484 | 6.2670 | 6.2595 | 6.06 | 0.0075 | 0.0889 |
| HEDP | 1665.33 | 6.0482 | 5.9473 | 5.9417 | 5.62 | 0.1053 | 0.0039 |
| Annotations: PAA, BTA, PBTCA, HEDP concentration are 5 mg/L, 5 mg/L, 10 mg/L, 15 mg/L. | |||||||
As can be seen from Table IX, the difference between the amount of fouling and corrosion of copper rings is not significant. THPS has good compatibility with commonly used corrosion and scale inhibitors.
| Pharmacy | Number of bacteria (units/mL) | Sterilization rate (%) | |||
|---|---|---|---|---|---|
| blank | 2.3*107 | — | |||
| THPS | 5.0*105 | 97.83 | |||
| BTA+THPS | 5.0*105 | 97.83 | |||
| PAA+THPS | 6.7*105 | 97.09 | |||
| PBTCA+THPS | 9.0*105 | 96.08 | |||
| HEDP+THPS | 4.2*105 | 98.17 | |||
| Annotations: Medicine concentration: 20 mg/L, Action time: 4h. | |||||
Commonly used corrosion and scale inhibitors do not affect the sterilization effect of THPS.
1.3 Dynamic experiments
Indoor dynamic simulation method. The test conditions are as follows.
Inlet temperature 44°C, concentration times 3.8, pH value natural adjustment, circulation 480 L/h.
The outlet temperature is 47°C, and continuous discharge is adopted.
The system runs stably, and the circulation is 480 L/h. The outlet temperature is 47°C, and continuous discharge is adopted.
After the stable operation of the system, shock dosing was applied at a concentration of 80 mg/L to investigate the killing effect of THPS.
| Action time (h) | Number of bacteria (units/mL) | Sterilization rate (%) |
|---|---|---|
| 0 | 2.1*107 | — |
| 4 | 20 | 100 |
| 24 | 2.3*102 | 100 |
| 48 | 1.9*105 | 99.10 |
| 72 | 2.6*106 | 87.62 |
| 96 | 5.8*106 | 72.38 |
As can be seen from Table XI, with the dosing of THPS, the bacterial count decreased to 72 hours and still remained at a low level. This indicates that the agent is effective in sterilization.
2. Impact of THPS on the environment
THPS has low toxicity and can be rapidly degraded to non-bactericidal activity by hydrolysis, oxidation, photodegradation, and biodegradation after use. And very low aquatic toxicity of non-toxic substances such as trihydroxyphosphine oxide ( THPO) and dihydroxyphosphonic acid (BMPA). And there is no cumulative effect of toxicity. Thus, health and safety incidents are greatly reduced, which is an important advantage.
3. Summary
Through the above experiments and discussions, the following conclusions can be drawn.
(1) Tetrahydroxymethyl phosphonium sulfate applied to water treatment systems, has a broad-spectrum bactericidal effect and strong bactericidal ability.
(2) tetrahydroxymethylsulfate phosphorus and corrosion inhibitors have good compatibility. Especially with the anionic corrosion inhibitor still has a good effect.
(3) phosphorus tetrahydroxymethyl sulfate and traditional biocides compared to the toxicity of small, environmentally friendly.
(4) tetrahydroxymethylsulfate phosphorus in the use of the process did not appear foaming phenomenon, better than commonly used quaternary ammonium salt type biocides.
In today’s emphasis on sustainable development, phosphorus tetrahydroxymethanesulfate has good prospects for application in circulating cooling water systems.