What non-oxidizing fungicides are used in industrial recycled water? Isothiazolinone and other mainstream comparison（二）
1.2.2 Glutaraldehyde
Glutaraldehyde as a fungicide is characterized by almost non-toxic, wide pH range, high temperature resistance, is a special drug to kill sulfate-reducing bacteria. At the recommended concentrations for cooling water, glutaraldehyde is almost nontoxic and biodegrades itself. With the strengthening of social environmental awareness, glutaraldehyde fungicide will have a great future.
Studies have shown that glutaraldehyde is particularly suitable for alkaline circulating water, and the bactericidal ability is enhanced with the increase of pH. The influence of pH value on the bactericidal effect of glutaraldehyde fungicide is shown in Table 1. This widens the selection of fungicides operating at high concentration multiples. Glutaraldehyde loses its activity in reaction with ammonia and amine compounds, and its price is expensive and its cost performance is low. However, relevant studies have found that the combination of glutaraldehyde and quaternary ammonium salt will greatly reduce the amount of glutaraldehyde, when the ratio of glutaraldehyde and quaternary ammonium salt is 1:1 or 2:1, the bactericidal stripping effect is better than that of using the two products alone.
1.2.3 Phosphonium quaternary salt
Phosphonium salt is a new, efficient, broad-spectrum water treatment fungicide introduced abroad in 1990, its molecular structure is similar to quaternary ammonium salt, with a long carbon chain alkyl, a positively charged central atom and the corresponding negative ions, only phosphonium cation instead of nitrogen cation. The most commonly used products in industrial circulating water are phosphonium tetramethylchloride (TMPC), Phosphonium tetrahydroxyalkyl sulfate (THPS), phosphonium tetrahydroxyalkyl chloride (THPC), etc. Phosphonium salt as a fungicide, can be used with a variety of negatively charged corrosion and scale inhibitors at the same time, not easy to precipitate, basically does not affect the use of corrosion and scale inhibitors. It can also have synergistic effect with other anionic corrosion inhibitors, and is a multifunctional agent with corrosion inhibition, scale inhibition and sterilization.
1.2.4 Quaternary ammonium salt
Quaternary ammonium salt is a kind of cationic surfactant, widely used in the control of circulating cooling water microorganisms, in addition to strong bactericidal effect, but also has a good penetration and dispersion ability, compatible with most water treatment agents, can play an effect in a wide pH range. Some studies have found that the length of the carbon chain in quaternary ammonium salt has a great impact on the bactericidal ability, when the carbon atom is less than 10 or more than 16, the bactericidal ability is not large, of which C14 has the strongest bactericidal ability. Long-term use of quaternary ammonium salt microorganisms are easy to develop resistance, the efficacy of the decrease, and the use of foam, difficult to remove. To overcome these shortcomings, new varieties of quaternary ammonium salts have been developed at home and abroad, such as products with a bisalkyl carbon chain length of C5-C8, which have the advantages of low dosage concentration, long duration of efficacy, good sterilization effect, and less foam.
1.2.5 Organic sulfur fungicide
The most widely used organic sulfur fungicide is dithiocyanomethane. It is a kind of broad spectrum fungicide, which has good bactericidal effect on bacteria, fungi, algae and protozoa, especially on sulfate-reducing bacteria. Dithiocyanomethane is not suitable for application in high alkalinity circulation systems, is very sensitive to the pH of water, and has a half-life in water with
The relationship of pH is shown in Table 2, and the appropriate pH value ranges from 6.0 to 7.0[16]. In addition, dithiocyanomethane is insoluble in water, so it is usually used together with some special dispersants and penetrants, so that the agent can be effectively dispersed, and increase the penetration of the agent for the algae and bacteria mucus layer, so as to improve the use of the agent.
