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The current status of biocide use is compared and analyzed, and the advantages of environmentally friendly biocide THPS in water treatment are proposed. As global environmental protection is increasing, people put forward more strict requirements on the use of biocides in water treatment, and the development and use of THPS is a far-reaching work.
Biocide is a widespread water treatment agent, mainly used in the circulating cooling water system. Due to the circulating cooling water system's unique ecological environment, microorganisms can quickly multiply in it. Simultaneously, the multiplication of microorganisms also produces a large amount of microbial slime in the circulating cooling water system. The microbial accumulation and the dirt made by the expansion will cause the cooling water quality to deteriorate rapidly and the corrosion-inhibiting and scale inhibiting chemicals from failing and may lead to the corrosion of the metal equipment in the cooling system, and in severe cases, may also block the pipeline, which directly threatens the safety and regular production. To avoid such situations, the most direct way is to add biocides to control the reproduction of microorganisms in the system.
1 Biocide
1.1 Types of biocides
Biocides can be divided into two categories according to their biocidal mechanism: oxidizing biocides and non-oxidizing biocides. Commonly used oxidizing biocides are chlorine, hypogas, indifferent and indifferent compounds, gas dioxide, ozone, hydrogen peroxide, peroxyacetic acid, etc. Oxidizing biocides are generally strong oxidizing agents that can kill microorganisms by oxidizing some enzymes in their bodies closely related to metabolism. Commonly used non-oxidizing biocides include quaternary salts, chlorophenols compounds, organosulfur compounds, organotin compounds, organo-acid compounds, isorem and ketones, glutaraldehyde and quaternary salts, etc. Non-oxidizing biocides do not kill microorganisms by oxidation but act as toxic agents on specific parts of microorganisms to destroy them.
1.2 Evaluation of biocides
A right biocide should meet the following conditions:
① From the performance point of view, biocides are required to have broad-spectrum (can kill fungi, bacteria, and algae); high efficiency (can kill microorganisms in the surface layer and the deep layer of slime), a wide range of use (effective at a wide range of pH, anti-system leakages such as amine or ammonia and organic pollution); can prevent biofouling (slime has a dispersion stripping effect); not with other water treatment agents in the system (scale inhibitors, corrosion inhibitors) ) reaction, no corrosion of the system metal.
② Considering the impact on the environment, the residues of biocides are required to have a high LD50 value, and the depositions are easily decomposed in the background.
③ From the economic point of view, it is required that the biocides are easy to use, safe, and low cost. After entering the 21st century, people have put forward higher requirements for biocides in terms of environmental protection. Whether the biocides are environmentally friendly is the most important indicator for evaluating biocides. According to the above criteria for assessing the biocides, the current use of biocides have certain defects, such as chlorine series of biocides with the high toxicity of residues, chlorine dioxide is less convenient to use, indifferent to the higher cost, peroxide, and ozone is easy to decompose, glutaraldehyde is easy to react with ammonia or amine compounds and failure, the quaternary salt biocidal effect is short-lived and easy to blister, the use of larger doses. In response to the existing situation, the search for a more perfect environmentally friendly biocide is a major direction of scientific research in this field.
2 THPS
2.1 THPS
THPS is the abbreviation of tetrahydroxymethyl sulfate, its structural formula is: (CH2OH)4PT/2 SO", in which the phosphorus atom belongs to the fifth main group of elements, using SP3 hybrid orbitals and the other four hydroxymethyls linked to form a tetrahedron, the monolith atom with a positive charge, the molecular structure is very stable. Due to the large radius of the phosphorus atom, its polarization increases, and the positive charge around it increases, so it is easier to produce electrostatic adsorption with negatively charged microorganisms, which can easily kill microorganisms and has no side effects on the environment. In 1995, THPS received EPS registration as a biocide, opening up the U.S. market. THPS was awarded the 1991 U.S. President's Green Chemistry Challenge Award based on a large amount of data provided during EPA registration on the toxicity and environmental safety of the biocide compared to stilts. In China, the application of THPS is in an advanced stage of research, and experimental studies have shown that THPS is an environmentally friendly biocide, and THPS is increasingly being used in cooling water treatment.
2.2 Advantages of THPS application in water treatment
THPS as a biocide applied to water treatment has its unique advantages.
①THPS has broad-spectrum (THPS can kill common Gram-negative bacteria, Gram-positive bacteria and molds, and algae, in addition to having a particularly strong killing effect on sulfate-reducing bacteria).
②THPS has high efficiency (THPS can kill microorganisms in water and slime, and can make slime fall off from the pipe wall to maintain the smooth flow of the pipeline).
③THPS has the compatibility (THPS application of a wide range of pH, and a variety of negatively charged corrosion inhibitors, scale inhibitors used at the same time, not easy to blister, the use of corrosion inhibitors and anionic scale agents do not affect the use of the effect of THPS itself does not reduce the killing effect, and even with the anionic corrosion inhibitor synergistic effect, while improving corrosion inhibition, scale inhibition, and biocidal effect).
④ THPS has environmental protection (THPS rapid sterilization, decomposition into the product is trimethylene oxidation transient THPO, ecotoxicological tests have confirmed the low aquatic toxicity of THPS, the toxicity of fish is even lower and does not kill life, the residues in the environment for a short residence time, easily biodegradable. Experiments have shown that the use of 50ug/g THPS in industrial water treatment can kill 2.5X105 SRB/ mL to 2.7X103 SRB/mL within 6 hours;
3 Conclusion
THPS is a broad-spectrum, highly efficient, rapid, environmentally friendly, and compatible biocide that has all the requirements of an excellent biocide, and its excellent environmental performance is its unique advantage. The use of THPS can eliminate pollution at the source, rationalize the use of resources and energy, reduce production costs, and meet the requirements of sustainable economic development, thus achieving the ambitious goal of comprehensive environmental protection. It is ideal for applying THPS as new low toxicity, rapidly degradable, and environmentally friendly biocide to all kinds of circulating cooling water systems, especially to those near ecologically sensitive areas. The development and application of THPS have become a task of far-reaching significance.
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