The isothiazolone is a kind of relatively new type of organic sulphur biocide. This type of biocide can achieve the killing effect by breaking the bond of the protein in the bacteria and the algae. With the concentration of 0.5 mg/L, it can not only effectively suppress the algae, the fungi and the bacteria in the cooling water system, with the advantages such as the broad spectrum, the long duration of action (with the usage amount of 0.5 mg/L, it is still effective after five weeks of usage), the low toxicity, the wide range of the PH value, the good miscibility and the compatibility, and the bubble free etc., it also have the advantage to prevent the slime generation in the application. Thereby, it has been very widely used in the treatment of the cooling water system around the world.

The quaternary ammonium salt biocide has been widely used due to its low cost, low toxicity and the inhibition effect, but the use of this kind of biocide also has the problems such as the easy drug resistance, the increased cost, the foaming in the application and the aggravation of the corrosion etc. Therefore, there are two new type of this kind of biocides being developed. The new synthesis of the octyl sixteen alkyl two methyl ammonium bromide (168) and the sixteen alkyl decyl two methyl bromide (1610), two kinds of dialkyl quaternary ammonium salts, has changed the surface activity and the molecular stability of the quaternary ammonium salt, it can generate the less foam, and can improve the killing effect.

The glutaric dialdehyde has the broad spectrum bactericidal effect and the algicide effect, it can also have a certain effect on the stripping of the biological slime. Under the recommended concentration int eh cooling water, the use of the glutaric dialdehyde is almost non toxic, its aqueous solution itself can degraded biologically. With the strengthening of the social awareness of the environmental protection, the development of the glutaric dialdehyde kind of the biocide will be promising.

In the development of the new type of the biocide, besides the consideration of the price, the toxicity, the usage safety, the storage stability and the microbial drug resistance etc factors, it also should be sonsidered the synergistic effect between the different biocides, the compound usage of different biocides can not only enhance the killing ability, but also can reduce the dosage of the drug.

4.The trend of the development on the water treatment agent

4.1The development of the special water treatment agent

In order to meet the needs of the treatment of different waste water system ( such as the paper making waste water, the printing and dyeing waste water, the food processing waste water etc.), it is imperative to research and develop for a class of chemicals varieties with strong specificity.

4.2 The development of the multifunctional water treatment agent

The multifunctional water treatment agent is one of the important aspects on the research of the water treatment agent. The appearance of this new type of water treatment technology will develop and widen the production of the water treatment agent and the application range of the water treatment agent. It has the significant role in promoting the development of the chemical treatment of the industrial waste water.

The research in this area includes: the corrosion - scale inhibitor, the flocculating – corrosion inhibitor, the flocculating - bactericidal agent, the flocculating - bactericidal – corrosion inhibitor, the flocculating – corrosion inhibitor – scale inhibitor etc.

4.2The development of the green water treatment agent

In the development of the green water treatment agent, the direction includes the non – toxic, the harmless and the easy biodegradation.

The most typical green water treatment agent is the dispersion inhibitor poly aspartic acid (PASP), which is developed in many countries in recent years. PASP is a synthesized biopolymer. It has the good biocompatibility and the good biodegradability. The toxicology studies show that the poly aspartic acid (PASP) has non – toxic, no sensitive or no mutation effect.

4.3The development of the water treatment agent with the high performance to price ratio

At the moment, the prices of the high performance water treatment agents are generally higher. It is workable to reach the purpose of reducing the cost by searching for the cheap raw materials and then developing a high performance product. It is also workable to reduce the cost by strengthening the research on the combination technology, that is to add the cheap auxiliary agent to reduce the practical dosage amount and at the same time to maintain the water purification efficiency.