Research on the Application of Polymer Water Purifiers

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Overview: In August and September 1997, our company faced the most severe cyanobacterial \"algal bloom\" since the introduction of water from the Luan River (with Microcystis as the dominant species). The rapid growth of these algae consumed large amounts of bicarbonates in the water, causing the alkalinity to drop below 100 mg/L, while the pH level rose to around 9, which posed significant challenges to water treatment operations. The amount of alum required has **exceeded the water treatment plant’s capacity to produce it; as a result, large quantities of acidic inorganic iron salts are added, causing the pH value of the water leaving the plant to drop below 7.0. The level of residual iron is above the acceptable limits, and various parameters such as color, turbidity, total bacterial count, and total coliforms are also not within the specified ranges. This has led to the water quality leaving our company reaching its lowest level ever. Users keep calling to report \"yellow water and red water,\" putting the company’s water quality management in a highly reactive situation. Keywords: Polymer-based water purifiers, algae removal, coagulants I. Introduction of the problem In August–September 1997, our company faced the most severe blue-green algae bloom since the introduction of water from the Luan River (with Microcystis as the dominant species). The rapid growth of these algae consumed large amounts of bicarbonates in the water, causing the alkalinity to drop below 100 mg/L, while the pH level rose to around 9, posing significant challenges to water treatment operations. The amount of alum required has **exceeded the water treatment plant’s capacity to produce it; as a result, large quantities of acidic inorganic iron salts are added, causing the pH value of the water leaving the plant to drop below 7.0. The level of residual iron is above the acceptable limits, and various parameters such as color, turbidity, total bacterial count, and total coliforms are also not within the specified ranges. This has led to the water quality leaving our company reaching its lowest level ever. Users keep calling to report \"yellow water and red water,\" putting the company’s water quality management in a highly reactive situation. 　　To this end, in November 1997, the Water Quality Department submitted a proposal to the managing director and the Water Production Department to systematically carry out monitoring of water sourced from the Luan River as well as research on the treatment of water contaminated with high levels of algae. The Water Quality Department reached a consensus on this matter with the company’s leadership, and by the end of 1997, the company included four research topics related to algae in its scientific research plan for 1998: 1. Algae monitoring ； 2. Pre-chlorination for alga removal ； 3. Research on various coagulants ； 4. Transformation of water treatment processes. The Water Quality Department is responsible for the first three tasks; here, we will focus on an overview of the research on alga-removing coagulants. 　　II. Applications of Polymer Water Purifiers At the beginning of 1998, as part of our research on this topic, we visited several water treatment companies with experience in algae removal; pre-chlorination for algae removal and air flotation sedimentation techniques were widely used for this purpose. Although pre-chlorination can remove more than 50% of the algae, the amount of chemical used remains high, resulting in a low pH value of the treated water. No ideal coagulant has yet been able to solve the problem of water contaminated with high levels of algae. Between August and September 1997, the laboratories at the Xinkai River Water Plant and Jieyuan Water Plant conducted experiments using polyferric salts, iron-aluminum complexes, and polyaluminum salts as coagulants, but none of these methods proved particularly effective. Although polyaluminum can address the issue of low pH levels in the treated water caused by excessive acidity resulting from iron coagulation, it still cannot solve the problems of high dosage requirements, high costs, and high levels of residual aluminum in the water. 　　In the research project titled “Experimental Study on Flocculants and Their Effects in Different Water Quality Conditions of the Luanhe River” conducted in 1993, it was found that the polymer cationic electrolyte (HCA-1) developed by East China University of Science and Technology (formerly East China Institute of Chemistry) was effective in treating water with high algae content. At the beginning of 1998, further studies on the use of HCA were carried out in the laboratory of Xinkai River Water Plant. In May, a technical plan for using HCA was proposed. From late August to early September of the same year, pilot tests were conducted in Pool No. 3 of Xinkai River Water Plant. The results showed that after adding ferric chloride, using 0.0 mg/L of HCA could reduce the amount of ferric chloride needed by 60%; the pH value of the treated water increased by about 0.4, while after sedimentation the pH value rose from 6.7 to 7.1. We preliminarily concluded that HCA is a good polymer flocculant for treating water containing algae. 　　Building on the production tests conducted in 1998, in 1999 the water supply company began using the polymer flocculant HCA on a full scale during the period of high algal growth (July–October), which played a decisive role in stabilizing production and improving water quality. By August 1999, the compliance rate for the urban water distribution network met 100% for four key indicators: turbidity, residual chlorine, total bacteria count, and total coliforms. 　　III. Problems associated with the use of polymer flocculants The use of polymer flocculants is a method that has to be adopted due to the severe pollution of water quality at present. Polymerous organic substances, owing to the presence of residual monomers, can have certain effects on human health. Given the increasingly serious situation of water source pollution, using polymer-based water purifiers is no longer a temporary solution; rather, long-term use of such agents is necessary. It is now necessary to consider the negative impacts that long-term use of polymer water purification agents may have on water quality and water treatment facilities, and to explore countermeasures. The current production process for polymer water purifiers manufactured in China has a low level of sophistication; the standards for controlling the content of monomers are low, and the viscosity is high. What impact will flocs containing viscous polymers have on the filter once they enter it? There are no answers to these questions yet, but we suspect that they will have an impact. When considering measures to reduce the negative effects of using polymer materials, the first thing that comes to mind is finding more efficient and less toxic types of agents. 　　IV. Research on the Application of Polymer-based Water Purification Agents Abroad With the advancement of reform and opening up in China, and especially as the country prepares to join the WTO, we will have a larger market for water purification agents in the future, allowing us to choose those that are more efficient and safer on a global scale. In 2000, we made attempts in this area. From May to October this year, Tianjin Water Supply Company, in collaboration with Ciba from Switzerland and SNF from France, obtained samples of polymer water purification agents for testing purposes. The testing began in June and was mainly carried out in the laboratories of Lingzhuang Water Plant and Xinkai River Water Plant. At Lingzhuang Water Plant, 11 types of agents from Ciba Switzerland were subjected to further screening tests, and some products from SNF were also tested. Based on these tests, SNF’s FL45C and Ciba’s LT35 were tried out in actual production. Xinkai River Water Plant, taking into account the characteristics of its own production process as well as the problems that arose during production, conducted tests on various agents in its laboratory. These test chemicals all come from world-renowned companies specializing in water treatment chemicals, and they meet high standards; for example, among HCA products of similar types, the content of the active ingredient is 0.5%, whereas that of domestically produced HCA is 5%. These products are low-toxicity substances designed specifically for drinking water treatment, and they have been approved for use by health authorities in the United States, the European Community, and other regions. In addition, these companies possess advanced production technologies and ensure consistent product quality. As China’s market becomes more open and tariffs decrease, their prices will gradually become comparable to those of domestic products, or at least remain at an acceptable level. For those materials that are widely used, it is also possible to reduce their costs by using domestic alternatives. 　　Polymer-based water purification materials used to be a topic that caused fear in the water purification industry, but with rising demands for water quality and advances in technology, they are gradually becoming more widely used. We should take advantage of their strengths and overcome their weaknesses to enable their proper application in water purification processes. 　　In terms of the application of polymer-based water purification materials, we are still in the early stages and lack experience. Here, we would like to share our insights for reference; please point out any mistakes.