Natural polymer flocculant and its application in water treatment

Natural polymer flocculant and its application in water treatment Lu Jinling, Chen Jianzhong (School of Environmental Science and Engineering, Kunming University of Science and Technology, Kunming, Yunnan, 650093). The research and application of natural polymer organic flocculants modified with starch, chitosan, lignin and plant gum as raw materials are summarized, and their application and development in wastewater treatment are reviewed.

Water treatment flocculants are divided into inorganic and organic types according to their molecular composition. The application of inorganic flocculants has a long history, but its application has been limited due to large quantities and low efficiency. In organic polymer flocculants, the application of synthetic organic polymer flocculants is also limited due to the high production cost and the presence of a certain amount of residual monomers, which inevitably brings about toxicity. The natural polymer flocculant is rich in raw material, low in price, large in selectivity, small in dosage, and high in flocculation speed. It is not affected by changes in coexisting salts, pH, and temperature, and the amount of sludge is small, and it is safe and non-toxic. Completely biodegradable, easy to handle, no secondary pollution, after the 1970s, its research and development have attracted much attention. After more than 20 years of development, there have been a large number of natural polymer flocculants with different properties and uses, such as starches, chitosans, lignin, plant gums, proteins, and algae.

1 Starch natural organic polymer Organic flocculant is a kind of high molecular polymer. Its molecular weight is large. It can be adsorbed on the particles in the dispersion system by some active functional groups on the long chain. Since the polymer is a long linear structure, each polymer compound has many functional groups and can adsorb a plurality of particles on the same molecule, and thus it plays a linking role between the particles, which is called bridging. effect. Due to the bridging effect of the high-molecular polymer, many particles can be linked together to form a floc, and the floc continuously becomes large flocks, thereby accelerating the sedimentation of the particles.

Starch resources are very abundant. The content in the natural world is far higher than that of other organic materials. It is one of the most abundant organic resources that humans can use, and it is also the earliest and most developed natural organic polymer flocculant. Chemical modification of starch, such as graft co-polymerization, etherification, esterification, xanthogenization, etc., adding active groups, branching molecular chains, and dispersion of flocculating groups, so that particles in the suspension system have Stronger capture and promotion effect.

The starch rigid chain has a hydrophilic character, and its hydroxyl group can be activated under certain conditions and can be copolymerized with ethylene monomers such as acrylamide, acrylic acid, propylene ester, butyl acrylate and styrene. When it was used as a flocculant with acrylamide graft copolymer, the treatment effect was better than that of polyacrylamide flocculant, and Saneev et al. conducted a study on the removal of heavy metals with water-soluble starch sulfonate (SSX) and found that SSX was used for Hg++ and Cu++. The removal effect is very good; Zhang Yihua, when chitosan is used as wastewater treatment flocculant, will have more advantages than traditional flocculants under the same treatment effect, and it is an ideal green water treatment agent. Chitin is a natural organic polymer compound which is second only to cellulose in nature and belongs to nitrogen-containing polysaccharides. Deacetylation of chitin can give chitosan (CTS), a wide range of sources. ctsS white flake powder, almost insoluble in neutral water, swollen. The CTS molecule contains many hydroxyl groups (mono-OH) and amino groups (mono-NH2). When it is dissolved in an acidic medium, it exhibits the characteristics of a cationic polyelectrolyte with the protonation of the amino group. CTS is a linear polymer with a relative molecular mass of about 105. It has a bridging and net trapping effect of high-molecular flocculants. It can trap organic and heavy metal ions in water, especially halogenated alkanes and nitroso-containing organic polymers. Heavy metal ions such as copper, nickel, zinc, mercury, copper, and lead have strong adsorption properties. CTS can also inhibit the proliferation and growth of microorganisms in the water and has a certain bactericidal effect. In recent years, the United States, Japan, and other countries have devoted themselves to the research and development of chitosan. The products are used in water treatment and sludge dewatering, and the production and sales volume have clearly grown. China is rich in shellfish resources, and has a good foundation for the application of chitosan. Further development of high-quality chitosan flocculants will have a broader market prospect.

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