Environmental protection water treatment: application and principle of microbial flocculants in water treatment

Flocculant is one of the most used chemicals in sewage treatment, and it is also widely used in other industries. It is mainly divided into three categories: inorganic flocculants, organic flocculants, and natural polymer flocculants. In terms of contact and understanding, most people are familiar with inorganic flocculants and natural polymer flocculants. They are cheap but have secondary pollution problems. Although natural polymer flocculants are environmentally friendly, they are expensive and unfamiliar. There are exceptions such as: microbial flocculants. Microorganisms have long been found to have flocculation. Microbial flocculant is a new type of water treatment agent that is safe, efficient, and can be naturally degraded by using biotechnology to extract and purify microorganisms or their metabolites. The components include glycoprotein, cellulose, protein and DNA. It has also received more and more attention from people, and has shown a trend of gradually replacing traditional flocculants. At present, microbial flocculants on the market are mainly used for decolorization of high COD organic wastewater and dye wastewater and recovery of activated sludge settling capacity.

01

The working principle of microbial flocculants

The principle of electric neutralization: the surface of suspended particles in the water body has a negative charge, and the particles of the same sex repel each other. The surface of the microbial flocculant has a positive charge, which will neutralize the negative charge and cause the suspended particles to undergo magnetic collision and coagulate and precipitate.

The principle of rolling and sweeping: the microbial flocculant is dissolved in the water body to form a net-like floc, which can be quickly caught by the net under the action of gravity, and the smaller suspended particles in the water body can be swept away.

Adsorption bridging mechanism: Flocculant macromolecules adsorb multiple colloidal particles at the same time by means of ionic bonds, hydrogen bonds and van der Waals forces, resulting in bridging between particles, thereby forming a three-dimensional network to precipitate.

01Microbial flocculant characteristics

Efficiency: Under the same dosage, the use efficiency of microbial flocculants is higher than that of conventional flocculants such as iron salts and aluminum salts.

Non-toxic: The microbial flocculant is a natural organic high-fraction flocculant, which is safe and non-toxic and will not affect the sludge.

No secondary pollution: The flocculants produced by microorganisms are complex and diverse, and vary with different strains. They are biochemical and can degrade themselves, so they will not cause secondary pollution.

Wide range of applications: The objects that can be treated are activated sludge, charcoal, ink, river bottom sediments, printing and dyeing wastewater, etc.

Short production cycle: Microorganisms grow and reproduce quickly, easily mutate, and are widely distributed, so they have a wide range of sources and a very short production cycle.

01Application in wastewater treatment

The application in river water treatment has been studied. The test shows that the flocculant produced by Bacillus isolated and screened is used to treat high turbidity river water, and the technical indicators after treatment are obviously better than those of conventional flocculants such as PAC.

Relief of sludge bulking: By adding microbial flocculants to activated sludge, the volume index of activated sludge will decrease, thereby eliminating sludge bulking and restoring the settling capacity of activated sludge. For example, in the sublimation treatment of licorice pharmaceutical wastewater, by adding a certain amount of microbial flocculant to the formed bulking sludge, the SVI of the sludge quickly drops from 290 to 50, thereby eliminating sludge bulking and restoring activated sludge sedimentation. effect of ability.

Decolorization of printing and dyeing wastewater: The composition of printing and dyeing wastewater is relatively complex, the chroma is high, and it contains refractory surfactants. For example, the treatment of dye wastewater with white rot fungi is a hot research topic at present.

Heavy metal enrichment: Many microbial flocculant-producing bacteria have the ability to adsorb heavy metal ions.

With the continuous improvement of people's understanding of water treatment, the secondary pollution caused by chemical flocculant residues has attracted much attention from the society, which gives microbial flocculants an excellent opportunity to enter the market, but the composition of productive wastewater in my country is increasingly Complex, the adaptability of microbial flocculants is also facing the test.

Future research on microbial flocculants may focus on the following aspects:

1. Research on the physical and chemical properties of microbial flocculants, the structure of flocculation groups, flocculation performance, flocculation kinetics and the factors affecting flocculation.

2. Select alternative microbial culture medium, optimize the production route of microbial flocculants, reduce production and use costs, and achieve the purpose of large-scale application.

3. The combined application of microbial flocculants and various flocculants realizes the complementary advantages of various flocculants and increases efficiency and energy saving.

4. Through genetic engineering technology, the pollution factor degradation plasmid is introduced into the engineering strain, so as to realize the integration of flocculation, sedimentation and degradation, and expand the application prospect of flocculants.