Control measures of green algae in artificial lake water

Cyanobacteria are also called cyanobacteria or blue-green algae. In the past, they were classified as algae, but recent research shows that their nuclear structure has no nucleoli of nuclear membrane and belongs to prokaryotes. In addition, cell walls are similar to bacteria, which are composed of peptidoglycan and Gram staining is negative, so they are now classified as prokaryotic microorganisms.

Cyanobacteria are unicellular organisms, larger than bacteria, and generally have a diameter or width of 3 ~ 15 micron. However, cyanobacteria rarely live as a single individual, but usually divide and gather together to form filamentous or single-celled populations. When many individuals gather together, they can form a large group, which can be seen by the naked eye.

Cyanobacteria contain pigment system. Because each cyanobacteria cell contains different pigments, it can appear blue, green, red and other colors. Cyanobacteria are simple in nutrition, do not need vitamins, use nitrate or ammonia as nitrogen source, and have many kinds of nitrogen fixation. Cyanobacteria, which perform oxygen release and photosynthesis, are specialized light-energy inorganic nutritional microorganisms, similar to ordinary algae. Its reproduction is mainly fission, and a few species have spores. Filamentous cyanobacteria can also be broken to form segmental colonies for series connection, and there is no sexual reproduction. Cyanobacteria have phototaxis (moving to light under low light intensity and moving to backlight under high light intensity).

Cyanobacteria have a * * * feature, that is, most of them have air cells, which are composed of hollow membrane subunits, namely air cells, arranged in a pile, and the walls of air cells are composed of insoluble protein. Its strength can withstand 200KPa, beyond which the airbag will burst. The airbag increases with the growth of algae age, and its main function is to provide buoyancy for algae to float on the water surface, so that algae can easily spread in the water. Some blue-green algae (such as Microcystis aeruginosa) can use light to adjust their buoyancy, but the buoyancy at night is uncontrollable. )

Harm of cyanobacteria: cyanobacteria have strong adaptability to the environment and fast reproduction. In eutrophic water, it can multiply in large quantities, causing the following main hazards: (1) forming water bloom, affecting the oxygen enrichment of water, leading to the death of aquatic animals such as fish, destroying the ecosystem, and (2) generating odor. Many unpleasant smells often appear in eutrophic water bodies, most of which come from algae, which not only pollutes the air, but also makes tap water have an odor, affecting drinking and human health. It will also reduce the quality of industrial products related to water. (3) Many toxins produced by algae belong to cyanobacteria, such as Microcystis aeruginosa. Drinking water containing toxic algae, such as ANABAENA bloom and red algae bloom, will kill wild animals and livestock, and will also cause harm to human health.

Microcystin is a kind of polypeptide toxin produced by poisonous algae in water, in which the isomers of microcystin LR and YR (microcystin MC-LR MC-YR) are the main toxic components. The acute toxicity test of microcystin showed that microcystin could cause congestion and swelling, and pathological observation showed that the liver was severely congested, bleeding and flaky necrosis, indicating that the liver was the target organ of microcystin. Microcystins can promote the proliferation of hepatocytes. Microcystins alone can not activate the expression of GSTPi gene, but can promote the expression of GSTPi gene that has been started, thus promoting the occurrence of liver cancer. (GB 0.00 1 mg/l)

The experimental study on cyanobacteria shows that although algae cells can also release toxins (40%) during the growth period, most toxins are released when cells are aging and dying (60-80%).

Microcystin MC-LR is biodegradable in environmental water, and its half-life is about one week. (In 2002, in view of the fact that the determination of algae cell density is easier than MC-LR, the School of Public Health of Fudan University in Shanghai put forward the safety limit, warning limit and danger limit of algae density in drinking water sources according to the relationship between the results of algae density determination and MC-LR for many years. On May 17, 2005, the National Environmental Hygiene Standards Committee organized by the Ministry of Health determined the limit value of cyanobacteria density in drinking water sources proposed by the Institute as 9.1X105/L, and reported it as the recommended draft national standard. )

Cyanobacteria usually breed at the turn of spring and summer, and are easy to grow in water with water temperature 15 ~ 30℃, PH greater than 8, COD Mn greater than 5mg/L and nitrate nitrogen higher than 0.12 ~ 0.13 mg/L.

1), adsorption pretreatment (odor)

A dosing device of powdered activated carbon was established, and powdered activated carbon was used to remove color and odor substances from water at home and abroad. Successful experience has achieved ideal therapeutic effect. The dosage of powdered activated carbon is related to the turbidity of water and the concentration of odor-producing substances, which should be determined according to the water quality characteristics. As a pretreatment method, powdered activated carbon has a relatively high operating cost, and is generally used as an emergency measure to solve the sudden deterioration of water quality.

Powdered activated carbon is widely used in water treatment in Europe and America, and the dosage is generally 2-5 mg/L.

(2) Chemical pre-oxidation treatment

1, potassium permanganate (algae)

Potassium permanganate (KMNO _ 4) is a strong oxidant, but its disinfection ability is weak (according to the data, the pre-oxidation of KMNO _ 4 will not cause the release of microcystins). The oxidation of KMNO _ 4 can control the formation of chlorophenol and FHMs, and has a certain removal effect on color, odor and taste, as well as olefins, aldehydes and ketones. However, in the oxidation products of potassium permanganate oxidation, after chlorination, the mutagenicity of water is greatly increased, and it is necessary to combine it with powdered activated carbon to achieve very ideal results. Generally, the dosage will not exceed 1mg/L, and the cost per ton of water is 0.02 yuan.

2. Chlorine dioxide (organic matter)

Chlorine dioxide (CLO2 _ 2) is highly oxidizing. Pre-oxidation can effectively destroy algae and phenol and improve the smell of water. Studies have shown that chlorine dioxide kills and breaks algae, and releases a lot of microcystins into water and produces odor (soil odor, 2-MIB). The instability of chlorine dioxide needs to occur on site, which requires higher operators. The general pre-oxidation amount is 1-2 mg/L, and the cost per ton of water is 0.024-0.048 yuan.

3. Biological pretreatment

With the help of the metabolic activities of microbial communities, the initial removal of organic substances such as ammonia nitrogen and nitrite is very beneficial to the subsequent conventional treatment. The change of water quality, water temperature and water quantity and the level of operation and management directly affect the effect of water treatment. Now it is widely used in Shanghai, Shenzhen and other places, but in the northeast, the water temperature changes by 30℃-2℃, especially in spring, autumn and winter.

According to the data, when the water temperature is lower than 10℃, the removal rate of ammonia nitrogen is only 10 ~ 15%. When the concentration of ammonia nitrogen in raw water is less than 1mg/L, the removal rate of ammonia nitrogen is less than 50%.

Features: high requirements for operation and management and large investment.