Diatoms

The word "diatom" is unfamiliar to many people. In fact, diatoms exist in different forms in every corner of our lives, but it is difficult for the naked eye to detect them. When it comes to it, diatoms and diatom mud are most associated with it. In fact, diatom and diatom mud are completely different. Diatoms are widely used. Don't look at it (micron level), but it's full of treasures. Let's talk about the "secret" of diatoms in detail.

Diatom is one of the most abundant algae on the earth, with hundreds of thousands of species, and the common species is about 16000. It is a unicellular plant with a size of 0.6 μ m ~ 10 μ m and various forms. The diatom shell is mainly composed of silica with micro-nano structure, and its purity is above 98%. Diatoms are also the most important phytoplankton, which are widely distributed. Where there is water, there is water. Because of its variety and large quantity, it is called "grassland" in the ocean.

70% of the oxygen on the earth is released by plankton, which produces 36 billion tons of oxygen every year, accounting for more than 70% of the oxygen content in the earth's atmosphere. The number of diatoms accounts for more than 60% of plankton. Assuming that there are no diatoms on the earth now, the oxygen on the earth will be exhausted in less than three years.

Diatoms can not only produce oxygen, but also have high industrial application value. Micro-nano biomaterials extracted from diatom shells have the characteristics of high strength, impact resistance, high temperature resistance, aging resistance, corrosion resistance, sound insulation and heat preservation, and are unique high-purity bio-inorganic materials in nature. Diatom shell micro-nano biomaterial is a fine honeycomb multi-level porous structure with high specific surface area.

Since 2007, researchers at Georgia Institute of Technology have been developing a technology of genetically engineering pseudohyenas, hoping to use it to create a new silicon structure. By using gene replication technology to study the process of diatom building complex siliceous cells, the ultimate goal of researchers is to find a technology to make nanomaterials in the laboratory.

Looking at the whole field, the closed culture of diatoms in China is limited to research and small-scale production, and it is impossible to carry out large-scale industrial production because of the high production cost. Tubular reactor is the most common closed diatom culture device, and its construction and operation costs are high, so it is difficult to be used for general large-scale culture with low added value.

The state-owned enterprises in Germany use tubular photobioreactor to cultivate Chlorella, and the annual output of algae powder is 130- 150 tons, but it is difficult to maintain due to the production cost. There are not many kinds of diatoms in open culture in China, such as spirulina, Chlorella and Dunaliella salina. Because it is mainly used to produce high value-added products such as health care products and pigment extraction, it cannot be used as industrial raw materials in large quantities.

At present, there are two main types of photobioreactors used for diatom culture: closed and open. Closed photobioreactor mainly includes tubular reactor and plate reactor. Its main advantages are less pollution, easy control and high density of algae liquid, but its disadvantages are also very obvious, such as high operating cost, large consumption of cooling water and difficult cleaning management.

Open photobioreactor refers to an open pool culture system, which has the advantages of low operating cost, no cooling and easy management, but it is easy to be polluted by exotic organisms, unstable production due to weather and low culture density.

In order to solve these problems, Academician Wang, the chief scientist of the Bioengineering Center, an internationally renowned aquaculture expert and academician of the American Academy of Engineering, has devoted himself to the research of open-scale cultivation of diatoms for many years, and his technology has now reached the world leading level.

▲ Zhao Kai Bioengineering R&D Center Diatom Breeding Base

Academician Wang established and successfully operated a commercial system in the late 1990s to cultivate diatom-Chaetoceros in an open system. The diatom produced is used in aquatic feed industry, and applied for related patents in the United States in 2004.

On this basis, Academician Wang led the domestic team to develop targeted technical solutions to the problems of open reactors, such as vulnerability to foreign biological pollution, low output and unstable production, which effectively solved the above problems. Through reasonable design and independent research and development of diatom open culture system technology, the production and maintenance costs are reduced, high-density and continuous production is realized, and the technical bottleneck of closed photobioreactor and traditional open bioreactor is solved.

At present, using the diatom culture technology in R&D Center, the annual output of diatom culture can reach 120 tons per hectare (dry diatom powder), while the annual output of crops on land is mostly below 15 tons per hectare.

▲ diatom dry powder

The daily output of diatoms cultured in Zhao Kai Bioengineering R&D Center is affected by sunshine and temperature. Dry algae can be produced between 0. 1-0.2g per liter of water, and the maximum daily production can reach 0.4g liter. According to the effective working days of 300 days per year and the reactor depth of 0.3m, it can produce 1.20 tons of dry algae per hectare per year, and 36,000 liters of bio-oil can be produced by 30% oil extraction.

Diatom bio-oil can be used to produce biodiesel and aviation fuel. Aviation kerosene has strict requirements on calorific value, density and low temperature performance, and aviation fuel extracted from diatom can replace conventional aviation kerosene. After using diatom aviation fuel, the emissions of nitrogen oxides and hydrocarbons in tail gas can be greatly reduced, and the emissions of sulfide can be reduced to 1/60 of that of traditional aviation kerosene.

The characteristics of diatom scale production system in Zhao Kai Bioengineering R&D Center are as follows:

1. Open diatom species screening is systematic, and traditional diatom species bank and expanded culture are not needed.

2. Diatom culture formula innovation, target diatom selective directional culture.

3. The special algae control process ensures that the target diatom dominance reaches 96%, and there is no need to pretreat the influent.

4. Effectively control the feeding of plankton, and there will be no yield reduction and algae agglomeration caused by the feeding of enemy organisms during the culture process.

5. Diatoms can be cultivated in an open way under natural conditions, and they can be produced stably under high temperature, strong light, rain and other natural conditions, and there is no need to build greenhouses or disinfect water bodies.

6. The production cost is low, and it can provide a large number of low-cost diatom raw materials for deep processing, which has a strong economic competitive advantage.

The open culture technology of diatom developed by R&D Center also has great advantages in production cost, which can be extended to many industries that could not be applied before because of cost problems, such as bioenergy, bio-environmental protection, biomedicine, feed additives, food additives and so on.

The development of diatom culture and deep processing industry is of great significance, which is mainly reflected in the following five aspects:

1, diatom culture does not "compete with grain for land". In diatom production, coastal areas, beaches, swamps and saline-alkali land can be selected. Developing diatom culture will not reduce the grain planting area, and saline-alkali land can be gradually transformed into fertile land.

2. Diatom culture is a green industry. For every 1 ton of diatom produced, it can absorb about 1.6 ton of carbon dioxide and release 1 ton of oxygen.

3. Diatoms have high application value, can extract natural porous nano-materials and produce antibacterial and antitumor drugs, and have great application prospects in feed, chemical industry and other industries.

4. Harmful chemicals such as herbicides and pesticides are not used in diatom production, and there is no adverse environmental impact.

5. Diatoms contain about 1/3 diatom shells, 1/3 plant proteins and 1/3 oils, all of which have high application value. Diatoms are high-quality sources of plant proteins and oils.

In a word, the development and application of diatom will be an extremely huge eco-industrial system and a revolution in the field of materials, which will not only meet the needs of all kinds of high, refined and cutting-edge materials in China, but also play a great role in industry, agriculture, national defense, medicine, food and energy security.