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  • 一般

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    • Professor Seki retired from Hokkaido University in March, 2024.

  • Dissolved Matter and Suspended Solid

    • Definition in industrial wastewater test method

      Suspended Solid, SS

      Substance passing through a 2 mm filter

      Substances that remain on a filter with a pore size of 1 mm

      Dissolved Matter, DM

      Substances that pass through a filter with a pore size of 1 mm

      *Suspended solids are abbreviated as “SS” below.

    • Typical SS separation method

      Filtration

      Flocculation

      Centrifugation

      Cyclone

    • SS aggregates with increasing salt concentration

      川から流入した泥土が沿岸で凝集・沈殿しています。

      Mud that flows in from the river is coagulating and sedimenting along the coast.




    • SS industrial wastewater standards

      •Kobe：40 mg/kg

      •Kawasaki・Yokohama：70 mg/kg

      •Tokyo：120 mg/kg

      •Nagoya・Hakodate：200 mg/kg

      •Sapporo：300 mg/kg

      The reason why the standard values ​​differ depending on the region is that there are "uniform wastewater standards" set by law by the country and more stringent "additional wastewater standards" established by each local government.

    • Electric double layer that creates repulsive force between SS particles

      電気的に反発する微粒子は、凝集せずに安定に分散：Electrically repulsive particles are stably dispersed without agglomeration

      電気二重層：electric double layer

      電気的反発が及ぶ距離：Distance of electrical repulsion



    • surface charge of suspended solids

      Marshall, Aust. H. Biol. Sci. (1967) 

      Huang & Lin, Adsorption from aqueous solutions (1981)

      正電荷：positive charge　負電荷：negative charge　微生物：microbe　泥粒子：biofluid

      ほとんどのSSが中性で負に荷電：Most SS negatively charged when neutral.

    • silica SiO₂ (It is the same substance as the silica gel of the desiccant.)

      dry state

    • the case of silica, SiO₂

      state of absorbing water

      Hydrogen ions dissociate in water and silica has a negative charge.

    • Mechanism of flocculation

      Mechanism of action of polymer flocculants

       

      高分子凝集剤：high polymer agglutinate

      微粒子と逆の電荷をもつ高分子(凝集剤)を加えると粒子表面に吸着し、凝集剤が微粒子を架橋し大きな凝集体を形成して速やかに沈降します。：When a polymer (flocculant) with an opposite charge to that of the particles is added, it is adsorbed onto the particle surface, and the flocculant cross-links the particles to form large aggregates that settle out quickly.


    • Development of biodegradable flocculants

      ＜Conventional flocculant＞

      Inorganic: PAC, aluminum sulfate, iron sulfate, etc.

      Organic: polyacrylamide, etc.

      ＜problem＞

      Carcinogenicity of Unreacted Monomers in Polyacrylamide

      Aluminum inhibits plant root growth

      ↓

      Development of biodegradable flocculants that are safe for living organisms and the environment

      ＜Efforts of our laboratory＞

      Development of "biodegradable flocculant" using protein as raw material

      Raw materials include chicken egg whites, milk, soybeans, scallop processing waste, etc.



  • Flocculation of diatomite

    • diatomaceous earth

      Diatomaceous earth is a fossil of diatom plankton, and more than 95% of its components are SiO2. It is common mud in Japan, found in paddy fields.

    • Frequency Distribution Curve

      This is the particle size distribution of diatomaceous earth. The mode diameter is 10-20 μm.

    • Aggregation experiment of diatomaceous earth with biodegradable coagulant

      We use a flocculant made from soy protein. The amount of coagulant added is 1% of the mass of diatomaceous earth.

      添加:addition　無添加:additive-free

      10sec. →20sec. →30sec.


    • Practical example: Ultra-high-speed coagulation-sedimentation equipment

      pH調整剤:pH adjuster 凝集剤:agglutinant 急速撹拌:Rapid agitation 凝集槽:agglomeration tank　緩慢撹拌:Slow agitation 沈降槽: sedimentation tank


    • Use of biodegradable flocculants

      Using conventional flocculants, SS becomes industrial waste that costs a lot of money to dispose of.

      Company A (soybean processing, West Japan)

      •Total wastewater: about 500 t/day

      •Solid waste (moisture content: approx. 50%): approx. 1 t/day

      •Treatment cost: landfill cost approx. 30 million yen/year + sewage treatment cost approx. 30 million yen/year

      Company B (surimi processing, Tohoku)

      •Total wastewater: about 500-800 t/day

      •Solid waste (moisture content: approx. 50%): approx. 5 t/day

      •Processing cost: 20,000 – 30,000 yen/t

      Company C (wheat processing, Tohoku)

      •Total wastewater: about 250 t/day

      •Solid waste (moisture content: approx. 50%): approx. 5 t/day

      •Processing cost: 20,000 – 30,000 yen/t

      Price of fishmeal for feed (1980~2010)

      The price of fishmeal, which is the main ingredient of aquaculture feed, is soaring.  We believe that if wastewater from food processing plants is treated with a safe protein-derived coagulant, the recovered SS can be used as a substitute for fishmeal.

      Coagulation treatment of wastewater from wheat gluten manufacturing plant

      Agglomeration treatment of wastewater from tofu manufacturing plants

    • Aggregation Magnetic Separation Experiment Device 1 (self-made)

      Separation of microorganisms that do not easily sink even if they aggregate

      Magnetic fine particles are mixed with aggregates and separated with a magnet

      Mechanism of increase in laser light intensity when aggregates are removed

    • Apparatus 2 for coagulation magnetic separation experiment (homemade)

      A device that measures the rate at which aggregates form interfaces and settle.