Types of biofuels. Household waste. Scheme, description

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Types of biofuels. Household waste. Encyclopedia of radio electronics and electrical engineering

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Encyclopedia of radio electronics and electrical engineering / Alternative energy sources

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City sewage treatment plant systems include aerotanks. In them, activated sludge additives are mixed with sewage water, the microorganisms of which use the organic matter of wastewater for nutrition and reproduction. These are aerobic microorganisms; for their development, air is pumped through the water of the aerotanks. Further, water with activated sludge enters the settling tanks, then the sludge is pumped into piles-methane tanks, where anaerobic methane digestion of organic matter takes place. The released gas contains up to 55% methane and can serve as fuel in boiler plants. Solid residues are compacted and dewatered in filter presses and deposited in sludge beds. Sludge can be used as fertilizer and as fuel. In Japan, 55% of sludge is burned, in the USA 27%. There is experience of incineration of sludge in boiler plants at wastewater treatment plants in St. Petersburg.

Modern cities produce a huge amount of municipal solid waste (MSW). By the end of the 3th century, the world production of MSW reached 4,5 billion tons per year; in St. Petersburg, 3 million m7.12 are placed at landfills per year. Solid waste includes combustible substances - waste paper, food waste, wood, their calorific value is 200 MJ / kg. Waste in landfills is processed by microorganisms with the release of methane. The total amount of anthropogenic methane emissions into the atmosphere from wastewater treatment plants, landfills, oil fields exceeds 55 million tons per year, and methane, like carbon dioxide, is a greenhouse gas and contributes to global warming. In the United States, several thermal power plants operate on landfill biogas. The waste is compacted, perforated polyethylene pipes are laid on them and covered with a film. The gas sampled by the pipes contains up to XNUMX% methane.

In a number of developed countries, separate collection of waste is practiced at the places of their generation. Recycling of waste paper and glass from MSW reaches 50%. After the separation of secondary resources, incineration of MSW in special boiler plants is increasingly used in world practice. In Sweden, the volume of incinerated MSW reaches 60%, in Switzerland - 75%, in Japan - 80%. Slag (up to 300 kg per ton of MSW) is sintered, which makes it non-toxic, and buried. The gaseous products of combustion are carbon dioxide and water vapour. Co-incineration of MSW with sludge from sewage systems is possible. The first combustion units are operated in St. Petersburg.

Author: Labeish V.G.

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Why do dinosaurs have a long neck 10.09.2000

Both artists and filmmakers usually depict long-necked lizards - diplodocus in the pose of a giraffe, when the giant stretches its small head to the tops of trees, eating juicy foliage and other gifts of flora. But is this how these communities were fed?

Two researchers from the University of Oregon (USA) argue that dinosaurs fed in a completely different way, and their long necks did not serve them in order to get food sent by nature "from above". It is likely that the computer model created by scientists will help put an end to the protracted paleontological dispute.

Previously, it was believed that, for example, sauropods had a curved neck, and they carried their heads high above the ground. There was a dispute about how the blood supply to the giant's head was carried out. One of the hypotheses even said that such lizards had several hearts, which by common efforts raised blood to a great height. Now, however, computer simulations have shown that long-necked lizards were most comfortable holding their necks parallel to the ground, even slightly lower, with a gentle slope forward. The head was as if drooping and almost touched the ground with its nose.

In addition, the necks turned out to be much flimsier than previously thought. Diplodocus, for example, barely had the strength to raise his head, but Apatosaurus could hardly move his head either in a vertical or horizontal plane. Therefore, it is unlikely that these colossus ate like modern giraffes - they rather grazed in the manner of cows. In this case, the question arises: if long necks were not needed for eating the tops of trees, then why are they so long?

There is a hypothesis according to which these giants lived mainly in water, where the law of Archimedes lightened their weight. Then a long neck was needed for breathing.

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