Read and translate the text. CITY GARBAGE: PROBLEMS AND SOLUTIONS

CITY GARBAGE: PROBLEMS AND SOLUTIONS

PART II

SOLUTIONS: HOW IS THIS DONE?

Experts have developed many productive processes which make it possible to reconvert mountains of garbage into substances that are of crucial importance to industry and agriculture. Among such enterprises is the St. Petersburg automatic plant which processes solid domestic wastes. It alone “gobbles up” 35 - 40 per cent of the city’s tips - 900000 cubic meters.

The garbage is first fed to belt conveyers, where magnetic separators extract ferrous metals from it, which are subsequently pressed into compact briquettes and shipped to metallurgical plants for resmelting. Domestic wastes in particular tin cans (and other discarded objects as well) also contain valuable materials like copper, zinc and brass. Until recently they were extracted in the metallurgical plants which receive the briquettes, but now this is being done in the automatic plant itself in special newly built departments.

Refuse relieved of metal then goes into biothermal drums — enormous cylinders up to 60 meters long and four meters in diameter. They slowly rotate, mixing the waste. The air which is fed into the drums provokes an intensive aerobic process. Under the action of microorganisms all the garbage’s organic components decompose. The temperature of that is no longer waste, but is known as the compost mass, rises up to 60-70° C. As a result, the disease-producing microbes die and the substance in the drums becomes harmless.

In 48 hours the compost mass ripens. Nevertheless, it still contains a wide variety of particles and fragments which biothermal treatment leaves unchanged. In order to dispose them the mass is sifted through giant sieves where the material processed in the biothermal drums is separated into compost and ballast. Now the main thing is to get rid of glass fragments – the enemy number one of compost. Obviously, fertilizer containing glass fragments cannot be introduced into soil. However, if they are reduced to the size of grains of sand and rolled smooth, they can no longer harm the roots of future plants.

That is why, all the material sifted through the giant sieves goes into a vertical shaft in which it gets into an upward air current. The light particles mostly organic ones are carried off. The glass and ceramics fragments which are left go to the grinding zone.

The ballast like rubber, plastics and wood fragments (this type of refuse accounts for almost a quarter of all domestic waste) had to be taken back to the garbage dumps. But nowadays even this ballast is processed by pyrolysis - the thermal disintegration of complex substances into simpler ones. As a result valuable products are obtained, such as fuel gas, bituminous resins and solid carbonaceous compounds, which in our day become widely used as graphite substitute in metallurgy.

The plant’s final and main product is compost. It looks like ordinary soil. In fact, it is a biologically, active substance which can be used far more effectively than an ordinary fertilizer. Due to a high temperature it is possible to employ it as a biological fuel to heat the soil in hot-houses. The compost’s biological energy is sufficient to grow two crops. After that it can be transferred to open ground as an ordinary fertilizer.

Such plants could improve ecological situation around cities by recycling of everything contained in city dumps to restore valuable materials to the national economy. Moreover, they neither pollute the environment in any way nor even consume water for their technological requirements.

8. Match the processes in A with the corresponding devices/units in B:

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