RUBBISH

Press, Volume CXV, Issue 34022, 11 December 1975, Page 7

RUBBISH

•FOCUS*

Many people are starting to think that rubbish is too valuable to throw away. Yesterday's trash is already regarded b.g many as today's prized source of materials and energy. Practically every raw material is shrinking in quantity and increasing in price. The answer, in the view of many experts, is not to throw away waste products but recover raw materials from rubbish for use in new products.

JI hat's in rubbish?

Three different sorts of materials are found in most rubbish — solid materials which will not bum, like metals and glass, combustible materials like paper and wood and organic materials like food wastes. Most recovers programmes today are geared to extracting solid materials which will not bum and either extracting or burning the other materials.

The first stage of almost any recovery programme is to shred the rubbish for easier separation.

After shredding, giant magnets can be used to pluck out ferrous metals like iron and steel. Aluminium can be separated by using a special electrostatic field. Blasts of air are used to blow off the paper and other lightweight. combustible materials, which can either be recycled into new products or burned as fuel. In a final

stage, an optical scanner can be used to sort glass fragments by colour, a necessary step for efficient recycling by the glass industry. . .

The biodegradable, organic portion of the rubbish can be composted to give a fertile soil.

Christchurch’s rubbish

People in Christchurch throw away about 80,000 tons of rubbish a year with a volume of about 400,000 cubic yards. At the Christchurch City Council's Bexley dump alone about 15 acres of land are covered to a depth of 10ft every year. Like the rubbish of most cities, Christchurch’s rubbish is a mixture of ashes, paper, food wastes, metals, glass, rags, plastics, rubber and organic garden rubbish. Probably about half of it, by weight, is paper; food wastes and other organic matter probably make up between five and 10 per cent and glass and metals about the same. The remainder is an odd mixture of cloth, rubber, plastics and other items. These figures are vague because noone has yet made any effort to find out just what there is in the 80,000 tons of rubbish thrown out in Christchurch each year. Even though the amount is relatively small by the standards of other developed countries, and even though no-one knows exactly what there is in Christchurch’s rubbish, there are probably significant amounts of various materials which could be recovered from the rubbish for reuse. The new scheme which has been proposed for the disposal of rubbish produced- in Christchurch does no more than make more efficient the collection and disposal of the rubbish. The rubbish is still used merely as landfill, and no effort is to be made to recover materials which can be reused from the rubbish or to extract the energy which can be found in it.

But the second stage of the new scheme does provide for the rubbish to be “shredded,” that is ground up and reduced to smaller pieces, and shredding is a necessary first step for most of the recovery processes described in this article.

Energy from rubbish

The most valuable resource to be found in rubbish may be energy. Energy can be recovered from rubbish in the form of heat by burning the rubbish, either in its “raw” state or after valuable materials which will not burn, like metals and glass have been taken from it. If the “raw” rubbish is burned in an incinerator or used to fire a boiler, the other useful materials in the rubbish can be extracted from the residue. Until a few years ago, rubbish was burned in Christchurch in an incinerator east of Manchester Street and the heat produced used to warm the water for the old Tepid Baths. Using rubbish as a fuel in incinerators generally creates more air pollution than people are willing to accept today. But new plants are being built which produce heat by burning rubbish without creating too much air pollution. A plant in St Louis, Missouri, in the United States bums rubbish which has been ground up after having the metals removed from it. The ground-up rubbish is used along with pulverised coal to fire boilers to create steam which is used to drive generators. About 350 tonnes of rubbish a day are burned in the plant. A much more advanced technique for extracting energy from rubbish is

pyrolysis. Organic rubbish Is heated in the absence of air to a temperature between 400 and 900 degrees Centigrade. Gas and oil are both given off and can be collected for use as fuels. A pilot scheme in San Diego, California, is expected to produce about one barrel of fuel oil from each ton of rubbish fed into the plant.

Plastics, rubber, paper, and glass

Each product that ends up in the rubbish tin presents its own problems of disposal or recycling. Plastics and rubber pose particularly difficult problems. Plastics do not degrade naturally in the environment and emit a noxious gas when burned. New varieties of plastic may be developed that decompose after use or can be burned without harmful side effects.

Burning old tyres also contributes to air pollution. Alternatives to burning waste rubber range from grinding it up and mixing it with asphalt to pave roads to heating it at high temperatures to produce fuel oil.

Much of the rubbish thrown out by New Zealanders is paper. Paper can be recycled relatively easily to produce cardboard and fibre boxes. New Zealand Forest Products already recycles about 43,000 tons of waste paper a year at three plants in New Zealand. By 1980 the firm expects to be recycling about 100.000 tons of waste paper a year.

Experiments are being done using micro-organisms which feed on wood pulp or waste paper and produce glucose which can be changed by further processing into food (a sugary syrup) or fuel (ethyl alcohol). One of the ways to deal with the problem of valuable resources being thrown away as rubbish is to stop the items being thrown away in the first place. This is especially applicable to glass. New Zealanders are still quite familiar with returnable bottles, but in the United States throw-away containers have, in recent years, almost completely replaced returnable bottles. The state of Oregon, in the northwest of the United States, recently outlawed flip-top cans and ordered merchants and manufacturers to offer refunds on bottles. The aim was to reduce the amount of litter in Oregon. Once glass is thrown away in rubbish, however, its recovery is not easy. In an experiment in Yorkshire it was found that the cost of collecting glass which people had thrown out was six times what the scrap glass could be sold for. Encouraging people to take glass to collection centres and keep it separated by colour can reduce these costs of collection considerably.

Old cars

Old cars are a relatively easy form of “rubbish” to deal with because they contain high concentrations of a few fairly valuable materials and because they can be collected into one place relatively easily. One million cars are junked each year in the United States, and recovering materials from them is now a big business there. At salvage yards

the car's battery, radiator, gas tank and tyres are removed and the remainder flattened (for ease of transportation), shredded and fed into furnances.

Car crushing and shredding facilities are expected to be set up in New Zealand in the near future. The scrap steel is needed for the process used by New Zealand Steel, Ltd. at its Glenbrook Steel Mill. Some scrap has to be imported at present to keep the mill’s furnaces operating.

Problems of recycling

It costs money to recover materials from rubbish, often 'so much money that materials produced from rubbish are more expensive than materials produced from raw materials. It is often difficult to find markets for recovered materials which will pay the costs of recovery.

A major hurdle for large-scale recycling is therefore economic. If there are no readily available markets for used paper, glass and metals, then attempting to recycle the materials can cost more than simply dumping them as landfill.

It was on these grounds that the engineers connected with the local bodies in Christchurch found it impossible to include full-scale recovery efforts in their plan for the reorganisation of the collection and disposal of Christchurch’s rubbish. The over-all costs of any recovery programme are greatly affected by the costs of collecting the rubbish. The more efficient, and cheaper, the system of collection is, the better chance there is that the materials recovered can be sold at a price which makes them competitive with materials produced from raw materials. Eventually pipeline systems may be used to transport rubbish which has been crushed and ground in the home to central processing stations where valuable materials can be recovered. This would amount to disposing of household rubbish in much the same

way as sewage is disposed of at present.

It would also be much easier to recover from rubbish materials which could be used again, if the composition of the rubbish was the same and if it was produced in the same amounts week by week. But the composition and rate or p oduction of rubbish both vary greatly from one week to the next in most cities. Recovery of reusable materials from rubbish is only ease when there is a relatively steady supply of relatively uniform rubbish.

But the recovery of materials from rubbish has certain long-term advantages. Recycling materials from rubbish reduces demand on natural resources and also, frequently, means re-

duced consumption of energy as well. Manufacturing new paper from used paper rather than wood pulp requires 60 per cent less energy and creates much less water and atmospheric pollution. Making steel from scrap consumes about 75 per cent less energy and cuts air pollution by over 80 per cent.

Recycled glass melts faster and at a lower temperature than glass manufactured from raw materials, while reused aluminium requires a mere 5 per cent of the electrical energy needed to process bauxite.

I dustbin holiday

To some extent rubbish is only a valuable source of materials because people in rich countries like New Zealand throw things away which people in poorer countries would use or conserve.

This story, reprinted from “1 he Sunday Times” of London, shows just how much that is useful or reusable is thrown away by people who have more than enough for their needs. But on health grounds it would be most unwise to follow the example of the two Norwegian students whose "dustbin” tour of Norway is described in the article. Two highschool students from the

Norwegian oil capital of Stavanger have recently completed a fortnight s holiday living out of other people s dustbins. They report that it was a very tasty gastronomic tour. Torbjoern Groenning. 16. and K. bjoem Opstad, 18. had planned tr ine as cheaply as possible 1 hey travelled by bike with their fishing rods intending to live off what they taught and wild berries, buying only strict essentials. They claim it was just a coicidence” that led them to look into one of the dustbins by the roadside "Before we went to fish for our supper on the first afternoon, we threw away some rubbish Inside the dustbin near Helleland, they discovered four eggs, half a packet of paprika-flavoured crisps, four ham sandwiches, a tin of mackerel, two litres of skimmed sour milk, three different cheeses, one kilo of strawberries and an unopeneed can of Californian fruit salad. They also found a tube of sausage meat, half a kilo of margarine, a jar of plub jam and several loaves of bread I'he boys decided to turn their holiday into an investigative dustbin crawl. Their journey at the height of the tourist season took them from Stavanger, on Norway's south-west coast, to Mandel, a resort 180 miles further south and then revelations have since shocked Norwegians into thinking about how much they waste. There was one recurring practical problem: the heat. Torbjoern explains: "We could feel the ashphalt melting under our bikes. So we never touched food that was not well-wrapped We preferred unopened things and submitted anything else to a strict smell-ing-test." This article was written hy .1. M. Wilson, a member of the staff of "The Press."

7 his is the last occasion on which "Focus" will appear this rear.