The integrated recycling plant for non-toxic urban wastes

Thursday, November 23, 1995

Integrated Recycling Plant for non-toxic Urban Wastes schematic
Due to the great variety of recycling plants in Ontario and to avoid confusion in our schools, I will describe the layout of such a facility and the problems that may result when operators are inadequately trained in the principles of metallurgy, biology, physics and chemistry.

A fully integrated plant consists essentially of a materials recovery or recycling component, an enclosed in-vessel composting facility and a water treatment facility. At such a recycling plant trucks will deliver pre-sorted solid urban non-toxic wastes at an unloading door and release the wastes onto a conveyor. At this point, large objects such as rakes and broken furniture are removed manually. Blue-boxed papers are collected, baled and shipped to a manufacturer of newsprint. The continuous conveyor then takes the wastes also known as "material resources," into the building where cardboard is mechanically removed and baled. Improvised conveyor systems tend to break down frequently due to metal fatigue and wear.

The remainder of the materials then pass through a completely enclosed cylinder in which a rotating electromagnetic separator separates aluminum from iron. Infrared systems separate coloured from clear glass. Failure to install the infrared system is common and permits manual separation of the glass only. The sorted glass, iron, aluminum and plastic bottles drop into large steel containers which are emptied into trucks that ship the recyclables to secondary industries.

The materials recovery and composting facilities are built on concrete slabs made water-repellent by the addition of fine silica sand to the concrete mix and finishing coats of epoxy. Failure to properly seal the concrete will lead to eventual run-off of metals and ground contamination. Adjacent to the concrete slab one may see piles of leaves, grass clippings, brushwood, pallets and bins of kitchen wastes. These organics are shredded and fed into the in- vessel composter. The air extracted from the in-vessel composter is led through a biofilter and returned into the composter with additional air to enrich the decomposing organics with oxygen. An in-vessel composter contains 6 to 8 large concrete bays in which the organic materials are turned continuously by rotating flails. The organic mix, which may also contain sludges from the water treatment facility, is kept slightly moist and at a temperature of 60 to 80 degrees Celsius. Excess fluids drained from the composter are pumped into the water treatment plant after undergoing a resin-exchange treatment.

The water-treatment facility receives urban waste water as well as the excess fluid drained from the Materials Recovery Centre and from the composter. The water treatment facility contains screens that remove rags, pieces of wood and other large objects that flow down the urban sewage pipes. In the primary stage of the water pollution control plant solids settle to the bottom of settling tanks and are returned to the aeration units for further treatment.

In the secondary stage of the water pollution control facility bacteria and fungi will decompose the organic matter, provided the temperature, oxygen level, pH and metal levels are within limits acceptable to the microorganisms. Frequently water pollution treatment plants also provide decomposition in anaerobic digesters at temperatures about 60 degrees C. A product of digestion is methane gas which, if not too high in water content, is utilized as fuel to heat buildings in the winter time or to heat the plants' heat exchangers and boilers. While in the past the sludges from the water pollution control plants were spread on farmfields and golf courses, these sludges can now be returned into the in- vessel composter and mixed with the organic residues obtained from urban residences.

Worker comfort is an important consideration in modern integrated urban waste recycling facilities. While the electromagnetic separators and the conveyor belt in early systems tended to be noisy and produced noise of 90 to 100 decibels or more, requiring workers to wear sound-absorbing earmuffs, the modern plants produce ambient noises in the 50 to 70 decibel range. Integrated waste management facilities are usually kept at slightly negative pressures and are fully ventilated and moisturized, the air is filtered in dustbag chambers.

The entire process of recycling, composting and water treatment, under ideal conditions and perfect operation simulates the natural material cycles as these exist in nature.

Bessel J. VandenHazel, St. Thomas, Ontario