Classification of industrial and domestic waste by the degree of toxicity for soil

Any soil contamination directly affects yield and the safety of agricultural produce. Waste from manufacturing and human activity inevitably comes into contact with agricultural land. To assess risks to arable land, an agronomist must understand how waste is classified by its toxicity level and how its storage is organized in adjacent areas.

Hazard classes of waste and toxicity index

All waste is divided into municipal and industrial. There is no single scientific classification for industrial waste — they are grouped by industry, specific production processes, tonnage, or ability to catch fire or cause corrosion. However, for agriculture, the most important classification is based on toxicity, which determines the impact of chemical substances on the environment.

The primary safety guideline is the maximum allowable concentration of a substance in the arable soil layer (ПДКп). This indicator is measured in mg/kg of the chemical substance. This standard ensures that the amount of the element will not have a direct or indirect negative impact on the environment in contact with the soil, human health, and the soil's ability to self-purify.

To determine the toxicity class, the hazard index of an individual component (Ki) is calculated. The calculation is based on the ratio of the maximum allowable concentration of the substance in the soil (PDKi), the dimensionless coefficient of substance solubility in water (S), and the content of this component in the total mass of waste (SVi, in fractions of unity ≤ 1.0). From the results obtained, 1 to n leading components (where n ≤ 3) with the minimum Ki value are selected, after which the total toxicity index (KΣ) is calculated.

Waste collection methods and landfill technologies

Municipal waste is primarily removed by collection. In municipal services, collection via refuse chutes into storage chambers, accumulation in street containers, or direct loading into garbage trucks is used. There are also systems with underground pneumatic transport to compaction stations and the disposal of shredded waste via kitchen disposers into the sewage system.

Containers and waste collection chambers are unhygienic, as they attract pests and spread odors. Uncontrolled suburban dumps present a particular danger to fields, where waste decomposes and burns, poisoning the air. Furthermore, rainwater and meltwater wash toxins into groundwater and water bodies, from where they can reach irrigated areas.

Specially equipped landfills serve as a safe alternative to open dumps. For these, sites in clay soil are selected, or an artificial water-resistant screen is created to prevent the leakage of harmful leachate beyond the site boundaries.

• Landfill service life — from 20–25 years
• Excavation pit depth — about 1.5 m
• Thickness of the clay water-resistant layer — 0.5 m
• Height of the layer compacted daily — up to 2 m
• Thickness of the insulating soil layer — 0.25 m
• Maximum height of the landfill — up to 60 m

To prevent fires and the spread of pests, the compacted daily layers of waste are covered with soil every day. After filling, the landfill is covered with topsoil, on which orchards can be planted or parks can be established. Wells are necessarily drilled along the perimeter of the facility for constant monitoring of groundwater quality. To preserve valuable arable land, efforts are made to use ravines and other areas unsuitable for agriculture for landfills.

Biogas use and co-disposal of waste

In layers closed off from the air in a landfill, municipal and food industrial waste decomposes without oxygen. As a result of this anaerobic process, biogas is actively released — a mixture of methane and carbon dioxide. This gas mixture can be collected and used as an alternative fuel.

Only industrial waste that does not violate ecological safety is suitable for co-disposal. Substances that meet strict physical and chemical criteria are allowed for acceptance. At landfills, this waste is used for a practical purpose — to create intermediate insulating layers in embankments.

• inertness and low toxicity;
• biological oxidizability and easy decomposition;
• low solubility in water.