Waste classification and hazard
During consumption and industrial production, waste is generated, which is typically divided by physical state into solid and liquid, and by origin into municipal and industrial.
Liquid fractions include sewage (urine and feces) and slops from food preparation and washing. Municipal solid waste includes street sweepings, food scraps, household trash, manure, and animal carcasses. Solid industrial waste consists of materials that have lost their consumer properties, such as metal shavings or paper scraps.
An epidemiological threat is posed primarily by physiological excretions and slops containing pathogens. The sites of their accumulation attract synanthropic rodents (vectors of tularemia, plague, leptospirosis) and flies, which spread intestinal infections. In addition, sewage plays a key role in the circulation of geohelminth pathogens (ascariasis, ancylostomiasis).
Toxicological hazard is associated with the colossal volumes of garbage (about 120 million tons of industrial and 30 million tons of municipal waste are generated annually in Russia). Landfills and dumps accumulate pesticides, dyes, and heavy metals (lead, cadmium, mercury). This leads to massive contamination of groundwater, soil, and the atmosphere. This pollution is considered a "delayed" ecological factor: its consequences for human health may manifest decades later.
Populated area cleaning systems
Sanitary and municipal welfare requires the regular removal of garbage and sewage. Two basic systems are used for this:
- Water-carriage system (sewerage). This is optimal from a hygienic point of view, as it completely eliminates human contact with contamination. Liquid sewage is collected through toilets, sinks, and bathtubs, removed via pipe collectors outside the city limits, and disinfected. Sewerage can be domestic, stormwater, industrial, or combined.
- Removal-based system (conservancy). Used for removing both solid and liquid fractions. Liquids are collected in cesspools and septic pits (with a strict requirement for maximum groundwater protection), after which they are transported by vacuum trucks to spreading fields for soil treatment. Solid garbage is removed via house-by-house or scheduled curbside collection, where residents bring out waste at strictly designated times to the garbage truck.
Wastewater treatment methods
Collected wastewater cannot be discharged directly into natural water bodies. There are two approaches to its treatment:
Artificial method is implemented at specialized facilities and consists of three stages:
- Mechanical: removal of floating objects and suspended solids using screens, sieves, grit chambers, and sedimentation tanks.
- Biological: breakdown of organic matter in biofilters (aerofilters).
- Disinfection: final chlorination of water before discharge into a water body.
Industrial wastewater treatment is even more complex and may involve combinations of physicochemical and chemical methods.
Natural (soil) method is carried out in specially designated areas through natural filtration processes:
- Filtration fields: land plots allocated exclusively for the distribution and treatment of wastewater.
- Irrigation fields: plots where, after the completion of the treatment cycle, crops are grown. It is strictly forbidden to plant vegetables, berries, melons, and salad crops here. Only technical, cereal, and fodder crops, as well as trees, are permitted.
Soil self-purification
Soil is capable of independently ridding itself of organic compounds and pathogens that enter it. This natural process is called self-purification. Epidemiologically hazardous organics are step-by-step transformed into humus, inorganic minerals, water, and gases through processes of mineralization, nitrification, and humification.
Due to competition with saprophytic microbes and the action of sunlight, pathogenic bacteria are eliminated, and the toxicity of sewage disappears. Self-purification occurs in two modes:
- Aerobic: in the presence of abundant oxygen. Organics (proteins, fats, carbohydrates) are oxidized to carbon dioxide, water, and nitrates without the release of foul-smelling gases. From a hygienic standpoint, this is the most favorable process.
- Anaerobic: in an oxygen-free environment involving putrefactive bacteria. Accompanied by the release of foul-smelling hydrogen sulfide and ammonia.
It is important to remember that the soil's capacity for self-purification is limited. Only the waste load that does not disrupt the oxygen supply necessary to maintain safe aerobic processes is permissible.
Briefly: answers to topical questions
Which types of medical waste belong to classes B and V?
Class B medical waste includes hazardous (risky) waste, and Class V includes extremely hazardous waste.
- Class B — hazardous (risky) waste.
- Class V — extremely epidemiologically hazardous waste, which includes biological excretions of patients (sputum, urine, feces, etc.).
What are the four hazard classes of general waste (I–IV) according to their degree of toxicity?
The four hazard classes of general waste are classified by their degree of hazard.
- Class I — extremely hazardous waste.
- Class II — highly hazardous waste.
- Class III — moderately hazardous waste.
- Class IV — low-hazard waste.
What sanitary-chemical and bacteriological indicators are used to assess the degree of soil contamination?
Specific sanitary-microbiological indicator parameters are used to assess the degree of soil contamination, whereas specific sanitary-chemical parameters are not detailed in the text. Bacteriological parameters include:
- Coliform index — the number of bacteria in 1 g of soil.
- Perfringens titer — the smallest mass of soil in which Clostridium perfringens is detected (an indicator of old contamination).
- Enterococcus titer — an auxiliary indicator of fresh fecal contamination.
- Soil microbial count — the total number of microorganisms.
- Thermophile titer — bacteria growing at 60 °C (an indicator of manure and compost contamination).
Medical waste classes (in healthcare facilities) are easy to remember by the logic of increasing threat and specifics: A — Absolutely safe, B — Pathogenic (risky), V — Very high hazard (extremely hazardous), G — General industry (close to industrial waste), D — Dose (radioactive).
Class and exam questions
Why is the waterborne sewerage system considered the best?
The waterborne sewerage system completely eliminates direct contact of the population with liquid domestic and industrial waste at all stages of its transportation and disposal, which minimizes the risk of infection spread.
What is the hygienic difference between aerobic and anaerobic waste decomposition in soil?
The aerobic process occurs in the presence of oxygen and leads to the safe oxidation of organics without the release of foul-smelling gases. The anaerobic process occurs without oxygen and causes putrefaction with an abundant release of foul-smelling hydrogen sulfide and ammonia.
What crops are permitted to be grown on irrigation fields?
Only cereal, technical, and fodder crops, as well as trees, may be grown on irrigation fields after the completion of wastewater treatment. The cultivation of any vegetable, berry, salad, and melon crops is strictly prohibited.
What else to study on this topic
- Stages of biochemical oxidation of proteins in soil (from amino acids to nitrates involving nitrogen-fixing bacteria).
- Types of soil absorption capacity (mechanical, physicochemical, biological, biochemical).
- Sanitary indicators for assessing the quality of residential area soils (toxicological, parasitological, chemical).
- The role of soil in the life cycle of specific infection vectors (fleas, mosquitoes, horseflies).
- Infrastructure design of irrigation fields: water conduits, drainage ditches, tubular irrigators, and distribution channels.
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Other topics in "Chapter 3. Ecological and Hygienic Problems of Soil and Sanitation of Populated Areas"
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