Hazards of High COD Levels in Wastewater
High COD (Chemical Oxygen Demand) in wastewater can cause multiple adverse impacts, mainly affecting the ecological environment, human health, and industrial and agricultural activities. The major hazards are summarized as follows:
1. Impacts on the Ecological Environment
Depletion of Dissolved Oxygen:
Excessive COD indicates a high concentration of organic matter in water. During biodegradation, these organics consume large amounts of dissolved oxygen (DO), leading to hypoxic conditions that inhibit the growth and survival of aquatic organisms and may cause mass mortality, disrupting aquatic ecosystem balance.
Accelerated Water Quality Deterioration:
As DO decreases, organic matter decomposes more rapidly, generating toxic by-products such as ammonia nitrogen, further degrading water quality and intensifying harm to aquatic life.
Eutrophication:
Nitrogen and phosphorus contained in organic matter can promote excessive algal growth under suitable conditions, resulting in algal blooms or red tides. These phenomena consume large amounts of DO and may release toxic gases such as hydrogen sulfide and methane. Dense algal coverage also blocks sunlight, inhibiting photosynthesis of submerged plants and further destabilizing aquatic ecosystems.
2. Impacts on Human Health
Threats to Drinking Water Safety:
Drinking water sources mainly include rivers and lakes. Elevated COD levels indicate the possible presence of harmful organic pollutants such as heavy metals, pesticides, and chlorinated hydrocarbons, which are difficult to completely remove during water treatment. Long-term exposure may damage the gastrointestinal tract, liver, and nervous system, and may even increase cancer risk.
Skin and Gastrointestinal Diseases:
Long-term contact with wastewater containing high concentrations of organic matter may cause skin disorders and gastrointestinal illnesses.
3. Impacts on Industrial and Agricultural Production
Industrial Impacts:
Many industrial processes require high-quality water. COD-exceeding water is unsuitable for such applications and may negatively affect production efficiency and product quality.
Agricultural Impacts:
Irrigation with high-COD water may lead to soil contamination, reducing crop growth and yields. Harmful substances may also enter the food chain, posing potential risks to human health.
4. Increased Treatment Load and Cost
Excessive COD increases the operational burden of wastewater treatment facilities, raising treatment complexity and costs. Additional investment in equipment and technology is required to meet discharge standards, which may place financial pressure on treatment plants.
