Wastewater Characteristics and Treatment Challenges
Wastewater Characteristics and Treatment
Types of Wastewater
Whitewater
Characterized by intermittent flow and significant pollution in the first 15-30 minutes of production. Pollutants include atmospheric deposits, waste, garbage, traffic residues (hydrocarbons, lead), garden contaminants (biocides, fertilizers), and other water pollutants.
Sewage
Characterized by more regular flow and pollution than whitewater, with lower volumetric quantities. Predominant components include organic compounds (proteins, sugars, urea, fatty acids, oils), salts (bicarbonates, sulfates, chlorides, nitrates), gases from organic matter decomposition (methane, hydrogen sulfide), bionutrients (nitrogen, phosphorus from detergents), and microorganisms (coliforms, streptococci, viruses).
Urban Wastewater
Includes domestic water from housing and services (kitchen, bathroom, washing, sewage), shops, and surface runoff (stormwater, sanitation, irrigation). It can also include wastewater from industries within urban areas.
Industrial Wastewater
Includes discharges from early production processes, heat exchange, and other facility discharges.
Agricultural Wastewater
Includes water for irrigation, livestock waste (manure), and water used in livestock rations and cleaning. Diffuse pollution from agriculture is difficult to treat. In Spain, each hectare of irrigation demands 6000 m3 of water per year. Runoff can contaminate groundwater and surface water. The use of synthetic fertilizers and intensive farming has increased agricultural pollution.
Livestock Wastewater
Originates from housed animal breeding. Studies show the pollution equivalence of housed animals to human contamination in terms of BOD:
- 500 kg stabled cow: 12-18 population equivalents
- 60 kg pig: 2-5 population equivalents
- Laying hen: 0.1-0.2 population equivalents
Characteristics of agricultural wastewater include dissolved salts from fertilizers, suspended solids, organic matter, nutrients, disinfectants and detergents (livestock), and traces of pesticides.
Negative Effects of Agricultural Discharges
Effects on Receiving Environments
Sewage discharge causes negative effects such as:
- Infections from pathogens
- Toxicity from organic, inorganic, and radioactive substances
- Deterioration of taste and smell of water for human consumption
- Persistent organic compounds
- Phosphorus compounds
- Mineral oils and hydrocarbons
- Cyanides and fluorides
- Substances affecting oxygen balance (ammonia, nitrites)
Problems Related to Wastewater Treatment
Attacks on Water Pipes
Water aggressiveness in sewer systems depends on water characteristics and pipe materials (concrete, basket, cast iron, steel). Factors like contact time, velocity, flow rate, and ventilation influence material attacks. Acidic and alkaline substances, dissolved gases, organic compounds, temperature, and low hardness can contribute to chemical and electrochemical corrosion.
Blockages in Pipes and Facilities
Blockages occur mainly in small-diameter pipes and pumps due to insoluble deposits. Contributing factors include:
- Anions (hydroxide, carbonate, sulfate, phosphate)
- Temperature and total dissolved solids
- Organic substances (detergents, soaps, oils, fats)
- High concentrations of suspended solids
Emissions of Toxic Compounds
Dissolved gases, volatile substances, and reactive species in treatment facilities can cause inflammation, spontaneous combustion, or explosions. These include cyanides, hydrogen sulfide, halogens, volatile organic compounds (hydrocarbons, solvents), and reactive substances (cyanides, carbides, peroxides, chlorates). Wastewater factors (temperature, pH, concentration) and environmental reactions influence the danger level.
Inhibition of Biological Treatment
Organic and inorganic substances in high concentrations can poison microorganisms in anaerobic biological treatment. Wastewater containing these substances requires pretreatment to remove contaminants.