Waste Management in Spain: From Collection to Treatment
Residual Fraction: Pseudo-Total Metals Content
Digestion Methods for Assessing Metal Mobility
Digestion in strong acids, such as nitric acid, hydrochloric acid, or aqua regia, can estimate the maximum amount of metals potentially mobilized by changing environmental conditions. Aqua regia is a standardized method for environmental analysis, dissolving metal pollutants in non-silicate-bound forms and providing a good estimate of long-term leaching potential. To determine the total metal content, including those bound in the silicate matrix, hydrofluoric and perchloric acids or alkaline fusion are used by specialized laboratories.
Municipal Waste Collection in Spain
Municipal waste collection involves transferring waste to treatment plants. There are two main types of collection:
Non-Selective Collection
Mixed waste is deposited in containers without separation.
Selective Collection
Waste is separated by class and deposited in designated containers:
- Green container: Glass
- Blue bin: Paper and cardboard
- Yellow bin: Packaging
- Gray or brown container: Organic waste
Additional services, such as collection points and eco-points, often handle hazardous waste from homes.
Collection Methods
Vehicle Collection: Trucks with compacting hoppers collect waste.
Air Collection: Requires substantial initial investment in underground facilities, feasible in new development areas.
Waste Treatment
Waste is transported to transfer stations, sorting plants, recycling facilities, energy recovery plants, or landfills. The selection process utilizes various systems:
- Ferrous metals: Magnetic fields
- Non-ferrous metals: Manual triage and eddy currents
- Paper and paperboard: Manual triage
- Hard plastics: Manual triage
- Plastic film: Pneumatic systems
- Stained glass: Manual triage
- White glass: Manual triage
- Organic matter: Excess from other processes
Treatment options depend on the nature and status of the waste and the management model implemented:
- Recycling
- Energy recovery
Biowaste: Types, Properties, and Treatment
Types of Biowaste
- Waste from agriculture, horticulture, aquaculture, forestry, hunting, fishing, food preparation, and processing
- Waste from wood processing, panel and furniture production, pulp, paper, and cardboard
- Waste from leather, fur, and textile industries
- Waste packaging, absorbents, wiping clothes, filter materials, and protective clothing
- Waste from waste management facilities, off-site wastewater treatment plants, and water preparation
- Municipal wastes, including separately collected waste
Properties of Biowaste
- Carbon provides the primary energy source
- Nitrogen quantity determines microbial population growth
- C:N ratio of 30:1 is optimal for microbes
- Phosphorus and potassium levels determine compost quality
- C/P ratio of 100:200 is desirable
Treatment of Biowaste: Composting
Composting is a bioprocess that decomposes organic matter into a stable, sanitized, humus-like material rich in organic matter and free from offensive odors.
Quality Classes for Compost and Digestate
Parameters analyzed include dry matter, organic matter, bulk density, heavy metals, phosphorus, potassium, and calcium.
Comparison of Anaerobic and Aerobic Treatment of Biowaste
Anaerobic treatment decomposes organic matter in the absence of oxygen.
Aerobic treatment decomposes organic matter in the presence of oxygen.
Advantages of Anaerobic Treatment
- Less energy required
- Less biological sludge produced
- Lower nutrient demand
- Smaller reactor volume
- Biomass acclimatization allows transformation of most organic compounds
- Rapid response to substrate addition
- Effective sanitation and disease removal
Disadvantages of Anaerobic Treatment
- Longer start-up time
- May require alkalinity and/or iron addition
- Biological nitrogen and phosphorus removal not possible
- Sensitive to lower temperatures
- May require heating
- Potential for odors and corrosive gas production
- May require further aerobic treatment