Introduction to Waste Engineering

Waste Engineering Introduction

• Waste management steps: generation, collection, transport, and treatment.
• Generation/production refers to the source, sorting, and collection of the waste, usually before management.
• Waste treatment can occur at transport stations via mechanical processes like compacting or shredding.
• Treatment aims to reduce odor, volume, and impurities.
• Thermal treatment types include incineration and gasification/pyrolysis.
• Biological treatment includes composting and biogasification.
• Waste utilization methods include land application, construction materials, and fuel production.
• Materials Recovery Facility (MRF) plants process and recover recyclable materials from mixed waste.

Waste Management in Denmark

• Denmark produces 12 million tons of waste annually.
• Construction and demolition waste is the largest contributor (40%), followed by households (29%).
• Residential waste categories include household, garden, bulky, and hazardous household waste.

Solid Waste Issues

• Municipal solid waste has 20 categories.
• Main solid waste issues include space issues, collection challenges, health concerns, toxicity, differences in waste management systems and costs of handling.
• The EU waste strategy prioritizes prevention first and disposal (landfill) last.

Waste Characterization

• Waste characterization faces challenges: spatial variability, temporal changes, and uncertainties from sample mixtures.
• Characterization methods include physical, chemical, and performance testing.
• A disc screen is used to characterize organic waste.

Sub-sampling Organic Household Waste

• The process involves steps including shredding, mixing, and drying.
• It details the proportion of the various parts of the process in kilograms.

Waste Definition

• Waste categories are broad classes of waste with common characteristics, such as residential, commercial, institutional, and construction & demolition waste.
• Waste types are subclasses of waste categories with similar source and composition characteristics, like household waste, garden waste, bulky waste, and hazardous household waste.
• Waste quantities are commonly measured by weight or volume.
• Generation rates are essential parameters for waste management calculations, given as a quantity of waste per defined time frame and unit (e.g., kg of waste per year/person, kg per week/household).

Waste Minimization and Recycling/Prevention

• Waste minimization aims for the best reduction in waste production.
• Unit generation rates, in a weight measure, specify the quantity of the waste by a given unit of time and other key characteristics.
• Mechanical waste treatment utilizes technologies such as separation, reduction in size, and compacting at MRFs.
• These methods aim to facilitate handling and transport, improve treatment performance, prepare material for treatment, and sort recyclables.
• Composting involves controlling several technological factors/process factors and parameters, such as oxygen content, particle size, and aeration, pH, biodegradation, temperature, moisture content, and nutrients.

Composting and Anaerobic Digestion

• Composting steps include degradation, stabilization, and curing.
• Nitrogen transformation in composting involves microbial stages from organic waste to nitrates and nitrites which are converted back to nitrogen gas in anaerobic conditions.
• Hydrolysis occurs via extracellular enzymes on carbohydrates/lipids/proteins, is part of biogas formation.
• Biogas production stages are Hydrolysis, Fermentation, Acetogenesis, and Methanogenesis.
• Factors determining methane potential are Oxidation state and degradability.
• Anaerobic digestion system steps (AD): reception & storage, pretreatment, digestion, gas collection/utilization, digestate management.

Energy and Waste Treatment

• Incineration yields energy and heating, with percentages of 6% energy and 24% heating.
• LHV and HHV: energy content from combustion, LHV considers water evaporation only; HHV calculates total potential energy.
• Pyrolysis is thermal degradation of carbon in the absence of oxidizing agents.
• Gasification is partial oxidation of carbon in the presence of oxidizing agents.
• Combustion is the full oxidation of carbon.
• Air pollution control (APC) systems address dust removal, acid neutralization, etc., in incineration.
• Carbon Capture and Storage (CCS) involves energy recovery, material recovery, heat recovery, and stored CO2.

Solid Residue and Ash

• Incineration produces residues like fly ash, bottom ash, wastewater, sludge, and other neutralization products and grate sifting/boiler ash and economizer ash.
• Bottom ash is a mix of metals and other solid residues, formed during combustion.
• Fly ash is collected via electrostatic precipitators.
• Fly ash and bottom ash treatment can involve extraction, separation, thermal treatment, chemical stabilization and solidification.
• Bottom ash utilization potential per ton of waste is 0.25.

Air-Pollution Control

• Air-pollution control (APC) methods include electrostatic precipitators, fabric filters, wet scrubbers, dry or semi-dry systems, dust filters, activated carbon, SNCR and SCR catalyst for NOX removal, activated carbon for dioxin, and carbon capture-amine for CO2.