Introduction to Waste Engineering

**Introduction to Waste Engineering** **What are the steps that follow waste?** - Generation - Collection and transport - Treatment - RUL **What does generation or production refer to?** The source and waste being generated, sorted, and collected "in-house". Where waste is quantified...

**Introduction to Waste Engineering** **What are the steps that follow waste?** - Generation - Collection and transport - Treatment - RUL **What does generation or production refer to?** The source and waste being generated, sorted, and collected "in-house". Where waste is quantified before management. **Can treatment be done in transport stations and which type of treatment?** Yes, mechanical like compacting or shredding **What is desired to reduce when treating waste?** Odour, volume and impurities **What are the types of thermal treatment?** Incineration and gasification/pyrolysis **What are the types of biological treatment?** Composting and biogasification (anaerobic digestion) **How can waste be utilized?** For land, construction and fuel **What is MRF?** Materials Recovery Facility. It is a specialized plant or facility designed to sort, process, and recover recyclable materials from mixed waste streams. 2. **Introduction to Waste Management** **How much waste is there in DK?** 12 million tons **What category is the biggest contributor?** Construction and demolition -- 40% followed by households with 29%. **Which types does residential waste have?** - Household - Garden - Bulky - Hazardous household **Which types does organic waste have?** **What factors affect the viewing/definition of waste?** - Time - Location - Culture - Social conditions **How many municipal waste categories are there?**\ 20 **Which are the main issues with solid waste?** - Space - Collection & Separation - Health problems - Toxicity - Different systems - Costs - Complex materials - Odour **Whats the first and last step in the EU strategy?** 1^st^ is prevention last is disposal (landfill) **2. Waste Characterization: Methods** **What are the challenges of waste characterization?** - Spatial - Temporal - Uncertainty due to mixture **What kind of tests are done when testing samples** - Physical - Chemical - Performance **What instrument is used when characterizing org. waste?** Disc screen  **What's the definition of waste category?** Broad classes of waste coming from sources with common characteristics. Residential waste, commercial and institutional waste, industrial waste, and construction and demolition (C&D) waste are the main categories. **What's the definition of waste type?** Subclasses of waste categories that have common characteristics with respect to source and composition potentially resulting in separate collection and handling. For example, residential waste includes the waste types: Household waste, garden waste, bulky waste and household hazardous waste. Industrial waste holds several types according to industrial branch. **\ *Waste quantities*** are often reported as wet weight, since this is easily measured. Occasionally quantities are given as volume. The **unit generation rate** is a key parameter and is the **quantity of waste per defined time frame and per generating characteristic unit.** For residential waste, the unit generation rate is often kg/year/person (used in this book), or kg/week/household. For commercial waste, the unit generation rate could be kg/year/employee, or kg/year/m2 of store, or kg/1000 Euros of sales. By multiplying together the number of characteristic units and the timeframe the total amount of waste is determined. The unit generation rate is also a convenient parameter for estimating future waste quantities in areas with a growing population. **\ *Material fractions*** are visually identifiable fractions in the waste with common features: Paper, plastic, glass, organic kitchen waste, etc. Each material fraction may be divided into subfractions such as, for example in the case of paper: Newspaper, advertisements, magazines, paper towels,etc. **\ *Substances*** are individual chemical substances in the waste, which typically require analytical techniques to identify. This could be water, protein, ash content, nitrogen, cadmium, etc. **3. Waste minimization and recycling / prevention** **Which type of weight are unit generation rates referring to?** Wet **5. Mechanical treatment at MRFs** **Whats the purpose?** To sort for recyclables and residual stream, facilitate handling and transport, pre-step of thermal and biological treatment -- improve performance **Which types of technologies?** Separation, size reduction, and compacting **I want to obtain glass and paper fine fibres? What flow should it go through? What types of technology and technologies?** Separation first, consisting of - a debris screen, followed by a new screen (vibrating), a polishing screen, and a negative sort. **Composting** **What are the technological process factors and controls?** 1. Oxygen content, particle size and aeration 2. pH 3. biodegradation 4. temperature 5. moisture content 6. nutrients **what are the steps within a composting plant design?** 1. Source 2. Weighting/storage 3. Pre-processing 4. Composting 5. Refining, screening 6. Market product **What are some environmental emissions coming from composting?** *Liquid emissions:* Leachate Condensate Run-off *Air emissions:* - NH3 - N2O - CH4 *Air emissions* - Dust - Bioerosols **What are the steps within composting?** 1. Degradation 2. Stabilization 3. Curing **Whats the nitrogen transformation during composting?** **Anaerobic Digestion** **What is hydrolysis?** Done by extracellular enzymes on carbohydrates, proteins and lipids. Means uptake of water is the first step in anaerobic degradation of organic waste leading to dissolved organic matter. Relevant in digestion and in landfills. **What are the processes involved in the formation of biogas?** - Hydrolysis - Fermentation - Acetogenesis - Methanogenesis **What does the methane potential depend on?** Oxidation state and degradability **What steps does the anaerobic digestion system have?** - Reception and storage - Pretreatment - Digestion - Gas collection and utilization - Digestate management - Odor control **Whats the typical methane yield and content?** 60-120 v/m3 and content 45-65% **Incineration** **How much energy from incineration contributes to energy and how much to heating in percentage?\ **6% energy, 24% heating **What is LHV? And HHV?** Energy content available from combustion. LHV indicates the energy potential -- the energy used for water evaporation. HHV indicates the highest energy potential when water leaves in its liquid state. **What is pyrolysis?** Thermal degradation of C in the absence of oxidizing agents. **What is gasification?** Partial oxidation of C with oxidizing agents **What is combustion?**\ full oxidation of carbon **What is the purpose of APC (air pollution control) systems?** - Dust/fly ash removal - Acid neutralization - Dioxin removal - Nox removal - Heavy metal removal **CCS** **What are the benefits and drawbacks?** Benefits: - Energy recovery - Material recovery - Heat recovery - Stored CO2 Burdens: - Electricity used - Air emissions - Residues materials - Extra materials **Whats the difference of the kg co2-eq with CCS?** -820. Reduction of 90% ish Methods in APC: **What are some solid residues coming from incineration?** - Fly ash - Bottom ash - Wastewater - Sludge - Neutralization products - Grate sifting - Boiler ash - Economizer ash **What is bottom ash and where does it come from?** Mix of metals and solid residues. Formed and transformed through combustion chamber through grate. **What is fly ash and how is it recovered?** Fine ash collected with dust removal, filters and electrostatic precipitators. **Which are some ash treatment methods?**\ - extraction and separation - Thermal treatment - Chemical stabilization - Solidification **Whats the potential of bottom ash utilization per ton of waste generated?** 0.25 **What are the methods for NOx removal within APC?** Selective catalytic reduction and selective non-catalytic reduction. SNCR is with added ammonia and temperatures for 900-1000. **What method is useful for both dioxin and heavy metal removal?** Activated carbon **What method is useful for both heavy metal and dust removal?** Filters **What methods are used for acid neutrification?** Wet and dry. If wet fly ash removal before, if dry after. **What is L/S?** Liquid to solid ratio is the amount of water that is in contact with solids like ash **Landfill** **What are some env emissions from landfill** 1. Global warming 2. Ozone depletion 3. Toxic gases 4. Odours 5. Noise 6. Vectors: Flies, rats.. 7. Litter, dust 8. Fire and explosion hazard 9. Vegetation damage 10. Soil pollution 11. Surface water pollution 12. Groundwater pollution **What's the contribution of CH4 from landfills?** 6-13% **What are the risks associated with landfills?** 1. Odour 2. Vectors 3. Explosion risks 4. Groundwater pollution 5. Surface water 6. Soil 7. Vegetation damages 8. Noise 9. Litter and dust 10. Global warming 11. Ozone depletion  **Why are there managed water inputs in landfill?** - To recirculate leachate, enhancing degradation and gas generation - Avoid dust **How much is landfilled in DK?** 3-4% **What are regulators for landfill and incineration?** - Tax on landfill - Ban of combustible waste disposal - Enhanced waste sorting - Post sorting at landfills **How does T affect CH4?** A T lower than 72 allows for more CH4 release **Why is landfilling not a good anaerobic digester?** - No pretreatment - Heterogeneity - Age differences **Whats the gas production at landfills?**\ Maximum over life-time: 120-150 m3 gas / ton waste (50% CH4 in gas) **How is landfill gas generated?** Anaerobic digestion of organic waste generates CH4 and CO2 **What does the gas generation depend on?** - Waste composition - Waste age - Temperature - Moisture - Covering **Around what year on the lifetime of landfill does CH4 picks?**\ 7 years **What are some issues with LFG utilization?** - Potential aeration - Vertical and horizontal pipes - Corrosion - Blockage by water - Discontinuity **Whats the gas collection efficiency in DK?** 50% **What factors affect leaching?** Water: diffusion, advection Chemical:\ - solubility - more water? Less concentration - Availability -- more water? More washed out - pH -- metals are more soluble at low pH values **What are some functions of liners?** 1. Control gas 2. Leachate drainage and collection 3. Impermeability 4. Separation 5. Water filtration, drainage and collection 6. Mechanical protection 7. Soil reinforcement **What is a liner composed of?** Either natural (sand, gravel, clay) or synthetic material (geomembranes (HDPE) and geotextiles) **What are the components of leachate?** Organic components -- degradation highest influence on composition Metals (Fe Nitrogen (Ammonia, NH3, NH4) XOCs **What are the treatment processes for leachate?** Biological Tertiary/advanced/polishing: reverse osmosis Physico-chemical What is one type of plant/system that can treat leachate A sequencing batch reactor + monitoring General questions: \#\#\# Question A1 What is the least favorable waste management option, and the most favorable waste management option in the waste hierarchy? \- Disposal and Recycling, respectively \- Energy recovery and material reuse, respectively \- Disposal and Prevention, respectively \-\-- \#\#\# Question A2 Which process has normally the highest unit generation rate? \- Remodeling \- Demolition \- Construction \-\-- \#\#\# Question A3 What is hydrolysis? \- Formation of hydrogen \- Breakdown of solid organic matter into water-soluble organic compounds \- Condensation of water inside a landfill \-\-- \#\#\# Question A4 What is a typical composite liner? \- A clay layer with on top a thin plastic sheet \- A mixture of bentonite and sand \- A thin plastic sheet with on top a clay layer \-\-- \#\#\# Question A5 What is the primary incentive of building a transfer station? \- Facilitate material recovery \- Avoiding landfilling of materials \- Savings in transportation costs \-\-- \#\#\# Question A6 What is NOT the role of a conventional MRF? \- Chemical transformation \- Mechanical separation \- Size reduction \-\-- \#\#\# Question A7 Positive sorting is when: \- Contaminants are removed from a stream of recyclables \- Target recyclables are removed from a mixed stream of recyclables \- When a magnet with the positive side down is used to sort out ferrous metal \-\-- \#\#\# Question A8 The biogenic carbon dioxide released to the atmosphere has, by the IPCC, been characterized with the following factor: \- 1 kg CO2-eq/kg biogenic CO2 \- 0 kg CO2-eq/kg biogenic CO2 \- -1 kg CO2-eq/kg biogenic CO2 \-\-- \#\#\# Question A9 Mercury (Hg) should be cleaned from the flue gas at waste incinerators prior to release to the atmosphere. How is this cleaning ensured? \- Removal of particles (fly ashes) in dust filters such as fabric filters. Mercury is removed because this is bound to the particles \- By injecting alkaline reagents (e.g., Ca(OH)2 or NaHCO3) into the flue gas. Mercury is captured in these reagents, which are then removed from the flue gas in a later stage \- By injecting activated carbon into the flue gas. Mercury is captured in the activated carbon, which is then removed from the flue gas in a later stage \-\-- \#\#\# Question A10 The lower heating value (LHV) is often used to describe the energy content in the waste. How much of this energy can be recovered in waste incinerators? \- Always less than the LHV \- Precisely the LHV \- Difficult to say a priori: potentially more than the LHV, but it could also be less than the LHV \-\-- \#\#\# Question A11 A range of different solid residues are generated from waste incineration. How can the fly ashes or air-pollution-control residues be characterized? \- A grey, coarse gravel-like material that can be utilized for road construction \- Fine grey powder that can be utilized as cement in the building and construction sector \- Fine grey powder that is hazardous waste and needs special treatment \-\-- \#\#\# Question A12 Which one of the following statements about waste incineration is correct? \- Bottom ashes are usually present in very small quantities, about 1.5-3% of the initial waste mass \- Wet flue gas cleaning systems often involve removal of fly ash after the wet scrubbers, e.g., in fabric filters \- The \"L/S ratio\" is a measure of the amount of water which has been in contact with a specific amount of material, e.g., incineration ashes \-\-- \#\#\# Question A13 Solid residues from waste incineration can be considered as both resources and environmental problems. Based only on the abundance in typical fly ashes, which of the following chemical elements may be most problematic? \- Hg \- As \- Zn \-\-- \#\#\# Question A14 Based on the C/N ratio, which of the listed types of waste would be most suitable for separate composting? \- Sewage sludge with a C/N ratio of 5-15 \- Source-segregated organic waste with a C/N ratio of 20-40 \- Wheat straw with a C/N ratio of 60-100 \-\-- \#\#\# Question A15 How much of the total carbon contained in the feedstock is typically lost as methane during composting? \- 0.1-0.5% \- 1-5% \- 6-10% \-\-- \#\#\# Question A16 In which form is nitrogen primarily lost during composting? \- N2O \- NH3 \- NO2-