The Waste Management Division of SWLS provides turnkey project solutions that include:
- Engineering and Economic Feasibility Studies;
- Project Design, Engineering & Permitting;
- Project Construction;
- Project Funding via Pytheas Equity Finance;
- Project Commissioning;
- Operations and Maintenance.
SWLS vast experience in Landfill Mining & Reclamation converts dumpsites into recreation, nature, agricultural, industrial and residential areas.
Our integrated Waste Management services and ability to funding ensure not only complete and sustainable solutions but also risk free maximum returns.
Municipal Solid Waste Management
Municipal Solid Waste (MSW) is defined to include refuse from households, non-hazardous solid waste from industrial, commercial and institutional establishments (including hospitals), market waste, yard waste and street sweepings.
Municipal Solid Waste Management (MSWM) encompasses the functions of collection, transfer, treatment, recycling, resource recovery and disposal of municipal solid waste.
MSWM is a major responsibility of local governments, typically consuming between 20% and 50% of municipal budgets in most countries. It is a complex task, which depends as much upon organization and cooperation between households, communities, private enterprises and municipal authorities as it does upon the selection and application of appropriate technical solutions for waste collection, transfer, recycling and treatment or disposal.
MSW consists of organic and inorganic constituents, which may or may not be biodegradable. On one hand, the recyclable components of solid waste could be useful as secondary resource for production processes. On the other hand, some of its toxic and harmful constituents may pose a danger if not handled properly.
Source reduction, recycling and composting, waste-to-energy conversion facilities, and landfilling are the four basic approaches to waste management.
SWLS covers all aspects of MSWM and is probably the only entity worldwide that provides a zero-landfill-no-chimney-solution.
Municipal solid waste – Broad categories
1. Biodegradable waste: Food, green waste (vegetable, flowers, leaves, fruit), garden waste, paper.
2. Recyclable material: Paper, glass, bottles, cans, metals, certain plastics, etc.
3. Inert waste: Construction and demolition waste, dirt, rocks, debris.
4. Composite wastes: Waste clothing, Tetra Packs, waste plastics such as toys, plastic chairs, etc.
5. Domestic hazardous & toxic waste: Medication, e-waste, paints, chemicals, light bulbs, fluorescent tubes, spray cans, fertilizer and pesticide containers, batteries, shoe polish, etc.
Anaerobic digestion (AD) is a naturally occurring biological process that uses microbes to break down organic material in the absence of oxygen. In engineered anaerobic digesters, the digestion of organic waste takes place in a special reactor, or enclosed chamber, where critical environmental conditions such as moisture content, temperature and pH levels can be controlled to maximize gas generation and waste decomposition rates.
One of the by-products generated during the digestion process is biogas, which consists of mostly methane and carbon dioxide. Methane is the same as natural gas.
The level of biogas produced depends on several key factors including the process design, the volatile solids in the feedstock (which varies depending on the composition of the feedstock) and the carbon/nitrogen (C:N) ratio. Note that it is possible to co-digest MSW with animal manure and bio-solids from wastewater treatment plants.
A benefit of an AD process is that it is a net generator of energy. The excess energy produced by the AD facility, which is not required for in-plant operations, can be sold offsite in the form of heat, steam or electricity.
AD has a significant benefit from a greenhouse gas point of view. It produces methane from the degradation of organic waste in a controlled environment. The methane can be used to displace fossil fuels. In addition, it avoids the production of this methane over a much longer period in a landfill, where its maximum energy potential would not be realized.
Key advantages of Anaerobic Digestion
- Can divert most organic materials and biodegradables; applicable to 40% to 50% of the municipal waste stream.
- Collects methane and provides a source of renewable energy (biogas) that is carbon neutral.
- Requires significantly less space than composting facilities.
- Can lower the odor from waste and slurries by up to 99%.
- Can lower the biological oxygen demand therefore pollution.
- Pathogens in the feedstock are lowered to negligible.
- It kills most weed seeds; therefore less need for herbicides.
- Plant nutrients can be exported off as a soil conditioner, or further processed into granular organic fertilizer or refuse derived fuel (RDF).
Anaerobic Digestion – Process
Most Anaerobic Digestion (AD) technologies use a similar approach to processing organic waste or mixed municipal waste; the difference is that mixed waste digestion requires additional front end processing steps to make the mixed waste stream suitable for digestion.
Pre-processing. The organic feedstock is processed through a range of equipment to reduce the size of the material and remove contaminants. Pre-processing may involve the use of a sieve, trommel screen, shredder, magnet, etc. to remove contaminants such as stones, metal, glass and plastic prior to the mixing stage. An AD plant which processes source-separated organics has a relatively simple front end processing system.
Mixing. In the mixing stage, the feedstock is mixed with heated water or steam to increase the moisture content and the temperature of the waste to be processed; a starter innoculum is added to initiate microbial activity at the mixing stage. The water is heated using biogas from the digestion process. Heat increases the rate of microbial reaction and therefore the extent of organic material degradation. The innoculum is supplied from either the digested waste stream from the AD reactor or from the wastewater produced during de-watering.
Digestion. The waste is then fed into the AD reactor. After a digestion period which of about 14 to 21 days, the AD reactor produces a material which is dewatered to produce a relatively solid residue (the digestate) and biogas.
Energy Production. An AD plant generates sufficient biogas to meet in-plant energy needs as well as to export energy to other users in the form of electricity, steam or heat.
Dewatering. The solid product that is produced by the digester is de-watered using centrifuges, belt filter presses or other dewatering equipment. The liquid from the dewatering process is re-introduced back into the earlier digestion steps.
Digestate. The solid produced by dewatering, the digestate, has a moisture content of about 50% and is treated to achieve biological stabilization.
Basic AD Flow Diagram
Production of biogas from an anaerobic digestion process will vary depending on (a) the anaerobic digestion process design chosen which impacts on the extent to which volatile solids in the waste are converted to biogas; this in turn depends on retention times and reaction temperature, etc., and (b) the volatile solids (VS) content of the feedstock which depends on the composition of the waste sent to the digester.
The level of biogas produced depends on several key factors including the process design, the volatile solids in the feedstock (which varies depending on the composition of the feedstock) and the carbon/nitrogen (C:N) ratio.
The composition of the material sent to the anaerobic digester affects residue rates (and therefore costs) and also gas production rates (and therefore the net energy balance of the facility).
Biogas from an anaerobic digester can be used as a substitute for natural gas, either in boilers producing hot water and steam for industrial processes, in combined heat and power (CHP) applications to generate electricity, as well as heat, as a pure natural gas substitute (high-graded for insertion into the natural gas supply), or for fuelling a fleet of vehicles or as a fuel for fuel cells.
Also production of pure methane and CO2 from biogas is important for the chemical industry and agriculture. Pure CO2 is used for production of polycarbonates, of dry ice or for surface treatment (sandblasting with CO2). CO2 from biogas can also be used in agriculture, as fertilizer in greenhouses.
Key advantages of Biogas from Anaerobic Digestion
- Is permanently renewable, as it is produced on biomass.
- Will not only improve the energy balance of a country but also make an important contribution to the preservation of the natural resources and to environmental protection.
- Reduces greenhouse gas emissions and mitigation of global warming.
- Reduces dependency on imported fossil fuels.
- Has the ability to transform waste material into a valuable resource, by using it as substrate for AD; followed by recycling of the digested substrate as fertilizer thus reducing the volume of waste and of costs for waste disposal.
- Is a flexible energy carrier, suitable for many different applications.
Landfill Mining & Reclamation
SWLS integrated approach to landfill reclamation includes, harvesting waste for recyclable products, capturing gas to be utilized as an energy source, engineering leachate collection systems that treat leachate and further exploit it via AD technology; not only preventing toxins from entering ground water but transforming worthless land into a valuable, income-producing asset.
Depending on the composition of the waste material, some of the waste excavated from a landfill may be recycled or further treated.
As complete excavation will be immensely expensive in most cases, partial excavation with planned reuse is recommended – if the landfill dimensions do not allow aftercare measures like capping or if particular risk hot spots are present.
Landfills contain a substantial amount of organic waste, which produces landfill gas as it degrades. Landfill gas is highly inflammable and may form safety risks. It can also affect the vegetation on the landfill and the emission of methane – a potent greenhouse gas that contributes to the climate change. The solution to the problem of uncontrolled emission is the implementation of a landfill gas extraction and treatment system for further utilization as an energy source.
Reactive barriers are also used which are permeable and designed to treat contaminated groundwater. Also a collection system for leachate recirculation is engineered, involving drainage for the re-infiltrated leachate/rainfall mix. The collected leachate is then directed for treatment and exploitation.