POSTING 4: Material and Energy Recovery Options

 POSTING 4: Material and Energy Recovery Options  

 

Our supervisor feels it is important for us to fully understand what happens to waste after it has been delivered to the waste management facility. So, in this posting, we have studied the processes of waste material and energy recovery. 

 

Cotton T-shirt: 

The recycling process depends on the quality of the shirt. If it is given to a specialised company like 'Pure waste', the t-shirt will undergo several stages. This Finnish company aims to manufacture fabrics from 100% recycled materials.  

 

1) The first step will be to sort the fabrics according to their colour and quality.  

2) Then, each batch of waste is mechanically split into fibres, and the colour of the final product will depend on the colour of the waste at the start.  

3) In the third step, the cotton wastes are mixed with chemically recycled polyester fibres from PET bottles.  

4) After this, the blended fibres are spun into rows, and this step is the same as when the fibres are spun with virgin materials.  

5) In the fifth stage, the final product begins to be designed, as it is at this stage that the threads are knitted.  

6) At the sixth stage of the process, depending on the final product, some need to be brushed or washed. 

7) During the seventh step, the final product is refined, trimmed and perfected to its final shape. 

8) That's it, our final product is ready.  

  

The quality of the final product is far superior to a product that comes from virgin material. Indeed, the quality of the fabric is sustainable, generates 50% less CO2 emissions and uses 99% less water. This represents a much lower environmental impact. 

 

As a general rule, ordinary clothes often cost less than recycled clothes. Indeed, as the price of recycled fibres is currently even higher than virgin fibres (10-20%), it is difficult to switch to recycled fibres.  However, the sector can only evolve if there is an apparent and abundant demand for recycled fibre from public purchasers and industry in general. 

 

  

Metal cans:  

The recycling process of metal cans:  

 

First, the metal cans need to be collected and then they are sorted out. Either by hand or by machine. Once only metal cans are left, a magnet is used to separate aluminium from steel. Then the different types of metals are compressed and shredded. The metal pieces are then heated in order to remove decoration thanks to blown air. Thus, the metal pieces are now pure.  

Then the pure metal pieces are thrown into a furnace heated at more than 750°C. The metals melt and after they are poured into a mould and cooled with water.  

At the end of this process, the recycled metals can be used again to create new metal cans. In just 8 weeks metal cans can be recycled and put back on the shelf. This process can be done repeatedly with aluminium. Recycling metal cans has vast benefits for the environment. This process allows the saving enough energy to power a light bulb for 4 hours.  

Using recycled metal cans as opposed to new metals reduces air pollution by 86%, and water pollution by 76%.  

 

 

Oil Paint: 

Hazardous waste can be used in fuel blending. This involves the mixing of fuel with hazardous waste to produce an alternative fuel for processes such as cement production. Although, this can affect the fuel quality and there are restrictions to the types of hazardous waste which can be used for this.  

 

Recycling of oil-based paint is very uncommon, unlike latex paints which are found to be of good quality are easily repurposed with filtering, treatments, and colour adjustments. Due to the chemistry of oil paints, they are usually shipped off for hazardous waste treatment and taken to a special landfill for energy recovery in incineration.  

It is still possible to recover the paint and recycle it into other types of coatings. 

If the paint is in good condition, has been properly stored and before expiry, partially used oil paint cans can be donated or given to others for different projects. 

The packaging and labelling give information on the hazard that the waste poses and from there the appropriate treatment can be given after it is sorted. The waste is analysed in a lab and the nature of the waste determines how it will be neutralised and have contaminants removed. Valuable fractions can be extracted using centrifugation and distillation. 

 

For the most common practice, incineration, the waste is burned at high temperatures (between 850-1100°C) to produce electricity. Therefore, when the waste cannot be processed, it is thermally processed using hazardous waste incineration, using especially high temperatures and monitoring of the gases released. The gases released are captured and filtered so that they do not enter the atmosphere. The residues are then taken to hazardous waste landfill sites where it is stabilised. It is then put into safety cells and covered by soil. 

 

 

Infected sharps: 

Due to their toxicity and the infection risk, infected sharps can’t be recycled. Many techniques exist to treat infectious waste like infected sharps. 

 

Autoclaves: 

 

Autoclave is a vessel where are placed the contaminated medical waste, infected by microbes. High pressure and temperature are applied by the addition of steam in the chamber. Microbial can’t survive these high temperatures and are killed during the process. Bigger autoclaves in hospitals can treat up to 800 kg of waste in one cycle. The treatment time is short (about an hour, however, autoclaves use a lot of energy and water to work (see Table 1). 

 

Table 1: Time, energy and water needed for waste treatment by autoclave 

 

 

Microwaves based technology: 

 

This treatment aims to stir the water molecules present in the waste using microwaves. By moving, the molecules create heat until the temperature reaches the boiling point, 100°C, and the water is changed to steam. Then the process is similar to autoclave: heat kills pathogen, viruses, microbes and other infectious agents. 

 

Table 2: Time, energy and water needed for waste treatment by micro-waves technology 

 

 

These two technologies are the most used. They are efficient and fast to apply. However, there are some limitations: the device needs to have an electricity and water connection and maintenance, and for microwave technology, a special bin is required. 

 

There are other technologies, less used, like chemical-based processes working with oxidation of the waste. 

 

Incineration can be used in accordance with the Stockholm Convention. The main requirements are the control and the treatment of flue gases and wastewater, a sufficient oxygen level, two burning chambers and an auxiliary chamber and high turbulence in exhaust gases. It is really expensive to monitor every parameter and only wealthy countries can afford these plants. 

 

 

Wooden table: 

  

As of today, furniture recycling is almost non-existent globally. This is explained by the complexity of furniture designs and raw materials used. Different materials used in furniture making include but are not limited to glass, timber, textiles, metals, chemicals, minerals, plastic, etc. 

There is also no clear legal solution or unified division of wood waste. For example, in the Netherlands A, B, C grading is used, where A grade is clean untreated wood, B grade is treated wood, and C grade is the wood that cannot be classified as neither A nor B grades. While in the UK, C grade is a fuel grade, and in addition, they have a fourth grade, D, which is considered hazardous waste and is all treated and painted wood. These grades mostly concern construction, industrial and agricultural wood waste, so if a wooden table has reached its end of life, then it can only be taken to incineration where it is converted into ash, flue gas and heat. 

 

 

 

 

 

 

 

A) For non-biowaste:  

 

BAT: Best Available Techniques 

  

The BAT conclusions established by the European IPCC Bureau: 

  

·       identification of the key environmental issues for the Waste Treatment sector; 

·       examination of the techniques most relevant to address these key issues; 

·       identification of the best environmental performance levels, on the basis of the available data in the European Union and worldwide; 

·       examination of the conditions under which these environmental performance levels were achieved, such as costs, cross-media effects, and the main driving forces involved in the implementation of the techniques; 

·       selection of the best available techniques (BAT), their associated emission levels (and other environmental performance levels) and the associated monitoring for this sector according to Article 3(10) of, and Annex III to, the Directive. 

  

In determining BAT for every waste type, we must consider techniques for monitoring the waste input, prevention or reduction of emissions to air and water, energy efficiency and overall environmental performance. In accordance with EU Waste Framework Directive, the first recommended option of treatment of waste is recycling, and then incineration. 

  

Some of the BAT for cotton t-shirts, metal cans, oil paint, infected sharps and wooden table include but are not limited to: 

  

·      Wastewater treatment techniques – ultrafiltration, nanofiltration, membrane filtration, electrodialysis, photocatalysis, etc. 

·      Metal shredding prior to material recovery, cryogenic grindings. 

·      Organizational techniques to improve environmental performance (policy, planning, implementation, follow up). 

·      Stream inventory/register. 

·      Utilization of qualified personnel in the plant. 

·      Waste tracking system and inventory. 

·      Segregation of waste (magnetic separation of ferrous metals, electromagnetic separation of non-ferrous metals, air classification, ballistic separation, sink-float tanks, vibration tables). 

• Emission diffusion 

 

 

 

Process of incineration including delivery monitoring and dealing with residual ash: 

 

Waste is collected with specialised trucks and delivered to incineration plants every day. Waste is unloaded in a large pit and well mixed to obtain a homogeneous mixture. Then it is taken with a grab and put in the incineration chamber, where they are burnt at high temperature, above 1000°C. This energy is used to heat water and create high temperature steam. Firstly, steam is used to activate turbines and produce electricity. Secondly, the steam creates hot water which will be distributed to individuals. 

After the combustion of waste, some materials like glass or metal remains in the chamber: clinkers. They don’t burn and are stored or reused for road construction for example. 

Flue gases and fumes have to be treated. Some are toxic and contain heavy metals like lead or mercury. To get rid of these pollutants, one method is to electrify them (charge them negatively with electrons) and to place a positively charged plate at the top of the pipe. The pollutants charged negatively will stay in the plate. This powder is controlled, especially to ensure that the chlorine concentration is low, and disposed of in a specialised centre for hazardous waste. 

 

 

 

Waste hierarchy and energy produced: 

 

Waste Type	t-shirt	Metal Cans	Oil-based Paint	Wooden table	Infected sharps
Does incineration follow waste hierarchy?	No	No	Yes	No	Yes
Energy produced by incineration	Between 5-31 MJ/kg	Between 5-31 MJ/kg	Between 5-31	17 MJ/kg	25-35MJ/kg

  

Metal cans and wooden table can be recycled, which is higher up in the waste hierarchy. Therefore, incineration would not be following the hierarchy and is not the ideal option. The textile material from a t-shirt can also be recycled, which would be preferable and less wasteful than incineration. 

Waste is lost during incineration during different processes such as radiation, steam condensation and convection. The overall efficiency is usually close to 21%. Although thermal efficiencies in some incinerators which are coupled with heat power can be 74%. 

On average the amount of energy produced from a ton of waste is between 500 to 600 kWh. Though there could be a large margin for error due to a lack of cross-checking. 

 

 

 

B) For biowaste:  Grass clippings. 

 

After several searches, we finally noticed the presence of grass in the dump. This recovered bio-waste will have to be composted. 

 

Compost is simply organic matter that decomposes over time. What can be found in compost is very broad, ranging from eggshells to grass clippings.  Composting is a thermophilic aerobic process (in the presence of a large amount of oxygen) and this degradation process can reach temperatures of up to 70°C. During this process, aerobic micro-organisms will break down the organic matter producing carbon dioxide (CO2), water, ammonia, and heat. Along with this humus is also produced, which is the relatively stable final organic product.  

  

There are two main types of composting processes, in-vessel composting and open windrow composting. These two methods are the most commonly used for sanitation and stabilisation of biowaste. In general, in-vessel composting is a better option for composting biosolids because uniform heating can be achieved through proper mixing during the process. The finished product is a nutrient-rich fertiliser that can be used for gardens and agricultural crops. This enriches the soil with nutrients and speeds up the growth process. 

 

Several uses are obtained from compost. Indeed, energy can be recovered either from the heap for open compost or from the fermenter for compost that takes place in a closed system. Several uses are obtained from compost. Energy can be recovered from the heap for open compost or from the fermenter for closed compost. Another is environmental recovery. Indeed, the humic macromolecules of composts have a strong adsorbent power. This active filter property can be used as an odour filtration system in a wastewater treatment plant, for example. 

 

Finally, our bio-waste found on the site can be passed on to Ecosairila in Mikkeli to be counted. Ecosairila is a project that is coming to fruition with an investment of €100 million. 

 

Waste hierarchy: prevention, re-use, recycle, recovery, disposal : 

 

If we follow the waste hierarchy, the best treatment option for grass clippings is recycling, so composting is one of the best options. Otherwise, when an individual mows their lawn they can leave the grass cut directly on the spot, which will fertilize the soil.  

So composting is one of the best options because we can’t prevent the grass to grow unless you graze animals on your land.  

So here, as the grass clippings have been disposed of in our site, our only and best option is to compost. 

 

 

During the composting process, the finished products which are rich in nutrients are created. We know that for 3kg of organic waste, 1 kg of compost is created. But a compost needs to be a different type of organic waste to work, not only grass clippings.  

 

 

 

 

 

 

References: 

 

Pure Waste, No date. The process. WWW document. Available at: https://www.purewaste.com/experience-pure-waste/production/the-process [Accessed 12.04.2021]. 

 

Sfgate, No date. Difference between recycled and regular clothing. Available at: https://homeguides.sfgate.com/difference-between-recycled-regular-clothing-79239.html  

[Accessed 12.04.2021]. 

 

Circular economy, No date. High value reuse textile recycling. Available at: https://publish.circle-economy.com/high_value_reuse_textile_recycling [Accessed 12.04.2021]. 

 

Recycled Textile Fibres and Textile Recycling, December 2017. PDF document. Available at: https://www.bafu.admin.ch/dam/bafu/en/dokumente/wirtschaft-konsum/externe-studien-berichte/Recycled-Textile-Fibres-and-Textile-Recycling.pdf.download.pdf/study-on-recycled-textiles-and-textile-recyclability-ch.pdf [Accessed 12.04.2021]. 

 

Grenn Matters, 6 February 2019. What is composting, WWW document. Available at: https://www.greenmatters.com/food/2018/12/07/ZboPlt/what-is-composting [Accessed 12.04.2021]. 

 

ScienceDirect, 6 February 2019. Composting, WWW document. Available at: https://www.sciencedirect.com/topics/earth-and-planetary-sciences/composting [Accessed 12.04.2021]. 

 

Ecosairila, 6 February 2019. Biological circle, PDF document. Available at:https://mikseimikkeli.fi/wp-content/uploads/Mikkeli_Ecosairila_brochure_ENGLISH.pdf [Accessed 12.04.2021]. 

 

 

Brunner, P.H. and Rechberger, H., 2015. Waste to energy–key element for sustainable waste management. Waste management, 37, pp.3-12. 

 

Tillman, D., Duong, D. and Harding, N.S., 2012. Solid fuel blending: principles, practices, and problems. Elsevier. 

 

Product Care Recycling. 2020. Paint Recycling: How it works - Product Care Recycling. [online] Available at: <https://www.productcare.org/about/blog/how-is-paint-recycled/> [Accessed 12 April 2021]. 

 

Archive.basel.int. 2002. Technical guideline for incineration on land. [online] Available at: <http://archive.basel.int/meetings/sbc/workdoc/old%20docs/tech-d10.pdf> [Accessed 12 April 2021]. 

 

WHO (World Health Organization), 2019, Overview of technologies for the treatment of infectious and sharp waste from health care facilities, Available at: https://apps.who.int/iris/bitstream/handle/10665/328146/9789241516228-eng.pdf?ua=1. [Accessed on 13/04/2021] 

Page Break 

 

YouTube, 29 February 2016, How are cans recycled, available at:  How are cans recycled? - YouTube [accessed 10/04/2021] 

 

Small business, 5 march 2021, An introduction to metals recycling, available at: Metal Types and Recycling Process (thebalancesmb.com) [accessed 10/04/2021] 

 

Wikipédia, no date, Compostage (biologie), available at: Compostage (biologie) — Wikipédia (wikipedia.org) [accessed 10/04/2021] 

 

Pinasseau A. et al., 2018. Best available technique (BAT) for waste treatment. PDF. 

 

Scarlat N. et al., 19 April 2018. Status and opportunities for energy recovery from municipal solid waste in Europe. WWW document. Available at: https://link.springer.com/article/10.1007/s12649-018-0297-7 [Accessed 19.04.2021]. 

 

Waste incineration and public health, 2000. Chapter 3, page 34.