Ultraclean waste water

Date: January; 08; 2015 | Author:
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Waste water. The word does not attach itself to clean spring water, but in actual fact, the quality requirements for water recovered from waste combustion at plants such as Copenhill, ARC's Amager Bakke, are more stringent than the requirements for our drinking water.

Water is not the first thing that comes to mind as a result of waste combustion. Nevertheless, more than 100 million litres of water is produced from 400,000 tonnes of waste, which is processed in a modern waste-to-energy plant by flue gas condensation.

Director of Technology and Marketing at Babcock & Wilcox Vølund, Ole Hedegaard Madsen, can therefore answer yes to the question: Does it make sense to burn a banana skin?

"Yes, it makes sense, as heat and electricity can be gained from the skin's energy content, while also recovering the moisture content," says Ole Hedegaard Madsen. He points out that it makes as much sense to process domestic waste as it does to process other types of biomass, for example wood chips. The moisture content is the same, roughly 35 percent.

Amager Bakke - spring

Recovering the moisture content: More than 100 million litres of spare water is recovered from 400,000 tonnes of waste each year at Copenhill, ARC's Amager Bakke, Copenhagen, Denmark. 

In the waste combustion process, the moisture content is evaporated and recovered in the plant's flue gas condensation. The quality of the recovered water is good. This becomes clear by comparing the limit values for drinking water with the limit values for the water that Amager Bakke is permitted to discharge. Figures for the content of, for example, nickel, chrome, arsenic, cadmium, copper and zinc are far lower for the cleaned waste water than for drinking water.

"It's about not leaving the tap running, as this can make it hard to maintain the requirements at the plant," teases Ole Hedegaard Madsen with a smile.

Ole Hedegaard Madsen, Director of Technology and Marketing, B&W Vølund 

Sludge with a difference

The alternative to treating the banana skin at the plant is to compost it and let the mulch replace chemical fertilizers. At the waste-to-energy plant, banana skins replace fossil fuels and yield metals, water and gravel. A third option is to convert the banana into biogas. 

"Rambøll has carried out a study using 10 tonnes of organic household waste. This showed that waste combustion and biogas plants provide roughly the same amount of electricity. On the other hand, the waste-to-energy plant provides four times as much heating. This is because there is a massive amount of unconverted energy in the biogas plant's sludge. But this entire calculation depends on whether we can use the sludge on agricultural land," says Hedegaard Madsen.

This brings us one step backwards – to the waste bin. Of course, this does not only contain organic banana skins; there is also lemon peel with pesticide residue, just as there are ballpoint pens comprising 30 different chemical elements, and aluminium trays with liver pate traces which are starting to rot. 

No toxic waste recycling

"It makes sense to sort out metal, glass, paper and plastic, as long as it is clean and can be separated from the rest of the waste. But take, for example, all the packaging in our waste bins. It doesn't pay to try to clean this with soap and hot water. Practically speaking, it's also hard to carry this out. We should try to keep the clean materials separate, reuse everything that we can and process what's left by recycling the resources," says Hedegaard Madsen, who explains that we can then also destroy any medicine remains contained in the waste, as well as phthalates, bacteria and pesticides, instead of spreading them on the fields and thereby sending the unwanted substances into our food production cycle.

"Toxic substances become concentrated in the waste, when, for example, we throw out the remains of cleaning detergent articles, or when we peel an orange with pesticide residues.  By waste combustion these toxic substances are destroyed. In modern plants with efficient flue gas treatment (FGT), the toxic substances are separated from the ecological cycle. The waste product from flue gas treatment is about 2%. This portion is deposited.

Energy and resources recovered from your waste

Electricity, heating, metals, water and gravel. Modern waste combustion technology transforms waste into energy and material resources.

Healthy dependency

But don't we risk making ourselves dependent on waste, if this is the solution for both energy supply and exploitation of resources?

"Under all circumstances, we are dependent on fuel for our combined heat and power (CHP) plants. But we are no more dependent on waste than we are on fossil fuels or we will be on biofuels. Waste just has a number of advantages: it is a local resource that we produce ourselves, it requires almost no transportation, we are not clearing any forests in other countries, we are not dependent on insecure regimes, we are destroying chemicals, and it's cheap fuel," lists the Director, adding:

"...and as long as 34 percent of the municipal waste in Europe ends up at waste depots, we will not have overcapacity. Furthermore, this indicates a very clear pattern that shows waste combustion and recycling go hand in hand with the utilization of resources. Those countries that have an effective waste combustion capacity also have an extensive and efficient recycling programme. Waste combustion does not undermine recycling efforts, but reduces landfill." 

The figures from EUROSTAT of EU countries' waste management for 2012 speak for themselves:


Related information

Waste-to-energy: How it works

Why W-t-E excels other waste technologies

A Europe without landfills and Russian gas 

Mining the bottom ash mountains - interview with AFATEK

ARC Amager Bakke, Copenhilll, Copenhagen

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