We understand that recycling materials from the waste stream helps to conserve resources. But the question often arises: How much material can be actually recovered, and is it worth spending energy and labor for it, or it is easier to extract fresh material from the environment? A useful metric to characterize technical performance of a recycling line is recycling efficiency. The general approach to estimate efficiency is as follows:
- Determine the input of the process: Input is measured as the mass or volume of all fractions or materials entering the recycling process per time period (usually per year) - mi(in)
- Determine the output of the process: Output includes the mass of the useful recycled components - mi(out), excluding any unrecycled material sent to refuse. Loss of the components to the refuse can be due to process inefficiencies, such as sorting losses, damages or loss of quality, loss to slag and emissions, accidental presence of non-recyclable items.
- Calculate the efficiency ratio (η) as follows:
Consider the case of recycling Pb-acid batteries. Input will include lead metal (Pb) together with liquids and other solids contained in a battery and also the external jacket. Let us count recovered Pb as useful output, but any chemicals that cannot be salvaged and must be disposed off are not included. Then efficiency of lead recovery can be estimated as: η = mPb(out) / mi(in) x 100%
Let us imagine that a small recycling facility treats 13,000 kg of old batteries per year. If the amount of the recovered lead is for example 7,000 kg per year, then
η = 7,000 / 13,000 × 100% = 54%
That means that the other 46% of material supplied to the recycling process is lost or discarded (e.g., non-recyclable acid and other chemicals, slag, etc.). Note the above numbers are randomly picked and used merely for example.
100% efficiency is possible only in the ideal case when no waste is sent to the landfill or incineration.
Source: adopted from the method described in the EU Commission Regulation 6/11/2012