Urban Biowaste Valorisation : Up to 99% reduction in the environmental impact of innovative processes
Biowaste is one of the major components of municipal waste. According to Eurostat, in 2017 the 28 members of the European Union (EU-28) produced 249 million of tonnes of municipal waste, of which around 34% (86 million tonnes) was biowaste, including both separately collected and mixed biowaste. If not managed well, this voluminous waste stream not only poses significant environmental and economic threats but also is a waste of nutrients, energy and potential resources for biobased products.
Biowaste is a key source for greenhouse gases emission from landfills, corresponding to about 3% of total EU greenhouse gas emissions, according to the European Environmental Agency (2019). Therefore, addressing municipal biowaste is crucial for meeting the targets set out in the 2018 Waste Framework Directive (WFD). This directive sets new targets regarding recycling and preparation for reuse: by weight, at least 55% by 2025, 60% by 2030 and 65% by 2035. In this context, the EU's common objectives for waste management cannot be achieved without addressing this waste stream.
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Innovative concept to valorise biowaste
In this sense, SCALIBUR, a Horizon 2020 project, presents an innovative concept to valorise organic waste and transform it into high-added-value products, aiming to help the implementation of Circular Economy in the European Union. Three important urban biowaste streams were valorised within SCALIBUR:
- the organic fraction of Municipal Solid Waste (OFMSW);
- biowaste from Hotels, Restaurants and Catering (HORECA) and
- Urban Sewage Sludge (USS) produced in Wastewater Treatment Plants (WWTP).
The project sought to cut urban biowaste and replace it with a new production chain of biobased products, applying a sustainable approach to generate new activities and benefits. It formed a partnership of waste management companies, technology developers, researchers and end users to recover and transform biowaste from three municipalities, Madrid (Spain), Albano (Italy), and Kozani (Greece), into value added products. This way, SCALIBUR helps cities to increase their recycling rate and creating a new circular economy business opportunity.
These new value chains developed under SCALIBUR transformed HORECA waste into proteins, lipids and chitin from insect rearing, while the OFMSW was hydrolysed into sugars that were further converted into biopesticides and bioplastics by fermentation. Besides this, the Urban Sewage Sludge (USS) was upgraded by bioelectrochemical treatment to produce commodity chemicals or fermented to obtain bioplastics.
In order to assess the SCALIBUR environmental and to compare it with the current situation, a Life Cycle Assessment (LCA) analysis was implemented. LCA is a technique that aims to assess potential environmental impacts associated with a process or product over its life cycle (from the raw material to its end of life). This analysis is based on the review and analysis of the inputs and outputs of the system to obtain, as a result, its potential environmental impact.
These potential environmental impacts are classified into different impact categories:
- Climate Change (CC), also known as Carbon Footprint, measured in kg CO2 eq, is an indicator of the potential global warming due to the emissions of greenhouse gases to the air.
- Ozone Depletion (OD), kg CFC-11 eq, is the indicator of emissions to air that cause the destruction of the stratospheric ozone layer.
- Particulate Matter (PM), which is a complex mixture of extremely small particles. Particle pollution can be made up of a number of components, including acids (such as nitrates and sulfates), organic chemicals, metals, and soil or dust particles. A multitude of health problems, especially of the respiratory tract, are linked to particle pollution. PM is measured in PM10 equivalents.
- Photochemical Ozone Formation (POF), ozone is protective in the stratosphere, but on the ground-level it is toxic to humans in high concentration. Photochemical ozone, also called “ground level ozone”, is formed by the reaction of volatile organic compounds and nitrogen oxides in the presence of heat and sunlight. The POF depends largely on the amounts of carbon monoxide (CO), sulfur dioxide (SO2), nitrogen oxide (NO), ammonium and NMVOC (nonmethane volatile organic compounds). POF, also known as summer smog, is measured in ethene and NOx equivalents.
- Acidification (AD), the Acidification Potential calculates the loss of the nutrient base (calcium, magnesium, potassium) in an ecosystem, and its replacement by acidic elements caused by atmospheric pollution. Acidification originates from the emissions of sulfur dioxide and nitrogen oxides. Here the AD is dominated by nitrogen (NO2) and sulfurdioxide (SO2) emissions. In the atmosphere, these oxides react with water vapor and form acids which fall down to the earth in the form of rain or snow, or as dry depositions. This affects soils, water, flora and fauna, and can even damage building materials. The resultant ‘acid rain’ is best known for the damage it causes to forests and lakes. AD is measured in kg mol H+.
- Freshwater eutrophication (FE), indicator of the enrichment of the freshwater ecosystem with nutritional elements, due to the emission of nitrogen or phosphor containing compounds, measured in kg of PO4-
eq. - Terrestrial eutrophication (TE), indicator of the enrichment of the terrestrial ecosystem with nutritional elements, due to the emission of nitrogen containing compounds, measured in mol of N eq.
- Marine eutrophication (ME), indicator of the enrichment of the marine ecosystem with nutritional elements, due to the emission of nitrogen containing compounds, measured in kg of N eq.
- Mineral resource depletion (RD), measured in kg Sb eq, is an indicator of the depletion of natural non-fossil resources.
- Water Resource Depletion (WRD), indicator of the relative amount of water used, based on regionalized water scarcity factors.
- Energy Resource depletion (ED), Indicator of the depletion of natural fossil fuel resources, measured in MJ, net calorific value.
The environmental performance for the three biowaste streams valorised within the SCALIBUR framework for the production of high-value bioproducts is presented below.
Conversion of OFMSW into biodegradable polyesters and biopesticides
In this value chain, the Organic Fraction of Municipal Solid Waste (OFMSW) was hydrolysed in order to obtain an intermediate product (second generation sugars) and two valuable final products: biobased and biodegradable polyesters and biopesticides. Focusing on the biopesticides, they were obtained through both, liquid and solid-state fermentation (SSF) process. This production of biopesticides from biowaste developed within SCALIBUR has a lower impact value compared to the conventional pesticides, which production data is included in the recognized database Ecoinvent, as can be seen in the graph. The methodology used for the analysis is the ILCD method.
The results showed that, in the Climate Change (CC) impact category, there is a 30% GHG emission saving for the fermented solid with biopesticide activity compared with fossil reference. In other categories such as ozone depletion and mineral fossil resource depletion, the saving in the impact categories is between 90-98%.
Read more on this topic here!
Insects to valorise organic waste from HORECA
In the HORECA value chain, insects are used as a sustainable source of proteins, as they can be reared on a wide range of substrates such as biowaste. In this case, the HORECA biowaste is first prepared and mixed in order to obtain the substrate. The next step is to use this substate to feed the insects (insect rearing). Once the insects are reared, the larvae are separated, stabilised and fractionated to obtain protein, fat and crude chitin.
The demand for animal protein is expected to rise by 70-80% between 2012 and 2050 and the current animal production sector already causes major environmental degradation. However, insects are considered as a less environmentally impacting source of proteins than meat products. For this reason, the LCA of this value chain is focused on the results obtained for the proteins.
SCALIBUR proteins obtained by rearing black soldier flies with HORECA biowaste have been compared with a different type of protein produced from microalgae[1], using the methodology Impact 2002+.
In the impact categories analysed, the results obtained for the production of 1 kg of proteins by SCALIBUR are lower than the microalgae proteins. For instance, in the category of Climate Change (CC) and Water Resource Depletion (WRD), the saving is around 64%. In other categories, such as eutrophication and acidification, the savings are even higher, at 85-99%.
[1] Sustainable use Hermetia illucens insect biomass for feed and food: attributional and consequentional Life Cycle Assessment. S. Smetana, E. Smichtt, A. Mathys. 2019
Bioconversion of Sewage Sludge through bioelectrochemical routes
This value chain aims to develop a circular valorisation process to obtain “ready-to-use” products operating high innovative technologies, based on advanced anaerobic digesters and bioelectrochemical processes. This technology will obtain high quality biosolids since the pathogen content is reduced in line with the new European regulations. Also, methane production and dewatering of the sludge was also improved leading to energy-rich biogas production, and sludge volume reduction. In addition, the undesired CO2 stream will be treated by bioelectrochemical reactors to produce added-value organic products, mainly alcohols and acids.
The results of the LCA for the treatment of 1 ton of Urban Sewage Sludge (USS) are included in the graph. On the one hand, the technologies developed within SCALIBUR, represented by the turquoise bars, in which the treatment of 1 ton of USS will produce acetic acid. On the other hand, the reference scenario in this case is the treatment of 1 ton of USS in a conventional wastewater treatment plant for obtaining biogas, represented by the green bars. The methodology used for the assessment is the ILCD method.
As can be seen, the conventional treatment of biowaste to obtain biogas has a higher impact (between 90-99% higher in almost every impact category) than the sludge treatment to obtain acetic acid.
Conclusions
According to the results shown, potential environmental savings can be obtained when the SCALIBUR value chains are being applied to the treatment of urban biowaste and urban sewage sludge. Even though the technologies and bioproducts developed in this process are in the early stages of development, the results are showing better environmental performances that can compete with the conventional technologies and products. In the future higher savings can be achieved by applying some process improvements:
- Reducing the use of chemical compounds in production processes, creating recirculation flows
- Using more environmentally friendly chemicals into the production processes
- Using renewable sources for electricity and heat production
- Improving overall conversion efficiency, so that inputs are lower per unit mass of output
