By Nicholas M. Holden, Beacon Bioeconomy Research Centre, University College Dublin, Ireland. Nick.Holden@ucd.ie
For Citation: SITE4society Brief No. 17-2019
Related to Sustainable Development Goal #SDG12 Ensure sustainable consumption and production patterns
Country Focus: Ireland, Europe and Developed Countries
SITE Focus: Technology and Engagement
Sub-disciplines: Agricultural Systems Technology, Food Systems Sustainability, Biosystems Engineering, Bioeconomy
Based on: Oldfield, T.L.,White, E., Holden, N. M. (2016). An environmental analysis of options for utilising wasted food and food residue. Journal of Environmental Management, 183, 826-835
Context: The vast majority of the food eaten today is unsustainable because it causes negative environmental impacts and depletes non-renewable resources. We can think of food as ‘fossil food’ because it needs fossil fuel, non-renewable mineral resources (e.g. phosphorus), depletion of groundwater reserves and excessive soil loss to be produced. Even organic production is far from sustainable in many cases, because it is only possible when operating as an island in a sea of conventional production. It still uses fossil resources (sometimes more intensively) and if operating in a water scare region, will have to deplete reserves to function. Nevertheless, there are local exceptions, but these are rare, and have little impact on the food supply for the majority of the world’s population. On top of this, estimates suggest between 30% and 50% of the food we produce is wasted, in other words, it is never eaten, and in many countries becomes a waste management problem. There has been a move towards encouraging innovation to find uses for wasted food, such as nutrient recycling by composting and anaerobic digestion to mitigate the impact of wasting food. Evaluation of the benefit of these actions has tended to focus on managing waste (an ‘end-of-pipe’ solution) rather than helping to create a sustainable food system.
Research Questions: So, a relevant question is “should we encourage wasted food management through nutrient recycling, and energy capture technologies?”
Another way of asking the same question is “does the recovery of nutrients and energy from wasted food offset the resource depletion and environmental impact caused by growing the food in the first place?”
Our options are: (1) cure the problem (composting, anaerobic digestion or incineration);
(2) avoid the problem (reduce wasted food altogether);
or (3) carry on as normal (business as usual) i.e. do nothing.
What should our priority be?
Motivation for Research Questions: The motivation for doing this work is the proliferation of research and innovation around ‘solving’ the food waste problem by making it a feedstock for a secondary process. Before we started the research, we had carefully defined types of waste in the food system to reduce ambiguity.
‘Waste’ is something that is not utilizable in any way and so must be disposed of by burning or landfilling
‘Residue’ is material that is unavoidable but not consumable, so is a (bio)resource suitable for (re)use, (re)cycling, composting or energy recovery; and;
‘Wasted food’ is mismanaged food (i.e. edible) that does not get eaten.
As these tend to be lumped together as ‘waste’, mismanagement of each type might not reduce the impact of the food system or contribute to sustainable consumption and production. Our focus was ‘wasted food’ and food ‘residue’ because these can be inseparable (e.g. banana has both edible flesh (food) and inedible skin (residue)).
Data, and Methodology Used
For this work, we used a method called Life Cycle Assessment (LCA), which is used to quantify all of the processes involved in the creation, use and disposal of a product, process or service. We also calculated the ‘Carbon Return on Investment’, which is the potential amount of carbon reduced per unit investment in a technology designed to reduce climate change impact. We made two assumptions. First, 70% of wasted food can be consumed. Second, 20% of wasted food is unavoidable residue. Then, using secondary data on municipal solid waste, we estimated that in 2010, Ireland wasted about 1,267,749 tonnes of food, which meant that about ~4,225,830 tonnes of food was available for purchase and around 1,014,199 tonnes was avoidable wasted food.
The different ways of dealing with wasted food and their implications for the eco-system are shown in Figure 1. Using a combination of these alternatives, five management options were considered:
(a) baseline or business-as-usual (BaU), which is a combination of landfill and composting based on current practice;
(b) wasted food reduction with unavoidable residue and minimal wasted food being either composted or used as feedstock for anaerobic digestion;
(c) composting of all current wasted food and residue instead of BaU;
(d) anaerobic digestion of all current wasted food and residue; and
(e) incineration of current wasted food and residue.
Figure 1. Technical options available for dealing with wasted food and implications for the system L = Landfill, C = Composting, WP = Waste prevention, AD = Anaerobic digestion, I = Incineration, Ca = Carbon sequestration, NPK = Fertilizer avoided, AFP = Avoided food production, E = Electricity generated.
As these different options for dealing with wasted food serve other purposes, these have to be accounted for when evaluating the environmental impact. We also calculated the consequence of using each option in terms of capture of carbon permanently in the soil or as a greater mass of living plants (i.e. the carbon is ‘tied-up’ in the living plants that were not there before, or is bound in the soil rather than being in the atmosphere), which has the effect of reducing, or offsetting the greenhouse gas emissions to the atmosphere, avoided fertilizer production (i.e. calculating the amount of mineral fertilizer that need not be used because of nutrients returned to the soil) and avoided food production (i.e. food that need not be produced if it is never going to be wasted).
1. Impact on climate change through reducing emissions: The results (Figure 2) showed that anaerobic digestion could make a tiny but positive contribution to reducing climate change impact (a very small negative value), but this was completely overshadowed by preventing wasted food (a very large negative value).
2. Impact on atmospheric acidification and surface water eutrophication: Atmospheric acidification occurs when sulfur, nitrogen and organic compounds are oxidized in the atmosphere to form acids. The acids can have an impact on vegetation, buildings and oceans when deposited by rain. Eutrophication occurs when surface waters become enriched by nutrients. Freshwater is usually low in phosphorus and sea water is usually low in nitrogen, which limits algal growth and keeps the water clear and ‘fresh’. If the concentration rises, algae grow, causing clouding of the water, and possibly putting toxins into the water and reducing the dissolved oxygen, in turn making it difficult or impossible for aquatic or marine life to survive. The results indicated that wasted food prevention is the only option that reduces these impacts, which mostly occur during when the food is produced (i.e. on the farm). The other waste management options generally caused small additional impacts (Figure 3).
Figure 3. Change in emissions causing (1) acidification and (2) eutrophication for (a) business as usual, (b) prevention, (c) composting, (d) anaerobic digestion and (e) incineration.
3. The carbon return on investment (i.e. reduction in kilograms of carbon dioxide (CO2) per €1 spent):
Investment in technologies can provide a net carbon benefit compared to business as usual (Table 1).
-Anaerobic digestion provide the greatest ‘bang for the buck’, with a -0.84 kg CO2e change per €1 spent.
-Composting is at the tipping point between benefit and detriment due to the emissions during the composting process.
-Incineration is slightly beneficial, due to the offset of fossil fuel generated electricity. As countries transition to sustainable energy, this benefit will disappear.
–Landfill is detrimental, causing emission for every €1 spent.
We can also understand the returns to climate change benefit in another way. Consider two options: food waste prevention and investing in anaerobic digestion to ‘cure’ the problem. It would only be necessary to ‘prevent’ 150 g wasted food for every €1 spent to achieve the same climate change benefit as investing that money in anaerobic digestion. In other words, a €1million investment in a wasted food prevention programme would only have to prevent 150 tonnes of wasted food to have the same climate change benefit (840,000 kg CO2e) as investing the same money in anaerobic digestion equipment to process the wasted food for nutrient recovery and energy generation. We have not estimated how much wasted food might be prevented by an investment of €1 million in a programme to reduce food waste, but it is very likely to be much more than 150 tonnes.
When it comes to wasted food, prevention is undoubtedly better than cure.
Thus, minimizing or avoiding wasted food and residues seems by far the best way to reduce the environmental impact of food waste. To produce food (in most circumstances) requires an investment of non-renewable resources (e.g. oil, phosphorus) and will cause polluting emissions (e.g. greenhouse gases). If the food that has been produced is wasted, there is nothing that can be done to offset, or compensate for the resources that have already been ‘spent’ be that recovery of nutrients, generation of energy or synthesis of new materials. It is impossible to compensate for the resources consumed and adverse environmental impacts that have been caused by growing the food in the first place. We can say with certainty, that for wasted food, prevention is far better than cure.
1. Investment in infrastructure, agriculture (what to grow, how and when) and education (what to eat and how to cook it) should focus on minimizing wasted food.
2. Financial support for innovation and companies operating in the bioeconomy should be targeted to only address unavoidable residues and should discourage financial incentives to valorize wasted food.
3. No policy should ever result in wasted food being valued as a feedstock or resource. Minimization is the only meaningful solution.
4. Management of wasted food should not be thought of as an end-of-pipe problem, but as a minimization problem.
 Based on correspondence with keywords published by Monash University for a group of Australia / New Zealand universities to map their activity to SDGs (http://ap-unsdsn.org/wp-content/uploads/2017/04/Compiled-Keywords-for-SDG-Mapping_Final_17-05-10.xlsx)
 This reasoning was formally summarised in the publication that this brief is based on.
 ISO 14040:2006, Environmental management — Life cycle assessment — Principles and framework
 Stoyke, G (2009). The Carbon Charter Blueprint for a Carbon Free Future. New Society Publishers. 114p.
 Based on (EPA) Environmental Protection Agency Ireland, 2013a. Stop Food Waste. http://www.stopfoodwaste.ie.
 Based on RPS, 2008. Municipal Waste Characterisation Surveys 2008. http://www.epa.ie/pubs and RPS, 2010. 3rd Bin Commercial Waste Bin Characterisation Report. http://www.epa.ie/pubs.
 The volume of a gas depends on its temperature and pressure, so the only way to express its amount is in terms of the mass (of molecules). Gases all have mass. Think of an ice cube. When it melts is remains at about the same volume (not quite), but as it boils, it expands to occupy a much larger volume. In a closed container, there would be the same number of molecules, but they would occupy a different volume, therefore, we express amount of a gas in the atmosphere in kg because this is the only unit that is independent of temperature and pressure. Note kg CO2 and kg CO2-e are not the same. The first is what it seems to be, but the second expresses different gasses in terms of the equivalent effect of CO2 in the atmosphere. 1 kg CO2 = 1 kg CO2e. 1 kg CH4 = ca. 26 kg CO2e. 1 kg N2 = ca. 298 kg CO2e (these numbers vary a little depending on what you read, but they are the right ball park).