Introduction
In our time, we are used to satisfy our nutritional requirements by simply buying raw or cooked food products at grocery stores or restaurants. Nowadays we can access pretty much any type of food product even if is coming from remote locations at affordable prices. However, there is an extra price to pay: unprecedented amounts of liquid and solid residues continuously accumulate in our soil, air, and water resources as a result of activities associated with food production and consumption. At the consumption end of the food chain, farm products are processed and packaged, distributed and finally eaten. Each of these steps generates undesirable contaminants.
Food waste: from sources to disposal
During food processing copious amounts of water are used to disinfect and remove particle materials such as soil. Some fruits may need a peeling process and in the meat industry bones, hair or feather remains, and fat are removed. Also, cooking and drying may be required producing thereby additional liquid residues. Distribution of products is generally in charge of supermarkets and wholesalers. At these locations incredible amounts of products are discarded and this happens when the expiration date is reached or products are spoiled. Also, this could be a direct consequence of the overproduction of certain types of products such as those subsidized by the government. Similar waste is also generated by restaurants, resorts, schools, and correctional and healthcare facilities. Once people decide not to eat what was served, either they take it home or is just discarded. All described waste materials are generally referred to as food waste. Accounting for approximately 12% of the total municipal waste in the U.S., food waste has attracted considerable attention due to the growing global concern of a food shortage during the coming years (Cheremisinoff, 2003). Approximately a quarter of food produced in the U.S. is eventually discarded. As population increases and living standards improve around the world, a much more sustainable food chain supply will be needed. As of today, food waste is generally taken to landfills or incinerated. Landfills are places where all sorts of residues are dumped and accumulated. Due to the biodegradability of some components of food waste, they are rapidly decomposed by anaerobic microorganisms, which in turn lead to a sustained production of the odorous greenhouse gases methane and carbon dioxide(Assamoi & Lawryshyn, 2012). Some of the microorganisms that proliferate are pathogens that can be dangerous if they manage to invade uncontaminated soil or water by runoff mechanisms (Cheremisinoff, 2003). Despite these issues, perhaps the most alarming concern with landfills is land scarcity. Second in popularity to landfilling is incineration. In this process, residues are combusted in a controlled environment to produce a less dangerous and more compact residue. The biggest concern with incineration is the emission of greenhouse and toxic gases to the atmosphere. Carbon monoxide, dioxins, furans, hydrogen chloride, sulfur dioxides and nitrogen oxides are some examples of harmful compounds that can be released upon incineration. When compared with landfilling, this technology requires a lot more investment and is designed based on the most predominant residues in the local waste, making it much less flexible (Cheremisinoff, 2003).
The environmental impact of food waste is not only present at the consumer end; it is also noticeable during production of food. Tremendous amounts of energy, fertilizers and water are invested to grow crops. As food is discarded, these precious resources are just flushed away. The main result of these extensive agricultural activities is the continuous loss of usable water and land.
Fossil fuels
Fossil fuels are also present in various stages of the food supply chain. For instance, fertilizers are derived from fossil fuels; also, they are used to power tractors and vehicles for herbicide aspersion and harvesting. Fossil fuels are a non-renewable energy sources mainly composed by organic molecules that store high levels of energy. They were formed by the continued accumulation of dead plants and animals over the course of millions of years. Depending on the conditions under which these organic sources were trapped, different types of fossil fuels were formed. The most commonly used fossil fuels in today´s society are petroleum, coal and natural gas. In any case, energy is removed out of fossil fuels by direct combustion in the presence of an abundant oxygen atmosphere. As of today, our societal energy needs are mainly satisfied with large amounts of fossil fuels. For instance, 36% of the U.S. energy demand alone comes from petroleum, which represents approximately 19 million barrels per day. Extraction and transportation of fossil fuels are conducted at a relatively low cost but with serious environmental implications. In the case of petroleum, important ecosystems are being contaminated with the effluents of drilling activities that are full of highly toxic and recalcitrant compounds. Additionally, when petroleum distillates (refined fractions, e.g., gasoline) are combusted, they release considerable amounts of Carbon dioxide, a greenhouse gas capable of altering the climate. The most abundant of all fossil fuels is coal with nearly 950 billion short tons worldwide. Coal mining is considered a soil depleting activity that leads to sustained erosion. Just like petroleum, its combustion is accompanied by greenhouse gas and particle emission. Natural gas produces the cleaner combustion of all three discussed here, however, it also requires non-environmentally friendly practices to search for it (Evans, 2007).
Comprehensive program for food waste management
The management of food waste residues should be done in a more comprehensive manner (Dorward, 2012). The extreme case of dumping all residues in landfills is no longer an option. The first step to approach to a sustainable an integral solid waste management program is to promote that food processing and packaging industries do more research on extending the life of their products. This should be accompanied by government regulations where these initiatives are awarded with green seals. A green seal should allow these industries to charge a high price for their products. One avenue to tackle this challenge is to make use of recent developments in nanotechnology that enable a new generation of materials to control ripening and therefore retard spoilage. The next step in generating this management program is to create a web-based and real-time detailed inventory of food waste generators. This can be done by taking advantage of the most recent developments in Geographic Information Systems. The system would allow wholesalers and distributors to have track of every single item in their stores and deposits. As time passes they can figure out what to do with their expiring inventory. Perhaps the most appropriate avenue to discharge these products is to join efforts with charity and donation centers. The needy would be very grateful if they have a continuous supply of products that are in good conditions but close to expiration. Every store joining these initiatives should receive a green seal as well. If definitively there is no option but to send food waste to the landfills, an intermediate step to separate recyclable materials should be there. The resulting organic products can then be treated much more efficiently. At this point, an energy generation step should follow. A combination of aerobic and anaerobic reactors with powerful microorganisms should be able to receive the residues to generate biogas in a very controlled manner. This is imperative to regain part of the energy spent during growing and harvesting or during cattle feeding if the residues are coming from meat industries. The obtained biomass can be treated for animal feeding purposes. If incineration is still required, the energy of the combustion process can be coupled to the bioreactors to accelerate the rate of microorganism’s proliferation. In case of excess energy availability, electricity can be also generated.
Renewable energy sources
At this point, it is clear that a highly reliable food waste management program should also address issues regarding the use of fossil fuels during several steps in the food supply chain. Vehicles and machinery for growing and harvesting are currently powered by gasoline or diesel. These sources can be replaced by sustainable biofuels. These types of fuels are obtained from woody trees, grasses, wheat, corn, sugar cane or oil rich crops. The most important attribute of biofuels is that their raw materials are fully renewable. Energy from biofuels is generated via combustion, gasification or fermentation. Combustion is generally applied to wood and vegetable oils to release energy in the form of heat that in turn can be used to generate electricity. The combustion of these materials is accompanied by gas emission albeit at a lower level compared with fossil fuels (Evans, 2007). Gasification also involves burning of biomass at high temperatures but in an anoxygenic environment (Basu, 2010). The produced gases are subsequently reacted following a relatively complex chemical scheme to produce liquid fuels. Fermentation is mostly for biomass with high levels of sugars and involves microorganisms capable of metabolizing the sugars into molecules with high energy content, i.e., alcohol or butanol. The obtained bioalcohols can be incorporated into modified internal combustion engines with much less gas emission. The major concerns with biofuels are the requirement of large extension of land to grow the biomass, and the use of biomass intended for human consumption. As alternative, researchers around the world are developing new bioalcohol production methods that use non-edible biomass sources such as cellulose (Goyal, Seal, & Saxena, 2008). Another attractive energy source that can be coupled to the food supply chain to improve sustainability is solar energy. Every year our planet receives from the sun approximately ten thousand times human energy consumption. To try to capture some of this energy, researchers have developed artificial cells that mimic plant leaves energy capturing capabilities. These artificial cells are called photovoltaics and they are design to capture photons and convert them to electricity. The major obstacle to overcome with this technology is efficiency, which is limited by the properties of the material contained in the cells and used as transducer, i.e., silicon. As solar light impacts the material, an excited state is created in the silicon from which electrons are then withdrawn to generate electricity. In an effort to improve efficiency, modified cells have been created including dye-sensitized, thin film and photoelectrochemical. Despite these engineering efforts, maximum efficiencies observed approach 30%, not enough to compete with mature fossil fuel technologies that reached 50-60% long ago. Solar cells are an interesting option to meet some of the energetic requirements not only during growing and harvesting but during transportation of food products. To date, high installation costs are required but the emergence of new materials such as graphene open up tremendous opportunities to build ultra-light and highly efficient cells.
Conclusion
As we move into the future, several concerns about the proper use of our resources have appeared. An increasing population that approaches 8 billion people will have to find a sustainable way of life to prevent extinction. One of the main aspects is to assure food supply to this large number of individuals. Thus far, our food system is not prepared to withstand these extreme forces of human expansion. At this point, we are producing much more food that is consumed with severe environmental implications and energy misuse. All the food discarded goes in a disorganized manner to landfills where is degraded to odorous and greenhouse gases. A closer look at how the system works reveals a number of alternatives that in sum propose a holistic assessment of every stage in the food supply chain. This approach involves the creation of an updated inventory of food waste generators, energy saving strategies and gradual replacement of fossil fuels.
References
Assamoi, B., & Lawryshyn, Y. (2012). The environmental comparison of landfilling vs. incineration of MSW accounting for waste diversion. Waste Management, 32(5), 1019–1030. doi:10.1016/j.wasman.2011.10.023
Basu, P. (2010). Biomass Gasification and Pyrolysis: Practical Design and Theory. Elsevier Science. Retrieved from http://books.google.com.co/books?id=QSypbUSdkikC
Cheremisinoff, N. P. (2003). Handbook of Solid Waste Management and Waste Minimization Technologies. Butterworth-Heinemann. Retrieved from http://books.google.com.co/books?id=5GOtjLrUsZ0C
Dorward, L. J. (2012). Where are the best opportunities for reducing greenhouse gas emissions in the food system (including the food chain)? A comment. Food Policy, 37(4), 463–466. doi:10.1016/j.foodpol.2012.04.006
Evans, R. L. (2007). Fueling Our Future: An Introduction to Sustainable Energy. Cambridge University Press. Retrieved from http://books.google.com.co/books?id=-NqBWrKaMZ0C
Goyal, H. B., Seal, D., & Saxena, R. C. (2008). Bio-fuels from thermochemical conversion of renewable resources: A review. Renewable and Sustainable Energy Reviews, 12(2), 504–517. doi:10.1016/j.rser.2006.07.014
