2.0 Literature survey

 

As the world’s population increases and the diets of the developing world continue to improve, demand for meat and crops means food production could need to increase by up to 70% by 2050 (High Level Expert Forum, 2009). However, according to the Guardian (2013), it estimates that a third of all the food produced in the world is never consumed, and the total cost of that food waste could be as high as $400 billion a year. Most of it ends up in landfill sites where it rots and releases methane, a damaging green house gas. Throwing away food is also a huge waste of the energy, water and packaging used in its production, transportation and storage. The most important reason that food waste should be recycled is for capturing the energy content. Food waste is highly biodegradable and has a much higher volatile solids destruction rate (86-90%) than biosolids. In fact, in a study done, it was revealed that foodwaste has up to three times as much energy potential as biosolids. (East Bay Municipal Utility District,2012). Reducing food waste from 20 to 50 percent globally could save $120 billion to $300 billion a year by 2030.

 

2.1   The varieties of available technologies

 

The technology of turning food waste into energy brings together relevant bodies of knowledge for development of a practical and low cost system of proven technologies to produce food organically, generate renewable energy, and protect the environment.

Among the technology of recycling food waste into a valuable product are as below:

 

• Fermentation

• Anaerobic Digestion

• Pyrolysis and Gasification

 

 

2.2       The Reactions Involved

2.2.1    Fermentation

 

The process of fermentation involved in the making of beer, wine, and liquor, in which sugars from fruit are converted to ethyl alcohol. Fermentation is a metabolic process that converts sugar from fruit to acids, gases or alcohol. The chemical breakdown of a substance by bacteria, yeasts, or other microorganisms, typically involving effervescence and the giving off of heat. The carbon dioxide gas bubbles out of the solution  into the air leaving a mixture of ethanol and water. Fermentation must be carried out in the absence of air to make ethanol. (District, March 2008). This is called anaerobic conditions. If air is present, ethanoic acid is made instead of ethanol. Fermentation will not happen without yeast. Yeast is a microorganism containing an enzyme which acts as a catalyst. Fermentation works best in warm conditions(between 18 and 35 °C) and at a neutral or acidic pH (between 4 and 7).

 

2.2.2    Anaerobic Digestion

 

Anaerobic digestion is the process in which organic matter is broken down into methane by microbial activity in the absence of air. The waste that is obtained by digesting human, animal, vegetable and other food wastes in specially designed digesters As it breaks down it gives off methane, which is collected and converted into biogas and used to generate electricity, heat or transport fuels. It also creates a nutrient-rich digestate that can be used as a fertiliser for agriculture and in land regeneration (Omer, 2007; Lardinois, 1993).

 

2.2.3    Pyrolysis and Gasification

 

Parr.C (2010) stated that pyrolysis is the thermal degradation of a substance in the absence of oxygen. This reaction involves molecular breakdown of larger molecules into smaller molecules in presence of heat. Temperatures between 300°C and 850°C in order to break down waste materials is used. Pyrolysis is also known as thermal cracking, cracking, thermolysis and depolymerization. Pyrolysis is used to convert biomass into syngas and biochar, to turn waste into safely disposable substances. Another process called gasification is a partial oxidation process whereby a carbon source such as coal, natural gas or biomass is broken down into syngas. Oxygen is added but the amount is not sufficient to allow the fuel to be completely oxidised and full combustion to occur. This process uses temperatures between 750°C and 1200°C in order to break down waste materials to produce simple fuel gasses of hydrogen,H2 and carbon monoxide,CO.

 

 

2.3       Researchers or practitioners that made these technologies successful

2.3.1 Fermentation

 

Alfa Laval, a Sweden-based company

 

The demand is on the rise for bio-based products, such as bio-plastics, and bio-chemicals. With growth of the fermentation-based industry come challenges, including sustainability issues, environmental concerns and production cost constraints.  Alfa Laval addresses these challenges through their broad portfolio of hygienic equipment and services for lab, pilot-scale and full-scale fermentation. Alfa Laval equipment helps to continuously extract valuable products from fermentation broth or solid-substrate cultures to produce viable cellular material, chemical compounds, enzymes and other proteins or transform substrates into viable products which are cost-effective and high sustainably.  

 

2.3.1    Anaerobic digestion

 

Disney World's biogas facility: a model for converting food waste into energy

 

Food waste, including table scraps, used cooking oils and grease is collected from selected restaurants in the Disney World complex, as well as area hotels and food processors, and sent to a system of giant tanks at a facility near the park. There, the food waste is mixed with biosolids, the nutrient-rich organic materials left over after sewage is treated and fed to microorganisms that produce biogas, a mix of methane and carbon dioxide. The biogas is combusted in generators to make electricity, and the remaining solids can be processed into fertilizer. This process for turning organic waste into energy, which is known as anaerobic digestion, could turn out to be the best way to extract value from food scraps and treated sewage that would otherwise wind up in a landfill.

 

According to Kathleen Ligocki, the chief executive of Harvest Power, a venture capital-funded clean-tech company that built the Florida facility that is their goal to turns pumpkins to power, waste to wealth. Typically the local utility, buys its electricity. And its fertilizers are used in agriculture, horticulture, professional turf, and retail lawn and garden applications.The plant will process about 120,000 tons of organic material per year and produce 5.4 megawatts of combined heat and electricity, which is enough to fuel 2,000 Florida homes. That meets only a fraction of the energy needs of Disney World, which has more than 30,000 hotel rooms (the Guardian,2013).

 

Harvest-to-Harvest™, United States 

 

The amount of food wasted each day in just the US alone is enormous, Harvest-to-Harvest™ take the initiative of converting recycled supermarket organic waste into a liquid fertilizer. The term anaerobic digestion simply indicates that it is the product of the digestion of food with enzymes into a liquid fertilizer. Harvest-to-Harvest™ contains complex forms of nutrients, including carbohydrates, amino acids, organic acids, and fats which are a great source of nutrients and energy for soil organisms and plants (California Safe Soil, 2015).

 

2.3.3    Pyrolysis and Gasification

 

Kouei Industries International, The Recycling Technology for Tomorrow’s Energy

 

Kouei Technology combines two different technologies into one which are pyrolysis and gasifiacation recycling. Pyrolysis recycling is a non-combustion heat treatment that chemically decomposes waste material by applying heat (directly or indirectly) to the waste material in an oxygen free environment. Pyrolysis typically occurs under pressure and at operating temperatures above 430°C (800°F). The process generally produces char, oil and syn-gas, the ratios of each depending on the feedstock and the specific pyrolysis conditions (temperature, residence time, heating rate, pressure and degree of mixing) that are used (Jomaa et al., 2003). 

 

Kouei Industries offers several types of pyrolysis units, including the rotary kiln, rotary hearth unit, and the fluidized bed unit where some systems provide direct heat, others indirect, and both continuous feed and batch feed variations are available. Both the pyrolysis recycling and the gasification recycling processes turn waste into energy rich fuels by heating the waste under controlled conditions. By contrast to incineration, which fully converts the input waste into energy and ash, these processes deliberately limit the conversion process so that the waste products can be controlled, resulting in the waste material becoming valuable intermediate products that can be directly re-used in a variety of industries or processed further for more specific industrial application.

 

Typical raw materials used are coal, petroleum-based materials, and organic materials. The feedstock is prepared and fed, in either dry or slurried form, into a sealed reactor chamber called a gasifier. The feedstock is subjected to high heat, pressure, and either an oxygen-rich or oxygen-starved environment within the gasifier. Most commercial gasification technologies do not use oxygen but all require an energy source to generate heat which starts the process.

 

 

 

 

 

 

 

 

 

 

 

 

 

                                                            Table 1 : Pyrolysis Technologies in Kouei Technology International

 

2.4       The pros and constraints of these technologies

 

2.4.1    Fermentation

 

Fermentation technology is one of the most favored organic technologies and that’s mainly due to its reaction simplicity, high specificity, low costs, and flexibility of application. Fermentation’s applications areas are many such as food stuff like, cheese and bread into high-value chemicals, pharmaceutical ingredients, and food-related chemicals. There are many reasons for the increasing demand of the fermentation processes such as the rising hydrocarbon costs and the depletion of fuel reserves. Fermentation is a renewable resource that never runs out and does not release harmful gases into the atmosphere (Skadowski).

 

Fermentation process production is very slow and the product contains impurity, needing further treatment.  Fermentation has limited ability to vary output rate and has very long start-up times which require continuous skilled technical support. This leads to lots of worker needed and require more energy. There is serious consequences of break-down or microbial contamination possibility of selection of yeast mutants.

 

2.4.2    Anaerobic Digestion

 

Anaerobic digestion can be a powerful resource for waste management and energy extraction as it harvesting both methane and ammonia as multiple fuel and provide an additional extracted usable energy from waste processing. Furthermore, valuable by-products where the compost and fertilizer can be used or sold, creating an additional revenue stream. (Joseph A.R. et al, 2014). Renewable Consistent Power. As the amount of waste is produced continually, there is a constant stream of inputs into the digester creating a stable source of electricity generation. Besides, it helps to reduce greenhouse gas by reducing the release of methane by 66% and odor reduction by placing food waste streams in digesters.

 

Anaerobic digestion process is very sensitive to temperature and feedstock, thus both need to be controlled very carefully so that digestion process can occur. The disadvantages of this method might be the time-constraints as the process of digestion of organic matter without using any catalyst might takes time from couple to weeks to occur, even with catalyst system operation and maintenance is estimated to take 30 to 60 minutes per day to ensure efficient operation. Improvements in process technology have concentrated on reducing production costs and minimizing the environmental impact. These include boosting CO2 conversion efficiency, increasing heat recovery, reducing utilities consumption and recovering residual NH3 and urea from plant effluents.

 

2.4.3    Pyrolysis and Gasification

 

Pyrolysis can generate electricity, heat and chemicals and decrease in landfill use. The waste-to-energy plants dispose municipal solid waste (MSW) that will otherwise be sent to landfills. Furthermore, the bio-char produced can be used on the farm as an excellent soil amender as it is highly absorbent and therefore increases the soil’s ability to retain water, nutrients and agricultural chemicals, preventing water contamination and soil erosion. Pyrolysis can be performed at relatively small scale and at remote locations where enhance energy density of the biomass resource and reduce transport and handling costs. Besides, it can reduce the Carbon Dioxide (CO2) emission. For example, it avoids CO2 emissions from fossil fuel combustion, when a megawatt of electricity is generated by a waste-to-energy facility, an increase in carbon dioxide emissions that would have been generated by a fossil-fuel fired power plant is avoided. Furthermore, the rate of recycling can be increase. Studies have demonstrated that communities served by waste-to-energy have recycling rates that are nearly 20% higher than the national average. It is a creation of new local jobs up to 30 full time jobs will be created for Plant Managers and Operators and 45 new construction jobs (Pyrolysis : Pros & Cons).

 

Gasification can be coupled with advanced turbine technology to produce electricity. Syngas produced by gasification can also be further processed into liquid fuels (diesel, gasoline, jet fuel, etc.), hydrogen and synthetic natural gas, or a range of fertilizers or other high-value chemicals including anhydrous ammonia, ammonium sulfate, sulfur, phenol, naphtha and CO2 as mentioned above, among many others. Biomass gasification technology is also environment-friendly, because of the firewood savings and reduction in CO2 emissions. (National Advanced Biofuels Consortium, 2010) 

 

The product stream is more complex than for many of the alternative treatments. Fuel is bulky and frequent refueling is often required for continuous running of the system. It is a quite complex and sensitive process. Getting the producer gas is not difficult, but obtaining in the proper state is the challenging task. Second, the product gases cannot be vented directly in the cabin without further treatment because of the high CO concentrations. The latter issue can be addressed by utilization of a water gas shift reactor or by introducing the product gases into an incinerator or high temperature fuel cell. High-moisture waste streams, such as sludge and meat processing wastes, require drying before subjecting to pyrolysis.

 

 

2.5 THE WAY FORWARD THAT WOULD HELP OUR PROJECT

 

The three technologies found in our literature survey which are available to convert food waste into wealth are Fermentation, Anaerobic Digestion and Pyrolysis and Gasification.

In conclusion, after comparing the pro and cons of these three technologies, our team decided to procees with the anaerobic digestion as the technology to be used in converting food waste into sustainable energy production. We choosed this method mainly because anaerobic digestion can be a powerful resource for waste management and energy extraction, valuable by-products where the compost and fertilizer can be used or sold, renewable consistent power and helps to reduce greenhouse gas.

 

 

REFERENCES