ENERGY FROM WASTE
A DAMASCENE CONVERSION? PROTECTING OUR ENVIRONMENTAL HERITAGE A recent UN report, produced by its Environment Programme, confirmed that in excess of 1,000,000 tonnes of food waste is generated globally per annum and causes between 8 & 10% of all greenhouse gas emissions. In the first of three articles, Chartered Engineer Professor Robert Jackson and Lawyer Peter McHugh examine the changes required in attitudes, expectations and regulation to permit a sustainable balance between environmental burden and environmental capacity.
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lthough he was not one of the Twelve Apostles, the Christian apostle Saint Paul spread the teachings of Jesus in the first-century Anno Domini (AD). Born in Syria, around the same time as Jesus, he was a Greekspeaking Jew who was converted to the Christian faith in or about 33AD and died in Rome circa 63AD. As one of the leaders of the first generation of Christians, he is often considered to be the most important person after Jesus in the history of Christianity. Whilst travelling to Damascus he had a vision in the form of a blinding bright light where God revealed his Son to him. This revelation convinced Paul that God had indeed chosen Jesus to be the promised Messiah and it changed his life forever. Hence, on the road to Damascus Paul witnessed a seminal moment that led to a sudden and dramatic transformation in his attitude and beliefs. Such a dramatic transformation and Damascene conversion is required in people’s attitudes and beliefs toward food wastage regarding its direct and profound implications to environmental pollution and human health. Interestingly, whilst AD has thus far denoted Anno Domini, in the context of environmental pollution AD denotes a most promising technology for food waste management in the form of anaerobic digestion. Globally, the traditional disposal methods of large amounts of food waste have, to date, principally comprised landfill, incineration, and composting. However, these chosen methods have resulted in significant environmental pollution and increased financial risks. Annual world-wide food production currently stands at 2.7 billion
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tonnes with one third lost or wasted throughout the food supply chain. By way of example, since 1974 the amount of food waste created in the United States alone has increased by 50% with 36 million tonnes of food waste now being discarded every year, whilst nearly 10% of its total population suffers from food insecurity. Currently, food waste equates to approximately 100kg per person and comprises the single largest component (22%) of municipal solid waste disposed to landfill. As a consequence, the food industry creates damaging social and economic side effects whilst simultaneously depleting the environment of limited natural resources; the problem is further compounded by the fact that in the US less than 2% of food waste is subject to AD. Likewise, within the European Union an estimated 20% of the total food produced is lost or wasted, equating to approximately 88 million tonnes, whilst 33 million people cannot afford a quality meal every second day. 70% of EU food waste arises from households, food services and retail outlets, with households alone generating 47 million tonnes forming more than 50% of the total. To assist in resolving this ongoing dilemma, anaerobic bacteria are able, by employing AD, to convert organic waste and biomass into biogas whilst leaving a nutrient-rich residue suitable for agricultural land use. AD is a process through which bacteria break down organic matter such as animal manure, wastewater bio-solids, and food waste, in the absence of oxygen. Biogas constituents typically comprise 60%70% methane, 30%-40% carbon dioxide,
ENERGY MANAGER MAGAZINE • MAY 2021
together with traces of hydrogen and hydrogen sulphide. Hence food waste, being a high-moisture, energy-rich substance, may provide substantial economic benefits from AD by way of renewable energy production. One of the principal advantages of AD over other bio-energy technologies is its ability to operate using a wide range of substrates i.e. those materials from which bacteria can obtain food and nourishment and on which they are able to grow and thrive. Food waste therefore comprises an excellent substrate for AD, due to its availability, quantity and high energy content. During the anaerobic digestion of food waste, a mixture of gaseous compounds (biogas) is released that commonly includes odourless methane and carbon dioxide, together with ammonia and highly odorous volatile sulphur compounds which include hydrogen sulphide (H2S - odour of rotten eggs). Other odorous compounds emitted include ethyl mercaptan (C2H6S - garlic, onions, and cabbage); methyl mercaptan (CH4S - cheese); carbon disulphide (CS2 - rotten vegetables); and dimethyl sulphide ((CH3)2S - rotten vegetables and cabbage). All of these odorous gases are prejudicial to human health. The benefits accrued from biogas generation using AD can often be further enhanced through chemical dosing to increase the biogas volumes yielded. This can be achieved by increasing the pH of the food waste. pH is a measure of the concentration of hydrogen ions in solution and is on a logarithmic scale from 0 (acid) to 14 (alkali). It is used to specify the acidity or alkalinity of an aqueous solution and a pH value of 7.0 is neutral, so a pH of 5.0 is ten times more
