Biogas from food processing waste
The idea behind this research project is to produce biogas from the fruit waste left by the processing of mango.
The country is Belize. The reader may be one of the few who has eaten a mango from Belize and knows where the country is located. It lies in Central America, a former, small English colony - British Honduras - with many Spanish speaking immigrant workers from the neighboring countries of El Salvador, Guatemala and Honduras.
Belize is a tropical country with fertile land in the flat areas around the many rivers, and large infertile plains with the so-called pine ridge soil.
Up to three meters of rain may fall in a year, and there are tropical rainforests in many places in Belize.
Tropical Produce Co. Ltd. produces bananas and mangos in Belize. The mangoes are exported as fresh fruit to the United States and Europe, including Denmark. "Belize Gold" is the name of the mangoes from Tropical Produce. Up to 2,000 tons of fresh mangoes are produced every year from the plantation of Tropical Produce on Monkey River Estate.
Some years ago, Tropical Produce began to produce juice from those mangoes which did not live up to the demands of the international fresh fruit market. This was done on a factory at the plantation. The process leaves quite some fruit waste. Only 50% of the mango becomes juice, and the rest is either seed, skin, or fruit pulp which is removed in the process. This kind of waste is not only a problem for Tropical Produce, but also for all other fruit producers in the country. It decomposes rapidly, and gives rise to the hatching of many fly larvae. Because of this it has to be quickly removed from the production areas, and buried.
The expense connected to the problem of hygiene and odor of the fruit waste could possibly be turned into an advantage by transforming the fruit waste partly to biogas, and partly to fertilizer. Since the mango is harvested only during a couple of months, organic waste would be lacking for the production of biogas during the rest of the year. A biogas plant is not turned on and off - when the process of fermentation has started, it has to be maintained with a constant supply of organic material. This is where the bananas come in, since the banana production takes place all year around.
Both the mango waste and the wasted bananas create a problem in Belize, and an inexpensive biogas solution would be very welcome. It was a question of combining the available knowledge of biogas plants, of fermentation, etc., and then use this knowledge in a Third World country where this knowledge had until know not been utilized - and then use it specifically with mangoes and bananas as the raw material.
To avoid too much and too expensive transport of the waste, it was necessary as a starting point to work on the development of a simple, efficient and inexpensive biogas plant, basically constructed in the form of a big hole in the ground, lined with plastic in the bottom and on the sides, and a "lid" consisting of a strong plastic sheet over the waste. The plant had to be economically feasible also for small scale farmers, possible to create on any farm and plantation.
The time was 1989. The previous two decades had shown much progress and great achievements within alternative energy and environment protection. Wind mills, solar collectors, solar cells, biogas - there were great expectations to these areas. Experiences were being gathered. Biogas, in that respect, was lagging behind. The number of biogas plants could by no means stand up to the number of windmills and solar collectors created. But nothing ventured, nothing gained!
Apart from its aim of doing research, the project also served as protection of the nature in that a biogas plant reduces the need for diesel to produce electricity and for fertilizer. The finished biogas plant could furthermore become an example for other farmers of how fruit waste can best be utilized. The common method of solving the problem with the waste in Belize is to "dump" the waste in big piles on distant fields. Here the waste rots relatively quickly - at times causing pollution since the remaining juices often find their way to the many water sources and creeks crossing the country. There have actually been numerous cases of such serious pollution of the water flowing through the Stann Creek Valley that the water supply to the town Dangriga has had to be stopped. The drinking water was so strongly polluted by citrus waste that it could not be sufficiently purified through existing purification plants. Thus this research project was also a project aiming at protecting the environment.
The idea was that the fruit waste would be mixed with the right amounts of lime, as well as with some fibrous materials to add air, such as straw, leaves and twigs, and possibly some nitrogen to boost the process.
Basically, Tropical Produce in cooperation with IFAS formulated the following research project:
The research project had the aim to prove that waste from the fruit processing can be used for the production of electricity and fertilizers in a biogas plant in Belize. The project would establish a laboratory, and research into how the biogas plant could function through using fruit waste as its energy source.
The raw material can, in principle, be any organic material. But some organic materials ferment quicker and easier than others. As had been seen in the project period: the fermentation process does not start automatically, but depends on which type of material is used. For example, the process does not start with pig manure alone. But together with cow manure and chicken manure, andmixed with fibrous organic materials like straw, leaves and twigs the proper preconditions are in place. However, Tropical Produce did not have pigs, cattle, or chickens in such a number that their manure could make a difference. The research project therefore aimed at finding ways to produce biogas and fertilizer from the existing large quantities of fruit waste.
When and if the fermentation process starts, methane gas is released. This gas can, instead of just disappearing out into the air like from a dunghill or a dump, be collected and burnt off. The energy from this burning can be used to heat water, which can either be used for the production of electricity or for heating houses and bath water.
The methane gas and its inherent energy is a valuable product of the fermentation. Another product is the altered waste. The waste, after the fermentation and release of the methane gas, is a more accessible and more valuable fertilizer than the original waste. The improved waste can be used in the fields and replace the expenses for other fertilizers. All in all, a well functioning biogas plant transforms the waste from a nuisance which takes up space, smells, and needs to be removed, into a considerable value.
The project cost 349,000 Dkr in all, ( who paid for it? ) and was carried out according to plan during five months, in a cooperation between IFAS's researchers and Tropical Produce Co. Ltd. Tropical Produce provided the premises for the researchers, and access to ample amounts of waste.
The following had to be done:
Fermentation tanks had to be set up to hold the fruit waste, involving the utilization of such materials and construction methods which would make it possible to build the tanks with locally available materials and without the need for specialized labor.
Testing facilities had to be designed and constructed, so that all the necessary measurements could be made during the two month harvesting period - that is, a number of tests should be carried out in parallel and independent of each other. The testing facilities had to be equipped with all the essential instruments for the accurate measurement of quantities, the quality of the waste, and of the volumes of resulting methane gas and of the fermented waste, which was to be used for fertilizer.
Minor adjustments had to be made at the mango juice factory so that the fruit waste could be transported to the fermentation tanks in the easiest way possible.
The personnel had to be trained to assist in the daily research work.
Investigations throughout the harvesting period had to be carried out to find the optimal method of waste treatment in order to reach the maximum methane production, with due regard to the fact that the final method had to be simple to carry out.
The results and the experiments had to be analyzed for the purpose of drawing a conclusion and making it available to all interested in Belize. The
se actions were carried out. Unfortunately, they did not have the expected result. It did not succeed to initiate and maintain the desired fermentation process, with its ensuing results, using mango and banana waste as the main ingredients.
The difficulties lay in the handling of the relatively large quantities of waste which were produced in a short time. For example, the juice factory produced 50-100 tons of wet, mushy waste in 24 hours. It showed to be more difficult than expected to achieve the appropriate consistency of the fermentation matter in the ground tanks - and very difficult to mix it inside the tanks.
Much intensive work was carried out to change the structure of the raw material.
Several shredding and grinding mechanism were developed, tested, and used. These were initiated as an attempt to grind the pit, which makes up app. 25% of the waste, and to thereby acquire a better consistency and a better chemical balance.
In order to raise the pH-value of the biomass and thus optimize the conditions for the methane producing microorganisms, many experiments with additional substances like burnt lime were carried out.
The modest amount of gas which was produced was used as "auxiliary fuel" for the factory's generator and steam plant. But the volume was too small. The production of biogas was not as simple as expected. The mixture of raw materials has importance. The temperature in the fermentation tanks and the stable supply of raw material has importance. Many factors have to be under control in order to achieve an economically profitable biogas production.
Was the project then legitimate as a research project? Yes, just like any other research project which started with its idea, its perspectives, and diligent practitioners, but which neither had its hypotheses confirmed or rejected.
The final report for the project was treated by the Foundation's board of directors in October 1990. The 349,000 Dkr were used in accordance with the objective and the specifications of the grant, and donated to an action research project in which the activities and achievements of the researchers focused on changing the prevailing reality, and the existing piles of waste, but without success at the time.
The laboratory was handed over to Belize's Banana Growers Association in 1994.
The Foundation for the Support of Humanitarian Purposes, for Promotion of Research and for Protection of the Natural Environment