Since ever civilization and wastes are two concepts that have advanced and developed together. The human groupings in a particularly location, like a village, town or city have taken with them the waste generation that were to be, if not treated, at least managed. It is amazing and indicative that a problem that has accompanied to the man from the beginnings of the civilizations follows without being satisfactorily solved in the 21st century.
In the Palaeolithic human’s settlements, holes excavated in the surroundings were used to deposit all the wastes that they generated. Obviously at those moments all the wastes were of organic nature.
This “processing” system continued staying in old Sumerian and Greek civilizations, being the origin of the garbage landfills.
There is not a well-known date that could be considered as the beginning of the use of the organic wastes in agriculture, but it is necessary to mark a difference that is created in the waste management from which the human’s settlements concentrate every time to a greater number of habitants, settling down a differentiation between urban and rural areas. Thus in the rural it existed an exploitation of the organic wastes, either human as animal, for its use in agriculture considering them a resource. Nevertheless, in the cities the wastes were considered a problem that must be eradicated, and it supposed management did not pretend more than to remove them outside the walls and get rid of them. That approach already existed in cities like old Crete, intensified during middle Ages, especially when streets were paved, and peculiarly it has stayed of generalized way to the present time.
Nevertheless there were exceptions like in Rome at 50 b.C., a city of a million habitants under the rule of the imperator Augustus, where there was a collection of the generated organic wastes that were used later in agriculture. In the city of Florence, during the 15th century, they were the same farmers who by the mornings entered the city with their carts full of fresh products to sell in the markets, those that, to the dusk, picked up the organic wastes of the city to use them in the culture of their fields.
Therefore the knowledge of the benefits of the use of fertilizing with organic wastes in the fields is demonstrated that goes back at the beginnings of the agriculture. If that is thus, when it was begun to turn them into compost. The first reference to the application of techniques to transform the agriculture and cattle wastes into fertilizers were find in China, India and Japan, where they knew and applied it from more than 4.000 years ago. By something they were civilizations with a very high number of habitants to whom one was due to feed and to maintain thanks to the agriculture.
The contact with other populations and civilizations during the centuries of invasions and conquests caused that this knowledge could be transmitted among others cultures. The Arabs were mainly who facilitated that these techniques arrived at Europe, where the first written reference of the composting process was realised.
The first master composters
It is in Trujillo (Cáceres, Spain) where a templar manuscript dated in 1182 appeared in 1963 and attributed to the great master templar Gualdim Pais, where the process to obtain a “living humus” or “fertile gold” from organic wastes of agriculture and cattle was described. Following the type of culture and/or soil, they offered different recipes for, by means of techniques of turning windrows, obtaining a quality fertilizer. It is important to indicate that they gave great importance to the particle size and to the moisture during the whole process, established in about 90 days.
There were not found other wrote references until the 16th century, although the knowledge remained and it was orally transmitted without known advances or implementations in the used methods.
Along the next centuries the agriculture became to be intensive, with extensive monocultures and the introduction of specialized machinery that replaced the animals so whose wastes could not be used as fertilizer. With time, the application of chemical fertilizers and pesticides to the fields to maintain their productivity became to be more and more necessary. Peculiarly the introduction at the 19th century of these agriculture techniques with monocultures such tea, tobacco, cotton, coffee,… in countries already mentioned as India and China that were the cradle of the agriculture techniques, lead to great extreme hungers.
Sir Albert Howard (1873 - 1947)
In certain way he is considered the “father” of modern composting and also he was vindicated like the pioneer in the concept of the “organic agriculture”. Been born and educated in England, he worked during 25 years like agricultural researcher in India (1905 – 1931), first like agricultural adviser of the states of Central India and Rajputana, and later like director of the Institute of Plant Industry in Indore, after which he returned definitively to England.
In his years of work in India, his experiments and observations, together with his talent as innovating and development of concepts, took him to adopt a vision of agriculture like a technique completely linked to the management of the organic matter. Against “learn more and more about less and less” that happened in the tests realised in laboratory under controlled conditions, Sir Howard focused his research works in how healthy and abundant cultures under the normal conditions of work in the field could be obtained.
“There is no nuisance of any kind -- no smell, no flies, no dustbins, no incinerators, no artificial sewage system, no water-borne diseases, no town councils, and no rates. On the contrary, the forest affords a place for the ideal summer holiday: sufficient shade and an abundance of pure fresh air. Nevertheless, all over the surface of the woods the conversion of vegetable and animal wastes into humus is never so rapid and so intense as during the holiday months -- July to September.” (Howard, 1940).
In this way, Sir Howard considered that the soil fertility passed through an effective recycling of all the organic wastes and their application, and thus, during his stay in the city of Indore, in centre of India, between years 1924 and 1931, he devised a process to produce humus from vegetal and animal wastes, to which he denominated “Indore Process”. The first detailed description of the method was published in the chapter four of his book The Waste Products in Agriculture (1931), although from later investigations he added new suggestions to the method without varying its two main principles: the mixture of vegetal and animal wastes with a base to neutralize the acidity, and the processing of the material so that the micro organisms responsible for the process would be in the most suitable conditions. The system described by Howard is realised in plateaus or ditches (following the climatology of the zone) during three months with two turnings and periodic watering.
From its publication, the description of the method spread quickly along the world. In 1931 it was built in Wijster, Holland, the first industrial composting facility whose system of processing is a modification of the Indore method. The specific proposal of this facility is to use organic wastes like fertilizers in the north of the country. The Indore method is translated to German in Der Tropenpflanzer in February of 1936 and to Spanish in the Revista del Instituto de Defensa del Café de Costa Rica in March of 1937. In 1940 the own Sir Howard introduced in his book An Agricultural Testament numerous references of farms that successfully applied his method in the five continents.
The mystification of the composting
It had to be the exponential increase of the rate of waste generation and the landscaping impact of the garbage dumps which modified the priorities of the public opinion with respect to the residues, superseded the economic aspect and the comfort like the most important factors of the waste management, what took to recognize the necessity to develop management and treatment systems with a minimum impact in the Nature and what offered the minimum risks of affection to the public health.
In addition, the economic crisis of the decade of 1930 stimulated the reutilization of the domestic wastes to try to replace the each time more expensive raw materials. This social panorama, with the popularity of the Sir Howard’s discoveries, allowed the takeoff of the industrial facilities of waste management through composting. But in the minds of the people in charge of waste management, the incineration already had reached the first position as alternative to the deposit of wastes in garbage dumps. The composting stayed like a system that only interested to a minority, whose main mistake was to consider the composting like a panacea of waste management. This concept so unreal optimistic of the system took to develop failed projects of facilities in many communities in the decades of 1950 and 1960. It was very usual to find since 1920 firm defenders of “anaerobic composting”, in which a phase of the process should be developed in the absence of oxygen, what comes to directly contravene to main characteristic of the composting process.
In 1937, the first closed composting system (in-vessel) denominated “DANO drums system” with the slogan “Domestic residues for organic manure”, appeared in Denmark. In the next 25 years in Denmark 19 facilities with the Dano system were established, and others were exported to the U.S.A., South America, the Middle East, the Far East, Australia and many European countries. Although it is included in the composting technologies is necessary to comment that it could be hardly considered a composting system by itself, thus the material do not spend more than 3 days in the rotator drum, where it is mixed and crumbled so that the later composting in windrows (or by other method) would be more efficient.
The fast qualitative and quantitative industrial growth during the 60's was a disaster for the composting as much for the lack of knowledge of the process as by its mystification like the panacea of the systems of waste management. At the beginning of that decade there were in Europe 37 composting plants: 25 with the DANO technology and 12 with the system of windrows, most of which would close in the following decade.
In the U.S.A. closed 14 of the 18 plants built since 1951. The increasing content in the wastes of non biodegradable plastics and other non organic substances, along with the increase in the heavy metals concentration, drastically reduced the commercial possibilities of the compost.
The Beltsville method and the Rutgers method
The following advances in the composting methods and techniques would be developed in universities of the United States. The most significant contributions were the related ones to the capacity of process control, essentially about the parameters: oxygen content and mass temperature.
In the department of agriculture of the University of Beltsville, MD, was developed a composting system in which a static windrow was periodically ventilated by an aspiration system of air from the ground. The development came from the research in composting of sludges coming from urban wastewater treatment plants, more specifically the problematic of bad odours that were generated during the process.
This method, denominated Beltsville, consists in placing in the ground two pipes of 15 cm of diameter perforated all along with holes of 0.25 inches and connected by its ends.
These pipes are covered with a layer of chipped wood or compost without sifting of about 30 cm height. The mixture to compost of sludge with chipped vegetal material that would acts like bulking, is made in a volumetric relation of 1:3.
With this mixture, a windrow of 12 meters in length, 6 meters of width and 2.5 meters of height is constituted over the covered pipes, covering next with a layer of 30 cm of screened compost. The system of pipes is connected to a centrifugal fan that works in aspiration taking air from the outside through the pipes and the windrow. Their cycles of turn on and off are established by a timer guaranteeing interstitial oxygen concentrations in the windrow between 5 and 15%. The gases caught by the fan are depurated making pass them through a windrow of screened compost. The suction is maintained between 16 and 20 days, after that, the position of the fan is changed to introduce air in the windrow by overpressure during other 8 to 10 days.
The Beltsville system supposed a very important step in the history of composting. For the first time, one of the key factors of the process was directly affected, controlling it since the beginning. Its simplicity and the facility of the operation turn it into a system very extended for the treatment of sledges from wastewater treatment plants. The main problem of the system is that it does not exert any control on the temperature. Besides, maintaining the aerobic conditions of the material throughout the process favours initially the derivative microbial activity and therefore the rise of temperature. This added to the insulating conditions of the material causes that the temperature arrives at 80ºC in several points of the mass, with a vertical gradient of temperature higher than 40ºC. These high temperatures inhibit most of the micro organisms that participate in the degradation of the waste which reduces the rate of decomposition of the organic matter, needing more time to complete the process and to obtain a stabilized product.
Professor Melvin Finstein and his collaborators from the University of Rutgers (NJ, United States) took another step developing a system in which a new strategy was considered: the control of the material temperature according to the necessities of the process. This system was denominated Rutgers system. Its main differences with the Beltsville method are focused in the control system of the mass temperature that it does not allow increasing temperatures higher than 60ºC, with the fan acting in overpressure or blowing, first thanks to the use of the timer and when the temperature of the material is higher than 60ºC, thanks to fan self-connexion according to the demand.
Both systems marked an inflexion point in the composting history, because they demonstrated that the knowledge of the process is the key to be able to act on it in an efficient way and obtain better outputs and a final product with higher quality. But at the same time they opened the Pandora box of automation and sophistication of the composting, since being based on its models they began to appear numerous companies that presented composting systems each time more complex and technically sophisticated. It was more important the amount of technology that carried against the knowledge of the needs and characteristics of the process like of the waste to compost.
From here, the composting technologies in trenches, the composting vessels (static or dynamic, in one or two phases) and the drums were developed. For all the others elements that compose the composting facilities and do not take part specifically on the biological process took place a “technological loan” of other industrial sectors, especially from the mining. This lack in the development of specific technology has caused lots of functional problems in the traditional composting plants of urban waste collected “all together”, problems that increase in the new plants of source selected waste.