The global carbon cycle

The movement of carbon, in its many forms, between the atmosphere, oceans, biosphere, and geosphere is described by the carbon cycle, illustrated in Figure This cycle consists of several storage carbon reservoirs and the processes by which the carbon moves between reservoirs. Carbon reservoirs include the atmosphere, the oceans, vegetation, rocks, and soil; these are shown in black text along with their approximate carbon capacities in Figure 1. The purple numbers and arrows in Figure 1 show the fluxes between these reservoirs, or the amount of carbon that moves in and out of the reservoirs per year. If more carbon enters a pool than leaves it, that pool is considered a net carbon sink. If more carbon leaves a pool than enters it, that pool is considered net carbon source.

A cartoon of the global carbon cycle. Pools (in black) are gigatons (1Gt = 1x109 Tons) of carbon, and fluxes (in purple) are Gt carbon per year                                                                                                        

The digester: the heart of the plant

The digester, a large airtight container, which is filled with substrates and co-substrates represents the heart of anaerobic digestion plants. Digester size depends on volume of effluent and the retention time that varies from 25-30 days with only livestock effluents to be raised to 40-50 days when other vegetal masses are co-digested. In this environment without oxygen the bacteria produce biogas.

 In most digesters, to accelerate the process of biogas production heat is given. The biogas produced can be used to produce both thermal energy, both  electricity and thermal energy or Biogas can be converted to Biomethane. The latter option, the conversion of Biogas into Biomethane, is the solution that is enjoying considerable consensus and is the most suitable for them. The biomethane produced can be used on site.

 digester section

In addition to the Biogas-Biomethane, anaerobic digestion process produces the digestate as final residue made of of a liquid and a solid fraction. This by-product can be used under certain conditions such as organic fertilizer to be deployed on the ground instead of chemical fertilizers. The size of a digester can be:

Raw materials used

The "raw" at the entrance to the plant consists basically of the organic fraction of urban solid waste (OFUSW). It is important to point out that our plant, unlike everyone else right now in business, can work only with the help of OFUSW.

Below the list of waste with E.W.C. code and description of waste:


               AND PROCESSING

0201      Waste from agriculture, horticulture, forestry, aquaculture, hunting and fishing.

020103  plant-tissue waste.

0203      Waste from the preparation and processing of fruit, vegetables, cereals, edible oils, cocoa, coffee, tea and tobacco; the production of                  canned food; the production of yeast and yeast extract; the preparation and fermentation of molasses.

020304  Materials unsuitable for consumption or processing.

0205      Wastes from the dairy products industry.

020502  Sludges from on-site effluent treatment.

0207      Waste from the preparation of alcoholic and non-alcoholic beverages (except coffee, tea and cocoa).

020701 Waste from washing, cleaning and mechanical reduction of raw materials.


0201     Separately collected fractions.

200108 Biowaste from kitchens and canteens.

2002     Garden and park waste (including cemetery waste).

200201 Biowaste.

2003     Other municipal waste.

200302 Markets Waste.

                           Comparison of anaerobic digestion and composting

By comparing these two modern waste disposal systems, you may notice how anaerobic digestion is the most comprehensive solution. In fact, in terms of energy anaerobic digestion  creates more possibilities, as it presents a production of 300/600 kWh per ton against a consumption of 20/100 kWh per ton of composting; in this way the energy obtained can be used both for indoor use and for sale. When it comes to emissions in digestion, working under negative pressure and sealed containers, the latter is greatly reduced, which does not happen in composting. The funds for the construction of a plant of this type are more than for composting, but spending is  repaid by the numerous benefits.