The vermicomposting systems will obviously vary depending on the installation scale, the area circumstances, and the characteristic of the waste to be treated and/or the final product to be obtained. But in all cases it will be necessary consider that adequate conditions to the development and the organisms activity that are going to realize the organic matter degradation work must be maintained. As the same that in composting, the previous conditions (conditioning) and control process can be classified.


Previous culture parameters (conditioning)

If we contemplate a natural grassland soil where there is high abundance of earthworms will verify that the land texture is spongy and soft, no compacted. So, any substrate where worm’s inoculation want to be made for vermicomposting must to have a porous physic structure, that it does not difficult or inhibit that the worms excavate galleries, as well as the water and air flow to the interior. It is essential that the substrate will be in aerobic conditions to allow the survival of any epigeous worm.

Other factor directly linked with this is the moisture. Between the Annelids the only group with terrestrial life is the Oligochaeta (where the earthworms are included), and not all of them, because many of them are fresh water, like the Hirudinea (another group of annelids), since the Polichaeta are mainly marine ones. So we are talking about one kind of animals that have been evolved from an aquatic medium to a terrestrial one, with the necessary adaptations to overcome some problems like to maintain the body form in a lower density medium, to ensure the embryo development rounded by vital fluids, to adapt the respiration system for oxygen capture from air instead than from water, to adapt to a terrestrial nutrition and to maintain an interior homeostasis. This means that they must control their interior medium, eliminating the metabolic residue products without excessive ions and water’s lost. To do that, they have adapted their respiration and excretory systems from the aquatic model of their ancestors. For do that they must secrete a mucus that can maintain the body surface moisture and that allows the cutaneous respiration by passive diffusion, and that their excretory system would create an abundant hypotonic urine for urea and ammonia elimination. Due to this, the medium or substrate where the worms would live, must to have a high constant moisture, but always between certain margins, because a moisture excess or flooding will kill the worms. This is one of the reasons for the necessity of a physic structure of the substrate where the worms are going to live must allow a water partial retention and also the excess’ percolation.

Both factors are directly going to influence the organic waste characteristics, waste that is going to be the nutrition of the worms. Sewage sludges, for example, due to its high moisture and density, need a previous conditioning (due to its dosage or mixture) to can correctly be vermicomposted.

For being animals that greatly depend on moisture of the medium where they are living, they are specially sensible to salinity, because of they must maintain a delicate osmotic equilibrium for their survival. Inorganic salts high concentration in the medium inhibits the reproduction and could be responsible of their death.

The ammonia is a very easy soluble component in water, so in the same way that the inorganic salts, its high quantity in the medium would be greatly toxic for the earthworms. This is one of the big problems at the moment of try to degrade some organic materials as excrement’s and some sewage sludges, for its often high ammonia quantity. One common solution consists in a previous aeration of the material to be treated to volatilise the ammonia before being given to the earthworms.

The pH is related with those parameters. The most used species prefer a neutral pH, but there are species that perfectly developed themselves to pHs lower than 5.5.
It is obviously necessary contemplate, or have consideration in, the possibility of finding elements or toxic substances in the organic matter to be vermicomposted. We can never forget that we are working with alive beings.



Process control parameters

If in the substrate and material to be vermicomposted, the previous conditions are respected, the earthworms will begin its detritus feeding activity, moving and eating the organic wastes that we give them. But for the maintenance and successful of the system it is also essential to ensure that the medium conditions favours the worms sexual maturity, its reproduction, development and growing of new individuals. So there are some conditions to maintain for controlling the correct development of the process.

In most of the cases, the initial worms population represents a low density in respect with the available medium volume. To optimize the system in relation with de degradation rate of organic wastes that are feeding the worms is necessary to arise an adequate worm population density. If the medium conditions are adequate, the worms will quickly increase their biomass, they will have a higher reproductive rate and new generations will be obtained with higher number of individuals in the medium each time. But the abundance of the population tends to be stabilized when they arrive to certain number, like if an auto-regulation mechanism could exist, and when the bed tends to the super population, the reproductive rate diminishes. This is the principal parameter that affects the growth and reproduction, so it must be important that once that optimum medium conditions are raised and controlled, the waste degradation velocity comes given by the worms population density; so it will be of high interest to have a clear knowledge about the population optimum density to ensure a high biomass production as well as a fast waste degradation. This supposes the periodical necessity of keep out individuals from the medium to obtain that density does not interfere over the degradation rate.

It was already commented in several occasions that the waste moisture is a main parameter for the worms survival, and to ensure this moisture rate constant during the process is also necessary. For that it is necessary to make periodical waterings of the medium to maintain the moisture in levels close to the optimum, that for example, in the case of E. fetida are situated between 80-90%.

The temperature tolerance range of the earthworms is quite ample, so it must not to be a problem. Whatever it is a factor that directly affects the worms metabolism, and, in consequence, to their activity and reproduction, so it is convenient to maintain the temperature as close as possible to the specie optimum. For E.fetida the optimum is between 15 and 20 ºC for vegetal and animal wastes degradation, but some authors situate the medium temperature in 20ºC.

To maintain the medium in aerobic conditions is a factor that not only must be foreseen during the conditioning of the material to degrade, it is also important to remember that an increase in the water content or a posterior waste package, can develop anaerobic conditions that could be terrible for the earthworms. For this reason, for an industrial scale vermicomposting system, it would be necessary foresee an appropriated drainage system to avoid water excesses, and to ensure the material porosity, that normally is produced by the worms movement.

pH values must also been controlled because, as we explained before, directly affects the worms activity.