**2. Earthworm species suitable for vermicomposting**

30 Management of Organic Waste

physical and biochemical properties (Domínguez, 2004). The biochemical decomposition of organic matter is primarily accomplished by microorganisms, but earthworms are crucial drivers of the process as they may affect microbial decomposer activity by grazing directly on microorganisms (Aira et al., 2009; Monroy et al., 2009; Gómez-Brandón et al., 2011a), and by increasing the surface area available for microbial attack after comminution of organic matter (Domínguez et al., 2010) (Figure 1). These activities may enhance the turnover rate and productivity of microbial communities, thereby increasing the rate of decomposition. Earthworms may also affect other fauna directly, mainly through the ingestion of microfaunal groups (protozoa and nematodes) that are present within the organic detritus consumed (Monroy et al., 2008); or indirectly, modifying the availability of resources for

Fig. 1. Positive (+) and negative (-) effects of earthworms on microbiota and microfauna

Furthermore, earthworms are known to excrete large amounts of casts (Figure 1), which are difficult to separate from the ingested substrate (Domínguez et al., 2010). The contact between worm-worked and unworked material may thus affect the decomposition rates (Aira & Domínguez, 2011), due to the presence of microbial populations in earthworm casts different from those contained in the material prior to ingestion (Gómez-Brandón et al., 2011a). In addition, the nutrient content of the egested materials differs from that in the ingested material (Aira et al., 2008), which may enable better exploitation of resources, because of the presence of a pool of readily assimilable compounds in the earthworm casts. Therefore, the decaying organic matter in vermicomposting systems is a spatially and temporally heterogeneous matrix of organic resources with contrasting qualities that result from the different rates of degradation that occur during decomposition (Moore et al., 2004).

these groups (Monroy et al., 2011) (Figure 1).

(modified from Domínguez et al., 2010).

Earthworms represent the major animal biomass in most terrestrial temperate ecosystems (Edwards & Bohlen, 1996). Indeed, more than 8,300 species of earthworms have been described (Reynolds & Wetzel, 2010), although for the great majority of these species only the names and morphologies are known, and little is yet known about their biology, life cycles and ecology. Different species of earthworms have different life histories, occupy different ecological niches, and have been classified, on the basis of their feeding and burrowing strategies, into three ecological categories: epigeic, anecic and endogeic (Bouché 1977). Endogeic species (soil feeders) forage below the surface soil, ingest high amounts of mineral soil and form horizontal burrows. Anecic species (burrowers) live in deeper zones of mineral soils, ingest moderate amounts of soil, and feed on litter that they drag into their vertical burrows. And, epigeic earthworms (litter dwellers and litter transformers) live in the soil organic horizon, in or near the surface litter, and mainly feed on fresh organic matter contained in forest litter, litter mounds and herbivore dungs, as well as in man-made environments such as manure heaps. These latter species, with their natural ability to colonize organic wastes; high rates of consumption, digestion and assimilation of organic matter; tolerance to a wide range of environmental factors; short life cycles, high reproductive rates, and endurance and resistance to handling show good potential for vermicomposting (Domínguez & Edwards, 2010b). In fact, few epigeic earthworm species display all these characteristics, and only four have been extensively used in vermicomposting facilities: *Eisenia andrei*, *Eisenia fetida*, *Perionyx excavatus* and *Eudrilus eugeniae* (Figure 2).

Fig. 2. Earthworm species *Eisenia andrei* (top left), *Eisenia fetida* (top right), *Eudrilus eugeniae* (bottom left) and *Perionyx excavatus* (bottom right).

Vermicomposting: Composting with Earthworms to Recycle Organic Wastes 33

unaffected and others are digested in the intestinal tract and thus decrease in number (Drake & Horn, 2007; Monroy et al., 2009). Such selective effects on microbial communities as a result of gut transit may alter the decomposition pathways during vermicomposting, probably by modifying the composition of the microbial communities involved in decomposition, as microbes from the gut are then released in faecal material where they continue to decompose egested organic matter. Indeed, as mentioned above, earthworm casts contain different microbial populations to those in the parent material (Domínguez et al., 2010), and in turn it is expected that the inoculum of those communities in fresh organic matter promotes modifications similar to those found when earthworms are present, altering microbial community levels of activity and modifying the functional diversity of

Upon completion of GAPs, the resultant earthworm casts undergo *cast associated processes* (CAPs; Figure 3), which are more closely related to ageing processes, the presence of unworked material and to physical modification of the egested material (weeks to months). During these processes the effects of earthworms are mainly indirect and derived from the GAPs (Aira et al., 2007). In addition, during this aging, vermicompost is expected to reach an optimum in terms of its biological properties, thereby promoting plant growth and suppressing plant diseases (Domínguez et al., 2010). However, little is yet known about when this "optimum" is achieved, how we can determine it in each case and if this

Since vermicomposting is a biological process, microorganisms play a key role in the evolution of the organic materials and in the transformations they suffer from wastes to safe organic amendments or fertilizers (vermicompost). Therefore, the effects that earthworms have on the microorganisms must be established because if the earthworms were to stimulate or depress microbiota or modify the structure and activity of microbial communities, they would have different effects on the decomposition of organic matter, and in turn on the quality of the final product. To address these questions we performed three

i. To investigate whether and to what extent the earthworm *E. andrei* is capable of altering the structure and activity of microbial communities through the gut associated

ii. To investigate how the earthworm species affect the structure and activity of microbial

iii. To investigate the effectiveness of the active phase of vermicomposting for the short-

To provide further light into the effect of gut transit on microbial communities, we carried out an experiment with microcosms filled with cow manure and inoculated with 25 mature individuals of the earthworm species *E. andrei*. The microcosms consisted of 250 mL plastic

**4.1 How do earthworms affect microbial communities through the gut associated** 

microbial populations in vermicomposting systems (Aira & Domínguez, 2011).

**4. Effects of earthworms on the structure and activity of microbial** 

"optimum" has some kind of expiration date.

**communities during vermicomposting** 

laboratory experiments, with the following objectives:

term stabilization of a plant residue.

communities during the active phase of vermicomposting.

processes.

**processes?** 
