LOS CRISTIANOS DEL PRIMER SIGLO…

Clive A. Edwards

I INtrODUCtION

In response to the extremely large amounts of organic wastes currently pro- duced, thermophilic composting technology has become increasingly popular for large-scale processing and disposal of a wide range of organic wastes. However, the process does not always produce high-quality products that have good potential for soil and land improvement, and most thermophilic composts do not have great economic value. Over the last 30 years, interest has increased progressively in the potential of a related process that involves the use of earthworms to break down CONtENtS

I Introduction ... 79 II Windrow Vermicomposting Systems ... 81 III Batch Systems of Vermicomposting ... 82 IV Earthworm-Harvesting Equipment... 83 A Typical Rotating Trommel ... 83 B Improved Comb-Type Mechanism of Separating Earthworms

from Vermicompost ...84 V Domestic Vermicomposting Systems ...85 VI Wedge Vermicomposting Systems ...86 VII Diseases and Predators of Earthworms in Vermicomposting Systems ...88 A Common Vermicompost Bed Organisms ...88 B Invertebrate Earthworm Enemies ... 89 C Vertebrate Earthworm Predators ... 89 D Diseases and Parasites of Earthworms ... 89 References ...90

organic wastes in a mesophilic process. In 1881, Charles Darwin first drew atten- tion to the great importance of earthworms in the breakdown of dead plant organic materials and the release of the essential nutrients they contain in his book The

Formation of Vegetable Mould through the Action of Worms. Many of his conclu-

sions have been confirmed and utilized extensively during the last century (Edwards and Bohlen 1996). However, only in recent years has the considerable potential of using earthworms in systems of breaking down organic wastes to produce vermi- composts been explored in more depth to full commercial ventures (Edwards and Neuhauser 1988).

Some species of earthworms inhabit organic litter on the soil surface. They fragment organic wastes extremely rapidly and increase microbial activity in them dramatically; these are termed epigeic earthworms. The main difference between ther- mophilic composting and vermicomposting is that whereas composting is an aerobic process that can reach temperatures of 60°C–70°C (140°F–158°F), vermicomposting systems are mesophilic and must be maintained at temperatures below 35°C (95°F). Exposure of the earthworms to temperatures above this, even for relatively short periods, will kill them, and, to avoid such overheating in vermicomposting systems, very careful management of the wastes is required. Epigeic earthworms are very active and will consume organic wastes located in a relatively narrow horizontal aerobic layer of 10–15 cm (4–6 in), that is, close to the surface of a bed or container, very rapidly. The critical key to successful vermicomposting lies in adding organic wastes to the surface in successive thin layers at frequent intervals, so that any ther- mophilic heating that may occur does not become excessive and, if well managed, this low level of heating will maintain the activity of the earthworms at a high level of efficiency through colder periods in temperate countries, since vermicomposting works best at temperatures between 20°C and 25°C (68°F–77°F).

Almost any kinds of agricultural, urban, or industrial organic wastes can be used for vermicomposting, but some may need some form of preprocessing before use to make them acceptable to earthworms. Such preliminary treatments can involve wash- ing, precomposting, macerating, or mixing the organic matter. Organic manures and wastes from the brewing, soft drink, processed potato, and paper industries; sewage biosolids; and yard, garden, and food wastes are particularly suitable for vermicom- posting. Often, mixtures of several different wastes can be processed more readily than single types of wastes, are easier to maintain aerobically with an acceptable moisture content, and result in a better product.

The species of earthworms that are used for vermicomposting, termed epigeic species, can consume organic wastes very rapidly and fragment them into much finer particles by passing them through a grinding gizzard inside their mouth that all earthworms possess. The earthworms obtain their nourishment from the micro- organisms that grow on the organic waste rather than the wastes themselves; at the same time, they promote further microbial activity in the wastes, so that the earth- worm casts, or vermicomposts, that they produce are much more fragmented and very much more microbially active than the organic wastes that the earthworms consume. During this process, the important plant nutrients that the wastes contain, particularly N, P, K, and Ca, are released and converted into forms that are much

low-teCHnology vermiComPosting systems 81 more soluble and readily available to plants than those in the original waste. The retention time of the waste in the earthworm gut is short, at most a few hours, and very large quantities of organic matter are often passed through an average popula- tion of earthworms more than once.

In the traditional thermophilic composting process using windrows, organic wastes have to be turned regularly, or aerated in some way, to maintain aerobic con- ditions in the waste. This may often involve extensive engineering and machinery to process the organic wastes as rapidly as possible on a large scale. In the vermicom- posting process, the earthworms, which can survive only under aerobic conditions, take over both the roles of turning over the waste and maintaining it in an aerobic condition, thereby lessening the need for expensive engineering to achieve these aims.

A major constraint to vermicomposting is that, in contrast to traditional com- posting, which is a thermophilic process that can raise temperatures in the waste to more than 65°C (149°F), vermicomposting systems must be maintained at tempera- tures below 35°C (95°F) to avoid killing the earthworms. The processing of organic wastes by earthworms occurs most rapidly at temperatures between 15°C and 25°C (60°F to 79°F) and at moisture contents of 70% to 90%. Outside these limits, earth- worm activity and productivity and the rates of waste processing can fall off, and for maximum efficiency, the wastes should be maintained as close to these environ- mental limits as possible, which usually means keeping the systems indoors or under cover. The earthworms are also sensitive to certain environmental conditions in the wastes. In particular, earthworms are very sensitive to ammonia, salts, and other chemicals. For instance, they will die quickly if exposed to wastes containing more than 0.5 mg of ammonia per g–1 _{of waste and more than 0.5% salts (Edwards and} Neuhauser 1988). However, salts and ammonia can be washed out of organic wastes readily or decreased by thermophilic precomposting. Contrary to common belief, earthworms do not have many serious natural enemies, diseases, or predators, and they can survive exposure to many adverse conditions; this will be discussed more later and also in other chapters.

II WINDrOW VErMICOMPOStING SYStEMS

In the United States and Canada there is a very extensive, but relatively small- scale, cottage industry that grows earthworms for fish bait in a variety of organic wastes. These use, almost exclusively, outdoor ground beds or windrows. Such sys- tems require large areas of land for large-scale earthworm and vermicompost pro- duction and are relatively labor-intensive, even when machinery is used for adding the organic wastes to the beds and harvesting the vermicomposts. More importantly, windrow systems process wastes relatively slowly, taking anywhere from 6 to 18 months to process a layer 45 cm deep (18 in), particularly when winters are cold. Since this is usually an outdoor process, there is evidence that a large proportion of the essential plant nutrients, which are in a relatively soluble form, are either washed out of the organic matter or can volatilize from it during this long processing period.

Such nutrient losses are undesirable, since they can contribute to groundwater pol- lution, and result in a poor, low-nutrient vermicompost product with relatively poor potential as a plant growth medium.

Windrow vermicomposting is common all over the United States and elsewhere in the world. However, it is labor- and land-intensive, is seasonal, and takes place outdoors. Moreover, some enterprises harvest only half the vermicompost produced, leaving the rest as an earthworm inoculum for the next windrow to be set up. Thus, it requires the separation of earthworms from the finished vermicompost using rotat- ing trommels or other equipment. Windrows are ground-based and require large areas of land, and they have potential for groundwater pollution with nutrients and contaminants, since they are watered regularly and usually have little protection against leaching. Windrows should have a firm concrete base to avoid harvesting soil with the vermicompost. It helps to minimize watering by using a permeable top cover such as sacking or bamboo strips held together with twine; these prevent evap- oration but allow watering. Under no circumstances should plastic or polyethylene sheeting be used to cover windrows because it turns the upper layers of the windrow anaerobic, so that the earthworms leave the windrow and lie below the cover where there is oxygen. The processing is slow, taking 4–18 months to complete. The har- vesting of the vermicompost is laborious and time-consuming, since the earthworms in the waste have to be separated, usually by some form of screening process, before marketing. Although the initial capital outlay, other than land, is low, labor costs are high at all stages of the operation (Table 7.1).

III BAtCh SYStEMS OF VErMICOMPOStING

Methods of batch vermicomposting in large or small stacked boxes or containers have been discussed by Edwards and Neuhauser (1988), Edwards (2004), and Carver and Christie (2007), who suggested that most of the batch processing methods he tested were too labor-intensive because the units had to be moved to add more wastes in thin layers to the surface of the unit. It is also difficult to access the earthworms in them or add water to them because they are usually stacked one above the other in racks to economize on space.

table 7.1 Characteristics of Windrow Vermicomposting Systems

benefits • low capital outlay • easily managed drawbacks • labor-intensive • needs large areas of land • slow processing time • Considerable loss of nutrients through leaching and volatilization • impossible to harvest vermicompost without earthworms

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Batch vermicomposting can be done in any size of container. There have been various attempts to develop improved batch systems and modular container systems. However, batch systems all have the same major disadvantage as wind- rows, that is, the need for a labor-intensive separation of earthworms from the vermicompost before it can be used or marketed. Additionally, there is a need to inoculate earthworms into each new container when a new batch system is started (Table 7.2).

IV EArthWOrM-hArVEStING EQUIPMENt

When organic wastes are broken down into vermicomposts by earthworms in windrows or batch systems, there is an essential step of extracting the earthworms from the vermicompost before it can be marketed. This is usually achieved by pass- ing the processed organic wastes or vermicomposts through equipment with rotating screens set on a slope with a cone-shaped solid unit at the end (Figure 7.1). These systems are commonly termed trommels.

A typical rotating trommel

Different-sized mesh apertures can be used in trommels to screen the vermicom- posts into different particle sizes. The better models have a range of screen sizes, with the smallest screen mesh at the loading end and increasingly larger aperture meshes further down the slope. A typical unit has a smallest screen size of 2 mm (0.079 in) and a largest mesh of 0.5 cm (0.2 in). The diameter of the screens can be as large as required, but a typical unit has a diameter of about 60 cm (23.6 in), and they are usually rotated by an electric motor at about 10 revolutions per minute (rpm). The funnel-shaped metal end has a maximum diameter of about 1 m (40 in). The vermicomposts can be collected into containers along the length of the trommel. At the funnel end, the earthworms adhere to the smooth metal surface as it rotates and drop off into a collection tray from the highest part in the metal cone. It is important that the vermicompost not be too moist to avoid compacting into balls that will not pass through the mesh.

table 7.2 Characteristics of Vermicompost Batch System benefits • needs relatively little space drawbacks • Considerable expenditure on containers and container-moving equipment • difficult to maintain optimal moisture conditions with sprays • labor-intensive • Harvesting of vermicompost without earthworms impossible without separating them from the vermicompost in a screening or trommel system

B Improved Comb-type Mechanism of Separating Earthworms from Vermicompost

Engineers at the U.K. National Institute of Agricultural Engineering, Silsoe, Beds, designed a much more efficient earthworm waste separator based on a comb system (Price and Phillips 1990; Figure 7.2). Steel combs constructed from nails 5.8 cm (2.2 in) long and 2.5 mm (0.1 in) in diameter are fitted to the inside of a cyl- inder 2.5 m (8.2 ft) long and 0.8 m (3 ft) in diameter. The combs are spaced at 50 mm (2 in)spacing axially and 60 mm (2.3 in) spacing circumferentially. They are set radially but with a trailing angle of 10° (in the prototype separator, masonry nails are used, hammered through undersized holes in a PVC cylinder). In a later model, the cylinder was rolled from steel sheet, and the comb teeth were made from spring steel, held in place with special steel clips.

The cylinder rests on rollers in a support frame, with jacks at one end to enable the whole machine to be tilted to an angle from the horizontal. A drive unit is pro- vided to rotate the cylinder at rates up to 10 rpm. A 4 m (4.3 yd) long by 0.5 m (20 in) wide conveyor belt is placed coaxially through the cylinder and fitted with a simple hopper at its rear end. The general arrangement of the components is shown in Figure 7.3.

In operation, the rear of the machine is jacked up, and the cylinder is set to rotate. The conveyor belt (B) draws a thin layer of earthworm-rich vermicompost from the hopper (A), the layer being swept off (B) into the rotating cylinder (D) by the deflec- tor (C). Earthworms become draped over the combs moving through the vermicom- post and are carried upward until the combs are nearly inverted. At this point they drop off and can be collected on the conveyor belt, forward of the deflector (C), and are transported forward (E) into a receptacle (F). Earthworm-free vermicompost tumbles forward within the cylinder because of its inclination from the horizontal and emerges at the end into a receptacle (G).

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The most suitable rotational speed for the cylinder is about 7 rpm, and the incli- nation of the machine about 2 degrees from horizontal. The machine can be operated continuously without any buildup of wet vermicompost. Coarse or lumpy vermi- composts are broken up successfully by the movement of the combs. The machine operates with greatest efficiency with an input of 5 L (10.57 pts) of vermicompost per minute but is still quite efficient with inputs of 15 L (31.7 pts) of vermicompost per minute.

V DOMEStIC VErMICOMPOStING SYStEMS

Small-scale systems of vermicomposting, for disposal of domestic household and food wastes, have been used extensively in homes, schools, and even jails (Appelhof Figure 7.2 the silsoe comb-type earthworm/vermicompost separator.

A - Hopper View from arrow J _{B - Conveyor}

C - Deflector D - Cylinder

E - Worm delivery section of conveyor F - Worm receptacle

G - Worm-free waste receptacle H - Combs set at trailing angle H E B B A _C D G E F J Figure 7.3 general arrangement of components of silsoe comb-type earthworm separator.

1997) (see Chapter 6) (Table 7.3). They range from simple containers with perforated lids for aeration to more sophisticated commercially produced stacking systems of different sizes and complexities, usually with mesh bottoms so processed vermicompost can fall into the lower container. These include circular stacking systems such as the Can-O- Worms, the Worm Wigwam System, a rectangular stacking system called Worm Factory, and systems such as the Eliminator (Figure 7.4), which has a side-operated breaker bar and collection drawer at the base, an opening glass door for inspection of the vermicom- post, a hinged lid to allow addition of wastes. These commercial systems have attracted the interest of some local urban-waste authorities, some of whom have encouraged home owners to use them, often by donating them to the users on condition that they put no food waste into the main organic-waste-disposal stream. The benefits and drawbacks of domestic vermicomposting system are summarized in Table 7.3.

VI WEDGE VErMICOMPOStING SYStEMS

A Dorset wedge vermicomposting system was designed by Edwards and col- leagues at Rothamsted with others from the National Institute of Agricultural Figure 7.4 eliminator domestic vermicomposting system.

low-teCHnology vermiComPosting systems 87

Engineering in the United Kingdom. It is based on adding successive thin layers of 5–10 cm (2–4 in) of organic waste at a 45 degree angle from a vertical removable barrier (Figure 7.5). The wedge system can be of any width or length but should be limited in height to about 1.2–1.5 m (1.1–1.6 yd) for ease of adding organic wastes to the leading edge. It should be situated on a concrete base or on some other solid surface from which vermicompost can be collected easily. The system starts with waste at a layer at an angle of 45 degrees against a removable barrier. Partially vermicomposted organic waste containing 9 kg (19.8 lb) (wet weight) of E. fetida (or other species) m–2 _{to a depth of about 15 cm (6 in) is used to start the system.} The surface is kept moist (80% moisture content) to a depth of 15 cm (6 in) by a fine water spray applied twice daily to the leading edge, which is covered by a layer of material such as sacking that can pass moisture. Additional layers of waste 2–3 cm (0.8–1.2 in) thick at an angle of 45 degrees are added daily, and then the pile is covered again.

table 7.3 Domestic Vermicomposting Systems

benefits • removal of significant amounts of organic wastes from landfill disposal • Provision of plant growth media and soil additives for home use • removal of odor from food wastes • useful educational tool drawbacks • need for careful management, especially moisture control • Possible breeding of flies Progressive harvest of 1st wedge 2nd wedge 1st wedge Direction of wedge advance

Fresh waste is applied in thin (30mm) layers to tlited wedge working faces Original working face Current working face (kept moist daily) Figure 7.5 Principles of the wedge vermicomposting system.

The earthworms move rapidly from the older layers of fully processed organic waste or vermicompost into the fresh feedstock material at the wedge surface, so that the entire earthworm population is always concentrated in the top 15 cm (6.0 in) below the leading surface of the wedge. At convenient intervals (e.g., every 1 to 2 months), the removable barrier can be taken away and replaced about 60 cm (0.6 yd) behind the leading face of the wedge, so that no earthworms are removed when the vermicompost is collected. All of the vermicompost behind this barrier can be removed with front loader machinery and collected free of earthworms, for subsequent drying to 35%–45% moisture, sieving, and packaging. Processing of wastes in a wedge system takes about 3–4 months, is much less labor-intensive than windrows, and needs much less space.

This system was adopted for large-scale use by a company called Green-Pyk in Russia that markets large quantities of vermicomposts produced in very large cattle sheds 100 m × 30 m (109 yd × 32.8 yd) using cattle wastes as feedstock. The company also markets aqueous extracts from vermicomposts, or “teas,” which are produced on-site. The benefits and drawbacks of the wedge system are summarized in Table 7.4.

VII DISEASES AND PrEDAtOrS OF EArthWOrMS IN VErMICOMPOStING SYStEMS

A Common Vermicompost Bed Organisms

Since vermicomposting systems use various forms of organic matter as feed- stocks, as the basis of vermicompost production, other invertebrates that live on decaying organic matter may also infest the vermicomposting system. Most of these