I wrote this essay in 2000 for assessment in the subject KGE 512/812 Environmental Technology as part of the Graduate Diploma of Environmental Studies at the University of Tasmania. I use the Harvard referencing system in the essay. A full list of references can be found at the end of the essay. If you wish to cite any part of it please use the following citation details. David Reid |
The plough is one of the most ancient and most valuable of man's inventions; but long before he existed the land was in fact regularly ploughed, and still continues to be thus ploughed by earthworms. It may be doubted whether there are many other animals which have played so important a part in the history of the world, as have these lowly organised creatures (Charles Darwin 1881 quoted in Mollison 1990; p.207).
Darwin spent ten years of his life studying earthworms. His work of 1881 was way ahead of its time. In the following 70 years scientific research relating to earthworms was restricted to faunistics, phylogeny, biogeography and natural history. It was only in the 1950s that scientists once again began studying earthworm ecology. Even then their studies were largely restricted to population biology. Now a new generation of scientists, with an interest in environmental protection, can capitalise on this research and apply it to the fields of soil science, plant production and waste management (Lee 1992 and Elliot 1992). 1978 saw the beginning of an increasing interest in the use of earthworms for processing organic wastes. A number of major international conferences on the topic have been held. Research and the setting up of commercial projects has been going on in many countries including Australia, the USA, England, India, France, Japan and Cuba (Edwards et al. 1996; pp.241-242).
In this essay I wish to examine the potential for earthworms to be used as a tool for managing organic waste. I will begin by examining the potential applications of earthworms for waste management and give some examples of how earthworms have been successfully used to manage organic waste. I will then detail some of the technical aspects of the use of earthworms for waste management, such as species selection and optimum conditions for earthworms. Finally I will examine the usefulness of vermicast as a fertiliser and then draw a conclusion on the overall potential of earthworms for the management of organic waste.
Potential applications of earthworms for waste management
Our society produces massive amounts of waste. This waste represents a squandered resource. Much of the waste is organic, and disposal methods like landfill and incineration are not sustainable. In the words of Uday Bhawalkar "there's no such thing as organic waste; only wasted organics" (quoted in White 1995). Lotzof (1999) recognises that vermiculture offers significant environmental advantages compared to other forms of waste disposal and is environmentally sustainable. There is no process pollution, low energy consumption and almost 100% of organic matter is captured for reuse. The idea of reusing human waste is not new. For example, in China the major cities remain self sufficient in food. They achieve this by having farm belts surrounding the city, which reuse human and other organic waste from the city as fertiliser (Girardet 1996).
Earthworms can be used to dispose of all sorts of organic waste including sewage, animal manure, waste paper pulp, brewery waste and mushroom compost (Edwards et al. 1992). Over 50% of waste going to landfill in the USA is organic. The processing of this waste by earthworms would help to reduce a major environmental problem (Edwards et al. 1996; p.241).
Vermiculture is an Environmentally Sound Technology (EST) according to the criteria defined by the United Nations Environment Program (UNEP). They define an EST as being less polluting, using resources in a sustainable manner, recycling more of their wastes and products and handling all residual wastes in a more environmentally acceptable way than the technologies for which they are substitutes. Vermiculture has significant advantages over other waste disposal methods such as composting, landfill and incineration according to the criteria defined by the UNEP (Lotzof 1999).
Management of sewage sludge
Sewage sludge can be decomposed and stabilised about three times faster by earthworms than by normal aerobic processes (Edwards et al. 1996; p.242). Edwards et al. (1996; pp.242-243) recognise the potential of earthworms to decompose sewage sludge, but suggest further research is required in several areas. Another problem they identify is toxic chemicals in the sludge affecting the vermicomposting process (p.244). There maybe an advantage in using earthworms for waste management in non-industrialised countries as the waste is less likely to be contaminated with toxic chemicals. Industrialised countries need to look at ways of keeping non-toxic organic waste separate from more hazardous waste (Lee 1992).
Sewage sludge can contain harmful human pathogens. These pathogens could be viral, bacterial or parasitic. These pathogens will die off naturally over time. A trial conducted by Vermitech showed that earthworms successfully destroyed helminth ova present in sewage sludge. There was also no regrowth of pathogens (Lotzof 2000a). One of the great advantages of using vermiculture for processing sewage sludge is that it turns an odourous material containing harmful pathogens into a stable substance that can be used as an organic fertiliser.
It is interesting to note that Edwards et al. (1996; p.244) argue that full scale vermiprocessing of sewage sludge has not been achieved. Vermitech, an Australian based company, has been extremely innovative in developing a large scale vermiculture system for processing sewage sludge into valuable fertiliser. More detail about this can be found in the section below.
Case study: Vermitech
In 1997 the Redland Shire Council in Queensland issued a tender for the disposal of 250m3/week of sludge from 4 sewage plants and one water treatment plant. Three processes were considered for the waste disposal: composting, lime stabilisation and vermiculture. Vermitech was the successful tenderer with a plan for treatment of the waste in an industrialised vermiculture operation. Redlands Shire Council chose the vermiculture process on the basis that it was environmentally sustainable. It was also seen to have a number of advantages including being odourless, producing a high value end product and the vermicast being easily transportable (Lotzof 2000a).
The project was capital intensive requiring an investment of about $3 million. It converts 20 000m3 of waste into 7 000m3 of vermicast per year with a wholesale value of $1.7 million (Lotzof 2000b). It is believed to be the largest worm farm in the world (ABC Landline 1998). The worm farm is on the site of the Cleveland sewage treatment plant. The site is environmentally sensitive; it drains into Moreton Bay, is adjacent to a koala habitat and is only 800 metres from a residential area (Lotzof 2000a). The Environmental Protection Authority has audited the site. Visitors to the site remark about the lack of odour (Lotzof 1999). It is divided into 2 main areas, a worm bed and waste receival area and a vermicast storage and post processing area. Incoming waste from the 5 sites is blended to improve its quality as a worm feed. The worms are fed daily. Feeding must be carefully controlled to prevent the material composting or becoming anaerobic. The beds are raised to maximise airflow and maintain aerobic conditions for the worms (Lotzof 2000b).
The vermicast is marketed as BioVerm. It is sold for horticulture, viticulture and seedling propagation. Research commissioned by Vermitech has shown that the product can be beneficial to plant production and there is a growing amount of scientific evidence to support this (Lotzof 1999). Vermitech has a target of capturing 2% of the Australian fertiliser market (Lotzof 2000b). Another advantage of vermicast is that it reduces the dependence on manufacturing, importing and use of chemical fertilisers, both an economic and environmental benefit (Lotzof 1999). Vermicast is stable and does not compost any further. Good quality castings have the following characteristics: an earthy non-offensive smell; they dissolve easily in water so they can be used as a liquid fertiliser; and they retain many times their own weight in water (Wilson 1999; p.82).
Management of animal, vegetable and industrial waste
Earthworms can break down most organic wastes, although some need a form of pretreatment and not all wastes are equally as good at supporting earthworms (Edwards et al. 1996; p.246). Traditional composting relies on mechanical aeration and microorganisms. A major advantage of vermicomposting is that it doesn't need the expensive earthmoving equipment that is needed to maintain compost heaps (McClellan 1993). The earthworms do the work of the earthmoving equipment. The vermicompost is also a much better fertiliser than compost because of its higher nitrogen content (McClellan 1993).
Edwards et al. (1996; pp.246-247) consider the value of various organic waste products as an earthworm feed. Animal manures are generally considered excellent, although pig and poultry manure may need some composting prior to being fed to worms because of their high ammonia content. Wastes of vegetable origin such as paper pulp, brewery waste and mushroom compost are all considered excellent materials for growing worms. Urban wastes, such as grass clippings and food waste, are good growth media for earthworms.
These urban wastes (grass clippings and food waste) account for 25% of residential garbage in Simi Valley, California and 40% in Thousand Oaks, California (McClellan 1993). Simi Valley is undertaking a program to separate green waste for vermicomposting. Most residents were happy to pay $2.25 per month to cover the cost of separating the waste (McClellan 1993). I think systems where the residents separate the waste themselves would be much better. This offers environmental and economic advantages in that it reduces the need for transport and other infrastructure. For example, Ecorecycle Victoria (2000) has launched a major campaign to encourage home composting. The aim of the program is to reduce the amount of waste going to landfill.
In traditional agricultural systems animal manure is a major source of fertiliser for crop production. However modern agricultural production systems such as feedlots and piggeries produce quantities of animal manure that are too great to dispose of and these often end up in landfill. Earthworms are useful for breaking down these wastes and incorporating them into soils (Edwards et al. 1996; p.266).
India provides another example of where earthworms have successfully been used for waste management. Although the amount of waste generated in India is small compared to industrialised countries, it still poses health and environmental hazards. Voluntary agencies in Pune and Bangalore are using vermiculture for waste treatment and garbage management. Wastewise, an agency in Bangalore has organised 400 residents to collect waste and recycle it using vermiculture. People collect waste from the residents. It is then segregated and glass and plastics are sold to local dealers, hazardous materials are collected by the City Corporation and organic materials are composted locally using earthworms. The compost material is sold back to the local residents for use in their gardens (Rao 2000).
Earthworms have even been used for the disposal of medical waste in India. A maternity hospital in Pune has been using a vermiculture system to dispose of hospital waste including potentially infectious material. The system has been operating for eight years and does not smell or attract flies. Incineration in small hospitals is not possible for both economic and environmental reasons, so the waste is often disposed of using the municipal garbage collection system. This poses a serious health risk to the public (Chaoji 2000).
Indian farmers are also adopting vermiculture. Much of India's agricultural land is degraded. Vermiculture can break down the toughest of agricultural wastes, such as sugar cane trash, feathers and bones and turn them into an organic fertiliser. Vermicompost is being applied to crops with good results and is helping to restore degraded land (Rao 2000 and White 1995).
Technical aspects
Vermiculture is most effective if the compost material is maintained at a temperature of 15-25°C. In places were temperatures are extremely high or low then vermiculture may be more difficult to maintain. The fact that the bedding material is insulating means that it is, to some extent, protected from fluctuations in outside temperature. The composting process going on in the worm beds generates some warmth (Edwards et al. 1992). Lotzof (2000a) says temperate climates with occasional sub-zero temperatures do not require a fully enclosed building. Where there are sub-zero temperatures for extended periods an insulated, fully enclosed building is required (Lotzof 2000a and Edwards et al. 1996; p.247).
Worms are sensitive to ammonia and cannot survive in materials containing high levels of ammonia like poultry manure. Worms tolerate a range of pH but prefer acid material with a pH of 5.0 (Edwards et al. 1996; p.249).
Feeding of earthworms needs to be carefully controlled. If the feed covers the beds too deeply then the material can become anaerobic. Also the amount of food fed daily must match the demand of the earthworms (Lotzof 2000b). Maintaining aerobicity as well as optimal temperature and moisture conditions is essential for good productivity (Edwards et al. 1992).
Only certain species of earthworm are suitable for vermiculture. Eisena fetida (tiger worm, sometimes also called the red worm) is considered the best worm for processing organic waste. It is ubiquitous, has a wide temperature tolerance and can be readily handled (Edwards et al. 1992). Species that have been used on a wide scale for waste management are E. fetida, Eisena andrei (red tiger worm), Eudrilus eugeniae (African night crawler), Perionyx excavatus, Dendrobaena veneta, and Lumbricus rubellus (red worm) (Edwards et al. 1996; pp.247-248). There is some variation in optimal conditions between species but this is not great (Edwards et al. 1996; p. 249). E. eugeniae and P. excavatus are less tolerant of cold temperatures and are therefore better suited to tropical conditions (Edwards et al. 1992).
The cost of civil works and buildings has been a major barrier to the more widespread adoption of vermiculture. The area of land used is an important issue in because of the additional capital cost it imposes on a project and because the availability of land in proximity to a sewage plant may be limited (Lotzof 2000a). The technology is still being developed but there is the potential for well engineered, highly productive and nonlaborious systems (Edwards et al. 1996; p.263-264).
Vermicast as a fertiliser
The main goal and benefit of using earthworms for waste management is to convert organic waste into fertiliser. How effective is vermicast as a fertiliser?
Many of the claims about the benefits of vermicast are anecdotal, although in Cuba and India vermicast is being used as a fertiliser on a large scale. They convert 160,000 tonnes of waste into fertiliser each year (Lotzof 1999). Long (2000) cites three examples of studies that have shown that the use of vermicast increases plant growth. Research by Dr. John Buckerfield at the CSIRO has shown yield increases of 35-50% in grapes grown in South Australia (Vermitech 2000). Edwards et al. (1996; pp. 254-257) say more research is needed, but good worm worked organic wastes are excellent growth media for a variety of plants. They also say there is a need for testing to ensure consistency of product and in some cases addition of nutrients that are deficient.
Conclusion
There is clearly great potential for increased use of earthworms for disposing of organic waste. The technology for some applications, like the treatment of sewage sludge, is just being developed and no doubt will become more widely used in the future. The fact that so much of our waste is simply disposed of with an out of sight out of mind attitude represents the squandering of a precious resource. Increasing environmental awareness and future scarcity of resources will demand a new approach to waste management. We must look to the fact that many indigenous cultures existed for thousands of years and produced no significant amounts of waste or pollution. Hopefully we will see increasing use of earthworms for waste management in the future. This will result in the greater reuse and recycling of organic wastes.
The main advantages of vermiculture are that it requires low energy input, it produces a product with a valuable end use (fertiliser) and it relies on a simple natural process without the input of noxious chemicals or reliance on large scale industrial processes. It is obviously an area deserving of more research and development.
References