The Suitability of Using Vermicomposting for the Stabilization of Septic Tank Waste


Many rural communities are not reticulated, relying on domestic on-site waste water treatment systems. In New Zealand, there are over 270,000 domestic on-site wastewater treatment systems and while 60,000 are for holiday homes the majority are for isolated communities. This compares to 26 million in the USA, 1 million in Australia and 300,000 in the UK. Many systems are simple holding tanks leading to disposal fields which require regular emptying to remove settled septic sludge. Commonly, this sludge is transported long distances to centralised wastewater treatment plants and once treated, and stabilised, may be suitable for beneficial re-use.

The treated sludge (or biosolids) has the potential to be used as a fertilizer as it is carbon rich and has high concentrations of valuable nutrients. In addition there is increased community awareness and support around achieving sustainable waste management. One disadvantage, however, is that sewage sludge may contain toxic elements and compounds found in organic wastes (e.g., heavy metals, pharmaceutical products and human pathogens), some of which may be hazardous to environmental and human health. This presents a significant road block to reuse and often results in landfilling of biosolids.

 Vermicomposting is emerging as an appropriate technology for small communities who wish to re-use their own waste as it has been shown to effectively transform organic waste into useful compost. Vermicompost is a nutrient-rich, microbiologically-active organic amendment that results from the interactions between earthworms and microorganisms during the breakdown of organic matter. It is a stabilized, finely divided peatlike material with a low C:N ratio, high porosity and high waterholding capacity, in which most nutrients are present in forms that are readily taken up by plants.

A diverse range of feed stocks can be incorporated into the process and providing certain parameters are maintained, this is a cost effective and fairly rapid treatment compared to standard composting. In previous studies, vermicomposting has been shown to enhance mineralisation of nitrogen and phosphorus, stabilise organic matter, reduce or even eliminate pathogens and produce a chemically and biologically enriched material.

Aaron Province
Journal of Bioremediation and Biodegradation
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