One of the key challenges of biowaste re-use is to ensure that the processed biowaste is safe, acceptable and poses no health hazards, particularly if it contains human waste. To help protect New Zealand’s health, guidelines [PDF, 845 KB] have been developed for the safe application of biowaste to land. Worms have been shown to reduce concentrations of some disease-causing organisms or ‘pathogens’ in compost, in addition to their widely known ability to recycle nutrients and improve soil structure. CIBR scientists have been investigating the potential of vermicomposting to treat biowaste, with CIBR social scientists looking at the economic and cultural viability of vermicomposting as a biowaste re-use option for small rural communities.
Vermicomposting is the process of non-thermophilic biodegradation and stabilization of organic materials by interactions between earthworms (Eisenia fetida or “Tiger Worms”) and microorganisms. ‘Vermicompost’ originated from the latin words vermes meaning “worms” and composite/compositum meaning “something put together”.
In 2016, an investigation into the viability of vermicomposting septic tank waste was carried out. Progression of the
composting process was monitored by analysing a range of chemical and biological parameters (dehydrogenase
enzyme activity, Escherichia coli (E. coli) levels, Olsen P, nitrate and ammonium). At the end of the composting period additional parameters were measured also.
Results demostrated that vermicomposting has the potential to transform septic tank waste into high value compost as it is effective in stabilizing nutrients and reducing pathogens. However, some pathogens, can still be present at potentially unsafe levels that would not allow the compost to be safely handled. Traditional “end-point” detection parameters such as mineralisation of organic N do not relate well to pathogen reduction. The study showed that the use of E. coli spp. as a surrogate for pathogen concentration was unsuitable. Pre-pasteurisation or further composting may be required to produce a pathogen free product.
The paper published was titled: The Suitability of Using Vermicomposting for the Stabilization of Septic Tank Waste [PDF, 519 KB]
Each year, 1500 tonnes of thermal dried biosolids from the Kapiti Coast are disposed of at the Otaihanga landfill. The current resource consent allows this disposal until 2020, when alternative options will be required. Funded by a Waste minimisation grant, ESR scientists investigated the potential for vermicomposting these biosolids, using plasterboard from the building industry as a bulking agent.
Construction and demolition waste (including plasterboard) currently accounts for 20% of waste going to landfill. Plasterboard is theoretically suitable for vermicomposting as it is composed of gypsum with a paper lining and has the potential to absorb excess water, aerate the compost, reduce the ammonia smell from biosolids and balance the C:N ratio required for vermicomposting success. In addition, as a final product, gypsum can be used as a soil amendment in agriculture to improve permeability in clay soils (the ability to allow water and air to pass through soil particles), and provide calcium and sulphur for plant growth.
The results demostrated that the addition of plasterboard to the mix appeared to positively impact the vermicomposting process when the C:N ratio was balanced for worm survival. This is good news as vermicomposting biosolids with a plasterboard bulking agent has the potential create a viable product and allow diversion of biosolids and some plasterboard waste from landfill.