Vermicomposting

Photo courtesy of M. Quintern (MyNoke) Technical Sheet: VERMICOMPOSTING

Vermicomposting is the process of composting using compost worms to create a heterogeneous mixture of decomposing vegetable or food waste, bedding materials, and vermicast. The material used for vermicomposting needs to be presented as a blended mass at an acceptable carbon to nitrogen ratio. If the carbon to nitrogen ratio is too high or too low, waste degradation is slowed.

Vermicast, also called worm castings, worm humus or worm manure, is the end-product of the breakdown of organic matter by an earthworm. These castings have been shown to contain reduced levels of contaminants and a higher saturation of nutrients than do organic materials before vermicomposting. Due to the lower composting temperature, vermicasts have higher microbial loading than compost and generally have reduced levels of pathogens such as E Coli but can show increases in other microorganism s due to spore germination in the worm gut.

Industrial-scale vermicomposting is increasing around the world as is the science relating to vermicomposting. Vermicompost can be used as a soil conditioner or as a fertiliser, depending on the starting biomass. Plant growth trials have shown that small amounts of vermicast added to soil or potting mix can increase the growth of plants and trees.

Pulp and paper derived vermicompost has low nutrient value but can be used as a soil conditioner. Pulp and paper waste solids can be combined with other high nutrient waste sources, such as municipal biosolids, to increase the nutrient value of the resulting vermicast.

scionresearch.com Materials Accepted • wood fibre • green waste (needs to be mulched first) • food wastes including coffee grounds • agricultural industry wastes • manure • biological sludge • wood ash

Examples in Current Use NZ My Noke – primary and secondary sludge at kraft mill and kraft and mechanical mill sites (blend with municipal, dairy and other organic waste) Envirofert – Waikato (range of wastes) Overseas Multiple. Large scale operations in Canada, Italy, Japan, Malaysia, the Philippines, and the United States for vermicompost from general municipal and agricultural organic waste.

Infrastructure and Space Biosolids require dewatering prior to vermicomposting. Materials such as Requirements green waste require mulching to reduce size for effective vermicomposting. Large land areas required. Worms aerate mix and grind (gizzard) the soil – heavy machinery is not required to turn the compost and therefore equipment costs are related to material preparation prior to vermicomposting and processing once vermicomposting ins complete. Vermicompost rows made from pulp mill waste solids in NZ do not require irrigation in summer due to the capping nature of the solids. However vermicomposting other materials may need irrigation, particularly if the process requires indoor operation in cold climates. Screening may be required prior to and after vermicomposting.

Capital Cost Land for vermicomposting and associate operations (purchase or lease, development) that is sufficiently buffered away from residential areas due to odour and vermin (if food waste is involved in vermicomposting). Machinery for laying and spreading the vermicompostable material, harvesting the vermicasts, screening, bagging etc.

Operating Cost Depends on operations pre, during and post composting e.g. size reduction or mixing prior to placement, screening compost, bagging product.

End Product Soil conditioner or fertiliser – quality dependent on inputs.

Operating capacity e.g. viable at Viable at nearly any tonnage – windrow systems are able to accommodate low tonnage vs. high tonnage seasonal fluxes of organic waste volume. Land access may be limiting factor as need up to 9 months for product maturity.

Potential consenting issues • Need buffer from sensitive land users (particularly if manures are used to increase the nutrient value as odour and flies become a problem). • Monitoring for biological and inorganic contaminants. • Operations and Site Management Planning • Use of product (for product made using waste materials)

Technology Risk A qualitative assessment of the likelihood of failure of the option or scenario due to issues related to the technological solution e.g. equipment failure, unable to achieve output standards 2 = med risk, technology proven commercially in New Zealand on a blend of kraft mill primary and secondary biosolids. Not proven for biosolids from mechanical pulp mills as yet.

www.scionresearch.com Commercial Risk No of suppliers Range of input materials A qualitative assessment of the likelihood of failure of the option or scenario due to issues related to the commercial arrangements e.g. supplier unable to maintain operations, increase in cost of process, transport or ongoing site management exceed those able to be reasonable recovered or those for comparable options. 1 = high risk, significant uncertainty in cost or newly established supplier. Risk is decreasing with increased interest and profile of vermicomposting.

Market Risk A qualitative assessment of the likelihood of failure of the option or scenario due to issues related to the ‘market’ for the product e.g. a use for the product cannot be found due to concerns about trace contaminants. 1 = high risk, potential for product to have no market if contamination concerns are raised. 2 = med risk, if biosolids are not included in blend. Organic certification of pulp solids-based vermicompost has also decreased market risk.

This Pulp & Paper Solid Waste Technology Assessment CONTACT was supported by the Ministry for the Environment’s Waste Minimisation Fund. Kim McGrouther 07 343 5772 [email protected]