Introduction
The zeolite trial was designed and supervised by BioCarbon Soil at a composting facility operated by Renew Organics on behalf of Tamworth Regional Council at 123 Forest Road, North Tamworth. Twenty-four (24) tonnes of zeolite was provided by Castle Mountain Zeolites, which is located near Quirindi, approximately 1 hour by road from the composting facility. The purpose of the trial was to determine if zeolite could reduce the cost of the production process while improving the properties and value of the product.

Results
Temperature and moisture content were monitored throughout the process, representative samples were collected, and the EAL at Southern Cross University performed the analysis (Table 1).
The composting process was significantly accelerated by addition of the zeolite. After 8 weeks 53% (3.8% zeolite) and 70% (7.3% zeolite) of mass loss compared to 44% mass loss with no zeolite. Results also showed greater breakdown of the woody fraction leaving less than half the >16mm fraction intact in the zeolite batches. Indicators of compost stability such as Nitrogen Drawdown Index and Wettability were also significantly improved in the zeolite batches. Carbon dioxide was 10-14% in all batches prior to sampling (7-11% oxygen).

Conclusions
1. Using 3% Zeolite of input tonnes by weight delivers production efficiencies and product benefits without excessive loss of product volume and weight.
2. The production cost savings are real (at least $500/batch) but are unlikely to justify the zeolite cost ($2,000/batch) alone, so product must also be sold at a price premium.
3. In some municipal organics composting facilities the reduction in ‘contaminated oversize’ that requires further decontamination or landfilling may justify the cost of Zeolite alone.
4. Compost containing Zeolite is likely to achieve the necessary price premium where the product benefits (such as increased soluble N) can be clearly promoted, and the competition is also value adding their products.

5. Repetition of the trial using 1% and 3% Zeolite would help validate results and test whether the costs and benefits are better balanced at lower rates.
6. Future trials should more closely monitor waste quantities at each stage, actual loader movements, water used, and odour.
7. Future trials should test <3mm zeolite rather than the <0.5mm zeolite to understand whether there is potential to reduce cost of zeolite but further improve the properties of the finished product.

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For additional information contact Angus Johnston on 0466 411 241 or info@biocarbonsoil.com.au .