5. Summary and conclusion
The design and functioning of a novel vermicomposting machine, acronymed HEVSTOW (High Efficiency Vertically Stacked vermicomposting system for Treating Organic Waste), on which a patent has recently been granted, is described. Over 6-month long uninterrupted operation HEVSTOW was able to simultaneously vermicompost different substrates with different species of earthworms. It functioned to its designed capability and efficiency throughout. By following the paradigm of high-rate vermicomposting, developed earlier by the authors, it was possible to directly vermicompost in HEVSTOW the weed water hyacinth (Eichhornia crassipes) without pre-composting it or doing any other form of pre-treatment. The machine was also able to vermicompost paper waste ─ which had been pre-soaked in water containing 10% (w/v) of fresh cow-dung ─ as swiftly as it processed water hyacinth. It was possible to achieve convertion of all the substrate to vermicompost within a solid retention time of just 20 days. The vertically stacked multi-module design of HEVSTOW was thus seen to enable unprecedentedly high efficiency of vermicomposting in terms of space as well as time.