Demonstrating leadership and commitment to sustainability through employing clean technology, the New Zealand Defence Force recently installed a Big Hanna commercial in-vessel composter for food waste at the Devonport Naval Base in Auckland, New Zealand. The composter, Big Hanna, sitting outside the Vince McGlone Galley, is the first of its kind in Australasia.
The New Zealand Defence Force has been implementing several successful green strategies across its operations for a number of years, working with among others Shaun Bowler, Managing Director of Big Hanna Composter Ltd in New Zealand. The machine’s simple yet elegantly engineered solutions matched the Navy’s requirements and he recommended its acquisition.
The Navy serves on average 2,700 meals per week Monday to Sunday to its staff, including staff on outstations such as ships. The navy chefs are frugal housekeepers and the food nutritious and tasty, yet invariably there are leftovers. All plate waste and food preparation waste were previously sent to landfill.
A Big Hanna model T240 was ordered in June 2014 from its builders Susteco AB in Sweden and upon its arrival on November 3, installed outside the galley’s back door following a small amount of siteworks. The Government’s Waste Minimisation Fund, which is administered by the Ministry for the Environment, supported the New Zealand Defence Force with the acquisition.
This model, the 48th of its kind in the world, can process up to 170kg material a day, turning each load into compost in eight weeks. On start-up it was loaded with 600 litres horse manure as bacteria starter, 600l mature compost, and 50kg wood pellets as food source for the bacteria to induce the composting process. “It was quite an exercise getting hold of all that horse poo…in the end the Rosedale Pony Club horses did their duty to their country and obliged in time, but it was touch and go,” Mr Bowler says.
The approximate 10kg compost it now produces per day is moved to maturation bays at the Navy sports fields for later use on the base. It replaces the compost the Navy bought in earlier years in a perfect example of resources going a second round. As more food scraps are fed into it and Big Hanna reaches its full capacity, the amount of compost produced will increase, too.
Mr Bowler says Big Hanna’s operation is based on in-vessel composting technology, which differs from the open windrow technique commonly used in large-scale industrial composting sites. “Pests cannot get into it and odours are contained and managed, so it can process all food waste, including meat, fish, dairy, eggs, and citrus, working quietly and unobtrusively even if installed indoors,” he comments.
Big Hanna requires a small daily dose of wood pellets with every scrap food load. The Navy chefs put scrap food, excluding bones, through a macerator that shreds it finely and remove excess water, thereby optimising it for the composting process. They load the scraps into the infeed hopper, from where an augur takes it into the cylinder. The bacteria do their work in three phases in the cylinder.
First is the thermophilic phase where the high temperature resulting from the biological processes, 50 to 65 degrees C, completely sterilises the material and brings the moisture content of the material down by 40 to 70 percent. Second is the mesophilic phase where the temperature is between 25 and 45 degrees C and moisture content decreases further. Last is the maturation phase, where the temperature averages 20 degrees C and the moisture content all but disappears.
Big Hanna automates the aerobic composting process by aerating and turning the feedstock through rotating the composting cylinder on average one to two minutes per hour. The fan runs constantly at a low airflow. The ventilation system supplies air to the biological processes. The material is aerated when the air is pulled through the cylinder by the fan. The ventilation system contains odours. Usually used air is let into a sewage connection, but it can also be let into the atmosphere via the Hanna biofilter.
The cylinder is always 60 to 70 percent full and automatic emptying is done little by little on each anticlockwise rotation of the cylinder. It empties the compost directly into a plastic bag or offtake bin that is attached on the outlet pipe. Mr Bowler says product arising from good aerobic composting – in New Zealand, this means compliance with the NZS4454 composting standard – is naturally pasteurised during thermophilic decomposition. “Escherichia coli and Salmonella spp. have not been detected in any analyses undertaken at Big Hanna sites,” he notes.
Four temperature sensors in the cylinder make it possible to monitor the composting process and if indicated the process can be manipulated – through changing the temperature, air flow, and rotation speed settings – at the machine’s control and display panel. Once Big Hanna is fully operational, it will also process food waste from the NES galley and wardroom, with the food waste capture from offices, barracks, Narrow Neck, and Torpedo Bay a future possibility. Different models of Big Hanna are available to suit a range of desired operational parameters.
Feature image of Royal New Zealand Navy ratings marching on New Zealand’s national day at Waitangi in 2013 courtesy of Shutterstock in association with The Natural Step New Zealand. Article courtesy of New Zealand Engineering News.