Counting on soldier flies to clean up after zoo animals

A dehydrator is used to extract liquid from the waste to keep it dry. The waste is then placed in compost bins and black soldier fly larvae are loaded into them to start the composting process. Black soldier fly pre-pupae climbing up ramps inside a c
Wildlife Reserves Singapore assistant director of zoology Francis Cabana with two containers of the larvae of the black soldier fly and principal investigator and Republic Polytechnic lecturer Lily Ganda with a container of carnivore dung at the Singapore Zoo's research facility yesterday.ST PHOTO: LIM YAOHUI
A dehydrator is used to extract liquid from the waste to keep it dry. The waste is then placed in compost bins and black soldier fly larvae are loaded into them to start the composting process. Black soldier fly pre-pupae climbing up ramps inside a c
Wildlife Reserves Singapore assistant director of zoology Francis Cabana with two containers of the larvae of the black soldier fly (above), and principal investigator and Republic Polytechnic lecturer Lily Ganda with a container of carnivore dung at the Singapore Zoo's research facility yesterday.ST PHOTO: LIM YAOHUI
A dehydrator is used to extract liquid from the waste to keep it dry. The waste is then placed in compost bins and black soldier fly larvae are loaded into them to start the composting process. Black soldier fly pre-pupae climbing up ramps inside a c
A dehydrator is used to extract liquid from the waste to keep it dry. The waste is then placed in compost bins and black soldier fly larvae are loaded into them to start the composting process.ST PHOTO: LIM YAOHUI
A dehydrator is used to extract liquid from the waste to keep it dry. The waste is then placed in compost bins and black soldier fly larvae are loaded into them to start the composting process. Black soldier fly pre-pupae climbing up ramps inside a c
Black soldier fly pre-pupae climbing up ramps inside a composting bin. They are seeking a drier environment, where they can turn into pupae. ST PHOTO: LIM YAOHUI

Wildlife Reserves S'pore, poly studying use of larvae to process animal food waste and dung

Black soldier flies are among nature's "sanitation workers", known for their excellent ability to convert waste into animal feed and fertilisers.

Now, Wildlife Reserves Singapore (WRS) has plans to outsource the "dirty" job of managing its animal residents' waste to these insect armies.

The 12,000 animal residents of the Singapore Zoo, the Night Safari and the River Safari produce more than 4,000kg of waste a day.

While the bulk of this is produced by herbivores such as elephants and zebras, about 200kg to 300kg are excreted by meat eaters, the biggest contributors being lions, tigers and bears.

In March, WRS joined hands with researchers from Republic Polytechnic for a one-year study to build a closed-loop waste management system to deal with a portion of waste at Wildlife Reserves Singapore.

The project is supported by the Mandai Research Fund, which was set up by Mandai Park Development to gain a deeper understanding of local biodiversity in the Mandai precinct.

Existing research on the waste-processing abilities of soldier flies has centred on herbivore waste and food waste, as there are concerns about the potential contamination of carnivore waste.

Professor Rudolf Meier of the Biological Sciences Department at the National University of Singapore pointed out that carnivore dung has lots of bacteria and is of a lower nutritional value compared with herbivore waste.

Dr Francis Cabana, assistant director of zoology at WRS, told The Straits Times yesterday that the team is studying how to process carnivore waste despite the concerns because the parks produce a large amount of it every day.

HUNGRY FOR ANIMAL FOOD WASTE

The black soldier fly larvae's uptake rate of animal food waste is twice the uptake rate of carnivore waste, and four times the uptake rate of herbivore waste.

DR LILY GANDA, the study's principal investigator. This is the first time that a study is looking into the viability of rearing black soldier flies on carnivores' dung. 

Current findings by the team show that the black soldier fly larvae favour animal food waste the most. 

This is the first time that a study is looking into the viability of rearing black soldier flies on carnivores' dung.

Current findings by the team show that the black soldier fly larvae favour animal food waste the most.

This is followed by carnivore waste, which are excreted by animals such as cheetahs and lions, and herbivore waste, said Dr Lily Ganda, the study's principal investigator.

"The black soldier fly larvae's uptake rate of animal food waste is twice the uptake rate of carnivore waste, and four times the uptake rate of herbivore waste," she added.

Black soldier fly larvae reared on carnivore waste are also expected to be larger in size than usual due to the high crude protein present in carnivore waste, noted Dr Ganda.

Currently, the facility at the Singapore Zoo set up for the study is able to process about 20kg of waste in a week using a black soldier fly larvae population of 5kg.

The team hopes to be able to convert 100kg of waste per day by January next year.

Each day, raw animal waste is collected from the various enclosures and segregated into carnivore, herbivore and animal food waste.

A machine is used to extract any liquid from the waste to keep it dry, so as to increase the compost rate.

The waste is then placed in compost bins, and the larvae are loaded into them to start the composting process.

 
 

The resulting frass, or compost, enters another container via a sieve. The compost is then collected and the process is repeated when more waste has been collected.

The compost can be used as plant fertiliser, while the fly larvae can be used as animal feed.

Dr Cabana said that none of the animal feed produced in the study has been given to the animals yet.

The team is currently running tests to see if it is safe for animal consumption and has sufficient nutritional value.

A version of this article appeared in the print edition of The Straits Times on October 18, 2019, with the headline 'Counting on soldier flies to clean up after zoo animals'. Print Edition | Subscribe