Evaluation of potential of black soldier fly larvae for organic waste management and production of nutrient-dense organic amendments

Abstract

This study aimed at evaluating the potential of black soldier fly (BSF) larvae for effective
organic waste management and the production of nutrient-rich organic fertiliser. The
experiment was carried out at Teaching and Research farm, Obafemi Awolowo University,
Ile-Ife, Nigeria, where BSF larvae were reared on poultry, cattle, swine, rabbit, and
combined wastes. Data were collected on waste reduction efficiency, larval biomass yield,
feed conversion ratio (FCR), bio-conversion efficiency (BCE), and nutrient composition
of frass. The results showed that poultry waste decreased in mass from 25 kg to 19.59 kg
frass, and an increase in weight gained by larvae from 0.250 kg to 1.1925 kg. Rabbit waste
produced the highest final frass among all the wastes used, with the decrease in mass of
larvae from 0.25 kg to 0.1149 kg. Cattle and swine wastes produced almost the same amount
of frass weight, whereas in combined waste mixture, the quantity gained in mass (153.1g)
by the larvae was lower than expected, likely due to imbalance of nutrient present in the
waste. The Feed Conversion Ratio (FCR) values were lowest in poultry manure (26.53),
indicating more efficient feed-to-biomass conversion. In contrast, swine manure and the
combined substrate mixture recorded very high FCR values (>150), reflecting inefficient
conversion. Poultry manure recorded the highest BCE, followed by cow dung. Poultry frass
had high P and K contents, a favourable C:N ratio, and optimum pH, making it ideal for soil
fertility improvement. Cattle frass recorded high ash and calcium content, making it suitable
for correcting soil acidity and calcium deficiencies. These variations in the nutrient present
in these frass samples are strongly influenced by the initial waste and the biochemical
transformations during BSF digestion. The study concluded that initial elemental
composition of the waste influenced the nutrient composition of the BSF larvae-frass
produced. The waste selection for BSF rearing should align with the intended soil fertility
goals and specific crop nutrient requirements. Further study on the field is highly
recommended to demonstrate the performance of BSF larvae-frass from different organic
wastes on nutrient uptake by plants.