In traditional composting, large amounts of bulking agents must be added to reduce the moisture of pig
manure, which increases the cost of composting and dilutes the N, P and K content in organic fertilizers.
In this study, maggot treatment was used in composting instead of bulking agents. In experiment of
selecting an optimal inoculum level for composting, the treatment of 0.5% maggot inoculum resulted
in the maximum yield of late instar maggots, 11.6% (maggots weight/manure weight). The manure residue
became noticeably granular by day 6 and its moisture content was below 60%, which was suitable
for further composting without bulking agents. Moreover, in composting experiment with a natural
compost without maggot inoculum and maggot-treated compost at 0.5% inoculum level, there were no
significant differences in nutrient content between the two organic fertilizers from the two treatments
(paired Student’s t15 = 1.0032, P = 0.3317). Therefore, maggot culturing did not affect the characteristics
of the organic fertilizer. The content of TNPK (total nitrogen + total phosphorus + total potassium) in
organic fertilizer from maggot treatment was 10.72% (dry weight), which was far more than that of
organic fertilizer made by conventional composting with bulking agents (about 8.0%). Dried maggots
as feed meet the national standard (GB/T19164-2003) for commercial fish meal in China, which contained
55.32 ± 1.09% protein; 1.34 ± 0.02% methionine; 4.15 ± 0.10% lysine. This study highlights housefly
maggot-treated composting can be considered sustainable alternatives for pig manure management to
achieve high-quality organic fertilizer and maggots as feed without bulking agents