Research article
Performance of black soldier fly larvae (Diptera: Stratiomyidae) for manure composting and production of cleaner compost

https://doi.org/10.1016/j.jenvman.2019.109593Get rights and content

Highlights

  • Black soldier fly larvae was applied as an inoculum for different manure composting.

  • Black soldier fly larvae inoculation improved total nutrient and organic matter degradation.

  • The addition of black soldier fly reduced the accumulation of volatile fatty acids.

  • Black soldier fly larvae accelerate the process and improved final compost quality.

Abstract

The increasing number of livestock farms has led to a great deal of manure generation, and its improper treatment results in threats to the environment. Black soldier fly larvae (BSFL) have the potential to effectively convert manure into high-quality fertilizer. The aims of this investigation were to observe the organic matter transformation of different livestock manures and volatile fatty acids (VFAs), and to evaluate the end product quality. Three types of manure [chicken (T1), pig (T2), and cow (T3)] were inoculated with BSFL (1.2:7 ratio on fresh weight basis), three types without BSFL were used as control (T4, T5, and T6), and both were composted for 9 days. The results showed that the BSFL composting reduced the organic matter by 20.31–22.18% and the accumulation of VFAs by 25.58–80.08% as compared to the control. BSFL composting greatly decreased the nitrogen, by 6.08–14.37%. The employment of BSFL significantly increased the total phosphorous (TP), total Kjeldahl nitrogen (TKN), and total nutrients by 42.30–64.16%, 45.41–88.17%, and 26.51–33.34%, respectively. This study showed that employing BSFL could improve the quality of the product and the maturity degree of the composting. Therefore, the BSFL could be added as a high-efficiency transformation agent for converting organic manure into stable compost, especially in developing countries, where adopting technical devices for composting is expensive and difficult to manipulate.

Introduction

In China, with the rapid development of the economy, living standards have gradually improved, and the demands for meat and milk have increased dramatically. The expanding rate of organic residues from livestock manure has become a serious problem, owing to characteristics such as abundant nitrogen and high organic matter (OM), which must be effectively disposed of (Soobhany, 2018). Though direct application of manure to farmland has a long history in China, it could result in environmental contamination, including atmospheric, water, and solid pollution, and can especially influence plant growth (Kong et al., 2018, Ravindran et al., 2019). Thus, it is important to determine an alternative way to handle manure. In this regard detail, composting technology is considered as a useful way to treat manure (Chen et al., 2018, Wang et al., 2017b), and can convert the OM into a stable and sanitary end product, which is considered as a fertilizer (Li et al., 2018, Xiao et al., 2017). Composting is an environmentally-friendly technique for the conversion of organic waste through a series of active microorganisms, and finally transformation to a humified ultimate produce called compost (Kong et al., 2018). However, unstable composting could cause the spread of disease, and release foul smell and/or greenhouse gas (GHGs) emissions, which could limit the development of composting technology (Hanifzadeh et al., 2017). Meanwhile, volatile fatty acids (VFAs) play a key role in the odorant emissions from livestock housing facilities (Jo et al., 2015). Therefore, it is extremely important to explore a more appropriate method regarding manure management.

Manure is the principal food of many insects in nature, and these insects can effectively convert manure into fertilizer while maintaining a low environmental cost and recycling waste, especially black solider fly larvae (BSFL) (Lalander et al., 2019). BSFL, i.e., Hermetia illucens (Diptera:Stratiomyidae), live outdoors and do not disturb the normal life of human beings (Cickova et al., 2015). BSFL had been previously used to manage different type of wastes, as they thrive on organic wastes such as food waste and livestock manure. One novel way of treating organic waste was by BSFL composting, in which waste is transformed into larval biomass and compost. The larval biomass can be utilized as a protein and fat source in animal feedstock, and the compost can be utilized as a biofertilizer (Lalander et al., 2019).

Employing BSFL for degradation of agricultural organic wastes causes an effect which requires a shorter time, and additional BSFL could be used for bioenergy and fodder, as reported by Kumar et al. (2018). In addition, BSFL showed antimicrobial activity against pathogens (Salmonella spp., and other gram-negative bacteria) and fly species in these wastes (Rehman et al., 2019, Xiao et al., 2018). Encouraged by these merits, the BSFL might have a potential effect on improving the compost quality, and can play a key role in providing nutrient value in organic and conventional agriculture. Different feedstocks have an impact on BSFL growth and the transformation of the final product (Lalander et al., 2019). Setti et al. (2019) reared the BSFL on the“Gainesville House Fly” diet, and found that the BSFL processing residue had the potential ability to replace commercial peat in agriculture. According to Rehman et al. (2019), the BSFL assisted with lignocellulosic exogenous bacteria, and could improve the conversion of lignocellulose in dairy and chicken manure (CM). The co-conversion of BSFL with functional bacteria and the aerobic fermentation could also enhance the conversion ability of CM (Xiao et al., 2018). Additionally, some have studied the BSFL from perspectives of survival, crude protein, and fatty acids, and the feedstocks were food waste (Li et al., 2018), livestock manure (Moula et al., 2018, Lalander et al., 2019), and human feces (Lalander et al., 2013). However, limited studies have been found regarding the BSFL conversion of different livestock manures into bio-fertilizers. Therefore, it is necessary to investigate the BSFL processing residue, including its use as an innovative biofertilizer.

The aims of this study are to investigate the effect of BSFL on the composting process and to enhance composting quality. These aspects were possibly revealed by the performances of pH, VFAs, OM degradation, and nutrient transformation during three types of manure composting. Meanwhile, this experiment also attempted to find a correlation between the analyzed parameters and OM degradation in each treatment, and evaluated the final product.

Section snippets

Materials collection and processing

The fresh CM, pig manure (PM), and cow manure (COM) used in this study were obtained from a local farm (Yangling, Shanxi Province, China). Hermetia illucens L. was used in this experiment, and was provided by the Xinyi Ecological Agriculture Technology Development Cooperation Limited (Yangling, Shanxi Province, China). The investigation was conducted under room temperature conditions of 29 °C and 52% humidity. For the first 6 days, the BSFL were fed with chicken feed, then were separated from

Effect of black soldier fly larvae on pH and volatile fatty acids during composting

The changes of pH value in all treatments during the composting are shown in Fig. 1a. The beginning pH values of each treatment were 6.78–7.81, beneficial for the BSFL (Ma et al., 2018). The tendency in typical manure composting (Onwosi et al., 2017) is a pH increase in the initial days, which could be caused by the ammonification of the manure, whereas its stabilization occurs because of NH3 emission or microorganism assimilation (Alavi et al., 2019). Another reason is the substrate

Practical applications and future research perspectives

Livestock manure is a primary source of plant nutrients, but its effective usage is only 20–40% as organic fertilizer (Rehman et al., 2019). However, there are worthy types of manure treatments around the world, depending on, e.g., sustainable corporate livestock production systems and government strategy. In that regard, the BSFL processing, as a clean composting, could transform the manure into bio-fertilizers and insect protein. The insect protein could replace fishmeal. From 2005 to 2013,

Conclusion

The BSFL added in the livestock manure enhanced the total nutrients and the value of the GI, and obtained a more stable fertilizer as compared to the control group. While employing the BSFL in the substrate of CM had the highest rate of increase of total nutrients, the lower GI was less than 50%, which indicates risks when applied to plant growth. Meanwhile, the BSFL added into the livestock manure could improve the value of GI, and the maximum increased level was found in the BSFL/COM system.

Acknowledgements

We thankfully acknowledge the financial support from a Research Fund for International Young Scientists from National Natural Science Foundation of China (Grant No. 31750110469), China. The Introduction of talent research start-up fund (No. Z101021904), Northwest A&F University, Yangling, China and Science and Technology Program of Yangling Demonstration Zone (China, 2017NY- 24), China.

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