Research articleReducing greenhouse gas emissions and enhancing carbon and nitrogen conversion in food wastes by the black soldier fly
Graphical abstract
Introduction
Globally, about 1.3 billion tons of food are wasted each year, equivalent to about $1 trillion in annual economic losses (FAO, 2014). Nowadays, the treatment of FW has become a serious issue worldwide due to the high costs related to its environmental management (Fersiz and Veli, 2015). The main approaches in FW management include disposal in landfills, incineration and composting for the production of fertilisers (Avagyan, 2017). Despite this, about one third of all the food produced today goes in landfills (Stuart, 2009). In Canada, for example, in the year 2017, 12.9 million tons of FW was produced, but only 4.4 million tons were recycled (Avagyan, 2017). In addition to the enormous financial costs, FW also result in many environmental problems, such as landfill consumption, odour nuisance and generation of leachate and landfill gas (Lee et al., 2007). On the other hand, the burning of FW reduces its economic value, and the dumped product can cause health and environmental problems (release of dioxins, etc.) (Avagyan, 2018). In order to alleviate this, it is necessary to develop economic and environmentally friendly alternatives (Avagyan, 2017, Avagyan, 2013).
Recently, composting has become an important way to manage FW, as it can reduce the volume and weight of FW, and produce innoxious, stable and rich in nutrients soil amendment materials even though it shows some limit (Avagyan, 2018, Yang et al., 2015). In particular, the biodegradation of organic matter can lead to the substantial loss of C and N during long processes, which both reduces the end-product quality and causes secondary environmental pollution. For example, some studies indicated that 16–74% of initial TN and 14–59% of initial TOC are lost during composting, mostly in the form of NH3 and CO2, respectively (Chen et al., 2019). About 0.2–9.9% of initial TN and 0.08–6% of initial TOC in organic wastes are lost in the form of N2O and CH4 (Yang et al., 2015), which are GHG of high concern (Chowdhury et al., 2014).
Currently, biowastes are treated by BSFL widely, and this new approach has attracted considerable interest by researchers worldwide. Previous studies were mostly focused on the bio-treatment of diverse organic wastes, and the residues can be utilised as fertiliser; Meanwhile, larvae provide protein- and fat-rich biomass, which can be further used for biodiesel production and animal feed (Salomone et al., 2017). In fact, the conversion of waste into protein for use as feed for aquaculture and poultry in USA (AAFCO, 2016), EU (Cutrignelli et al., 2018), and other parts of the world is allowed. Hermetia. Illucens L. is one of the authorised insect species. Practical approaches have been applied to ensure the retention of nutrients and control C and N loss in composting (Wang et al., 2018), including the use of different kinds of bulking agents which can increase the C/N ratio in raw materials, the modification of the aeration rate, and the addition of chemical agents or mineral additives. Compared with these methods, BSFL biowaste treatment can lead to end-products of higher economic value at lower costs.
The sustainable use of waste, including recycling and valorisation, is the current trend in waste management (Avagyan, 2013, Sánchez et al., 2015). However, there are few studies focused on the environmental benefit related to the treatment of wastes with BSFL in terms of sustainability. Mertenat et al. (2019) and Ermolaev et al. (2019) found that the BSFL FW treatment has potential to cut down GHG emissions compared with conventional composting. These researchers also suggest that there is still need of further exploration based on various raw materials and process parameters, to study the direct GHG emissions, C and N recycling during BSFL treatment, in order to correctly evaluate its environmental sustainability. Additionally, the FW biodegradation during composting has been reported to be mostly controlled by factors such as pH, moisture, C/N ratio and temperature (Cerda et al., 2018). Especially, the quick biodegradation of readily available organic matter can intensively acidify the substrate, resulting in low pH values in the initial phase of FW treatment and eventually inhibiting the larval growth and microbial activity (Chan et al., 2016, Ma et al., 2018). For this reason, to optimise the biowaste treatment by adjusting the initial pH of the substrate is of great significance. This may not only accelerate the decomposition of FW but also increase the yield and quality of BSFL. To date, the effects of pH on the bioconversion of C and N and on the emissions of GHG and NH3 during BSFL bio-treatment of FW have not been reported, to the authors' knowledge. This study aims to investigate the GHG and NH3 emissions during BSFL bio-treatment of FW under different pH conditions of the feeding substrate, as well as to improve the recycling of C and N from FW to larvae, and to mitigate the GHG emissions by adjusting the initial pH of FW. Besides, the amount of C and N was monitored alongwith parameters such as changes in larvae weight and physico-chemical properties of the substrate. The results of this study can provide important insights for the sustainable use of wastes by BSFL biowaste treatment.
Section snippets
Raw materials
BSFL (Hermetia illucens L., Stratiomyidae: Diptera) used in this study were bred at Wuhan ChaoTuo Ecology Agricultural Ltd. Food waste was collected from the restaurants in Wuhan, China, Hubei Tianji Bioengineer Co. Ltd, China. The chopped rice straw (RS) was obtained from the experimental field of Huazhong Agricultural University, Wuhan China. The physical and chemical characteristics are shown in Table 1.
Experimental design
Before BSFL rearing, FW and RS were mixed at a fixed ratio (FW:RS, 9: 1 w/w) to adjust
Dynamics of pH value, larval growth during black soldier fly larvae bioconversion process
As one of the crucial factors affecting the BSFL activity and GHG emissions, time-changes in pH are presented in Fig. 1a, with reference to treatments at different nominal pH (from 3.0 to 11.0). BSFL were able to adjust the pH of the substrate. However, this capability was not observed when the substrate was highly acidic (pH 3.0). The final pH value (after 10 days), for treatments at nominal pH from 5.0 to 11.0, ranged from about 8 to 9, indicating that the residues after BSFL conversion could
Conclusions
This study demonstrates that increasing the pH of the initial substrate effectively accelerates the BSFL growth and decreases CO2 emissions, but simultaneously increases NH3 emissions. The BSFL bio-treatment of FW could reduce CH4, N2O and NH3 emissions, when compared with traditional composting methods. BSFL can be harvested and preserved, providing a short-term means of C and N sequestration, rather than allowing them to be directly decomposed by microbes and released in the form of gases.
Credit author statement
Wangcheng Pang: Designed experiments, Carried out experiments, Writing- Original draft preparation. Dejia Hou: Designed experiments, Carried out experiments, Writing-Reviewing and Editing. Jiangshan Chen: Carried out experiments, Analysed data. Elhosseny E. Nowar: Commentary and revision. Zongtian Li: Commentary and revision. Jeffery K. Tomberlin: Commentary and revision. Ziniu Yu: Financial support for the project leading to this study. Ronggui Hu: Financial support for the project leading to
Declaration of competing interest
The authors declare that we have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Acknowledgments
This study was financially supported by the National Key Research and Development Program of China (Project No. 2018YFD0500203). Fundamental Research Funds for the Central Universities (Project No. 2662017JC045 and Project No. 2662017JC026).
References (41)
- et al.
Reducing nitrogen loss and salinity during ‘struvite’ food waste composting by zeolite amendment
Bioresour. Technol.
(2016) - et al.
Potential of aeration flow rate and bio-char addition to reduce greenhouse gas and ammonia emissions during manure composting
Chemosphere
(2014) - et al.
Evaluation of an insect meal of the Black Soldier Fly (Hermetia illucens) as soybean substitute: intestinal morphometry, enzymatic and microbial activity in laying hens
Res. Vet. Sci.
(2018) - et al.
Composting of food wastes: status and challenges
Bioresour. Technol.
(2018) - et al.
Greenhouse gas emissions from small-scale fly larvae composting with Hermetia illucens
Waste Manag.
(2019) - et al.
Effects of earthworms on physicochemical properties and microbial profiles during vermicomposting of fresh fruit and vegetable wastes
Bioresour. Technol.
(2014) - et al.
Effect of temperature on thermophilic composting of aquaculture sludge: NH3, recovery, nitrogen mass balance, and microbial community dynamics
Bioresour. Technol.
(2018) - et al.
Carbon dioxide and ammonia emissions during composting of mixed paper, yard waste and food waste
Waste Manag.
(2006) - et al.
Evaluation of environmental burdens caused by changes of food waste management systems in Seoul, Korea
Sci. Total Environ.
(2007) - et al.
Nutrient transformations during composting of pig manure with bentonite
Bioresour. Technol.
(2012)
Effects of C/N ratio and earthworms on greenhouse gas emissions during vermicomposting of sewage sludge
Bioresour. Technol.
Effects of mixing and covering with mature compost on gaseous emissions during composting
Chemosphere
Black Soldier Fly biowaste treatment– Assessment of global warming potential
Waste Manag.
Vermicomposting as a technology for reducing nitrogen losses and greenhouse gas emissions from small-scale composting
J. Clean. Prod.
Cellulose decomposition and larval biomass production from the co-digestion of dairy manure and chicken manure by mini-livestock (Hermetia illucens, L.)
J. Environ. Manag.
Environmental impact of food waste bioconversion by insects: application of Life Cycle Assessment to process using Hermetia illucens
J. Clean. Prod.
Short-term effects of nitrogen addition and vegetation removal on soil chemical and biological properties in a freshwater marsh in Sanjiang Plain, Northeast China
Catena
Combining biochar, zeolite and wood vinegar for composting of pig manure: the effect on greenhouse gas emission and nitrogen conservation
Waste Manag.
Anaerobic digestion of black solider fly larvae (BSFL) biomass as part of an integrated biorefinery
Renew. Energy
Effects of phosphogypsum and superphosphate on compost maturity and gaseous emissions during kitchen waste composting
Waste Manag.
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Wancheng Pang and Dejia Hou contributed equally to this work.