Black soldier fly (Hermetia illucens L.) as a high-potential agent for bioconversion of municipal primary sewage sludge

Environmental Science and Pollution Research https://doi.org/10.1007/s11356-022-20250-w RESEARCH ARTICLE Black soldier fly (Hermetia illucens L.) as a high‑potential agent for bioconversion of municipal primary sewage sludge Silvia Arnone1 · Massimiliano De Mei1 · Francesco Petrazzuolo1 · Sergio Musmeci2 · Lorenzo Tonelli3 · Andrea Salvicchi4 · Francesco Defilippo5 · Michele Curatolo5 · Paolo Bonilauri5 Received: 27 September 2021 / Accepted: 10 April 2022 © The Author(s) 2022 Abstract The treatment of municipal wastewater produces clean water and sewage sludge (MSS), the management of which has become a serious problem in Europe. The typical destination of MSS is to spread it on land, but the presence of heavy metals and pollutants raises environmental and health concerns. Bioconversion mediated by larvae of black soldier fly (BSFL) Hermetia illucens (Diptera, Stratiomyidae: Hermetiinae) may be a strategy for managing MSS. The process adds value by generating larvae which contain proteins and lipids that are suitable for feed and/or for industrial or energy applications, and a residue as soil conditioner. MSS from the treatment plant of Ladispoli (Rome province) was mixed with an artificial fly diet at 50% and 75% (fresh weight basis) to feed BSFL. Larval performance, substrate reduction, and the concentrations of 12 metals in the initial and residual substrates and in larval bodies at the end of the experiments were assessed. Larval survival (> 96%) was not affected. Larval weight, larval development, larval protein and lipid content, and waste reduction increased in proportion the increase of the co-substrate (fly diet). The concentration of most of the 12 elements in the residue was reduced and, in the cases of Cu and Zn, the quantities dropped under the Italian national maximum permissible content for fertilizers. The content of metals in mature larvae did not exceed the maximum allowed concentration in raw material for feed for the European Directive. This study contributes to highlight the potential of BSF for MSS recovery and its valorization. The proportion of fly diet in the mixture influenced the process, and the one with the highest co-substrate percentage performed best. Future research using other wastes or by-products as co-substrate of MSS should be explored to determine their suitability. Keywords Scavenger insects · Waste management · Municipal sewage sludge · Biorefinery · Circular economy · Green chemistry · Metals Responsible Editor: Ta Yeong Wu * Silvia Arnone 1 ENEA ‑ Italian National Agency for New Technologies, Energy and Sustainable Economic Development - TERIN-BBC - Casaccia, Via Anguillarese 301, 00123 S. Maria Di Galeria, Rome, Italy 2 ENEA ‑ Italian National Agency for New Technologies, Energy and Sustainable Economic Development - SSPT-BIOAG - Casaccia, Via Anguillarese 301, 00123 S. Maria Di Galeria, Rome, Italy 3 Località Canonica 44, 05018 Orvieto, TR, Italy 4 Via dei Monti di Creta 49, 00167 Rome, Italy 5 IZSLER - Istituto Zooprofilattico Sperimentale Lombardia ed Emilia-Romagna, Via A. Bianchi, 7/9, 25124 Brescia, Italy Abbreviations BSFL Black solder fly larvae DM Dry matter (%) DMis Dry matter of initial substrate (%) DMrs Dry matter of residual substrate (%) DMl Dry matter of larvae (%) GLM Generalized linear model statistic test IS Initial substrate (g) LS Larval survival (%) LW Larval weight (mg) Mis Metal content in the initial substrate (mg kg−1DM) Ml Metal content in larvae after bioconversion (mg kg−1DM) Mrs Metal content in the residual substrate (mg kg−1DM) MR Metal reduction (%) MSS Municipal sewage sludge 13 Vol.:(0123456789) Environmental Science and Pollution Research PrCR Protein conversion ratio (%) RS Residual substrate (g) WR Waste reduction (% fresh weight basis) WRI Waste reduction Index Introduction The continuous growth of global population and urbanization is increasing the generation of waste and overexploitation of natural resources (fuels, minerals, water, land, and biodiversity). More sustainable development practices are urgently needed. Waste management is one of the main challenges of the latest decades and represents an increasingly important area of resource recovery (EEA 2020). Among wastes, urban wastewater and related sewage sludge represent a serious harm for the environment. Wastewater is a mixture of black and grey water derived from domestic activities, stormwaters, and other urban runoff. High-income countries treat about 70% of urban wastewater (UNWWDR 2017) by collecting it in sewer networks and conveying it to treatment plants with the purpose of separating clean water from the solid component, the municipal sewage sludge (MSS or biosolids). The more efficient the wastewater treatment plant and the higher the quantity of the wastewater treated, the greater the amount of MSS produced that must be managed (Bianchini et al. 2015). Currently, more than 10 million tons (dry matter) of MSS are produced per year in Europe (Eurostat 2019). The characteristics of MMS depend on the quality of the wastewater and on the treatment system. MSS is composed of organic matter (as high as 30-60%), which includes lipids (over 20%), carbohydrates (about 50%, including sugar, starch and fiber), nitrogen, phosphorus, and potassium (about 3, 1.5 and 0.7%, respectively), with a C/N ratio ranging from 10 to 20% (dry matter basis) (Kumar et al. 2017; Wei et al. 2010). This represents a potential resource for energy and valuable products (Puyol et al. 2016). However, it also can contain high levels of heavy metals (Islam et al. 2013; Kumar et al. 2017), pathogens (Clarke and Smith 2011), and physical, chemical, and biological pollutants (Strauch 1991), such as microplastics (NIVA 2018), polycyclic aromatic hydrocarbons, perfluorinated surfactants (Tavazzi et al. 2012), and polychlorinated biphenyl (Kaya et al. 2015). MSS naturally undergoes decomposition with emission of the greenhouse gases carbon dioxide, methane, and nitrous oxide (Hofman et al. 2011). In the past, landfill and sea disposal were the most frequently used way of MSS management (EC 2001). Application of MSS on land has been considered for a long period to be the most appropriate strategy of reuse since it contributes to improvement of soil fertility and crop productivity (Sommers 1977). At present, it is the main route (50%) followed in Europe (Collivignarelli et al. 2019). On the other hand, 13 the presence of toxic metals raises environmental and health concerns regarding long-term impact of MSS land application (Charlton et al. 2016; Elmi et al. 2020; Singh and Agrawal 2007). Evidence of persistence of heavy metals in the soil that impair microbial diversity (Chaudri et al. 1993; McGrath 1987) and affect the growth of crops and modify trophic chain (Larsen et al. 1994) formed the basis for having a precautionary approach in regulation of heavy metal concentrations in soil (Witter 1996; EC 2000). In Europe, (...truncated)