Sort It or Convert It? A 2026 Head-to-Head on Mechanical-Biological Treatment (MBT/MRBT) and Decentralized BSF Bioconversion
When a municipality or waste operator cannot yet separate its organic waste at source, the standard engineering answer in Europe and increasingly in Asia is mechanical-biological treatment (MBT), or its more ambitious cousin, material recovery and biological treatment (MRBT). Mixed waste goes in; sorted recyclables, refuse-derived fuel (RDF) and a stabilised organic fraction come out. It is a respectable technology, and fairness demands that we say so. But as COP31 approaches in Antalya this November, with the presidency putting methane and municipal waste on the agenda, the more useful question for ESG teams and municipal planners is not whether MBT beats raw landfill. It does. The question is whether building more of it is the right way to manage organic waste at all, or whether decentralized Black Soldier Fly (BSF) bioconversion at the point of generation is a better use of the next dollar of capital.
What MBT and MRBT actually do
MBT plants combine mechanical sorting (shredding, screening, magnetic and eddy-current separation) with a biological stage, either aerobic stabilisation or anaerobic digestion. Their purpose is to pre-treat residual waste so that it meets the EU Landfill Directive, which prohibits landfilling untreated waste, and to pull out fuel and recyclables on the way. According to a 2011 ecoprog study reported by Waste & Recycling, Europe already had around 330 MBT plants with capacity to treat roughly 34 million tonnes of municipal waste a year, and the industry expected that to grow. Those figures are old, but they show how embedded the technology is in the European system.
The more recent policy argument is that MBT should be upgraded rather than abandoned. Zero Waste Europe has called for mixed-waste MRBT to be made mandatory, citing a commissioned study that found it cost-competitive with incineration and landfilling and a 2022 Reloop study that identified it as the most climate-friendly option for mixed waste. ZWE also notes that the EU still burns or landfills roughly 116 million tonnes of waste a year, against about 115 million tonnes recycled or composted. If your waste arrives as a mixed bag and stays that way, MRBT is a defensible choice, and a far better one than a bare landfill or an incinerator.
The structural problem: it starts with contamination
The weakness of MBT is not engineering; it is the input. Organic waste that has been tipped into a mixed bin with plastics, textiles, glass and batteries is contaminated before it reaches the plant. Sorting can remove much of the inert material, but the organic fraction that emerges is wet, heterogeneous and carries a residual load of fragments and contaminants. That limits where it can go. In practice the stabilised output is often restricted to landfill cover, land reclamation or further disposal rather than being a premium input for agriculture, and the fuel fraction is only as valuable as the market for RDF. The biological stage is designed to stabilise waste so it stops producing methane in a landfill, not to turn it into a product with a named buyer.
Contrast that with where policy is heading. Article 22 of the EU Waste Framework Directive requires member states to organise separate collection of biowaste, and the direction of travel in the EU Waste Framework Directive revisions, in extended producer responsibility (EPR) schemes and in corporate Scope 3 emissions reporting is towards keeping organic streams clean. Yet the BioCycle-reported 2024 update of EU biowaste capture puts the share of theoretical food waste actually captured by separate collection at only 26 percent, about 15.1 million tonnes of an estimated 60 million tonnes or more. Roughly three quarters of the food waste potential still flows into mixed residual waste, which is exactly the stream MBT is built for. MBT is a sensible response to that gap. It is also a plant that gets less necessary the better separate collection becomes, a point ZWE itself concedes when it says MRBT sites should be flexible enough to shift towards cleaner separate-collection streams over time.
Where decentralized BSF bioconversion is different
BSF larvae (BSFL) are voracious processors of exactly the material MBT struggles to monetise: clean, wet, nutrient-rich food and agro-industrial residues. A decentralized BSF unit sits at the hotel kitchen, the wholesale market, the food factory or the municipal collection point and converts that waste in days. The outputs are larval biomass that can be processed into insect protein and oil for sustainable animal feed, and frass fertilizer that returns nutrients to soil, supporting soil health and regenerative agriculture. That is waste valorization in the literal sense: a defined product stream with a defined buyer, rather than a stabilised residue that needs a home.
The climate case is supported by independent life cycle assessment (LCA). A study from Eawag and partners (Mertenat et al., 2019) assessed a BSF pilot facility in Surabaya, Indonesia, and found that treating a tonne of biowaste with BSF larvae emitted just under 50 kg CO2-equivalent, compared with over 100 kg for conventional composting, with direct emissions from the larval stage itself roughly 47 times lower than from composting. Using the larvae to replace fishmeal cut the global warming potential further, by up to 30 percent in the study's abstract. The authors are candid that most of the remaining emissions come from post-composting of the residue (about 69 percent) and from electricity for shredding and sieving, and that residue treatment should be improved. That candour is useful: it tells operators where to focus, and it shows the same kind of modelling that supports MRBT claims can be applied to BSF. This is one pilot in one location compared against literature values for composting, so it should be read as strong directional evidence rather than a universal number.
Head-to-head: where each approach wins
Speed and methane. Methane forms when organic waste sits and decomposes without oxygen. MBT concentrates waste at a central site, which means collection, consolidation and transport delays before the biological stage starts. A decentralized BSF unit treats waste within hours or days of generation, close to where it arises. For methane emissions, the interval between generation and treatment is one of the variables that matters most, and decentralization shortens it.
Output value. MBT yields RDF, recyclables and a stabilised residue whose end markets are limited by contamination. BSF yields insect protein, oil and frass fertilizer, each with commercial buyers in aquafeed, pet food and farming. This is the clearest advantage for the circular economy argument.
Transport and Scope 3 emissions. Hauling mixed waste to a regional MBT plant adds truck kilometres. For a food manufacturer or retailer reporting under the GHG Protocols and setting SBTi targets, waste treatment sits inside the value-chain footprint, so shortening the haul reduces reportable Scope 3 emissions.
Land and capital. MBT plants are large, capital-intensive and slow to permit; the 2011 market data itself records a wave of early technical problems and closures. Modular BSF units have a small footprint, scale by adding units and can be sited in dense industrial areas where permitting for large waste infrastructure is hard.
Where MBT still wins. Be clear-eyed about the limits of BSF. It is a bioconversion technology for source-separated or at least clean organic feedstock, not a universal solution for mixed municipal solid waste. If a city's waste truly arrives as an unsorted mix and will for years, MBT or MRBT is a legitimate tool for the residual stream, and it recovers materials that BSF cannot touch. The honest framing is that the two are not rivals for the same input. The more organic waste is diverted to clean decentralized treatment, the smaller and cleaner the residual stream MBT must handle.
What this means for COP31 and net zero planning
The COP31 presidency in Antalya has pointed to studies attributing around 30 percent of current global warming to methane and has called on countries to halve the projected growth in annual municipal solid waste generation by 2035. Waste is a smaller share of total emissions than fossil fuels, as critics rightly note, but it is one of the cheapest places to cut methane quickly, and the Paris Agreement pathway to net zero depends on fast methane cuts. Policy is converging on organic waste diversion at source. Investing heavily in new mixed-waste infrastructure risks locking in a collection model that policy is trying to leave behind, while decentralized BSF capacity fits the direction of travel and builds climate resilience by avoiding dependence on a single plant or haul route.
The bottom line
MBT and MRBT are good engineering for a problem that should be shrinking: mixed waste that nobody separated. They are far better than untreated landfill and a credible choice for residual waste. But for the organic fraction that can be kept clean at the source, sorting it later is a more expensive and less valuable route than converting it where it arises. Decentralized BSF bioconversion treats organic waste faster, emits less per tonne in the evidence available, takes less land, and ends in products with buyers instead of a residue that needs a destination. For food businesses, markets, hospitality groups and municipalities planning their next five years of organic waste capacity, the sound sequence is to separate at source, convert locally with BSF, and keep MBT for what is genuinely left.
B-BOX designs decentralized Black Soldier Fly systems for organic waste treatment. To explore an onsite pilot, get in touch with the B-BOX team.
Sources
Waste & Recycling, "Mechanical biological treatment in the EU" (reporting the 2011 ecoprog study: ~330 plants, ~34 Mt/yr capacity): https://wasterecyclingmag.ca/circular-economy/mechanical-biological-treatment-in-the-eu
Packaging Insights (17 April 2023), "Biological waste treatment: EU 'throwing away wealth' in landfill and incineration, as ZWE calls for tougher policies" (116 Mt vs 115 Mt; MRBT; Reloop 2022): https://www.packaginginsights.com/news/biological-waste-treatment-eu-throwing-away-wealth-in-landfill-and-incineration-as-zwe-calls-for-tougher-policies.html
BioCycle, "Biowaste Capture in the European Union" (2024 update: 26% capture, 15.1 Mt): https://www.biocycle.net/biowaste-capture-in-the-european-union/
Eawag, "Fly larvae make biowaste disposal more climate-friendly" (Mertenat et al., 2019, Surabaya LCA): https://www.eawag.ch/en/info/portal/news/news-detail/fly-larvae-make-biowaste-disposal-more-climate-friendly
Eco-Business (15 September 2026), "At a Turkish waste plant, COP31's case for climate action goes beyond fossil fuels": https://www.eco-business.com/news/at-a-turkish-waste-plant-cop31s-case-for-climate-action-goes-beyond-fossil-fuels/
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