A new model of the stages of disintegration and hydrolysis, and co-digestion process following the classical Anaerobic Digestion Model No.1 (ADM1) structure is proposed. In the new method, substrate-microorganism relationships are represented using the Contois equation rather than the first order models previously used to represent substrates in the degradation process. This model was validated by assessing the biogas production from the co-digestion of vegetable (V) and manure (M) with variations in the V/M ratio in the feed. The highest biogas and yield levels were obtained when the feed ratio was 50/50 V/M. This finding was reproduced by running simulations of the original and modified ADM1. The original ADM1 explains the low digestibility and utilization of manure for biogas production as a consequence of a slow disintegration or hydrolysis stage, which depends exclusively on the disintegration and hydrolysis constants used. The new model offers a more mechanistic explanation; it assumes unfavorable substrate-microorganism relationships, which cause disintegration to become a limiting factor in the process. In addition, biogas production in the new model is primarily associated with carbohydrate degradation, as well as low concentrations and rapid consumption of intermediary metabolites, which do not favor the proliferation of acetanogenic or methanogenic communities. En este trabajo se propone un nuevo modelo de las etapas de desintegración e hidrólisis y un modelo de co-digestión, siguiendo la estructura del Anerobic Digestion Model No. 1 (ADM1). En el nuevo modelo, las relaciones sustrato-microorganismo se representan mediante la ecuación de Contois en lugar de los modelos de primer orden utilizados anteriormente para representar el proceso de degradación de los sustratos. Este modelo se validó evaluando la producción de biogás a partir de la co-digestión de vegetales (V) y estiércol (M) con variaciones en la relación V/M en la alimentación. Los niveles más altos de biogás y rendimiento se obtuvieron cuando la relación de alimentación fue de 50/50 V/M. Este hallazgo se reprodujo ejecutando simulaciones del ADM1 original y modificado. El ADM1 original explica la baja digestibilidad del estiércol para la producción de biogás como consecuencia de una etapa de desintegración e hidrólisis lenta, que depende exclusivamente de las constantes de desintegración e hidrólisis utilizadas. El nuevo modelo ofrece una explicación más mecanicista; asume relaciones de sustrato-microorganismo desfavorables, lo que hace que la desintegración se convierta en un factor limitante en el proceso.

Waste to energy processes from anaerobic digestion (WtE-AD) from cattle manure (CM) have low CH₄ yields due to CM’s structural composition. The search for alternatives to increase the energy yields of these processes must consider the optimization of operating parameters within a framework of mitigating the environmental footprint. The goal of this paper is to provide a statistical optimization strategy based on experimental designs to improve CH₄ yields and reduce the environmental profile of CM valorization through a WtE-AD process. Biochemical methane potential tests were conducted to determine the energetic and environmental effects that alkaline pretreatments, different AD temperatures, and co-digestion formulations with fruit and vegetable waste (FVW) have on the WtE-AD process from CM. The evaluation was conducted following a life cycle assessment approach through energy balances. The results indicate that the highest CH₄ yield (384.3 mL CH₄ g VS⁻¹) and the lowest environmental impact (−0.06 kg CO₂ eq kWh⁻¹ of electricity production) were achieved with the co-digestion of CM with FVW 1:1, pretreatment with 10 g NaOH 100 g⁻¹ of VS of CM, and a temperature of 45 °C. It was found that the CM pretreatment with NaOH substantially increases the energy profile of the WtE-AD process without compromising the environmental impact since greenhouse gas emissions in chemical production are negligible.

This two-part study assesses the impact of biogas inhibition on large-scale waste-to-energy anaerobic digestion (WtE-AD) plants through techno-economic and life cycle assessment approaches. The first part addresses technical and economic aspects. An anaerobic co-digestion system using vegetable waste (FVW) and meat waste (MW) was operated at laboratory scale in a semi-continuous regime with daily feeding to establish a stable process and induce programmed failures causing methanogenic inhibition, achieved by removing MW from the reactor feed and drastically reducing the protein content. Experimental data, combined with bioprocess scale-up models and cost engineering methods, were then used to evaluate the effect of inhibition periods on the profitability of large-scale WtE-AD processes. In the experimental stage, the stable process achieved a yield of 521.5 ± 21 mL CH₄ g⁻¹ volatile solids (VS) and a biogas productivity of 0.965 ± 0.04 L L⁻¹ d⁻¹ (volume of biogas generated per reactor volume per day), with no failure risk detected, as indicated by the volatile fatty acids/total alkalinity ratio (VFA/TA, mg VFA L⁻¹/mg L⁻¹) and the VFA/productivity ratio (mg VFA L⁻¹/L L⁻¹ d⁻¹), both recognized as effective early warning indicators. However, during the inhibition period, productivity decreased by 64.26 ± 11.81% due to VFA accumulation and gradual TA loss. With the progressive reintroduction of the FVW:MW management and the addition of fresh inoculum to the reaction medium, productivity recovered to 96.7 ± 1.70% of its pre-inhibition level. In WtE-AD plants processing 60 t d⁻¹ of waste, inhibition events can reduce net present value (NPV) by up to 40.2% (from 0.98 M USD to 0.55 M USD) if occurring once per year. Increasing plant capacity (200 t d⁻¹), combined with higher revenues from waste management fees (99.5 USD t⁻¹) and favorable electricity markets allowing higher selling prices (up to 0.23 USD kWh⁻¹), can enhance resilience and offset inhibition impacts without significantly compromising profitability. These findings provide policymakers and industry stakeholders with key insights into the economic drivers influencing the competitiveness and sustainability of WtE-AD systems.

Mexico generated 8.9 million tons of food loss and waste (FLW) in the year 2022, which was primarily managed through linear economy schemes where final disposal sites are predominant, leading to significant contributions to climate change and economic losses. This study, as a continuation of a prior work (Part 1), aims to evaluate the economic and environmental feasibility of implementing waste-to-energy anaerobic digestion (WtE-AD) plants for FLW management across Mexico, identifying the key factors that influence the competitiveness of these systems compared to conventional waste management practices. Using the outcomes of an energy feasibility analysis (Part 1), alongside life cycle assessment (LCA), geographic information systems, and cost engineering, this research analyzes the eco-efficiency and viability of WtE-AD for FLW valorization throughout the Mexican territory. The results indicate that, with a conventional waste management fee of USD 35.4 t⁻¹, only the largest WtE-AD plant in the State of Mexico (treatment capacity of 2536.8 t FLW d⁻¹) achieved a positive net present value (NPV) of USD 70.1 million, while all the other plants remained economically unviable. Conversely, under an optimistic scenario with a fee of USD 139 t⁻¹, plants processing over 50 t FLW d⁻¹ achieved profitability, with the largest plant reaching an NPV of USD 1.15 billion. The environmental assessment showed that larger plants effectively act as carbon sinks, with the largest plant reducing emissions by up to −89.8 kg CO₂ eq t⁻¹ of FLW. These findings emphasize the need for appropriate waste management fees and governmental incentives to ensure the economic viability of WtE-AD plants. This study provides valuable insights for policymakers, highlighting the potential of WtE-AD technologies to contribute to Mexico’s energy transition and the shift toward a circular economy.

Anaerobic digestion under a Waste-to-Energy (WtE-AD) framework represents a sustainable alternative for managing organic waste and generating bioenergy in developing countries. However, most life cycle assessment (LCA) studies implicitly assume stable operation, overlooking the environmental implications of process instability. In practice, large-scale WtE-AD plants are frequently affected by methanogenic inhibition events that reduce methane production and compromise their technical, economic, and environmental performance. This study—Part 2 of a two-paper series—addresses this gap by quantifying, from a life cycle perspective, the environmental consequences of recurrent methanogenic inhibition events in large-scale WtE-AD systems, complementing the techno-economic analysis presented in Part 1. Large-scale WtE-AD plants were modeled using design equations based on treatment capacity (60–200 t d⁻¹), considering scenarios with up to ten inhibition events over a 25-year operational period. The LCA was conducted in accordance with ISO 14040:14044 standards, defining as the functional unit one ton of co-digested fruit and vegetable residues with meat industry wastes, under an attributional approach with system boundary expansion and evaluating midpoint indicators through the ReCiPe 2016 method. Results show that inhibition events increase greenhouse gas emissions by up to 400% (from 28.1 to 138.6 kg CO₂ eq t⁻¹ of waste treated), while plants with capacities above 125 t d⁻¹ exhibit environmental credits (negative emission balances), demonstrating greater environmental resilience. Electricity substitution from the Mexican grid generated savings of up to 0.624 kg CO₂ eq kWh⁻¹, although the magnitude of the benefits strongly depends on the regional electricity mix. This dependency was further explored through comparative electricity mix scenarios representative of different levels of power sector decarbonization, allowing the sensitivity of WtE-AD environmental performance to regional grid characteristics to be assessed. Compared to landfill disposal (1326 kg CO₂ eq t⁻¹), WtE-AD plants significantly reduce impacts across all assessed categories. By explicitly integrating operational instability into an industrial-scale LCA framework, this work highlights the importance of evaluating methanogenic inhibition events from a life cycle perspective, providing key insights for the design of more sustainable and resilient WtE-AD processes within a Latin American context.