Contents lists available at ScienceDirect Applied Energy journal homepage: www.elsevier.com/locate/apenergy Effect of co-digestion of milk-whey and potato stem on heat and power generation using biogas as an energy vector: Techno-economic assessment Jimmy Anderson Martínez-Ruano a,b , Daissy Lorena Restrepo-Serna a , Estefanny Carmona-Garcia a , Jhonny Alejandro Poveda Giraldo a , Germán Aroca b , Carlos Ariel Cardona a, ⁎ a Universidad Nacional de Colombia sede Manizales, Instituto de Biotecnología y Agroindustria, Departamento de Ingeniería Química, Carrera 27 # 64-60, Manizales, Colombia b Pontificia Universidad Católica de Valparaíso, Escuela de Ingeniería Bioquímica, Av. Brasil 2085, Valparaíso, Chile HIGHLIGHTS • Assessment of co-digestion of milk whey and potato stem was performed for the first time. • Raw material cost was the main economic parameter to define the codigestion viability. • Sensitivity analyses were performed to assess the influence of raw material cost. • Heat and electricity generation through co-digestion was simulated with Aspen Plus. • Digestate valorization increases the viability of heat and electricity generation. ARTICLE INFO Keywords: Co-digestion Potato stem Milk whey Heat and electricity Economic assessment Biofertilizer ABSTRACT Energy conversion strategies based on lignocellulosic and industrial waste streams is considered a challenge in many countries producing huge quantities of biomass. The production of biogas as an energy vector has been gaining attention in the industry sector due to the energy policies for wastes managements or the feasibility of using the biogas for electricity and steam generation. An interesting feedstock alternative for the biogas pro- duction is milk whey, one of the main residues of the dairy industry. Additionally the potato stem generated in the harvest stage can be an attractive raw material for biogas production. Co-digestion is the combination of biodegradable raw materials to improve the balance of nutrients in anaerobic digestion. In this context, the characteristics of milk whey and potato stem are not enough to consider it as a good single substrate. However, the synergetic use of these two residues can represent an improvement in biogas production. The biogas pro- duction was calculated in Aspen Plus software using stoichiometric and kinetic models based on the experi- mental characterization of both materials. Through seven different scenarios: potato stem digestion, milk whey digestion and five co-digestion relations of both materials. Heat and electricity generation using biogas was analyzed. Then the generation of heat and electricity was simulated, where the economic profit was evaluated in terms of the production cost, capital cost, revenues and net present value. In terms of biogas production, the scenarios that involved high organic load were the best. For the economic assessment the raw material cost had the most influence over the total processing cost (80% approximately). However, even if energy is produced it is necessary to include the valorization of the digestate as biofertilizer in order that the different scenarios present economic viability. 1. Introduction The valorization of residues through different transformation pro- cesses allows obtaining chemical and energy products. Last years, the preference has been for energy production by thermochemical or biochemical ways [1]. Additionally first and third generation raw ma- terials are also a subject of intensive research for these purposes [2]. All this tendency to establish biomass as a future substrate for energy production resulted in the implementation of several projects over the world focused on reducing fossil fuels dependence, creating the https://doi.org/10.1016/j.apenergy.2019.03.005 Received 28 October 2018; Received in revised form 15 February 2019; Accepted 3 March 2019 ⁎ Corresponding author. E-mail address: ccardonaal@unal.edu.co (C.A. Cardona). Applied Energy 241 (2019) 504–518 Available online 13 March 2019 0306-2619/ © 2019 Elsevier Ltd. All rights reserved. T