Anaerobic Digestion for Producing Renewable Energy—The Evolution of This Technology in a New Uncertain Scenario

Abstract

Anaerobic digestion is a well-known technology with wide application in the treatment of high-strength organic wastes. The economic feasibility of this type of installation is usually attained thanks to the availability of fiscal incentives. In this review, an analysis of the different factors associated with this biological treatment and a description of alternatives available in literature for increasing performance of the process were provided. The possible integration of this process into a biorefinery as a way for producing energy and chemical products from the conversion of wastes and biomass also analyzed. The future outlook of anaerobic digestion will be closely linked to circular economy principles. Therefore, this technology should be properly integrated into any production system where energy can be recovered from organics. Digestion can play a major role in any transformation process where by-products need further stabilization or it can be the central core of any waste treatment process, modifying the current scheme by a concatenation of several activities with the aim of increasing the efficiency of the conversion. Thus, current plants dedicated to the treatment of wastewaters, animal manures, or food wastes can become specialized centers for producing bio-energy and green chemicals. However, high installation costs, feedstock dispersion and market distortions were recognized as the main parameters negatively affecting these alternatives.

Biogas Production from Organic Wastes: Integrating Concepts of Circular Economy

“…Thus, reducing compression stages by supplying biogas directly to large consumers will avoid additional compression costs. If biogas is to be considered a substitute for natural gas or to be used as a supplementary fuel along with natural gas, then upgrading is imperative, but this also causes an increment in costs that when summed up to the already high installation costs of this type of facilities makes this mature technology just a promising process that encounters several difficulties in attaining economic feasibility [7]. Great efforts should be placed on developing high rate reactors with an outstanding capacity to operate under solid-phase conditions without experiencing detriments in biogas yields.…”

“…The presence of improper materials in organic wastes and in some cases, high concentrations of heavy metals, translates into a plant design of high complexity needing special pre-treatment units for preparing a homogenous feeding slurry. We should also add the intrinsic difficulty of separating inert materials and avoiding the presence of toxic elements in digestates that prevents any agronomic use [7].…”

High-Solid Anaerobic Digestion: Reviewing Strategies for Increasing Reactor Performance

“…However, trying to set a specific C/N ratio for industrial digesters in an attempt to extrapolate results is not always easy. Large-scale digestion plants have to deal with the resources available in their surroundings all year round [18]. Therefore, these findings help predict 1.…”

“…However, trying to set a specific C/N ratio for industrial digesters in an attempt to extrapolate results is not always easy. Large-scale digestion plants have to deal with the resources available in their surroundings all year round [18]. Therefore, these findings help predict the effect on plant performance based on the carbon proportion of the feed, although industrial plants still have to operate under optimum conditions based on the resources available to them.…”

“…Several pre-treatment methods have been evaluated with success under laboratory conditions, achieving a significant enhancement in the solubilization of organics. However, the capacity of thermal pre-treatments to recover heat makes these superior when considering their performance in terms of the energy balance [18].…”