A Review of the Role of Critical Parameters in the Design and Operation of Biogas Production Plants

Abstract

Many operating parameters, individually or together, may influence the performance of anaerobic digestion towards biogas or digestate yield and quality maximization. The most preferred method of optimizing an anaerobic digestion plant often relies on how carefully the crucial parameters, such as pH, temperature, organic loading rate, hydraulic retention time, and pressure, are chosen. There is a large amount of literature available on optimization of anaerobic digestion; however, given the continued development and implementation of innovative technologies, together with the introduction of increasingly complex systems, it is necessary to update present knowledge on process parameters and their role on operational ranges and flexibilities in real-life anaerobic digestion system. Accordingly, the present review discusses the importance of the selection of operational parameters in existing technologies and their impact on biogas yield. Notably, the four broad areas of feedstock utilization (substrate, inoculum, codigestion and pretreatment), process condition (pH, temperature, pressure, and reactor design), reactor control (HRT and OLR) and inhibition (Ammonia and VFAs) are covered in this review. In addition, particular emphasis is placed on the most recent innovations that have been or may be implemented in current or future biogas plants.

Operational Parameters of Biogas Plants: A Review and Evaluation Study

“…Anaerobic digestion is a biological process, in which the microorganisms degrade the complex organic matter to simpler components under anaerobic conditions to produce biogas and fertilizer [6,8]. This process has many environmental benefits, such as green energy production, organic waste treatment, environmental protection, and greenhouse gas emissions reduction [2,[9][10][11][12][13]. The biodegradation of the complex organic matter undergoes four main steps.…”

Lessons Learned from an Experimental Campaign on Promoting Energy Content of Renewable Biogas by Injecting H2 during Anaerobic Digestion

“…In contrast, the VFA concentration increased (~820 mg/L; Figure 3), which however was less likely to contribute to any process imbalance [7]. Despite the increased H 2 loading, the decreased biogas yield at this stage maybe attributed to overdosed S:I, while the methane content might be correlated with weaker methanogenesis spontaneity, either caused by inefficient H 2 mass transfer or by thermodynamic instability [33].…”

“…While the biogas yield, methane content, and pH after H 2 addition during "Batch 2" remained almost constant, surprisingly, total VFA formation almost doubled near to the H 2 feed during "Batch 3" (Table 3). This perhaps was due to the slight substrate overloading, as S:I input kept increasing (Table 1) [7,31], which ultimately resulted in imbalance between acedogenesis and methanogenesis and/or acetogenesis and methanogenesis. However, since the level of developed VFA was still below 1 g/L and the pH remained stable at around 7.2, the increased VFA neither compromised the reactor stability nor was it directly correlated to the elevated level of H 2 feed.…”

“…Normally, less methane is produced via this route compared to acetoclastic methanogenesis (i.e., methane generation from acetic acid by acetoclasts) [5]. However, the syntrophy between methanogenesis archaea and fermentative bacteria (i.e., microbes present in the pre-methanogenesis steps), responsible for the degradation of various acids (e.g., proprionate, butarate), only becomes thermodynamically feasible if hydrogenotrophes remove H 2 quickly, which in turn depends on H 2 partial pressure [6,7]. With the objective of promoting hydrogenotrophic methanogenesis, direct injection of external hydrogen can interrupt optimum H 2 partial pressure [8], influencing syntrophy and consequently reducing pH level outside the microbes' operating limit [5], eventually causing formation of flocs, granules, and/or biofilms, or in the worst case process failure [9].…”

Development of an efficient and sustainable energy storage system by hybridization of compressed air and biogas technologies (BIO-CAES)

“…Since the complete mix reactors are the digesters more prevalent, given that they can be fed with wide range of organic substrates (urban solids, manures, green wastes and others), this technology was chosen in this proposal. Reactor consists in a cylinder of 22 m of diameter and 11 m of height with a pneumatic cover shaped like spherical cap with a partial height of 4.1 m. A complete description of this technology has been previously reported [15,62,59].…”