Anaerobic Digestion of Lignocellulosic Waste Materials

Abstract

Nowadays, the climate mitigation policies of EU promote the energy production based on renewable resources. Anaerobic digestion (AD) constitutes a biochemical process that can convert lignocellulosic materials into biogas, used for chemical products isolation or energy production, in the form of electricity, heat or fuels. Such practices are accompanied by several economic, environmental and climatic benefits. The method of AD is an effective method of utilization of several different low-value and negative-cost highly available materials of residual character, such as the lignocellulosic wastes coming from forest, agricultural or marine biomass utilization processes, in order to convert them into directly usable energy. Lignin depolymerization remains a great challenge for the establishment of a full scale process for AD of lignin waste. This review analyzes the method of anaerobic digestion (biomethanation), summarizes the technology and standards involved, the progress achieved so far on the depolymerization/pre-treatment methods of lignocellulosic bio-wastes and the respective residual byproducts coming from industrial processes, aiming to their conversion into energy and the current attempts concerning the utilization of the produced biogas. Substrates’ mechanical, physical, thermal, chemical, and biological pretreatments or a combination of those before biogas production enhance the hydrolysis stage efficiency and, therefore, biogas generation. AD systems are immensely expanding globally, especially in Europe, meeting the high demands of humans for clean energy.

Current Status and Review of Waste-to-Biogas Conversion for Selected European Countries and Worldwide

“…AD processes take about three to six weeks, depending on the ease and degree of conversion of the input material into biogas and the technology used. Pretreatment, co-digestion, bioaugmentation, biohythane, temperature, organic loading rate and reactor design are some of the ways to increase biogas yield [89]. It has also been shown that pretreatment methods, such as substrate preparation, mechanical solubilisation in combination with low-temperature heat treatment, affect biogas yield in AD processes with wastewater sludge because of a higher ability to dissolve sludge and consequent acceleration of anaerobic digestion [90].…”

“…With appropriate upgrades, biogas produced by the AD process can be used in many applications including systems with gas turbines and generators, internal combustion engines, production of heat for commercial and residential use and as a transport fuel at a very competitive price [89]. As mentioned previously, the two main components of biogas are methane CH 4 and carbon dioxide CO 2 , which are accompanied by other impurities such as nitrogen N 2 , oxygen O 2 , hydrogen H 2 , hydrogen sulphide H 2 S and ammonia NH 3 .…”

“…At the time of writing, the re are currently 302 AD biowaste plants in operation with Germany being the leader in terms of both the number of biogas plants and the amount of biogas produced with 92 AD biowaste plants in operation, followed by Italy, France and Austria. On a global scale, China has the largest number of plants for the production of biogas from waste worldwide [89]. Germany also has 1900 agricultural digesters out of the 2429 currently existing in Europe [89].…”

“…On a global scale, China has the largest number of plants for the production of biogas from waste worldwide [89]. Germany also has 1900 agricultural digesters out of the 2429 currently existing in Europe [89]. However, only around 50% of the mobilisable technical biomass potential of animal manure is used for energy purposes in Germany [102].…”

“…However, only around 50% of the mobilisable technical biomass potential of animal manure is used for energy purposes in Germany [102]. Overall, the technical potential of biogas in the EU is estimated to be between 151-246 billion Nm 3 of biomethane from AD [89].…”