Principles and potential of the anaerobic digestion of waste-activated sludge

Biogas from anaerobic digestion and landfills consists primarily of CH 4 and CO 2 . Trace components that are often present in biogas are water vapor, hydrogen sulfide, siloxanes, hydrocarbons, ammonia, oxygen, carbon monoxide and nitrogen. In order to transfer biogas into biomethane, two major steps are performed: (1) a cleaning process to remove the trace components and (2) an upgrading process to adjust the calorific value. Upgrading is generally performed in order to meet the standards for use as vehicle fuel or for injection in the natural gas grid. Different methods for biogas cleaning and upgrading are used. They differ in functioning, the necessary quality conditions of the incoming gas, the efficiency and their operational bottlenecks. Condensation methods (demisters, cyclone separators or moisture traps) and drying methods (adsorption or absorption) are used to remove water in combination with foam and dust. A number of techniques have been developed to remove H 2 S from biogas. Air dosing to the biogas and addition of iron chloride into the digester tank are two procedures that remove H 2 S during digestion. Techniques such as adsorption on iron oxide pellets and absorption in liquids remove H 2 S after digestion. Subsequently, trace components like siloxanes, hydrocarbons, ammonia, oxygen, carbon monoxide and nitrogen can require extra removal steps, if not sufficiently removed by other treatment steps. Finally, CH 4 must be separated from CO 2 using pressure swing adsorption, membrane separation, physical or chemical CO 2 -absorption.

Techniques for transformation of biogas to biomethane

Pretreatment of lignocellulosic biomass for enhanced biogas production.

Pretreatment methods to improve sludge anaerobic degradability: a review.

The uncontrolled discharge of large amounts of food waste (FW) causes severe environmental pollution in many countries. Within different possible treatment routes, anaerobic digestion (AD) of FW into biogas, is a proven and effective solution for FW treatment and valorization. The present paper reviews the characteristics of FW, the principles of AD, the process parameters, and two approaches (pretreatment and co-digestion) for enhancing AD of food waste. Among the successive digestion reactions, hydrolysis is considered to be the rate-limiting step. To enhance the performance of AD, several physical, thermo-chemical, biological or combined pretreatments are reviewed. Moreover, a promising way for improving the performance of AD is the co-digestion of FW with other organic substrates, as confirmed by numerous studies, where a higher buffer capacity and an optimum nutrient balance enhance the biogas/methane yields of the co-digestion system.

Reviewing the anaerobic digestion of food waste for biogas production

It is clear that renewable resources will play a crucial role in limiting the CO2 emissions. Energy from biomass and waste is regarded as one of the most dominant future renewable energy sources, since it can provide a continuous power generation. In this regard, the application of anaerobic digestion is emerging spectacularly. This manuscript lists and discusses the main beneficial properties of anaerobic digestion. Different types of biomass and waste are suitable for anaerobic digestion: the organic fraction of municipal solid waste, waste oils and animal fat, energy crops and agricultural waste, manure and sewage sludge. The potential, opportunities and challenges of these biomasses are discussed. Typical biogas yield and points of attention are included. The manuscript concludes with an overview and discussion of the major research trends in anaerobic digestion, including the analysis of microbial community development, the extension of anaerobic digestion models, the development of pre-treatment techniques and upgrading of the biogas produced.

Lise Appels

Papers

Principles and potential of the anaerobic digestion of waste-activated sludge

Anaerobic digestion in global bio-energy production: Potential and research challenges

Challenges and opportunities in improving the production of bio-ethanol

Influence of low temperature thermal pre-treatment on sludge solubilisation, heavy metal release and anaerobic digestion.

Energy use of biogas hampered by the presence of siloxanes.