Preface

Anaerobic digestion (AD) of biomass to methane and carbon dioxide is promoted by the activity and interactions of many different physiological groups of microorganisms that form specialized microbial communities. These microorganisms are responsible for four steps of AD: hydrolysis of polymeric organic matter to monomers, acidogenesis (acidic fermentations), acetogenesis (degradation of acidic fermentation products to dioxide, hydrogen, and acetic acid, which are substrates for methanogenesis), and finally methanogenesis, that is, the formation of methane. AD is a key process in the global carbon cycle and energy flow in ecosystems. It commonly occurs in natural anoxic ecosystems such as water sediments, wetlands, marshlands, and the digestive tracts of animals.

Biomethane and carbon dioxide are also generated in the environment as the result of human activity at landfill sites, anaerobic wastewater treatment plants, and biogas plants. Thus AD is an excellent method for utilization of wastes and production of green energy in local facilities located at small factories, workplaces, and in rural areas and housing complexes.

This book presents examples of AD solutions in specific regions and sites. Local installations are particularly important for producing dispersed energy and protecting the environment via the utilization of different types of waste such as textile processing wastewater, wastes of the pulp and paper industry, waste streams from grain processing, and domestic sewage. Through AD, energy and heat are supplied to nearby consumers, which has great economic significance. Furthermore, biogasproducing local installations contribute to increasing the share of renewable energy in overall energy production and to reducing greenhouse effects on a global scale.

> **Anna Sikora** Laboratory of White Biotechnology, Institute of Biochemistry and Biophysics, Polish Academy of Sciences, Warsaw, Poland

### Section 1
