Anaerobic Digestion for Sustainable Development

Anaerobic digestion processes for the treatment of wastewaters and sludges are well over 100 years old. The anaerobic process is a natural gasification process, producing very useful end-products. It has taken a long time to prove that these processes are useful tools in sustainable development. A breakthrough was the development of the Upflow Anaerobic Sludge Bed reactor by Professor Gatze Lettinga. This showed that the anaerobic process could be operated as a highly effective and high-rate wastewater treatment process, opening the way to its implementation under practical conditions. It has, so far, been a struggle to prove the feasibility of anaerobic treatment, despite the obvious advantages in energy consumption, sludge production, and required land area; its drawbacks, i.e. required effluent polishing, odours, sensitivity to toxic compounds, made potential users reluctant to choose anaerobic instead of the conventional aerobic systems. However, as shown by the contributions in this issue, intensive research has overcome most of these drawbacks. To celebrate the career of Professor Lettinga, leading experts on anaerobic digestion processes were invited to highlight the state-of-the-art and future developments in their specific fields of interest. Seminar topics included microbiology, treatment of industrial wastewaters, xenobiotics and extreme environments, the biological S-cycle, treatment of domestic wastewater and the history of anaerobic digestion. The selected 20 papers in these proceedings represent the state of the art of anaerobic digestion, highlighting its impacts and potentials. They also recognised the stimulating role of Professor Gatze Lettinga in this development and agree with him that anaerobic digestion's full potential is still unexploited.