Fundamentals and applications of anaerobic digestion for sustainable treatment of food industry wastewater

Abstract

Developments in production technology have frequently resulted in the concentrated local accumulation of highly organic-laden wastewaters, a factor that therefore must be taken seriously into account with respect to the disposal technology. With conventional aerobic wastewater treatment (the activated-sludge process) the greater the organic load, the more problematic the process, since the required level of oxygen transfer rapidly approaches limits that are both technical and economically unattainable in practice. The anaerobic treatment of industrial wastewater has become increasingly important in recent years as a result of environmental protection legislation, increased energy costs, and problems with the disposal of excess sludge formed in aerobic treatment processes. Efforts are now being made to remove organic contaminants insofar as possible without external resources of energy, taking advantage of the biogas produced, where the desired level of purification is ultimately achieved with the aid of a subsequent aerobic biological clarification step. The fundamental advantages of anaerobic wastewater treatment are: 1. Energy-intensive oxygen transfer is avoided. 2. The energy content of the resulting biogas can be put to further use. 3. Very little excess sludge is formed, while at the same time up to 95% of the organic contamination is converted into a combustible gas, constituting a case of true disposal. 4. Heavy metals are not subjected to oxidative mobilization, but rather to reductive precipitation (as heavy-metal sulfides), facilitating their orderly disposal rather than wider dispersal. 5. Aerosol formation accompanying oxygen transfer is avoided. 6. Space-time yields (bioreactor performances) reach a level fundamentally unattainable in the activated-sludge process because of the limitations imposed by oxygen transfer. 7. Anaerobic biomass can be preserved without feed for long periods of time without any significant deterioration of its properties. © 2007 Springer Science+Business Media, LLC.