About this Research Topic
Anaerobic digestion (AD) has existed as a technology almost 160 years and is utilized worldwide. The process engineering and biotechnology of the AD, as well as the microbiology of methane digestion, have been examined intensively in the last decade. It has been identified that converting organic mantillas to methane involves three physiological groups of bacteria; however, more investigations are in progress by the numerous researchers in this area. The hydrolyzing and fermenting bacteria convert complex organic materials to alcohols, carbon dioxide, fatty acids, ammonia and hydrogen. While the hydrogen producing acetogenic bacteria convert the products of the above into hydrogen, carbon dioxide and acetic acid. The methane forming bacteria convert hydrogen and carbon dioxide or acetate to methane. The AD process yields valuable energy and byproducts, and this process proceeds as a chain process in the presence of complex microbial activities utilizing complex substrates.
The solid concentration in the wastewater treatment system plays the important roles especially when the solid concentration is very low (1 to 2%). Furthermore, several sustainable technologies are available to degrade particulate organics at high rate in the solid-state fermenters. In systems operating in the thermophilic range (50 - 60°C), not only high volumetric conversion rates are obtained, but also a stable and hygienic end-product, humus. Significant progress has been made on the direct anaerobic treatment of wastewaters at low temperatures (8 - 25°C). The reactors with granular sludge beds and with polyurethane carrier matrices have been shown to hold potential for direct treatment of domestic wastewaters. However, the anaerobic treatment process of wastewater is not entirely known and further investigation is in progress.
Since anaerobic fermentation results in a lower cellular yield, less sludge is generated, and hence lower sludge handling costs would be possible. Existing limitations are driving new research and insights into the development of other anaerobic reactor technologies which may lead to promising new generations of anaerobic treatment systems, such as expanded granular sludge bed (EGSB), membrane bioreactor (AnMBR), fluidized-bed membrane reactor (MFMBR), baffled reactors (ABR), migrating blanket reactors (AMBR), staged multi-phase (MPSA) reactors and microbial fuel cell (MFC) reactor systems.
These AD reactor designs, among others, may provide a higher efficiency at higher loading rates, are applicable for extreme environmental conditions (e.g. low and high temperatures) and to inhibitory compounds. Moreover, by integrating the anaerobic process with other biological methods (sulphate reduction. micro-aerophilic organisms) and with physical-chemical methods, a complete treatment of the wastewater can be accomplished at very low costs, while at the same time valuable components can be recovered for reuse.
Taking into account all the relevant and emerging issues as mentioned above, this call for the special topic will help to update the wastewater treatment communities about the current state-of-art knowledge and observations on the anaerobic process of low strength wastewater treatment (WWT). This call will also provide an invaluable opportunity to better understand the development and implementation of suitable treatment approaches for low-strength WWT needed to achieve greater sustainability and the development of self-sufficient wastewater treatment.
Keywords: anaerobic digestion process, fermenting bacteria, fluidized bed, low strength wastewater treatment, methane producing bacteria, sulphate reducing bacteria, upflow anaerobic sludge blanket process
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