Anaerobic treatment is well over 100 years old. Its initial development was for the treatment of domestic wastewaters, it then progressed in application to separate sludge digestion, then to treatment of dilute industrial waste-waters. Several processes have been developed that accomplish efficient treatment of wastewaters at short detention times.
The anaerobic granulation system has been known for its unique ability to convert highly objectionable wastes into useful products. With global concerns over energy shortages and greenhouse gas formation through combustion of fossil fuels, more efforts towards renewable energy supplies is clearly needed. Greater efforts are now needed for broader applications of anaerobic granulation system for ridding the environment of unwanted organic materials by converting them into methane, a renewable energy source. The anaerobic granulation process leading towards efficient methane production from wastewaters clearly fits this need. Research towards even broader application is clearly of importance. Problems that need addressing are process reliability, toxicity causes and effects, odor production and control, and better understanding of refractory organic degradation.
From all the numerous and the latest published research on anaerobic processes, cited in the earlier section, it is arguably the most promising wastewater treatment system that is able to meet the desired stringent criteria for future technology in environmentally sustainable development.
Anaerobic granulation process would be the one that is able to minimize environmental harm while increasing industrial productivity and improving quality of life.
At the moment, the most popular treatment process is the UASB reactor. However, with the recent development of EGSB and "Staged Multi-Phase Anaerobic" (SMPA) reactor systems, this may lead to a very promising new generations of anaerobic treatment system (Lettinga et al., 1997). These concepts behind the EGSB will 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 (sulfate 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.
It becomes clear that anaerobic treatment is an established technology for a wide variety of industrial applications. The technology is accepted in the industrialized western world as well as in less developed countries. The granular sludge-based UASB and EGSB processes gradually take a large portion of these applications. Although UASB still is the predominant technology in use, at present EGSB type processes are gaining more popularity driven by economics. The data evidence that the design load for EGSB systems is approximately double that of the UASB process, which results in a competitive advantage over lower loaded systems. It should however be noted that the data presented represents approximately 50-60% of total anaerobic systems installed and contribution of EGSB and IC systems may be relatively high in the current database relative to the total number of systems installed. It is also foreseen that the higher loaded EGSB type systems are gradually replacing at least some of the UASB applications (Frankin, 2001).
In the fields of psychrophilic and thermophilic anaerobic treatment, specific reactor development may contribute to further enhance volumetric conversion capacities. Due to reduced water usage, both COD and salt concentrations tend to increase for industrial effluents. As a consequence, there is a need for the development of anaerobic reactors retaining floc-culant or granular biomass. The membrane bioreactors (MBR) offer a solution for certain niches in wastewater treatment (Mulder et al., 2001). However, poor oxygen transfer economy and biomass fouling are major problems of MBR to be overcome. Membrane bioreactors coupled with granular-based anaerobic processes are worth exploring into.
Environmental protection- and resource conservation-concepts focus on pollution prevention and on a minimum of consumptive use of energy, chemicals, and water in pollution abatement and a maximum of re-use of treated wastewater, by-products, and residues produced in the treatment of wastewater. Consequently, by implementing these concepts, wastewaters like sewage and industrial effluents become an important source of water, fertilizers, soil conditioners, and frequently energy instead of a social threat. In addition, a bridge is made between environmental protection and agriculture practice, stimulating urban agriculture in the neighborhood of large cities. Anaerobic granulation process is considered as the core technology for mineralizing organic compounds in highly polluted wastewater streams.
Nowadays, processes based on anaerobic treatment appear to be an excellent option as the core of an integrated process for waste and waste-water treatment (Lema and Omil, 2001). Environmental regulations in the European Union, based on the concept of integrated prevention and control of pollution, are oriented towards the sustainability of the production processes, and this leads to better recovery of resources from raw materials, energy saving, etc. In the last few decades, granular sludge-based anaerobic processes have been receiving widespread acceptance and has been successfully used to treat a variety of industrial wastewaters. The processes offer high degree of organics removal, low sludge production, and low energy consumption along with energy production in the form of biogas. It may not be an unreasonable expectation that, in the future, the treatment technologies will experience a global shift towards usage of highly efficient granular sludge-based anaerobic processes for treatment of wastewaters.
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