CHAPTER II
REVIEW OF LITERATURE
2.1 GENERAL
The steady increase in slaughterhouse wastewater quantities is substantial, which requires many facilities to provide a high degree of treatment methods. Among different treatment methods, anaerobic treatment is considered as one of the best treatment option for slaughterhouse wastewater. In this section microbiology and factors affecting anaerobic digestion, different types of anaerobic treatment systems, slaughterhouse process and its pollution potential, slaughterhouse wastewater treatment methods, sludge granulation reported in literatures are discussed.
2.2 CHRONOLOGICAL DEVELOPMENT IN UASB REACTOR
The problem associated with packed bed anaerobic filters and fluidized or expanded bed
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In 1890, Scott Moncrieff constructed a crude anaerobic filter that was capable of developing a bacterial film on stones. The basic system treated small quantities of wastewater and reduced sludge volume. By the 1930s, German cities using anaerobic digestion employed compressors to store the biogas as motor fuel. Aerobic technology later took hold and interest in anaerobic technology was getting lost. Modern highrate anaerobic waste treatment systems began with the development of the anaerobic filter at Stanford in 1964. This technology became popular with the development of the UASB system in the late 1970s. Since then a variety of high-rate systems have been employed successfully in many diverse applications (Lettinga, 2010). Each system has its own advantages and disadvantages and is typically suitable for specific wastewater compositions. Lettinga (2010), Stuckey (2010), and Khanal (2008) summarized some major milestones that led to the invention of modern high-rate anaerobic bioreactors (Table …show more content…
Recognized the importance of bacterial immobilization as flocs or biofilms Khanal, 2008
1978
Anaerobic Membrane Bioreactor External cross-flow membrane coupled with anaerobic reactor. First commercial-scale AnMBR developed in 1980s Stuckey, 2010
1979 Upflow Anaerobic Sludge Blanket (UASB) Improved upflow system developed by Gatze Lettinga at the Wageningen University Lettinga, 2010
1980 Expanded-Bed Reactor Developed fixed-film expanded-bed reactor Khanal 2008
1981 Anaerobic Baffled Reactor Retained biomass within baffles Khanal 2008
1992 Anaerobic Sequencing Batch
Reactor Developed first ASBR Khanal 2008
Although UASB reactors have been built and operated since 1971, a specially desirable variant of the anaerobic sludge, (granular sludge) was observed after 1976 inside a pilot plant treating sugar beet factory wastewater. The superior settling characteristics of these sludge granules allowed higher sludge concentrations to be retained and consequently permitted the system to handle much higher organic loading rates. Granular sludge development has now been observed in UASB reactors treating various types of wastewater (de Zeeuw,