Environmental Engineering Reference
In-Depth Information
wineries, breweries, distilleries, slaughterhouses, potato processing, and ice cream
factories. The organic compounds in these wastewaters can be readily degraded and
converted to methane biogas, but the initial major objective of anaerobic treatment
of such wastewaters was to degrade and reduce the organic pollutants in the wastew-
aters to satisfy governmental discharge requirements. With the push for bioenergy,
the focus of anaerobic treatment of high-strength organic wastewaters has been
shifted to methane biogas production. High-rate AD (HRT <24 h) has been com-
monly used to both reduce the organic strength of the wastewaters and recover the
energy as methane biogas. UASB reactors [32] are among the most popular digesters
used by many industries. A new variant of UASB reactors is the expanded gran-
ular sludge bed (EGSB) reactors. The advantages of EGSB over UASB, such as
improved mass transfer and digestion rate, enhanced ability to handle high-strength
influents, and high hydraulic loading rates (HRT <2 h), have been well recognized
[82]. Therefore, during the last decade the number of EGSB reactors built exceeds
that of new UASB reactors [32].
In addition to UASB and EGSB reactors, the following digesters have also been
successfully used in the AD of these high-strength wastewater streams: CSTR (sin-
gle staged, e.g. [74], or two-staged e.g. [72],), anaerobic contact filter reactor [83],
anaerobic filter reactor [1], down-flow fluidized bed reactor [34], internal circulation
(IC) reactors [29], and anaerobic hybrid reactors [14]. The sand-bed filter reactor
manufactured by NewBio E Systems, Inc, [91] is another promising AD technology
for such wastewater (unpublished data). Compared to the digesters used to digest
feedstocks with high SS, most of these reactors have much higher loading rates.
Thus, they have smaller footprints, but they need to be operated by well-trained
digester operators. Detailed descriptions of each of these reactors and vendors is
beyond the scope of this chapter, but interested readers should consult other recent
topics [79, 91] or reviews [10, 77]. Anaerobic treatment or digestion of specific
high-strength wastewaters have also been extensively reviewed (e.g., see [56, 57,
66] for distillery wastewaters; and [18] for meat- and potato-processing and dairy
wastewaters).
It should be noted that performance data from an existing AD digester can only
be regarded as broadly indicative of how a similar AD technology may perform
elsewhere, especially with respect to stability, efficiency of organic removal, biogas
yield and quality. Only through studies using laboratory- and pilot-scale AD reactors
on the feedstock of interest can the most suitable AD technology be identified for
that feedstock.
4 Drivers and Barriers for Commercial Implementation
of Anaerobic Digestion to Convert Biomass Wastes
to Renewable Energy
The commercial installation of AD technologies is facilitated or obstructed by multi-
ple interactive factors, respectively termed drivers or barriers. Drivers are factors that
stimulate, enable, or facilitate implementation of a technology or project, whereas
barriers are the factors that function in the opposite direction. Both drivers and
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