Page 76 - Energy from Toxic Organic Waste for Heat and Power Generation

62 Energy from Toxic Organic Waste for Heat and Power Generation

An improved system has, therefore, been developed whereby the sulfate is
completely removed as elemental sulfur and the treatment of the tannery
waste water is carried out in conventional UASB reactor, thereby generat-
ing energy. This system ensures removal of COD and sulfate TDS by 60%
and 90%, respectively, whereby the sulfur can be recovered [49].
UASB technology, normally referred to as UASB reactor, is a form of
anaerobic digester that is used for wastewater treatment. The UASB re-
actor is a methanogenic (methane-producing) digester that evolved from
the anaerobic clarigester. A similar but variant technology to UASB is the
expanded granular sludge bed digester. Fig. 5.1 depicts the schematic of an
UASB reactor. As shown, wastewater enters the reactor from the bottom
and flows upward [50].
UASB uses an anaerobic process while forming a blanket of granular
sludge which suspends in the tank. Wastewater flows upward through the
blanket and is processed (degraded) by the anaerobic microorganisms. The
upward flow combined with the settling action of gravity suspends the blan-
ket with the aid of flocculants. The blanket begins to reach maturity at around
3 months. Small sludge granules begin to form whose surface area is covered
in aggregations of bacteria. In the absence of any support matrix, the flow
conditions create a selective environment in which only those microorgan-
isms capable of attaching to each other survive and proliferate. Eventually, the
aggregates form into dense compact biofilms referred to as “granules” [51].
Biogas with a high concentration of methane is produced as a by-
product, and this may be captured and used as an energy source, to generate

Biogas

Outlet

Gas
bubbles Sludge granule

Inlet
Fig. 5.1 Schematic of an upflow anaerobic sludge blanket reactor (UASB).