Modification of UASB reactor by using CFD simulations
for enhanced treatment of municipal sewage
Suprotim Das, Supriya Sarkar and Sanjeev Chaudhari
ABSTRACT
Up-flow anaerobic sludge blanket (UASB) has been in use since last few decades for the treatment of
organic wastewaters. However, the performance of UASB reactor is quite low for treatment of low
strength wastewaters (LSWs) due to less biogas production leading to poor mixing. In the present
research work, a modification was done in the design of UASB to improve mixing of reactor liquid
which is important to enhance the reactor performance. The modified UASB (MUASB) reactor was
designed by providing a slanted baffle along the height of the reactor having an angle of 5.7
with the
vertical wall. A two-dimensional computational fluid dynamics (CFD) simulation of three phase gas-
liquid-solid flow in MUASB reactor was performed and compared with conventional UASB reactor.
The CFD study indicated better mixing in terms of vorticity magnitude in MUASB reactor as compared
to conventional UASB, which was reflected in the reactor performance. The performance of MUASB
was compared with conventional UASB reactor for the onsite treatment of domestic sewage as LSW.
Around 16% higher total chemical oxygen demand removal efficiency was observed in MUASB
reactor as compared to conventional UASB during this study. Therefore, this MUASB model
demonstrates a qualitative relationship between mixing and performance during the treatment of
LSW. From the study, it seems that MUASB holds promise for field applications.
Suprotim Das (corresponding author)
Supriya Sarkar
Research & Development, Tata Steel Limited,
Jamshedpur 831001,
India
E-mail: suprotimdas@gmail.com
Sanjeev Chaudhari
Centre for Environmental Science and Engineering
(CESE),
Indian Institute of Technology Bombay,
Powai, Mumbai 400076,
India
Key words | anaerobic reactor, CFD study, low strength wastewaters, mixing, UASB
INTRODUCTION
Anaerobic treatment of wastewater is a cost-effective tech-
nology compared to aerobic treatment process. This
process has significant advantages like low energy consump-
tion, low sludge production, biogas production in form of
methane (CH
4
) and formation of stabilized sludge (Cherni-
charo & Nascimento ; Nykova et al. ). In an
anaerobic process, complex organic matter is converted
into a mixture of biogas (CH
4
and CO
2
) in number of
steps. All reactions of anaerobic process take place in a
single reactor in anaerobic digester where sludge retention
time (SRT) is almost same as hydraulic retention time
(HRT). In the last decades, various high-rate anaerobic sys-
tems were developed which allows maintaining higher
SRT during the operation with lower HRT. Among various
high-rate reactors, up-flow anaerobic sludge blanket
(UASB) reactor is the most commonly used. The ability to
retain high concentration of biomass by achieving granula-
tion is the major advantage of UASB reactor over other
high-rate anaerobic reactors (Lettinga et al. ). It has
been reported that UASB reactor has high efficiency for
the treatment of high strength wastewaters (HSWs) but
UASB reactor has limitations for the treatment of low
strength wastewaters (LSWs) like municipal sewage (Sato
et al. ; Tare & Nema ). Researchers have described
LSWs as those which contain chemical oxygen demand
(COD) concentration below 500 mg/L. Wastewaters pro-
duced domestically (domestic sewage) are also usually of
low strength (Ganesh et al. ). Several studies were con-
ducted for the treatment of industrial LSW as well as
domestic sewage by using UASB reactor. It was observed
that the efficiency of the UASB reactor was in the range of
55–86% during the treatment of industrial low and
medium strength wastewaters when the influent concen-
tration was in the range of 300 mg/L to 1,850 mg/L (Sayed
et al. ; Kato & Field ; Monroy et al. ; Ahn
et al. ; Buzzini et al. ). Wide variation in the effi-
ciency of UASB reactor (COD removal 26–85%) was
reported during the treatment of municipal sewage (Sanz
766 © IWA Publishing 2018 Water Science & Technology | 77.3 | 2018
doi: 10.2166/wst.2017.584
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