J. R. Banu, et al.
Treatment of domestic wastewater using upflow anaerobic
sludge blanket reactor
1
J. R. Banu;
2
S. Kaliappan;
1
*
I. T. Yeom
1
Civil and Environmental Engineering Centre for Zero Emission Technology Sung Kyun Kwan University, Korea
2
Centre for Environmental Studies (CES) Anna University, Chennai- 600025 Tamilnadu, India
Int. J. Environ. Sci. Tech., 4 (3): 363-370, 2007
ISSN: 1735-1472
© Summer 2007,
IRSEN, CEERS, IAU
Received 4 March 2006; revised 27 August 2006; accepted 5 April 2007; available online 20 June 2007
*Corresponding Author Email: yeom@skku.ac.kr
Tel.: 82 31299 3092; Fax: 82 31299 6658
ABSTRACT: This paper presents the findings of the study on treatment of domestic wastewater using a laboratory
scale Hybrid Upflow Anaerobic Sludge Blanket (HUASB) reactor. The reactor with a working volume of 5.9 L and
plastic cut rings as packing media was operated at varying Hydraulic Retention Time (HRT) for a period of 110 days.
While the COD removal varied from 75-86%, the BOD removal was in the range of 70-91%. Methane content in the
biogas was 62±3%. VFA levels fluctuating between 100 and 186 mg/L (as acetate) did not pose operational problems
such as souring of the reactor. During the treatment, nutrient levels exhibited an increasing trend. HUASB system could
be designed with very short HRT of 3.3 hours, which will reduce the treatment cost significantly. It appears to be a
promising alternative for the treatment of domestic wastewater in developing countries like India
Key words:
HUASB, domestic wastewater, biogas, treatment efficiency
INTRODUCTION
In developing countries like India where access to
safe drinking water is not guaranteed for a majority of
the population, it is of great importance to maintain the
quality of surface water sources. Chennai, one of the
four-mega cities in India is the best example for
pollution of surface water bodies caused by discharge
from sewer outfalls. For instance, Central Pollution
Control Board (CPCB) and Ministry of Environment
and Forests (MoEF) (2001) have reported that Adyar
and Coovum rivers passing through the city receive
wastewaters from 141 and 276 sewer outfalls,
respectively. At present, there are 6 Sewage Treatment
Plants in Chennai with an overall treatment capacity of
267 MLD. It is estimated that the domestic wastewater
generation in Chennai would be of the order of 800 MLD
by the year 2021 (CPCB and MoEF, 2001). This scenario
warrants an urgent need to develop technologies to
treat huge volumes of wastewaters in shortest possible
time frame. Advances in anaerobic treatment of
domestic wastewater offer a few promising options
including Upflow Anaerobic Sludge Blanket (UASB -
Heertjes and Van der Meer, 1978; Lettinga and Vinken,
1980; Lettinga, et al., 1980), Anaerobic Filter (AF -
Chernicharo and Machado, 1998; Bodik, et al., 2000),
Expanded Granular Sludge Bed (EGSB – Van der Last
and Lettinga, 1992; Seghezzo, 1997), Anaerobic Baffled
Reactor (ABR- Langenhoff and Stuckey, 2000 and
Bodik, et al., 2003), Hybrid reactor (HR - Elmitwalli, et
al., 2002a and 2002b) and Anaerobic Migrating Blanket
Reactor (AMBR - Angenent and Sung, 2001). It is
reported that most of the negative aspects of high rate
anaerobic reactors can be overcome by restricting the
supported material to the top 25 to 30% of the reactor
volume (Guiot and Van den berg, 1984; 1985). This
would help realize the advantages of both fixed film
and up flow sludge blanket treatment. This kind of
reactor is called Hybrid Upflow Anaerobic Sludge
Blanket (HUASB) and is considered more stable for
the treatment of a series of soluble or partially soluble
wastewaters (Tilche and Vieira, 1991). Over the years,
HUASBs have been used to treat a variety of industrial
effluents (Coates and Colleran, 1990; Rajesh, et al.,
2006 a,b; Shivayogimath and Ramanujam, 1999). In the
present study, HUASB has been used to treat domestic
wastewater.
MATERIALS AND METHODS
The laboratory scale HUASB reactor was fabricated
using PVC tube with an internal diameter of 11 cm and
an overall height of 88 cm (Fig. 1). The working volume
J. R. Banu, et al.
364
of the reactor was 5.9 L. A gas headspace of 1.5 L was
maintained above the effluent line. A screen was
placed at a height of 60 cm to arrest the floating carrier
material – plastic cut rings. One hundred and fifty
plastic cut rings were used as carrier material. A
peristaltic pump (Make: Miclins, Model: PP 20) was
used for feeding wastewater into the reactor. The
effluent pipeline in turn was connected to a water
seal to prevent the escape of gas. The gas outlet was
connected to a wet gas meter (Make: Ritter, Model:
TG 05).
Fig. 1: Schematic diagram of the HUASB with PVC cut rings
Wastewater
The domestic wastewater used for the present study
was collected from Nessapakkam STP (Sewage
Treatment Plant), Chennai, India.
Acclimatization
“Start-up” phase of the reactor during the study was
not warranted, as the HUASB used was a granulated
one. To acclimatize the methanogens to the new
substrate, the reactor was operated for a period of 30
days at a HRT of 7.4 hours with domestic wastewater.
D
B
A
Effluent
C
F
Influent
Feed tank
E
88 cm
28 cm
60 cm
11 cm
A - Peristaltic pump B- Sludge bed C- Floating filter (PVC Cut rings)
D - Screen E - Wet gas meter F - Water seal
J. R. Banu, et al.
365
Int. J. Environ. Sci. Tech., 4 (3): 363-370, 2007
Operational Condition during the study
The initial HRT was 7.3 h and it was gradually
decreased to 3.3 h over a period of 110 days. This was
achieved by increasing the flow rate from 800 mL/h to
1800 mL/h.
Chemical analysis
Chemical Oxygen Demand (COD), Volatile Fatty Acids
(VFA), Alkalinity, Total Solids (TS), Volatile solids (VS)
and Total Kjeldhal Nitrogen (TKN) of the raw and treated
wastewater were analysed following Standard Methods
(1998).Phosphate (PO
4
3-
), sulphate (SO
4
2-
) and chloride
(Cl
-
) were analyzed employing ion exchange
chromatography (Make: Dionex, Model: DX-120) after
filtering the samples through a 0.45µm filter. The eluent
was a combination of 3.5 mM bicarbonate and 1 mM
carbonate; the flow rate was 1.2 mL/min with an injection
volume of 25 µL. Methane content in the biogas was
measured by Gas Chromatography (Make: Chemito,
Model: GC 1000) equipped with Flame Ionization Detector
(FID). The column used was Proapak Q.
RESULTS
Fig. 2 illustrates the influence of Hydraulic retention
time (HRT) on pH and biogas production. The pH of the
treated wastewater was in the range of 7.4 - 8.1, which is
indicative of satisfactory condition of the reactor. It is
known that pH value less than 6.8 and greater than 8.3
would cause souring of reactor during anaerobic
digestion (Stronach et al 1986; Wheatly, 1991). The
biogas production was in the range of 1800 to 7080 mL/
day. Gas production rates were highly variable due to
the fluctuation of organic concentration in the influent.
Maximum gas production (7080 mL/day) was recorded
at a HRT of 3.3 h. The present values are relatively higher
than those reported by earlier workers (Kobayashi, et
al., 1982; Ligero and Soto, 2002). Higher volumes of
biogas recorded during the present study can be
attributed to higher concentrations of organic matter
present in the wastewater. Methane content in the biogas
was 62 ± 3 %. This value is comparable to 59 ± 3.2 %
reported for gas produced during the treatment of
domestic wastewater using anaerobic hybrid reactor
(Elmitwalli, et al., 2002a). In contrast to the present
observations, Kobayashi et al. (1982) has reported very
high methane content of 92 % for biogas produced
during the treatment of domestic wastewater using
anaerobic filter. It is known that gas generated during
treatment using anaerobic filter generally has higher
methane content as compared to any hybrid reactor
(Elmitwalli, 2002b). Fig. 3 depicts the influence of HRT
on alkalinity and volatile fatly acids (VFA) accumulation
in the wastewater during the treatment. Alkalinity of the
medium increased from 610 mg/L at a HRT of 7.3 h to 744
mg/L at a HRT of 3.3 h. The alkalinity in the medium was
stabilized during the last three operational phases. At
different phases, the VFA as acetate in the medium varied
from 100 to 165 mg/L. Low VFA levels in anaerobically
treated domestic wastewater have been reported by
several workers (Kobayashi, et al., 1982; Ligero and
Soto, 2002; Elmitwalli, et al., 2002a). VFA has been
recognized as one of the important intermediates during
the anaerobic digestion (Ahring and Angelidaki, 1997;
Wang, et al., 1999) and is considered a central parameter
for anaerobic treatment (Ahring and Angelidaki, 1995;
Pind, et al., 1999; 2002). Fig. 4 presents the data on COD
removal during different phases of operation. COD
removal rate varied from 76 to 86 %. Beyond a HRT 3.9 h
marginal decrease in COD removal was noticed and the
rate varied from 75 to 79 % up to a HRT of 3.3 h. The
concentration of organics as COD in the raw domestic
wastewater varied from 700 - 1368 mg/L and in the treated
wastewater it was in the range of 140 - 295 mg/L. As can
be seen from Fig. 5 the BOD removal rate was between
70 and 92 %. This is comparable to 76-88 % BOD removal
reported during the treatment of domestic wastewater at
a HRT of 4 and 6 h by Chernicharo and Machado (1998).
While the BOD of the influent wastewater varied from
434 - 721 mg/L that of the treated wastewater was in the
range of 47 - 175 mg/L. Increase in HRT beyond 4.5 h
caused a gradual decrease in BOD removal. The least
BOD removal of 70 % was recorded when the HRT was
3.3 h. Fig. 6 depicts the influence of OLR on the removal
of TS and VS from the wastewater during the study.
Removal of TS varied from 30 to 35 % during most of the
operational period; the removal was slightly less (28 –
29 %) during the final two HRTs namely 3.5 h to 3.3 h.
This may be attributed to the increase in flow rate that
applied in the final two HRTs. Removal of VS varied from
48 to 56 % and as in the case of TS, at higher HRTs the
removal efficiency decreased. Determination of VS is
useful in the control of wastewater treatment plant
operation because it offers rough approximation of the
amount of organic matter present in the solid fraction of
wastewater (Standard Methods, 1998). Table 1 presents
the characteristics of raw and treated domestic
wastewater during the treatment. It is evident from the
table that the levels of nitrogen, phosphorus and
J. R. Banu, et al.
366
Treatment of domestic wastewater using upflow anaerobic sludge...
potassium in the treated wastewater were higher than
in raw wastewater. Increase in nutrient levels during
the anaerobic treatment of wastewater is a common
occurrence and is attributed to the mineralization of
organic compounds (Hanndel and Lettinga, 1994). This
nutrient rich treated wastewater needs further
treatment, as nitrogen and phosphorus cause algal
blooms in receiving water bodies. Ammonia
concentration in the wastewater during all the phases
of operation increased as a result of ammonification.
The removal of sulphate from the wastewater during
the treatment was significant. The chloride
concentration in the effluent remained unaffected
during the treatment.
0
1000
2000
3000
4000
5000
6000
7000
8000
7.36.55.95.44.94.54.23.93.73.53.3
Hydraulic retention time (h)
Gas (mL)
7
7.5
8
8.5
9
9.5
pH
GAS pH
0
50
100
150
200
250
300
350
400
7.3 6.5 5.9 5.4 4.9 4.5 4.2 3.9 3.7 3.5 3.3
Hydraulic retention time (h)
VFA as acetate (mg/L)
0
100
200
300
400
500
600
700
800
VFA Alk
Fig. 3: Influence of HRT on VFA and alkalinity during the treatment of domestic
wastewater using HUASB with PVC
Fig. 2: Influence of HRT on biogas production and pH durin the treatment of domestic
wastewater using HUASB with PVC
Total alkalinity (mg/L)
J. R. Banu, et al.
367
Int. J. Environ. Sci. Tech., 4 (3): 363-370, 2007
DISCUSSION AND CONCLUSION
Anaerobic treatment of domestic wastewater
employing HUASB efficiently removed organics both
COD and BOD with in very short period of time.
Comparatively lower organics removal efficiencies
during the treatment of domestic wastewaters using
UASB at different HRTs have been reported by several
workers (65% at a HRT of 4 h - Haskoning, 1989; 53% at
a HRT of 4.4 h - Viera and Garcia, 1991; 72% at a HRT of
5 h - Schellinkhout and Callazos, 1991). The commonly
encountered problem of VFA induced ‘souring’ of the
reactor was not encountered during the present study
as the VFA levels were quite low. Interestingly, the
BOD inf.
BOD eff.
0
200
400
600
800
1000
1200
1400
1600
1800
2000
7.3 6.5 5.9 5.4 4.9 4.5 4.2 3.9 3.7 3.5 3.3
Hydraulic retention time (h)
0
10
20
30
40
50
60
70
80
90
100
COD inf COD eff COD removal (%)
Fig. 4: influence of HRT on COD removal during the treatment of domestic
wastewater using HUASB with PVC
0
200
400
600
800
1000
1200
1400
7.3 6.5 5.9 5.4 4.9 4.5 4.2 3.9 3.7 3.5 3.3
Hydraulic retention time (h)
0
10
20
30
40
50
60
70
80
90
100
BODinf BOD eff BOD removal (%)
Fig. 5: influence of HRT on BOD removal during the treatment of domestic
wastewater using HUASB with PVC
COD (mg/L)
BOD removal (%)
BOD (mg/L)
BOD removal (%)
COD inf.
COD eff.
Hydraulic retention
