The present study evaluates effectiveness of up-flow anaerobic sludge blanket (UASB) reactor followed by two post-anaerobic treatment options, namely free-surface, up-flow constructed wetland (FUP-CW) and oxygen-limited anaerobic nitrification/denitrification (OLAND) processes in treating sewage from the peri-urban areas in India receiving illegal industrial infiltrations. The UASB studies yielded robust results towards fluctuating strength of sewage and consistently removed 87–98% chemical oxygen demand (COD) at a hydraulic retention time of 1.5–2 d. The FUP-CW removed 68.5 ± 13% COD, 68 ± 3% NH4+-N, 38 ± 5% PO43−-P, 97.6 ± 5% suspended particles and 97 ± 13% fecal coliforms. Nutrient removal was found to be limiting in FUP-CW, especially in winter. Nitrogen removal in the OLAND process were 100 times higher than the FUP-CW process. Results show that UASB followed by FUP-CW can be an excellent, decentralized sewage treatment option, except during winter when nutrient removal is limited in FUP-CW. Hence, the study proposes bio-augmentation of FUP-CW with OLAND biomass for overall improvement in the performance of UASB followed by FUP-CW process.

INTRODUCTION

Most of the cities in India have a network of sewage canals or open drainage systems that have intricate linkage with storm water drainage, domestic sewage and treated industrial effluent disposal. Often, some industries illegally discharge untreated or partially treated effluent into the sewer network that make the composition of sewage complex and varied. Generally, sewage treatment plants (STPs) are not designed to meet the extra load of industrial effluent (Rajaram & Das 2008). As a result, most of the STPs in Indian cities do not meet the performance criteria. Hence, a robust sewage treatment process must be designed to cope with extra pollution load in the sewage.

Up-flow anaerobic sludge blanket (UASB) is a proven technology for the sewage treatment in warm climates due to their low operating costs, flexibility and versatility (Lettinga et al. 1993; Banihani & Field 2013). But UASB alone rarely complies with the discharge standards and a post-treatment unit such as oxidation or stabilization ponds, shallow duckweed ponds, constructed wetland (CW), trickling filters, etc. is often recommended for removal of residual organics, nutrients and pathogens (van der Steen et al. 1999; Bastos et al. 2010; Banihani & Field 2013; Khan et al. 2013; Vieira et al. 2013). CW is one of the most sustainable, natural, cost-effective, and robust technologies for post-anaerobic treatment of sewage (Sehar et al. 2013).

Oxygen-limited autotrophic nitrification/denitrification (OLAND) is a biological process based on partial nitritation/anammox, using the enchained action of aerobic and anoxic ammonium-oxidizing bacteria (AerAOB and AnAOB) for nitrogen removal from the wastewater (Vlaeminck et al. 2012). Compared to conventional nitrification/denitrification, OLAND has a considerable cost saving due to decreased needs in aeration (60%), sludge treatment (90%) and organic carbon addition (100%). OLAND and partial nitritation/anammox in general, is an established technology in European countries at higher temperatures (>20 °C) and high nitrogen levels (>500 mg N/L) (Lackner et al. 2014), yet its application in treatment of low-strength wastewater such as pre-treated sewage has not yet been fully explored.

The objectives of this study were to evaluate the effectiveness of UASB, CW and OLAND processes in treating sewage of highly variable characteristics and to propose an effective treatment process. More specifically, the UASB process was studied for its robustness to combat fluctuations in sewage receiving unscrupulous industrial discharges while the CW and OLAND processes were explored as two post-anaerobic alternatives (Figure 1).

Figure 1

Experimental plan for treatment of sewage using UASB followed by two post-anaerobic treatment options, namely the FUP-CW and OLAND processes.

Figure 1

Experimental plan for treatment of sewage using UASB followed by two post-anaerobic treatment options, namely the FUP-CW and OLAND processes.

MATERIALS AND METHODS

Sewage

Sewage from three different sources was used in this study: one from an industrial area of Nagpur city, India, another from a residential area of the same city, and the last was obtained from an STP at Breda (The Netherlands) (Table 1).

Table 1

Characteristics of various types of sewage used in the study

  Sewage from industrial area for UASB studies* Sewage from residential area 
Meters High strength Moderate strength For FUP-CW studies For OLAND studies 
CODtotal (mg/l) 3495 ± 590 1589 ± 373 231 ± 141 123 ± 13 
BOD5 (mg/l) 2250 ± 75 980 ± 50 125 ± 55 47 ± 18 
Kjeldahl nitrogen (mg/l) 28 ± 8 19 ± 11 36 ± 5 20 ± 4 
TP (mg/l) 12 ± 3 15 ± 4 10 ± 6 3 ± 1 
SS (mg/l) 218 ± 97 325 ± 85 150 ± 28.6 57 ± 18 
FC (CFU/100 ml) 22 × 105 ± 1 × 105 17 × 105 ± 15 × 104 90 × 104 ± 35 × 103 NM 
  Sewage from industrial area for UASB studies* Sewage from residential area 
Meters High strength Moderate strength For FUP-CW studies For OLAND studies 
CODtotal (mg/l) 3495 ± 590 1589 ± 373 231 ± 141 123 ± 13 
BOD5 (mg/l) 2250 ± 75 980 ± 50 125 ± 55 47 ± 18 
Kjeldahl nitrogen (mg/l) 28 ± 8 19 ± 11 36 ± 5 20 ± 4 
TP (mg/l) 12 ± 3 15 ± 4 10 ± 6 3 ± 1 
SS (mg/l) 218 ± 97 325 ± 85 150 ± 28.6 57 ± 18 
FC (CFU/100 ml) 22 × 105 ± 1 × 105 17 × 105 ± 15 × 104 90 × 104 ± 35 × 103 NM 

*Pre-settled sewage from an industrial area of Nagpur city, India.

Pre-settled sewage from a residential area of Nagpur city, India.

Biologically treated sewage from STP of Breda, The Netherlands.

NM, not measured; CFU, colony forming units.

Experimental set-up

An 82.5 L capacity, pilot-scale UASB was used in this study. The sewage that was pre-settled for 30 minutes, was pumped from the bottom of the reactor at various flow rates using a Watson Marlow peristaltic pump and the effluent was collected from the top. The biogas was collected in 10% caustic solution through downward displacement method (Figure 1).

The free-surface, up-flow constructed wetland (FUP-CW) consisted of an inlet tank (0.45 × 2 × 0.92 m), mesocosm (2.5 × 2 × 0.92 m) and outlet tank (0.62 × 0.62 × 0.92 m) (Badhe et al. 2014). The mesocosm was filled with gravel of 40–60 mm diameter and was planted with an emergent macrophyte species, Typha latifolia. The pre-settled sewage from the residential area was pumped into the inlet tank of the FUP-CW at a controlled flow rate. The sewage flowed into the mesocosm from the bottom of the inlet tank in an up-flow manner. The effluent was collected into the outlet tank from a tap provided at a height of 57 cm at the outlet side of the mesocosm (Figure 1).

The OLAND experiments were conducted in batches under controlled conditions using sludge taken from a mature (more than a decade old) OLAND unit installed at Belgium (Courtens et al. 2014) and pre-treated sewage from an STP, Breda, The Netherlands.

The UASB and FUP-CW studies were carried out in India while the OLAND tests were performed in Belgium due to limitations in international shipping of biomass and/or wastewater.

Experimental method

The UASB unit was operated with variable strength, pre-settled sewage from the industrial area. The organic loading rate (OLR) and hydraulic retention time (HRT) were adjusted as per the strength of sewage and were varied between 1 to 3 kg/m3.d and 0.5 to 3 d, respectively.

The pilot-scale FUP-CW treating pre-settled sewage from the residential area has been in operation since 2009. The present study of FUP-CW was conducted at an average HRT of 3 d.

The OLAND batch assays were conducted under aerobic and anoxic conditions at 20 °C using pre-treated sewage to analyze the maximum AerAOB and AnAOB activities, respectively. Since the tests were performed in Belgium, pre-treated sewage was taken from a high-rate-activated sludge unit, removing mainly chemical oxygen demand (COD) in Breda (The Netherlands), in order to mimic COD/N concentrations of the UASB effluent in India. OLAND biomass at a final concentration of 4 g/l volatile suspended solids (VSS) was used as inoculum in each test. For the aerobic test, 250 ml Erlenmeyer flasks were incubated under shaking condition (100 rpm). For the anoxic test, experiments were conducted in sealed 125 ml penicillin bottles, flushed with N2 gas. The control solution (100 ml, pH 7.4) for the aerobic test, consisted of 4.2 g KH2PO4/l, 5.8 g K2HPO4/l and 150 mg NaHCO3/l, while that in the anoxic test consisted of 0.14 g KH2PO4/l, 0.24 g KH2PO4/l and 150 mg NaHCO3/l. For the experimental solution containing 100 ml pre-treated sewage, the same amounts of phosphate were added for aerobic test, while no phosphate was used in anoxic test. Substrate (NH4Cl) was spiked in each assay to reach a starting concentration of 30 mg . The nitrogen species were followed over time and their conversion rate was expressed relative to the amount of biomass present.

Analytical methods

Wastewater samples were analyzed for pH, temperature, dissolved oxygen (DO), COD, biological oxygen demand (BOD5), suspended solids (SS), volatile fatty acid, total alkalinity, total Kjeldahl nitrogen (TKN) ammonia-nitrogen (), total phosphate (TP) and soluble phosphate (), nitrate (), nitrite (), fecal coliforms (FC) biogas and gaseous methane concentrations. Temperature, DO and pH were measured with a Multiparameter PCD 650 (Eutech Instruments, Singapore). All the parameters except nitrate (), nitrite (), methane, and biogas were determined as per Standard Methods (APHA 2005). and measurements in the batch activity tests were determined on a 761 Compact Ion Chromatograph (Metrohm, Switzerland) equipped with a conductivity detector. The biogas produced was measured by water displacement method. The methane concentration in biogas was measured by a methane analyzer (Technovation, India).

RESULTS AND DISCUSSION

Sewage characteristics

Table 1 presents the characteristics of various types of sewage used in the study. As seen in the table, the settled sewage from the industrial area was characterized with unusually high strength which changed drastically on the 87th day (Table 1). This could be due to some major changes in the volume of industrial wastewater illegally discharged into the sewage canal. Henze & Comeau (2008) have classified sewage receiving minor industrial infiltrations into three categories: high (CODtotal ≥ 1200 mg/l), moderate (CODtotal ≥ 750 mg/l), and low (CODtotal ≤ 500 mg/l). As per this classification, the sewage from the industrial areas can be categorized as high (1st–86th day) and moderate strength (87th day onwards), while that from the residential area as low strength, respectively.

Performance of UASB

Based on the strength of sewage received, the operation of UASB is categorized into high strength and medium strength situations (Table 2 and Figure 2(a)). During a sudden change in the characteristic of sewage, the reactor efficiency reduced due to organic shock but recovered soon thereafter indicating robustness of the process against fluctuating COD concentrations. Throughout the study period, total COD removal efficiency was between 87 and 98%, except during the organic overloading, when the efficiency dropped to 55%.

Table 2

Performance of the UASB and FUP-CW processes under stable conditions

  Performance of UASB* Performance of FUP-CW 
 High strength situations Moderate strength situations       
Parameters Influent Treated effluent Removal, % Influent Treated effluent Removal, % Influent Treated effluent Removal, % 
COD total (mg/l) 3495 ± 590 231 ± 141 93 ± 5 1589 ± 373 143 ± 93 91 ± 6 231 ± 141 45 ± 19 68.5 ± 13 
Kjeldahl nitrogen (mg/l) 28 ± 8 6 ± 2 74.5 ± 30 19 ± 11 17 ± 8 1 ± 54 17 ± 8 5.3 ± 0.5 68 ± 3 
TP (mg/l) 12 ± 3 9 ± 5 29 ± 5 15 ± 4 15 ± 6 −5 ± 49 15 ± 6 9 ± 4.5 38.5 ± 5 
SS (mg/l) 218 ± 97 50 ± 9 89 ± 25 325 ± 85 45 ± 12 85 ± 12 50 ± 28.6 5 ± 2 97.6 ± 5 
FC (CFU/100 ml) 22 × 105 ± 1 × 105 14 × 105 ± 3 × 105 36 ± 15 17 × 105 ± 15 × 104 90 × 104 ± 35 × 104 47 ± 17 90 × 104 ± 35 × 103 55 × 103 ± 48 × 102 97 ± 13 
DO (mg/l) 0.8 ± 0.2 – 
  Performance of UASB* Performance of FUP-CW 
 High strength situations Moderate strength situations       
Parameters Influent Treated effluent Removal, % Influent Treated effluent Removal, % Influent Treated effluent Removal, % 
COD total (mg/l) 3495 ± 590 231 ± 141 93 ± 5 1589 ± 373 143 ± 93 91 ± 6 231 ± 141 45 ± 19 68.5 ± 13 
Kjeldahl nitrogen (mg/l) 28 ± 8 6 ± 2 74.5 ± 30 19 ± 11 17 ± 8 1 ± 54 17 ± 8 5.3 ± 0.5 68 ± 3 
TP (mg/l) 12 ± 3 9 ± 5 29 ± 5 15 ± 4 15 ± 6 −5 ± 49 15 ± 6 9 ± 4.5 38.5 ± 5 
SS (mg/l) 218 ± 97 50 ± 9 89 ± 25 325 ± 85 45 ± 12 85 ± 12 50 ± 28.6 5 ± 2 97.6 ± 5 
FC (CFU/100 ml) 22 × 105 ± 1 × 105 14 × 105 ± 3 × 105 36 ± 15 17 × 105 ± 15 × 104 90 × 104 ± 35 × 104 47 ± 17 90 × 104 ± 35 × 103 55 × 103 ± 48 × 102 97 ± 13 
DO (mg/l) 0.8 ± 0.2 – 

*Pre-settled sewage from an industrial area of Nagpur city, India.

Pre-settled sewage from a residential area of Nagpur city, India.

CFU, colony forming unit.

Figure 2

(a) Performance of UASB in terms of inlet and outlet COD concentrations; (b) COD removal efficiency at varying OLRs and HRTs.

Figure 2

(a) Performance of UASB in terms of inlet and outlet COD concentrations; (b) COD removal efficiency at varying OLRs and HRTs.

The COD removal efficiencies were higher than those reported for the treatment of low strength and high strength domestic wastewater (Bandara et al. 2012). Stable performance was obtained at OLR of 1–2 kg/m3.d and at HRT 1.5–2 d under variable influent characteristics with more than 90% of COD removal efficiency. Other researchers have reported OLR range of 0.37–3.7 kg/m3.d for treating domestic sewage (Bandara et al. 2012; Banihani & Field 2013). Total biogas generation was between 3.2 and 7.9 L/d with highest methane yield of 0.38 NL/g CODremoved.d (range 0.03–0.38 NL CH4/g COD.d). Similar methane yield of 0.2–0.3 NL/g CODremoved.d has been obtained during anaerobic treatment of domestic wastewater (Gopala Krishna et al. 2008).

The overall performance of the UASB reactor at 1.5 d detention time is shown in Table 2. Nutrient removal in UASB was varying and inconsistent. It was perhaps due to mere entrapment of particulate fractions of the wastewater in the sludge blanket of UASB (Aiyuk et al. 2010). The overall characteristic of the treated effluent from UASB was similar to that of the sewage from the residential area and hence needed further treatment.

Performance of FUP-CW

Figure 3 presents a typical month-wise performance of FUP-CW. Throughout the year, COD removal was around 44–84% but nutrient removal was limited especially during the winter season (November–February). T. latifolia being a perennial macrophyte undergoes senescence in winter and translocates the nutrients accumulated in the shoots to the underground parts like rhizomes and roots. During translocation, some of the nutrients are released into the environment (Badhe et al. 2014). In addition to reduced plant uptake in winter, lower temperature and reduced redox potentials in plant rhizosphere reduce microbial uptake rates (Brix 1994; Morari & Giardini 2009; Badhe et al. 2014). The phosphate removal can particularly be affected due to saturation of the adsorption capacity of the filter bed (Kyambadde et al. 2005). As the FUP-CW unit has been in operation since 2009, saturation of the adsorption capacity of the filter bed is not very unlikely. Other factors causing reduced efficiency are evapo-transpirational losses and climatic factors (Morari & Giardini 2009). On average, the FUP-CW unit achieved 65% removal of total COD, 11% removal of TKN and 18% removal of TP annually.

Figure 3

A typical month-wise performance of FUP-CW in a year.

Figure 3

A typical month-wise performance of FUP-CW in a year.

The overall performance of FUP-CW during the growing season of T. latifolia (from May–November) is depicted in Table 2. During this period, FUP-CW effectively removed total COD, soluble nutrients, SS and FC from the sewage. The influent characteristics of settled sewage used for FUP-CW matched fairly well with the effluent characteristics of the UASB unit and hence the FUP-CW can be used as an effective post-treatment option to UASB.

OLAND feasibility

To assess the feasibility for OLAND to serve as nitrogen polishing step on pre-treated sewage, batch activity tests at 20 °C were performed (Figure 4).

Figure 4

Activities of aerobic and anoxic ammonium-oxidizing bacteria on synthetic medium and pre-treated sewage, expressed in NH4+ for AerAOB and Ntot for AnAOB.

Figure 4

Activities of aerobic and anoxic ammonium-oxidizing bacteria on synthetic medium and pre-treated sewage, expressed in NH4+ for AerAOB and Ntot for AnAOB.

The tests showed that the sewage matrix and the present C/N ratio caused no AerAOB nor AnAOB inhibition nor retardation compared to the control in synthetic medium without organic carbon under similar conditions. At the obtained nitrogen removal rate of 25 mg N g−1 VSS d−1, and a typical OLAND biomass concentration of 4 g VSS l−1, this would yield 100 mg N l−1 d−1 as removal rate. In comparison to the FUP-CW, which removed nitrogen at an average rate of 0.85 mg N l−1 d−1, this is about 100 times higher, and hence more compact. Hence OLAND can be used as post-anaerobic treatment option to UASB for carbon and nitrogen mitigation in sewage. However, as compared to wetlands, OLAND does not offer a solution for phosphate removal, and its pathogen removal capacity is yet to be explored. Nevertheless, bio-augmentation of FUP-CW with OLAND biomass can potentially overcome the bottleneck of limited and seasonal variation of nitrogen removal efficiency in CW.

CONCLUSIONS

The UASB reactor was found to be robust against the fluctuating strength of sewage while the FUP-CW process is an ideal post-anaerobic option removing residual organics, nutrients and pathogens. The bottleneck of CW process, however, is low nutrient removal during winter. The OLAND biomass was found to be effective in high-rate ammonia removal from pre-treated sewage. Hence, at present, the prospect of enhanced ammonia removal efficiency by bio-augmenting the FUP-CW with OLAND biomass appears exciting and an excellent sewage treatment solution is expected using the process throughout the year.

ACKNOWLEDGEMENTS

The authors acknowledge NEW INDIGO ERA-NET for funding the study. S.S., S.E.V., and D.S. were supported with University Grants Commission's junior research fellowship, Government of India, a postdoctoral fellowship from the Research Foundation Flanders (FWO Vlaanderen), and a PhD scholarship from strategic basic research of the IWT (Agency for Innovation by Science and Technology), respectively.

REFERENCES

REFERENCES
Aiyuk
S.
Odonkor
P.
Theko
N.
van Haandel
A.
Verstraete
W.
2010
Technical evaluation of potential drawbacks in direct UASB treatment of raw domestic sewage
. In:
Environmental Engineering and Applications (ICEEA), 2010 International Conference on IEEE
,
IEEE, Singapore
, pp.
320
326
.
APHA, AWWA &WEF
2005
Standard Methods for the Examination of Water and Wastewater
.
American Public Health Association
,
21st edn
,
Washington, DC
.
Bandara
W. M.
Kindaichi
T.
Satoh
H.
Sasakawa
M.
Nakahara
Y.
Takahashi
M.
Okabe
S.
2012
Anaerobic treatment of municipal wastewater at ambient temperature: Analysis of archaeal community structure and recovery of dissolved methane
.
Water Research
46
(
17
),
5756
5764
.
Bastos
R. K.
Calijuri
M. L.
Bevilacqua
P. D.
Rios
E. N.
Dias
E. H.
Capelete
B. C.
Magalhães
T. B.
2010
Post-treatment of UASB reactor effluent in waste stabilization ponds and in horizontal flow constructed wetlands: a comparative study in pilot scale in Southeast Brazil
.
Water Science & Technology
61
(
4
),
995
1002
.
Brix
H.
1994
Use of constructed wetlands in water pollution control: historical development, present status, and future perspectives
.
Water Science & Technology
30
(
8
),
209
224
.
Courtens
E. N.
Boon
N.
De Clippeleir
H.
Berckmoes
K.
Mosquera
M.
Seuntjens
D.
Vlaeminck
S. E.
2014
Control of nitratation in an oxygen-limited autotrophic nitrification/denitrification rotating biological contactor through disc immersion level variation
.
Bioresource Technology
155
,
182
188
.
Gopala Krishna
G. V. T.
Kumar
P.
Kumar
P.
2008
Treatment of low strength complex wastewater using an anaerobic baffled reactor (ABR)
.
Bioresource Technology
99
,
8193
8200
.
Henze
M.
Comeau
Y.
2008
Chapter 16
. In:
Biological Wastewater Treatment Principles, Modeling and Design
(
Henze
M.
Van Loosdrecht
M. C. M.
Ekama
G. A.
Brdjnovic
D.
, eds).
IWA Publishing
,
London
,
UK.
Khan
A. A.
Gaur
R. Z.
Kazmi
A. A.
Lew
B.
2013
Chapter 8 Sustainable Post Treatment Options of Anaerobic Effluent
. In:
Biodegradation Engineering and Technology
(
Chamy
R.
, ed.).
InTech
,
Rijeka, Croatia. DOI: 10.5772/56097
.
Kyambadde
J.
Kansiime
F.
Dalhammar
G.
2005
Nitrogen and phosphorus removal in substrate-free pilot constructed wetlands with horizontal surface flow in Uganda
.
Water, Air, and Soil Pollution
165
(
1–4
),
37
59
.
Lackner
S.
Gilbert
E. M.
Vlaeminck
S. E.
Joss
A.
Horn
H.
Van Loosdrecht
M. C. M.
2014
Full-scale partial nitritation/anammox experiences – an application survey
.
Water Research
55
,
292
303
.
Lettinga
G.
de Man
A.
van der Last
A. R. M.
Wiegant
W.
van Knippenberg
K.
Frijns
J.
van Buuren
J. C. L.
1993
Anaerobic treatment of domestic sewage and wastewater
.
Water Science & Technology
27
(
9
),
67
73
.
Sehar
S.
Aamir
R.
Naz
I.
Ali
N.
Ahmed
S.
2013
Reduction of Contaminants (Physical, Chemical, and Microbial) in Domestic Wastewater through Hybrid Constructed Wetland
.
ISRN Microbiology
2013
,
1
9
. .
Van der Steen
P.
Brenner
A.
Van Buuren
J.
Oron
G.
1999
Posttreatment of UASB reactor effluent in an integrated duckweed and stabilization pond system
.
Water Research
33
,
615
620
.
Vieira
P. C.
von Sperling
M.
Nogueira
L. C. M.
Assis
B. F. S.
2013
Performance evaluation of a novel open trickling filter for the post-treatment of anaerobic effluents from small communities
.
Water Science & Technology
67
(
12
),
2746
2752
.
Vlaeminck
S. E.
De Clippeleir
H.
Verstraete
W.
2012
Microbial resource management of one-stage partial nitritation/anammox
.
Microbial Biotechnology
5
(
3
),
433
448
.