SBR System for Agrochemical Industry - Feasibility & Implementation
Pravin Manekar, Rima Biswas & Tapas Nandy
CSIR-National Environmental Engineering Research Institute, Nagpur 440 020, India
[email protected]; [email protected]; [email protected]
Abstract
Feasibility of sequential batch reactor (SBR) was investigated to treat an agrochemical
effluent by overcoming factor affecting process stability such as microbial imbalance and
substrate sensitivity. The full-scale aerobic process was evaluated under the existing
operating condition lead to non-optimal performance. Laboratory study was conducted in
a bench scale SBR system stage-I&II model. SBR system stage-I&II achieved biooxidation at 6 days hydraulic retention time in an extended aeration mode. The
maximum removal of chemical oxygen demand (COD) and biochemical oxygen demand
(BOD) by heterotrophic bacteria in the first stage reactor was 87% and 90%,
respectively. Removal of toxic ammoniacal-nitrogen by autotrophic bacteria in a second
stage bio-oxidation was 97%. SBR system stage-I&II showed a great promise for
improving the process stability and treating the agrochemical effluent. SBR system
stage-I&II was implemented at full-scale level to treat the agrochemical effluent.
Key words: Agrochemical industry; SBR; bio-oxidation process; implementation
1 Introduction
Agrochemical industries consume enormous water for producing the pesticides,
insecticides, herbicides and fungicides and generate multi-stream complex effluents.
Discharging of untreated or partially treated agrochemical effluent render adverse effects
on receiving water bodies (Delorenzo et al., 2001). Chemicals present in agrochemical
effluent are often toxic to aquatic life. Agrochemical effluents are typically characterized
with high concentrations of COD and ammonia. Treatment technologies for high COD
concentration and ammonia comprise physico-chemical and biological processes.
However, unlike chemical treatment biological process does not produce a huge quantity
of sludge and thus are more environmentally friendly. Biological processes such as ASP,
SBR, anaerobic–aerobic (A/O) biofilm reactors, moving bed membrane bioreactor,
packed-bed biofilm reactor and pre-denitrification can effectively remove carbonaceous
and nitrogenous pollutants (Kim et al., 2009; Yang and Yang, 2011; Karkare and Murthy,
2012).
The SBR has been successfully employed in the treatment of both municipal sewage
and industrial effluent (Mace and Mata-Alvarez, 2002). It is simple in process
engineering, design and requires less foot print (Vazquez et al., 2006). This technology
is a cyclic batch process operated in a sequence of fill, react, settle and decant for
effective removal of pollutants (Akin and Ugurlu, 2005) and best suitable for
accommodating multiple microbial reaction in a single reactor. However, carbon and
nitrogen removal can suffer from disagreement of demand and supply of substrates
between two metabolically different groups of microorganism namely the heterotrophsand the autotrophs often lead to failure.
The competition become more intense when complex industrial effluent are treated such
as effluent from steel industry, coal carbonization, and municipal leachates, etc.
(Marttinen et al., 2002; Manekar et al., 2011b). To overcome the incompatibility between
heterotrophic and autotrophic bacteria in a single stage reactor or multiple-stage
processes is often advocated for treating high strength effluent (Kim et al., 2013). This
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paper addressed the feasibility and implementation SBR system stage-I&II for carbon
and nitrogen removal from agrochemical industry. Thus, the work aimed for feasibility
and implementation of the SBR system for treating the agrochemical effluent.
2 Methodology
2.1 Effluent segregation and quantification
The agrochemical industry is located in the southern part of India. The production
capacity of the industry is 12.5 tonnes per day. The production unit comprises four
process blocks designated I-IV, and produces a comprehensive range of pesticides,
technical, formulations and custom manufactured fine chemicals. The complex process
effluents generated from the four manufacturing units (namely block I-IV) were
segregated into three main streams, and designated as stream A-C. The stream A was
generated after product separation; ejector condensates from all the process blocks
were channelized in the stream B. Stream C, highly organic in nature was left over
solvent separation. The quantum of streams A, B and C generated were 250, 300 and
30 m3d-1, respectively.
2.2 Treatment facility
Stream A was treated in evaporative system, and condensate obtained was stripped in
an air stripper. The stripped effluent was further combined with stream B before feeding
to aerobic system. The sludge from biological process and concentrate from the
evaporator system were dried separately, the dried sludge and concentrate were
disposed off to a treatment storage and disposal facility. Hourly samples were collected
in polypropylene bottles and composited for 24 h at different stages of the effluent
treatment plant (ETP). The composite samples were analyzed as referred in the
Standard Methods (APHA, 2005).
2.3 Sequential batch reactor
Ammonia stripped effluent was treated in a bench scale SBR system consists of two
cubical acrylic tanks of size (30×30×30 cm3). The SBR stage-I was inoculated with the
biomass collected from the existing ETP of the agrochemicals industry. Biomass to be
inoculated in SBR stage-II was obtained from an industrial nitrification unit and
acclimatized with domestic sewage. The SBR stage-I was fed with stripped effluent (pH
7.2) at different HRTs in an extended aeration mode. The SBR stage-I&II was operated
in a cyclic batch mode having a time schedule as follows: 4 h-filling, 18 h-filling and
aeration (both oxic); 2 h-settling, 4 h-decanting (both anoxic). The SBR stage-I&II was
optimized by operating reactors at different HTRs (1-4 d). Air was supplied to maintain a
DO concentration 2.5 mgl-1 and to ensure proper contact of substrates and
microorganisms during fill and aeration mode.
3 Results and discussion
3.1 Physico-chemical characterization of effluents
A detailed physico-chemical characterization of streams A and B, generated from the
different process blocks I-IV was carried out, and the results are summarized in Table 1.
TDS and COD concentrations of stream A (from process blocks I-IV) were very high in
the range 160,000-253,000 and 56,280-84,000 mgl-1, respectively and hence stream A
was characterized as high TDS and high COD effluent. The COD concentration of
stream B (from process blocks I-IV) was 5-7 times more than its TDS concentration.
Therefore, it was characterized as low TDS and high COD effluent. Additionally,
ammonia and SS concentrations in stream A were much higher than stream B. In
totality, all the stream from agrochemical effluent was characterized high strength
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effluent containing high concentration of organic, inorganics and ammonia. The process
effluents were found to be free from pesticides, herbicides, fungicides and insecticides.
3.2 Assessment of existing aerobic system
Performance of the aerobic system and treated effluent quality as per the stipulated
discharge norms into Inland Surface Waters is summarized in Table 2. The influent to
SBR was high in ammonia concentration (305-385 mgl-1). The DO concentration during
the fill and the aeration period was found to be less than 1 mgl-1. The mixed liquor
volatile suspended solid (MLVSS) and mixed liquor suspended solid (MLSS)
concentrations were 1452-2000 and 2100-2500 mgl-1, respectively.
3.3 SBR stage-I
In the existing aerobic system, 59-65% SS, 72-83% BOD and 68-77% COD removals
were achieved. Ammonia removal was not taking place even after operating the reactor
at an extremely high HRT of 24 days. The treated water quality from the existing aerobic
system did not conform to the Indian Inland Surface Waters (ISW) standard discharged
with respect to BOD, COD and ammonia concentration (Table 2). Laboratory studies
were carried out in a 24 h cyclic SBR stage-I bio-oxidation reactor at mixed liquor
suspended solid (MLSS) concentration of 3200-3500 mgl-1 with varying HRTs (1-4 days).
Biological process depends on the bacterial growth/decay rate and HRT that yield
desired treatment efficiency. The characteristic of FSSBR feed was as follows: pH: 7.07.3; TDS: 2700 mgl-1; COD: 3000 mgl-1; BOD: 2500 mgl-1 and ammonia 200mgl-1.
The results from this set of the experiments are presented in Fig. 1.The removal of the
major pollutant parameters such as COD and BOD at HRT 1 day was 70% and 75%,
respectively. When the reactor was operated at higher HRTs, the increase in the
removal of pollutants (COD and BOD) was observed. However, at HRT greater than 3
days, COD and BOD removal efficiency dropped to 80% and 86%, respectively. The
highest removal of carbonaceous substrate was obtained at 3 d (72 h) HRT with more
than 90% removal efficiency. Maranon et al. (2008b) reported a very similar COD
removal efficiency at HRT of 115 h in a single stage SBR for treatment coke effluent.
The treated effluent characteristics from the SBR stage-I were as follows: COD: 400 mgl1
; BOD 250 mgl-1; ammonia nitrogen: 200 mgl-1. The results obtained were comparatively
better than the existing aerobic system. However, treated effluent did not meet the
Indian ISW discharge standards. Therefore, further treatment was necessary to meet the
regulatory norms.
3.4 SBR stage-II
The SBR stage-II was targeted for nitrification of SBR stage-I effluent. Therefore, to
develop nitrifying activity in SBR stage-II biomass from a full-scale nitrifying reactor was
acclimatized with SBR stage-I effluent. After acclimatization, which lasted for around 3
months it was found 18% and 7% of biomass was composed of ammonia oxidizing
bacteria (AOB) and nitrite oxidizing bacteria (NOB) with bacterial count of 5-27×107 and
2-10×07 CFU ml-1, respectively. The nitrification performance of SBR stage-II was
observed at different HRTs (Fig. 2). At lower HRT, the removal efficiency of the
ammonia was inefficient. Removal efficiency increased with increase in HRT up to 3 d.
However, further increase in HRT resulted in decrease in removal of ammonia. Peak
97% removal efficiency of ammonia was obtained at 3 d HRT in an extended aeration
mode. Many researchers have reported a minimum of 2.5-8 d for more than 70%
nitrification efficiency (Maranon et al., 2008a; Biswas et al., 2010; Manekar et al.,
2011b). At 3 d optimal HRT, the SBR stage-II treated effluent had the following
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characteristics COD ≤110 mgl-1, BOD≤ 50 mgl-1, ammonia ≤10 mgl-1, nitrite: BDL and
nitrate≤ 7mgl-1. Thus, along with ammonia removal, the COD of 72.5% and BOD of 80%
removals were also observed in SBR stage-II.
Heterotrophic bacteria oxidized the carbonaceous substrate to more than 90%
efficiency. Autotrophic bacteria in the SBR stage-II effectively oxidized ammonia
concentration to 97% and thus, improved the stability of nitrification process. The stage
separation provided separate environmental condition for optimum activities of
heterotrophic and autotrophic bacteria (Vazquez et al., 2006; Biswas et al., 2010). Thus,
fends off the competition between heterotrophic and autotrophic bacteria, improves the
process stability for substrate sensitivity through active interaction of substrates and
renders the optimum environmental conditions to microbes for effective oxidation of
carbonaceous and nitrogenous substrates. Effective carbon-nitrogen removal in the SBR
stage I&II was achieved at an optimal HRT of 6 d. The final effluent from the SBR stageII met the discharge standards for ISW, with respect to all parameters.
3.5 Full-scale SBR system design & implementation
The full-scale SBR stage-I&II was designed for a flow rate of 600 m3d-1 to operate in a
cyclic batch mode with a time schedule as described earlier. The yield coefficient (Y) of
the SBR stage-I&II cycle was 0.4 gg-1, while the endogenous respiration coefficient (kd)
was: 0.035 d-1.The full-scale SBR stage-I&II was designed with 6 days total HRT and 3
days at each stage, operating in an extended aeration mode with 2 Nos. each for SBR
stage-I(14.2×14.2 ×5.5) and SBR stage-II(13.5×13.5×5.5). The loading rates for SBR
stage I&II were 0.750 and 0.083 kgBODm-3d-1, respectively. The oxygen demand for
stage-I and stage-II was 2220 and 565 kgd-1O2-1, respectively. The power requirement to
meet the oxygen demand of SBR stage-I&II was 150 kW.
Conclusions
Agrochemical effluent is composed of high concentration of ammonia-nitrogen, organic
and inorganic matter. The effluent poses serious threat on aquatic on discharge
environment, and hence essentially requires an effective bio-oxidation process.
Feasibility of SBR system in two stages has studies, designed and implemented on full
scale. Carbon management in the first-stage SBR and nitrogen in the second-stage SBR
fends off microbial competition and improves the process stability through active
interaction of substrates and bacteria that a single-stage conventional process often
suffers. The full scale implementation demonstrates that the sequential batch reactor
system is a techno-economically viable for treating agrochemical effluent.
References
1. Akin, B.S., Ugurlu, A., 2005. Monitoring and control of biological nutrient removal in a
sequencing batch reactor. Process Biochem. 40, 2873-2878.
2. APHA, 2005. Standard Methods for the Examination of Water and Wastewater, 21st
ed. American Public Health Association, Washington, DC, USA.
3. Biswas, R., Bagchi, S., Urewar, C., Gupta, D., Nandy, T., 2010. Treatment of
wastewater from a low-temperature carbonization process industry through biological
and chemical oxidation processes for recycle/reuse: a case study. Water Sci.
Technol. 61 (10), 2563-2573.
4. Delorenzo, M.E., Scott, G.L., Ross, P.E., 2001. Toxicity of pesticides to aquatic
microorganisms: a review. Environ. Toxicol. Chem. 20, 84-98.
4
5. Karkare, M.V., Murthy, Z.V.P., 2012. Kinetic studies on agrochemicals wastewater
treatment by aerobic activated sludge process at high MLSS and high speed
agitation. J. Ind. Eng. Chem. 18 (4), 1301-1307.
6. Kim, Y.M., Park, D., Lee, D.S., Jung, K.A., Park, J.M., 2009. Sudden failure of
biological nitrogen and carbon removal in the full-scale pre-denitrification process
treating cokes wastewater. Bioresour. Technol. 100, 4340-4347.
7. Kim, Y.M., Park, H., Choc, K.H., Park, J.M., 2013. Long term assessment of factors
affecting nitrifying bacteria communities and N-removal in a full-scale biological
process treating high strength hazardous wastewater. Bioresour. Technol. 134, 180189.
8. Mace, S., Mata-Alvarez, J., 2002. Review of SBR technology for wastewater
treatment: an overview. Ind. Eng. Chem. Res. 41, 5539-5553.
9. Manekar, P., Biswas, R., Manikavasagam, K., Nandy, T., 2011b. Novel two stage
biooxidation and chlorination process for high strength hazardous coal carbonization
effluent. J. Hazard. Mater. 189, 92-99.
10. Maranon, E., Vazquez, I., Rodríguez, J., Castrillon, L., Fernandez, Y., 2008a. Coke
wastewater treatment by a three-step activated sludge system. Water Air Soil Pollut.
192, 155-164.
11. Maranon, E., Vazquez, I., Rodríguez, J., Castrillon, L., Fernandez, Y., Lopez, H.,
2008b. Treatment of coke wastewater in a sequential batch reactor (SBR) at pilot
plant scale. Bioresour. Technol. 99, 4192-4198.
12. Marttinen, S.K., Kettunen, R.H., Sormunen, K.M., Soimasuo, R.M., Rintala, J.A.,
2002. Screening of physical–chemical methods for removal of organic material,
nitrogen and toxicity from low strength landfill leachate. Chemosphere 46, 851-858.
13. Vazquez, I., Rodriguez, J., Maranon, E., Castrillon, L., Fernandez, Y., 2006. Study of
the aerobic biodegradation of coke wastewater in a two and three-step activated
sludge process. J. Hazard. Mater. 137, 1681-1688.
14. Yang, S., Yang, F., 2011. Nitrogen removal via short-cut simultaneous nitrification
and denitrification in an intermittently aerated moving bed membrane bioreactor. J.
Hazard. Mater. 195, 318-323.
Table1:Physico-chemical characteristics (range) of Low TDS&high COD and high TDS &
high COD
Multi-streams effluent
Parameters
Low TDS and high COD
High TDS and high COD
5
I&II
10.6-11.3
416-1270
2-68
1290-2020
7120-13760
4000-8780
280-616
2-15
pH
Alkalinity
SS
TDS
COD
BOD
Ammonia
Phenols
Process block
IV
8.1-8.6
150-1860
2-74
1420-2120
1360-2880
2400-3166
11.2-56
10-114
III
9.1-10.3
184-1480
2-4
348-2370
3360-6640
2000-2800
380-716
10-119
I-IV
10.4-11.3
5300-14730
1650-6110
160000-253000
56280-84000
2114-3220
-
All values are expressed in mgl-1, except pH.
Table 2: Performance of existing Aerobic system vis-à-vis Inland Surface Waters
discharge standard norms
a
Parameters
Aerobic system
Discharge Standard
Inlet
outlet
pH
10.0-10.7
6.7-8.1
5.5-9.0
SS
100-200
41 -70
100
550-1502
250
COD
1750-6400
250-505
30
BOD
892-2995
Phenol
2.2-20.9
BDL-2.0
5
172 -400
50
Total NH3 -N
305-385
Indian Standards for discharge into Inland Surface Waters; All values are in mgl−1, except pH.
a
Effluent COD±65
Effluent BOD±20
Effluent Ammonia±40
BOD removal
Effluent COD±25
Effluent Ammonia±4
Nitrite: BDL
COD removal
COD removal
100
25 days operation for each set of HRT
160
-1
600
500
80
400
300
70
200
60
100
0
50
2
3
140
120
90
100
80
80
60
40
70
20
0
4
60
1
HRT, days
Per cent removal
Effluent average concentration, mgl
90
1
100
25 days operation for each set of HRT
Per cent removal
Effluent average concentration, mgl -1
700
Effluent BOD±15
Nitrate±1
BOD removal
Ammonia removal
2
3
4
HRT, days
Fig.1. Performance of SBR stage-I at different HRTs.
Fig.2. Performance of SBR stage-II at different HRTs.
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