Feasibility of bioengineered two-stages sequential batch reactor and filtration–adsorption process...

Accepted Manuscript

Feasibility of Bioengineered Two Stages Sequential Batch Reactor and Filtra‐

tion-Adsorption Process for Complex Agrochemical Effluent

Pravin Manekar, Rima Biswas, Chaitali Urewar, Sukdeb Pal, Tapas Nandy

PII: S0960-8524(13)01396-5

DOI: http://dx.doi.org/10.1016/j.biortech.2013.08.145

Reference: BITE 12344

To appear in: Bioresource Technology

Received Date: 27 June 2013

Revised Date: 23 August 2013

Accepted Date: 25 August 2013

Please cite this article as: Manekar, P., Biswas, R., Urewar, C., Pal, S., Nandy, T., Feasibility of Bioengineered Two

Stages Sequential Batch Reactor and Filtration-Adsorption Process for Complex Agrochemical Effluent,

Bioresource Technology (2013), doi: http://dx.doi.org/10.1016/j.biortech.2013.08.145

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Feasibility of Bioengineered Two Stages Sequential Batch Reactor and

Filtration-Adsorption Process for Complex Agrochemical Effluent

Pravin Manekar*, Rima Biswas, Chaitali Urewar, Sukdeb Pal, Tapas Nandy

CSIR- National Environmental Engineering Research Institute, Nagpur 440 020, India

Abstract

In the present study, the feasibility of a bioengineered two-stage sequential batch reactor

(BTSSBR) followed by filtration-adsorption process was investigated to treat the agrochemical

effluent by overcoming factor that affecting process stability such as microbial imbalance and

substrate sensitivity. An air stripper stripped 90% of toxic ammonia, and combined with other

streams for bio-oxidation and filtration-adsorption. The BTSSBR system achieved bio-

oxidation at six days hydraulic retention time by fending off microbial imbalance and substrate

sensitivity. The maximum reduction in COD and BOD by heterotrophic bacteria in the first

reactor was 87 and 90%, respectively. Removal of toxic ammoniacal-nitrogen by autotrophic

bacteria in a post-second stage bio-oxidation was 97%. The optimum filtration and adsorption

of pollutants were achieved at a filtration rate of 10 and 9 m3m

-2h

-1, respectively. The treatment

scheme comprising air stripper, BTSSBR and filtration-adsorption process showed a great

promise for treating the agrochemical effluent.

Key words: Agrochemical industry; multistream effluents; air stripper; BTSSBR; filtration-

adsorption process.

*Corresponding author

Tel.: +91 712 2249763;

Fax: +91 712 2249900;

E-mail address: p_manekar@neeri.res.in

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1. Introduction

Agrochemical industries play an important role in Indian economy, and in satisfying the food

needs of 1.21 billion populations. India is the fourth largest producer of agrochemicals after the

United States, Japan and China (FICCI, 2010). Agrochemicals are bioactive agents used for

controlling pests and insects to enhance crop production (Kenawy and Macromol, 1998), and

are classified as pesticides, insecticides, herbicides and fungicides. In India, consumption of

insecticides is around 67% as compared to 33% globally.

Agrochemical industries consume enormous water for producing the pesticides, insecticides,

herbicides and fungicides and generate multistream 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.

Technologies such as multiple effect evaporation (MEE), mechanical vapor recompression and

spray dryers (Vishnu et al., 2008; Narmine et al., 2003), available for treating the high total

dissolved solids (TDS) and high COD effluent are energy intensive. Condensates obtained

through these processes typically low in TDS and high in COD, and are heavily loaded with

toxic ammonia. Steam or air stripper is commonly used to effectively remove ammonia from

wastewater due to its simplicity of operation and cost effectiveness. (Minhalma and Pinho,

2004; Maranon et al., 2008)

Pretreatment technologies for the low TDS and high COD effluent comprise physico-chemical

and biological processes (Minhalma and Pinho, 2004). However, unlike chemical treatment

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biological process does not produce a huge quantity of sludge and thus are more

environmentally friendly (Eckenfelder and Grau, 1992).

Biological processes such as activated sludge process (ASP), sequential batch reactors (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; Chang et al., 2012; Karkare and Murthy,

2012; Sandoval-Carrasco et al., 2013). Recently many new technologies based on anaerobic

ammonium oxidation process (ANAMMOX) have come up such as SHARON-ANAMMOX,

CANON, OLAND, and DEAMOX etc., (Bagchi et al., 2012). However, these technologies are

applicable for wastewater with low C:N ratio. Various researchers have also tested the

possibility of advanced oxidation process such as wet air oxidation, catalytic wet air oxidation,

ozonation and microwave radiation for treatment of complex industrial wastewater (Yang et

al., 2007; Lin et al., 2009).

Agrochemical effluents are typically characterized with high concentrations of COD and

ammonia. Treatment of wastewater with high concentrations of COD and ammonia requires

step-by-step removal of carbon and nitrogen through COD oxidation, nitrification and

denitrification. Such treatment scheme is not only complicated, but also cost intensive. Single

stage process such as ASP with extended aeration and SBR process are often used as an

alternative to nitrification and denitrification process. 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 (Vazque

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

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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 heterotrophs-that oxidized

carbonaceous pollutant and the autotrophs-that oxidized ammonia. This disagreement coupled

with competition between various groups of autotrophic and heterotrophic microorganisms in

the same space for nutrients and oxygen often leads to failure. (Kim et al., 2013a). The

competition become more intense when complex industrial effluent are treated such as effluent

from steel industry, coal carbonization, cove oven industry and municipal leachates, etc.

(Marttien et al., 2002, Pi et al., 2009; Biswas et al., 2010; Manekar et al., 2011) To overcome

the incompatibility between heterotrophic and autotrophic bacteria in a single stage reactor,

two stage processes are often advocated for treating high strength effluent (Luo et al., 2011;

Kim et al., 2013). Agrochemical industry also generates wastewater with high concentration of

COD and ammonia. To the best of our knowledge, no studies have been reported in literature

on biological treatment of agrochemical effluent. This paper described the first ever report on

two stages bio-oxidation of agrochemical effluent for carbon and nitrogen removal.

Additionally, dwindling availability and increasing demand of fresh water have put industries

under intense pressure to comply with the zero liquid effluent discharge (ZLD) norms for

recycling the treated water. In absence of adequate treatment processes, enhanced membrane

fouling, and increased the membrane pressure becomes the bottleneck for producing good

quality recycled water (Manekar et al., 2011).

The objective of the present study is to develop the process for treating the agrochemical

effluent by overcoming the microbial imbalance between the demand and supply of substrate

in autotrophic and heterotrophic bacteria, improving the process stability and finally achieving

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effective treatment with minimum chemical consumption meeting the criteria of MFWQ and

Inland Surface Waters standards of India. A well bioengineered two stage bio-oxidation

processes integrated with physico-chemical could be a viable pretreatment process for treating

and generating MFWQ from agrochemical effluent. Thus, the work aimed at the investigation

of the bioengineered two-stage SBR for treatment of agrochemical effluent. Further to this,

applicability of the physico-chemical techniques such as air stripping and filtration-adsorption

were also explored at the primary and tertiary level. Additionally, herein we also report the

design aspect of the BTSSBR process for setting up a full scale effluent treatment facility.

2. Materials and Methods

2.1 Study area

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, II, III & IV, and produces a comprehensive range of pesticides, technical,

formulations and custom manufactured fine chemicals. Multiple streams of agrochemical

effluents are generated during the manufacturing process.

2.2 Quantify of process effluent

Segregation of process effluents is an important step for isolating specific pollutant and treating

them in a techno-economical way. The complex process effluents generated from the four

manufacturing units (namely block I, II, III &IV) were segregated into three main streams, and

designated as stream A, B & 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 process effluent generated from the

various blocks and their segregation is shown schematically in Fig.1. The quantum of streams

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A, B and C generated were 250, 300 and 30 m3d

-1, respectively. Stream C was directly

incinerated and hence was not considered in the present study.

2.3 Existing treatment facility

Flow scheme of the existing treatment facility is presented in Fig.1. 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 a single-stage aerobic

bioreactor. The sludge from biological process and concentrate from the evaporator system

were dried separately on sludge drying beds, and finally, the dried sludge and concentrate were

disposed off to a treatment storage and disposal facility.

2.4 Effluent sampling

Hourly samples were collected in polypropylene bottles and composited for twenty four hours

at different stages of the effluent treatment plant. The parameters like pH, temperature,

dissolved oxygen (DO) concentration and total dissolved solids (TDS) were immediately

analyzed at the site using a digital multi-meter. The composite samples were also analyzed for

selected parameters relevant to effluent treatment and discharge standards. The parameters such

as suspended solid (SS), chemical oxygen demand (COD), biochemical oxygen demand

(BOD), phenol, and ammonia nitrogen (NH3-N) were analyzed according to the standard

protocols as referred in the Standard Methods for the Examination of Water and Wastewater

(APHA, 2005).

2.5 Experimental setup

Lab scale studies on agrochemical effluent were carried out in a custom made experimental

setup (Fig. 2). Brief descriptions of the experimental setup are given below.

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2.5.1 Air stripper

A vertical glass column (5 cm diameter), uniformly packed with pebbles of an average size

(1.5×0.75 cm2) was used as a stripping medium for ammonia stripping. Effective height of the

stripping bed was 32 cm. Three portions of condensates from the evaporative system was

mixed with one portion of composite stream B (ratio of effluent from blocks II, III and IV

3:3:3), and the pH of the composite effluent was adjusted to specific values (9.5, 10, 11 and

11.5) using 1N NaOH solution. The stripping experiments were conducted by feeding

composite effluent from the top using a peristaltic pump and to facilitate the transfer of

ammonia from the effluent to gas phase, counter current compressed air was injected from the

bottom for a batch period of 2 h. During the batch operation, stripped effluent was continuous

recycled. The studies were carried out on four sets of pH (9.5, 10, 11 and 11.5) and air to

effluent ratio (925, 1100, 1333, and 1525) by varying the feed ammonia concentration from

738 to 1370 mgl-1

for each set.

2.5.2 BTSSBR

Ammonia stripped effluent was treated in a bench scale BTSSBR as shown in Fig. 2. The

BTSSBR consists of two cubical acrylic tanks of size (30×30×30cm3). The first-stage SBR

(FSSBR) was inoculated with the biomass collected from the existing ETP of the

agrochemicals industry. Biomass to be inoculated in SSSBR was obtained from an industrial

nitrification unit and acclimatized for 30 days with domestic sewage. The FSSBR was fed with

stripped effluent (pH 7.2) at different hydraulic retention times (HRTs) in an extended aeration

mode. The bioengineered first and second stage SBRs were operated in a cyclic batch mode

having a time schedule as follows: 2 h-filling, 18 h-aeration (both aerobic); 2 h-settling, 2 h-

decanting (both anoxic).

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The BTSSBR system was optimized by operating reactors at different HTRs (1-4 d). The HRT

was maintained at a desired value by controlling the flow rate of feed using a peristaltic pump.

In the second-stage SBR (SSSBR), the pH was maintained around 6.9± 0.25 using dilute

phosphoric acid. An alkalinity to NH3-N ratio of 5 was maintained by adding sodium

bicarbonate. It also served as a carbon source for autotrophic bacteria. Air was supplied

artificially so as to maintain a DO concentration 2.5 mgl-1

and to ensure proper contact of

substrates and microorganisms during fill and aeration mode. The bio-oxidized effluent from

the BTSSBR was subsequently subjected to a combined filtration-adsorption process.

2.5.3 Combined filtration- adsorption process

2.5.3.1 Sand filtration

First, the bio-oxidized effluent was passed vertically downwards through a packed bed (4 cm

diameter, 3 cm in height) of sand and gravel at different flow rates (7-11m-3

m-2

h-1

). The height

of the gravel (particle size 1-2 cm) bed at the bottom was 5 cm. The middle portion of the

column (18 cm) was filled up with 0.8-1.2 mm, whereas the top 5 cm was packed with sand of

particle size less than 0.8 mm. The uniformity coefficient of sand (D60/D20) was 1.45.

2.5.3.2 Activated carbon column

After effective trapping of suspended solids in the sand filter bed, the filtrate effluent was fed

into the top of a packed bed (4cm×32 cm) of granular activated carbon ( GAC) using a

peristaltic pump. The column flow rate was varied from 7-9 m3m

-2. d

-1. GAC characteristics

were as follows: Sieve size -4+8 BSS; bulk density 0.55 gcc-1

; hardness 96. The residual

organic were adsorbed, and hence got removed as the effluent moved downward through the

GAC bed.

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3. Results and Discussions

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 160000-

253000 and 56280-84000 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& II,

III and 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 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 Performance evaluation of existing treatment facility

The ETP of the agrochemical industry was equipped with multiple effect evaporators (MEE)

and force circulation evaporation (FCE), air stripper and single-stage biological oxidation unit.

The biological unit was operated on the principle of a single-stage carbon-nitrogen removal in a

sequential batch reactor (SBR). The layout of the existing treatment scheme is presented in Fig.

1. The performance of the ETP under the existing operating condition was assessed, and the

physico-chemical characteristics range of feed, concentrate and condensate for MEE and FCE

is presented in Table 2. The TDS concentration of MEE concentrate was 58-73%, and further

concentrated in FCE to 90-92%. The MEE-feed was over loaded with high TDS concentration

(16.0-25.3%) as against 10% design, resulting in high TDS and ammonia concentrations (5040-

5444 and 2260-2870 mgl-1

, respectively) in condensate. This in turn adversely affected the

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performance of the downstream air stripper. The influent and effluent characteristics from air

stripper are presented in Table 3. The stripping efficiency (%), as evident from Table 3 was

extremely poor.

Ammonia laden effluent from the air stripper was biologically treated in a single-stage SBR

operated in a cyclic batch mode with a cyclic period 2 h-filling (oxic); 20 h-mixing and

aeration (oxic); 1 h-settling (anoxic); 1h-decanting (anoxic). Diffused aeration was used for

mixing and aerating the content in SBR tank. The performance of the single-stage SBR and

treated effluent quality as per the stipulated discharge norms into Inland Surface Waters and

required membrane feed water quality for reverse osmosis are summarized in Table 4. The

influent to SBR was high in ammonia concentration (305-385 mgl-1

). The dissolved oxygen

(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 mg l−1

, respectively. The desirable DO

concentration in the tank during aeration period for nitrification is 2.5 mgl-1

. Similarly biomass

concentration as reflected by MLSS should be more than 3000 mg l

−1 for effective bio-

oxidation (Metcalf & Eddy, 2003).

3.3 Bench scale treatability studies

Presence of high concentration of ammonia in the stripped effluent and inadequate removal of

COD and NH3 in the existing single stage SBR demanded further improvement in the treatment

process so as to meet a MFWQ.

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3.3.1 Air stripper

Inadequate air to effluent ratio (430) in the existing air stripper resulted in high concentrations

of ammonia (1428-1834 mg-1

) in stripped effluent. High concentrations of NH3 have toxic

impact on the biological process. To carry out a bench scale experiment, stream B was first pre-

composited from process P-I and II effluent, P-III process effluent and P-IV process effluent in

a ratio of 3:3:4, and further combined with MEE condensate in a ratio of 3:1 before feeding to

the air stripper. The characteristic of air-stripper feed was as follows: pH: 9.2-9.7; TDS: 1460-

2700 mgl-1

; COD: 2889-6320 mgl-1

; BOD: 2000-4833 mgl-1

and ammonia 738-1240 mgl-1

.

The air stripper was operated in a batch mode by varying the feed ammonia concentration for

four sets of pH and air to effluent ratio. During each set, the ammonia removal was observed to

increase with increased in feed pH from 9.5-11.5 and air to effluent ratio (800-1333) (Fig. 3).

Among four sets of experiments conducted with the combined effluent, the highest and the

lowest ammonia removal efficiency achieved was 92% at pH 11.5 and air to effluent ratio

1333 and 59% at pH 9.5 and air to effluent ratio 800, respectively. Volatile COD removal was

25% at pH 9.5 and air to effluent ratio 800 to 45% at pH 11.5 and air to effluent ratio 1333.

The maximum ammonia removal efficiency achieved at an optimum pH of 11.5 and air to

effluent ratio of 1333 with an air flow rate 1.2 ls-1

.

Previously, Pi et al., (2009) and Marttinen et al., (2002) has reported similar results, but with

much higher air to effluent ratio (3500). Supplying air flow rate of 1.4 ls-1

, Quan et al., (2009)

achieved a little higher ammonia removal efficiency (97%). In our case, the ammonia

concentration in the stripped effluent was less than 200 mgl−1

. Thus, the optimized air

stripping process effectively stripped ammonia more than 90% from the combined process

effluent, and helped to reduce the toxic load on the downstream bio-oxidation process.

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However, further treatment of stripped effluent was necessary to remove dissolved

carbonaceous and nitrogenous substrates.

3.3.2 First- stage SBR ( FSSBR)

In the existing treatment facility, 59-65% SS, 72-83% BOD and 68-77% COD removals were

achieved in the single-stage SBR. Ammonia removal was not taking place in the existing

facility even after operating the reactor at an extremely high HRT of 24 days. The treated water

quality from the existing SBR neither conformed to the Indian ISW standard discharged nor

met the MFWQ with respect to BOD, COD and ammonia concentration (Table 4). Due to the

inadequate stripping of ammonia in the air stripper, ammonia laden effluent posed toxicity risks

on the downstream, single-stage bio-oxidation process. This was further confirmed by low

numbers of nitrifying bacteria present in the biomass (7-78×102CFUml

-1) in comparison to total

bacterial counts (500-650×107 CFUml

-1). Nitrification failure due to low population of nitrifiers

in a full- scale plant treating industrial effluent has also been reported by other workers (Kim et

al., 2013a).

Laboratory studies were carried out in a 24 h cyclic first stage bio-oxidation reactor at mixed

liquor suspended solid (MLSS) concentration of 3200-3500 mgl-1

with varying HRTs (1-4

days). The results from this set of the experiments are presented in Fig. 4. 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 three days, COD and

BOD removal efficiency dropped to 80 and 86 %, respectively. Biological process depends on

the bacterial growth/decay rate and HRT that yield desired treatment efficiency. A large reactor

often overrules the economically viability of the treatment. Therefore, to ensure desired

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efficiency yield in a cost-effective way, optimization of HRT is of prime importance to ensure

maximum efficiency yield for the FSSBR. The highest removal of carbonaceous substrate was

obtained at 3d (72 h) HRT with more than 90% removal efficiency. Maranon et al., (2008)

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 FSSBR were as follows:

COD: 400 mgl-1

; BOD 250 mgl-1

; ammonia nitrogen: 200 mgl-1

. The results obtained were

comparatively better than the existing full-scale SBR. This was mainly due to effective

stripping of ammonia in stripper that reduced the toxicity and enhanced the degradation of

carbonaceous substrate through heterotrophic bacteria in FSSBR. However, treated effluent did

not meet the Indian ISW discharge standard. Therefore, further treatment was necessary to

meet the regulatory norms.

3.3.3 SSSBR

Presence of biodegradable COD in ammonia laden effluent directly promoted growth of

heterotrophic bacteria. Also, considering the fact that the growth rate of heterotrophic bacteria

is higher than autotrophic bacteria, nitrification failure due to weeding effect of heterotrophic

bacteria is not unlikely. In single stage process, heterotrophic bacteria out compete the

autotrophic bacteria for space, oxygen demand and other nutrients, resulting in repression of

nitrification. Once the repressed, nitrifying bacteria take a long time to recover (Kim et al.,

2013a). For effective nitrification, it was essential to remove the major portion of organic

matter from the effluent (Metcalf & Eddy, 2003). Thus, the FSSBR oxidized around 90% of

COD at HRT 3 d leaving behind around 200 mgl-1

of ammonia and 400 mgl

-1 of residual COD.

The SSSBR was targeted for nitrification of FSSBR effluent. Therefore, to develop nitrifying

activity in SSSBR biomass from a full-scale nitrifying reactor was acclimatized with FSSBR

effluent. After acclimatization, which lasted for around three months it was found 18% and 7%

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14

of biomass was composed of ammonia oxidizing bacteria (AOB) and nitrite oxidizing bacteria

(NOB) with bacterial count of 5-27×107and 2-10×10

7CFUml

-1, respectively.

The nitrification performance of SSSBR was observed at different HRTs. Fig. 5 presents the

average performance of the SSSBR against varying HRTs of 1, 2, 3and 4 d. 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. The time needed for nitrifying ammonia in the present study was accordance to

removal of carbonaceous and nitrogenous substrates in wastewater by a mixed microbial

population (Metcalf and Eddy, 2003) which takes approximately 5-8 d after the start period of

organics matter degradation. Many researchers have reported a minimum of 2.5 d to 8 d for

more than 70% nitrification efficiency (Amor et al., 2005; Maranon et al., 2008a; Biswas et al.,

2010; Manekar 2011). At 3 d optimal HRT, the SSSBR treated effluent had the following

characteristics COD ≤110 mgl-1

, BOD ≤50 mgl-1

, ammonia ≤10 mgl-1

, nitrite: BDL and nitrate

≤ 7 mgl-1

.

Thus, along with ammonia removal, the COD of 72.5% and BOD of 80% removals were also

observed in SSSBR. Recent studies have revealed that Nitrosomonas sp., can utilize some low

molecular weight organic compound and VOCs. (Arp et al., 2007). Similarly, the heterotrophic

sp., are commonly found in nitrifying system when operated at an extended aeration mode and

various communities co-exist in a manner similar to the natural environment (Biswas et al.,

2011; Kalyeszhnyi et al., 2010). Also, some aerobic heterotrophic bacteria like Bacillus sp., P.

Stutzeri, P. aernginosa, Propinibacteriun theonii, Paracoccus denitrificans etc., that are

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commonly found in a nitrification unit are capable of reducing the both COD and ammonia

(Bagchi et al., 2012).

Results of two stage bio-oxidation process demonstrated that carbon and ammonia served as

the primary substrate to the microorganisms in FSSSBR and SSSBR, respectively.

Heterotrophic bacteria oxidized the carbonaceous substrate to more than 90% efficiency.

Autotrophic bacteria in the SSSBR 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; Manekar et al., 2011a).

Bioengineering of the single-stage biological process into a two-stage 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.

Thus, effective carbon-nitrogen removal in the BTSSBR system was achieved at an optimal

HRT of 6 d. The final effluent from the BTSSBR met the discharge standards for ISW, with

respect to all parameters except BOD.

3.3.4 Tertiary treatment

To achieve MFWQ the effluent from BTSSBR was treated through tertiary treatment. The

sand filter was fed with BTSSBR clarified effluent at different flow rates (8-12 m3m

-2h

-1 for 5

runs). The effect of filtration rates on SS, COD and BOD removal is presented in Fig. 6. The

optimum COD and BOD removals were 40 and 45%, respectively at a filtration rate of 10 m3m

-

2-h

-1. The minimum removal of COD and BOD (25 and 30%, respectively) was obtained at a

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65

16

higher filtration rate of 12 m3m

-2-h

-1. The SS removal efficiency for all the runs was 100%. The

optimum removal efficiencies of SS, COD and BOD (100, 40 and 45%, respectively) as

obtained in this study at a filtration rate of 10 m3m

-2-h

-1 were better than the optimal removal of

these parameters achieved by sand filtration of a post-secondary process effluent at a two

times slower filtration rate of 5 m3m

-2-h

-1 (Hamoda et al., 2004).

Sand-filtered effluent was passed through an activated carbon column at different flow rates (7-

11 m3m

-2h

-1 for 5 runs). The effect of filtration on the BOD and COD removal efficiency is

presented in Fig. 6. The optimum COD and BOD removal (44 and 55%, respectively) was

obtained at a filtration rate of 9 m3m

-2h

-1. The physico-chemical characteristics of GAC treated

effluent were as follows: pH 6.5-7.5, TDS 2700 mgl-1

, COD 50 mgl-1

, BOD 15 mgl-1

and ammonia 10 mgl-1

. The combined filtration- adsorption process was found to consistently

produce membrane feed-quality water from the BTSSBR effluent.

3.4 Design of full-scale ETP

Partial removal of high organic content and ammonia nitrogen from complex agrochemical

effluent through the single-stage bio-oxidation process leads to serious deleterious effects on

the receiving aquatic bodies. Operational parameters of the BTSSBR and combined filtration-

adsorption process optimized in bench scale models were further elaborated to design a

technically viable treatment scheme for agrochemical effluent having low TDS and high COD

content. The main objective of the BTSSBR followed by combined filtration-adsorption

process was to design and implement full-scale ETP to meet the discharge norms for ISW as

well as to produce MFQW for intended reuse. The proposed schematics of the ETP along with

the design characteristics of various unit operations and processes are presented in Fig. 6a, and

the details are presented in Table 5.

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65

17

The equalization basin volume for a detention time of one day required before air stripping is

calculated using the following equation:

timeDetentionFlowVolume

Wherein volume is expressed in m3, flow in m

3d

-1 and detention time in h. The power required

to keep the entire effluent in suspension was 12 kW. The full-scale BTSSBR was designed to

operate in a cyclic batch mode with a time schedule 2 h-filling, 18 h-aeration (both bio-

oxidation); 2 h-settling, 2 h-decanting (both anoxic). The yield coefficient (Y) of the BTSSBR

cycle was 0.4 gg-1

, while the endogenous respiration coefficient (kd) was: 0.035 d-1

. The full-

scale BTSSBR was designed with 6 days total HRT and 3 days at each stage, operating in an

extended aeration mode. The loading rates for FSSBR and SSSBR were 0.750 and 0.083

kgBODm-3

d-1

, respectively. The oxygen demand for the BTSSBR was determined as described

previously (Manekar et al., 2011a). The oxygen demand for the FSSBR and the SSSBR was

2220 and 565 kgd-1

O2-1

, respectively. The power requirement to meet the oxygen demand of

BTSSBR was 150 kW. The sand filtration and activated carbon column were designed for the

optimized filtration rate 10 and 9 m3m

-2h

-1, respectively. The contact time in the adsorption

column was 30 min.

4. Conclusions

Agrochemical effluent is composed of high concentration of ammonia-nitrogen, organic and

inorganic matter. This effluent poses a serious threat on bio-oxidation and aquatic lives, and

hence essentially requires an effective BTSSBR process. Ammonia is stripped in air stripper.

Carbon management in the first-stage and nitrogen in the SSSBR fends off microbial

competition and improves the process stability through active interaction of substrates and

bacteria that a single-stage process often suffers. The study demonstrates that the process

comprising air stripper, bioengineered two-stage sequential batch reactor and filtration-

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65

18

adsorption is a techno-economically viable scheme for treating agrochemical effluent to

environmentally acceptable form.

Acknowledgement

The authors acknowledge Dr. S.R. Wate, Director, CSIR-National Environmental Engineering

Research Institute for providing valuable suggestions during the course of study.

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65

19

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Table 1

Physico-chemical characteristics (range) of stream A and B

Parameters

Multistream effluent

Stream A Stream B

Process block

I-IV I&II III IV

pH 10.4-11.3 10.6-11.3 9.1-10.3 8.1-8.6

Alkalinity 5300-14730 416-1270 184-1480 150-1860

SS 1650-6110 2-68 2-4 2-74

TDS 160000-

253000 1290-2020 348-2370 1420-2120

COD 56280-84000 7120-13760 3360-6640 1360-2880

BOD - 4000-8780 2000-2800 2400-3166

Ammonia 2114-3220 280-616 380-716 11.2-56

Phenols - 2-15 10-119 10-114 All values are expressed in mgl-1, except pH.

Table 2

Physico-chemical characteristics (rangea) of feed, condensate, concentrate for MEE and FCE

Parameters Feed

MEE FCE

Condensate Concentrate Condensate Concentrate pH 10.4-11.3 10.3-10.8 10.7-11.1 11.1-11.2 10.7-10.9

Alkalinity 5300-14730 1020-1620 12140-12800 10800-19100 64700-82700

SS 1650-6110 2-12 11180-133490 96-118 23200-225680

COD 56280-84000 5040-5444 162700-205800 67200-117600 268800-428400

Ammonia 2114-3220 2260-2870 70-1134 1400-2604 126-196

TDS 160000-253000 496-989 582000-737000 43900-144000 622000-820000

Chloride 28031-39760 215-238 157673-158330 7739-34037 168674-173176

Sulphate 9385-25385 BDL-17 40615-67250 5558-5762 54154-88476

Sodium 22724-38029 148-153 121982-135194 7698-24890 135632-155030

Potassium 190-309 2-4 488-541 37-100 620-678 All values are expressed in mgl-1except pH; MEE- Multiple effects evaporator; FCE: forced circulation evaporation

Table 3

Performance of air stripper

Parameters Inlet Outlet after Ammonia removal (%)

0.5 h 1 h 1.5 h 2 h 0.5 h 1 h 1.5 h 2 h

pH 9.4-9.7 9.4-9.7 9.3-9.7 9.4-9.7 9.4-9.7

NR-16 NR-14 4-24 NR-13 COD 5600-6880 4870-5440 4920-5458 4765-4900 5120-5312

TDS 3060-3250 2920-3020 2940-3030 2830-3000 2945-3070

Ammonia 1428-1834 1456-1540 1498-1568 1372-1400 1450-1596

Phenol 100-121 100-127 100-124 100-125 100-122 All values are expressed in mgl-1, except pH. NR- No Renoval.

Table 4

Performance of existing SBR vis-à-vis Inland Surface Waters discharge standard Parameters SBR Discharge standard

a Inlet feed water

quality for RO Inlet Outlet

pH 10.0-10.7 6.7-8.1 5.5-9.0 6.4

SS 100-200 41-70 100 100

COD 1750-6400 550-1502 250 250-350

BOD 892-2995 250-505 30 50-150

Phenol 2.2-20.9 BDL-2.0 5 5

Total NH3-N 305-385 172-400 50 50 aIndian standards for discharge into Inland Surface Waters; All values are in mgl

−1, except pH; BDL-Below

dectable limit.

Table 5

Details of proposed effluent treatment plant

Unit description Quantity Dimension (LxBxD) m

Equalization tank One 12.25x12.25x4(+0.5 FB)

SBR-I Two 14.2x14.2x5(+0.5 FB)

SBR-II Two 13.5x13.5x5(+0.5 FB)

Collection tank One 2 x2 x1.25(+0.3 FB)

Pressure sand filter One 2 Dia.x3(+0.5 FB)

Collection tank One 4.1x4.1x3(+0.5 FB)

Activated carbon tank One 2.1Diax5 height

Treated effluent collection tank One 14.2x14.2x3(+0.5 FB)

Gravity thickener One 3.9 Dia.x3 H (+0.5 FB) L-Length; B-Breath; D-depth; FB-Free board.

Figure Captions

Fig. 1. Flow scheme of multistream effluent generation and treatment of agrochemical

industry.

Fig. 2. Laboratory experimental setup of two-stage SBRs.

Fig. 3. Effect of pH on ammonia removal.

Fig.4. Performance of first-stage bio-oxidation process at different hydraulic retention

time.

Fig.5. Performance of second-stage bio-oxidation process at different hydraulic retention

time.

Fig. 6. Effect of filtration rate on removal of SS, BOD and COD (sand and activated

carbon media).

Fig. 6a. Schematics of proposed treatment process.

Product separation

& mother liquor

Process blocks

(I,II,III,&IV)

Solvent recovery &

product separation

Rotary kiln

incinerator

Forced circulation

evaporator

Multiple effects

evaporators

Rejects to

MEE

Spray

Dryer

Ejector condensate

Bio-oxidation

Membrane System

Ammonia stripper

Permeates

Cooling tower

makeup

Stream B

Stream A

To rotary kiln

incinerator

Stream C

Fig. 1

Dired

salt

Flue gas

Condensate

Fig. 2

Legends FSSBR : First stage SBR DA : Diffused aeration SSSBR : Second stage SBR SSZ : Sludge settling zone C : Compressor SW : Sludge withdrawal P : Pump

Air

feed

P C

P DA

DA

FSSBR SSSBR

SSZ SW

SSZ SW

FSSBR effluent

Feed

Stripped effluent

P

C

Air stripper

To tertiary treatment

50

55

60

65

70

75

0

2

4

6

8

10

12

14

1 2 3 4 5

Inlet ammonia Outlet ammonia

Per cent removal

No. of run Avera

ge a

mm

onia

Conc. m

gl-1

x 1

00

Pe

r ce

nt re

mo

va

l

50

55

60

65

70

75

0

2

4

6

8

10

12

14

1 2 3 4 5No. of run

Per c

ent re

moval

60

65

70

75

80

85

0

2

4

6

8

10

12

14

1 2 3 4 5No. of run

Per c

ent re

moval

70

75

80

85

90

95

0

2

4

6

8

10

12

1 2 3 4 5

Inlet ammonia Outlet ammonia

pH Per cent removal

No. of run

Perc

ent re

moval

pH

andA

mm

onia

concentr

atio

n, m

g/l

70

75

80

85

90

95

0

2

4

6

8

10

12

14

1 2 3 4 5No. of run

Per c

ent re

moval

a) pH:9.5; Air to effluent ratio:800

d) pH:11.5; Air to effluent ratio;1333

b) pH:10; air to effluent ratio:925

c) pH:11; Air to effluent ratio:1100

Avera

ge a

mm

onia

Conc. m

gl-1

x 1

00

Avera

ge a

mm

onia

Conc. m

gl-1

x 1

00

Avera

ge a

mm

onia

Conc. m

gl-1

x 1

00

Fig. 3

0

100

200

300

400

500

600

700

1 2 3 4

50

60

70

80

90

100

Effluent COD±65 Effluent BOD±20

Effluent Ammonia±40 BOD removal

COD removal

25 days operation for each set of HRT

Effl

ue

nt a

vera

ge

co

nce

ntr

atio

n, m

gl-1

Per c

ent re

moval

HRT, days

Fig. 4

60

70

80

90

100

0

5

10

15

20

25

30

35

1 2 3 4

Effluent Ammonia±4 Nitrate±1

Nitrite: BDL Ammonia removal

Per ce

nt re

mova

l

Eff

lue

nt a

vera

ge

co

nce

ntr

atio

n, m

gl-1

HRT, days

25 days operation for each set of HRT

Fig. 5

0

10

20

30

40

50

60

70

7 8 9 10 11 12

COD removal (Sand)

BOD removal (Sand)

BOD removal (Activated carbon)

COD removal (Activated carbon)

Per

cent

rem

oval

Filtration rate m-3m-2d-1

Five sets for each filtration rate

Fig. 6

pH: 6.5-7.5

TDS:2700mgl-1

COD: 100mg l-1

BOD: 30 mg l-1

NH3: 50 mg l-1

Stripper

P

P

CT

Flow: 600m3d

-1

pH: 7.0-7.3

TDS:2700mgl-1

COD: 3000 m l-1

BOD: 2500 mgl-1

NH3: 200 mgl-1

Equalization

basin

P

Flow: 600m3d

-1

pH: 11.5

TDS:2800mgl-1

COD: 5290 mgl-1

NH3: 1395 mgl-1

A

B

o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o

o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o

Centrifuge

P

pH: 6.5-7.5

TDS:2700mgl-1

COD: 250mg l-1

BOD: 100 mg l-1

NH3: 50 mg l-1

pH: 6.8 -7.3

TDS:2700mgl-1

COD: 700mgl-1

BOD: 250 mgl-1

NH3: 200 mgl-1

CT CT ACC

Gravity

thickener

Sludge collection tank

SBR stage-II SBR stage-I

P

P P

Legend o - Diffused aeration P - Pump

- Mixer

A - Sodium hydroxide tanks B& B1 - Orthophosphoric acid tanks C - Sodium bicarbonate SBR - Sequential batch reactor PSF - Pressure sand filter ACC - Activated carbon column MEE - Multiple effects evaporator TSDF - Treatment storage and disposal facility SDBs - Sludge drying beds.

B1 C

P Process from Blocks Effluent I-V

MEE Condensate

P

P

PSF

Membrane separation process

Supernatant

P P

TSDF

SDBs

Fig. 6a

Highlights

We investigated applicability of BTSSBR as against SSBR for agrochemical effluent.

More than 90% of ammonia was removed in air stripper improving BTSSBR system.

BTSSBR system fends off competition between heterotrophic and autotrophic bacteria.

Air stripper, BTSSBR and filtration-adsorption process treat agrochemical effluent.

Bioengineered

Graphical abstract

Single stage bio-oxidation process BTSSBR process