Acetogenic Aerobic Sequential Batch Reactors in Series Operation for Textile Wastewater Treatment

Journal of Environmental Treatment Techniques

2020, Volume 8, Issue 2, Pages: 766-769

J. Environ. Treat. Tech.

ISSN: 2309-1185

Journal web link: http://www.jett.dormaj.com

Acetogenic Aerobic Sequential Batch Reactors in

Series Operation for Textile Wastewater Treatment

Nadim Reza Khandaker , Faisal Fahad Rio , Lina Sarkar , Ayesha Sharmin

Department of Civil Engineering, North South University, Bangladesh

Department of Chemistry, Bangladesh University of Engineering and Technology, Bangladesh

Received: 05/08/2019

Accepted: 22/03/2020

Published: 20/05/2020

Abstract

This paper reports on the efficacy of textile wastewater treatment using series operation of acetogenic sequential batch reactor followed

by aerobic sequential batch polishing reactor. The experimental protocol was conducted using wastewater obtained from the equalization

basin of a composite textile wastewater treatment plant. The experimental reactors were operated at the bench level under controlled

conditions. The acetogenic reactor was maintained in a washout mode with daily shock aeration and the aerobic reactor was constantly

aerated. Both acetogenic lead reactor and aerobic polishing reactor influent and effluent water were monitored for color, COD, BOD , TDS,

and pH. The reactor HRT, TSS, F/M ratio, and temperature, were also monitored and controlled. The treatment train was operated till steady

state operation was ensured and the data analyzed to determine the efficacy of the treatment system with respect to textile wastewater

treatment. The results indicated that after a period of culture acclimation high rates of wastewater stabilization was achieved by the system.

The color, BOD , COD, removal efficient were greater than 95%. The experimental program confirmed that acetogenic pretreatment

followed by aerobic polishing is a viable option for treating textile processing wastewater.

Keywords: Textile wastewater, Acetogenic/Aerobic, Treatment

Introduction¹

The complexity of textile wastewater calls for treatment

Acetogenic

Aerobic

systems that are complex requiring multiple stages of treatment.

The process flow train for textile wastewater treatment involves

pH adjustment, colloidal solid and color removal by chemical

addition and clarification, followed by degradation of soluble

biochemical oxygen demand through extended aeration aerobic

treatment (1). The soluble biochemical oxygen demand removal

is the heart of the treatment process with hydraulic retention time

higher than conventional aeration basin application in sewage

treatment. Hydraulic retentive higher than thirteen hours is

mandated by the Department of Environment (2). In actuality

treatment systems are designed with hydraulic detention times

from thirty to eighty hours. Although the combined physical

chemical biological treatment system is the industry norm, the

process is expensive to operate due to the requirement of

chemicals in the chemically aided settling to remove color, and

the high energy intensity of the extended aeration process to

remove the soluble organics. This places an undue burden to

resource challenged countries in developing economies. To make

the textile industry more sustainable we have developed a process

that is independent of chemicals and is also less energy intensive

than the combined physical chemical biological process. This

process is a two-step process, that involves acetogenic treatment

requiring very little aeration as the first step followed by aerobic

polishing.

Treated

water

Wastewater

Figure 1: Schematic of the two stage process

In the proposed process the textile wastewater enters after

screening directly to the acetogenic reactor where acetogenic

microorganisms prevail. The acetogenic reactor has a hydraulic

retention time (HRT) of four days with only a periodic shock

aeration once per day instead of continuous aeration to maintain

acetogenic operation. The reactor effluent is sent to a clarifier

where the acetogenic biomass is recycled back to the acetogenic

reactor periodically to prevent reactor washout. The effluent from

the clarifier is polished in a continuously aerated aerobic reactor

operated in a sequential batch mode. The reactor effluent is passed

through a membrane ensuring that the polishing reactor mixed

liquor suspended solids are kept in the reactor.

Corresponding author: Nadim Reza Khandaker, Department of Civil Engineering, North South University. E-mail:

nadim.khandaker@northsouth.edu.

Journal of Environmental Treatment Techniques

2020, Volume 8, Issue 2, Pages: 766-769

The efficacy of the process was evaluated through a period of

steady state operation ensuring high degree of wastewater

stabilization defined by extent of chemical oxygen demand

effluent samples for the acetogenic reactor were sent for Furrier

Transformation Inferred Spectrophotometric analysis (FT-IR).

(COD), bio chemical oxygen demand (BOD ), and color removal.

The overall objective was to develop an energy efficient

alternative to the conventional treatment process used for textile

wastewater treatment that also does not require any chemicals for

operation. This process will go a long way to make the textile

processing more sustainable.

Materials and Methods

Raw wastewater: The test wastewater was collected from the

wastewater equalization basin of one of the largest towel

manufacturer in the world, Talha Terry Towel, in Gazipur,

Bangladesh. The wastewater was a time proportioned sample

collected over twenty-four hour of operation of the wastewater

treatment plant.

Seed: Both the acetogenic and aerobic polishing rector was

seed with waste mixed liquid suspended solids from the

wastewater treatment plant sludge thickener of the Talha Terry

Towel.

Figure 2: Acetogenic aerobic wastewater treatment used at the bench

level

Specific oxygen consumption (SOUR): The oxygen utilization

rate (OUR) was measured at day twenty by transferrin the aerobic

culture to two 100 ml beakers. One reactor was fed 10 ml

untreated textile wastewater and the other reactor was fed 10 ml

of acetogenic reactor effluent. The surface of the liquid volume

was covered with plastic foil to prevent oxygen transfer and the

reactor dissolved oxygen was measured real time to determine the

oxygen consumption for an hour to determine the OUR. The

Specific oxygen consumption for both the wastewater were then

determined by dividing the OUR by the reactor MLSS.

Reactor Configuration: In the bench scale react setup the

textile wastewater was fed directly to the acetogenic reactor

where acetogenic microorganisms prevailed. The acetogenic

reactor has a hydraulic retention time (HRT) of four days with

only a periodic shock aeration once per day instead of continuous

aeration to maintain acetogenic operation. The acetogenic reactor

effluent was sent to a clarifier where the acetogenic biomass was

recycled back to the acetogenic reactor periodically to prevent

reactor washout. The effluent from the clarifier was polished in a

continuously aerated aerobic reactor operated in a sequential

batch mode with the effluent passed through a membrane

ensuring that the mixed liquor is kept in the reactor. The treated

effluent was analyzed on a daily basis for water quality

parameters.

Anaerobic acetogenic reactor: The bench scale reactor was a

glass vessel with a liquid volume of 1.0 L. The reactor content

was completely mixed (Figure 2). The reactor was maintained at

a (HRT) of 4.0 days. Every day 250 ml was wasted and 250 ml of

the wastewater was fed to the reactor. The short HRT reflects an

operation condition known as washout mode of operation that is

the food to microorganism ration (F/M) increases with every day

of operation. To further prevent methanogenic microorganisms

from growing in the reactor in a daily basis, the reactor content is

purged with air and raise the dissolved oxygen level in the reactor

to 2.0 mg/L (3) (4) (5). Based on our prior experience in operating

anaerobic acetogenic reactor that F/M ratio of greater than 1.0

causes reactor failure (6). To negate this the reactor waste MLSS

recycled back to the acetogenic reactor periodically. The reactor

pH, temperature and MLSS were monitored on a daily basis.

Aerobic Membrane Batch Reactor: The aerobic batch reactor

had a liquid volume of 500 ml and was maintained in a waste feed

mode on a daily basis (50 ml waste/feed volume). The reactor was

continually aerated. The reactor effluent was passed through a

membrane to separate the liquid from the biomass. The MLSS

was not wasted for the duration of the testing program.

Results and Discussions

In line with biological treatment process to treat wastewater

from industries this experimental program looked at textile

processing wastewater treatment possibility using biological

acetogenic process (6, 10, 11). The composite wastewater

characteristic used in the study was a complex wastewater with

high BOD (3500 ± 114 mg/L), COD (5186 ± 138 mg/L), and

color (3540 ± 353 ptco). The BOD/COD ratio of 0.67 makes the

wastewater a good candidate for biological treatment and served

as the challenge wastewater for the combined acetogenic aerobic

polishing treatment process. The total dissolved solids and the

total suspended solids of the test wastewater were 1963 ± 10 mg/L

and 1783 ± 619 mg/L on an individual basis. The pH of he

wastewater was 9.6 ± 0.26.

The picture contrasting the color removal between the

influent untreated wastewater and the treated water along with the

biochemical oxygen demand (BOD ) and the chemical oxygen

demand (COD) removal trends for the combined process are

shown in Figure 3a-c. From the onset the combined acetogenic

aerobic process was able to treat the wastewater to a high degree

of efficiency. Over the period of 20 days of operation the system

consistently achieved complete removal of color as shown by the

picture contrasting the influent blue color and clear treated water

and greater than 95% removal efficiency of BOD , and COD for

the twenty days of operation. Also the system did not require any

period of acclimation prior to achieve the high degree of waste

stabilization observed. The reason may be that the seed source

was from the same wastewater treatment plant where the test

wastewater was from and the culture is already acclimated to the

wastewater. The microorganism present had the ability to produce

Analysis: The composite wastewater was analysed for COD,

BOD

centrifuged and the supernatant was saved on a daily basis and

analysed for COD, BOD , and color for all days of operation as

per standard methods (7). For spaced days of operation saved

, color, and TDS. The aerobic reactor effluent was

Journal of Environmental Treatment Techniques

2020, Volume 8, Issue 2, Pages: 766-769

the enzymes for degradation of the wastewater. The quality of the

treated water (Table 1) is within the regulatory standards of the

Government of Bangladesh Standards for discharge into inland

adjustment for operation, or any color removal chemicals. FT-IR

scan shows that in the acetogenic process complex aromatic

compounds that is the chemical constituents of organic dyes get

broken down.

water bodies such as lakes and rivers of pH = 6-9, BOD < 50

mg/L, COD < 200 mg/L, TSS = 150 mg/L, and color < 150 ptco

Environment, 2008). This emphatically emphasizes that the

(

Table 1: Characteristics of the treated discharge from the bench

scale system

acetogenic pretreatment followed by aerobic polishing is a viable

process of treating textile processing wastewater.

BOD

mg/L)

COD

(mg/L)

Color

(ptco)

TSS

(mg/L)

(

.2 ± 0.10 17.5 ± 5.0 163 ± 10

193 ± 42 77 ± 16

The specific oxygen uptake rate (SOUR) for the acetogenic

pretreated wastewater by the microorganisms in the aerobic

polishing reactor (1.64 mg oxygen/g MLSS-hr). Was 32% less

than that for the untreated influent test wastewater (2.40 mg

oxygen/g MLSS-hr). Acetogenic pre-treatment of textile

processing wastewater produces a net reduction of utilization that

would correlate to less reactor aeration requirement and thus

reduction in the energy required for aeration in the aeration basin.

The acetogenic pretreatment produced and average COD

reduction of the textile processing wastewater by 94% and at the

energy requirement of 3.2 KWh per Kg of COD loading (8) to an

aeration basin one can look at a net saving in energy of aeration

by 15.74 KWh per meter cube of wastewater treated for this test

case wastewater from a composite textile processing facility. The

combination of acetogenic pretreatment followed by aerobic

polishing is a viable energy efficient option of textile processing

wastewater that meets the discharge criteria set by the government

of Bangladesh and will go a long way if scaled up towards

sustainable operation of textile processing facilities wastewater

treatment systems.

(

Conclusion

The combined acetogenic aerobic polishing process is a

viable process for treatment of textile processing wastewater with

over 95% removal of BOD , COD, and color when it was applied

at the bench level to a composite textile processing wastewater.

This process is less energy intensive that extended aeration, did

not require pH adjustment, and chemicals for color removal.

(

Ethical issue

Authors are aware of, and comply with, best practice in

publication ethics specifically with regard to authorship

(avoidance of guest authorship), dual submission, manipulation

of figures, competing interests and compliance with policies on

research ethics. Authors adhere to publication requirements that

submitted work is original and has not been published elsewhere

in any language.

Competing interests

The authors declare that there is no conflict of interest that

would prejudice the impartiality of this scientific work.

(

Figure 3: Acetogenic aerobic wastewater treatment (a) picture of color

removal (b) percent biochemical oxygen demand (BOD ) removal, and

c) percent chemical oxygen demand (COD) removal

Authors’ contribution

All authors of this study have a complete contribution for data

collection, data analyses. Manuscript writing was done by Nadim

Reza Khandaker.

(

The advantage of this process is that it is energy efficient due

to the reduction of BOD loading to the aerobic polishing reactor

for the acetogenic reactor removes BOD , does not require pH

Journal of Environmental Treatment Techniques

2020, Volume 8, Issue 2, Pages: 766-769

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