Journal of Environmental Treatment Techniques  
2020, Volume 8, Issue 2, Pages: 766-769  
J. Environ. Treat. Tech.  
ISSN: 2309-1185  
Journal web link:  
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  
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  
The complexity of textile wastewater calls for treatment  
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  
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:  
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  
Figure 2: Acetogenic aerobic wastewater treatment used at the bench  
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  
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,  
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.  
.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.  
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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