Abstract

NO3-N and dye colors discharged from textile wastewater pose environmental problems in Thailand. This study aimed to observe the nitrogen removal rate (NRR) with and without RB-5 color contamination via hydrogenotrophic denitrification (HD) processing, which uses H2 gas as electron donor to reduce NO3-N and NO2-N; comparing with bioreactors treatment to evaluate systems that can simultaneously remove NO3-N and dye color. Five reactors under different operation and gas supply conditions were set-up under HRT of 24 h, including an aerobic reactor using air, two anaerobic reactors using argon and H2, and a combined process using intermittent air/argon and air/H2. NRR without dye varied between 45 and 90% for H2 and air/H2 by HD processing, while it was completely removed when adding color. H2 and air/H2 reactors experienced partial decolorization of approximately 20–30%, whereas the other three reactors remained unchanged. Effluent of NO3-N were close to wastewater standards, but the color was still easy to detect, which indicated that the treatment time needs to be sufficient. In conclusion, HD and intermittent air/H2 processing can completely remove NO3-N and NO2-N when contaminated with RB-5 color. Furthermore, RB-5 did not affect the NRR, whereas some particles of dye color can also reduce in these processes.

HIGHLIGHTS

  • NRR with and without RB-5 dye contamination was evaluated in HD reactors and compared with bioreactors under various conditions using air, argon and H2 gas supplies.

  • Simultaneous NO3-N, NO2-N and RB-5 dye removal occurred in H2 and combined air/H2 reactors.

  • HD processing accelerated when contaminated with RB-5 dye.

  • RB-5 dye does not affect the NRR removal, while some partial removal can occur with HD processing.

  • NO3-N, NO2-N was removed faster than RB-5 dye color.

Graphical Abstract

Graphical Abstract
Graphical Abstract

INTRODUCTION

Thailand is a newly industrialized and developing country, and textiles are one of its most important export industries, with 14,400 tons/yr of leather and textile fibers being produced and exported. Various processing stages such as bleaching, dyeing, printing, finishing, sizing and stiffening use chemical reagents and large volumes of water, thereby generating huge quantities of effluent wastewater that require discharging. Presently, the textile industry in Thailand generates approximately 2.55 × 106 m3/yr of wastewater contaminated with various toxic pollutants, in particular, nitrate (NO3-N) (Sahinkaya et al. 2017; Sairiam et al. 2019). NO3-N is a common pollutant that can be converted into nitrite (NO2-N), which is another toxic pollutant generally found in groundwater, surface water, and wastewater. Normally, NO3-N from textile wastewater is produced from salts such as sodium nitrate used in dye baths to improve textile fibers. The concentration of NO3-N can be in the range of 40–100 g/L in textile effluents (Cirik et al. 2013). These levels are problematic and have a harmful impact on groundwater and human health, for example, they cause methemoglobin in children (Rahman et al. 2020). The World Health Organization (WHO) recommends NO3-N and NO2-N concentration to be less than 11.3 and 0.91 mg/L in drinking water, respectively (WHO 2011). Many techniques have been developed to treat NO3-N pollution, including chemical–physical processes such as ion exchanger and ultra-filtration reverse osmosis, and biological denitrification. The biological denitrification system involves both heterotrophic and autotrophic processes and is commonly applied for treating NO3-N and NO2-N. The system is based on the respiration of facultative bacteria as heterotrophic denitrification bacteria (HDB) and autotrophic denitrification bacteria (ADB), with NO3-N used as an electron acceptor under anaerobic and anoxic conditions.

Hydrogenotrophic denitrification (HD) or hydrogen-based autotrophic denitrification is a type of treatment processing that is used to reduce inorganic compounds such as NO3-N and NO2-N using H2 as electron donors, and bicarbonate or carbon dioxide for biosynthesis. Owing to its low biomass, low residual organic compounds, low system costs and high nitrogen removal efficiency compared with heterotrophic denitrification, HD is most commonly used to treat groundwater (Eamrat 2017). Theoretical equations for heterotrophic (Equation (1)) and hydrogenotrophic (Equation (2)) denitrification are given below.

Heterotrophic denitrification using methanol as a carbon source (Rezvani et al. 2017): 
formula
(1)
HD using bicarbonate as an inorganic carbon source and H2 as electron donors (Rujakom et al. 2019): 
formula
(2)
However, various HD systems have been developed for municipal wastewater treatment, while only a few studies have reported on its application in industrial and textile wastewater treatment. As textile wastewater has a high pollutant contamination, mainly due to the variety of dyes used in the textile industry, the concentration of pollutants in this type of wastewater often does not adhere to the current wastewater standards in Thailand. The characteristics of textile wastewater in Thailand are presented in Table 1.
Table 1

Characteristics of wastewater from the textile industry in Thailand

ParametersEffluent industrial wastewater standard in ThailandInfluentaEffluentbEffluentc
pH 5.5–9 7.0 7.77 – 
BOD (mg/L) < 60 800–1200 1050 90–250 
COD (mg/L) ≤ 400 6000–8000 3056 800 
TN (mg/L) ≤ 100 100–700 154 50 
TSS (mg/L) ≤ 150 1500–3000 975 – 
TDS (mg/L) ≤ 3,000 8725 4000–9000 – 
Cr3+(mg/L) ≤ 0.5 – 13 0.2 
Color (ADMI) Not objectionable 800–1200 – 450 
Color (mg/L)d 40–500 – 2–112 
ParametersEffluent industrial wastewater standard in ThailandInfluentaEffluentbEffluentc
pH 5.5–9 7.0 7.77 – 
BOD (mg/L) < 60 800–1200 1050 90–250 
COD (mg/L) ≤ 400 6000–8000 3056 800 
TN (mg/L) ≤ 100 100–700 154 50 
TSS (mg/L) ≤ 150 1500–3000 975 – 
TDS (mg/L) ≤ 3,000 8725 4000–9000 – 
Cr3+(mg/L) ≤ 0.5 – 13 0.2 
Color (ADMI) Not objectionable 800–1200 – 450 
Color (mg/L)d 40–500 – 2–112 

a,cInfluent and effluent qualities from a textile factory in Thailand).

bEffluent textile wastewater from the central wastewater treatment plant in Thailand.

dInfluent and effluent color concentrations from anaerobic and combined anaerobic/aerobic treatment processing in Thailand (2015).

Dye colors that are mostly made from organic acids and salts, inorganic acid and salts, a bleaching agent, and trace metals, are usually discharged into an effluent as 50% of the influent feed. Even a small portion of dye color is highly visible and can influence the visual appearance of streams and other water resources. Generally, dye colors can be removed under anaerobic and combined systems through anoxic processes because the reductive cleavage of the azo bond that occurs as an electron acceptor can transfer to aromatic amines under anaerobic conditions. Consequently, aromatic amines are generated and then reduced under aerobic conditions (Sheng et al. 2018). Therefore, modern wastewater treatment processes such as adsorption, electrochemical oxidation, ozone, ion exchange, membrane and biological processing are used to treat textile wastewater. However, effective treatments of NO3-N and dye color are often low in anaerobic treatment processes due to bacterial activities and the deficiency of electron donors. Electron donation is a key step in the removal of NO3-N, NO2-N, and color (Li et al. 2014). A previous study that focused on the effect of NO3-N removal on anaerobic azo dye reduction with various electron donors, i.e. acetate, methyl-group, and CO2/H2, found no observable dye color in the effluent, whereas CO2/H2 was determined to be the best electron donor (Saroyan et al. 2019). The study also found that H2 gas and formate are better electron-donors for decolorization than acetate and methanol.

Hence, the primary aim of this study was to apply HD treatment processing to remove high concentrations of NO3-N from wastewater when it is contaminated with dye color. This study also attempts to evaluate the systems that can simultaneously reduce NO3-N contaminated with dye color in a single reactor. For this purpose, five reactors were set up under the following process conditions, i.e. aerobic, anaerobic, and combined system, to investigate the treatment performance in the simultaneous removal of NO3-N and NO2-N, without and with dye contamination. In the aerobic system, air was constantly supplied to a reactor to observe the effect of all parameters when mixed with oxygen. Two anaerobic reactors were operated using various types of biological denitrification: the first was heterotrophic and operated using argon supplies, while the other used HD processing and was supplied with H2 gas, which acted as the electron donor. The combined system (anaerobic/aerobic), which is widely used in the removal of dye color and organic matter, was supplied by an intermittent feeding of air/argon and an air/H2 supply. Reactive Black 5 (RB-5), which is a type of azo dye color and is most commonly used in dyeing processes, was selected as the model dye color combined with NO3-N contamination.

MATERIALS AND METHODS

Experimental configuration

Five reactors under various operating conditions were set up including an aerobic (with air), two anaerobic (one with argon and another with H2), and a combined system reactor (one with air/argon and another with air/H2); these reactors were used to observe the treatment performance for the removal of NO3-N, NO2-N, and dye color. All the reactors that were made from plastic were fabricated in a cylindrical form; 3.5 cm in diameter and 28 cm in height. The working volume of each of the reactors was approximately 2 L. All the reactors were fixed inside a water tub to control their temperatures in the range of 30–33 °C. Furthermore, the reactors were connected with an influent synthetic wastewater tank, and for gas feeding, the pipe lines were fixed on the operating conditions of the reactors. The schematic of the experimental configuration of the reactors is depicted in Figure 1.

Figure 1

Schematic of the experimental setup.

Figure 1

Schematic of the experimental setup.

Preparation of synthetic textile wastewater

Synthetic wastewater was prepared using tap water based on the actual concentrations and the chemical reagents (g/L) adapted from a previous study (Panswad & Luangdilok 2000). The composition of wastewater is presented in Table 2. The influent NO3-N concentrations considered in this study ranged from 40, 50 and reached 80 mg-N/L at the end of the experiment. In the second phase, RB-5 dye color was added into these reactors. The dye concentration for all the reactors was 80 mg/L in the primary phase, reduced to 20 mg/L toward the end of the experiment. RB-5 was obtained from the Fujifilm Wako Pure Chemical Corporation. Co., Ltd (Sigma-Aldrich, US). More information about the dye is provided in Table 3 (Bouraie & Din 2016).

Table 2

Composition of synthetic wastewater

ChemicalConcentration (mg/L
NaNO3 0.486 g/L as 80 mg NO3-N/L 
KH2PO4 0.110 g/L as 12.5 mg P 
NaHCO3 1.0 g/L as an inorganic carbon source 
CaCl2 0.021 g/L as 7.5 mg Ca 
MgSO4.7H20.038 g/L as 3.75 mg Mg 
Trace elements (I)a 1 ml/L 
Trace elements (II)b 1 ml/L 
Reactive Black 5 dye 0.08 g/L as 80 mg/L color 
ChemicalConcentration (mg/L
NaNO3 0.486 g/L as 80 mg NO3-N/L 
KH2PO4 0.110 g/L as 12.5 mg P 
NaHCO3 1.0 g/L as an inorganic carbon source 
CaCl2 0.021 g/L as 7.5 mg Ca 
MgSO4.7H20.038 g/L as 3.75 mg Mg 
Trace elements (I)a 1 ml/L 
Trace elements (II)b 1 ml/L 
Reactive Black 5 dye 0.08 g/L as 80 mg/L color 

aTrace element I contained: 5 g/L EDTA and 5 g/L FeSO4.

bTrace element II contained: 15 g/L EDTA, 0.43 g/L ZnSO4.7H2O, 0.24 g/L CoCl2.6H2O, 1 g/L MnCl2.4H2O, 0.25 g/L CuSO4.6H2O, 0.22 g/L MnCl2.5H2O, 0.22 g/L NaMoO4.5H2O, 0.19 g/L NiCl2.6H2O, 0.21 g/L NaSeO4.10H2O, and 0.014 g/L H3BO4.

Table 3

Commercial information of Reactive Black 5 dye color

Color indexReactive Black 5Dye structure
Type Reactive  
Synonyms Remazol BlacK B 
λmax 597 nm 
Molecular formula C26H21N5Na4O19S6 
Molecular weight 991.82 g/mol 
Color indexReactive Black 5Dye structure
Type Reactive  
Synonyms Remazol BlacK B 
λmax 597 nm 
Molecular formula C26H21N5Na4O19S6 
Molecular weight 991.82 g/mol 

Influent loading rate and gas supply conditions

To examine the influent loading rates, experiments were conducted in two phases: NO3-N without RB-5 contamination, and NO3-N with RB-5 contamination. The treatment performance of each reactor was tested for 24 h, in a continuous feeding mode. At the beginning, the enhanced sludge from the HD reactor, which was operating for more than 400 d, was added to each reactor. This reactor was operated at an HRT of 8 h at a controlled temperature of 30 °C and fed with influent water at approximately 8.7 mL/min, with an H2 supply of 30 mL/min. The nitrogen loading rate (NLR) was 313 g-N/m3/d. The HD reactor showed the best performance, with the removal rates of NO3-N and NO2-N close to 85–95%. The enriched sludge was added between 0.2 and 0.4 g of volatile suspended solids (VSS)/L to each reactor. In the first phase in days 1–7, the air, argon, air/argon, and air/H2 gas reactors were set up to maintain an NLR of 40 g-N/m3/d. On day 8, the H2 reactor was constructed, and an NLR of 50 g-N/m3/d was maintained in all the reactors. On day 18, an NLR of 80 g-N/m3/d was maintained in the air, argon, air/argon, and air/H2 reactors; this change was also done on day 11 for the H2 reactor. These changes were made to observe the effect on the nitrogen removal rate (NRR) when the influent loading is increased. In the second phase, NO3-N with RB-5 was introduced on day 33 for all the reactors except for the H2 reactor, where the pollutant was introduced on day 27, at 80 mg/L of RB-5 (amount equivalent to NLR). On day 48, for the four reactors, and on day 42, for the H2 reactor, the RB-5 dose was reduced to 20 mg/L to isolate the effect of NO3-N removal on the dye.

For gas supply feeding, the pipelines were fixed depending on the operating conditions of each reactor. One of the aerobic reactors was continuously supplied with air to grow aerobic bacteria, while the two anaerobic reactors were continuously supplied with argon and H2 gas for bacterial growth and for the comparison of treatment performances under the presence of heterotrophic and hydrogenotrophic denitrifying bacteria, respectively. Of the other two reactors, one was intermittently supplied with air/argon and the other with air/H2, and controlled under the combined anaerobic/aerobic system. Air was released from an air pump to each reactor, while argon was discharged from a cylinder tank and H2 was supplied from an H2 generator, via an air stone diffuser. Initially, the volume of the continuous supply of air and argon was controlled at 300 mL/min, and H2 at 100 mL/min. After a supply of 18 days of air and argon supply, and 12 days of H2, it was reduced to 50 mL/min. For the intermittently fed reactors of air/argon and air/H2, all the gases including air, argon, and H2 were supplied at 50 mL/min under an aerobic to non-aerobic time ratio of 30:60 min and controlled using a timer. Plastic beads were selected to cover the top of each reactor to maintain the anaerobic conditions, whereas a magnetic stirrer was used to mix the liquid and sludge. The experimental conditions are detailed in Table 4.

Table 4

Summary of the operating conditions used in this study

Operating condition
Phase I (without RB-5 dye)
Phase II (with RB-5 dye)
Time (day) Air, Argon, Air/argon and Air/H2 reactors 1–7 8–17 18–32 33–47 48–66 
H2 Reactor – 0–10 11–26 27–41 42–60 
Influent feeding NO3-N (mg/L) 40 50 80–85 80–85 80 
RB-5 dye color (mg-N/L) – – – 80 20 
Gas supply conditions Continuous feeding (mL/min) Air 300 300 50 50 50 
Argon 300 300 50 50 50 
H2 100 100 50 50 50 
Intermittent feeding (mL/min) Air/Argon
Air/H2 
Cycle Times 30 min of aerobic and 60 min of non-aerobic 
Gas flow 50 mL/min in each type 
Operating condition
Phase I (without RB-5 dye)
Phase II (with RB-5 dye)
Time (day) Air, Argon, Air/argon and Air/H2 reactors 1–7 8–17 18–32 33–47 48–66 
H2 Reactor – 0–10 11–26 27–41 42–60 
Influent feeding NO3-N (mg/L) 40 50 80–85 80–85 80 
RB-5 dye color (mg-N/L) – – – 80 20 
Gas supply conditions Continuous feeding (mL/min) Air 300 300 50 50 50 
Argon 300 300 50 50 50 
H2 100 100 50 50 50 
Intermittent feeding (mL/min) Air/Argon
Air/H2 
Cycle Times 30 min of aerobic and 60 min of non-aerobic 
Gas flow 50 mL/min in each type 

Analytical methods

The influent and effluent from all the reactors were centrifuged (Hitachi CF 16RXII, Japan) at 10,000 rpm for 10 min, and stored in a freezer (–18 °C) until the analyses. pH, dissolved oxygen (DO), and dissolved hydrogen (DH) were directly measured inside the reactors using a pH meter (Horiba-B712, Japan) and DO probe (YSI 58 Dissolved Oxygen Meter, Japan), respectively. The temperature was checked with a digital thermometer (WT-6, China). NO3-N and NO2-N concentrations were then measured using the exhausting ultraviolet spectrophotometric screening method for NO3-N and a colorimetric method for NO2-N (UV-1800, Shimadzu-Spectrophotometer, Japan) (APHA 2012). Moreover, the rate of decolorization was calculated on the basis of the Lambert–Beer law as various concentrations of RB-5 were prepared, and their absorbance values were measured at a maximum wavelength of RB-5 at 597 nm in a spectrophotometer. The abscissa were presented dye concentrations and the absorbance values as the ordinate, a standard curve draw of the correlation coefficient corrected was R2 = 0.9980 and linear equation was y = 0.0214x + 0.0201 (Assadi et al. 2018). However, the nitrogen removal and decolorization efficiency were calculated using Equations (3)–(6): 
formula
(3)
 
formula
(4)
 
formula
(5)
 
formula
(6)

Statistical analysis

To test the differences between the treatments performance of decolorization, all the reactors during the second phase were analyzed by the analysis of variance (ANOVA) and least significant difference (LSD) using the SPSS statistical software tool version 25. Statistical significance was kept at p < 0.05.

RESULTS AND DISCUSSION

Effluent NO3-N and NO2-N concentrations

In this study, the reactors were continuously fed with synthetic wastewater at an HRT of 24 h to observe the nitrogen removal rate (NRR). The experiments were conducted in two phases: the first NO3-N did not contain the RB-5 dye color contamination, while the second did. Influent concentrations of NO3-N feeding varied between 40 and 85 g-N/m3/d. The actual effluent NO3-N and NO2-N concentrations and nitrogen removal efficiency from all the reactors by operating times are provided in Figure 2(a)–2(j).

Figure 2

NO3-N and NO2-N concentrations and nitrogen efficiency during two phases of operation (a) and (b) from Air reactor, (c) and (d) from Argon reactor, (e) and (f) from H2 reactor, (g) and (h) from Air/argon reactor and (i) and (j) from Air/H2 reactor.

Figure 2

NO3-N and NO2-N concentrations and nitrogen efficiency during two phases of operation (a) and (b) from Air reactor, (c) and (d) from Argon reactor, (e) and (f) from H2 reactor, (g) and (h) from Air/argon reactor and (i) and (j) from Air/H2 reactor.

Figure 2(a) and 2(b) shows the results from the reactor that was continuously fed with air: the effluent concentration of NO3-N was stable at the same amount of influent feeding, while NO2-N concentration and NRR were close to zero. Under anaerobic conditions, the reactors were separated into two reactors to compare the treatment performance by various types of denitrifying bacteria under continuous feeding with argon to make heterotrophic conditions as shown in Figure 2(c) and 2(d), and the other with H2 as hydrogenotrophic conditions (HD) as shown in Figure 2(e) and 2(f). The results of NO3-N and NO2-N concentrations from the argon reactor had still accumulated with the same amount of influent feeding; this was similar to the results obtained from the air reactor; however, NO2-N concentration and NRR were also close to zero. However, the conditions in these reactors were almost entirely anaerobic; the DO concentrations were found to be ranging from 0.15 to 4.70 mg/L. On the contrary, the results showed that the NO3-N and NO2-N removal rates were acceptable when H2 was supplied as shown in Figure 2(e) (without RB-5 dye) and Figure 2(f) (with RB-5 dye). During the addition of 50 g-N/m3/d from day 1 to 10 into this reactor, with a 100 mL/min H2 gas supply, the NO3-N and NO2-N effluent concentrations reached only around 10 mg-N/L on day 1 due to the start-up process and slow growth of denitrifying bacteria. On day 11, after the influent loading rate increased to 80 g-N/m3/d and the H2 supply dropped to 50 mL/min, there was a minimal change in the NO3-N and NO2-N concentrations owing to the lack of electron donors (H2). We found that H2 and a high concentration of influent load can affect the nitrogen accumulation rate. Therefore, the nitrogen removal efficiency of this phase decreased but remained stable in the range of 80–100%. After day 27, 80 mg/L of RB-5 was added. This amount was decreased to 20 mg/L on day 42. Concentrations of NO3-N and NO2-N in the effluent at this stage were nearly zero, whereas the nitrogen removal efficiency was stable and close to 100%. Hence, the nitrogen removal efficiency improved in the second phase compared to that in the first phase where RB-5 was not added.

In the combined system under intermittent gas supplies including air/argon and air/H2, as shown in Figure 2(g)–2(j), respectively, the NO3-N and NO2-N concentration decreased noticeably in the air/H2 reactor. In the first phase, as shown in Figure 2(i), the results from air/H2 highlighted that NO3-N and NO2-N concentrations in this reactor were still high due to the HD process being incomplete. The treatment performance of NRR was reduced when the influent loading rate increased. However, after the addition of dye color (day 33), as shown in Figure 2(j), NO3-N effluent concentrations decreased; and the increase in NO2-N concentrations was significantly higher than that without dye color feeding. Moreover, after day 48, influent dye concentration decreased from 80 to 20 mg/L. The results showed that NO3-N and NO2-N effluent concentrations were higher than the previous concentration while NRR also dropped. Therefore, the concentration of dye color may be effective for the NO3-N and NO2-N removal. However, the nitrogen removal efficiency in this reactor fluctuated more as compared to the H2 reactor and was dependent on the amount of NO3-N and NO2-N accumulations in each operating time, in the range of 45–90% and 80–100%, with and without RB-5 dye, respectively. Hence, the air/H2 reactor showed a reduction to the levels lower than in the H2 reactor because the air or oxygen usually slowed down the HD process. The DO concentrations confirmed the effect of oxygen on NRR in this reactor. The DO concentrations in the air/H2 reactor ranged from 0.04 to 5.90 mg/L. The recommended value of DO concentration for improving NRR varies between 0.5 and 0.8 mg/L. However, DO concentrations higher than 4.5 mg/L in the anaerobic and combined system can affect nitrogen removal. Previous studies found that when oxygen ranges from 0.36 to 3.36% under anaerobic conditions, it can inhibit nitrate removal while denitrifying bacteria in the high oxygen environment does not synthesize the nitrogen-reducing enzyme (Griessmeier et al. 2019). As the results for the air reactor are the same; NRR is close to zero because high value oxygen mixing may have affected the bacterial growth rate in this reactor.

In this experiment, NO3-N and NO2-N of the H2 and air/H2 reactors were completely removed by the HD process that occurred in both reactors. Denitrifying bacteria, which are autotrophic organisms, were used as the electron donor from H2 with HCO3 as an inorganic carbon source.to completely reduce NO3-N and NO2-N under hydrogenotrophic processing. Notably, the pH increased in both reactors. The pH of effluent wastewater varied between 9.47 and 11.17 in the H2 reactor and between 9.21 and 11.05 in the air/H2 reactor; the original pH values were in the range of 8.02–8.50 during influent feeding. As the HD process occurred in both reactors, one acid equivalent (H+) was consumed based on a stoichiometric equation for NO3-N reduced to N2 gas, which converts to an alkalinity rate of 3.579 g per 1 g of NO3-N reduced. This concentration can lead to an increase in the pH values in these reactors. In contrast, the pH concentrations from the air, argon and air/argon reactors were the same as those in influent feeding, thereby proving that no reaction occurred in these reactors. According to the previous reports, the optimum pH conditions for the HD process ranged from 7.6 to 8.6 (Eamrat 2017). Similarly, pH levels from 9.13 to 9.93 can lead to high denitrification rates (Li et al. 2013). Conversely, owing to the lack of carbon sources in air, argon and air/argon can lead to a slower NO3-N reduction and bacterial growth compared to the heterotrophic process using organic matter.

In conclusion, HD processing can completely reduce NO3-N and NO2-N when contaminated with RB-5 dye; in contrast, this dye color did not affect the combined NO3-N and NO2-N removal. The dye color also did not significantly affect NO3-N removal because NO3-N had a faster oxidation-reduction reaction than the dye color (Panswad & Luangdilok 2000; Cirik et al. 2013). Furthermore, dye color can lead to an increase in the reaction rates of NO3-N and NO2-N, thus reducing the time required for treatment.

Effluent dye color concentrations

The biological degradation of a dye mostly occurs in anaerobic processes by the reductive cleavage of dye bonds and through an oxidation-reduction reaction that removes aromatic amines in the aerobic process. Conversely, the dye is an electron acceptor with limited reduction when it exists alongside more effective electron acceptors (Assadi et al. 2018; Chen et al. 2018). In this experiment, the treatment efficiencies of RB-5 dye when contaminated with NO3-N under different operating conditions were investigated using various dye concentrations. In the first stage, 80 mg/L of RB-5 dye color was fed into the air, argon, air/argon, and air/H2 reactors on days 33–47, which was then decreased to 20 mg/L on days 48–66. Similarly, 80 mg/L of RB-5 dye coloring was added to the H2 reactor on day 27, which was then reduced to 20 mg/L on day 42. The effluent RB-5 dye concentrations and decolorization rate of all reactors are shown in Figure 3(a)–3(e).

Figure 3

RB-5 dye concentrations and decolorization rate. (a) from Air reactor; (b) Argon reactor; (c) H2 reactor; (d) Air/argon reactor; (e) Air/H2 reactor.

Figure 3

RB-5 dye concentrations and decolorization rate. (a) from Air reactor; (b) Argon reactor; (c) H2 reactor; (d) Air/argon reactor; (e) Air/H2 reactor.

The statistical analysis results showed that different operating conditions and gas feeding had significant interaction effects on the effluent concentrations of the dye color. The dye color concentration was slightly reduced in both the H2 and air/H2 reactors as shown Figure 3(c)–3(e). The dye color amounts in these reactors decreased at a slightly faster rate than in the other reactors. The dye concentrations in the air, argon and air/argon reactors accumulated at a constant influent feeding rate, as presented in Figure 3(a), 3(b) and 3(d). A lack of bacterial growth incompletely influenced the biodegradation processing. The results show that the decolorization rate was approximately 20–35% in H2 and 10–20% in air/H2 reactors, respectively. The average effluent concentrations in the H2 and air/H2 reactors were approximately 58 and 67 mg/L at a feeding rate of 80 mg/L of RB-5, and 16 and 18 at a feeding rate of 20 mg/L of RB-5, respectively. However, the decolorization rates remained unchanged when the dye concentration was reduced from 80 to 20 mg/L. Hence, the RB-5 dye color can cause a slight reduction together with NO3-N and NO2-N during HD processing.

Dissolved organic carbon (DOC) was measured for the influent and effluent to check the bacterial activities in both reactors. The results of DOC increased by 23.4 and 13.7 mg/L for the H2 and air/H2 reactors, respectively, while the influent feeding DOC result was 8.5 mg/L. The DOC value may have increased from ADB activity that produced extracellular polymeric substances (ESP), which are biopolymers used to protect cells from external environmental or strength conditions. Bacterial activities in these reactors can help in the removal of NO3-N along with the dye color by the process of denitrification. Hence, the metabolism of ADB under HD processing can also generate NADH, which is another factor that facilitates dye color removal using azo-reductases to break azo bonds in the dye molecule, which then act as electron acceptors to produce colorless aromatic amines. One of the advantages of using H2 gas for decolorization is that its electron-donating substrates can reduce and charge form of azo dye to aromatic amines (Saroyan et al. 2019). However, the reduction in dye concentrations was very minimal in the H2 reactor and, to a slightly larger extent, in the air/H2 reactor in the presence of NO3-N. The dye color was removed faster in the presence of lower NO3-N concentration (Lourenço et al. 2000). Conversely, oxygen and NO3-N are more active electron acceptors than a dye, and lead to incomplete decolorization (Lee et al. 2010).

Table 1 shows that the actual influent and effluent concentrations of dye color under anaerobic and combined anaerobic/aerobic treatment processing in Thailand were found in the range of 40–500 mg/L reducing to 2–112 mg/L due to effective treatment processing and long-term operation. Hence, HRT is a crucial factor that can improve the treatment efficiency of decolorization using HD and the combined system in this study.

Relationship between nitrogen removal and decolorization rate

Table 5 presents the relationship between NRR compared with the decolorization rate from all the reactors under different influent feeding regimes, including actual NO3-N and NO3-N contaminated with RB-5 dye. NRR and dye were mostly removed in the anaerobic and combined systems when H2 gas was used during HD processing, whereas the aerobic, anaerobic, and combined systems using air and argon gas remained unchanged.

Table 5

Summary of the average nitrogen efficiency compared to the decolorization rate

ReactorHRT (h)Nitrogen efficiency (%)
Decolorization rate (%)
Reference
Without RB-5With 80 mg/L of RB-5With 20 mg/L of RB-5With 80 mg/L of RB-5With 20 mg/L of RB-5
Air  This study 
Argon 24 
H2 95 100 100 28 24 
Air/Argon 
Air/H2 61 80 42 13 14 
Previous studies 
  • 1.

    Anaerobic-biofilm anoxic-aerobic membrane bioreactor

 
24 – 100 60–80 Spagni et al. (2010)  
2. sequencing batch reactors – 100 63 Cirik et al. (2013)  
3. Membrane bioreactor 72 – – 80–100 Friha et al. (2015)  
4. Anaerobic reactor 120–240 – – 95–99 Thailand (2015)  
5. Up-flow anaerobic filter 48 – – > 95 
6. Combine Anaerobic-Aerobic reactor 48 – – 58 
7. Membrane bioreactor 70 – 100 20–60 Luong et al. (2016)  
8. Anaerobic-aerobic-anoxic sequencing batch reactors – 40–75 60–85 Chen et al. (2018)  
9. Hydrolysis/acidification and multiple anoxic/aerobic process – 100 63 Gu et al. (2018)  
ReactorHRT (h)Nitrogen efficiency (%)
Decolorization rate (%)
Reference
Without RB-5With 80 mg/L of RB-5With 20 mg/L of RB-5With 80 mg/L of RB-5With 20 mg/L of RB-5
Air  This study 
Argon 24 
H2 95 100 100 28 24 
Air/Argon 
Air/H2 61 80 42 13 14 
Previous studies 
  • 1.

    Anaerobic-biofilm anoxic-aerobic membrane bioreactor

 
24 – 100 60–80 Spagni et al. (2010)  
2. sequencing batch reactors – 100 63 Cirik et al. (2013)  
3. Membrane bioreactor 72 – – 80–100 Friha et al. (2015)  
4. Anaerobic reactor 120–240 – – 95–99 Thailand (2015)  
5. Up-flow anaerobic filter 48 – – > 95 
6. Combine Anaerobic-Aerobic reactor 48 – – 58 
7. Membrane bioreactor 70 – 100 20–60 Luong et al. (2016)  
8. Anaerobic-aerobic-anoxic sequencing batch reactors – 40–75 60–85 Chen et al. (2018)  
9. Hydrolysis/acidification and multiple anoxic/aerobic process – 100 63 Gu et al. (2018)  

The average NRR results without and with RB-5 dye were reduced in the H2 and air/H2 reactors, at close to 95% in the H2 reactor without RB-5 and close to 100% with RB-5 dye, although the latter dropped slightly to 90–100% after the azo dye concentration was reduced from 80 to 20 mg/L. Similarly, there were decreases in the nitrogen removal efficiency of the air/H2 reactor after the RB-5 dye concentration was reduced from 80 to 20 mg/L, at 80 and 42%, respectively. Hence, the HD process was accelerated when contaminated with dye color while it was delayed when the dye concentrations decreased at this stage. Previous studies suggested that NO3-N and NO2-N is an electron acceptor similar to dye color but it is highly effective; therefore these substances can compete for electrons with dye color leading to an increase in oxidation-reaction that grew NRR contaminated with high amount of dye color and thus limit decolorization (Lee et al. 2010; Chen et al. 2018).

For the decolorization rate, both the reactors had a steady and low percentage of color removal, although there was a reduction in the influent concentrations of dye color owing to the lack of electron donors. In the previous studies that focused on the treatment schemes to remove color contaminated with NO3-N, the denitrification process began at the first stage and dye color reduced only after the denitrification had been completed (Chen et al. 2018). However, in our study the RB-5 removal rate from HD processing with a high dye concentration was 28%, which subsequently dropped to 24% when the dye color concentration was reduced. The rate of decolorization was still low when compared with the previous studies due to the small size of the reactor, high amount of NO3-N contamination and short operating time.

According to previous studies that evaluated advanced treatment processing to simultaneously remove nitrogen and dye color in a single reactor, the treatment efficiency of both the parameters was varied based on the operation time (i.e. HRT) and the treatment process, such as anaerobic-biofilm anoxic-aerobic membrane bioreactor, sequencing batch reactor, anaerobic reactor, up-flow anaerobic filter, and hydrolysis/acidification, or multiple anoxic/aerobic process. The results obtained in most of these studies showed the complete removal of nitrogen, while the decolorization rate was found to be in the range of 20–100%, except in the case of the membrane bioreactor and up-flow anaerobic filter, which exhibited high decolorization rates. However, the combined system is generally used to improve the quality of textile wastewater.

CONCLUSIONS

HD processing was performed under different operating and gas supply conditions; the reactors included an aerobic, two anaerobic (one supplied with argon, and the other with H2) and two combined systems (one with intermittent air/argon, and the other with air/H2). The results of NRR and decolorization rate showed high treatment efficiencies of the anaerobic processes and combined systems that used H2 and air/H2 as electron donors. The concentrations of NO3-N and dye color were significantly and simultaneously reduced when HD processing was performed in a single reactor. However, in the air, argon and air/argon reactors, no oxidation-reduction reactions occurred owing to a lack of bacterial growth. Furthermore, H2 reactors showed higher NRR than the air/H2 reactors because oxygen negatively affected the HD process. The NRR and decolorization rates were high in H2 reactors when both NO3-N and RB-5 dye color were presented, thereby providing optimal conditions for H2 to donate electrons. The performance of the H2 reactors in terms of nitrogen removal was 90–100% and the decolorization ranged from 20 to 35%, whereas the air/H2 reactor showed a 40–100% NRR and a 10–20% decolorization rate after an HRT of 24 h. This is because NO3-N is a better electron acceptor compared to the azo dye, and therefore, the decolorization rate was low. However, there was a reduction in the nitrogen removal efficiency after the concentration of RB-5 in the influent was reduced. The dye color may compete with NO3-N and NO2-N to improve the oxidation-reduction reaction rates of nitrogen. Hence, HD processing can still completely remove NO3-N and NO2-N when contaminated with RB-5 dye color, and RB-5 did not affect the NO3-N and NO2-N removal rates. However, the concentration of NO3-N after processing met the effluent wastewater standard in Thailand, and the concentration of color was easy to detect even in contaminated wastewater. In the future, HD and combined systems should use appropriate H2 levels and sufficient treatment time to help facilitate the reduction of the concentration of dye color in a single reactor. Furthermore, these systems should be applied to textile wastewater to observe their performance in a real situation. This method provides an opportunity to improve and develop advanced technologies that can lower treatment costs, ensure sustainability and improve wastewater quality before being discharged, as well as reduce freshwater consumption in developing countries like Thailand.

ACKNOWLEDGEMENTS

The authors are grateful to the University of Yamanashi, Japan, for the facilities provided and the financial support for this research through the Science and Technology Research Partnership for Sustainable Development (SATREPS) program of JST and JICA.

DATA AVAILABILITY STATEMENT

Data cannot be made publicly available; readers should contact the corresponding author for details.

REFERENCES

REFERENCES
APHA/AWWA/WEF
2012
Standard Methods for the Examination of Water and Wastewater
, 22nd edn.
American Public Health Association/American Water Works Association/Water Environment Federation
,
New York
,
USA
.
Assadi
A.
,
Naderi
M.
&
Mehrasbi
M. R.
2018
Anaerobic–aerobic sequencing batch reactor treating azo dye containing wastewater: effect of high nitrate ions and salt
.
J. Water Reuse Desal.
8
(
2
),
251
261
.
doi:10.2166/wrd.2017.132
.
Bouraie
M. E.
&
Din
W. S. E.
2016
Biodegradation of Reactive Black 5 by Aeromonas hydrophila strain isolated from dye-contaminated textile wastewater
.
Sustainable Environ. Res.
26
(
5
),
209
216
.
doi:10.1016/j.serj.2016.04.014
.
Chen
A.
,
Yang
B.
,
Zhou
Y.
,
Sun
Y.
&
Ding
C.
2018
Effects of azo dye on simultaneous biological removal of azo dye and nutrients in wastewater
.
R. Soc. Open Sci.
5
(
8
),
180795
.
doi:10.1098/rsos.180795
.
Cirik
K.
,
Kitis
M.
&
Cinar
O.
2013
Effect of nitrate on anaerobic azo dye reduction
.
Bioprocess Biosyst. Eng.
36
(
1
),
69
79
.
doi:10.1007/s00449-012-0762-9
.
Eamrat
R.
2017
Development of Microbiological Water Denitrification Under Anaerobic Condition by Using Hydrogen gas Supply
.
PhD Thesis
,
University of Yamanashi
,
Yamanashi
,
Japan
.
Friha
I.
,
Bradai
M.
,
Johnson
D.
,
Hilal
N.
,
Loukil
S.
,
Amor
F. B.
,
Feki
F.
,
Han
J.
,
Isoda
H.
&
Sayadi
S.
2015
Treatment of textile wastewater by submerged membrane bioreactor: in vitro bioassays for the assessment of stress response elicited by raw and reclaimed wastewater
.
J. Environ. Manage.
160
,
184
192
.
doi:10.1016/j.jenvman.2015.06.008
.
Griessmeier
V.
,
Leberecht
K.
&
Gescher
J.
2019
NO3-removal efficiency in field denitrification beds: key controlling factors and main implications
.
Environ. Microbiol. Rep.
11
(
3
),
316
329
.
doi:10.1111/1758-2229.12758
.
Gu
M.
,
Yin
Q.
,
Wang
Z.
,
He
K.
&
Wu
G.
2018
Color and nitrogen removal from synthetic dye wastewater in an integrated mesophilic hydrolysis/acidification and multiple anoxic/aerobic process
.
Chemosphere
212
,
881
889
.
doi:10.1016/j.chemosphere.2018.08.162
.
Guidelines management for color removal of dyeing factories in Thailand
2015
Draft Final Report 2015
.
Chulalongkorn University
,
Bangkok
,
Thailand
.
Lee
J. W.
,
Lee
K. H.
,
Park
K. Y.
&
Meng
S. K.
2010
Hydrogentrophic denitrification in a packed bed reactor: effect of hydrogen-to-water flow rate ratio
.
Bioresour. Technol.
101
(
11
),
3940
3946
.
doi:10.1016/j.biortech.2010.01.022
.
Li
P.
,
Xing
W.
,
Zuo
J.
,
Tang
L.
,
Wang
Y.
&
Lin
J.
2013
Hydrogentrophic denitrification for tertiary nitrogen removal from municipal wastewater using membrane diffusion packed-bed bioreactor
.
Bioresour. Technol.
144
,
452
459
.
doi:10.1016/j.biortech.2013.06.070
.
Li
Y.
,
Zhang
Y.
,
Quan
X.
,
Zhand
J.
,
Chen
S.
&
Afzal
S.
2014
Enhanced anaerobic fermentation with azo dye as electron acceptor: simultaneous acceleration of organics decomposition and azo decolorization
.
J. Environ. Sci.
26
(
10
),
1970
1976
.
doi:10.1016/j.jes.2014.07.009
.
Lourenço
N. D.
,
Novais
J. M.
&
Pinheiro
H. M.
2000
Reactive textile dye colour removal in a sequencing batch reactor
.
Water Sci. Technol.
42
(
5–6
),
321
328
.
doi:10.2166/wst.2000.0531
.
Luong
T. V.
,
Schmidt
S.
,
Deowan
S. A.
,
Hoinkis
J.
,
Figoli
A.
&
Galiano
F.
2016
Membrane bioreactor and promising application for textile industry in Vietnam
.
Proc. CIR
40
,
419
424
.
doi:10.1016/j.procir.2016.01.083
.
Panswad
T.
&
Luangdilok
W.
2000
Decolorization of reactive dyes with different molecular structures under different environmental conditions
.
Water Res.
34
(
17
),
4177
4184
.
doi:10.1016/S0043-1354(00)00200-1
.
Rahman
M. M.
,
Bodrud-Doza
M.
,
Muhib
M. I.
,
Hossain
K. F. B.
,
Sikder
M. T.
,
Shammi
M.
,
Akter
R.
&
Uddin
M. K.
2020
Human health risk assessment of nitrate and trace metals via groundwater in Central Bangladesh
.
Pollution
6
(
2
),
263
276
.
doi:10.22059/poll.2019.288090.691
.
Rezvani
F.
,
Sarrafzadeh
M.
,
Ebrahimi
S.
&
Oh
H.
2017
Nitrate removal from drinking water with a focus on biological methods: a review
.
Environ. Sci. Pollut. Res.
26
,
1124
1141
.
doi:10.1007/s11356-017-9185-0
.
Rujakom
S.
,
Shinoda
K.
,
Kamei
T.
&
Kazama
F.
2019
Investigation of hydrogen-based denitrification performance on nitrite accumulation under various bicarbonate doses
.
Environ. Asia
12
(
Special issue
),
54
63
.
doi:10.14456/ea.2019.63
.
Sahinkaya
E.
,
Yurtsever
A.
&
Cinar
O.
2017
Treatment of textile industry wastewater using dynamic membrane bioreactor: impact of intermittent aeration on process performance
.
Sep. Purif. Technol.
174
,
445
454
.
doi:10.1016/j.seppur.2016.10.049
.
Sairiam
S.
,
Thuptimang
P.
&
Painmanakul
P.
2019
Decolorization of reactive black 5 from synthetic dye wastewater by Fenton process
.
Environ. Asia
12
(
2
),
1
8
.
doi:10.5897/AJB12.1226
.
Saroyan
H.
,
Ntagiou
D.
,
Rekos
K.
&
Deliyanni
E.
2019
Reactive black 5 degradation on manganese oxides supported on sodium hydroxide modified graphene oxide
.
Appl. Sci.
9
(
10
),
2167
.
doi:10.3390/app9102167
.
Sheng
S.
,
Liu
B.
,
Hou
X.
,
Wu
B.
,
Yao
F.
,
Ding
X.
&
Huang
L.
2018
Aerobic biodegradation characteristic of different water-soluble azo dyes
.
Int. J. Environ. Res. Public Health
15
(
1
),
35
.
doi:10.3390/ijerph15010035
.
Spagni
A.
,
Grilli
S.
,
Casu
S.
&
Mattioli
D.
2010
Treatment of a simulated textile wastewater containing the azo-dye reactive orange 16 in an anaerobic-biofilm anoxic-aerobic membrane bioreactor
.
Int. Biodeterior. Biodegrad.
64
(
7
),
676
981
.
doi:10.1016/j.ibiod.2010.08.004
.
WHO
2011
Nitrates and Nitrites in Drinking-Water: Rolling Revision of the WHO Guidelines for Drinking-Water Quality. Draft for Review and Comments
.
World Health Organization
,
Geneva
,
Switzerland
.