Hydrogenotrophic denitrification for treating nitrate contaminated without/with reactive black 5 dye

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.

Hydrogenotrophic Denitrification of Groundwater Using a Simplified Reactor for Drinking Water: A Case Study in the Kathmandu Valley, Nepal

“…The effluent of the nitrification system contains high DO as previously reported [20], which is the same as the influent of the simplified HD reactor. However, the HD system can be inhibited by high DO concentrations [47,48], and Singhopon et al has suggested that the DO value should be between 0.5 and 0.8 mg-O 2 /L to improve NRR [48]. In the present study, supplying H 2 gas into the reactor was instrumental in maintaining the preferred range of DO concentrations for HD.…”

Factors Affecting the Simultaneous Removal of Nitrate and Reactive Black 5 Dye via Hydrogen-Based Denitrification

“…Considering that the functional bacteria require an adaptation time in order to function properly under a high amount of toxic contamination, nitrogen removal was enhanced when the RB-5 dye was added. A previous study revealed that NO3-N and NO2-N could be removed when the environment is contaminated with high RB-5 concentrations, and NRE was greater when RB-5 was added to the system [21].…”

“…Synthetic textile wastewater was prepared based on the quality of textile wastewater in Thailand, which has a composition as previously described: 486 mg NaNO 3 /L (80 mg NO 3 -N/L), 110 mg KH 2 PO 4 /L, 1000 mg NaHCO 3 /L, 21 mg CaCl 2 /L, 38 mg MgSO 4 •7H 2 O/L, and 1.0 mL of trace elements (I) and (II) [21,22] [23]. Furthermore, in this study, the concentrations of the azo dye were varied (10, 15, 30, and 60 mg/L) depending on the operating conditions of each phase, as described in Table 1.…”

“…Initially, enhanced sludge from the HD reactor that had been operated for more than 400 days was added into both reactors A and B as initial sludge. Thereafter, these reactors were operated under various operating conditions for more than 60 days, as previously described [21]. These reactors were continuously operated in this study in run 1 (day zero).…”

“…Additionally, previous studies attempted to develop the HD process and evaluated its performance in relation to the simultaneous treatment of various pollutants in textile wastewater, especially NO 3 − , NO 2 − and dye [21]. Their results showed the possibility of the simultaneous reduction of nitrogen and a small amount of dye in both anaerobic and combined aerobic/anaerobic reactors.…”