Coupled anaerobic ammonium oxidation and hydrogenotrophic denitrification for simultaneous NH4-N and NO3-N removal

Advances in AHLs-mediated quorum sensing system in wastewater biological nitrogen removal: mechanism, function, and application

Biological nitrogen removal process is to convert organic nitrogen and ammonia nitrogen into nitrogen via a series of reactions by microorganisms, and is widely used in wastewater treatment for its costless, high-effective, secondary pollution-free characteristics. Quorum sensing (QS) is a communication mode for microorganisms to regulate bacteria's physiological behaviors in response to environmental changes. N-acyl-homoserine lactones (AHLs)-mediated QS system is widespread in nitrogen removal-related functional bacteria and promotes biological nitrogen removal performance by regulating bacteria behavior. Recently, there has been an increasingly investigated AHLs-mediated QS system in wastewater biological nitrogen removal process. Consequently, the AHLs-mediated QS system is considered a promising regulatory strategy in the biological nitrogen removal process. This article reviewed the QS mechanism in various nitrogen removal-related functional bacteria and analyzed its effect on biological nitrogen removal performance. Combined with the application research of the QS system for enhanced biological nitrogen removal, it further put forward some prospects and suggestions which are of practical significance in practical application.

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

Textile wastewater (TW) contains toxic pollutants that pose both environmental and human health risks. Reportedly, some of these pollutants, including NO3−, NO2− and reactive black 5 (RB-5) dye, can be removed via hydrogen-based denitrification (HD); however, it is still unclear how different factors affect their simultaneous removal. This study aimed to investigate the effect of H2 flow rate, the sparging cycle of air and H2, and initial dye concentration on the TW treatment process. Thus, two reactors, an anaerobic HD reactor and a combined aerobic/anaerobic HD reactor, were used to investigate the treatment performance. The results obtained that increasing the H2 flow rate in the anaerobic HD reactor increased nitrogen removal and decolorization removal rates. Further, increasing the time for anaerobic treatment significantly enhanced the pollutant removal rate in the combined reactor. Furthermore, an increase in initial dye concentration resulted in lower nitrogen removal rates. Additionally, some of the dye was decolorized during the HD process via bacterial degradation, and increasing the initial dye concentration resulted in a decrease in the decolorization rate. Bacterial communities, including Xanthomonadaceae, Rhodocyclaceae, and Thauera spp., are presented as the microbial species that play a key role in the mechanisms related to nitrogen removal and RB-5 decolorization under both HD conditions. However, both reactors showed similar treatment efficiencies; hence, based on these results, the use of a combined aerobic/anaerobic HD system should be used to reduce organic/inorganic pollutant contents in real textile wastewater before discharging is recommended.

Newly established process combining partial hydrogenotrophic denitrification and anammox for nitrogen removal

The anaerobic ammonium oxidation (anammox) process holds great promise for treating nitrogen-contaminated water; stable nitrite-nitrogen (NO₂ ^--N) production is significant to anammox performance. In this study, partial hydrogenotrophic denitrification (PHD) was used to stably and efficiently produce NO₂ ^--N from nitrate-nitrogen (NO₃ ^--N). An investigation of the effects of initial pH on the PHD process revealed that a high NO₂ ^--N production efficiency (77.9%) could be ensured by setting an initial pH of 10.5. A combined PHD-anammox process was run for more than three months with maximal ammonium-nitrogen (NH₄ ⁺-N), NO₃ ^--N, and total dissolved inorganic nitrogen removal efficiencies of 93.4, 98.0, and 86.9%, respectively. The NO₂ ^--N to NH₄ ⁺-N and NO₃ ^--N to NH₄ ⁺-N ratios indicated that various bioprocesses were involved in nitrogen removal during the anammox stage, and a 16S rRNA gene amplicon sequencing was performed to further clarify the composition of microbial communities and mechanisms involved in the nitrogen removal process.