Individual and combined inhibition of phenol and thiocyanate on microbial activity of partial nitritation

Long-term effect of phenol, quinoline, and pyridine on nitrite accumulation in the nitrification process: performance, microbial community, metagenomics and molecular docking analysis

Phenol, quinoline, and pyridine, commonly found in industrial wastewater, disrupt the nitrification process, leading to nitrite accumulation. This study explores the potential mechanisms through which these biotoxic organic compounds affect nitrite accumulation, using metagenomic and molecular docking analyses. Despite increasing concentrations of these compounds from 40 to 160 mg/L, ammonia nitrogen removal was not hindered, and stable nitrite accumulation rates exceeding 90 % were maintained. Additionally, these compounds inhibited nitrite-oxidizing bacteria (NOB) and enriched ammonia-oxidizing bacteria (AOB) in situ. As the concentration of these compounds rose, protein (PN) and polysaccharide (PS) concentrations also increased, along with a higher PN/PS ratio. Metagenomic analysis further revealed an increase in hao relative abundance, while microbial community analysis showed increased Nitrosomonas abundance, which contributed to nitrite accumulation stability. Molecular docking indicated that these compounds have lower binding energy with hydroxylamine oxidoreductase (HAO) and nitrate reductase (NAR), theoretically supporting the observed sustained nitrite accumulation.

Advances in treatment of coking wastewater - a state of art review

Coking wastewater poses a serious threat to the environment due to the presence of a wide spectrum of refractory substances such as phenolic compounds, polycyclic aromatic hydrocarbons and heterocyclic nitrogenous compounds. These toxic substances are difficult to treat using conventional treatment methods alone. In recent years much attention has been given to the effective treatment of coking wastewater. Thus, this review seeks to provide a brief overview of recent developments that have taken place in the treatment of coking wastewater. In addition, this article addresses the complexity and the problems associated with treatment followed by a discussion on biological methods with special focus on bioaugmentation. As coking wastewater is refractory in nature, some of the studies have been related to improving the biodegradability of wastewater. The final section focuses on the integrated treatment methods that have emerged as the best solution for tackling the highly unmanageable coking wastewater. Attention has also been given to emerging microwave technology which has tremendous potential for treatment of coking wastewater.

Inhibitory effect of phenol on wastewater ammonification

This study aimed to elucidate inhibitory effect of phenol on ammonification of dissolved organic nitrogen (DON) in wastewater. Laboratory incubation experiments were conducted using primary and secondary effluent samples spiked with phenol (100-1000 mg/L) and inoculated with mixed cultures, pure strains of phenol-degrading bacteria (Acinetobacter sp. and Pseudomonas putida F1), and/or an ammonia oxidizing bacterium (Nitrosomonas europaea). DON concentration was monitored with incubation time. Phenol suppressed the ammonification rate of DON up to 62.9%. No or minimal ammonification inhibition was observed at 100 mg/L of phenol while the inhibition increased with increasing phenol concentration from 250 to 1000 mg/L. The inhibition was curtailed by the presence of the phenol-degrading bacteria. DON was ammonified in the samples inoculated with only N. europaea and the ammonification was also inhibited by phenol. The findings suggest that high phenol in wastewater could result in low ammonification and high DON in the effluent.

Performance and microbial community in a single-stage simultaneous carbon oxidation, partial nitritation, denitritation and anammox system treating synthetic coking wastewater under the stress of phenol

As a highly toxic pollutant, phenol is typically present in some high-strength nitrogenous wastewater. In this study, a synthetic coking wastewater with 400 mg L^-1 ammonia-nitrogen and 50-250 mg L^-1 phenol was treated. Results showed that simultaneous carbon oxidation, partial nitritation, denitritation and anammox (SCONDA) was successfully achieved by step-wise phenol addition. At 200 mg L^-1 phenol, 99.8% phenol, 97.5% COD and 89.8% nitrogen could be together removed. However, further increase in phenol concentration caused significant deterioration of the short-terms nitrogen removal efficiency. High-throughput sequencing revealed remarkable evolution in microbial biodiversity, community composition, especially functional species at different phenol concentrations. When the phenol addition was increased from 200 to 250 mg L^-1, the relative abundance of Candidatus Kuenenia as predominant anammox species decreased by 87.1%, while phenol-degrading bacteria was increasingly abundant. Furthermore, the removal mechanism of phenol and nitrogen was elucidated by the collaboration among different key functional microbial consortia.

Performance of Anammox Processes for Wastewater Treatment: A Critical Review on Effects of Operational Conditions and Environmental Stresses

The anaerobic ammonium oxidation (anammox) process is well-known as a low-energy consuming and eco-friendly technology for treating nitrogen-rich wastewater. Although the anammox reaction was widely investigated in terms of its application in many wastewater treatment processes, practical anammox application at the pilot and industrial scales is limited because nitrogen removal efficiency and anammox activity are dependent on many operational factors such as temperature, pH, dissolved oxygen concentration, nitrogen loading, and organic matter content. In practical application, anammox bacteria are possibly vulnerable to non-essential compounds such as sulfides, toxic metal elements, alcohols, phenols, and antibiotics that are potential inhibitors owing to the complexity of the wastewater stream. This review systematically summarizes up-to-date studies on the effect of various operational factors on nitrogen removal performance along with reactor type, mode of operation (batch or continuous), and cultured anammox bacterial species. The effect of potential anammox inhibition factors such as high nitrite concentration, high salinity, sulfides, toxic metal elements, and toxic organic compounds is listed with a thorough interpretation of the synergistic and antagonistic toxicity of these inhibitors. Finally, the strategy for optimization of anammox processes for wastewater treatment is suggested, and the importance of future studies on anammox applications is indicated.

Performance and recovery of a completely separated partial nitritation and anammox process treating phenol-containing wastewater

Anammox process is considered as a promising technology for removing total nitrogen from low-strength ammonium and phenol-containing wastewater. However, it is still a challenge for the anammox process to treat high-strength ammonium and phenol-containing wastewater. A completely separated partial nitritation and anammox (CSPN/A) process was developed to remove total nitrogen from high-strength phenol-containing wastewater. About 92% of COD, 100% of phenol, and 82.4% of total nitrogen were successfully removed at a NH₄⁺-N concentration of 200 mg L^-1 with a phenol/NH₄⁺-N mass ratio of 0.5 in the CSPN/A process. Furthermore, a shock loading of 300 mg phenol L^-1 with a phenol/NH₄⁺-N mass ratio of 1.5 led to a complete failure of partial nitritation, but the performance was rapidly recovered by the increase of NH₄⁺-N concentration. Although the activities of ammonium-oxidizing bacteria and anammox bacteria were severely inhibited at a phenol/NH₄⁺-N mass ratio of 1.5, the enrichment of efficient phenol degraders in the CSPN stage could strengthen the performance robustness of partial nitritation and anammox process. Therefore, this study presented a new insight on the feasibility of the anammox process for treating high-strength ammonium and phenol-containing wastewater.

Carbon nanotube-grafted chitosan and its adsorption capacity for phenol in aqueous solution

Chitosan was covalently grafted onto the surface of multi-walled carbon nanotubes to create a novel chitosan/multi-walled carbon nanotube. The structure of the new material was characterized using Fourier transform-infrared spectroscopy, cross polarization magic angle spinning ¹³C nuclear magnetic resonance, thermogravimetric analysis, XRD ray diffraction analysis, differential scanning calorimetry and scanning electron microscopy. The phenol adsorption capacity was determined and the Langmuir and Freundlich models were used to describe the adsorption isotherms. The adsorption capacity of the novel chitosan/multi-walled carbon nanotube material for phenol (86.96 mg/g) was improved compared to the original chitosan (61.69 mg/g). The kinetic studies showed rapid adsorption, exhibiting Lagergren second-order kinetics. Therefore, this study provides a reference for preparing functional materials from biological substrates that are able to remove toxic pollutants from an aqueous environment.

Optimized aeration strategies for nitrogen removal efficiency: application of end gas recirculation aeration in the fixed bed biofilm reactor

Aeration strategy played an important role in reactor performance. In this study, when superficial upflow air velocity (SAV) decreased from 0.16 to 0.08 cm s^-1, low dissolved oxygen concentration (DO) of 2.0 mg L^-1 occurred in reactor. The required depth for anoxic microenvironment in biofilm decreased from 902.3 to 525.9 μm, which enhanced the growth of denitrifying bacteria and total nitrogen (TN) removal efficiency. However, decreasing aeration intensity resulted in insufficient hydraulic shear stress, which led to weak biofilm matrix structure. Mass biofilm detachment and reactor deterioration then occurred after 87 days of operation. An end gas recirculation aeration strategy was proposed to separately manipulate DO and aeration intensity. Low DO and high aeration intensity were simultaneously achieved, which enhanced the metabolism of denitrifying bacteria (such as Flavobacterium sp., Pseudorhodobacter sp., and Dok59 sp.) and EPS-producing bacteria (such as Zoogloea sp. and Rhodobacter sp.). Consequently, high TN removal performance (82.1 ± 2.7%) and stable biofilm structure were achieved.

Application of metabolic division of labor in simultaneous removal of nitrogen and thiocyanate from wastewater

Metabolic division of labor is a key ecological strategy in bacteria to allow concurrent execution of multiple tasks through functional differentiation and metabolite exchange. While it is prevalent in nature, a lot of novel interactions remain to be further explored for improved wastewater biological treatment. Here, we present a combined experimental and modeling study on the simultaneous removal of nitrogen and thiocyanate from wastewater by using a syntrophic microbial community. The syntrophic division of labor was achieved by coupling autotrophic denitrification (AD) and anaerobic ammonium oxidation (AN) through both cooperative and competitive interactions. We demonstrated that the syntrophic community can achieve almost complete removal of all pollutants under certain initial conditions. We then perturbed the initial condition by varying the concentration ratio between ammonium to thiocyanate as well as the biomass ratio between AD and AN. Our observations show that adding ammonium negatively impacts the thiocyanate removal efficiency and adding anammox bacteria have opposite effects on the removal efficiency of thiocyanate and ammonium. Using a mathematical model, we simultaneously varied these two initial conditions and identified the parameter regime where our syntrophic ecosystem can be most efficient in removing total nitrogen. By highlighting the utility of syntrophic pair of functional bacteria in removing pollutants, our study will facilitate the rational design of more complex microbial consortia for the removal of toxic and hazardous compounds from industrial wastewater.

Synergistic inhibition of anaerobic ammonium oxidation (anammox) activity by phenol and thiocyanate

Coke-oven wastewater discharged from the steel-manufacturing process is phenol and thiocyanate (SCN)-rich wastewater, which inhibits microbial activities in biological wastewater treatment processes. In the present study, synergistic inhibition of anaerobic ammonium oxidation (anammox) activity by phenol and SCN was examined by batch incubation and continuous operation of an anammox reactor. The comparison of anammox activities determined in the batch incubation, in which the anammox biomass was anoxically incubated with 10-250 mg L^-1 of i) phenol, ii) SCN, or iii) both phenol and SCN, showed that synergistic inhibition by phenol and SCN was greater than the inhibitions by phenol or SCN alone. The synergistic inhibition by phenol and SCN was further investigated by operating an up-flow column anammox reactor for 262 d. The removal efficiencies of NH₄⁺ and NO₂^- deteriorated when phenol and SCN concentrations in the influent increased to 16 and 32 mg L^-1, respectively, and the inhibition of anammox activity was further investigated by a¹⁵NO₂^- tracer experiment. Addition of phenol and SCN resulted in a population shift of anammox bacteria, and the dominant species changed from "Candidatus Kuenenia stuttgartiensis" to "Ca. Brocadia sinica". The relative abundance of Azoarcus and Thiobacillus 16S rRNA gene reads increased during the operation, suggesting that they were responsible for the anaerobic phenol and SCN degradation. The present study is the first to document the synergistic inhibition of anammox activity by phenol and SCN and the microbial consortia involved in the nitrogen removal as well as the phenol and SCN degradations.

Inhibitory effects of heavy metals and antibiotics on nitrifying bacterial activities in mature partial nitritation

To facilitate the use of partial nitritation (PN) in nitrogen removal processes for livestock wastewater, this work investigated the inhibitory effects of heavy metals and antibiotics on the nitrifying bacterial activities of the PN processes. Biomass was collected from a continuous-flow internal-loop airlift reactor and cultured with fixed ammonium concentrations of 921 mg N L^-1. Batch activity tests were conducted to determine the specific oxygen uptake rate. The individual and interactive inhibitory effects of Zn²⁺, Cu²⁺, oxytetracycline (OTC) and sulfamethazine (SMZ) were evaluated using an orthogonal test. The results showed that the half maximal inhibitory concentration (IC₅₀) values of Zn²⁺, Cu²⁺, OTC and SMZ on PN sludge were 50.1, 35.4, 447 and 1890 mg L^-1, respectively. The joint toxicities of heavy metals (Zn²⁺ and Cu²⁺) and antibiotics (OTC and SMZ) in the PN mixed culture were generally synergistic, except for between Zn²⁺ and Cu²⁺, which was antagonistic. In joint toxicity tests, the significance of the inhibitory effect of Zn²⁺ (15.3-164.3 mg L^-1), Cu²⁺ (13.8-90.9 mg L^-1), OTC (27.0-866.5 mg L^-1) and SMZ (290-3490 mg L^-1) on the nitrifying bacterial activity can be ranked in the following order: SMZ > Cu²⁺ > Zn²⁺ > OTC. Additionally, different exposure times (1 h, 3 h and 24 h) with or without aeration were also comparatively studied. These results show that a greater PN sludge activity loss than when exposure without aeration.