Substantially enhanced degradation of nitrobenzene by biosponge iron system: Process and mechanisms

Treating nitrobenzene (NB) wastewater via an enhanced iron‒manganese oxides electron transfer strategy: Methods and mechanisms

Nitrobenzene (NB) is widely used in the fine chemical, pharmaceutical, and textile industries, but its toxicity and resistance to degradation present challenges, and traditional treatment methods are limited due to costs and a lack of efficiency. In this study, using a three-dimensional biofilm electrode reactor (3D-BER) enhanced with iron-manganese oxide catalysts was explored for the treatment of NB wastewater. Modifying polyurethane (PU) sponge fillers with Fe₃O₄ and Mn₃O₄ improved the conductivity and microbial electron transfer of the 3D-BER, significantly enhancing organic compound degradation, nitrogen and phosphorus removal. At the optimal voltage of 6 V and hydraulic retention time (HRT) of 24 h, the reactor achieved CODCr and ammonia nitrogen removal rates of 93.04 % and 86.25 %, respectively, which were more than 20 % higher than those in the control group. The iron and manganese present facilitated increased microbial activity and electron transfer efficiency, and metagenomic sequencing revealed shifts in the microbial communities and the enrichment of specific functional genes related to NB degradation. This integrated bioelectrochemical approach offers an effective and low-cost solution for treating NB wastewater, with broader implications for organic chemical wastewater management.

Mechanism of cooperative migration and transformation of nitrobenzene and iron co-contaminated water and soil

Zero-valent iron (ZVI) has found extensive application in the remediation of contaminated soil and groundwater. However, it is essential to remain vigilant about its potential adverse impacts. This study is based on a real field pollution incident, supplemented by experimental simulations. A chemical plant's leakage of nitrobenzene and ZVI led to contamination at the site, with some of the nitrobenzene transforming into aniline, a compound with increased mobility and toxicity. The peak concentrations of nitrobenzene and aniline in the soil were recorded at 2710 mg/kg and 145 mg/kg, respectively. In groundwater, the highest concentrations of nitrobenzene and aniline reached 132 mg/L and 723 μg/L, respectively, exhibiting similar pollution plume distributions. Laboratory simulations were conducted to examine the transformation process of nitrobenzene in both aqueous and soil media in the presence of ZVI and its oxidation products. These investigations also explored the influence of various factors on the conversion of nitrobenzene and the yield of aniline. The column experiment methodology was employed to investigate the migration and transformation pathways of nitrobenzene in simulated media and actual field soils augmented with iron. Upon introducing iron powder, the maximum concentrations of aniline in quartz sand columns and silty clay columns were observed to be 694 mg/L and 1068 mg/L, respectively. During the reaction process, elemental iron primarily acted as a reductant, converting nitrobenzene to aniline, while being oxidized to Fe3O4 and γ-Fe2O3. This finding provides deeper insights into the mechanism underlying the synergistic transformation of iron and nitrobenzene within the contaminated site's aquifer.

Biocathode-anode cascade system in PRB: Efficient degradation of p-chloronitrobenzene in groundwater

The consistent presence of p-chloronitrobenzene (p-CNB) in groundwater has raised concerns regarding its potential harm. In this study, we developed a biocathode-anode cascade system in a permeable reactive barrier (BACP), integrating biological electrochemical system (BES) with permeable reactive barrier (PRB), to address the degradation of p-CNB in the groundwater. BACP efficiently accelerated the formation of biofilms on both the anode and cathode using the polar periodical reversal method, proving more conducive to biofilm development. Notably, BACP demonstrated a remarkable p-CNB removal efficiency of 94.76 % and a dechlorination efficiency of 64.22 % under a voltage of 0.5 V, surpassing the results achieved through traditional electrochemical and biological treatment processes. Cyclic voltammetric results highlighted the primary contributing factor as the synergistic effect between the bioanode and biocathode. It is speculated that this system primarily relies on bioelectrocatalytic reduction as the predominant process for p-CNB removal, followed by subsequent dechlorination. Furthermore, electrochemical and microbiological tests demonstrated that BACP exhibited optimal electron transfer efficiency and selective microbial enrichment ability under a voltage of 0.3-0.5 V. Additionally, we investigated the operational strategy for initiating BACP in engineering applications. The results showed that directly introducing BACP technology effectively enhanced microbial film formation and pollutant removal performance.

Sponge iron enriches autotrophic/aerobic denitrifying bacteria to enhance denitrification in sequencing batch reactor

Sponge iron (SFe) coupled with a sludge system has great potential for improving biological denitrification; however, the underlying mechanism is not yet fully understood. In this study, the denitrification performance and microbial characteristics of ordinary sludge and SFe-sludge systems were investigated. Overall, the SFe-sludge reactor had faster ammonium degradation rate (94.0 %) and less nitrate accumulation (1.5-53.3 times lower) than ordinary reactor during the complete operation cycle of sequencing batch reactors. The addition of SFe increased the activities of nitrate and nitrite reductases. The total relative abundance of autotrophic denitrifying bacteria (Acidovorax, Arenimonas, etc.) in the SFe-sludge system after 38 days of operation was found to be 10.6 % higher than that in the ordinary sludge reactor. The aerobic denitrifying bacteria (Dokdonella, Phaeodactylibacter, etc.) was 5.3 % higher than ordinary sludge. The SFe-sludge system improved denitrification by enriching autotrophic/aerobic denitrifying bacteria in low carbon-to-nitrogen ratio wastewater treatment.

Degradation of different wastewater by a biological sponge iron system: microbial growth and influencing factors

The bio-ZVI process has undergone widespread development in wastewater treatment in recent years. However, there has been limited examination of the growth and degradation characteristics of functional microorganisms within the system. In the present research, strains were isolated and identified from the bio-ZVI system constructed by sponge iron (encoded as SFe-M). The consistency of operating conditions in treating different wastewater was explored. Three SFe-acclimated microorganisms exhibiting characteristics of degrading organic pollutants and participating in the nitrogen removal process were isolated. The adaptation time of these microorganisms prolonged as the substrate toxicity increased, while the pollutant degradation was related to their metabolic rate in the logarithmic phase. All these functional bacteria exhibited the ability to treat wastewater in a wide pH range (5-8). However, the improper temperature (such as 10 °C and 40 °C) significantly inhibited their growth, and the optimal working temperature was identified as 30 °C. The iron dosage had a significant impact on these function bacteria, ranging from 1 g L-1 to 150 g L-1. It was inferred that the SFe-acclimated microorganisms are capable of resisting the poison of excessive iron, that is, they all have strong adaptability. The results provide compelling evidence for further understanding of the degradation mechanism involved in the bio-ZVI process.

Impact of zero-valent iron on nitrifying granular sludge for 17α-ethinylestradiol removal and its mechanism

Aerobic granulation of nitrifying activated sludge could enhance the removal of 17α-ethinylestradiol (EE2) via abiotic nitration induced by reactive nitrogen species, cometabolism by ammonia-oxidizing bacteria and biodegradation by heterotrophic bacteria. Zero-valent iron (ZVI), a promising and low-cost material, has previously been applied to effectively enhance biological wastewater treatment. The impact and the effect mechanism of ZVI on nitrifying granular sludge (NGS) for EE2 removal was investigated in this study. The results showed that the addition of ZVI achieved better EE2 removal, though ZVI was not conducive to the accumulation of nitrite in NGS which reduced the abiotic transformation of EE2. Moreover, ZVI enriched heterotrophic denitrifying bacteria such as Arenimonas, thus changing the EE2 removal pathway and improving the degradation and mineralization of EE2. In addition, ZVI reduced the emission risk of the greenhouse gas N₂O and strengthened the stability of the granules. Metagenomic analysis further revealed that the functional genes related to EE2 mineralization, nitrite oxidation, N₂O reduction and quorum sensing in NGS were enriched with ZVI addition. This study provides meaningful guidance for ZVI application in the NGS process to achieve efficient and simultaneous removal of ammonia and emerging contaminants.

Low strength wastewater anammox start-up and stable operation by inoculating sponge-iron sludge: Cooperation of biological iron and iron bacteria

The application of anaerobic ammonium oxidation (Anammox) technology in low-strength wastewater treatment still faces difficult in-situ start-ups and unstable operations. Sponge-iron sludge (R1) was used as a novel inoculum to provide a promising solution. Conventional activated sludge (R0) was used as the control. However, little is known about the feasibility and performance during the start-up and operation of Anammox combined with biological iron and iron bacteria in an iron sludge system. Anammox was successfully started both in R1 (87 days) and R0 (89 days) with a low-strength influent (with a nitrogen loading rate (NLR) of 43.64 ± 0.41 g N/(m3⋅d)). During long-term operation, the R0 nevertheless produced higher nitrates (9.7 ± 0.1 mg/L) than expected. In contrast, R1 presented no excess nitrate production (2.1 ± 0.06 mg/L). The total inorganic nitrogen (TIN) removal efficiency increased from 78.2 ± 7.1% in R0 to 86.1 ± 4.3% in R1. The iron sludge in R1 was divided equally into three parts and three different nitrogen-feeding methods were used over the 34 days of operation, as follows: first using a mixture of ammonium (27.15 ± 1.0 mg/L) and nitrite (32.7 ± 1.7 mg/L), then only ammonium (27.15 ± 1.0 mg/L) and lastly only nitrite (32.7 ± 1.7 mg/L) as the influent. R1 was a coupled system composed of Anammox, Feammox, and NOx--dependent Fe(II) oxidation (NDFO). The contribution of Feammox and NDFO to TIN removal was 27.1 ± 1.2% and 31.9 ± 0.7%. However, Anammox was the primary nitrogen transformation pathway. X-ray diffraction (XRD) analysis shows that iron hydroxide (Fe(OH)3) and iron oxide hydroxide (FeOOH) were generated in R1. The produced Fe(OH)3 and FeOOH were capable of participating in Feammox and formed a Fe(II)/Fe(III) cycle which further removed nitrogen. Therefore, a highly stable and impressive nitrogen removal performance was demonstrated in the iron sludge Anammox system under the cooperation of biological iron and iron bacteria. The study considered the enrichment of norank_c_OM190, Desulfuromonas, and Thiobacillus and their contribution to the Anammox, Feammox, and NDFO processes, respectively. This study provides a new perspective for the start-up and stable operation of low-strength wastewater Anammox engineering applications.

Recent advances in biological removal of nitroaromatics from wastewater

Various nitroaromatic compounds (NACs) released into the environment cause potential threats to humans and animals. Biological treatment is valued for cost-effectiveness, environmental friendliness, and availability when treating wastewater containing NACs. Considering the significance and wide use of NACs, this review focuses on recent advances in biological treatment systems for NACs removal from wastewater. Meanwhile, factors affecting biodegradation and methods to enhance removal efficiency of NACs are discussed. The selection of biological treatment system needs to consider NACs loading and cost, and its performance is affected by configuration and operation strategy. Generally, sequential anaerobic-aerobic biological treatment systems perform better in mineralizing NACs and removing co-pollutants. Future research on mechanism exploration of NACs biotransformation and performance optimization will facilitate the large-scale application of biological treatment systems.