Effects of glucose and starch on the toxicity of nitrobenzene to plants and microbes in constructed wetlands

Phytotoxicity of nitrobenzene bioaccumulation in rice seedlings: Nitrobenzene inhibits growth, induces oxidative stress, and reduces photosynthetic pigment synthesis

Nitrobenzene (NB) has been used in numerous industrial and agricultural fields as an organic compound intermediate. NB has mutagenicity and acute toxicity, and is typically a toxic pollutant in industrial wastewater worldwide. To evaluate its phytotoxicity, we treated rice (Oryza sativa) with different concentrations of NB (0, 5, 25, 50, 75, and 100 mg L-1). NB inhibited growth indices of rice (shoot and root length, fresh shoot and root weight, and dry shoot and root weight) as NB treatment concentrations increased. High concentrations (>25 mg L-1) of NB significantly inhibited rice root and shoot growth; root growth was more susceptible to NB. NB treatment could damage the structure and reduce the activity of rice seedling roots. The result of high performance liquid chromatography (HPLC) indicated that the bioaccumulation of NB in rice seedlings had a dose-dependent effect on the growth inhibition. NB reduced the photosynthetic pigment content and the expression levels of chlorophyll synthesis genes. NB treatment increased active oxygen radicals, electrical conductivity, malondialdehyde (MDA), proline, and soluble sugar contents. The expressions of antioxidant enzyme genes were induced by NB stress, and exhibited a phenomenon of initial increase followed by decrease. When the NB concentration was higher than 50 mg L-1, the gene expression levels decreased rapidly. This study provides insight into the association between exposure to NB and its phytotoxic effects on rice seedlings, and assesses the potential risk of NB bioaccumulation for crops that require a large amount of irrigation water.

Performance of nitrobenzene and its intermediate aniline removal by constructed wetlands coupled with the micro-electric field

The degradation of nitrobenzene and its intermediate aniline from wastewater by constructed wetlands coupled with the micro-electric field (CW-MEF) technology was studied. The results showed that the CW-MEF system had good degradation. With the increase of influent concentration of nitrobenzene, the removal rate of the anode was excellent which remained above 86%, but the degradation of CW-MEF for COD decreased. In different stages, the power generation capacity was different. In the second stage, the power generation voltage reached 430 V and the average power density was 85.07 MW m^-3, while the maximum reached 87.47 MW m^-3. Through high-throughput sequencing analysis, the A1 sludge layer contained 36% of thick-walled bacteria and 20% of bacteroides, the A2 contained about 20% of campylobacter green, and the A3 contained 10% of green campylobacter, pachyphyte and bacteroides.

Synthesis and Characterization of Zinc Peroxide Nanoparticles for the Photodegradation of Nitrobenzene Assisted by UV-Light

The contamination of both soil and water by nitrobenzene (NB) is a problem that has been studied, where several reactive agents have been developed for the degradation of this compound as well as different methods. Nanoparticles with semiconductive properties have been studied for organic compounds photodegradation due to their assistance in optimizing the degradation processes. Two of the most promising photocatalysts are ZnO and TiO2 because of their optimal results. In the present work the performance of the zinc peroxide (ZnO2) nanoparticles was evaluated. ZnO2 nanoparticles were synthesized from zinc acetate and hydrogen peroxide using the Sol-Gel method under ultrasound assistance. The characterization was carried out by UV–Vis spectroscopy, infrared Fourier transform total reflectance (ATR-FT-IR) spectroscopy, Raman spectroscopy, X-ray diffraction (XRD), Zeta potential, dynamic light scattering (DLS), field emission scanning electron microscopy (FE-SEM), and Energy Dispersive X-ray spectroscopy (EDX). The experiments for the degradation of NB were carried out in a photoreactor with UV lamps of 254 nm at 25 °C, using a solution of nitrobenzene with the nanoparticles. The best conditions for NB photodegradation were 30 ppm (ZnO2) and 15 ppm (NB) at pH 2, reaching up to 90% degradation in 2 h. The intermediates formed during the photodegradation of NB were identified by gas chromatography mass spectrometry.

Influence of plant radial oxygen loss in constructed wetland combined with microbial fuel cell on nitrobenzene removal from aqueous solution

This study investigated the effects of radial oxygen loss (ROL) of three different plants on nitrobenzene (NB) wastewater treatment and bioelectricity generation performance in constructed wetland-microbial fuel cell (CW-MFC). ROL and root biomass from wetland plants showed positive effects on NB wastewater compared to unplanted CW-MFC. Scirpus validus exhibited higher tolerance to NB than Typha orientalis and Iris pseudacorus at 20-200 mg/L NB. As NB concentration reached 200 mg/L, the CW-MFC with Scirpus validus had relatively high DO (2.57 ± 0.17 mg/L) and root biomass (16.42 ± 0.18 g/m²), which resulted in the highest power density and voltage (19.5 mW/m², 590 mV) as well as NB removal efficiency (93.9 %) among four reactors. High-throughput sequencing results suggested that electrochemically active bacteria (EAB) (e.g., Geobacter, Ferruginibacter) and dominant NB-degrading bacteria (e.g., Comamonas, Pseudomonas) could be enhanced by wetland plants, especially in CW-MFC with Scirpus validus. Therefore, Scirpus validus was a good option for simultaneously treating NB wastewater and producing bioelectricity.