Graphene enhanced detoxification of wastewater rich 4-nitrophenol in multistage anaerobic reactor followed by baffled high-rate algal pond

The presence of 4-nitrophenol (4-NP) in the wastewater industry causes toxicity and inhibition of the anaerobic degrading bacteria. The anaerobes in the multistage anaerobic reactor were loaded by 30.0 mg/gVS Graphene nanoparticles (MAR-G_n) as an electron acceptor to detoxify wastewater industry. The half maximal inhibitory concentration (IC₅₀) was reduced from 455 ± 22.5 to 135 ± 12.7 μg Gallic acid equivalent/mL at 4-NP loading rate of 47.9 g/m³ d. Furthermore, 4-NP was decreased by a value of 83.7 ± 4.9% in MAR-G_n compared to 65.6 ± 4.8% in control MAR. The 4-aminophenol (4-AP) recovery was accounted for 44.8% in the MAR-G_n at an average oxidation-reduction potential (ORP) of − 167.3 ± 21.2 mV. The remaining portions of 4-NP and 4-AP in the MAR-G_n effluent were efficiently removed by baffled high rate algal pond (BHRAP), resulting in overall removal efficiency of 91.6 ± 6.3 and 92.3 ± 4.6%, respectively. The Methanosaeta (52.9%) and Methanosphaerula (10.9%) were dominant species in MAR-G_n for reduction of 4-NP into 4-AP. Moreover, Chlorophyta cells (Chlorella vulgaris, Scenedesmus obliquus, Scenedesmus quadricauda and Ulothrix subtilissima were abundant in the BHRAP for complete degradation of 4-NP and 4-AP.