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-Gn) 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/m3d. Furthermore, 4-NP was decreased by a value of 83.7 ± 4.9% in MAR-Gn compared to 65.6 ± 4.8% in control MAR. The 4-aminophenol (4-AP) recovery was accounted for 44.8% in the MAR-Gn 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-Gn 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-Gn 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. [Display omitted] •Graphene amended anaerobes improved the reduction of 4- nitrophenol.•Algal cultures utilized 4-aminophenol for biomass rich protein and carbohydrate.•Excessive NH4/P ratio affected the anaerobic degradation of 4- nitrophenol negatively.•Methanosaeta and Methanosphaerula was dominant species degrading 4- nitrophenol.•Chlorella vulgaris, Scenedesmus obliquus and Ulothrix subtilissima was abundant.