Abstract
Owing to the implementation of increasingly stringent water conservation policies and regulations, the pulp and paper mill industry must make increased efforts to meet the limits for pollutant emissions. The primary pretreatment and secondary biochemical treatment methods used currently generally fail to meet the country-specific environmental regulations, and the wastewater must be processed further even after being subjected to secondary biochemical treatments. In this work, we synthesized Fe3O4/MnO2 nanocomposites (FMNs) with a flower-like structure for use in the heterogeneous photocatalytic treatment of biotreated papermaking wastewater. FMNs1.25, which were formed using a KMnO4/Fe3O4 molar ratio of 1.25, could be separated readily using an external magnetic field and exhibited higher photocatalytic activity than those of the other samples as well as MnO2 and Fe3O4. The effects of various experimental parameters on the photocatalytic activity of FMNs1.25, including the initial pH of the wastewater and the catalyst dosage, were determined. The common chemical oxygen demand (CODCr) reduction rate in the case of this sample reached 56.58% within 120 min at a pH of 3, the CODCr of effluent after treatment was 52.10 mg/L. Further, even under neutral conditions, the CODCr of the treated effluent was below the current limit for discharge in China. Moreover, the nanocomposites exhibited good recyclability, and their catalytic activity did not decrease significantly even after five usage cycles. This study should serve as a platform for the fabrication of effective photocatalysts for the advanced treatment of biotreated papermaking effluent and refractory organic wastewater.
Highlights
The effective treatment of wastewater plays an important role in maintaining the ecological balance of the natural environment [1,2,3,4,5,6,7]
Primary pretreatments and secondary biochemical treatments are the main steps in wastewater treatment [10,11]
FMNs0.5 and FMNs1, the absorption peak at 574 cm−1 can be assigned to the Fe-O stretching vibrations that occur in iron Fe oxide
Summary
The effective treatment of wastewater plays an important role in maintaining the ecological balance of the natural environment [1,2,3,4,5,6,7]. Pulp and paper mills consume a lot of water and, at the same time, emit a considerable amount of wastewater [8,9]. In China, because of the increasingly strict environmental protection guidelines and the implementation of stricter regulations, it has become essential to subject wastewater to additional treatments. These advanced treatments for wastewater pose an urgent problem in case of the pulp and paper industry [12].
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