Search

As salicylic acid (SAC) is an extensively used pharmaceutical, discharge of SAC into the environment has caused serious threats to ecology in view of its toxicity. Therefore, SO4•−-involved chemical oxidation methods have been employed for eliminating SAC. Since monopersulfate (MPS) has become a popular reagent for producing SO4•−, an alternative heterogeneous Co-based catalyst is proposed by using a Co-coordinated covalent organic polymers (Co-COP) as a precursor. Via carbonization, Co-COP is transferred by conversion of Co ions to Co/CoO nanoparticle and conversion of COP to N-doped carbon nanocapsules (CNC), respectively, to form a unique composite of Co NPs embedded into carbon nanocapsule (CoCNC). CoCNC exhibits a higher catalytic activity than Co3O4 nanoparticle for activating MPS to degrade SAC because of synergistic effects between Co NPs and the N-doped CNC which not only acts as the support but also provides active sites. Hence, CoCNC+MPS could afford a much lower Ea value (25.4 kJ/mol) of SAC degradation than the reported values. Moreover, CoCNC is still efficient for removing SAC even in the presence of high-concentration NaCl and SDS. CoCNC can be also recyclable over many cycles and maintain its catalytic activities, confirming that CoCNC is an advantageous catalyst for MPS activation.

The efficiency of arsenic removal from source waters and artificial freshwaters during coagulation with ferric chloride and alum was examined in bench-scale studies. Arsenic(V) removal by either ferric chloride or alum was relatively insensitive to variations in source water composition below pH 8. At pH 8 and 9, the efficiency of arsenic(V) removal by ferric chloride was decreased in the presence of natural organic matter. The pH range for arsenic(V) removal with alum was more restricted than with ferric chloride. For source waters spiked with 20 μg/L arsenic(V), final dissolved arsenic(V) concentrations in the product water of less than 2 μg/L were achieved with both coagulants at neutral pH. Removal of arsenic(III) from source waters by ferric chloride was both less efficient and more strongly influenced by source water composition than removal of arsenic(V). The presence of sulfate (at pH 4 and 5) and natural organic matter (at pH 4 through 9) adversely affected the efficiency of arsenic(III) removal by ferric chloride. Arsenic(III) could not be removed from source waters by coagulation with alum.

Bench-scale studies were conducted in model freshwater systems to investigate how various parameters affected arsenic removal during coagulation with ferric chloride and arsenic adsorption onto preformed hydrous ferric oxide. Parameters included arsenic oxidation state and initial concentration, coagulant dosage or adsorbent concentration, pH, and the presence of co-occurring inorganic solutes. Comparison of coagulation and adsorption experiments and of experimental results with predictions based on surface complexation modeling demonstrated that adsorption is an important (though not the sole) mechanism governing arsenic removal during coagulation. Under comparable conditions, better removal was observed with arsenic(V) [As(V)] than with arsenic(III) [As(III)] in both coagulation and adsorption experiments. Below neutral pH values, As(III) removal-adsorption was significantly decreased in the presence of sulfate, whereas only a slight decrease in As(V) removal-adsorption was observed. At high pH, removal-adsorption of As(V) was increased in the presence of calcium. Removal of As(V) during coagulation with ferric chloride is both more efficient and less sensitive than that of As(III) to variations in source water composition.