Treatment of contaminants by a cathode/FeIII/peroxydisulfate process: Formation of suspended solid organic-polymers.

Treatment of highly contaminated wastewaters containing refractory or toxic organic contaminants (e.g. industrial wastewaters) is becoming a global challenge. Most technologies focus on efficient degradation of organic contaminants. Here we improve the cathode/FeIII/peroxydisulfate (PDS) technology by turning down the current density and develop an innovative mechanism for organic contaminants abatement, namely polymerization rather than degradation, which allows simultaneous contaminants removal and resource recovery from wastewater. This polymerization leads to organic-particles (suspended solid organic-polymers) formation in bulk solution, which is demonstrated by eight kinds of representative organic contaminants. Taking phenol as a representative, 83% of PDS is saved compared to degradation process, with 87.2% of DOC removal. The formed suspended solid organic-polymers occupy 59.2% of COD of the original organics in solution, and can be easily separated from aqueous solution by sedimentation or filtration. The separated organic-polymers are a series of polymers coupled by phenolic monomers, as confirmed by FTIR and ESI-MS analyzes. The energy contained in the recovered organic polymers (4.76 × 10-5 kWh for 100 mL of 1 mM phenol solution in this study) can fully compensate the consumed electrical energy (2.8 × 10-5 kWh) in the treatment process. A representative polymerization model for this process is established, in which the SO4•- and HO• generated from PDS activation initiate the polymerization and improve the polymerization degree by the production of oligomer intermediates. A practical coking wastewater treatment is carried out to verify the research results and get positive feedback, with 56.0% of DOC abatement and the suspended solid organic-polymers accounts for 42.5% of the total COD in the raw wastewater. The energy consumption (47 kWh/kg COD, including electricity and PDS cost) is lower than the values in previous reports. This study provides a novel method for industrial wastewater treatment based on polymerization mechanism, which is expected to recover resources while removing pollutants with low consumption.