The degradation of di-(2-ethylhexyl) phthalate, DEHP, in sediments using percarbonate activated by seaweed biochars and its effects on the benthic microbial community

Abstract

Di-(2-ethylhexyl) phthalate (DEHP) is a highly toxic and persistent contaminant. Elimination of DEHP from the environment is crucial to safe guard ecological and human health. Red seaweed-derived biochar (RSB), made from Agardhiella subulata residues, was used to activate sodium percarbonate (SPC) for the degradation of DEHP in contaminated estuarine surface sediments. The RSB was characterized by scanning transmission electron microscope-energy dispersive X-ray spectroscopy (STEM-EDS), micro-attenuated total reflectance-Fourier transform infrared spectroscopy (MATR-FTIR), elemental analysis (EA), thermogravimetric analysis (TGA), X-ray photoelectron spectrometry (XPS), linear sweep voltammetry (LSV), and Tafel measurements. Results revealed that the increase in SPC dosage, specifically, [DEHP] to [SPC] molar ratio of 1:1000, increased DEHP removal in the sediment. The pyrolysis temperature (300–900 °C) for biochar preparation significantly controlled the particle size and catalytic capacity of RSB. Pristine RSB contributed catalytic sites, which effectively activated SPC via electron transfer through the RSB matrix, that generated HO• and facilitated the carbocatalysis degradation of DEHP. RSB900 was the best-performing SPC activator. Under the optimal initial pH of 9, total DEHP degradation was 63% in 12 h. Treatment with RSB and SPC, significantly increased the bacterial abundance in the sediment. Results of next-generation sequencing analyses showed that Proteobacteria and Bacterioidetes were the dominant bacterial phyla. The microbial abundance and diversity of the sediment ecosystems were improved significantly upon treatment by the RSB–SPC process, indicating the efficacy of the remediation technology. Results provide valuable insights into the role of microbial communities as indicators of sediment quality.