Metal-free carbocatalysts derived from macroalga biomass (Ulva lactuca) for the activation of peroxymonosulfate toward the remediation of polycyclic aromatic hydrocarbons laden marine sediments and its impacts on microbial community

Potential toxic chemicals, specifically, polycyclic aromatic hydrocarbons (PAHs), are major sediment contaminants. Herein, green seaweed (Ulva lactuca) was used as a feedstock and pyrolyzed at temperature in the range between 300 and 900 degrees C. The metal-free carbocatalyst (GSBC) for peroxymonosulfate (PMS) activation to degrade PAHs contaminated sediments was studied. The effects of GSBC-PMS treatment on microbial community abundance was studied as well. The pyrolysis temperature of GSBC preparation affected the PMS activation performance. Results show that GSBC700 exhibited remarkable catalytic characteristics in PAHs degradation by effective activation of PMS. The results also demonstrated that the sulfate radical-carbon-driven advanced oxidation processes (SR-CAOP) reaction achieved 87% and apparent rate constant (k(obs)) of 6.3 x 10(-2) h(-1) of total PAHs degradation in 24 hat 3.3 g/L of GSBC, PMS dose of 1 x 10(-4) M, and pH 3.0. The degradation of 2-, 3-, 4-, 5-, and 6-ring PAHs was 84, 83, 83, 80, and 89%, respectively. The synergetic effect established between GSBC and PMS enhanced the formation of ROSs, namely, SO4 center dot-, HO center dot, and O-1(2), which were major species contributing to PAHs degradation. The synergistic effect of pi-pi stacking structure and graphitization of GSBC formed electron shuttle, which contributed to PAHs degradation performance. Microbial community structure analyses in the GSBC-PMS treated sediments showed that the relative abundance of Lactobacillus rhamnosus species, most of which belonged to the Lactobacillus genus and Firmicutes phylum, which aided in continuing PAHs biodegradation post GSBC-PMS treatment. Therefore, GSBC can be a promising carbocatalyst produced via biomass-to-biochar conversion as biowaste-to-energy source used in the SR-CAOP-mediated process for sediment remediation.

Automated summary

This study investigated the use of green seaweed (Ulva lactuca) as a feedstock for the production of metal-free carbocatalyst (GSBC) for the degradation of polycyclic aromatic hydrocarbons (PAHs) in contaminated sediments. The results showed that GSBC700 exhibited remarkable catalytic characteristics in PAHs degradation by effective activation of peroxymonosulfate (PMS). The study also found that the microbial community abundance in the treated sediments was affected by the GSBC-PMS treatment. This research suggests that GSBC has great potential as a carbocatalyst in the sediment remediation process.