This research evaluated the feasibility of using vetiver plantlets (Vetiveria zizanioides (L.) Nash) on a floating platform with aeration to degrade phenol (500 mg/L) in illegally dumped industrial wastewater (IDIWW). The IDIWW sample was from the most infamous illegal dumping site at Nong Nae subdistrict, Phanom Sarakham district, Chachoengsao province, Thailand. Laboratory results suggested that phenol degradation by vetiver involves two phases: Phase I, phytopolymerization and phyto-oxidation assisted by root-produced peroxide (HO) and peroxidase (POD), followed by phase II, a combination of phase I with enhanced rhizomicrobial degradation. The first 360-400 h of phenol degradation were dominated by phytopolymerization and phyto-oxidation yielding particulate polyphenols (PPP) or particulate organic matter (POM) as by-products, while phenol decreased to around 145 mg/L. In Phase II, synergistically, rhizomicrobial growth was ∼100-folds greater on the roots of the vetiver plantlets than in the IDIWW and participated in the microbial degradation of phenol at this lower phenol concentration, increasing the phenol degradation rate by more than three folds. This combination of phytochemical and rhizomicrobiological processes eliminated phenol in IDIWW in less than 766 h (32 days), while without the vetiver plantlets, phenol degradation by aerated microbial degradation alone may require 235 days. To our knowledge, this is the first that systematically reveals the complete phenol degradation mechanism by vetiver plantlets in real aerated wastewater.

a b s t r a c tIllegal dumping of phenol-concentrated industrial wastewater in a residential area poses serious health risks to the community in Thailand. Thus, a low-cost and easily implementable treatment technique that the affected community can perform is greatly beneficial. Here, we evaluated the enhanced phenol-degradation kinetics using a rhizomicrobial-augmented mature vetiver root system on a floating platform (with and without aeration) in comparison to a previously published study of a young vetiver root system. The mature vetiver root was covered with a biofilm of phenol-degrading rhizomicrobes including bacteria (Enterobacter spp., Pseudomonas spp., Rhodococcus spp., and Acinetobacter spp.) and fungi (Candida spp., Rhizopus spp., Aspergillus spp., and Fusarium spp.). Phenol (500 mg L -1 ) was degraded to 1 mg L -1 in 249 h using rhizomicrobial-augmented mature vetiver with aeration. Using young vetiver plantlets with aeration, this occurred in 675 h, and using rhizomicrobial-augmented mature vetiver without aeration, this occurred in 766 h. The findings suggest that, in addition to augmented rhizomicrobes, vetiver maturity and aeration substantially contribute to the enhancement. The vetiver maturity increased the root biomass, which releases more peroxidase for accelerating phenol transformation, and enhanced the superoxide dismutase activity, which decreases the side effects of phenol detoxification. Aeration enhanced the peroxidase and superoxide dismutase activity in the vetiver and augmented rhizomicrobes to accelerate the phenol polymerization to non-toxic by-products.

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