Decolorization of high concentration crystal violet by periphyton bioreactors and potential of effluent reuse for agricultural purposes

Current wastewater treatment biomeasures are dominated by single microbial species, which can only decolorize low concentrations (≤150 mg L−1) of crystal violet (CV). Considering the advantages of microbial aggregates, with micro-porous structure and complete hierarchical trophic communities, several innovative bioreactors based on periphyton (i.e. epiphyton, metaphyton and epilithon) were examined. The results showed that periphyton could tolerate high concentration of CV (1000 mg L−1) and the immobilized periphyton bioreactors could completely decolorize up to 1000 mg L−1 of CV within 168 h showing 50-100% removal by bioreactors. The removal of CV was a synergistic process accomplished by adsorption (with insignificant desorption) followed by the dominant mechanism of biodegradation. The CV was converted into non-toxic aliphatic compounds in the presence of periphyton. Phytotoxicity and microbial toxicity tests showed that biodegradation of CV did not produce any toxic secondary metabolite, leading to environmentally benign effluents meeting the standards of agricultural irrigation. These results provide an insight into the processes involved in removing CV by periphyton or similar microbial aggregates, and indicate the potential of periphyton as a green material to purify water contaminated by high concentrations of CV.