Nanodiamonds improve amaranth biodegradation in a lab-scale biofilter

Abstract

Nanodiamonds (ND) are nano-particles with a size of 4–5 nm which are intensively investigated for a number of properties that make them suitable for bio-applications. They could be chemically modified, they have a high adsorption capacity, high mechanical and chemical stability. Because ND have all these properties, they are also suitable for application in specific wastewater treatment and especially when the treated water is polluted with toxic compounds. The effect of ND applied in laboratory sand biofilter was investigated in this research. Synthetic wastewater with a model toxicant, the azo-dye amaranth, was used. The results showed that, in the presence of ND, the efficiency of amaranth removal remained high (more than 90%) in concentrations close to the critical one. The level of carbon-containing pollutants (assessed as chemical oxygen demand (COD) and total organic carbon (TOC)) decreased. The number of bacteria from the key detoxification groups increased 98 times for Pseudomonas sp. and 105 times for azo-degrading bacteria, while aerobic heterotrophs increased only 6 times after ND were applied. The abundance of Pseudomonas spp. after ND addition was confirmed with fluorescence in-situ hybridization.The activities of the key enzymes increased with 26–57%. Also, the activities of cathechol-1,2-dioxygenase and catechol-2,3-dioxygenase were found after ND addition but not before that. The obtained data showed that after ND were introduced in the wastewater treatment system, the number of biodegrading bacteria increased. They synthesized large amounts of azoreductases and oxygenases that led to the improved parameters of azo-detoxification process.