Biodegradation of toluene using Candida tropicalis immobilized on polymer matrices in fluidized bed bioreactors

Enhanced efficiency and mechanism of low-temperature biochar on simultaneous removal of nitrogen and phosphorus by combined heterotrophic nitrification-aerobic denitrification bacteria

In this study, three strains of heterotrophic nitrification-aerobic denitrification (HN-AD) capable of simultaneously removing phosphorus were isolated from activated sludge, and low-temperature coconut shell biochar was prepared. The metabolic effects of combined HN-AD bacteria on the total nitrogen (TN) and total phosphorus (TP) were investigated, and the enhanced efficiency and mechanism of low-temperature biochar on the combined bacteria were also explored. The results indicated that the combined bacteria could adapt to environmental impacts and multiple nitrogen sources. The low-temperature biochar containing more aliphatic carbon and oxygen-containing functional groups enhanced the metabolic activity of combined HN-AD bacteria and accelerated the electron transfer process during nitrogen and phosphorus degradation. The removal efficiencies of TN and TP increased by 68% and 88%, respectively, in the treatment of actual sewage by biochar attached with combined bacteria. The findings form a basis for the engineering utilization of HN-AD and are of great practical significance.

Improved peroxidase-mediated biodegradation of toluene vapors in the moving-bed activated sludge diffusion (MASD) process using biosurfactant-generating biomass stimulated with H2O2

Two strategies were attempted to improve the biodegradation and mineralization of toluene vapors in the activated sludge diffusion (ASD) process using biosurfactant-generating Pseudomonas spp. and Bacillus spp. mixture. Different operational parameters including toluene concentration, superficial air velocity, biomass concentration, moving-media insertion and H₂O₂ were evaluated on toluene removal in the ASD process within 550 days of operation. It was found that complete biodegradation and 79.8% mineralization of toluene vapors at inlet loading rate of 144 g/m³.h could be achieved in the ASD process by inserting moving media (MASD) at a volume ratio of 20% along with stimulation of bacteria with H₂O₂. The concentration of biosurfactant and peroxidase generated in the integrated process (H₂O₂-stimulated MASD reactor) was 3.7 and 2.5 times of that in the conventional ASD process. The maximum toluene elimination capacity obtained in the H₂O₂- stimulated MASD process was 285 g/m³.h at an inlet loading rate of around 430 g/m³.h. Accordingly, H₂O₂-mediated MASD process could be a promising technique for efficient biodegradation and mineralization of aromatic hydrocarbons in the contaminated air streams.

Plant-growth promoting Candida sp. AVGB4 with capability of 4-nitroaniline biodegradation under drought stress

This study focused on rhizospheric yeast capable of degrading a priority pollutant, 4-nitroaniline (4-NA), under drought stress. Candida sp. AVGB4 (AVGB4) inhabiting in soil was isolated and characterized with plant-growth promoting (PGP) traits. 4-NA-dependent growth kinetic and biodegradation kinetics were analyzed and revealed 4-NA complete degradation and tolerance property. AVGB4 proliferation, PGP activities, and 4-NA degradation activity were well maintained under drought stress induced by PEG-6000 incorporation, and could be strengthened in the presence of succinate, an organic compound generally found in plant root exudates. The in vitro experiments proved that AVGB4 significantly enhanced plant growth and increased the shoot and root biomass of Vigna radiata plant in the absence or presence of 4-NA. The overall results including cytogenotoxicity and phytotoxicity test with legumes indicated that not only AVGB4 was capable of 4-NA detoxification facilitating plants to cope with chemical-toxicity stress, but it also has advantageous role in promoting plant growth and sustainable rhizoremediation of 4-NA contaminated sites.