Remediation of petroleum-contaminated site soil by bioaugmentation with immobilized bacterial pellets stimulated by a controlled-release oxygen composite.

Bioaugmentation techniques still show drawbacks in the cleanup of total petroleum hydrocarbons (TPHs) from petroleum-contaminated site soil. Herein, this study explored high-performance immobilized bacterial pellets (IBPs) embed Microbacterium oxydans with a high degrading capacity, and developed a controlled-release oxygen composite (CROC) that allows the efficient, long-term release of oxygen. Tests with four different microcosm incubations were performed to assess the effects of IBPs and CROC on the removal of TPHs from petroleum-contaminated site soil. The results showed that the addition of IBPs and/or CROC could significantly promote the remediation of TPHs in soil. A CROC only played a significant role in the degradation of TPHs in deep soil. The combined application of IBPs and CROC had the best effect on the remediation of deep soil, and the removal rate of TPHs reached 70%, which was much higher than that of nature attenuation (13.2%) and IBPs (43.0%) or CROC (31.9%) alone. In particular, the CROC could better promote the degradation of heavy distillate hydrocarbons (HFAs) in deep soil, and the degradation rates of HFAs increased from 6.6% to 33.2%-21.0% and 67.9%, respectively. In addition, the IBPs and CROC significantly enhanced the activity of dehydrogenase, catalase, and lipase in soil. Results of the enzyme activity were the same as that of TPH degradation. The combined application of IBPs and CROC not only increased the microbial abundance and diversity of soil, but also significantly enhanced the enrichment of potential TPH-biodegrading bacteria. M. oxydans was dominant in AP (bioaugmentation with addition of IBPs) and APO (bioaugmentation with the addition of IBPs and CROC) microcosms that added IBPs. Overall, the IBPs and CROC developed in this study provide a novel option for the combination of bioaugmentation and biostimulation for remediating organic pollutants in soil.

Bioleaching of metals from spent fluid catalytic cracking catalyst using adapted Acidithiobacillus caldus.

In this study, an adapted bioleaching strain of Acidithiobacillus caldus UVS10 was successfully developed. Batch tests and tests in bioreactor were conducted to evaluate the metals bioleaching performance of A. caldus UVS10 to spent FCC catalyst (SFCCC). Results of batch experiments showed the bioleaching efficiency of Ni, V, La, and Ce in SFCCC reached 19.40%, 22.06%, 53.75%, and 59.56%, respectively. High SFCCC pulp density inhibited the leaching of metals. Sb leaching was inhibited in acidic environment caused by A. caldus UVS10. Contents of Ni, V, La, and Ce in extracellular polymeric substances (EPS) were significantly higher than those intracellular. Accumulation of metal in EPS and cytosol increased with the increase of SFCCC pulp density. V was less intercepted by EPS than Ni, La, and Ce, because of lower toxicity. Experimental results in bioreactor showed that Ni, V, La, and Ce could be effectively leached by A. caldus UVS10 under 10% pulp density. The aeration and stirring operating environment in bioreactor improved the leaching efficiency of metals in SFCCC. After bioleached in bioreactor, the available fraction content of four metals in SFCCC decreased significantly. Ecological risk analysis demonstrated the environmental risks of bioleached SFCCC were significantly lower than raw SFCCC. Different reaction kinetic models were used to represent metals leaching behavior under bioleaching of A. caldus UVS10, leaching of La and Ce showed good agreement with the product layer diffusion model, while Ni and V leaching kinetics fit well with the surface chemical reaction models.

Analysis of the mechanism of sludge ozonation by a combination of biological and chemical approaches.

Using the practical sludge obtained from municipal sewage treatment plants, the mechanism of the sludge ozonation process was systematically investigated by a combination of biological and chemical approaches, including analysis of the changes in biological response by CFU and PCR-DGGE, bio-macromolecular activity and radical scavenging activity. The results indicated that after the sludge was exposed to ozone at less than 0.02 g O(3)/g TSS, the DGGE fingerprint remained constant and there was still some enzyme activity, indicating that the sludge solubilization was the main process. At greater than 0.02 g O(3)/g TSS, the bacteria began to be broken down and ozone was used to oxidize the bio-macromolecules such as proteins and DNA released from the sludge. Bacteria belonging to 'G-Bacteria' were able to conserve their DNA in the presence of less than 0.08 g O(3)/g TSS. At levels higher than 0.10 g O(3)/g TSS, the disintegration of the sludge matrix became slow and the microbes lost most of their activity, and ozone was used to transform the bio-macromolecules into small molecules. However, at levels higher than 0.14 g O(3)/g TSS, the ozone failed to oxidize the sludge efficiently, because several radical scavengers such as lactic acid and SO(4)(2-) were released from the microbial cells in the sludge.

Enhanced sludge solubilization by microbubble ozonation.

A microbubble ozonation process for enhancing sludge solubilization was proposed and its performance was evaluated in comparison to a conventional ozone bubble contactor. Microbubbles are defined as bubbles with diameters less than several tens of micrometers. Previous studies have demonstrated that microbubbles could accelerate the formation of hydroxyl radicals and hence improve the ozonation of dyestuff wastewater. The results of this study showed that microbubble ozonation was effective in increasing ozone utilization and improving sludge solubilization. For a contact time of 80 min, an ozone utilization efficiency of more than 99% was obtained using the microbubble system, while it gradually decreased from 94% to 72% for the bubble contactor. The rate of microbial inactivation was obviously faster in the microbubble system. At an ozone dose of 0.02g O(3)g(-1) TSS, about 80% of microorganisms were inactivated in the microbubble system, compared with about 50% inactivation for the bubble contactor. Compared to the bubble contactor, more than two times of COD and total nitrogen, and eight times of total phosphorus content were released from the sludge into the supernatant by using the microbubble system at the same ozone dosage. The application of microbubble technology in ozonation processes may provide an effective and low cost approach for sludge reduction.

Enhanced ozonation of simulated dyestuff wastewater by microbubbles.

The ozonation of synthetic wastewater containing azo dye, CI Reactive Black 5, was investigated using a microbubble generator and a conventional bubble contactor. The microbubble generator produced a milky and high intensity microbubble solution in which the bubbles had a mean diameter of less than 58 microm and a numerical density of more than 2.9 x 10(4) counts ml(-1) at a gas flow rate of less than 0.5 l min(-1). Compared with the bubble contactor, the total mass transfer coefficient was 1.8 times higher and the pseudo-first order rate constant was 3.2-3.6 times higher at the same initial dye concentration of 100 mg l(-1), 230 mg l(-1) and 530 mg l(-1) in the proposed microbubble system. The amount of total organic carbon removed per g of ozone consumed was about 1.3 times higher in the microbubble system than in the bubble contactor. The test using terephthalic acid as the chemical probe implied that more hydroxyl radicals were produced in the microbubble system, which contributed to the degradation of the dye molecules. The results suggested that in addition to the enhancement of mass transfer, microbubbles, which had higher inner pressure, could accelerate the formation of hydroxyl radicals and hence improve the oxidation of dye molecules.