Biosurfactant assisted recovery of the C5-C11 hydrocarbon fraction from oily sludge using biosurfactant producing consortium culture of bacteria.

A biosurfactant producing culture of bacteria was isolated from an automobile engine oil dump site which was later used as an inoculum in batch and continuous flow oil recovery from oily sludge. Initially, an emulsion of oily sludge was prepared by mixing 5% m/v solids: 21% v/v bituminous sludge: 77% v/v water. The isolated cultures were added to vessels with stable emulsions to facilitate the separation of oil droplets from the sludge matrix. In batches with live cultures, up to 35% oil recovery was achieved after incubation for 10 days. Further investigations were conducted in a semi-continuous feed, fed-batch plug flow reactor (FB-PFR) system. Up to 99.7% was achieved in the FB-PFR after operation for 10 days, much higher than the recovery achieved in the pure batch systems where only 35% oil was recovered after incubation for 10 days. The improved performance in the FB-PFR was attributed to differential separation of particles under variable velocity along the reactor. The culture in the reactor was predominated by Klebsiellae, Enterobacteriaceae and Bacilli throughout the experiment. A crude biosurfactant produced by the cultures was partially purified and analyzed using the liquid chromatograph coupled to a tandem mass spectrometer (LC-MS/MS) which showed that the molecular structure of the biosurfactant produced closely matched the structure of lipopeptides identified in earlier studies. This process is aimed at recovering useful oil from oily waste sludge with the added advantage of degrading aromatic organic impurities in the oil to produce a cleaner oil product. The further advantage of the FB-PFR system was that, the bacteria discharged together with effluent sludge residue further degraded chemical oxygen demand (COD) in the treated sludge thereby reducing the polluting potential of the final disposed sludge.

Photoassisted Biodegradation of Irradiated Organics in Simulated Nuclear Wastewater.

The extent of dehalogenation and degradation of toxic aromatic compounds in a nuclear wastewater was evaluated using a two-stage system consisting of a photolytic reactor followed by a biological reactor. Experiments were performed by varying the initial 4-chlorophenol (4-CP) concentration from 50 to 1000 mg/L. The UV pretreatment stage improved the overall efficiency of biodegradation of the recalcitrant compound by facilitating degradability in the biological stage. Removal efficiencies greater than 98% were achieved at 4-CP feed concentrations < 50 mg/L. Adding an H2O2 dose of 0.1 mg/L as an oxidant further improved biodegradation under optimum operating conditions for the entire system. Some known aromatic compound degraders such as Pseudomonas aeruginosa and Pseudomonas mendocina were detected in the consortium using the 16S rRNA genetic fingerprint technique. To the authors' knowledge, this is the first study on biodegradation of halogenated aromatic compounds that are copollutants of metallic radionuclides in radioactive wastewater.

Assessment of nutritional value of single-cell protein from waste-activated sludge as a protein supplement in poultry feed.

The amount of protein wasted through sludge in Gauteng, South Africa, amounts to 95 000 metric tonne/yr, with the order of magnitude of the national protein requirement of approximately 145 000 metric tonne/yr. Waste-activated sludge (WAS) from wastewater treatment plants (WWTPs) that treat domestic wastewater contains protein in a ratio of 2:1 against fishmeal. This protein source has not been utilized because of the high content of toxic heavy metals and other potential carcinogenic pollutants in the sludge. In this study, a pretreatment method of modified aqua regia dilute acid wash was used to lower the metal content by approximately 60%. However, this resulted in a 33% loss of amino acids in the acid-washed WAS. A feed substitution test in poultry with different fishmeal-sludge ratios (0%, 25%, 50%, 75%, and 100% WAS as percent substitution of fishmeal) showed no impact of sludge single-cell protein (SCP) on mortality rate. However, sludge substitution in the feed yielded weight gains and cost savings up to 46%.

Characterization and biodegradation of polycyclic aromatic hydrocarbons in radioactive wastewater.

PAH degrading Pseudomonad and Alcaligenes species were isolated from landfill soil and mine drainage in South Africa. The isolated organisms were mildly radiation tolerant and were able to degrade PAHs in simulated nuclear wastewater. The radiation in the simulated wastewater, at 0.677 Bq/µL, was compatible to measured values in wastewater from a local radioisotope manufacturing facility, and was enough to inhibit metabolic activity of known PAH degraders from soil such as Pseudomonas putida GMP-1. The organic constituents in the original radioactive waste stream consisted of the full range of PAHs except fluoranthene. Among the observed PAHs in the nuclear wastewater from the radioisotope manufacturing facility, acenaphthene and chrysene predominated--measured at 25.1 and 14.2mg/L, respectively. Up to sixteen U.S.EPA priority PAHs were detected at levels higher than allowable limits in drinking water. The biodegradation of the PAHs was limited by the solubility of the compounds. This contributed to the observed faster degradation rates in low molecular weight (LMW) compounds than in high molecular weight compounds.

Microbial culture dynamics and chromium (VI) removal in packed-column microcosm reactors.

Microbial Cr(VI) reduction in groundwater aquifer media was investigated in microcosm reactors extracted from Cr(VI) contaminated sites in South Africa. The reactors were operated under an influent Cr(VI) concentration of 40 mg/L to simulate the current Cr(VI) level at the contaminated site. Near complete Cr(VI) removal was observed in microcosm reactors inoculated with Cr(VI) reducing bacteria from dried activated sludge collected from a treatment plant receiving periodic loadings of Cr(VI). The best performance was observed under low hydraulic loading (flow rate, Q=0.310 cm(3)/hr). Microbial culture characterisation results showed a change in culture composition after 17 days of reactor operation, indicating Bacillus and Lysinibacillus species as the most dominant organisms in reactors that reduced Cr(VI). The predominance of Bacillus and Lysinibacillus species was either due to resilience against toxicity or adaptation to the changing conditions in the reactor. This research was the initial step towards the development of an in situ bioremediation process to contain the spread of a Cr(VI) plume in a groundwater aquifer at contaminated site in Brits, South Africa. South Africa holds about 72% percent of the world's chromium resources, the majority of which is mined in the North Eastern region of the country formally known as Transvaal.

Chromium (VI) reduction in activated sludge bacteria exposed to high chromium loading: Brits culture (South Africa).

A mixed-culture of bacteria collected from a wastewater treatment plant in Brits, North-West Province (South Africa) biocatalytically reduced Cr(VI) at much higher concentrations than previously observed in cultures isolated in North America. Cr(VI) reduction rate up to 8 times higher than the rate in previous cultures was achieved by the Brits culture under aerobic conditions. Near complete Cr(VI) reduction was observed in batches under initial concentrations up to 200mg Cr(VI)/L after incubation for 65h in aerobic cultures. Under anaerobic conditions up to 150mg Cr(VI)/L was completely removed after incubating for 130-155h. In the previous cultures, complete removal was only achieved in cultures at an initial Cr(VI) concentration lower than 30mg/L after incubation for 96-110h. Consortium cultures were characterised using 16S rRNA partial sequence analysis. Results showed that the Gram-positive Bacillus genera predominated under aerobic conditions with a small composition of the Gram-negative Microbacterium sp. More biodiversity was observed in anaerobic cultures with the marked appearance of Enterococcus, Arthrobacter, Paenibacillus and Oceanobacillus species. Experiments run on purified individual species did not achieve the same level of Cr(VI) reduction as observed in the original consortium from sludge indicating possible existence of interspecies interactions necessary for optimum Cr(VI) reduction. All Cr(VI) reduced was accounted for as Cr(III) with a small error range (2-6%).

Modeling hexavalent chromium removal in a Bacillus sp. fixed-film bioreactor.

A one-dimensional diffusion-reaction model was developed to simulate Cr(VI) reduction in a Bacillus sp. pure culture biofilm reactor with glucose as a sole supplied carbon and energy source. Substrate utilization and Cr(VI) reduction in the biofilm was best represented by a system of (second-order) partial differential equations (PDEs). The PDE system was solved by the (fourth-order) Runge-Kutta method adjusted for mass transport resistance using the (second-order) Crank-Nicholson and Backward Euler finite difference methods. A heuristic procedure (genetic search algorithm) was used to find global optimum values of Cr(VI) reduction and substrate utilization rate kinetic parameters. The fixed-film bioreactor system yielded higher values of the maximum specific Cr(VI) reduction rate coefficient and Cr(VI) reduction capacity (kmc = 0.062 1/h, and Rc = 0.13 mg/mg, respectively) than previously determined in batch reactors (kmc = 0.022 1/h and Rc = 0.012 mg/mg). The model predicted effluent Cr(VI) concentration well with 98.9% confidence (sigmay2 = 2.37 mg2/L2, N = 119) and effluent glucose with 96.4 % confidence (sigmay(w)2 = 5402 mg2/L2, N = 121, w = 100) over a wide range of Cr(VI) loadings (10-498 mg Cr(VI)/L/d).