Zhongzhi Zhang

Biogas productivity by co-digesting Taihu blue algae with corn straw as an external carbon source

A batch anaerobic test was conducted to evaluate the effects of adding high carbon content of corn straw to the digestion of Taihu blue algae to attain an optimal C/N ratio for higher methane yield. The addition of corn straw in algae at a C/N ratio of 20/1 increased methane yield by 61.69% at 325 mL g(-1)VS(-1) (compared with 201 mL g(-1) VS(-1) of algae digestion alone), followed by C/N ratios of 16/1 and 25/1, all operated at 20 g VSL(-1) and 35 °C. The results suggest the optimal C/N ratio for co-digestion of algae with corn straw is 20/1. The findings could offer options for efficient methane production and waste treatment.

Effect of biological pretreatments in enhancing corn straw biogas production

A biological pretreatment with new complex microbial agents was used to pretreat corn straw at ambient temperature (about 20°C) to improve its biodegradability and anaerobic biogas production. A complex microbial agent dose of 0.01% (w/w) and pretreatment time of 15 days were appropriate for biological pretreatment. These treatment conditions resulted in 33.07% more total biogas yield, 75.57% more methane yield, and 34.6% shorter technical digestion time compared with the untreated sample. Analyses of chemical compositions showed 5.81-25.10% reductions in total lignin, cellulose, and hemicellulose contents, and 27.19-80.71% increases in hot-water extractives; these changes contributed to the enhancement of biogas production. Biological pretreatment could be an effective method for improving biodegradability and enhancing the highly efficient biological conversion of corn straw into bioenergy.

Remediation of petroleum-contaminated soil after composting by sequential treatment with Fenton-like oxidation and biodegradation

A laboratory study was conducted to enhance removal of residual contaminants after composting in a highly petroleum-contaminated soil by combining Fenton-like pretreatment with biodegradation. The contaminants were characterized by Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) during soil treatment. The optimum molar ratio of H(2)O(2) and Fe(3+) was 300/1 determined in batch experiments. At the end of Fenton-like treatment, total dichloromethane-extractable organics (TEO) decreased from 32,400 to 21,800 mg kg(-1) soil, and the toxicity of soil was reduced greatly in the preoxidation process. A significant loss of the number of soil microorganisms was observed in the Fenton-like reaction. During the microbial treatment period, 50.6% of TEO was destroyed. Numerous varieties of polar compounds containing nitrogen and oxygen were identified by FT-ICR MS. The number of compounds containing two oxygen atoms dropped from 604 to 163 during Fenton-like oxidation, and increased again to 577 after biodegradation.

Oil recovery from refinery oily sludge using a rhamnolipid biosurfactant-producing Pseudomonas

In this study, a rhamnolipid biosurfactant-producing strain, Pseudomonas aeruginosa F-2, was used to recover oil from refinery oily sludge in laboratory and pilot-scale experiments. The optimum values of carbon to nitrogen ratio, temperature, sludge-water ratio and inoculum size for oil recovery were determined as 10, 35 °C, 1:4 and 4%, respectively. An oil recovery of up to 91.5% was obtained with the equipping of draft tubes during the field pilot-scale studies. The results showed that strain F-2 has the potential for industrial applications and may be used in oil recovery from oily sludge.

Interaction of Heavy Metals and Pyrene on Their Fates in Soil and Tall Fescue (Festuca arundinacea)

90-Day growth chamber experiments were performed to investigate the interactive effect of pyrene and heavy metals (Cu, Cd, and Pb) on the growth of tall fescue and its uptake, accumulation, and dissipation of heavy metals and pyrene. Results show that plant growth and phytomass production were impacted by the interaction of heavy metals and pyrene. They were significantly decreased with heavy metal additions (100-2000 mg/kg), but they were only slightly declined with pyrene spiked up to 100 mg/kg. The addition of a moderate dosage of pyrene (100 mg/kg) lessened heavy metal toxicity to plants, resulting in enhanced plant growth and increased metal accumulation in plant tissues, thus improving heavy metal removal by plants. In contrast, heavy metals always reduced both plant growth and pyrene dissipation in soils. The chemical forms of Cu, Cd, and Pb in plant organs varied with metal species and pyrene addition. The dissipation and mineralization of pyrene tended to decline in both planted soil and unplanted soils with the presence of heavy metals, whereas they were enhanced with planting. The results demonstrate the complex interactive effects of organic pollutants and heavy metals on phytoremediation in soils. It can be concluded that, to a certain extent, tall fescue may be useful for phytoremediation of pyrene-heavy metal-contaminated sites. Further work is needed to enhance methods for phytoremediation of heavy metal-organics co-contaminated soil.

Removal of residual contaminants in petroleum-contaminated soil by Fenton-like oxidation

The degradation of bioremediation residues by hydrogen peroxide in petroleum-contaminated soil was investigated at circumneutral pH using a Fenton-like reagent (ferric ion chelated with EDTA). Batch tests were done on 20 g soil suspended in 60 mL aqueous solution containing hydrogen peroxide and Fe(3+)-EDTA complex under constant stirring. A slurry reactor was used to treat the soil based on the optimal reactant conditions. Contaminants were characterized by Fourier transform infrared spectroscopy and Fourier transform ion cyclotron resonance mass spectrometry. The results showed that the optimal treatment condition was: the molar ratio of hydrogen peroxide to iron=200:1, and pH 7.0. Under the optimum condition, total dichloromethane-extractable organics were reduced from 14,800 to 2300 mg kg(-1) soil when the accumulative H(2)O(2) dosage was 2.45 mol kg(-1) soil during the reactor treatment. Abundance of viable cells was lower in incubated Fenton-like treated soil than in untreated soil. Oxidation of contaminants produced remarkable compositional and structural modifications. A fused ring compound, identified as C(34)H(38)N(1), was found to exhibit the greatest resistance to oxidation.

Enhanced methane production from Taihu Lake blue algae by anaerobic co-digestion with corn straw in continuous feed digesters.

Anaerobic digestion of Taihu blue algae was tested in laboratory scale, continuous feed digesters (hydraulic retention time 10 days) at 35°C and various organic loading rates (OLR). The methane production and biomass digestion performed well at OLR below 4.00 gVSL(-1)d(-1) but deteriorated as OLR increased due to the increased ammonia concentration, causing inhibition mainly to acetate and propionate degradation. Supplementing corn straw as co-feedstock significantly improved the digestion performance. The optimal C/N ratio for the co-digestion was 20:1 at OLR of 6.00 gVSL(-1) d(-1). Methane yield of 234 mL CH4 gVS(-1) and methane productivity of 1404 mL CH4 L(-1) d(-1) were achieved with solid removal of 63%. Compared with the algae alone, the methane productivity was increased by 46% with less accumulation of ammonia and fatty acids. The reactor rate-limiting step was acetate and propionate degradation.

Exopolysaccharide production by a genetically engineered Enterobacter cloacae strain for microbial enhanced oil recovery.

Microbial enhanced oil recovery (MEOR) is a petroleum biotechnology for manipulating function and/or structure of microbial environments existing in oil reservoirs for prolonged exploitation of the largest source of energy. In this study, an Enterobacter cloacae which is capable of producing water-insoluble biopolymers at 37°C and a thermophilic Geobacillus strain were used to construct an engineered strain for exopolysaccharide production at higher temperature. The resultant transformants, GW3-3.0, could produce exopolysaccharide up to 8.83 g l(-1) in molasses medium at 54°C. This elevated temperature was within the same temperature range as that for many oil reservoirs. The transformants had stable genetic phenotype which was genetically fingerprinted by RAPD analysis. Core flooding experiments were carried out to ensure effective controlled profile for the simulation of oil recovery. The results have demonstrated that this approach has a promising application potential in MEOR.

Biodegradation of decabromodiphenyl ether (BDE-209) by a metal resistant strain, Bacillus cereus JP12

A metal resistant bacterial strain, Bacillus cereus JP12, could use decabromodiphenyl ether (BDE-209) as the sole carbon and energy source for growth in mineral salt medium. Under the conditions of pH 6.0, 30°C, 150 rpm and an inoculum of OD600=0.6, more than 88% of the initial BDE-209 (1mg/L) was degraded after 12 days. The addition of appropriate surfactants and additional carbon sources could enhance the biodegradation efficiency of BDE-209. The presence of Cu(2+) (≤ 8 mg/L) and Zn(2+) (≤ 15 mg/L) provided a slight stimulating effect on BDE-209 removal. However, BDE-209 biodegradation efficiency was decreased when adding higher levels of metals due to reduced substrate availability caused by excess metal adsorption into the cell surface. Biosorption of heavy metals by JP12 led to release of light metals such as K(+) and Na(+). A BDE-209 biodegradation pathway was proposed on the basis of metabolite identification.

Biogas production from supernatant of hydrothermally treated municipal sludge by upflow anaerobic sludge blanket reactor.

The supernatant of hydrothermally treated sludge was treated by an upflow anaerobic sludge blanket (UASB) reactor for a 550-days running test. The hydrothermal parameter was 170°C for 60 min. An mesophilic 8.6L UASB reactor was seeded with floc sludge. The final organic loading rate (OLR) could reach 18 kg COD/m(3)d. At the initial stage running for 189 days, the feed supernatant was diluted, and the OLR reached 11 kg COD/m(3)d. After 218 days, the reactor achieved a high OLR, and the supernatant was pumped into the reactor without dilution. The influent COD fluctuated from 20,000 to 30,000 mg/L and the COD removal rate remained at approximately 70%. After 150 days, granular sludge was observed. The energy balance calculation show that heating 1.0 kg sludge needs 0.34 MJ of energy, whereas biogas energy from the supernatant of the heated sludge is 0.43MJ.