Zaixing Li

The new incorporation bio-treatment technology of bromoamine acid and azo dyes wastewaters under high-salt conditions

The accelerating effect of quinones has been studied in the bio-decolorization processes, but there are no literatures about the incorporation bio-treatment technology of the bromoamine acid (BA) wastewater and azo dyes wastewaters under high-salt conditions (NaCl, 15%, w/w). Here we described the BA wastewater as a redox mediator in the bio-decolorization of azo dye wastewaters. Decolorization of azo dyes was carried out experimentally using the salt-tolerant bacteria under the BA wastewater and high-salt conditions. The BA wastewater used as a redox mediator was able to increase the decolorization rate of wastewater containing azo dyes. The effects of various operating conditions such as dissolved oxygen, temperature, and pH on microbial decolorization were investigated experimentally. At the same time, BA was tested to assess the effects on the change of the Oxidation–Reduction Potential (ORP) values during the decolorization processes. The experiments explored a great improvement of the redox mediator application and the new bio-treatment concept.

Reduction of Cr(VI) by Escherichia coli BL21 in the presence of redox mediators

Anthraquinone-2,7-disulfonate (2,7-AQDS), anthraquinone-1-sulfonate (α-AQS), anthraquinone-2-sulfonate (AQS), anthraquinone-2,6-disulfonate (AQDS) and anthraquinone-1,5-disulfonate (1,5-AQDS) were selected as redox mediators for Cr(VI) reduction by Escherichia coli BL21. In the presence of 0.8mmoll(-1) AQS, the Cr(VI) reduction efficiency was 98.5% in 7.5h, whereas it was only 21-34% in the absence of a mediator or in the presence of α-AQS, 1,5-AQDS, AQDS, 2,7-AQDS. A linear correlation, k=0.768C(AQS)+1.5531 (R(2)=0.9935), was found for the reaction constant, k (mg Cr(VI) g(-1) dry cell weight h(-1)) and the AQS concentration (C(AQS)). The Arrhenius equation described the Cr(VI) reduction in the tested temperature range, and the pre-exponential factor A was 13.249mg Cr(VI) g(-1) dry cell weight h(-1),and the activation energy Ea was 28.01kJmol(-1). Glucose was the best carbon sources, and the optimum pH was 6.0. The Cr(VI) reduction rate obtained with AQS is a significant improvement over low conventional anaerobic reduction rates.

Effect of thermal–alkaline pretreatment on the anaerobic digestion of streptomycin bacterial residues for methane production

The anaerobic digestion of streptomycin bacterial residues, solutions with hazardous waste treatments and bioenergy recovery, was tested in laboratory-scale digesters at 35°C at various organic loading rates (OLRs). The methane production and biomass digestion were efficient at OLRs below 2.33 gVS L(-1) d(-1) but were deteriorated as OLR increased because of the increased total ammonia nitrogen (TAN) concentration from cell protein decay. The thermal-alkaline pretreatment with 0.10 NaOH/TS at 70°C for 2 h significantly improved the digestion performance. With the thermal-alkaline pretreatment, the volumetric reactor productivity and specific methane yield of the pretreated streptomycin bacterial residue increased by 22.08-27.08% compared with those of the unpretreated streptomycin bacterial residue at an OLR of 2.33 gVS L(-1) d(-1). The volatile solid removal was 64.09%, with less accumulation of TAN and total volatile fatty acid.

Development of bioreactor systems with functional bio-carrier modified by disperse turquoise blue S-GL for disperse scarlet S-BWFL decolorization

The effect of redox mediator has been studied in details in the bio-decolorization processes, but there are little literatures about bioreactor systems with functional bio-carrier modified by redox mediator. Two different bioreactor configurations (bioreactor R1 with functional bio-carrier modified by disperse turquoise blue S-GL (as redox mediator) and bioreactor R2 with non-modified bio-carrier) were designed and tested for disperse scarlet S-BWFL decolorization by Halomonas sp. GYW (EF188281) in this study. Influencing factors such as co-substrate, temperature and pH were optimized through batch experiments. Compared to bioreactor R2, bioreactor R1 exhibited good decolorization efficiency and performance ability for the disperse scarlet S-BWFL decolorization, which showed higher decolorization efficiency (over 96% color removal with 0.8 g L(-1) dye concentration) and less hydraulic retention time to attain the same decolorization efficiency. The combinational technology of redox mediator and bio-carrier was a new bio-treatment concept and a great improvement for the application of redox mediator.

Enhanced biogas production from penicillin bacterial residue by thermal-alkaline pretreatment

In this study, the orthogonal experimental design was used to determine the optimum conditions for the effect of thermal-alkaline pretreatment on the anaerobic digestion of penicillin bacterial residue. The biodegradability of the penicillin bacterial residue was evaluated by biochemical methane potential tests in laboratory. The optimum values of temperature, alkali concentration, pretreatment time and moisture content for the thermal-alkaline pretreatment were determined as 70 °C, 6% (w/v), 30 min, and 85%, respectively. Thermal-alkaline pretreatment could significantly enhance the soluble chemical oxygen demand solubilization, the suspended solid solubilization and the biodegradability. Biogas production was enhanced by the thermal-alkaline pretreatment, probably as a result of the breakdown of cell walls and membranes of micro-organisms, which may facilitate the contact between organic molecules and anaerobic microorganisms.

Anaerobic digestion of thermal-alkaline–pretreated cephalosporin bacterial residues for methane production

ABSTRACT Optimum anaerobic conditions of cephalosporin bacterial residues after thermal-alkaline pretreatment were determined by orthogonal experiments. And through biochemical methane potential tests (BMPs) for cephalosporin bacterial residues, the ability for bacterial degradation of cephalosporin was also evaluated. The thermal-alkaline pretreatment with the optimum values of 6% NaOH at 105 °C for 15 min significantly improved digestion performance. With the thermal-alkaline pretreatment, the specific methane yield of the pretreated cephalosporin bacterial residue increased by 254.79% compared with that of the un-pretreated cephalosporin bacterial residue. The results showed that anaerobic digestion of thermal-alkaline–pretreated cephalosporin bacterial residues could be one of the options for efficient methane production and waste treatment. Implications: This work investigates the thermal-alkaline pretreatment of cephalosporin bacterial residues, which can increase their methane yield by 254.79% compared with no pretreatment. The digestion performance is significantly improved under the condition of 6% NaOH at 105 °C for 15 min. The results show that anaerobic digestion of thermal-alkaline–pretreated cephalosporin bacterial residues could be one of the options for efficient methane production and waste treatment.

Effects of metal ions on the reduction of penicillin fermentation residue by thermophilic bacteria

ABSTRACT Extracellular enzymes produced by thermophilic bacteria played an important role in promoting the reduction of penicillin fermentation residue after appropriate amounts of metal ions are added in this study. The results showed that soluble chemical oxigen demand (SCOD) quickly reached the maximum value of 3943 mg•L−1 within 2 h during biological pretreatment by thermophilic bacteria at an optimum value of 200 μmol•L−1 Na+ with a suspended solid (SS) removal rate of 90.96%. Na+ also promoted NH4+-N. At 200 μmol•L−1 K+ and at 20 h, SCOD increased, and its maximum concentrations were higher than those of the blank test. NH4+-N concentration also reached 102.04 mg•L−1. At 200 μmol•L−1 Ca2+, the SS removal rate was 78.66%. Ca2+ addition did not promote the release of SCOD. NH4+-N was also inhibited.

Assessment of food waste biodegradability by biochemical methane potential tests

ABSTRACT In this study, the biochemical methane potential tests were conducted to assess the methane yield of 12 food waste substrates which were common in North China. The 12 food substrates were digested at 35°C, respectively, which were divided into 4 parts, staple food, vegetables, meat, and fruit. The results showed that the methane production changed from 318 (white radish) to 374 mL (cooked chicken) normalized by per gram volatile solid (VS) added. It can be estimated that each ton of food waste on VS produced 328 m3 of methane in North China according to the proportion of food waste composition.ABSTRACTIn this study, the biochemical methane potential tests were conducted to assess the methane yield of 12 food waste substrates which were common in North China. The 12 food substrates were digested at 35°C, respectively, which were divided into 4 parts, staple food, vegetables, meat, and fruit. The results showed that the methane production changed from 318 (white radish) to 374 mL (cooked chicken) normalized by per gram volatile solid (VS) added. It can be estimated that each ton of food waste on VS produced 328 m3 of methane in North China according to the proportion of food waste composition.

Effects of Contaminants on Oxygen Transfer in Microbubble Aeration

Contaminants in wastewater influenced oxygen transfer in aeration process greatly. The effects of different typical contaminants on oxygen transfer in microbubble aeration were investigated and compared with traditional bubble aeration, including surfactant SDBS, soybean oil, phenol and nitrobenzene as well as kaolin. The results indicated that these contaminants showed different effect on oxygen transfer in microbubble aeration, compared with traditional bubble aeration. The negative effect of both soluble organic contaminants and suspended solid in traditional bubble aeration seemed to be counteracted in microbubble aeration. The range of KLa values were 7.44~11.56 h-1 and the range of α-factors were 0.77~1.20 under all test conditions, larger than these in traditional bubble aeration. In addition, both KLa values and α-factors increased along with an increasing of concentration for soluble organic contaminants, whereas the maximum KLa value and α-factor existed for suspended solid kaolin with concentration of 100 mg/L. The gas holdup and average bubble retention time in microbubble aeration containing these contaminants increased, compared with these in clean water. So the improvement of microbubble generation and stability in presence of these contaminants should be responsible for oxygen transfer enhancement probably.

Effects of Surfactants on Oxygen Transfer in Microbubble Aeration

Surfactants were the important contaminants in wastewater and influenced oxygen transfer in aeration processes. The effects of four types of surfactants, including anionic, zwitterionic, cationic and nonionic surfactants, on oxygen transfer in microbubble aeration were investigated and compared with traditional bubble aeration. The results indicated that the oxygen transfer was enhanced with and without addition of surfactants in microbubble aeration. The KLa values were 7.44~11.56 h-1 when the concentration of four types of surfactants varied from 5 to 20 mg/L, larger than that in traditional bubble aeration. Different types of surfactants showed different effects on oxygen transfer in microbubble aeration. When surfactant concentration increased, ionic surfactants showed strong positive effect on oxygen transfer and the α-factors were 0.77~1.20, even larger than 1.0 at high surfactant concentrations. The KLa values of ionic surfactants followed the sequence: cationic ≫ zwitterionic ≫ anionic under the same concentration condition. On the contrary, nonionic surfactant showed negative effect on oxygen transfer, similar with that in traditional bubble aeration. The gas holdup and bubble retention time were as high as 1.02 %~2.67 % and 1.2 min~3.2 min in microbubble aeration in the presence of surfactants, respectively, demonstrating their important role in oxygen transfer enhancement. The surfactant properties also influenced oxygen transfer greatly.