Shoushuai Feng

A novel and highly efficient system for chalcopyrite bioleaching by mixed strains of Acidithiobacillus.

An integrated bioleaching system (stable pH-silver ion-chloride ion) was firstly proposed to for improving the efficiency of chalcopyrite bioleaching by mixed strains of Acidithiobacillus. The individual effects of stable pH, silver ion, and chloride ion on bioleaching were respectively studied. The highest copper ion concentrations in each system were 45.8, 50.2, and 45.2 mg/l, respectively, when it was only 28.0 mg/l the blank system. Compared with the individual stable pH, silver or chloride ion systems, the relevance of biological and chemical reactions achieved a better balance in the integrated system (stable pH 1.3, 2.0 mg/l silver ion, and 2.5 g/l chloride ion). Moreover, the highest ferrous and sulfate ion concentrations implied less production of S0 membrane and jarosite precipitation. It was also demonstrated by the highest copper ion concentration 55.5 mg/l. These results all indicated that this system was a novel and believable strategy for effectively operating chalcopyrite bioleaching.

Novel integration strategy for enhancing chalcopyrite bioleaching by Acidithiobacillus sp. in a 7-L fermenter

An integrated strategy (additional energy substrate-three stage pH control-fed batch) was firstly proposed for efficiently improving chalcopyrite bioleaching by Acidithiobacillus sp. in a 7-L fermenter. The strain adaptive-growing phase was greatly shortened from 8days into 4days with the supplement of additional 2g/L Fe(2+)+2g/L S(0). Jarosite passivation was effectively weakened basing on higher biomass via the three-stage pH-stat control (pH 1.3-1.0-0.7). The mineral substrate inhibition was attenuated by fed-batch fermentation. With the integrated strategy, the biochemical reaction was promoted and achieved a better balance. Meanwhile, the domination course of A. thiooxidans in the microbial community was shortened from 14days to 8days. As the results of integrated strategy, the final copper ion and productivity reached 89.1mg/L and 2.23mg/(Ld), respectively, which was improved by 52.8% compared to the uncontrolled batch bioleaching. The integrated strategy could be further exploited for industrial chalcopyrite bioleaching.

Community dynamics of attached and free cells and the effects of attached cells on chalcopyrite bioleaching by Acidithiobacillus sp.

The community dynamics of attached and free cells of Acidithiobacillus sp. were investigated and compared during chalcopyrite bioleaching process. In the mixed strains system, Acidithiobacillus ferrooxidans was the dominant species at the early stage while Acidithiobacillus thiooxidans owned competitive advantage from the middle stage to the end of bioprocess. Meanwhile, compared to A. ferrooxidans, more significant effects of attached cells on free biomass with A. thiooxidans were shown in either the pure or mixed strains systems. Moreover, the effects of attached cells on key chemical parameters were also studied in different adsorption-deficient systems. Consistently, the greatest reduction of key chemical ion was shown with A. thiooxidans and the loss of bioleaching efficiency was high to 50.5%. These results all demonstrated the bioleaching function of attached cells was more efficient than the free cells, especially with A. thiooxidans. These notable results would help us to further understand the chalcopyrite bioleaching.

Improved chalcopyrite bioleaching by Acidithiobacillus sp. via direct step-wise regulation of microbial community structure.

A direct step-wise regulation strategy of microbial community structure was developed for improving chalcopyrite bioleaching by Acidithiobacillus sp. Specially, the initial microbial proportion between Acidithiobacillus ferrooxidans and Acidithiobacillus thiooxidans was controlled at 3:1 with additional 2 g/L Fe(2+) for faster initiating iron metabolism. A. thiooxidans biomass was fed via a step-wise strategy (8-12th d) with the microbial proportion 1:1 for balancing community structure and promoting sulfur metabolism in the stationary phase. A. thiooxidans proportion was further improved via another step-wise feeding strategy (14-18th d) with the microbial proportion 1:2 for enhancing sulfur metabolism and weakening jarosite passivation in the later phase. With the community structure-shift control strategy, biochemical reaction was directly regulated for creating a better balance in different phases. Moreover, the final copper ion was increased from 57.1 to 93.2 mg/L, with the productivity 2.33 mg/(Ld). The novel strategy may be valuable in optimization of similar bioleaching process.

Insights to the effects of free cells on community structure of attached cells and chalcopyrite bioleaching during different stages.

The effects of free cells on community structure of attached cells and chalcopyrite bioleaching by Acidithiobacillus sp. during different stages were investigated. The attached cells of Acidithiobacillus thiooxidans owned the community advantage from 14thd to the end of bioprocess in the normal system. The community structure of attached cells was greatly influenced in the free cells-deficient systems. Compared to A. thiooxidans, the attached cells community of Acidithiobacillus ferrooxidans had a higher dependence on its free cells. Meanwhile, the analysis of key biochemical parameters revealed that the effects of free cells on chalcopyrite bioleaching in different stages were diverse, ranging from 32.8% to 64.3%. The bioleaching contribution of free cells of A. ferrooxidans in the stationary stage (8-14thd) was higher than those of A. thiooxidans, while the situation was gradually reversed in the jarosite passivation inhibited stage (26-40thd). These results may be useful in guiding chalcopyrite bioleaching.

Insights into the enhancement mechanism coupled with adapted adsorption behavior from mineralogical aspects in bioleaching of copper-bearing sulfide ore by Acidithiobacillus sp.

The enhancement mechanism of adapted adsorption behavior in the bioleaching of copper-bearing sulfide ore by Acidithiobacillus sp. was systematically investigated from a mineralogical viewpoint and compared to adsorption-deficient (DF) and adsorption-unadapted (UA) systems. With the assistance of the adapted adsorption behavior, both iron and sulfur metabolism was enhanced, which was proven by a series analysis of key chemical parameters, including scanning electron microscopy (SEM) and X-ray diffraction (XRD). SEM analysis revealed smaller jarosite and S0 granules as well as more potential adsorption sites on the ore’s surface, thus indicating a stronger “contact” mechanism. XRD analysis showed that more chemical derivatives were generated owing to active iron/sulfur metabolism. Additionally, the attached and free biomasses of A. ferrooxidans and A. thiooxidans were increased by 33.3–58.9% and 25.0–33.9%, respectively. Moreover, the final concentration of the extracted copper ions was improved by 22.8% (A. ferrooxidans) and 28.9% (A. thiooxidans). All results proved that the adsorption behavior coupled to the attached cells was greatly stimulated and accelerated by the adapted evolution and further contributed to a higher bioleaching efficiency. The adapted method and its mechanism will be useful to further guide similar bioleaching processes in the near future.

Microbial community succession mechanism coupling with adaptive evolution of adsorption performance in chalcopyrite bioleaching

The community succession mechanism of Acidithiobacillus sp. coupling with adaptive evolution of adsorption performance were systematically investigated. Specifically, the μmax of attached and free cells was increased and peak time was moved ahead, indicating both cell growth of Acidithiobacillus ferrooxidans and Acidithiobacillus thiooxidans was promoted. In the mixed strains system, the domination courses of A. thiooxidans was dramatically shortened from 22th day to 15th day, although community structure finally approached to the normal system. Compared to A. ferrooxidans, more positive effects of adaptive evolution on cell growth of A. thiooxidans were shown in either single or mixed strains system. Moreover, higher concentrations of sulfate and ferric ions indicated that both sulfur and iron metabolism was enhanced, especially of A. thiooxidans. Consistently, copper ion production was improved from 65.5 to 88.5 mg/L. This new adaptive evolution and community succession mechanism may be useful for guiding similar bioleaching processes.

Enhancement of dibenzothiophene biodesulfurization by weakening the feedback inhibition effects based on a systematic understanding of the biodesulfurization mechanism by Gordonia sp. through the potential “4S” pathway

Gordonia sp. JDZX13 (source: industrial petroleum soil) shows good potential for dibenzothiophene (DBT) biodesulfurization. With the GC/MS analysis of metabolites and PCR-sequencing verification of the key desulfurization operon (dszA/dszB/dszC), the valuable “4S” pathway of DBT biodesulfurization in Gordonia sp. is identified. The key rate-limiting factors (2-hydroxybiphenyl/sulfate ions) suggest significant feedback inhibition effects on cell growth (μx) and biodesulfurization efficiency. Moreover, the qRT-PCR analysis of the dszA/dszB/dszC operon transcriptions also indicates the prominent negative effects on the key desulfurization enzyme activity, particularly under sulfate ion stress. Based on the abovementioned analysis, the oil/aqueous ratio in the two-phase system was optimized as 1 : 2 for better weakening of the inhibition effect, and a higher DBT removal efficiency (improved by 100.7%) was achieved. In addition, the DBT biodesulfurization mechanism is proposed. Related methods and mechanisms would be useful to further guide similar biocatalysis processes in the near future.

System-level understanding of the potential acid-tolerance components of Acidithiobacillus thiooxidans ZJJN-3 under extreme acid stress

In previous study, two extremely acidophilic strains Acidithiobacillus thiooxidans ZJJN-3 (collection site: bioleaching leachate) and ZJJN-5 (collection site: bioleaching wastewater) were isolated from a typical industrial bio-heap in China. Here, we unraveled the potential acid-tolerance components of ZJJN-3 by comparing the physiological differences with ZJJN-5 under different acid stresses. The parameters used for comparison included intracellular pH (pHin), capsule morphology, fatty acid composition of cell membrane, transcription of key molecular chaperones, H+-ATPase activities and NAD+/NADH ratio. It was indicated that the acid-tolerance of A. thiooxidans ZJJN-3 was systematically regulated. Capsule first thickened and then shed off along with increased acid stress. Cell membrane maintained the intracellular stability by up-regulating the proportion of unsaturated fatty acid and cyclopropane fatty acids. Meanwhile, the transcription of key repair molecular chaperones (GrpE–DnaK–DnaJ) was up-regulated by 2.2–3.5 folds for ensuring the proper folding of peptide. Moreover, low pHin promoted ZJJN-3 to biosynthesize more H+-ATPase for pumping H+ out of cells. Furthermore, the NAD+/NADH ratio increased due to the decreased H+ concentration. Based on the above physiological analysis, the potential acid-tolerance components of A. thiooxidans ZJJN-3 were first proposed and it would be useful for better understanding how these extremophiles responded to the high acid stress.

Biodesulfurization of sulfide wastewater for elemental sulfur recovery by isolated Halothiobacillus neapolitanus in an internal airlift loop reactor

The biodesulfurization of sulfide wastewater for elemental sulfur recovery by isolated Halothiobacillus neapolitanus in an internal airlift loop reactor (IALR) was investigated. The flocculant producer Pseudomonas sp. strain N1-2 was used to deposit the produced elemental sulfur during biodesulfurization. The functional group analysis indicated that biofloculation was closely associated with NH and CO. The biodesulfurization system performed well under moderate water quality fluctuations (1.29-3.88 kg·m-3·d-1 COD; 1.54-3.08 kg·m-3·d-1·S2-) as it maintained stable S2- removal and sulfur flocculation rates. Meanwhile, the qRT-PCR analysis indicated that the transcriptional level of cbbL decreased in the presence of organic carbon, while the expressions of sqr, sat, and cytochrome C3 increased under higher sulfide stress. Moreover, the relative proportions of Halothiobacillus was strengthened via microbial intervention of the LJN1-3 strain. The S2- removal efficiency and elemental sulfur production was further improved by 32.5% and 28.2%, respectively, in an IALR.