Controlled Biosynthesis of ZnCdS Quantum Dots with Visible-Light-Driven Photocatalytic Hydrogen Production Activity.

The development of visible-light-responsive photocatalysts with high efficiency, stability, and eco-friendly nature is beneficial to the large-scale application of solar hydrogen production. In this work, the production of biosynthetic ternary ZnCdS photocatalysts (Eg = 2.35-2.72 eV) by sulfate-reducing bacteria (SRB) under mild conditions was carried out for the first time. The huge amount of biogenic S2- and inherent extracellular proteins (EPs) secreted by SRB are important components of rapid extracellular biosynthesis. The ternary ZnCdS QDs at different molar ratios of Zn2+and Cd2+ from 15:1 to 1:1 were monodisperse spheres with good crystallinity and average crystallite size of 6.12 nm, independent of the molar ratio of Cd2+ to Zn2+. All the ZnCdS QDs had remarkable photocatalytic activity and stability for hydrogen evolution under visible light, without noble metal cocatalysts. Especially, ZnCdS QDs at Zn/Cd = 3:1 showed the highest H2 production activity of 3.752 mmol·h-1·g-1. This excellent performance was due to the high absorption of visible light, the high specific surface area, and the lower recombination rate between photoexcited electrons and holes. The adhered inherent EPs on the ZnCdS QDs slowed down the photocorrosion and improved the stability in photocatalytic hydrogen evolution. This study provides a new direction for solar hydrogen production.

Generation behavior of extracellular polymeric substances and its correlation with extraction efficiency of valuable metals and change of process parameters during bioleaching of spent petroleum catalyst.

The vital functions of extracellular polymeric substances (EPS) have been well recognized in bioleaching of sulfide ores. However, no report is available about the role of EPS in bioleaching of spent catalyst. To completely and deeply understand the functions of EPS in bioleaching of spent catalyst, the generation behavior of EPS at various pulp densities during bioleaching was characterized by three-dimensional excitation-emission matrix (3DEEM), and its relevance with bioleaching performance and process parameters were analyzed using mathematical means. The results showed that the EPS contain humus-like substances as main component (>70%) and protein-like substances as minor component (<30%). Both total EPS and humus-like substances mainly keep growing over the whole duration of bioleaching at low pulp density of 5.0% or lower; whereas total EPS and humus-like fraction keep declining at high pulp density of 7.5% or higher. Among the total EPS and its components, humus-like substances only have a positive significant correlation with bioleaching efficiencies of both Co and Mo and affect bioleaching process more greatly due to greater correlation coefficient. Biofilm appears at the spent catalyst surface under 2.5% of pulp density mediated by EPS while no biofilm occurs at 10% of pulp density due to shortage of EPS, accounting for the great difference in bioleaching efficiencies between high and low pulp densities which are 48.3% for Mo and 50.0% for Co at 10% of pulp density as well as 75.9% for Mo and 78.8% for Co at 2.5% of pulp density, respectively.

Quick extracellular biosynthesis of low-cadmium Zn x Cd1-x S quantum dots with full-visible-region tuneable high fluorescence and its application potential assessment in cell imaging.

The biosynthesis of metal nanoparticles/QDs has been universally recognized as environmentally sound and energy-saving, generating less pollution and having good biocompatibility, which is most needed in biological and medical fields. In the arena of chemical routes, however, biosynthesis has long been criticized for its low productivity, time-consuming process, and poor control over size, shape and crystallinity, keeping the much-needed technology away from practical application. In this work, a rapid and extracellular biosynthesis of multi-colour ternary Zn x Cd1-x S QDs by a mixed sulfate-reducing bacteria (SRB)-derived supernatant was carried out for the first time to solve the problems plaguing this field of biosynthesis. The results showed that about 3.5 g L-1 of Zn x Cd1-x S QDs with size of 3.50-4.64 nm were achieved within 30 minutes. The PL emission wavelength of Zn x Cd1-x S QDs increased from 450 to 590 nm to yield multicolor QDs by altering the molar ratio of Cd2+ to Zn2+. The SRB-biogenic Zn x Cd1-x S QDs have high stability in gastric acid and at high temperature, as well as excellent biocompatibility and biosafety, successfully entering growing HeLa cells and labelling them without detectable harm to cells. The SRB-secreted peculiar extracellular proteins (EPs) play a decisive function in the time-saving, high-yield biosynthesis of PL-tuned multicolor QDs, which cover an abnormally high concentration of acidic amino acids to provide tremendous negatively charged sites for the absorption of Cd2+/Zn2+ for rapid nucleation and biosynthesis. The strongly electrostatic connection between the QDs and the EPs and the increasing amount of EPs attached to the QDs in response to the increase of Cd2+ concentration account for their high stability and excellent biocompatibility.

Improved bioleaching of copper and zinc from brake pad waste by low-temperature thermal pretreatment and its mechanisms.

A considerable amount of brake pad waste which is composed of phenolic resin and a variety of toxic heavy metals is produced both in China and around the world owing to the flourishing automobile industry. The safe, low cost and eco-sound bioleaching was utilized to extract the valuable metals Cu and Zn from the waste. The results showed that although bioleaching is more efficient in the extraction of Cu and Zn than the chemical counterpart, rather low bioleaching yields of 34% for Cu and 72% for Zn were obtained because of the complicated components and refractory nature of the waste. However, a low-temperature thermal pretreatment at 400 °C notably lifted the bioleaching efficiencies of Cu and Zn to 98% and nearly 100%, respectively. The thermal treatment removed the oil substances, transformed the acid insoluble Cu0 into acid soluble CuO and destroyed the chelation/complexation of the phenolic resin to loose Cu and Zn, promoting bioleaching performance of Cu and Zn. The combined processes of low-temperature thermal pretreatment and bioleaching is totally qualified for the extraction of Cu and Zn from the refractory waste.

High-Yield Extracellular Biosynthesis of ZnS Quantum Dots through a Unique Molecular Mediation Mechanism by the Peculiar Extracellular Proteins Secreted by a Mixed Sulfate Reducing Bacteria.

This work describes a high-yield extracellular biosynthesis of ZnS QDs via a unique molecular mediation mechanism driven by the mixed sulfate reducing bacteria (SRB). The mixed SRB have obtained the highest ever ZnS QD biosynthesis rate of 35.0-45.0 g/(L·month). The biogenic ZnS QDs with an average crystallite size (ACS) of 6.5 nm have greater PL activity and better uniformity than that of a chemical route. Peculiar extracellular proteins (EPs) with molecular weights of approximately 65 and 14 kDa specially adhere to the ZnS QDs, which cover extraordinarily high contents of acidic amino acids (14.0 mol % Glu and 13.0 mol % Asp) and of nonpolar amino acids (12.0 mol % Ala, 11.0 mol % Gly, and 7.0 mol % Phe), for novel molecular mediation. The vast amount of negative charges in Glu and Asp guides the strong absorption between the EPs and Zn2+ via electrostatic attraction to reach a maximum absorption capacity of 745.9 mg/g within 2.0 h, motivating large and rapid nucleation as the first step of biosynthesis. Meanwhile, bridging and interlinkage occur inside the EPs or between the EPs via hydrophobic interactions dominated by the nonpolar amino acids, resulting in the formation of massive microcavities to control and restrict the growth of ZnS QDs as a template. The novel molecular mediation mechanism triggered by the peculiar EPs with an extraordinary amino acid composition and structure accounts for the high-yield biosynthesis of ZnS QDs. The mixed SRB have also successfully fabricated other metal sulfide QDs, including PbS, CuS, and CdS, through the novel molecular mediation.

Effect of aeration and hydraulic loading rate on nitrogen removal by subsurface infiltration systems.

This study investigated the effect of hydraulic loading rate (HLR) on matrix dissolved oxygen (DO), organic matter removal, nitrogen removal, N2 O emissions, and the abundances of functional genes participating in nitrogen removal in intermittent aerated mode (IAM) and nonaerated mode (NAM) subsurface infiltration systems (SISs). In contrast to NAM SISs, IAM SISs were able to create aerobic conditions in the upper matrix (above 50 cm depth) and anoxic or anaerobic conditions in the lower matrix (below 80 cm depth). Subsequently, this enhanced the abundance of functional genes related to nitrogen removal. Chemical oxygen demand (COD) and nitrogen removal performance were significantly higher under IAM SISs than with NAM SISs. Under a HLR of 0.3 m3 /(m2  d), the IAM SIS was able to achieve low N2 O emissions (12.6 mg/[m2  d]) along with removal efficiencies of 90.5%, 91.4%, and 85.7% for COD, ammonia nitrogen ( NH 4 + -N), and total nitrogen (TN), respectively. PRACTITIONER POINTS: Intermittent aeration successfully realized sequential aerobic and anaerobic conditions at 50 cm depth and at 80 and 110 cm depths of a subsurface infiltration system. Intermittent aeration reduced N2 O emissions and improved hydraulic loading rate and organic matter, nitrogen removal efficiencies. Intermittent aeration enhanced the abundances of amoA, nxrA, napA, narG, nirS, nirK, qnorB, and nosZ.

Nitrogen Removal and N2O Emission in Biochar-Sludge Subsurface Wastewater Infiltration Systems.

Nitrogen removal and N2O emission of biochar-sludge amended subsurface wastewater infiltration systems (SWISs) with/without intermittent aeration under different organic surface loading rates (OSLRs) were investigated. Under OSLR, between 8.5 and 54.6 g COD/(m2 d), average chemical oxygen demand (COD), , and total nitrogen (TN) removal rates decreased with OSLR increasing in non-aerated SWISs amended with/without biochar-sludge; increasing OSLR hardly affected COD and removal in biochar-sludge amended SWIS with intermittent aeration; N2O emission rate decreased with influent OSLR increasing in the SWISs. Biochar-sludge amended SWIS with intermittent aeration obtained higher removal rates for COD (94.9 to 95.5%), (90.5 to 93.7%), TN (86.5 to 89.9%) and lower N2O emission rates [13.4 to 14.7 mg/(m2 d)] under high influent OSLR of 36.2 and 54.6 g COD/(m2 d) were compared with non-aerated SWISs with/without biochar-sludge. Furthermore, the abundances of amoA, nxrA, napA, narG, nirS, nirK, qnorB, and nosZ genes involved in nitrogen removal were enhanced under high influent OSLR in biochar-sludge amended SWIS with intermittent aeration.

Does influent COD/N ratio affect nitrogen removal and N2O emission in a novel biochar-sludge amended soil wastewater infiltration system (SWIS)?

Nitrogen removal and N2O emission of a biochar-sludge amended soil wastewater infiltration system (SWIS) with/without intermittent aeration under different influent COD/N ratios was investigated. Nitrogen removal and N2O emission were affected by influent COD/N ratio. Under a COD/N ratio between 1:1 and 15:1, average chemical oxygen demand (COD), NH4 +-N and total nitrogen (TN) removal rates decreased with COD/N ratio increase in non-aerated SWISs amended with/without biochar-sludge; an increasing COD/N ratio hardly affected COD and NH4 +-N removal in a biochar-sludge amended SWIS with intermittent aeration; the N2O emission rate decreased with COD/N ratio increase in the studied SWISs. The biochar-sludge amended SWIS with intermittent aeration achieved high COD (92.2%), NH4 +-N (96.8%), and TN (92.7%) removal rates and a low N2O emission rate (10.6 mg/(m2 d)) under a COD/N ratio of 15:1, which was higher than those in non-aerated SWISs amended with/without biochar-sludge. Combining the biochar-sludge amended SWIS with intermittent aeration enhanced the number of nitrifying bacteria, denitrifying bacteria, nitrate reductase activities, nitrite reductase activities, and improved the abundance of nitrogen removal functional genes under a high influent COD/N ratio. The results suggested that the joint use of intermittent aeration and biochar-sludge in a SWIS could be an effective and appropriate strategy for improving nitrogen removal and reducing N2O emissions in treating high COD/N ratio wastewater.

Organics removal, nitrogen removal and N2O emission in subsurface wastewater infiltration systems amended with/without biochar and sludge.

Organics removal, nitrogen removal, N2O emission and nitrogen removal functional gene abundances in four subsurface wastewater infiltration systems (SWISs), named SWIS A (no intermittent aeration without biochar and sludge), SWIS B (no intermittent aeration with biochar and sludge), SWIS C (intermittent aeration without biochar and sludge), SWIS D (intermittent aeration with biochar and sludge) were investigated. Intermittent aeration enhanced chemical oxygen demand (COD), ammonia nitrogen (NH4+-N), total nitrogen (TN) removal and the abundances of nitrogen removal functional genes (amoA, nxrA, napA, narG, nirS, nirK, qnorB and nosZ) compared to non-aerated SWISs. High COD (95.4 ±â€¯0.2%), NH4+-N (96.2 ±â€¯0.6%), TN (86.4 ±â€¯0.5%) removal efficiencies and low N2O emission rate (18.4 mg/(m2 d)) were obtained simultaneously in intermittent aerated SWIS amended with biochar and sludge. The results suggested that intermittent aerated SWISs amended with biochar and sludge could be an effective and appropriate method for improving treatment performance and reducing N2O emission.

Nitrogen removal and N2O emission in subsurface wastewater infiltration systems with/without intermittent aeration under different organic loading rates.

Nitrogen removal, N2O emission and nitrogen removal functional gene abundances in intermittent aerated (IA) and non-aerated (NA) subsurface wastewater infiltration systems (SWISs) under different organic loading rates (OLRs) were investigated. Aeration successfully created aerobic condition at 50cm depth and did not change anoxic or anaerobic condition at 80 and 110cm depths under OLR of 5.3, 10.9 and 16.5g BOD/(m2d). Meanwhile, aeration enhanced COD, NH4+-N, TN removal and the enrichment of nitrogen removal functional genes (amoA, nxrA, napA, narG, nirS, nirK, qnorB and nosZ) compared to NA SWIS. High COD removal rate of 91.6%, TN removal rate of 85.9% and low N2O emission rate of 32.4mg/(m2d) were obtained in IA SWIS under OLR of 16.5g BOD/(m2d). Intermittent aeration is a sensible strategy to achieve high OLR, low N2O emission, satisfactory organic matter and nitrogen removal performance for SWISs.

Effects of hydraulic loading rate and aeration mode on nitrogen removal and nitrogen functional gene abundances in subsurface wastewater infiltration systems.

Matrix dissolved oxygen, nitrogen removal and nitrogen functional gene abundances in two artificial aeration modes, continuous aeration (CA) and intermittent aeration (IA), in subsurface wastewater infiltration systems (SWISs) under different hydraulic loading rates (HLRs) were investigated. Aeration not only successfully created aerobic conditions at 50 cm depth, but also did not change anoxic or anaerobic conditions at 80 and 110 cm depths. Meanwhile, aeration significantly enhanced chemical oxygen demand, NH4+-N, and total nitrogen (TN) removal and the enrichment of nitrogen removal functional genes (amoA, nxrA, napA, narG, nirK and qnorB) compared to the non-aerated SWIS, especially for high HLRs. IA SWIS (79.7%-85.8%) had a better performance on TN removal compared with CA SWIS (73.8%-82.2%) when the HLRs ranged from 0.06 to 0.3 m3/(m2 d). Intermittent aeration is a sensible strategy to achieve high HLR, good nitrogen removal performance and comparatively low operation cost for SWISs.

Nitrogen removal and nitrogen functional gene abundances in three subsurface wastewater infiltration systems under different modes of aeration and influent C/N ratios.

Matrix DO, nitrogen removal and nitrogen functional gene abundances in non-aerated (NA), continuously aerated (CA) and intermittently aerated (IA) subsurface wastewater infiltration systems (SWISs) under different influent C/N ratios were studied. Aeration created aerobic condition in 50cm depth and did not change anoxic or anaerobic condition in 80 and 110cm depths, which enhanced NH4+-N and TN removal and the enrichment of nitrogen removal functional genes (amoA, nxrA, narG, napA, nirK, nirS, qnorB and nosZ) compared to NA SWIS, especially under high influent C/N ratio. High TN removal rate (89.6%) was obtained in IA SWIS under the influent C/N ratio of 12, which was higher than that in CA SWIS (87.1%). The results suggested that intermittent aeration was a reliable option to achieve high TN removal in SWISs, especially under high influent C/N ratio.

Effect of COD/N Ratio on Removal Performances in Two Subsurface Wastewater Infiltration Systems.

Dissolved oxygen (DO), were investigated. Aerobic conditions were effectively developed in 50 cm depth of the matrix and anoxic or anaerobic conditions were not changed in 80 and 110 cm depth by intermittent aeration, which encouraged nitrification. Increased influent COD/N ratio led to lower COD and nitrogen removal in conventional SWISs. Sufficient carbon source in high COD/N ratio influent promoted denitrification with intermittent aeration. High removal rates of COD (95.68 ± 0.21%), TP (92.02 ± 0.28%), -N (99.33 ± 0.05%), and - (89.65 ± 0.6%) were obtained with influent COD/N ratio of 12 in aerated SWISs. Under the COD/N ratio of 12 and 18, intermittent aeration boosted the growth and reproduction of nitrifying bacteria and denitrifying bacteria. Meanwhile, nitrate and nitrite reductase activities with intermittent aeration were higher than that without aeration in 80 and 110 cm depths.

Controllable biosynthesis of high-purity lead-sulfide (PbS) nanocrystals by regulating the concentration of polyethylene glycol in microbial system.

We demonstrated a simple biological method to explore the controllable synthesize of high-purity PbS nanocrystals by regulating the concentration of polyethylene glycol in microbial system. The biogenic H2S produced via the reduction of sulfate precipitated Pb2+ ions as sulfide extracellularly, and the optimal removal rate of Pb2+ ions is up to 96.7 % in 2 weeks. The characterization results showed that PbS nanocuboids with a particle size 50 × 50 × 100 nm obtained from Case A with 4 mM polyethylene glycol as a dispersant, and can completely degrade methylene blue from solution within 20 h; PbS nanosheets with a thickness size ca. 10 nm attained from Case B with 12 mM polyethylene glycol, and it can degrade 61.6 % dye within 24 h; PbS nanoparticles with a uniform diameter of ca. 60 nm formed from Case C with 20 mM polyethylene glycol, only degrade 14.1 % dye within 24 h. It is interesting that the factor affecting their catalytic activities is not the specific surface area, but the number of [200] crystal plane. This work not only displayed a simple synthetic method to control the morphology of PbS nanocrystals in microbial system, but also provided an economic and environmentally friendly approach for resourceful treatment and efficient bioremediation of wastewater-containing heavy metal.

Extracellular synthesis of cuprous selenide nanospheres by a biological-chemical coupling reduction process in an anaerobic microbial system.

Biosynthesis of metal nanoparticles represents a clean, eco-friendly and sustainable "green chemistry" engineering. Lately, a number of metal selenides were successfully synthesized by biological methods. Here, cuprous selenide (Cu2 Se) nanospheres were prepared under mild conditions by a novel biological-chemical coupling reduction process. The simple process takes place between EDTA-Cu and Na2 SeO3 in presence of an alkaline solution containing NaBH4 and a selenite-reducing bacteria, Pantoea agglomerans. It is noteworthy that the isolated Pantoea agglomerans and Cu+ ions, where the latter are obtained from reducing Cu2+ ions by NaBH4 , play a key role, and Cu+ ions not only can promote the generation of Se2- ions as a catalyst, but also can react with Se2- ions to form Cu2 Se. XRD pattern, SEM, and TEM images indicated that Cu2 Se nanoparticles were tetragonal crystal structure and the nanospheres diameter were about 100 nm. EDX, UV-vis, and FTIR spectra show that the biosynthesized Cu2 Se nanospheres are wrapped by protein and have a better stability. This work first proposes a new biosynthesis mechanism, and has important reference value for biological preparation of metal selenide nanomaterials. © 2016 American Institute of Chemical Engineers Biotechnol. Prog., 32:1264-1270, 2016.

Distribution of antibiotic-resistant bacteria in chicken manure and manure-fertilized vegetables.

Veterinary manure is an important pollution reservoir of antibiotics and antibiotic-resistant bacteria (ARB). However, little is known of the distribution of ARB in plant endophytic bacteria and the number/types of ARB in chicken manure. In this study, 454-pyrosequencing was used to investigate the distribution and composition of ARBs in chicken manure and fertilized vegetables. The prevalence of ARB in the samples of the chicken manure compost recovered from farms on which amoxicillin, kanamycin, gentamicin, and cephalexin were used was 20.91-65.9% for ARBs and 8.24-20.63% simultaneously resistant to two or more antibiotics (multiple antibiotic resistant bacteria (MARB)). Antibiotic-resistant endophytic bacteria were widely detected in celery, pakchoi, and cucumber with the highest rate of resistance to cephalexin. The pyrosequencing indicated that the chicken manure dominantly harbored Firmicutes, Bacteroidetes, Synergistetes, and Proteobacteria and that Bacteroidetes was significantly enhanced in farms utilizing antibiotics. In the total cultivable colonies, 62.58-89.43% ARBs and 95.29% MARB were clustered in Bacteroidetes with the dominant species (Myroides ordoratimimus and Spningobacterium spp., respectively) related to human clinical opportunistic pathogens.