Removal of refractory organics and heavy metals in landfill leachate concentrate by peroxi-coagulation process.

Landfill leachate is a complex effluent and it is difficult to deal with. Electrochemical methods have been considered as a promising alternative technology for treatment of landfill leachate with refractory organic contaminants and heavy metals. Peroxi-coagulation (PC) process with iron anode and modified graphite felt cathode was developed for efficient landfill leachate concentrate treatment. Compared to electro-Fenton (EF) and electrocoagulation (EC) processes, the PC process was more cost-effective due to the combined action of •OH oxidation and iron hydroxides coagulation. A maximal TOC removal of 77.2% ± 1.4% was obtained after 360 min at initial pH = 5.0 and current density of 10 mA/cm2. After the PC process, concentrations of all seven heavy metals in the final effluents were below the allowable emission limits given by the present regulatory standards. The method preference for heavy metal removal was PC > EC > EF. Based on the three-dimensional fluorescence spectroscopy coupled with regional integration analysis during the PC treatment, the florescence peaks of both humic acids and fulvic acids disappeared after treatment for 360 min. Decreasing trends were observed in the fluorescent regional standard volumes for aromatic protein I (31.4%), aromatic protein II (63.7%), fulvic acid-like (69.5%), soluble microbial by-product-like (75%) and humic acid-like regions (76.3%). The results indicate that comparing to the EF and EC process, the PC process provide a promising and more cost-effective alternative for the treatment of landfill leachate concentrate.

Effects of aqueous phase circulation and catalysts on hydrothermal liquefaction (HTL) of penicillin residue (PR): Characteristics of the aqueous phase, solid residue and bio oil.

Hydrothermal liquefaction (HTL) is a promising thermochemical technology for the treatment of hazardous wastes such as penicillin residue (PR). For the treatment of aqueous waste produced by PR in the HTL process, aqueous phase circulation is an attractive solution, both environmentally and economically. The present study shows that aqueous phase circulation can promote the transfer of organic matter from the aqueous phase to bio-oil. The content of organic acids and alcohols in the aqueous phase decreased significantly, and the bio-oil yield and energy recovery efficiency also increased. Under non-catalytic conditions, the bio-oil yield increased from 26.09 wt% to 33.72 wt%. The use of Na2CO3 as a catalyst further improved the bio-oil yield. After a single aqueous phase circulation, the bio-oil yield increased to 34.63 wt%, and the energy recovery efficiency increased to 66.94%. Under catalytic hydrothermal conditions, the content of organic acids in the bio-oil was reduced using aqueous phase circulations, which improved the quality of the bio-oil. At the same time, the Na2CO3 catalyst promoted the hydrolysis of PR to form small molecule organic matter, inhibited the formation of coke, and reduced the content of carbon, hydrogen and oxygen in the solid residue. An increase of cycle times led to excessive accumulation of Na2CO3, which had a negative impact on the yield of bio-oil. Nitrogen-containing compounds in the bio-oil increased to a certain extent, which renders it necessary to consider denitrification treatments in the future. The work provides a useful reference for further research on the preparation of high quality bio-oil by PR hydrothermal liquefaction.

Catalytic upgrading of penicillin fermentation residue bio-oil by metal-supported HZSM-5.

Antibiotic fermentation residue (AR) is composed of hazardous organic waste produced by the pharmaceutical industry. AR can be effectively converted into bio-oil by fast pyrolysis, but its high nitrogen content limits the prospect of bio-oil as a fuel resource. In order to further reduce the nitrogen content of AR bio-oil, we have examined the catalytic removal of N and O from penicillin fermentation residue (PR) bio-oil under fast pyrolysis conditions. We have used M/HZSM-5 (M = Fe, Co, Ni, Cu, Zn, Zr, Mo, Ag and Ce) metal catalysts, with a metal oxide content of 10%. Additionally, the effect of mixed and separated catalytic forms on catalytic upgrading were analyzed, and changes in the catalyst itself before and after pyrolysis under separated catalytic conditions were specifically investigated. Our results show that the metal elements in the fresh catalyst will exist in the form of oxides, ions and simple metals. In-situ reduction caused by pyrolysis gas in the catalytic pyrolysis process makes some ionic metals (e.g., Co2+, Cu2+ and Ag+) in the catalyst transform into oxides, and some metal oxides are reduced to simple metals or suboxides (including Fe, Ni, Cu and Mo). The N content in the mixed catalytic bio-oil decreased from 10.09 wt% to Zn/HZSM-5 (6.98 wt%), Co/HZSM-5 (7.1 wt%), Cu/HZSM-5 (7.18 wt%) and Ce/HZSM-5 (7.18 wt%). We also observed significant reduction in the O content (9.77 wt%) with Ag/HZSM-5 (3.75 wt%), Mo/HZSM-5 (6.86 wt%), Ce/HZSM-5 (8.39 wt%) and Fe/HZSM-5 (8.54 wt%) in the separated catalytic bio-oil. The Ni/HZSM-5 catalystcan reduce the organic acid content in bio-oil from 22.9% to 10.8%. The separated catalysis methodology also promoted an increase of hydrocarbons in the bio-oil: Zn/HZSM-5, Ag/HZSM-5, Mo/HZSM-5, Zr/HZSM-5 and Ce/HZSM-5 reached 11.6%, 11.5%, 11.1%, 10.1%, and 8.8%, respectively. Carbon deposition formed by aromatic carbon/graphite carbon, pyrrole and pyridine compounds leads to deactivation of the catalyst.

Preparation of bio-oils by hydrothermal liquefaction (HTL) of penicillin fermentation residue (PR): Optimization of conditions and mechanistic studies.

Response surface methodology (RSM) was used to investigate factors influencing the yield of bio-oil from the hydrothermal liquefaction (HTL) process of penicillin fermentation residue (PR). The reaction mechanism of the HTL was also studied. The hydrolysis of organic compounds in PR was enhanced, and the bio-oil yield increased with an increase of temperature. When the temperature rose from 280 °C to 320 °C, the yield of bio-oil decreased due to condensation and pyrolysis. Both the residence time and total solid content had effects on the bio-oil yield. The predicted values from the RSM model was in good agreement with the experimental values. Optimized conditions showed that the predicted value of the highest bio-oil yield was 25.91 wt%. The optimized reaction conditions were as follows: reaction temperature was 300 °C, residence time was 174 min, and total solid content was 18 wt%. The bio-oil was analyzed by GC-MS, and showed that it consisted mainly of hydrocarbons, nitrogen-containing heterocyclic compounds, and oxygen-containing compounds. Finally, the formation mechanism of these components and their possible reaction paths are presented and discussed. The results will provide useful guidance for regulating the characteristics of antibiotic residues, and realizing their further utilization as a chemical feedstock.

Onsite quantifying electron donating capacity of dissolved organic matter.

Electron donating capacity (EDC) of dissolved organic matter (DOM) impacts the redox behaviors of DOM in surface waters, groundwaters, wetlands, sediments and soils but lacks applicable onsite quantification methods. To address these disadvantages, a simple and portable device with pre-injected [2,2'-azino-bis(3-ethylbenzothiazoline-6-sulfonicacid), ABTS·+] was developed that can be used for EDC onsite measurements of DOM in this work. The proposed device and method had better limits of quantification of Trolox (0.2 nmol) and more flexible DOC concentration requirement of 0.5-20 mg L-1 than that of flow injection analysis (FIA) (5-10 mg L-1) or mediated electrochemical oxidation (MEO) (>20 mg L-1). The proposed device and method greatly reduced the preparation and measurement time for sample tests compared to MEO or FIA method, enabling time-efficient EDC determination for large amount of samples. Meanwhile, the proposed device presented comparable accuracy with established MEO method when quantifying the EDCs of 7 standard humic and fulvic acids. Humic acids with higher molecular weight (MW) (<15,000 Da) had higher EDC than that with low MW (<5000 Da). EDCs of DOM in natural and reclaim water samples were both presented significantly positive correlations with their corresponding chemical oxygen demand, chromophoric DOM content, molecular weight and humification of the DOM in water samples. These results suggested that our device could accurately quantify the EDCs of DOM onsite and had promising applications on the fast quality assessment of natural and reclaimed waters.

Tradeoff between groundwater arsenite removal efficiency and current production in the self-powered air cathode electrocoagulation with different oxygen reduction pathways.

Naturally occurring arsenic enrichment in aquifers posts a huge threat to drinking water safety. To achieve energy-efficient arsenite [As(III)] removal, a self-powered iron electrocoagulation was developed that coupled iron corrosion anode with oxygen reduction air cathode for simultaneous As(III) oxidation and removal. Activated carbon (AC), which favored the four-electron oxygen reduction reaction (ORR, O2+4e-+4H+→2H2O, E0' = 0.816 V), and carbon black (CB), which favored two-electron ORR (O2+2e-+2H+→H2O2, E0' = 0.283 V), were evaluated for As(III) removal efficiency and current production performance. The comparison showed a tradeoff between higher current (i.e., higher iron corrosion rate) attributed to the higher reduction potential with four-electron ORR, and higher H2O2 production for improved As(III) oxidation with two-electron ORR yet the lower reduction potential The CB cathode that favored H2O2 production had the best As(III) removal of 99.2 ±â€¯0.4% and the lowest maximum power density of 60 ±â€¯0.3 mW m-2, while the AC cathode showed the opposite trend. These results suggested that cathode catalysts need to be carefully evaluated for the balance of As(III) removal and current production to provide a sustainable and effective solution for groundwater As(III) removal.

Improving sludge dewaterability by combined conditioning with Fenton's reagent and surfactant.

The effect of Fenton's reagent combined with dodecyl dimethyl benzyl ammonium chloride (DDBAC) on sludge dewaterability was studied. The capillary suction time (CST) and water content (WC) of sludge cake were used to evaluate sludge dewaterability. Bound water content (W B), extracellular polymeric substance (EPS) concentration, and organic acid concentration in the sludge supernatant were measured to explain the change of dewaterability in the conditioning process. Results indicated that Fenton's reagent combined with DDBAC could enhance sludge dewaterability significantly. When the dosage of Fe2+, H2O2, and DDBAC were 40, 40, and 60 mg g-1 at pH 4, WC of 57.17 % and CST of 17.2 s could be achieved. The protein (PN) and polysaccharide (PS) concentrations in each layer of EPS decreased during the composite conditioning, especially in tightly bound EPS (TB-EPS) and slime layer EPS (S-EPS). And, approximately 68 % of the bound water was released in this process. Further studies through high-performance liquid chromatography (HPLC) demonstrated that the composite conditioning process could oxidize and hydrolyze EPS into small organic molecules, resulting in an increase of small-molecule organics in the species and quantities.

Multiple factors affect diversity and abundance of ammonia-oxidizing microorganisms in iron mine soil.

Ammonia oxidation by microorganisms is a critical process in the nitrogen cycle. In this study, four soil samples collected from a desert zone in an iron-exploration area and others from farmland and planted forest soil in an iron mine surrounding area. We analyzed the abundance and diversity of ammonia-oxidizing archaea (AOA) and ammonia-oxidizing bacteria (AOB) in iron-mining area near the Miyun reservoir using ammonia monooxygenase. A subunit gene (amoA) as molecular biomarker. Quantitative polymerase chain reaction was applied to explore the relationships between the abundance of AOA and AOB and soil physicochemical parameters. The results showed that AOA were more abundant than AOB and may play a more dominant role in the ammonia-oxidizing process in the whole region. PCR-denaturing gradient gel electrophoresis was used to analyze the structural changes of AOA and AOB. The results showed that AOB were much more diverse than AOA. Nitrosospira cluster three constitute the majority of AOB, and AOA were dominated by group 1.1b in the soil. Redundancy analysis was performed to explore the physicochemical parameters potentially important to AOA and AOB. Soil characteristics (i.e. water, ammonia, organic carbon, total nitrogen, available phosphorus, and soil type) were proposed to potentially contribute to the distributions of AOB, whereas Cd was also closely correlated to the distributions of AOB. The community of AOA correlated with ammonium and water contents. These results highlight the importance of multiple drivers in microbial niche formation as well as their affect on ammonia oxidizer composition, both which have significant consequences for ecosystem nitrogen functioning.

Dewaterability of sludge conditioned with surfactant DDBAC pretreatment by acid/alkali.

The potential benefits of surfactant-conditioned sludge dewatering treatment with acid/alkali pretreatment were investigated in this study. The water content of dewatered sludge (W C) and specific resistance of filtration (SRF) were used to evaluate sludge dewaterability. Extracellular polymeric substance (EPS) content, bound water content, zeta potential, and rheological properties were measured to explain the change of dewaterability observed in the conditioning process. By introducing dodecyl dimethyl benzyl ammonium chloride (DDBAC), the EPS content of the sludge supernatant changed, and bound water content, charge strength, and apparent viscosity decreased simultaneously. Although DDBAC-conditioned sludge in strong alkaline had low bound water content, W C and SRF increased rapidly because of the dramatically increasing of EPS in sludge supernatant. Remarkable decrement was observed in bound water content and W C in DDBAC-conditioned sludge which was in weak acid environment for comparison. The results indicated that 75 mg/g of DDBAC at pH 4.84 was the optimum under which W C and SRF were at their lowest point in sludge, 58.22 % and 0.521 × 10(13) m/kg, respectively.

Illumina MiSeq sequencing investigation on the contrasting soil bacterial community structures in different iron mining areas.

Mine activities leaked heavy metals into surrounding soil and may affected indigenous microbial communities. In the present study, the diversity and composition of the bacterial community in soil collected from three regions which have different pollution degree, heavy pollution, moderate pollution, and non-pollution, within the catchment of Chao River in Beijing City, were compared using the Illumina MiSeq sequencing technique. Rarefaction results showed that the polluted area had significant higher bacterial alpha diversity than those from unpolluted area. Principal component analysis (PCA) showed that microbial communities in the polluted areas had significant differences compared with the unpolluted area. Moreover, PCA at phylum level and Matastats results demonstrated that communities in locations shared similar phyla diversity, indicating that the bacterial community changes under metal pollution were not reflected on phyla structure. At genus level, the relative abundance of dominant genera changed in sites with degrees of pollution. Genera Bradyrhizobium, Rhodanobacter, Reyranella, and Rhizomicrobium significantly decreased with increasing pollution degree, and their dominance decreased, whereas several genera (e.g., Steroidobacter, Massilia, Arthrobacter, Flavisolibacter, and Roseiflexus) increased and became new dominant genera in the heavily metal-polluted area. The potential resistant bacteria, found within the genera of Thiobacillus, Pseudomonas, Arthrobacter, Microcoleus, Leptolyngbya, and Rhodobacter, are less than 2.0 % in the indigenous bacterial communities, which play an important role in soil ecosystem. This effort to profile the background diversity may set the first stage for better understanding the mechanism underlying the community structure changes under in situ mild heavy metal pollution.