Phosphorus sorption - Desorption behaviors in the sediments cultured with Hydrilla verticillata and Scripus triqueter as revealed by phosphorus fraction and dissolved organic matter.

The migration of sediment phosphorus (P) could be affected by the existence of aquatic plants. To explore the effects of aquatic plants on the P sorption-desorption behaviors in the sediments, sediment in Caohai wetland was collected and cultured with the submerged plant (Hydrilla verticillata) and emerged plant (Scripus triqueter). Then the sorption and desorption experiments were performed, and physicochemical properties, P fractions, and dissolved organic matter (DOM) characteristics were evaluated. Results showed that the treated sediments exhibited similar P sorption kinetic process fitted well with the two-compartment first-order model. Nevertheless, H. verticillata cultured sediment could be well described by the modified Langmuir isotherm model, while S. triqueter cultured sediment fitted the modified Freundlich equations well. The obvious changing P fractions in cultured sediments were BD-P and NaOH-SRP during sorption. H. verticillata and S. triqueter displayed different sorption-desorption behaviors by altering BD-P, humification index, fluorescence intensity, and PARAFAC component contents in sediments. Compared to raw sediment, H. verticillata presented higher P sorption and lower P release from sediments by decreasing BD-P and increasing DOM (fulvic acid-like and humic-like components) content, while S. triqueter showed adverse P sorption and release effects by reducing DOM components. The growth of submerged plants was suggested to make a positive influence on the high efficiency of P retention capacity and low release risk.

Analysis of the characteristics of phosphine production by anaerobic digestion based on microbial community dynamics, metabolic pathways, and isolation of the phosphate-reducing strain.

Although phosphine is ubiquitously present in anaerobic environments, little is known regarding the microbial community dynamics and metabolic pathways associated with phosphine formation in an anaerobic digestion system. This study investigated the production of phosphine in anaerobic digestion, with results indicating that phosphine production mainly occurred during logarithmic microbial growth. Dehydrogenase and hydrogen promoted the production of phosphine, with a maximum phosphine concentration of 300 mg/m3. The abundance of Ruminococcaceae and Escherichia was observed to promote phosphine generation. The analysis of metabolic pathways based on the Kyoto Encyclopedia of Genes and Genomes (KEGG) and the MetaCyc pathway database revealed the highest relative abundance of replication and repair in genetic information processing; further, the cofactor, prosthetic group, electron carrier, and vitamin biosynthesis were observed to be closely related to phosphine formation. A phylogenetic tree was reconstructed based on the neighbor-joining method. The results indicated the clear evolutionary position of the isolated Pseudescherichia sp. SFM4 strain, adjacent to Escherichia, with a stable phosphate-reducing ability for a maximum phosphine concentration of 26 mg/m3. The response surface experiment indicated that the initial optimal conditions for phosphine production by SFM4 could be achieved with nitrogen, carbon, and phosphorus loads of 6.17, 300, and 10 mg/L, respectively, at pH 7.47. These results provide comprehensive insights into the dynamic changes in the microbial structure, isolated single bacterial strain, and metabolic pathways associated with phosphine formation. They also provide information on the molecular biology associated with phosphorus recycling.

Removal of tetracycline from an aqueous solution using manganese dioxide modified biochar derived from Chinese herbal medicine residues.

Biochar (BC) derived from Chinese herbal medicine residues has been investigated for its performance as a potential adsorbent in tetracycline (TC) removal. In the present study, a chemical co-precipitation method was carried out to prepare manganese dioxide modified biochar (Mn-BC) to increase its sorption capacity. The properties of the modified biochar were characterized for further enhancing TC removal from an aqueous solution. Mn-BC was successfully synthesized and resulted in a much higher specific surface area, total pore volume and pore diameter. The sorption kinetics of TC on Mn-BC was described by the pseudo-second-order model. The sorption data of Mn-BC were fitted by Langmuir and Freundlich models. The study findings revealed a maximum adsorption capacity of Mn-BC (1:10) to TC was up to 131.49 mg/g. The adsorption process was endothermic and spontaneous. The degradation of TC was further enhanced by MnO2 acting as an oxidizer on Mn-BC. Overall, the modified biochar derived from Chinese herbal medicine residues is a superior alternative for the removal of TC from an aqueous solution.

Source apportionment of heavy metal and their health risks in soil-dustfall-plant system nearby a typical non-ferrous metal mining area of Tongling, Eastern China.

The agricultural land-atmospheric dustfall-plant system around the mining area is at high risks of heavy metal pollution caused by mining-smelting activities. In this study, 118 samples (including rhizospheric soils, background soils, soil-forming parent rocks, crops, vegetables, medicinal plants and atmospheric dustfall) were collected nearby Tongling Cu-Fe-Au mining area, Eastern China. We studied the concentrations, migration, sources, and health risks through consumption of two main crops (corn and rice), six kinds of vegetables, and medicinal plants (Fengdan, Paeonia ostii) for six metal elements (Cu, Zn, Cr, Cd, Pb and Hg). Results revealed Cr and Cd in soils, and Cd, Cr, Pb, Cu and Zn in dustfall showed a relatively high contamination degree. The mean contents of Cr and Pb in corn kernels, as well as Cd, Cr and Pb in rice grains and all vegetables, and Cr in Fengdan cortex moutan exceeded the corresponding food safety limits in China. The transfer capability of Cr in corn kernels and rice grains, Pb in edible vegetables, and Cd in cortex moutan were the strongest, respectively. Health risk assessment results showed Cr had the greatest non-carcinogenic risk, followed by Pb and Cd. The results of pearson's correlation analysis (CA), hierarchical cluster analysis (HCA), and principal component analysis (PCA) indicated Zn-Cr, Pb and Cd-Cu-Hg in the plants might derive from different geochemical end-members. Source apportionment based on lead isotope showed that mining-smelting activities were the major source of Pb in atmospheric dustfall and agricultural soils, with the average contribution rates of 66% and 50%, respectively. Vehicle emissions from diesel fuels (50%-68%) and mining-smelting activities (16%-25%) contributed mainly to Pb accumulation in plants. Hence, our study suggested the accumulations of Pb in plants might be mainly from the direct foliar uptake of atmospheric Pb related to vehicle emissions and mining-smelting activities.

Physiological and biochemical responses of Microcystis aeruginosa to phosphine.

The frequent outbreaks of cyanobacteria bloom are often accompanied by the generation and release of reduced phosphorus species (e.g., phosphine), which raises interesting questions regarding their potential algae-related effects. To clarify the physiological and biochemical responses of cyanobacteria to phosphine, Microcystis aeruginosa was treated with different concentrations of phosphine. Net photosynthetic rate, total antioxidant capacity (T-AOC), catalase (CAT) activity, and the concentrations of chlorophyll a, carotenoid and total protein were investigated and scanning electron microscopy (SEM) was conducted to elucidate the physiological and biochemical responses of M. aeruginosa to phosphine. The results showed that phosphine was beneficial to the growth of algal cells after M. aeruginosa acclimatized to the treatment of phosphine, and treatment with 2.48 × 10-2 mg/L phosphine had a greater positive effect on the growth and reproduction of M. aeruginosa than 7.51 × 10-3 mg/L phosphine, in which most algal cells were smooth and flat on day 16. Treatment with the high concentration of phosphine (7.51 × 10-2 mg/L) for 16 d reduced T-AOC, CAT activity, net photosynthetic rate, and the concentrations of chlorophyll a, carotenoid and total protein of M. aeruginosa to the minimums, resulting in the lysis and death of M. aeruginosa cells, which indicates phosphine has a toxic effect on the growth of algal cells. However, the high concentration of phosphine (7.51 × 10-2 mg/L) had a greater positive effect on the growth of M. aeruginosa cells than the lower two (7.51 × 10-3 mg/L and 2.48 × 10-2 mg/L) from 3 d to 12 d. Our findings provide insight into how phosphine potentially affects the growth of M. aeruginosa cells and the important roles of elevated phosphine on the outbreak of cyanobacteria bloom.

Mechanism of matrix-bound phosphine production in response to atmospheric elevated CO2 in paddy soils.

To explore the effect of elevated CO2 concentrations ([CO2]) on phosphine formation in paddy fields, the matrix-bound phosphine (MBP) content, different phosphorus fractions and various carbon forms in soil samples from rice cultivation under varying CO2 concentrations of 400 ppm, 550 ppm and 700 ppm by indoor simulation experiment were determined. This study showed that MBP concentration did not increase significantly with elevated [CO2] over four-week cultivation periods of rice seedlings, regardless of soil layers. MBP had a significant positive correlation with total phosphorus (TP) and inorganic phosphorus (IP), and multiple stepwise linear regression analysis further indicated that MBP preservation in neutral paddy soils with depths of 0-20 cm may have been due to conversion from FeP and CaP. Based on redundancy analysis and forward selection analysis, speculated that the formation of MBP in the neutral paddy soils as the response to atmospheric elevated [CO2] was due to two processes: (i) FeP transformation affected by the changes of soil respiration (SCO2) and TOC was the main precursor for the production of MBP; and (ii) CaP transformation resulting from variation in HCO3- was the secondary MBP source. The complex combination of these two processes is simultaneously controlled by SCO2. In a word, the soil environment in the condition of elevated [CO2] was in favor of MBP storage in neutral paddy soils. The results of our study imply that atmospheric CO2 participates in and has a certain impact on the global biogeochemical cycle of phosphorus.

Effect of static magnetic field on electricity production and wastewater treatment in microbial fuel cells.

The effect of a magnetic field (MF) on electricity production and wastewater treatment in two-chamber microbial fuel cells (MFCs) has been investigated. Electricity production capacity could be improved by the application of a low-intensity static MF. When a MF of 50 mT was applied to MFCs, the maximum voltage, total phosphorus (TP) removal efficiency, and chemical oxygen demand (COD) removal efficiency increased from 523 ± 2 to 553 ± 2 mV, ∼93 to ∼96 %, and ∼80 to >90 %, respectively, while the start-up time and coulombic efficiency decreased from 16 to 10 days and ∼50 to ∼43 %, respectively. The MF effects were immediate, reversible, and not long lasting, and negative effects on electricity generation and COD removal seemed to occur after the MF was removed. The start-up and voltage output were less affected by the MF direction. Nitrogen compounds in magnetic MFCs were nitrified more thoroughly; furthermore, a higher proportion of electrochemically inactive microorganisms were found in magnetic systems. TP was effectively removed by the co-effects of microbe absorption and chemical precipitation. Chemical precipitates were analyzed by a scanning electron microscope capable of energy-dispersive spectroscopy (SEM-EDS) to be a mixture of phosphate, carbonate, and hydroxyl compounds.

Effect of dissolved oxygen on nitrogen and phosphorus removal and electricity production in microbial fuel cell.

Performance of a two-chamber microbial fuel cell (MFC) was evaluated with the influence of cathodic dissolved oxygen (DO). The maximum voltage, coulombic efficiency and maximum power density outputs of MFC decreased from 521 to 303 mV, 52.48% to 23.09% and 530 to 178 mW/m(2) with cathodic DO declining. Furthermore, a great deal of total phosphorus (TP) was removed owing to chemical precipitation (about 80%) and microbial absorption (around 4-17%). COD was first removed in anode chamber (>70%) then in cathode chamber (<5%). Most of nitrogen was removed when the cathodic DO was at low levels. Chemical precipitates formed in cathode chamber were verified as phosphate, carbonate and hydroxyl compound with the aid of scanning electron microscope capable of energy dispersive spectroscopy (SEM-EDS), X-ray diffractometer (XRD) and Fourier transform infrared spectroscopy (FTIR).

Photodegradation of methyl orange by photocatalyst of CNTs/P-TiO(2) under UV and visible-light irradiation.

A novel nanoscale photocatalyst CNTs/P-TiO(2) was successfully prepared by hydrothermal method. The morphology and the physicochemical properties of the prepared samples were investigated using TEM, XPS, XRD, BET, FTIR, TG-DSC and UV-vis DRS spectroscopy. The photocatalytic activity was evaluated by degradation of methyl orange (MO) dye. The results demonstrated that CNTs/P-TiO(2) nanoparticles could effectively photodegrade MO not only under UV irradiation but also under visible-light (VL) irradiation. The MO degradation performance on CNTs/P-TiO(2) was superior to that of the commercial P25. The optimal mass ratio of CNTs to P-TiO(2) in the nanocomposite catalyst was 5:100. The synergetic effect was discussed in terms of different roles played by phosphorus doping and introducing CNTs into the composite catalysts.

Effect of different types of electron acceptors on the anoxic phosphorus uptake activity of denitrifying phosphorus removing bacteria.

The effect of different types of electron acceptors (O(2), NO(3)(-) and NO(2)(-)) on anoxic phosphorus uptake was investigated to obtain a better understanding of the metabolic behavior of denitrifying phosphorus removing bacteria (DPB). Two sets of sequencing batch reactor (SBR) were used to enrich phosphorus accumulation organisms (PAOs) by alternative anaerobic and aerobic operations (oxygen was used as the electron acceptor), batch experiments under two different electron acceptor conditions, nitrate and nitrite, were performed by using activated sludge generated from the above-operated SBR reactors. Anoxic phosphorus uptake achieved successful both by using nitrate or nitrite as the electron acceptor. However, the relative small amount of anoxic phosphorus was taken up by microorganisms with nitrite used as the electron acceptor in comparison with nitrate. The optimal stoichiometric loading amount of electron acceptors of nitrate and nitrite to phosphorus (N/P ratio) were 0.89 and 0.60, respectively. If the initial concentration of electron acceptors was controlled below the optimal ratio, the amount of phosphorus taken up increased with the concentration, otherwise it would decrease. It was also found that DPB lost the ability of phosphorus release and uptake rapidly under continuous anaerobic-anoxic operation condition.

Advanced treatment of landfill leachate by a new combination process in a full-scale plant.

Advanced treatment of mature landfill leachate from a municipal landfill located in southern China (Jiangmen) was carried out in a full-scale plant using a new process. The combined process has a sequencing batch reactor (SBR) serving as the primary treatment, with polyferric sulfate (PFS) coagulation coupled with a Fenton system as secondary treatment, and a pair of upflow biological aerated filters (UBAFs) in parallel as tertiary treatment. The overall removal efficiency of chemical oxygen demand (COD) in this process was 97.3%, with an effluent COD less than 100 mg/L. Up to 99% ammonia (N-NH3) removal efficiency was achieved in the SBR, with an effluent of less than 3 mg/L, which meets the discharge standard (< or =25 mg/L) with only primary treatment. The total phosphorus (TP) and suspended solids (SS) in the final effluent were reduced to less than 1 mg/L and 10 mg/L, respectively. The experience gained in the operation and maintenance will lead to a more stable performance of this combined process. An economic analysis shows that the overall operating cost of the advanced treatment was $2.70/m(3). This new combination process was proved to be highly compatible and efficient in a small-scale landfill leachate treatment plant and is recommended for small-scale landfill leachate treatment plants.

Use of dewatered municipal sludge on Canna growth in pot experiments with a barren clay soil.

The present study evaluated the possibility of using the dewatered municipal sludge for non-agricultural purposes. The sludge was amended with soil and was applied at 0, 165, 330, 495 and 660 t/ha to promote the growth of Canna. The results showed that the Canna growth pattern exhibited a pronounced positive growth response in the range of 165-495 t/ha, and the Canna could not survive at an amendment rate of 660 t/ha. The analysis of chlorophyll fluorescence parameters showed that sludge did no harm to Canna, while under the conditions of barren soil alone, the plants were put into nutrients stress conditions. Due to the application of sludge, the concentration of heavy metals (Cu, Zn, Cr, Cd, Pb and Ni) in soil increased. However, by planting of Canna, contents of Cd, Ni and Zn showed trends of decline; Cd and Ni have shown a significant decline in concentration, while Zn had only limit response. As a result, dewatered sludge might be used to amend the barren soil and Canna could be used for phytoremediation of sludge.