Zhongwu Li

Assessment of surface water quality using multivariate statistical techniques in red soil hilly region: a case study of Xiangjiang watershed, China

In the study, multivariate statistical methods including factor, principal component and cluster analysis were applied to analyze surface water quality data sets obtained from Xiangjiang watershed, and generated during 7 years (1994–2000) monitoring of 12 parameters at 34 different profiles. Hierarchical cluster analysis grouped 34 sampling sites into three clusters, including relatively less polluted (LP), medium polluted (MP) and highly polluted (HP) sites, and based on the similarity of water quality characteristics, the watershed was divided into three zones. Factor analysis/principal component analysis, applied to analyze the data sets of the three different groups obtained from cluster analysis, resulted in four latent factors accounting for 71.62%, 71.77% and 72.01% of the total variance in water quality data sets of LP, MP and HP areas, respectively. The PCs obtained from factor analysis indicate that the parameters for water quality variations are mainly related to dissolve heavy metals. Thus, these methods are believed to be valuable to help water resources managers understand complex nature of water quality issues and determine the priorities to improve water quality.

Adsorption characteristics of Cu and Zn onto various size fractions of aggregates from red paddy soil

Soil aggregate is the basic structure unit of soils and the ability of various size fractions are different in the aspect of adsorbing and transferring heavy metals in the environment. In this study, bulk soil from red paddy field was partitioned into four aggregate-size fractions and their adsorption characteristics for Cu and Zn were studied. Our results showed that: Pseudo-second order model was more successful to fit the adsorption process in the kinetic experiments and the isothermal experiments data can be described well with the Freundlich model as a whole. Due to higher contents in organic matter, CEC and free iron oxide, the <0.002mm fraction was found to have the highest initial sorption rate and maximum adsorption capacity. The adsorption amount of metals increased as the increasing of pH and the percentage of adsorbed metal susceptible to desorption into 0.01M NaNO3 was greater for Zn than for Cu, while their variation trends were quite opposite. More specific adsorption sites in the <0.002mm fraction lead to more desorption amount for this particle size of soil at low pH condition. After 60 days of incubation, Cu and Zn were observed to enrich in the clay-size aggregates with fractions more stable than other particles.

Biochar to improve soil fertility. A review

Soil mineral depletion is a major issue due mainly to soil erosion and nutrient leaching. The addition of biochar is a solution because biochar has been shown to improve soil fertility, to promote plant growth, to increase crop yield, and to reduce contaminations. We review here biochar potential to improve soil fertility. The main properties of biochar are the following: high surface area with many functional groups, high nutrient content, and slow-release fertilizer. We discuss the influence of feedstock, pyrolysis temperature, pH, application rates, and soil types. We review the mechanisms ruling the adsorption of nutrients by biochar.

Competitive removal of Cd(II) and Pb(II) by biochars produced from water hyacinths: performance and mechanism

Three biochars converted from water hyacinth biomass at 300, 450, and 600 °C were used to investigate the adsorption properties of Cd2+ and Pb2+. In addition, the competitive adsorption mechanisms between Cd2+ and Pb2+ were also conducted. Adsorption kinetics and isotherms indicated that the maximum adsorption capacity of Pb2+ was larger than that of Cd2+, and the adsorption process in the mixed solutions of two heavy metals (Cd2+ and Pb2+) was more favorable for Pb2+. Further investigation about the characterization of biochars demonstrated that cation exchange, surface complexation, cation–π interaction and precipitation were the main mechanisms responsible for the heavy metal removal. In this study, competitive adsorption may also be explained by these mechanisms. These results are useful for the application of biochars in selective adsorption and in practical wastewater treatment.

Transport, fate, and stimulating impact of silver nanoparticles on the removal of Cd(II) by Phanerochaete chrysosporium in aqueous solutions.

Despite the knowledge about increasing discharge of silver nanoparticles (AgNPs) into wastewater and its potential toxicity to microorganisms, the interaction of AgNPs with heavy metals in the biological removal process remains poorly understood. This study focused on the effect of AgNPs (hydrodynamic diameter about 24.3±0.37 nm) on the removal of cadmium (Cd(II)) by using a model white rot fungus species, Phanerochaete chrysosporium. Results showed that the biological removal capacity of Cd(II) increased with the concentration of AgNPs increasing from 0.1 mg/L to 1 mg/L. The maximum removal capacity (4.67 mg/g) was located at 1 mg/L AgNPs, and then decreased with further increasing AgNPs concentration, suggesting that an appropriate concentration of AgNPs has a stimulating effect on the removal of Cd(II) by P. chrysosporium instead of an inhibitory effect. Results of Ag(+) and total Ag concentrations in the solutions together with those of SEM and XRD demonstrated that added AgNPs had undergone oxidative dissolution and transported from the solution to the surface of fungal mycelia (up to 94%). FTIR spectra confirmed that amino, carboxyl, hydroxyl, and other reducing functional groups were involved in Cd(II) removal, AgNPs transportation, and the reduction of Ag(+) to AgNPs.

Compost as a Soil Amendment to Remediate Heavy Metal-Contaminated Agricultural Soil: Mechanisms, Efficacy, Problems, and Strategies

Compost or composting has been widely investigated under the background of heavy metal pollution of agricultural soils and rapid growth of organic wastes. Compost is rich in nutrients, humic matter, and microorganisms; it may be added to agricultural soil as a fertilizer to improve soil fertility and promote the growth of crops and microorganisms, and as a soil amendment to relieve heavy metal pollution. However, the effectiveness and security of compost application in agricultural soil continue to generate concern. In this review, the efficacy and mechanisms of compost remediation technologies for heavy metal-contaminated agricultural soil are presented. Poor quality, unsuitability for multiple heavy metal-contaminated soils, and potential long-term risks are the main limitations of the effectiveness and security of compost application to soils. Therefore, improving the quality of the compost, adding amendments, or combining with phytoremediation may be considered when adopting compost to remediate polluted agricultural soil. In addition, we propose several approaches to optimize these strategies and render the remediation of heavy metal-contaminated agricultural soil using compost safer and more effective. The findings of this review will help support the large-scale application of compost in agriculture in the future.

Aging effect on the leaching behavior of heavy metals (Cu, Zn, and Cd) in red paddy soil

Aging effect can influence the fractions distribution and mobility of metals after they are added into soil. In this study, incubation and soil column experiments under simulated acid rain condition were conducted to evaluate aging effect on the leaching characteristic of Cu, Zn, and Cd in artificial polluted red paddy soil. Our results showed that aging effect reduced metal contents in exchangeable and HoAc soluble fractions. Power function was the most excellent to describe the variation of exchangeable fraction, while pseudo first- and second-order functions were more successful to describe the leaching characteristic of metals from soil columns. The leaching amount of the metals from the polluted soil only accounted for a small part of their total content in soil, and the leachability of Cu was the weakest. Both the exchangeable and HoAc soluble fraction were available as indicators to evaluate the leachability of metals in red paddy soil. The shorter time the soil was contaminated, the more amounts of metals released from the soil. The reduction of exchangeable fraction caused by aging effect was the main reason for the decrease of metal mobility in soil.

Soil Organic Carbon Loss and Selective Transportation under Field Simulated Rainfall Events

The study on the lateral movement of soil organic carbon (SOC) during soil erosion can improve the understanding of global carbon budget. Simulated rainfall experiments on small field plots were conducted to investigate the SOC lateral movement under different rainfall intensities and tillage practices. Two rainfall intensities (High intensity (HI) and Low intensity (LI)) and two tillage practices (No tillage (NT) and Conventional tillage (CT)) were maintained on three plots (2 m width × 5 m length): HI-NT, LI-NT and LI-CT. The rainfall lasted 60 minutes after the runoff generated, the sediment yield and runoff volume were measured and sampled at 6-min intervals. SOC concentration of sediment and runoff as well as the sediment particle size distribution were measured. The results showed that most of the eroded organic carbon (OC) was lost in form of sediment-bound organic carbon in all events. The amount of lost SOC in LI-NT event was 12.76 times greater than that in LI-CT event, whereas this measure in HI-NT event was 3.25 times greater than that in LI-NT event. These results suggest that conventional tillage as well as lower rainfall intensity can reduce the amount of lost SOC during short-term soil erosion. Meanwhile, the eroded sediment in all events was enriched in OC, and higher enrichment ratio of OC (ERoc) in sediment was observed in LI events than that in HI event, whereas similar ERoc curves were found in LI-CT and LI-NT events. Furthermore, significant correlations between ERoc and different size sediment particles were only observed in HI-NT event. This indicates that the enrichment of OC is dependent on the erosion process, and the specific enrichment mechanisms with respect to different erosion processes should be studied in future.

Influence of fulvic acid on the colloidal stability and reactivity of nanoscale zero-valent iron.

This study investigated the effect of fulvic acid (FA) on the colloidal stability and reactivity of nano zero-valent iron (nZVI) at pH 5, 7 and 9. The sedimentation behavior of nZVI differed at different pH. A biphasic model was used to describe the two time-dependent settling processes (i.e., a rapid settling followed by a slower settling) and the settling rates were calculated. Generally, the settling of nZVI was more significant at the point of zero charge (pHpzc), which could be varied in the presence of FA due to the adsorption of FA on the nZVI surface. More FA was adsorbed on the nZVI surface at pH 5-7 than pH 9, resulting in the varying sedimentation behavior of nZVI via influencing the electrostatic repulsion among particles. Moreover, it was found that there was a tradeoff between the stabilization and the reactivity of nZVI as affected by the presence of FA. When FA concentration was at a low level, the adsorption of FA on the nZVI surface could enhance the particle stabilization, and thus facilitating the Cr(VI) reduction by providing more available surface sites. However, when the FA concentrations were too high to occupy the active surface sites of nZVI, the Cr(VI) reduction could be decreased even though the FA enhanced the dispersion of nZVI particles. At pH 9, the FA improved the Cr(VI) reduction by nZVI. Given the adsorption of FA on the nZVI surface was insignificant and its effect on the settling behavior of nZVI particles was minimal, it was proposed that the FA formed soluble complexes with the produced Fe(III)/Cr(III) ions, and thus reducing the degree of passivation on the nZVI surface and facilitating the Cr(VI) reduction.

Fluorescent sensing of sulfide ions based on papain-directed gold nanoclusters

A sensitive and selective method has been developed for the determination of sulfide ions (S2−) based on S2− triggered fluorescence quenching of papain-directed Au nanoclusters. Under the optimized experimental conditions, the proposed method facilitated the determination of S2− in the linear range 0.5–80.0 μM; the limit of detection was 0.38 μM at a signal-to-noise ratio of 3. In addition, the fluorescence intensity decreased selectively in response to S2− relative to other ions. Based on multiple analyses, it is proposed that the fluorescence was quenched through the unique reactions between S2− and the Au atoms/ions, and that the formation of Au2S induced aggregation of the Au nanoclusters. The practicality of the proposed method for the determination of S2− in natural water samples was verified. The results were in good agreement with those determined by the methylene blue colorimetric method. This new method may broaden the scope of techniques available for the determination of S2−.