Haipeng Wu

The interactions of composting and biochar and their implications for soil amendment and pollution remediation: a review

Abstract Compost and biochar, used for the remediation of soil, are seen as attractive waste management options for the increasing volume of organic wastes being produced. This paper reviews the interaction of biochar and composting and its implication for soil amendment and pollution remediation. The interaction of biochar and composting affect each other’s properties. Biochar could change the physico-chemical properties, microorganisms, degradation, humification and gas emission of composting, such as the increase of nutrients, cation exchange capacity (CEC), organic matter and microbial activities. The composting could also change the physico-chemical properties and facial functional groups of biochar, such as the improvement of nutrients, CEC, functional groups and organic matter. These changes would potentially improve the efficiency of the biochar and composting for soil amendment and pollution remediation. Based on the above review, this paper also discusses the future research required in this field.

Efficiency of biochar and compost (or composting) combined amendments for reducing Cd, Cu, Zn and Pb bioavailability, mobility and ecological risk in wetland soil

Biochar and compost are two inexpensive and effective in situ remediation materials for heavy metal contaminated soils. The interaction between biochar and compost (or composting material) calls for further studies to maximize the potential benefits of both. In this study, we examined the short-time efficiency of compost (C), biochar (B), a mixture of compost and biochar (B + C), composted biochar (Bced) and biochar-composting material (BCing, biochar and biomass mixed before composting) for reducing bioavailability, mobility and ecological risk of Cd, Cu, Zn and Pb in wetland soil. Adding these amendment materials to the contaminated soil changed the total organic carbon (TOC), water-extractable organic carbon (WEOC) and pH. All the materials decreased the available Cd, Cu, Zn and Pb concentrations in the soil (compost increased the available Cu concentration) and Cd, Cu, Zn and Pb concentrations in pore water. As a whole, soil with Bced and BCing had the biggest decrease in these concentrations. These results indicated that all the materials reduced the bioavailability and mobility of heavy metals (compost improved the bioavailability of Cu), and Bced and BCing had the greatest capacity for that. The materials improved soil microbial biomass and BCing created the biggest improvement, which suggested all the amendment materials reduced the ecological risk of heavy metals and BCing had the greatest capacity for that.

Treatment of landfill leachate using immobilized Phanerochaete chrysosporium loaded with nitrogen-doped TiO2 nanoparticles

This study investigated the performance of immobilized Phanerochaete chrysosporium loaded with nitrogen-doped TiO2 nanoparticles in the treatment of raw landfill leachate with a very low biodegradability ratio (BOD5/COD) of 0.09. The effects of various operating parameters, such as initial chemical oxygen demand (COD) concentration, pH, temperature, and biosorbent dosage, were evaluated with respect to the removal efficiency of total organic carbon (TOC) and ammonia nitrogen (NH3-N). For the immobilized biosorbents, an optimum pH of 6.0 for TOC and 7.0 for NH3-N were found suitable for TOC and NH3-N removal at temperature of 37°C, respectively. The most superior removal efficiencies of TOC and NH3-N of landfill leachate were over 75% and 74% in 72 h at an initial COD concentration of 200 mg L(-1), respectively. In addition, heavy metals were partly removed by the immobilized biosorbents during the process of landfill leachate treatment. The species and mass percentage of organic compounds in landfill leachate after the treatment were found to have considerably declined according to the gas chromatography coupled with mass spectrometry (GC-MS) system. These results indicate that the immobilized P. chrysosporium loaded with nitrogen-doped TiO2 nanoparticles could be a convenient and efficient method for the treatment of landfill leachate.

Changes in heavy metal mobility and availability from contaminated wetland soil remediated with combined biochar-compost

The combination of biochar and compost has been proven to be effective in heavy metals contaminated wetland soil restoration. However, the influence of different proportions between biochar and compost on immobilization of heavy metals in soil has been less studied up to date. Therefore, we investigated the effect of different ratios of biochar-compost mixtures on availability and speciation distribution of heavy metals (Cd, Zn and Cu) in wetland soil. The results showed that applying all amendment combinations into wetland soil increased gradually the total organic carbon (TOC) and water-extract organic carbon (WEOC) as the compost percentage rose in biochar-composts. The higher pH was obtained in a certain biochar addition (20% and 40%) in combinations due to efficient interaction of biochar with compost. All amendments could significantly decrease availability of Cd and Zn mainly from pH change, but increase available Cu concentration as the result of increased water-extract organic carbon and high total Cu content in compost. Moreover, amendments can decrease easily exchangeable fraction and increase reducible of Cd and Zn greatly with increase of compost content in combinations, while amendments containing compost promote transformation of Cu from Fe/Mn oxide and residual fractions to organic bindings. These results demonstrate that different ratios of biochar and compost have a significant effect on availability and speciation of heavy metals in multi-metal-contaminated wetland soil.

Synthesis and evaluation of a new class of stabilized nano-chlorapatite for Pb immobilization in sediment

During the past years, efforts have been made to deal with the Pb contaminated sediment in Xiawangang River in Hunan province, China, but it remains a serious problem since the smelting pollutants were accumulated. According to previous studies, phosphate showed an effective ability to transfer labile Pb to pyromorphite (Pb5(PO4)3X, X=F, Cl, Br, OH) but its application was limited by its solubility and deliverability. Hence a new class of nano-chlorapatite was synthesized by using sodium dodecyl sulfate (SDS) as a stabilizer and characterized by TEM, FESEM, DLS, FTIR, and EDAX. Results demonstrated that the SDS stabilized nano-chlorapatite (SDS-nClAP) was in spherical or spheroidal shape with a hydrodynamic diameter of 40.4nm. Experimental data suggested that SDS-nClAP was effective in transforming labile Pb to stable fraction with a maximum increase of 38.3%, also the reduction of TCLP-leachable Pb from 0.30 to 0mg/L after 45-d treatment. The increase of available phosphorus in both SDS-nClAP and ClAP treated sediment samples verified dissolution-precipitation mechanism involved in Pb immobilization. Additionally, the increment of organic matter in 10:1 treated samples was approximately 5-fold than that in 2:1 treated samples, which revealed that the micro-organisms may play an important role in it.

Integrating hierarchical bioavailability and population distribution into potential eco-risk assessment of heavy metals in road dust: A case study in Xiandao District, Changsha city, China

Modified eco-risk assessment method (MEAM) integrated with the hierarchical bioavailability determined by the fraction detection of Cd, Pb, Zn, Cu, Cr in road dust samples and the local population distribution derived from the local land use map, was proposed to make the hierarchical eco-risk management strategy in Xiandao District (XDD), China. The geo-accumulation index (Igeo), the original potential eco-risk index (Er(i)) and the modified eco-risk assessment index (MEAI) were used to identify the priority pollutant. Compared with the Hunan soil background values, evaluated metal concentrations were found to different extent. The results of mean Igeo, Er(i) and bioavailability of studied metals revealed the following orders: Cd>Pb ≈ Zn>Cu ≈ Cr, Cd>Pb>Cu>Cr>Zn and Cd>Zn>Cu ≈ Pb>Cr, respectively. Therefore, Cd was regarded as the priority pollutant. To identify the priority areas taking into account cost consideration, the hierarchical risk map based on the results of the modified eco-risk assessment index with overlay of the population density map was needed and made. The west and partly south areas of XDD were under higher eco-risk generally. Moreover, the whole XDD area was divided into 4 area categories with different management priorities based on the possibility of occurrence of eco-risk, and the hierarchical risk management strategy associated with protecting local population was suggested to facilitate allocation of funds for risk management.

Biological technologies for the remediation of co-contaminated soil

Abstract Compound contamination in soil, caused by unreasonable waste disposal, has attracted increasing attention on a global scale, particularly since multiple heavy metals and/or organic pollutants are entering natural ecosystem through human activities, causing an enormous threat. The remediation of co-contaminated soil is more complicated and difficult than that of single contamination, due to the disparate remediation pathways utilized for different types of pollutants. Several modern remediation technologies have been developed for the treatment of co-contaminated soil. Biological remediation technologies, as the eco-friendly methods, have received widespread concern due to soil improvement besides remediation. This review summarizes the application of biological technologies, which contains microbial technologies (function microbial remediation and composting or compost addition), biochar, phytoremediation technologies, genetic engineering technologies and biochemical technologies, for the remediation of co-contaminated soil with heavy metals and organic pollutants. Mechanisms of these technologies and their remediation efficiencies are also reviewed. Based on this study, this review also identifies the future research required in this field.

Effects of heavy metals and soil physicochemical properties on wetland soil microbial biomass and bacterial community structure.

Heavy metals (HMs) contamination is a serious environmental issue in wetland soil. Understanding the micro ecological characteristic of HMs polluted wetland soil has become a public concern. The goal of this study was to identify the effects of HMs and soil physicochemical properties on soil microorganisms and prioritize some parameters that contributed significantly to soil microbial biomass (SMB) and bacterial community structure. Bacterial community structure was analyzed by polymerase chain reaction-denaturing gradient gel electrophoresis (PCR-DGGE). Relationships between soil environment and microorganisms were analyzed by correlation analysis and redundancy analysis (RDA). The result indicated relationship between SMB and HMs was weaker than SMB and physicochemical properties. The RDA showed all eight parameters explained 74.9% of the variation in the bacterial DGGE profiles. 43.4% (contain the variation shared by Cr, Cd, Pb and Cu) of the variation for bacteria was explained by the four kinds of HMs, demonstrating HMs contamination had a significant influence on the changes of bacterial community structure. Cr solely explained 19.4% (p<0.05) of the variation for bacterial community structure, and Cd explained 17.5% (p<0.05), indicating Cr and Cd were the major factors related to bacterial community structure changes.

Responses of bacterial community and functional marker genes of nitrogen cycling to biochar, compost and combined amendments in soil

Biochar and compost are seen as two attractive waste management options and are used for soil amendment and pollution remediation. The interaction between biochar and composting may improve the potential benefits of biochar and compost. We investigated soil physicochemical properties, bacterial community, bacterial 16S rRNA, and functional marker genes of nitrogen cycling of the soil remedied with nothing (S), compost (SC), biochar (SB), a mixture of compost and biochar (SBC), composted biochar (SBced), and a composted mixture of biochar and biomass (SBCing). The results were that all amendments (1) increased the bacterial community richness (except SB) and SBCing showed the greatest efficiency; (2) increased the bacterial community diversity (SBCing > SBC > SC > SBced > SB > S); and (3) changed the gene copy numbers of 16S rRNA, nirK, nirS, and nosZ genes of bacteria, ammonia-oxidizing archaea (AOA), and ammonia-oxidizing bacteria (AOB). All amendments (except SB) could increase the gene copy number of 16S rRNA, and SBCing had the greatest efficiency. The changes of soil bacterial community richness and diversity and the gene copy numbers of 16S rRNA, nirK, nirS, nosZ, AOA, and AOB would affect carbon and nitrogen cycling of the ecosystem and also implied that BCing had the greatest efficiency on soil amendment.

Metal-based quantum dots: synthesis, surface modification, transport and fate in aquatic environments and toxicity to microorganisms

Semiconductor quantum dots (QDs) have attracted considerable attention for their superior optical properties and wide utilization in biological and biomedical studies. Recently, intense concerns have been focused on the cytotoxicity assessment of QDs because most QDs are made of heavy metal ions (e.g., Cd2+), which pose a threat to human beings and simultaneously hamper the practical applications of QDs. This review provides an overview of the synthetic methods, surface modification, dissolution mechanism and cytotoxicity of core–shell QDs. Accordingly, the effects of polymer coating materials and environmental conditions on the dissolution kinetics of polymer-coated core–shell QDs are discussed in detail. To offer a systematic analysis of the cytotoxicity of QDs to microorganisms, correlative factors such as particle size, surface coating materials, photolysis and oxidation, charge, concentration, exposure time and mechanical stability are taken into consideration with respect to the mechanism of their toxicity. Future research will concentrate on toxicological and pharmacological studies of QDs to find new strategies with lower risk and higher benefits for public health, providing a unique technique for nanopharmaceutical applications.