Recent Advance on Torrefaction Valorization and Application of Biochar from Agricultural Waste for Soil Remediation

With the increase of global proportion of soil pollution and the number of areas at risk,researchers have sought to develop various pathways to repair or relieve the pollutants in soil.Among them,biochar represents one multi-dimensional soil amendment which has got great deal of attention on its physicochemical properties towards the removal or mitigation of contaminants in soil.A variety of agricultural wastes like straw and manure prepared from different torrefaction process have been employed as feedstock for the production of biochar,which can be applied to the contaminated soil to facilitate the growing environment for crops,and to improve soil fertility and microbial environment.In addition,the utilization of biochar for soil remediation is also considered as a pro-cess of carbon sequestration.The purpose of this review is to summarize the latest research progress in torrefac-tion processes and mechanism of agricultural waste,the effects of different torrefaction methods on the formation and properties of biochar were explained,coupled with the effects of process parameters.Especially,the conver-sion and mechanisms of biochar prepared from agricultural wastes composed mainly with lignocellulosic material were discussed,and the characteristics of biochar prepared for improving soil physical and chemical character-istics,microbial community characteristics,nutrients,and the stability and relief of soil pollutants,especially heavy metals,are compared.Finally,this work discussed the application and future technical challenges of soil remediation based on agricultural waste derived biochar.

Research Progress on Effects of Continuous Cropping on Soil Microbial Florae and Its Restoration

Continuous cropping has become a common form of agricultural production at present, but with the increase of continuous cropping years, continuous cropping obstacles such as soil-borne diseases and plant growth potential decline are becoming more and more common. At present, the causes of continuous cropping obstacles and continuous cropping restoration have become a hot issue in agricultural research. This paper summarized the effects of continuous cropping obstacles on soil microbial community structure and main technical methods to repair continuous cropping obstacles, such as agricultural measure management, microbial balance adjustment and soil improvement, aiming to provide theoretical reference for protecting the sustainable utilization of soil ecosystem and ensuring the stability of crop production.

Technique of Earthworms Restoring Soil in Greenhouse Cultivation

The production environment of greenhouse cultivation is relatively closed,the multiple cropping index is high,the management of fertilizationwatering and pesticideapplication isblindtosomeextent,andthe phenomenonofcontinuous cropping isalsocommonSoilquali-ty affects the sustainable development of greenhouse cultivation.Earthworm is a ubiquitous invertebrate organism in soil,an important part of soil system,a link between terrestrial organisms and soil organisms,an important link in the small cycle of soil material organisms,and plays an important role in maintaining the structure and function of soil ecosystem.Different ecotypes of earthworms are closely related to their habi-tats(soil layers)and food resource preferences,and then affect their ecological functions.The principle of earthworm regulating soil function is essentially the close connection and interaction between earthworm and soil microorganism.Using different ecotypes of earthworms and bio-logical agents to carry out combined remediation of greenhouse cultivation soil is a technical model to realize sustainable development of green-house cultivation.

Overview of Patented Technologies for Remediation of Soil Pollution

Soil, an important material basis for human activities, is an indispensable natural rasource that is difficult to regenerate. It is also an important part of human ecological environment. Currently, soil pollution has affected China＇s agricultural production and threatened human health and ecological safety, so it has been paid more attention to by the people and has become a hot spot in environmental field. Through continuous research, a variety of soil remediation patents and technologies also emerge. Here, by retrieving the main words through the website （www. soopat. corn） and Chinese patent net, types of soil pollution and remediation technologies under the authorization status of the patents were analyzed, and the major species of soil pollutants and soil remediation technologies were reviewed.

Optimization of reed-specific degrading bacteria by response surfaces for remediation of crude oil-polluted soil in Xinjiang,China

This paper discussed the optimization of conditions for remediation of crude oil-polluted soil based on pot experiment by applying reed-specific degrading bacteria, and using response surfaces methodology. We took the initial crude oil concentration, the amount of inoculation, the ratio of nitrogen and phosphorus, and the use of surfactant （Tween-80） as independent variables （factors）, and the degrading ratio of crude oil as the dependent variable （response） after a 90-day experiment. The experiment explored the impacts of each independent variable and their interactions on the bioremediation of crude oil-polluted soil using the Box-Behnken design. Working with a simulated forecasting model the study obtained optimization va reed＋specific degrading bacteria, a nitrogen to phosphorus ues for the treatment parameters of 200 g/kg of the ratio of about 6.0. and 0.2% surfactant. Under experimental conditions, for crude oil concentrations of 10, 30 and 50 g/kg, the optimal effects of the treatments achieved 71.87%, 66.61% and 54.52% degradation of the crude oil, respectively. The results can provide a basis for the technical development of plant-microorganism combined bioremediation of crude oil-polluted soil.

Stabilization-based soil remediation should consider longterm challenges

Soil remediation is of increasing importance globally, especially in developing countries. Among available remediation options, stabilization, which aims to immobilize contaminants within soil, has considerable advantages, including that it is cost-effective, versatile, sustainable, rapid, and often results in less secondary pollution. However, there are emerging challenges regard- ing the long-term performance of the technology, which may be affected by a range of environmental factors. These challenges stem from a research gap regarding the development of accurate, quantitative laboratory simula- tions of long-term conditions, whereby laboratory accel- erated aging methods could be normalized to real field conditions. Therefore, field trials coupled with long-term monitoring are critical to further verify conditions under which stabilization is effective. Sustainability is also an important factor affecting the long-term stability of site remediation. It is hence important to consider these challenges to develop an optimized application of stabilization technology in soil remediation.

Study of Remediation of Soil Contamined with Heavy Metals by Coal Fly Ash

The labile fraction of heavy metals in soils is the most important for toxicity for plants. Thus it is crucial to reduce this fraction in contamined soils to decrease the negative effect of heavy metals. In an experiment, the effects of two additives on the labile fractions of Cu, Mn and Zn were investigated in a soil contamined during long-term application. The additive used was the coal fly ash. The treated soil was further enriched with heavy metals and allowed to age at room temperature for 30 days. After this period, they were extracted plant-available (EDTA;HNO3;CH3COOH) metal species. The addition of fly ash strongly reduced the plant-available of Mn for plants but to a lesser extent this applies to the plant-available of Cu and Zn for plants. By addition of 1% of fly ash as well as 2% of fly ash, the labile fraction of Cu, Mn and Zn were lowered by 6.3, 145.0 and 29.7 mg?kg-1, respectively. Moreover essential correlation between total Cu and Zn contents was stated in the soil with plant-available content of metals, with reference to both metals. Value of coefficients of correlation is attesting to it between the total and plant-available Cu and Zn contents which are respectively equal: R(Cu) = 0.845, R(Mn) = 0.864 and R(Zn) = 0.872 for p = 99.5%. The results suggested that leading into the soil of the additional amount of fly ash can be an effective way of chemical remediation with reference to soils contaminated by Cu or Mn or Zn. Because he causes immobilization of examined heavy metals in the soil and in the process in the arrangement a—soil is limiting the availability of these metals plant and more distant bonds of the food chain.

Contamination and Remediation of Heavy Metals in Soils near E-waste Recycling Area

In order to assess heavy metals pollution in agricultural soil after renovation in typical e-waste recycling areas, 212 soil samples were col- lected and the mass fractions of 7 kinds of heavy metals （Cd, Cr, Cu, Hg, Ni, Pb and Zn） were analyzed. The results indicated that heavy metals pollution in agricultural soil was commonly existed in the study areas, and the soil was slightly contaminated by Pb but was moderately or critically polluted by Cd and Cu. However, the carcinogenic risk and non-carcinogenic risk status by heavy metals pollution were beyond acceptable levels, and soil remediation was quite necessary. After some investigations of bioremediation, we found that saponin as washing agent could highly strenqthen the behavior of heavy metals desorption from soil ,which had a good prospect of engineering practice.

Research Progress on Remediation Technology Suitable for Farmland Soil Contaminated by Cd

Cd contamination range of farmland soil in China is wide,which has constituted a major threat for food safety and residents＇ health. Via multi-year development,there are more remediation methods suitable for soil contaminated by Cd among the world,but some methods are only suitable for the contaminated sites and indoor research,and can not be applied in large-range contaminated farmland. We analyze the source of Cd in farmland soil. By combining farmland＇s characteristics,three remediation techniques（ low-absorption crops plantation,soil solidification and phytoremediation） and their effects are analyzed,and the existing problems and research prospects of the above techniques are explored. The research could provide reference for restoring farmland soil contaminated by Cd in China,recovering its production function and enhancing food safety standards.

Boosting extraction of Pb in contaminated soil via interfacial solar evaporation of multifunctional sponge

Interfacial solar water evaporation is a reliable way to accelerate water evaporation and contaminant remediation.Embracing the recent advance in photothermal technology,a functional sponge was prepared by coating a sodium alginate(SA)impregnated sponge with a surface layer of reduced graphene oxide(rGO)to act as a photothermal conversion medium and then subsequently evaluated for its ability to enhance Pb extraction from contaminated soil driven by interfacial solar evaporation.The SA loaded sponge had a Pb adsorption capacity of 107.4 mg g^(-1).Coating the top surface of the SA sponge with rGO increased water evaporation performance to 1.81 kg m^(-2)h^(-1)in soil media under one sun illumination and with a wind velocity of 2 m s^(-1).Over 12 continuous days of indoor evaporation testing,the Pb extraction efficiency was increased by 22.0%under 1 sun illumination relative to that observed without illumination.Subsequently,Pb extraction was further improved by 48.9%under outdoor evaporation conditions compared to indoor conditions.Overall,this initial work shows the significant potential of interfacial solar evaporation technologies for Pb contaminated soil remediation,which should also be applicable to a variety of other environmental contaminants.

Remediation Effects of Different Concentration of Nano-Hydroxyapatite Level on Pb-Contaminated Soil

Phosphorus-containing amendments can reduce the mobility of Pb in soil. Hydroxyapatite (HAP) is one of the most commonly used phosphorus-containing amendments. With the development of nanotechnology, nano-hydroxyapatie (n-HAP) was gradually applied to remediate soil polluted by heavy metals. Considering the concentrations of HAP/n-HAP were not more than 5% in most studies, soil polluted by Pb was artificially prepared and three different concentrations of n-HAP: 5%, 7% and 10% by weight, were added into the Pb-polluted soil separately. The mixtures of soil and n-HAP were incubated for 180 d and sampled regularly. The bioaccessibility of Pb in soil was determined using simulated gastric juices of two in-vitro digestion tests: USPM (United States Pharmacopeia Methodology) and PBET (Physiologically-Based Extraction Test). The results showed that the immobilizing efficiency of 5% n-HAP to Pb in soil was the highest in PBET. The extractable Pb from soil by USPM was not affected by concentration of n-HAP. So, the least concentration of n-HAP, i.e. 5% n-HAP treatment, was the most cost-effective in USPM. Soil pH increased with concentration of n-HAP. However concentration of n-HAP had little effects on content of soil OM. According to regression analysis, more than 50% differences of the extractable Pb from soil by PBET can be explained by soil pH, while soil pH, organic matter content and incubation time together explained nearly 85% differences of extractable Pb from soil by USPM.

Field demonstration of reduction of lead availability in soil and cabbage (Brassica Chinensis L.) contaminated by mining tailings using phosphorus fertilizers

A field demonstration of reduction of lead availability in a soil and cabbage (Brassica Chinensis L.) contaminated by mining tailings, located in Shaoxing, China was carried out to evaluate the effects of applications of phosphorus fertilizers on Pb fractionation and Pb phytoavailability in the soil. It was found that the addition of all three P fertilizers including single super phosphate (SSP), phosphate rock (PR), and calcium magnesium phosphate (CMP) significantly decreased the percentage of water-soluble and exchangeable (WE) soil Pb and then reduced the uptake of Pb, Cd, and Zn by the cabbage compared to the control (CK). The results showed that the level of 300 g P/m2 soil was the most cost-effective application rate of P fertilizers for reducing Pb availability at the first stage of remediation, and that at this P level, the effect of WE fraction of Pb in the soil de- creased by three phosphorus fertilizers followed the order: CMP (79%)>SSP (41%)>PR (23%); Effectiveness on the reduction of Pb uptake by cabbage was in the order: CMP (53%)>SSP (41%)>PR (30%). Therefore our field trial demonstrated that it was effective and feasible to reduce Pb availability in soil and cabbage contaminated by mining tailings using P fertilizers in China and PR would be a most cost-effective amendment.

Removal of heavy metals from a contaminated soilusing tartaric acid

This study reports the feasibility of remediation of a heavy metal （HM） contaminated soil using tartaric acid, an environmentally-friendly extractant. Batch experiments were performed to test the factors influencing remediation of the HM contaminated soil. An empirical model was employed to describe the kinetics of riM dissolution/desorption and to predict equilibrium concentrations of HMs in soil leachate. The changes of HMs in different fractions before and after tartaric acid treatment were also investigated. Tartaric acid solution containing HMs was regenerated by chestnut shells. Results show that utilization of tartaric acid was effective for removal of riMs from the contaminated soil, attaining 50%-60% of Cd, 40%-50% of Pb, 40%-50% of Cu and 20%-30% of Zn in the pH range of 3.5-4.0 within 24 h. Mass transfer coefficients for cadmium （Cd） and lead （Pb） were much higher than those for copper （Cu） and zinc （Zn）. Sequential fractionations of treated and untreated soil samples showed that tartaric acid was effective in removing the exchangeable, carbonate fractions of Cd, Zn and Cu from the contaminated soil. The contents of Pb and Cu in Fe-Mn oxide fraciton were also significantly decreased by tartaric acid treatment. One hundred milliliters of tartaric acid solution containing HMs could be regenerated by 10 g chestnut shells in a batch reactor. Such a remediation procedure indicated that tartaric acid is a promising agent for remediation of HM contaminated soils. However, further research is needed before the method can be practically used for in situ remediation of contaminated sites.

Studies on Heavy Metal Pollution in Soil-Plant System:A Review

Heavy metal pollution in soil-plant system is of major environmental concern on a world scale and in China in particular with the rapid development of industry. The heavy metal pollution status in soil-plant system in China, the research progress on the bioavailability of heavy metals (affecting factors, extraction methods, free-ion activity model, adsorption model, multivariate regression model, Q-I relationship, and compound pollution), and soil remediation are reviewed in the paper. Future research and monitoring is also discussed.

Electrokinetic movement of multiple chlorobenzenes in contaminated soils in the presence of β-cyclodextrin

This study investigated the electrokinetic （EK） behavior of multiple chlorobenzenes, including 1,2,3,4-tetrachlorobenzene （TeCB）, 1,2,4,5-tetrachlorobenzene （i-TeCB）, and 1,2,3-trichlorobenzene （TCB） in contaminated clayed soils. The effect of β-cyclodextrin （β- CD） on the EK removal of the chlorobenzenes was studied. The largest removal was obtained when Na2CO3/NaHCO3 buffer was used as anodic purging solution without β-CD. The removal efficiencies were related to the aqueous solubilities of chlorobenzenes. With the same cumulative electroosmotic flow, greater solubility led to higher removal efficiency. The addition of β-CD inhibited the EK removal efficiency of all chlorobenzenes. The inhibition increased with the increase of β-CD concentration. With the same β-CD concentration, the inhibition increased with the rise of electric potential. It was found that the inclusion compounds between β-CD and chlorobenzenzes were less soluble than chlorobenzenes. The formation of the less soluble inclusion compounds reduced the aqueous solubility of chlorobenzenes and led to the partial immobilization of the chlorobenzenes that desorbed from soil. It was feasible to use the EK technology to remove chlorobenzenes in contaminated soils using water as the anodic flushing solution. The addition of β-CD was not recommended for the EK removal of chlorobenzenes.

Enhanced photodegradation of phenolic compounds by adding TiO_2 to soil in a rotary reactor

Photodegradation ofpentachlorophenol （PCP） and p-nitrophenol （PNP） in soil was carried out in a designed rotary reactor, which can provide the soil particles with continually uniform irradiation, and on a series of thin soil layers. TiO2, as a kind of environmental friendly photocatalyst, was introduced to the soil to enhance the processes. Compared with that on the soil layers, photodegradation of PCP at initial concentration of 60 mg/kg was improved dramatically in the rotary reactor no matter whether TiO2 was added, with an increase of 3.0 times in the apparent first-order rate constants. The addition of 1 wt% TiO2 furthered the improvement by 1.4 times. Without addition of TiO2, PNP （initial concentration of 60 mg/kg） photodegradation rate in the rotary reactor was similar to that on the soil layers. When 1 wt% additional TiO2 was added, PNP photodegradation was enhanced obviously, and the enhancement in the rotary reactor was 2 times of that on the soil layers, which may be attributed to the higher frequency of the contact between PNP on soil particles and the photocatalyst. The effect of soil pH and initial concentrations of the target compounds on the photodegradation in the rotary reactor was investigated. The order of the degradation rate at different soil pH was relative to the aggregation of soil particles during mixing in the rotary reactor. Photodegradation of PCP and PNP at different initial concentrations showed that addition of TiO2 to enhance the photodegradation was more suitable for contaminated soil with higher concentration of PCP, while was effective for contaminated soil at each PNP concentration tested in our study.

Research progress on the soil vapor extraction

Soil vapor extraction (SVE), the most common, efficient and economical means of remediation, is an in-situ remediation technique for removing volatile pollutants from unsaturated soil. The paper brie fly introduced the technological rationale and characteristics, summarized the theories and application research for SVE at home and abroad, and made the expectations and suggestions for the research on SVE. The international scholars have systematically researched the influence factors, remediation mechanism and numerical simulation of SVE. At present, SVE has been mostly integrated with other techniques to form enhanced SVE techniques, such as thermally enhanced SVE and AS-SVE (Air sparging- SVE), to be used for the field remediation widely. Compared with foreign countries, researches of Chinese scholars mainly focus on the laboratory research, especially on the influence factors, but rarely study the SVE model and the mass transfer mechanism of pollutant in SVE process. The SVE pilot studies are rare in China, and the field application has not been reported. In view of this situation, Chinese scholars in the future research can focus on the following aspects: (1) strengthening the research and systematized summary of SVE technical parameters and related knowledge;(2) strengthening the research on the mechanism and model of gas-phase mass transfer of pollutants in soil during SVE process;(3) strengthening the research on the enhanced SVE techniques and its application to actual site remediation.

Synergistic effects of phosphoric acid modified hydrochar and coal gangue-based zeolite on bioavailability and accumulation of cadmium and lead in contaminated soil

In this paper,a novel compound was developed by mixing H_(3)PO_(4)-modified cauliflower leaves hydrochar(CLH)and coal gangue-based Na-X zeolite(ZL).An alkaline soil contaminated with cadmium(Cd)and lead(Pb)was amended through the individual and synergistic application of CLH and ZL(1%CLH,2%CLH,1%ZL,2%ZL and 1%CLH+1%ZL),and Chinese cabbage was grown on it.Individual application of CLH was superior to ZL on decreasing the pH of alkaline soil and increasing soil available phosphorus(Olsen-P)and soil organic matter(SOM).In contrast,their combined application significantly improved the soil cation exchange capacity(CEC).Besides,the 1%CLH+1%ZL was the most efficient treatment in decreasing diethylenetriamine pentaacetate(DTPA)-extractable Cd/Pb and concentrations of these two metals in cabbage root and shoot.Their synergistic application could better increase Cd and Pb immobilization and cabbage yield than their alone application.Furthermore,the immobilization of Pb for all treatments was higher than that of Cd.The synergistic immobilization mechanism of CLH and ZL reflected that the CLH precipitated and complexed with these two metals,which may block the pores of hydrochar or wrap on the surface of hydrochar.So the continuous adsorption and complexation were prevented.Nevertheless,ZL could probably alleviate this obstacle.This finding provides helpful information about using CLH combined with ZL as a soil stabilizer to immobilize heavy metals in contaminated alkaline soil.

Remediation performance and mechanisms of Cu and Cd contaminated water and soil using Mn/Al-layered double oxide-loaded biochar

The combined pollution of heavy metals is ubiquitous worldwide.Mn/Al-layered double oxide-loaded crab shells biochar (LDO/BC) was prepared,so as to remediate the combined pollution of Cd and Cu in soil and water.The pristine and used LDO/BC were characterized and the results revealed that the layered double oxide was successfully loaded on crab shells biochar (BC) and metal element Ca in crab shells was beneficial to the formation of more regular layered and flake structure.The maximal adsorption capacity (Qm) of LDO/BC for aqueous Cu^(2+)and Cd^(2+)was 66.23 and 73.47 mg/g,respectively.LDO/BC and BC were used to remediate e-waste-contaminated soil for the first time and exhibited highly efficient performance.The extraction amount of Cu and Cd in the contaminated soil by diethylene triamine penta-acetic acid (DTPA) after treating with 5% LDO/BC was significantly reduced from 819.84 to 205.95 mg/kg (with passivation rate 74.8%) and 8.46 to 4.16 mg/kg(with passivation rate 50.8%),respectively,inferring that the bioavailability of heavy metals declined remarkably.The experimental result also suggested that after remediation by LDO/BC the exchangeable and weak acid soluble Cu and Cd in soil translated to reducible,residual and oxidizable fraction which are more stable state.Precipitation,complexation and ion exchange were proposed as the possible mechanisms for Cd and Cu removal.In general,these experiment results indicate that LDO/BC can be a potentially effective reagent for remediation of heavy metal contaminated water and soil.

Remediation of Cu and As contaminated water and soil utilizing biochar supported layered double hydroxide:Mechanisms and soil environment altering

Preparing materials for simultaneous remediation of anionic and cationic heavy metals contamination has always been the focus of research. Herein a biochar supported FeMnMg layered double hydroxide(LDH) composites(LB) for simultaneous remediation of copper and arsenic contamination in water and soil has been assembled by a facile co-precipitation approach. Both adsorption isotherm and kinetics studies of heavy metals removal by LB were applied to look into the adsorption performance of adsorbents in water. Moreover, the adsorption mechanisms of Cu and As by LB were investigated, showing that Cu in aqueous solution was removed by the isomorphic substitution, precipitation and electrostatic adsorption while As was removed by complexation. In addition, the availability of Cu and As in the soil incubation experiments was reduced by 35.54%–63.00% and 8.39%–29.04%, respectively by using LB. Meanwhile, the addition of LB increased the activities of urease and sucrase by 93.78%–374.35% and 84.35%–520.04%, respectively, of which 1% of the dosage was the best. A phenomenon was found that the richness and structure of microbial community became vigorous within 1% dosage of LB, which indirectly enhanced the passivation and stabilization of heavy metals. These results indicated that the soil environment was significantly improved by LB. This research demonstrates that LB would be an imaginably forceful material for the remediation of anionic and cationic heavy metals in contaminated water and soil.