Physico-chemical properties and microbial responses in biochar-amended soils: Mechanisms and future directions

Biochar is a carbon-rich solid material derived from the pyrolysis of agricultural and forest residual biomass. Previous studies have shown that biochar is suitable as an adsorbent for soil contaminants such as heavy metals and consequently re- duces their bioavailability. However, the long-term effect of dif- ferent biochars on metal extractability or soil health has not been assessed. Therefore, a 1-year incubation experiment was carried out to investigate the effect of biochar produced from bamboo and rice straw (at temperatures ≥500 °C) on the heavy metal (cadmium (Cd), copper (Cu), lead (Pb), and zinc (Zn)) extract- ability and enzyme activity (urease, catalase, and acid phospha- tase) in a contaminated sandy loam paddy soil. Three rates (0, 1, and 5 %) and two mesh sizes (<0.25 and <1 mm) of biochar applications were investigated. After incubation, the physico- chemical properties, extractable heavy metals, available phos- phorus, and enzyme activity of soil samples were analyzed. The results demonstrated that rice straw biochar significantly (P<0.05) increased the pH, electrical conductivity, and cation exchange capacity of the soil, especially at the 5 % application rate. Both bamboo and rice straw biochar significantly (P<0.05) decreased the concentration of CaCl2-extractable heavy metals as biochar application rate increased. The heavy metal extractability was significantly (P<0.01) correlated with pH, water-soluble organic carbon, and available phosphorus in soil. The 5 % appli- cation rate of fine rice straw bioc har resulted in the greatest re- ductions of extractable Cu and Zn, 97.3 and 62.2 %, respectively. Both bamboo and rice straw biochar were more effective at de- creasingextractableCu andPb thanremoving extractable Cdand Zn from the soil. Urease activity increased by 143 and 107 % after the addition of 5 % coarse and fine rice straw biochars, respectively. Both bamboo and rice straw biochars significantly (P<0.05) increased catalase activity but had no significant im- pact on acid phosphatase activity. In conclusion, the rice straw biochar had greater potential as an amendment for reducing the bioavailability of heavy metals in soil than that of the bamboo biochar. The impact of biochar treatment on heavy metal extract- ability and enzyme activity varied with the biochar type, appli- cation rate, and particle size.

Effect of biochar on the extractability of heavy metals (Cd, Cu, Pb, and Zn) and enzyme activity in soil.

Biochar produced from oak sawdust by Lanthanum (La)-involved pyrolysis for adsorption of ammonium (NH4+), nitrate (NO3−), and phosphate (PO43−)

Biomass is a promising renewable energy resource despite its low energy density, high moisture content and complex ash components The use of biomass in energy production is considered to be approximately carbon neutral, and if it is combined with carbon capture technology, the overall energy conversion may even be negative in terms of net CO2 emission, which is known as BECCS (bioenergy with carbon capture and storage) The initial development of BECCS technologies often proposes the installation of a CO2 capture unit downstream of the conventional thermochemical conversion processes, which comprise combustion, pyrolysis or gasification Although these approaches would benefit from the adaptation of already well developed energy conversion processes and CO2 capture technologies, they are limited in terms of materials and energy integration as well as systems engineering, which could lead to truly disruptive technologies for BECCS Recently, a new generation of transformative energy conversion technologies including chemical looping have been developed In particular, chemical looping employs solid looping materials and it uniquely allows inherent capture of CO2 during the conversion of fuels In this review, the benefits, challenges, and prospects of biomass-based chemical looping technologies in various configurations have been discussed in-depth to provide important insight into the development of innovative BECCS technologies based on chemical looping

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Biomass-based chemical looping technologies: the good, the bad and the future

Application of biochar to soils changes soil physicochemical properties and stimulates the activities of soil microorganisms that influence soil quality and plant performance. Studying the response of soil microbial communities to biochar amendments is important for better understanding interactions of biochar with soil, as well as plants. However, the effect of biochar on soil microorganisms has received less attention than its influences on soil physicochemical properties. In this review, the following key questions are discussed: (i) how does biochar affect soil microbial activities, in particular soil carbon (C) mineralization, nutrient cycling, and enzyme activities? (ii) how do microorganisms respond to biochar amendment in contaminated soils? and (iii) what is the role of biochar as a growth promoter for soil microorganisms? Many studies have demonstrated that biochar-soil application enhances the soil microbial biomass with substantial changes in microbial community composition. Biochar amendment changes microbial habitats, directly or indirectly affects microbial metabolic activities, and modifies the soil microbial community in terms of their diversity and abundance. However, chemical properties of biochar, (especially pH and nutrient content), and physical properties such as pore size, pore volume, and specific surface area play significant roles in determining the efficacy of biochar on microbial performance as biochar provides suitable habitats for microorganisms. The mode of action of biochar leading to stimulation of microbial activities is complex and is influenced by the nature of biochar as well as soil conditions.

Response of microbial communities to biochar-amended soils: a critical review

Biochar is a useful material for carbon storage in soils. In this report, we explored conversion of water hyacinth (Eichornia crassipes) to biochar as a sustainable weed management strategy, as it also has potential for improving soil quality. Eichornia biomass samples were carbonised with limited supply of air in a muffle furnace at varied temperature (200 to 500 °C) and residence time (30 to 120 min). The biochar yield decreased with temperature and time, but biochar carbon stability increased with temperature. The optimum condition for obtaining maximum stable carbon in Eichornia biochar (EBC) is 300–350 °C temperature with 30–40 min residence time. TGA and FTIR studies showed that EBC has increased aromaticity and carbon stability compared to the starting biomass. Impact of the EBC on soil quality was studied using a red soil, from Dhanbad, India. Soil biochemical properties (dehydrogenase, fluorescein hydrolases, catalase, respiration, active microbial biomass) and maize seedling growth were used to investigate the effects of biochar addition to the soil. Maize seedling vigour index increased from 1.0 at control to 1.61 in 20 g/kg EBC treatment. The maximum increase in soil enzymes like acid phosphatase activity (+ 32%), alkaline phosphatase activity (+ 22.8%), and fluorescein hydrolases activity (50%) occurred at the EBC dose of 20 g/kg. EBC significantly enhanced the soil biological activity particularly the active microbial biomass which has increased by 3 times and soil respiration by 1.9 times. The study shows that the waste Eichornia weed could be gainfully utilised as a soil quality amendment material by converting it to EBC.

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Biochar from water hyacinth (Eichornia crassipes) and its impact on soil biological activity

World climate change occurring mainly due to human activities has led to an environmental concern all over the planet. Global CO2 emission has reached an alarming level which is regarded as the most lethal anthropogenic greenhouse gas emissions. To have a check on the carbon emissions, many clean coal technologies were proposed out of which Chemical Looping Combustion (CLC) technology came out as the most promising technology of all. The process of CLC avoids direct contact between the fuel and the air. It is based on the transfer of oxygen from air to fuel by means of a metal based oxygen carrier and this process is blessed with inherent sequestration of CO2. This paper presents a review of the CLC technology and it׳s all round advancement during last 10-15 years. The all round development of the process include progress in terms of the use of gaseous, solid as well as liquid fuels, the evolution in the oxygen carriers and the reactor systems being used in the process. The development in the oxygen carriers has gained maturity, the use of solid fuels is gaining momentum, and the liquid fuels need further attention for its development. Recently, a fair number of hours of continuous operation in pilot plants have instilled the confidence required in further development of this process towards commercialization. The big stride that the CLC technology has taken in such a small duration of time, there leaves no doubt that this technology has the potential to grow manifolds with further research.

Present status and overview of Chemical Looping Combustion technology

Biochar preparation from Parthenium hysterophorus and its potential use in soil application

Predictive equations for CO2 emission factors for coal combustion, their applicability in a thermal power plant and subsequent assessment of uncertainty in CO2 estimation

Pinaki Sarkar

Papers

Biochar from water hyacinth (Eichornia crassipes) and its impact on soil biological activity

Present status and overview of Chemical Looping Combustion technology

Biochar preparation from Parthenium hysterophorus and its potential use in soil application

Predictive equations for CO2 emission factors for coal combustion, their applicability in a thermal power plant and subsequent assessment of uncertainty in CO2 estimation

Evaluation of combustion behaviour of coal blends for use in pulverized coal injection (PCI)