Ajit K. Sarmah

Biochar application to soil: agronomic and environmental benefits and unintended consequences.

Abstract Biochar is increasingly being recognized by scientists and policy makers for its potential role in carbon sequestration, reducing greenhouse gas emissions, renewable energy, waste mitigation, and as a soil amendment. The published reviews on biochar application to soil have so far focused mainly on the agronomic benefits, and have paid little attention to the potential unintended effects. The purpose of this chapter is to provide a balanced perspective on the agronomic and environmental impacts of biochar amendment to soil. The chapter highlights the physical and chemical characteristics of biochar, which can impact on the sorption, hence efficacy and biodegradation, of pesticides. As a consequence, weed control in biochar-amended soils may prove more difficult as preemergent herbicides may be less effective. Since biochars are often prepared from a variety of feedstocks (including waste materials), the potential introduction of contaminants needs to be considered before land application. Metal contaminants, in particular, have been shown to impact on plant growth, and soil microbial and faunal communities. Biochar has also been shown to influence a range of soil chemical properties, and rapid changes to nutrient availability, pH, and electrical conductivity need to be carefully considered to avoid unintended consequences for productivity. This chapter highlights some key areas of research which need to be completed to ensure a safe and sustainable use of biochar. In particular, understanding characteristics of biochars to avoid ecotoxicological impacts, understanding the effects of biochar on nutrient and contaminant behavior and transport, the effects of aging and the influence of feedstock and pyrolysis conditions on key properties are some of the areas that require attention.

Using biochar for remediation of soils contaminated with heavy metals and organic pollutants

Soil contamination with heavy metals and organic pollutants has increasingly become a serious global environmental issue in recent years. Considerable efforts have been made to remediate contaminated soils. Biochar has a large surface area, and high capacity to adsorb heavy metals and organic pollutants. Biochar can potentially be used to reduce the bioavailability and leachability of heavy metals and organic pollutants in soils through adsorption and other physicochemical reactions. Biochar is typically an alkaline material which can increase soil pH and contribute to stabilization of heavy metals. Application of biochar for remediation of contaminated soils may provide a new solution to the soil pollution problem. This paper provides an overview on the impact of biochar on the environmental fate and mobility of heavy metals and organic pollutants in contaminated soils and its implication for remediation of contaminated soils. Further research directions are identified to ensure a safe and sustainable use of biochar as a soil amendment for remediation of contaminated soils.

A feasibility study of agricultural and sewage biomass as biochar, bioenergy and biocomposite feedstock: production, characterization and potential applications

In this study, we pyrolysed six waste derived biomass: pine sawdust (PSD), paunch grass (PG), broiler litter (BL), sewage sludge (SS), dewatered pond sludge (DWP), and dissolved air-floatation sludge (DAF) into biochar. Biochars were characterized using scanning electron microscopy, energy dispersive X-ray spectrometry, X-ray diffraction, Fourier transform infrared spectroscopy, inductively-coupled plasma mass spectrometry, (13)C-solid-state nuclear magnetic resonance spectroscopy, and X-ray photoelectron spectroscopy to evaluate their feasibility for potential agronomic and environmental applications. Syngas produced during the pyrolysis process was also analyzed to determine the energy values. Results show that PSD biochar has the utmost potential for carbon sequestration and contaminant remediation due to its high surface area, aromaticity and carbon content. Additionally given its low ash content, PSD biochar could also potentially be used as filler in wood plastic biocomposites. Low levels of heavy metals (Cr, Cu, Zn, As, Cd, Hg, and Pb) in all biochars suggest that biochars are also applicable for land application according to the United States Environmental Protection Agency regulation 40 CFR part 503. The composition of syngas evolved during the pyrolysis of feedstocks showed little difference in the calorific values, ranging from 12-16 MJ/dsm with PSD having the maximum calorific value of 16 MJ/dsm.

Fate and behaviour of triasulfuron, metsulfuron-methyl, and chlorsulfuron in the Australian soil environment: a review

The sulfonylurea herbicides comprise a group of compounds designed to control broad-leaved weeds and some grasses in a variety of crops. The herbicides have become popular because of their low application rates (10{40 g/ha), low mammalian toxicity, and unprecedented herbicidal activity. We present a review of the fate and behaviour of these herbicides in soils with particular reference to alkaline soils of Australia. The review shows that the low application rates of sulfonylurea herbicides continue to present an analytical challenge, although in recent years a number of new methods capable of detecting them at very low concentrations have been developed. A range of analytical methods is available, including high performance liquid chromatography, gas chromatography, immunoassay, and bioassay. However, analytical sensitivity required to detect trace levels of these herbicides continues to pose problems in routine detection of herbicide residues in soils. The review reveals that there are no reports of studies of the behaviour of sulfonylureas in soils with pH >8¢2. This is of particular signiflcance to Australian conditions because a number of Australian soils are even more alkaline, and the pH(water) in subsoils can be as high as 10¢2. Sorption of sulfonylureas is pH-dependent and has a strong negative correlation with pH. At pH >8¢0 sorption is very low. In acid soils, however, sorption of chlorsulfuron, metsulfuron-methyl, and triasulfuron is strongly in∞uenced by the soil temperature, clay content, and, particularly, organic matter content. The principal modes of degradation of the herbicides are acid hydrolysis and microbial degradation with the latter being the only major pathway in alkaline soils. Hydrolysis of the sulfonylureas is more rapid under acidic conditions (pH 4{7), and the data suggest that hydrolysis is likely to be very slow in alkaline soils. Data from other countries suggest that the half-life of chlorsulfuron increases exponentially with pH, and that it is also in∞uenced by variations in the temperature and water content of the soil. Being acidic in nature, the herbicide molecules become anionic at high pH and can move to a considerable depth in the soil proflle by leaching. Movement of the sulfonylureas in soil is largely in∞uenced by organic matter content and soil pH and the reviewed data show that sulfonylureas have substantial leaching potential in the sandy alkaline soils of Australia. This is likely to result in increased persistence in alkaline subsoils lacking in organic matter and biological activity. Computer models to predict the persistence and movement of the sulfonylureas are available; however, additional input parameters are required to predict accurately the behaviour of speciflc herbicides in alkaline soils under Australian conditions. Since new herbicides with chemistry similar to existing sulfonylureas are increasingly likely to be available for use, there is a need to develop comprehensive understanding of their fate, behaviour, and impact on Australian cropping and ecological systems.

Retention of estrogenic steroid hormones by selected New Zealand soils.

We performed batch sorption experiments for 17beta-estradiol (E2) and 17alpha-ethynylestradiol (EE2) on selected soils collected from dairy farming regions of New Zealand. Isotherms were constructed by measuring the liquid phase concentration and extracting the solid phase with dichloromethane, followed by an exchange step, and analysis by HPLC and UV detection. The corresponding metabolite estrone, (E1) formed during equilibration of E2 with soil was taken into account to estimate the total percentage recoveries for the compounds, which ranged from 47-105% (E2 and E1) and 83-102% (EE2). Measured isotherms were linear, although some deviation from linearity was observed in a few soils, which was attributed to the finer textured particles and/or the allophanic nature of the soils having high surface area. There was a marked difference in K(d)(eff) (effective distribution coefficient) values for E2 and EE2 among the soils, consistent with the soils organic carbon content and ranged from 14-170 L kg(-1) (E2), and 12-40 L kg(-1) (EE2) in the soils common for both compounds. The sorption affinity of hormones in the soils followed an order: EE2<E1<E2 in Manawatu and Horotiu soils, and, E1<EE2<E2 in Pukekohe soil with average log K(oc) of about 3 (+/-0.1-0.2 log units) which was consistent with earlier published values. Formation of the transformation product E1 appears to be concomitant with E2 sorption in all but one soil. Given that quite a large amount of E1 was generated during 72 h of contact time, and given E1 sorbed to solid phases greater than the liquid phase, dissolved organic carbon facilitated transport of these hormones needs to be considered when assessing the leaching risk for these compounds in the environment.

A novel approach in organic waste utilization through biochar addition in wood/polypropylene composites

In an attempt to concurrently address the issues related to landfill gas emission and utilization of organic wastes, a relatively novel idea is introduced to develop biocomposites where biochar made from pyrolysis of waste wood (Pinus radiata) is added with the same wood, plastic/polymer (polypropylene) and maleated anhydride polypropylene (MAPP). Experiments were conducted by manufacturing wood and polypropylene composites (WPCs) mixed with 6 wt%, 12 wt%, 18 wt%, 24 wt%, and 30 wt% biochar. Though 6 wt% addition had similar properties to that of the control (composite without biochar), increasing biochar content to 24 wt% improved the composites tensile/flexural strengths and moduli. The biochar, having high surface area due to fine particles and being highly carbonised, acted as reinforcing filler in the biocomposite. Composites having 12 wt% and 18 wt% of biochar were found to be the most ductile and thermally stable, respectively. This study demonstrates that, WPCs added with biochar has good potential to mitigate wastes while simultaneously producing biocomposites having properties that might be suited for various end applications.

Characterisation of agricultural waste-derived biochars and their sorption potential for sulfamethoxazole in pasture soil: a spectroscopic investigation.

We investigated the effects of feedstock type and pyrolysis temperatures on the sorptive potential of a model pastoral soil amended with biochars for sulfamethoxazole (SMO), using laboratory batch sorption studies. The results indicated that high temperature chars exhibited enhanced adsorptive potential, compared to low temperature chars. Pine sawdust (PSD) biochar produced at 700°C using the steam gasification process exhibited the highest sorptive capacity (2-fold greater than the control treatment) for SMO among the three biochars used. Soils amended with green waste (GW) biochars produced at three different pyrolysis temperatures showed a small increase in SMO sorption with the increases in temperature. The NMR spectra, the elemental molar ratios (H/C, O/C) and polarity index (O+N)/C of the biochars revealed that PSD biochar possessed the highest degree of aromatic condensation compared to CC and GW chars. These results correlated well with the sorption affinity of each biochar, with effective distribution coefficient (Kd(eff)) being highest for PSD and lowest for GW biochars. X-ray photoelectron spectroscopy results for the biochars showed a relatively large difference in oxygen containing surface functional groups amongst the GW biochars. However, they exhibited nearly identical sorption affinity to SMO, indicating negligible role of oxygen containing surface functional groups on SMO sorption. These observations provide important information on the use of biochars as engineered sorbents for environmental applications, such as reducing the bioavailability of antibiotics and/or predicting the fate of sulfonamides in biochar-amended soils.

Laboratory degradation studies of four endocrine disruptors in two environmental media

We investigated the degradation of 17beta-estradiol (E(2)), 17alpha-ethinylestradiol (EE(2)), bisphenol-A (BPA), and 4-n-nonylphenol (4-n-NP) in river water-sediment and groundwater-aquifer material under aerobic and anaerobic conditions. The results showed rapid degradation of all four compounds in both media with >90% of the four compounds degraded within the first 2 to 4 d under both conditions. However, degradation rates were extremely slow for the remaining period. Model derived 50% dissipation time (DT50) values in river water-sediment slurries ranged from 0.24 to 1.5 d (E(2)), 0.29 to 1.1 d (EE(2)), 1.2 to 1.4 d (BPA), and 0.42 d (4-n-NP), while the 90% dissipation time (DT90) values for the four endocrine-disrupting chemicals (EDCs) ranged from 0.9 to 2.8 d under both conditions. A minor difference was observed in DT50 and DT90 values for the four EDCs in groundwater- aquifer material under aerobic conditions as compared with river water-sediment. Under anaerobic conditions, DT90 values ranged from >1,000 d (EE(2)) to >300 d (BPA), in groundwater-aquifer material. Degradation of the four compounds under anaerobic conditions was attributed to the sulfate-, nitrate-, and iron-reducing conditions within the tested media; however, it was postulated that overall degradation of the compounds was also influenced by abiotic factors, accounting for nearly 6 to 40% (river water- sediment) and 0 to 18% (groundwater-aquifer material) under the two conditions tested.

Mechanism of waste biomass pyrolysis: Effect of physical and chemical pre-treatments

To impart usability in waste based biomass through thermo-chemical reactions, several physical and chemical pre-treatments were conducted to gain an insight on their mode of action, effect on the chemistry and the change in thermal degradation profiles. Two different waste biomasses (Douglas fir, a softwood and hybrid poplar, a hardwood) were subjected to four different pre-treatments, namely, hot water pre-treatment, torrefaction, acid (sulphuric acid) and salt (ammonium phosphate) doping. Post pre-treatments, the changes in the biomass structure, chemistry, and thermal makeup were studied through electron microscopy, atomic absorption/ultra violet spectroscopy, ion exchange chromatography, and thermogravimetry. The pre-treatments significantly reduced the amounts of inorganic ash, extractives, metals, and hemicellulose from both the biomass samples. Furthermore, hot water and torrefaction pre-treatment caused mechanical disruption in biomass fibres leading to smaller particle sizes. Torrefaction of Douglas fir wood yielded more solid product than hybrid poplar. Finally, the salt pre-treatment increased the activation energies of the biomass samples (especially Douglas fir) to a great extent. Thus, salt pre-treatment was found to bestow thermal stability in the biomass.

Repair of the structure of a compacted Vertisol via wet/dry cycles

Abstract The effect of wet/dry cycles on repairing a compacted Vertisol was studied. The change in soil structure was assessed by infiltration, clod bulk density, shear strength and image analysis of surface morphology. Wetting was done by flooding and by simulated rainfall. Drying was achieved by surface evaporation. Five flood-wet/dry cycles resulted in a two fold and one and a half fold increase in water infiltration rate for the wheel track and bed cores, respectively. This increase was associated with a marked decrease in surface shear strength of the cores after only one wet/dry cycle for both types of wetting. Quantification of the soil structure on the soil surface indicated that both % total crack and shrinkage block size decreased for wheel cores with the increasing number of wet/dry cycles. Cracks became narrower and size of shrinkage blocks smaller as the number of flood wet/dry cycles increased. Rain wetting produced bigger cracks and blocks but fewer in number compared with flood wetting. For flood-wet bed cores, higher values of clod specific volume after one flood-wet/dry cycle in the 0.05–0.2 m depth suggest that bulk density had decreased and porosity increased, relative to the original field condition.