Biochar, like most other adsorbents, is a carbonaceous material, which is formed from the combustion of plant materials, in low-zero oxygen conditions and results in a material, which has the capacity to sorb chemicals onto its surfaces. Currently, research is being carried out to investigate the relevance of biochar in improving the soil ecosystem, digestate quality and most recently the anaerobic digestion process. Anaerobic digestion (AD) of organic substrates provides both a sustainable source of energy and a digestate with the potential to enhance plant growth and soil health. In order to ensure that these benefits are realised, the anaerobic digestion system must be optimized for process stability and high nutrient retention capacity in the digestate produced. Substrate-induced inhibition is a major issue, which can disrupt the stable functioning of the AD system reducing microbial breakdown of the organic waste and formation of methane, which in turn reduces energy output. Likewise, the spreading of digestate on land can often result in nutrient loss, surface runoff and leaching. This review will examine substrate inhibition and their impact on anaerobic digestion, nutrient leaching and their environmental implications, the properties and functionality of biochar material in counteracting these challenges.

Isoprene basal emission (the emission of isoprene from leaves exposed to a light intensity of 1000 m m m m mol m ----2 s ----1 and maintained at a temperature of 30 ∞ ∞ ∞ ∞ C) was measured in Phragmites australis plants growing under elevated CO 2 in the Bossoleto CO 2 spring at Rapolano Terme, Italy, and under ambient CO 2 at a nearby control site. Gas exchange and biochemical measurements were concurrently taken. Isoprene emission was lower in the plants growing at elevated CO 2 than in those growing at ambient CO 2 . Isoprene emission and isoprene synthase activity (IsoS) were very low in plants growing at the bottom of the spring under very rich CO 2 and increased at increasing distance from the spring (and decreasing CO 2 concentration). Distance from the spring did not significantly affect photosynthesis making it therefore unlikely that there is carbon limitation to isoprene formation. The isoprene emission rate was very quickly reduced after rapid switches from elevated to ambient CO 2 in the gas-exchange cuvette, whereas it increased when switching from ambient to elevated CO 2 . The rapidity of the response may be consistent with post-translational modifications of enzymes in the biosynthetic pathway of isoprene formation. Reduction of IsoS activity is interpreted as a long-term response. Basal emission of isoprene was not constant over the day but showed a diurnal course opposite to photosynthesis, with a peak during the hottest hours of the day, independent of stomatal conductance and probably dependent on external air temperature or temporary reduction of CO 2 concentration. The present experiments show that basal emission rate of isoprene is likely to be reduced under future elevated CO 2 levels and allow improvement in the modelling of future isoprene emission rates.

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The short-term fate of polychlorinated biphenyl (PCB) and organochlorine (OC) pesticides in the surface snowpack was investigated by taking consecutive air and snow samples over a 12 day period at Tromsø in the Norwegian Arctic. A wide range in PCB and OC pesticide concentrations was observed in snow and was attributed to the systematic decrease in concentrations that occurred over the study period. For example, sigmaPCB concentrations ranged from 2500 to 300 pg L(-1) (meltwater) with a rapid decrease observed during the first 96 h. Rates of decline (ks) conformed to first-order kinetics, with similar rates observed for all compounds measured in this study (k5 = 0.01 +/- 0.001 h(-1)). Because the particle bound fraction accounted for <10% of the individual PCB and OC burden in the snow, then the fraction lost may be accounted for by desorption, following notable increases in snow density (and presumably, decreases in snow surface area). The fraction of chemical present in the fresh snow (phis) was found to be exponentially related to changes in snow density (deltarho). Relatively small increases in p following snowfall result in a large loss of sorbed chemical, presumably due to decreases in snow surface area. Later sampling of the same snow layer, but buried under fresh snowfall, revealed a notable increase in both PCB and OC concentrations. This would indicate a possible downward migration of these chemicals from the fresh snow into deeper snow layers, suggesting that re-emission of desorbed chemical from the interstitial pore spaces to the overlying atmosphere may be complicated by this process.