The effects of biochar or activated carbon amendments on the fate of volatile petroleum hydrocarbons in an aerobic sandy soil

PhD ThesisThe impact of biochar or activated carbon (AC) amendments on the biodegradation of a mixture of 12 volatile petroleum hydrocarbons ( VP Hs) in an aerobic sandy soil was investigated in batch microcosms and column experiments. The impacts of biochar amendments on nutrient availability and biogenic gases activity were also studied by batch microcosms. The maximum nutrient amount adsorbed by biochar (9 max) was very high. Therefore, biochar amendments decreased the readily available nitrogen with increasing biochar application rate and contact period. Biogenic gas activities in biochar amended soils had varied responses because these activities were dependent on soil properties. The effects of sorbent amendment significantly depended on the compound chemical structure and type of sorbent material. In the batch microcosms, the AC and biochar amendments resulted in a large increase in the K values. The biodegradation of the water-dissolved OC fraction of most compounds was as fast or faster in the soil amended with activated carbon compared to the soil with or without biochar, but the strong sorption capacity of activated carbon, in particular, greatly reduced water-dissolved concentrations. The nutrient amendments accelerated the biodegradation of VPHs in the batch microcosms and nutrient availability was the main factor controlling the biodegradation rates of total petroleum hydrocarbons in sandy soil; whereas sorption was a secondary factor influencing the biodegradation of total petroleum hydrocarbons in biochar and activated carbon amended sandy soil. The biodegrada tion in sorbent amended columns was difficult to predict. The sorbent amendments decreased the availability of both VP Hs and nutrients. Therefore, the biodegradation rate was reduced. However, the petroleum hydrocarbon vapour migration and volatilization was also reduced, which increased the residence time of contaminants in the sorbent amended column. This means there was more time available to degrade the pollutants before they emanated from soil, and therefore the sorbent amendments may result in a greater amount of biodegradation, if considered over a certain distance and over a long time period. It is concluded that b iochar and activated carbon amendments are potentially a sustainable remediation strategy for dealing with volatile petroleum hydrocarbons pollution. These sorbents are able to reduce the risk of VPHs to biota and the also surrounding environments without using large scale, energy intensive and treatment processes

Predicting the effects of biochar on volatile petroleum hydrocarbon biodegradation and emanation from soil: a bacterial community finger-print analysis inferred modelling approach

We investigated the response of the dominant bacterial taxa in gravelly sand to the addition of biochar and/or mixtures of volatile petroleum hydrocarbons (VPHs) using denaturing gradient gel electrophoresis (DGGE) and sequencing of cut bands. Biochar addition alone had only weak effects on the soil bacterial community composition in batch study samples, while VPH addition had strong effects. Indirect effects of biochar on soil bacterial communities were apparent in column study samples, where biochar-enhanced sorption affected VPH spreading. Following VPH addition, cell abundance increased by no more than a factor of 2 and several Pseudomonas spp. became dominant in soil with and without biochar. We present a VPH fate model that considers soil bacterial biomass dynamics and a nutrient limited soil biomass carrying capacity. The model simulates an apparent lag phase before the onset of a brief period of intensive VPH biodegradation and biomass growth, which is followed by substantially slower VPH biodegradation, when nitrogen needs to be recycled between decaying and newly formed biomass. If biomass growth is limited by a factor other than the organic pollutant bioavailability, biochar amendment may enhance VPH attenuation in between a VPH source below ground and the atmosphere by reducing the risk of overloading the soil's biodegradation capacity

Application of a full-scale wood gasification biochar as a soil improver to reduce organic pollutant leaching risks

BACKGROUND: The application of biochar to sandy loam soil to reduce leaching of three representative pollutants (a persistent hydrocarbon (phenanthrene; logKOW 4.46), a herbicide (isoproturon; logKOW 2.50), and an antibiotic (sulfamethazine; logKOW 0.28)) were investigated. The wood-derived biochar evaluated in our laboratory study was the solid co-product of a full-scale gasifier feeding a combined heat and power plant. The research aimed to demonstrate multiple environmental benefits with the innovative use of this biochar as a soil improver. RESULTS: Batch sorption experiments indicated 5% biochar added to soil enhanced the partitioning coefficient (Kd) by factors of 2 for phenanthrene and 20 for both sulfamethazine and isoproturon. Column leaching experiments indicated a reduced porewater flow rate, up to 80% slower in the column amended with 5% biochar, and reduced pollutant leaching risks. Numerical models interlinked batch and column study observations. CONCLUSION: (i) Biochar enhanced sorption for the hydrophobic pollutant phenanthrene, and also the less hydrophobic pollutants sulfamethazine and isoproturon; (ii) reduced porewater flow rates following biochar amendment gave rise to greater opportunity for pollutant-solid interaction; (iii) mixing with soil resulted in biochar fouling affecting pollutant partition, and (iv) irreversible retention of pollutants by the soil was an important mechanism affecting pollutant transport

Effect of Activated Carbon Amendment on Bacterial Community Structure and Functions in a PAH Impacted Urban Soil

ABSTRACT: We collected urban soil samples impacted by polycyclic aromatic hydrocarbons (PAHs) from a sorbent-based remediation field trial to address concerns about unwanted side-effects of 2 % powdered (PAC) or granular (GAC) activated carbon amendment on soil microbiology and pollutant biodegradation. After three years, total microbial cell counts and respiration rates were highest in the GAC amended soil. The predominant bacterial community structure derived from denaturing gradient gel electrophoresis (DGGE) shifted more strongly with time than in response to AC amendment. DGGE band sequencing revealed the presence of taxa with closest affiliations either to known PAH degraders, e.g. Rhodococcus jostii RHA-1, or taxa known to harbor PAH degraders, e.g. Rhodococcus erythropolis, in all soils. Quantification by real-time polymerase chain reaction yielded similar dioxygenases gene copy numbers in unamended, PAC-, or GACamended soil. PAH availability assessments in batch tests showed th

Effect of biochar on the fate of volatile petroleum hydrocarbons in an aerobic sandy soil

Biochar addition to soil is currently being investigated as a novel technology to remediate polluted sites. A critical consideration is the impact of biochar on the intrinsic microbial pollutant degradation, in particular at sites polluted with a mixture of readily biodegradable and more persistent organic pollutants. We therefore studied the impact of biochar (2% on dry weight basis) on the fate of volatile petroleum hydrocarbons in an aerobic sandy soil with batch and column studies. The soil-water partitioning coefficient. K(d), was enhanced in the biochar-amended soil up to a factor 36, and petroleum hydrocarbon vapor migration was retarded accordingly. Despite increased sorption, in particular of monoaromatic hydrocarbons, the overall microbial respiration was comparable in the biochar-amended and unamended soil. This was due to more rapid biodegradation of linear, cyclic and branched alkanes in the biochar amended soil. We concluded that the total petroleum hydrocarbon degradation rate was controlled by a factor other than substrate availability and the reduced availability of monoaromatic hydrocarbons in the biochar amended soil led to greater biodegradation of the other petroleum compounds