New insights into microwave pyrolysis of biomass: preparation of carbon-based products from pecan nutshells and their application in wastewater treatment

Microwave pyrolysis of pecan nutshell (Carya illinoinensis) biomass was used to produce carbon-based solid products with potential application in contaminated water treatment. A range of analytical techniques were applied to characterize the intermediate products of microwave pyrolysis in order to monitor the physio-chemical effects of the interacting energy on the biomass. The performance of the carbon-based products was tested through evaluation of lead ion removal capacity from solution. Further analyses demonstrated that ion-exchange by calcium ions on the material surface was the main mechanism involved in lead removal. Calcium compound development was directly correlated to the interaction of the electromagnetic waves with the biomass. Through monitoring the physio-chemical effects of biomass-microwave interactions during microwave pyrolysis, we have shown for the first time that the intermediate products differ from those of conventional pyrolysis. We hypothesise that selective heating leads to the (hemi)cellulosic and lignin degradation processes occurring simultaneously, whereas they are largely sequential in conventional pyrolysis. This work provides optimization parameters essential for the large scale design of microwave processes for this application as well as an understanding of how the operating parameters impact on functionality of the resulting carbon-based materials

Risk assessment of nitrate transport through subsurface layers and groundwater using experimental and modeling approach

Landfills are one of the main point sources of groundwater pollution. This research mainly aims to assess the risk of nitrate (NO-3) transport from the unlined landfill to subsurface layers and groundwater using experimental results and the SESOIL model. Samples from 12 groundwater wells downstream of the landfill were collected and analyzed in 2008, 21 years after the landfill construction. The average NO-3 concentration in the wells was 54 mg/L, slightly higher than the World Health Organization (NO-350 mg/L) standards. SESOIL model was used to predict the NO-3 concentration at the bottom of the unsaturated zone. Results indicated that the current mean NO-3 concentration at the bottom of the unsaturated zone is 75 mg/L. the model predicted that the level of NO3 will increased up to 325 mg/L within 30 years. Accordingly, the NO-3 concentration in groundwater wells near the landfill area is expected to gradually increase with time. Although the current risk associated with the NO-3 level might not be harm to adults, however, it might pose severe risks to both adults and infants in the near future due to NO-3 leaching. Urgent mitigation measures such as final cell cover (cap), lining system and vertical expansion should be considered at the landfill to protect the public health in the area. © 2017, © 2017 Informa UK Limited, trading as Taylor & Francis Group

Simultaneous multifunctional sorption of PFOS and Cr(VI) on activated carbon prepared by one-step microwave activation

Multifunctional sorbents, activated carbons (AC), were prepared by one-step microwave activation utilizing peanut shells and sunflower seed husks. The influence of the original particle size of raw materials on the yield and specific surface area of AC was studied, which reached 33.5 % and 1133.27 m(2)/g, respectively. The repetitive and competitive uptakes of perfluorooctane sulfonate (PFOS) and chromium were applied to investigate the sorption properties of AC. The sorption mechanisms were demonstrated using sulfur Kedge X-ray absorption near edge structure analysis (XANES). In the repetitive experiment, AC made from peanut shells (AC(P05)) still retained 70 % removal efficiency of PFOS after the fourth sorption because sorbed PFOS might form a new organic phase that supplied effective sites for the hydrophobic partition of PFOS. However, the removal efficiency of Cr(VI) decreased dramatically from 60 to 11 % after the fourth uptake because electrostatic attraction was its only removal pathway. In the binary solutes system, AC(P05) possessed perfect sorption performance for both PFOS and Cr(VI), which were 885 and 192 mg/g, respectively. In the multivariate solutes system, the XANES spectra indicated that the thiol functional group existed in the resulting AC and a metal chelate was formed between thiol and Zn2+/Cu2+. Hence, the presence of Zn2+/Cu2+ further promoted the removal of PFOS and Cr(VI) through the electrostatic attraction between the anions and positive metal chelate