Zhengang Liu

Removal of lead from water using biochars prepared from hydrothermal liquefaction of biomass

Hydrothermal conversion of biomass into biofuel could produce a special type of biochar as byproduct. This biochar is quite different from biochar derived from high temperature pyrolysis. In the present study, two biochars, prepared from hydrothermal liquefaction of pinewood (P300) and rice husk (R300), were characterized and investigated for lead removal from aqueous solution. The results indicated that the biochars contained a large amount of oxygen-containing groups on the surface, which were quite effective for lead removal with capacities of 4.25 and 2.40 mg/g for P300 and R300, respectively. The adsorption equilibrium was achieved around 5h. Higher temperature favored the removal capacity implying that the adsorption was an endothermic process. The adsorption data at optimum solution pH 5 could be well described by Langmuir model and the adsorption process was well fitted by pseudo-second-order model. Moreover, it was found that the adsorption was mainly controlled by film diffusion. Thermodynamics analysis suggested that lead adsorption onto the biochars was physical endothermic process.

Thermogravimetric investigation of hydrochar-lignite co-combustion

Co-combustion of hydrochar with lignite was investigated by means of thermogravimetric analysis. Hydrochars were produced from coconut fibers and eucalyptus leaves under hydrothermal conditions at 250°C. The hydrochar was added in varying amounts to lignite for combustion. The results indicated that hydrothermal treatment decreased the volatile matter content and increased the fixed carbon content of the biomaterials. The elevated energy density and decreased ash content of the hydrochar improved its combustion behavior when co-fired with lignite for energy production. The hydrochars derived from coconut fiber and eucalyptus leaves had similar chemical compositions and showed similar influences on lignite combustion. Hydrochar addition increased the burnout and shortened the combustion range of the hydrochar-lignite blends. High combustion efficiency was observed due to the synergistic interactions between hydrochar and lignite during the co-combustion process. A kinetic study showed that the combustion process of hydrochar-lignite blends followed first-order reaction rates.

Nano-zerovalent iron contained porous carbons developed from waste biomass for the adsorption and dechlorination of PCBs.

The low-cost composite, nano-zerovalent iron (NZVI) contained in porous carbon (PC), was prepared using pinewood sawdust and ferric chloride as starting materials. The key point of this strategy was that the production of PC and the formation of NZVI were accomplished simultaneously through a simple process. The composite PC/NZVI was characterized by XRD, BET and the adsorption and simultaneous dechlorination of PCBs were efficiently demonstrated. The results showed the pinewood sawdust was activated by ferric chloride and the surface area and the pore volume of obtained composite were 423 m(2)/g and 0.23 cm(3)/g, respectively. The produced NZVI, around 27 nm in diameter, catalyzed the formation of substantial mesopores in the composite. PC/NZVI exhibited an efficient dechlorination of PCBs at room temperature, and the dechlorinated-products could be completely adsorbed onto the composite. Accordingly, it is believed that PC/NZVI developed in the present study is practically applicable for PCBs-contaminated water purification.

Typical pollutants in bottom ashes from a typical medical waste incinerator

Abstract Incineration of medical waste (MW) is an important alternative way for disposal of this type of hazardous waste, especially in China because of the outbreak of severe acute respiratory syndromes (SARs) in 2003. Thus, far, fly ash has received much attention but less attention has been paid to bottom ash. In this study, bottom ash samples were collected from a typical MW incinerator, and typical pollutants including heavy metals and polycyclic aromatic hydrocarbons (PAHs) in the ash were examined. X-ray fluorescence spectroscopy results indicated that CaO, SiO2 and Al2O3 were the main components of the bottom ash. Inductively coupled plasma-optical emission spectroscopy showed that the ash contained large amounts of heavy metals, including Zn, Ti, Ba, Cu, Pb, Mn, Cr, Ni and Sn. Most of the heavy metals (e.g., Ba, Cr, Ni, and Sn) presented in the residual fraction; whereas Mn, Pb and Zn presented in Fe–Mn oxides fraction, and Cu in organic-matter fraction. Toxicity characteristic leaching procedure tests indicated that the leached amounts of heavy metals were well below the limits. The sum of 16 US EPA priority PAHs (ΣPAHs) varied from 10.30 to 38.14mgkg−1, and the total amounts of carcinogenic PAHs ranged between 4.09 and 16.95mgkg−1, exceeding the limits regulated by several countries. This research provides basic information for the evaluation of the environmental risk of MW incinerator bottom ash.

Co-liquefaction of microalgae and lignocellulosic biomass in subcritical water

This study investigated co-liquefaction of microalgae (Chlorella pyrenoidosa, CP) and lignocellulosic biomass (Rice husk, RH) in subcritical water for bio-oil production. The effects of liquefaction temperature (200-350°C), residence time (10-90min), solid concentration (10-30wt.%) and mass ratio of CP/RH on product distribution were investigated. The results showed that the highest yield of bio-crude oils at the combination of 50% CP with 50% RH was obtained at 300°C temperature, 60min residence time and 20wt.% solid concentration. The oil yields increased gradually with the increased mass ratio of CP/RH. The major compounds identified in bio-crude oils from hydrothermal liquefaction (HTL) of RH were cyclic oxygenates (20.62%), followed by esters, ketones and alcohols (17.19%). As for CP, the main components were straight & branched amides (28.38%). A synergistic interaction was observed between CP and RH during co-liquefaction, resulting in decreased acidity and nitrogen content of bio-crude oils.

Combustion behavior and kinetics of low-lipid microalgae via thermogravimetric analysis

Thermogravimetric analysis and differential thermal analysis were employed to investigate combustion characteristics of two low-lipid microalgae, Chlorella pyrenoidosa (CP) and Spirulina platensis (SP) and iso-conversional Starink approach was used to calculate the kinetic parameters in the present study. The results showed that three stages of mass loss, including dehydration, devolatilization and char oxidation, were observed during combustion of both of two low-lipid microalgae. The whole weight loss of combustion of two microalgae was both shifted to higher temperature zones with increased heating rates from 10 to 40 K/min. In the 0.1-0.9 conversion range, the apparent activation energy of CP increased first from 51.96 to 79.53 kJ/mol, then decreased to 55.59 kJ/mol. Finally, it slightly increased to 67.27 kJ/mol. In the case of SP, the apparent activation energy gradually increased from 68.51 to 91.06 kJ/mol.

A comparison of thermal behaviors of raw biomass, pyrolytic biochar and their blends with lignite

In this study, thermal characteristics of raw biomass, corresponding pyrolytic biochars and their blends with lignite were investigated. The results showed that pyrolytic biochars had better fuel qualities than their parent biomass. In comparison to raw biomass, the combustion of the biochars shifted towards higher temperature and occurred at continuous temperature zones. The biochar addition in lignite increased the reactivities of the blends. Obvious interactions were observed between biomass/biochar and lignite and resulted in increased total burnout, shortened combustion time and increased maximum weight loss rate, indicating increased combustion efficiencies than that of lignite combustion alone. Regarding ash-related problems, the tendency to form slagging and fouling increased, when pyrolytic biochars were co-combusted with coal. This present study demonstrated that the pyrolytic biochars were more suitable than raw biomass to be co-combusted with lignite for energy generation in existing coal-fired power plants.

Enzyme-assisted hydrothermal treatment of food waste for co-production of hydrochar and bio-oil.

Food waste was subjected to enzymatic hydrolysis prior to hydrothermal treatment to produce hydrochars and bio-oil. Pre-treatment of food waste with an enzyme ratio of 1:2:1 (carbohydrase:protease:lipase) proved to be effective in converting food waste to the two products with improved yields. The carbon contents and calorific values ranged from 43.7% to 65.4% and 17.4 to 26.9 MJ/kg for the hydrochars obtained with the enzyme-assisted pre-treatment, respectively while they varied from 38.2% to 53.5% and 15.0 to 21.7 MJ/kg, respectively for the hydrochars obtained with no pre-treatment. Moreover, the formation of carbonaceous microspheres with low concentrations of inorganic elements and diverse surface functional groups was observed in the case of enzyme-assisted food waste hydrochars. The enzymatic pre-treatment also facilitated the formation of the bio-oil with a narrow distribution of organic compounds and with the highest yield obtained at 350 °C.

Emission, distribution and toxicity of polycyclic aromatic hydrocarbons (PAHs) during municipal solid waste (MSW) and coal co-combustion.

Emission and distribution characteristics of polycyclic aromatic hydrocarbons (PAHs) were investigated during municipal solid waste (MSW) and coal combustion alone and MSW/coal blend (MSW weight fraction of 25%) co-combustion within a temperature range of 500°C-900°C. The results showed that for all combustion experiments, flue gas occupied the highest proportion of total PAHs and fly ash contained more high-ring PAHs. Moreover, the 3- and 4-ring PAHs accounted for the majority of total PAHs and Ant or Phe had the highest concentrations. Compared to coal, MSW combustion generated high levels of total PAHs with the range of 111.28μg/g-10,047.22μg/g and had high toxicity equivalent value (TEQ). MSW/coal co-combustion generated the smallest amounts of total PAHs and had the lowest TEQ than MSW and coal combustion alone. Significant synergistic interactions occurred between MSW and coal during co-combustion and the interactions suppressed the formation of PAHs, especially hazardous high-ring PAHs and decreased the TEQ. The present study indicated that the reduction of the yield and toxicity of PAHs can be achieved by co-combustion of MSW and coal.

Effect of H2O2 concentrations on copper removal using the modified hydrothermal biochar.

This study investigated effect of H2O2 concentrations on copper removal using H2O2 modified hydrothermal carbonization Cymbopogon schoenanthus L. Spreng (HLG). Sorption behaviors of Cu (II) on the modified HLG by 20% H2O2 (mHLG2) could be the most desirable. Based on Langmuir isotherm, the maximum amount of Cu (II) uptake was in the sequence of mHLG2 (53.8mgg(-1))>mHLG1 (44.2mgg(-1))>mHLG3 (42.0mgg(-1))>mHLG0 (35.8mgg(-1)), which was higher than the results from majority of previous studies, suggesting that H2O2 modification advanced sorption capacity of hydrothermal biochars evidently. Effect mechanisms exploration indicated that the difference of Cu (II) removal by biochars before and after the modification was mainly related to functional groups. Carboxylic group was responsible for the best sorption property of Cu (II) by mHLG2, which was attributed to its significant relationships with H2O2 modification and Cu (II) removal.