Bibo Xu

Influence of sewage sludge-based activated carbon and temperature on the liquefaction of sewage sludge: Yield and composition of bio-oil, immobilization and risk assessment of heavy metals

The influence of sewage sludge-based activated carbons (SSAC) on sewage sludge liquefaction has been carried out at 350 and 400°C. SSAC increased the yield and energy density of bio-oil at 350°C. The metallic compounds were the catalytic factor of SSAC obtained at 550°C (SSAC-550), while carbon was the catalytic factor of SSAC obtained at 650°C. Liquefaction with SSAC redistributed the species of heavy metals in solid residue (SR). With the addition of SSAC, the risk of Cu, Zn and Pb decreased at 350°C, while at 400°C the risk of Cd, Cu, and Zn were decreased. Ecological risk index indicated that 400°C was preferable for the toxicity decrement of SR, while risk assessment code indicated that SR obtained at 350°C contained lower risk. Considering the bio-oil yield, liquefaction at 350°C with SSAC-550 was preferable.

Source identification and potential ecological risk assessment of heavy metals in PM2.5 from Changsha

The probable sources and potential ecological risks of Cu, Zn, Cd and Pb in PM2.5 in Changsha were analyzed. The intelligent medium-flow total suspended particle sampler was used to collect the PM2.5 samples from Yuelu (YL), Kaifu (KF), and Yuhua (YH) districts of Changsha in March-April of 2013. The total concentration of heavy metals (HMs) in PM2.5 was used for source identification by correlation coefficients and principal component analysis (PCA). Otherwise the potential ecological risks indices (RIs) were calculated based on the bioavailable fractions of HMs which were obtained through BCR sequential extraction. Almost 50% of Cu, Cd and Pb in PM2.5 of all sites were accumulated in soluble and reducible fractions by speciation analysis. The correlation coefficients and PCA analysis showed that HMs in PM2.5 of Changsha in spring were mainly from vehicular emissions, fuel combustion, resuspension of dust and other pollution sources. The average potential ecological RIs of HMs in PM2.5 of Changsha were 6193.80 which suggests that HMs in PM2.5 was extremely serious. These results would be a good reference for health studies and formulation of environmental regulations.

Mass concentration and health risk assessment of heavy metals in size-segregated airborne particulate matter in Changsha

This study was performed to investigate the concentration and the health risk of heavy metals (HMs: Zn, Pb, Cd, Ni, Fe, Mn, Cr and Cu) in size-segregated airborne particulate matter (APM). APM samples were collected into 9 size fractions (>9.0 μm, 5.8-9.0 μm, 4.7-5.8 μm, 3.3-4.7 μm, 2.1-3.3 μm, 1.1-2.1 μm, 0.7-1.1 μm, 0.4-0.7 μm, <0.4 μm) by an 8 Stage Non-Viable Cascade Impactor in the campus of Hunan University in Changsha. And then 9 fractions of APM were analyzed for HMs by ICP-OES. The total size-segregated APM concentration in the campus of Hunan University ranged from 120.24 to 271.15 μg/m(3), and the concentration of HMs in APM was in the range of 38.08-13955.14 ng/m(3). The health risk of HMs in APM was evaluated by hazard quotient (HQ) and hazard index (HI) and the results showed that dermal contact and ingestion of APM were the major exposure pathways to human health. The HI values of Cd, Mn, Pb and Cr for children and Cd, Mn and Pb for adults exhibited to be higher than 1 indicating that a non-carcinogenic health effect existed in the APM of the campus of Hunan University. The carcinogenic risks of Cd, Ni and Cr were all bellow the safe value.

Fate and risk assessment of heavy metals in residue from co-liquefaction of Camellia oleifera cake and sewage sludge in supercritical ethanol.

The fate and risk assessment of heavy metals (HMs) in solid residue from co-liquefaction of sewage sludge (SS) and Camellia oleifera cake (COC) in supercritical ethanol (SCE) were investigated. SCE effectively stabilized HMs in solid residues and a better stabilization was presented on Zn than Cd. Moreover, SCE significantly transformed Cd, Cu and Zn into F4, which reduced the risk to the environment. Furthermore, risk assessments of Igeo, Er(i), RI and RAC demonstrated that the addition of COC was beneficial to the contamination decrement of HMs since pollution levels of HMs all decreased after treatment, and the lowest pollution level was obtained with SC-350. Therefore, SS treated by SCE with the addition of COC could be a promising technology for disposal of SS, especially considering the safety of COC as regards HMs problem.

Influence of temperature on nitrogen fate during hydrothermal carbonization of food waste

The influence of temperature (180-260°C) on the fate of nitrogen during hydrothermal carbonization (HTC) of food waste (FW) was assessed. The distribution and evolution of nitrogen in aqueous products and bio-oil, as well as hydrochar, were conducted. Results suggested that elevated temperature enhanced the deamination and the highest ammonium concentration (929.75mg/L) was acquired at 260°C. At temperatures above 220°C, the total N in the hydrochar became stable, whereas the mass percentage of N increased. Amines and heterocyclic-N compounds from protein cracking and Maillard reactions were identified as the main nitrogen-containing compounds in the bio-oil. As to the hydrochar, increasing temperature resulted in condensed nitrogen-containing aromatic heterocycles (e.g. pyridine-N and quaternary-N). In particular, remarkable Maillard reactions at 180°C and the highest temperature at 260°C enhanced nitrogen incorporation (i.e. quaternary-N) into hydrochar.

Characterization of bio-oil and biochar from high-temperature pyrolysis of sewage sludge

The influence of temperature (550–850°C) on the characteristics of bio-oil and biochar from the pyrolysis of sewage sludge (SS) in a horizontal tube reactor was investigated. Results showed that when the pyrolysis temperature increased from 550°C to 850°C, the yield of bio-oil decreased from 26.16% (dry ash-free basis) to 20.78% (dry ash-free basis). Main components of bio-oil were phenols, esters, cholests, ketones, amides, indoles, and nitriles. Besides, the elevated heating rate of 25°C/min was demonstrated to favour the complete combustion of bio-oil. Moreover, caused by the increase in temperature, the yield of biochar decreased from 54.9 to 50.6wt%, Brunauer–Emmet–Teller surface area increased from 48.51 to 81.28 m2/g. Furthermore, pH was increased from 5.93 of SS to 7.15–8.96 of biochar. The negative ζ-potential was also strengthened (−13.87 to −11.30 mV) and principal functional groups on the surface of biochar were –OH, C=O, C=C, –NO2, and S=O.

Co-liquefaction of sewage sludge and oil-tea-cake in supercritical methanol: yield of bio-oil, immobilization and risk assessment of heavy metals

In this study, attention was concentrated on the yields of bio-oil and toxicities of heavy metals (HMs) in liquefaction residues (LRs). Liquefaction of sewage sludge (SS) or oil-tea-cake (OTC) or mixtures of SS and OTC were carried out under the condition of supercritical methanol (SCM). Results showed that the addition of OTC extraordinarily increased the yields of oil from 37.9% (SS) to 86.2% (SS + OTC). Furthermore, with the liquefaction of SS and OTC mixture, the bioavailable fraction (F1 + F2) of Cd and Cu (F1 + F2) was decreased from 2.47 to 1.64 mg/kg and from 98.84 to 67.48 mg/kg, respectively. However, the bioavailable fraction of Zn (F1 + F2) increased from 122.03 to 204.69 mg/kg with the liquefaction of SS. The bioavailable fraction (F1 + F2) of Pb in LRs was 0%, which did not express any changes during the liquefaction process. Risk assessments of geo-accumulation index (Igeo), risk assessment code (RAC) and modified potential ecological risk index (MRI) were applied to evaluate the bioavailabilities, the potential ecological risks and the pollution levels of HMs. The results show that the OTC in SS can decrease the risk of HMs in LRs. Cd attracted many concerns for the highest risk to the environment among all of the HMs. Here, the good results obtained means that SCM liquefaction of mixture of SS and OTC could be a preferable method for SS treatment.

Nitrogen-doped porous carbon from Camellia oleifera shells with enhanced electrochemical performance

Nitrogen doped porous activated carbon was prepared by annealing treatment of Camellia oleifera shell activated carbon under NH3. We found that nitrogen content of activated carbon up to 10.43 at.% when annealed in NH3 at 800 °C. At 600 °C or above, the N-doped carbon further reacts with NH3, leads to a low surface area down to 458 m(2)/g and low graphitization degree. X-ray photoelectron spectroscope (XPS) analysis indicated that the nitrogen functional groups on the nitrogen-doped activated carbons (NACs) were mostly in the form of pyridinic nitrogen. We discovered that the oxygen groups and carbon atoms at the defect and edge sites of graphene play an important role in the reaction, leading to nitrogen atoms incorporated into the lattice of carbon. When temperatures were lower than 600 °C the nitrogen atoms displaced oxygen groups and formed nitrogen function groups, and when temperatures were higher than 600 °C and ~4 at.% carbon atoms and part of oxygen function groups reacted with NH3. When compared to pure activated carbon, the nitrogen doped activated carbon shows nearly four times the capacitance (191 vs 51 F/g).

Recovery of phosphorus from sewage sludge in combination with the supercritical water process

In this paper, the fraction transformation and recovering of phosphorus (P) from sewage sludge (SS) residues, derived from supercritical water process, was investigated by extraction and precipitation processes. In addition, the form of heavy metals existing during the recovery process is also discussed. First, P in the solid residues was recovered by acid leaching with HCl, and then the derived P was adsorbed by activated alumina (Al(2)O(3)). Finally, the Al2O3 was desorbed with low concentration of NaOH. Results showed that 80% organic P was converted into HCl-P. The total P (the chief ingredient of HCl-P) in solid residue increased from 86.1 to 95.6% as temperature increased from 350 to 400 °C. The amount of P in the solid residue that was dissolved by 1 M HCl was 97.8%, and over 95% of P in the leaching solution (15 mg/L for P concentration) was adsorbed after 5.0 g of Al(2)O(3) powder was added. The amount of P desorbed from Al(2)O(3) with 0.1 M NaOH was 98.7%. Ultimately, over 85% of TP in SS was recovered. Moreover, the proportion of Cu, Zn and Pb in the extracted P products was lower than 5%.

Feedwater pH affects phosphorus transformation during hydrothermal carbonization of sewage sludge

In this study, the effect of feedwater pH (3-11) on phosphorus (P) transformation during the hydrothermal carbonization (HTC) of sewage sludge (SS) was investigated at a temperature range of 200-260°C. The HTC significantly accumulated P in the hydrochar. Different feedwater pH stimulated the transformation of various forms of P. An acidic feedwater pH promoted the transformation of apatite phosphorus (AP) to non-apatite inorganic phosphorus (NAIP), and of organic P (OP) to inorganic P (IP). The NAIP tended to transformation to AP and a small part of the IP was transformed to OP when the SS was treated in a basic environment. The combination of three P analysis methods (chemical extractive fractionation, X-ray powder diffraction (XRD) and energy dispersive spectroscopy (EDS)) showed that metal cations (e.g. Al and Ca) and the pH played important roles in the transformation of different forms of P during the HTC of the SS.