Applied Mechanics and Materials Vol. 768

Abstract: Coconut fiber (CF) and eucalyptus leaves (EL) were upgraded by hydrothermal carbonization (HTC) and fuel qualities of corresponding hydrochars were determined in the present study. Compared to raw biomass, the hydrochars have increased energy density, and the decreased nitrogen and sulfur contents showed that reduced pollutant emissions are produced during hydrochar combustion. The ignition temperatures of hydrochars were higher and the combustion also shifted to higher temperature ranges. In addition, HTC significantly reduced the slagging and fouling tendencies of raw biomass and the fouling index of CF and EL changed from 2.59 to 0.09 and 1.11 to 0.24, respectively. This study demonstrated that solid fuel with high quality can be produced by HTC and improved thermal efficiency and environmental benefits can be achieved by hydrochar combustion.

Abstract: Based on dry distillation temperature and properties, coal tar can be divided into high temperature coal tar and medium & low temperature coal tar. This paper introduces current status of generation and comprehensive use of high temperature coal tar and medium & low temperature coal tar in China, analyzes poor practice and management problems in the process of comprehensive use of coal tar, and puts forward countermeasures and recommendations for comprehensive use of coal tar in China.

Abstract: Biochar, a production of cotton/sludge pyrolysis, was used as an adsorbent for the removal of heavy metals from aqueous solutions. In this paper, it was assessed that the effect of biochar produced parameters including pyrolysis temperature and heating rate, adsorption time, solution pH and biochar modification on removal of Cd from aqueous solution, and the removal effect of heavy metals from mixed aqueous solution was also studied. The results showed that the optimum conditions were pyrolysis temperature of 550°C, heating rate of 5°C/min, adsorption time of 90min, biochar dosage of 10g/L and solution pH=6, respectively. And the effect was a little increased when the biochar were impregnated with chemicals. About 99% Cd, Pb and Zn were removed from aqueous solution using biochar under the optimum conditions.

Abstract: In order to study the combustion characteristics of sludge, coal, biomass and the mixed sample in micro-oxygen-rich environment (simulating micro-oxygen-rich environment with 30%O2/70%CO2), thermogravimetric analysis method is used in the paper. The experimental results show that under the micro-oxygen-rich environment, sludge has low ignition temperature, the average burning rate, burnout rate and flammability index, so combustion performance of sludge alone is poor and the weightlessness is more obvious in 200~600°C. But after mixing coal or biomass, combustion performance of sludge is improved. We use comprehensive application of flammability index and burnout characteristics index to determine the best mixing ratio is about 65% of sludge and coal, about 45% of sludge and biomass. Comprehensive combustion characteristic index may not be suitable for determining combustion performance of the sludge and its samples by comparison to S under the optimum mixing ratio of the sample and there are some errors. Biomass activation energy is the largest, the activation energy of sludge minimal. But the activation energy of the mixed sample doesn’t change regularly with the increase of sludge mixing proportion. So there is a deviation that we determine the mixing characteristics by a simple comparison of the activation energy of the samples. This paper provides a theoretical and data support for the selection and calculation of combustion parameters of mixed sludge and resource utilization of sludge.

Abstract: ‘Sonication - cryptic growth’ technology can reduce 30-80% excess sludge in wastewater treatment systems. Various mechanisms contribute to the sludge reduction but the role of each one is unclear. This paper quantitatively studied the potential mechanisms in ‘sonication - cryptic growth’. The operation condition was: every day 20% sludge was sonicated under 1.2 Wml^-1 for 15 min and then returned to the wastewater treatment reactor for cryptic growth. The results showed that under such conditions, ‘sonication - cryptic growth’ reduced the excess sludge by 57.3% and the effluent met the national discharge standard. Multiple mechanisms were involved in the process. Detailed analysis showed that the ‘lysis-cryptic growth’ mechanism was the most important one and accounted for 49.1% of sludge reduction. Biodegradation of residual sludge was the second important one and contributed 19.5%. Other potential mechanisms included the altered microbial community, longer sludge retention time, and accumulation of persistent materials. But organic load increase had virtually no impact.

Abstract: This work reports a special bio-fuel derived from sludge. Heat value, density, dropping intensity and heating stability were examined, and the influences of various process parameters were established. It was found that the addition of an aiding agent could increase the caloric value and higher briquetting pressure contributed to the quality and stability of the bio-fuel. Furthermore, the combustion properties of the bio-fuel products under different temperature were investigated.

Abstract: Waste frying oil is abundant and can be used as a cheaper carbon source in PHA production. The utilization of waste frying oil for production of PHA not only enhances the economics of such products,but also provides with a strategy to overcome disposal problems. In this study, the waste frying oil is used as the carbon source for the synthesis of PHA by Cupriavidus necator (formerly known as Ralstonia eutropha) to find out the best growth conditions in order to provides the basis for producing PHA in industry. The results showed that the optimal conditions for production of PHA was at the temperature of 25°C, pH 7, C/N ratio (w/w) 20:0.75 and incubation time 72h. The maximum concentration of PHA was obtained as 7.04g/L.

Abstract: The national general survey manifests that the Chinese soil is suffering from serious contamination, mainly arising from heavy metals (HM). Due to the large amount of heavy metal waste, many researchers have performed the feasibility studies on co-processing this kind of waste in cement kilns. In this paper, we review these results from the perspectives of national standards, the crystal structure of clinker, and the volatility of metals in cement kiln system. The crystal structure of clinker mineral offers physical possibility for the solidification of HM atoms. The volatility studies also indicate that most of the metals will not emit from the kiln system. For the incorporated metals in clinker, their release ratio is very low, and the leaching HM atoms can be immediately enclosed by the cement hydration products. Based on these theoretical results, we measured the HM in the raw materials and in the cement product for 1 year in a cement plant. The bag filter dust contained high level of Tl with an average of 219.30 ppm. The other metals were almost solidified by the clinker. With the vaporization of Tl in the raw materials, the circulation pattern causes the accumulation and buildup of Tl in the system. The incorporation capacity of clinker on HM is predicted in this paper, but the incorporation ratio of HM from contaminated soil, the circulation pattern of HM in cement kiln system, and the emission of HM is currently not clear and further work is in progress.

Abstract: The purpose of this study reports chemical immobilization of As in contaminated soil, using ferric sulfate (Fe₂(SO₄)₃) and ferric chloride hexahydrate (FeCl₃·6H₂O) as stabilizing agents. The optimum treatment solutions were identified based on the immobilizing efficiency of water-soluble and NaHCO₃-extractable arsenic. The results showed significant decreases of water and NaHCO₃-extractable arsenic in soil. Optimization of technological parameters: dosage, treatment time and soil moisture, on arsenic remediation were studied. The immobilization efficiency of NaHCO₃-extractable As attained 83.64% with using 5.5% Fe₂(SO₄)₃, meanwhile that of As could reach 74.50% with adding the same ratio of FeCl₃·6H₂O. The relationship between As immobilization effects and reaction time indicated that arsenic mobility obtained stability after 7 days treatment. Simultaneously, moisture had slightly influence on chemical stabilization, while the immobilization efficiency of ferric chloride hexahydrate was relatively higher under less moisture content. However, soil pH value decreased with the amount of stabilizing agents increasing, which limited the mass ratio of fixative/soil cannot to be much high during treating process.

Abstract: Due to the influence of human, industrial and agricultural activity, a large amount of toxic and harmful heavy metal enter into the soil environment. Heavy metal can easily bio-accumulate through food chain, which cause serious damage to human health. Phytoremediation emerges as a new technology in exploration of effective methods for remediation and rebuild of heavy metal contaminated soils. Although phytoremediation shows great potential in remediation of heavy metal contaminated soil, there still exists many problems in practical application. This article analysis the problems existing in phytoremediation, summarizes the research progress of the technology in application from all the perspective of phytoremediation processes.