Software analyser design using data mining technology for toxicity prediction of aqueous effluents

Database and information technology has been widely used in process industries to manage data related to environmental performance. However, apart from being collected and archived for subsequent retrieval, the data has not been effectively exploited for improving environmental performance. In this paper we report our work on application of data mining and knowledge discovery technology to the analysis of a database of aqueous effluents from an organic manufacturing plant. The focus is on developing a software analyser for Microtox prediction. However, this methodology is applicable to any ecotoxicity measurement and will therefore offer a means of minimising difficult and tedious testing. Principal component analysis is used to pre-process the data for removing noise and reducing dimensionality. Automatic clustering is employed to group the multidimensional data into classes, and from each class training and testing data sets are selected for developing a back-propagation neural network to predict Microtox. The result shows that the software analyser is able to give satisfactory predictions for both training and test data. The errors for all the training and testing data are shown to satisfy a normal distribution. The software analyser is further used to carry out sensitivity studies in order to identify compounds responsible for observed toxicity value, based on which improved process operational strategies can be developed. Several approaches are investigated, including correlation coefficient analysis, sensitivity study based on differential analysis, one variable deletion, fuzzy curve approach and combination of the above with principal component analysis.     

Seasonal Variation of the Particle Size Distribution of n-Alkanes and Polycyclic Aromatic Hydrocarbons (PAHs) in Urban Aerosol of Guangzhou, China

Seasonal aerosol samples have been collected by Andersen Hi-Vol pumping system equipped with a five stage cascade impactor and a backup filter (size range: 10–7.2 μ m, 7.2–3.0 μ m, 3.0–1.5 μ m, 1.5–0.95 μ m, 0.95–0.49 μ m, ≤0.49 μ m) in the Liwan district, Guangzhou. n-Alkanes were measured using gas chromatography and PAHs were measured using gas chromatography/mass spectrometry analysis. The bimodal log-normal distributions of n-alkanes and semi-volatile PAHs were found, while for non-volatile PAHs that was unimodal, so much as the mode of semi-volatile PAHs was similar with that of the particles. The n-alkanes and PAHs were preferably associated with fine particles. C _max (carbon number maximum) (C₂₂–C₂₆), CPI (carbon preference index) (1.12–1.21), U/R (unresolved to resolved components ratio) (7.42–10.7), wax% (0.9–3.12%) and the diagnostic ratios for PAHs revealed that vehicular emission was the major source of these organic compounds during the study periods, while the contribution of epicuticular waxes emitted by terrestrial plants was minor. CPI₂ (values for petrogenic hydrocarbons), CPI₃ (values for biogenic n-alkanes) and wax% revealed that the natural preferentially accumulated in the larger aerosol while the anthropogenic in the smaller. In addition, the different MMDs (mass median diameters) for n-alkanes and PAHs were observed in different seasons. The MMDs for n-alkanes and PAHs were higher in autumn/winter than those in spring/summer. The seasonal effect was related to the hydrocarbon content in the individual particulate fractions, showing a preferential association of n-alkanes and PAHs with larger particles in the autumn/winter season.     

Evaluation of analytical strategies for the determination of metal concentrations to assess landfill leachate contamination

Due to the complex nature of landfill leachates, metal and metalloid analyses prove to be tricky and suffer from a lack of standard protocols. A complete approach has been adopted to investigate the influence of the different steps during the sample processing of French landfill leachates. The validation of the entire protocol has been achieved using a laboratory reference material. This material, which is a real landfill leachate, is representative of real samples. Its evaluation has allowed a quality control for metal and metalloid analyses in landfill leachates. Precautions concerning storage temperature, aeration and filtration are proposed to perform accurate metal analyses in these complex matrices. The sample processing has been applied to the seasonal monitoring of a French landfill. The assessment of major leachate metallic contaminants such as As, Cr, Sb, Sn, has been performed by evaluating the relative enrichment of metals and metalloids in comparison with rain water and groundwater. In addition, hydrological data are useful and complementary information for pointing out the main factors affecting metal concentrations and thus their potential remobilisation pathways.     

Estimating mercury emissions from a zinc smelter in relation to China’s mercury control policies

Mercury concentrations of flue gas at inlet/outlet of the flue gas cleaning, electrostatic demister, reclaiming tower, acid plant, and mercury contents in zinc concentrate and by-products were measured in a hydrometallurgical zinc smelter. The removal efficiency of flue gas cleaning, electrostatic demister, mercury reclaiming and acid plant was about 17.4%, 30.3%, 87.9% and 97.4% respectively. Flue gas cleaning and electrostatic demister captured 11.7% and 25.3% of the mercury in the zinc concentrate, respectively. The mercury reclaiming tower captured 58.3% of the mercury in the zinc concentrate. About 4.2% of the mercury in the zinc concentrate was captured by the acid plant. Consequently, only 0.8% of the mercury in the zinc concentrate was emitted to the atmosphere. The atmospheric mercury emission factor was 0.5 g t⁻¹ of zinc produced for the tested smelter, indicating that this process offers the potential to effectively reduce mercury emissions from zinc smelting.     

Characterization, sources, and potential risk assessment of PAHs in surface sediments from nearshore and farther shore zones of the Yangtze estuary, China

The assessment of polycyclic aromatic hydrocarbons (PAHs) contamination in surface sediments from the Yangtze estuary which is a representative area affected by anthropogenic activity (rapid industrialization, high-population density, and construction of dams upstream) in the world was systematically conducted. Fifty-one samples were analyzed by high-performance liquid chromatography (HPLC). The ??PAHs in all sediments varied from 76.9 to 2,936.8?ng?g^?1. Compared with other estuaries in the world, the PAH levels in the Yangtze estuary are low to moderate. Phenanthrene, acenaphthylene, fluoranthene, and pyrene were relatively abundant. The ??PAH levels and composition varied obviously in different estuarine zones due to different sources. The highest ??PAHs concentration was observed in the nearshore of Chongming Island. The PAH composition showed that four to six ring PAHs were mainly found in the nearshore areas, while two to three ring PAHs were in the farther shore zones. The PAHs in the Yangtze estuary were derived primarily from combustion sources. A mixture of petroleum combustion and biomass combustion mainly from coal combustion and vehicle emission was the main source of PAHs from the nearshore areas, while the spill, volatilization, or combustion of petroleum from shipping process and shoreside discharge were important for PAHs in the farther shore areas. The result of potential ecotoxicological risk assessment based on sediment quality guidelines indicated low PAH ecological risk in the Yangtze estuary. The study could provide foundation for the protection of water quality of the Yangtze estuary by inducing main sources input.     

Distribution of Stipa purpurea steppe in the Northeastern Qinghai-Xizang Plateau (China)

The aims of this study were to examine the spatial distribution pattern of Stipa purpurea steppe and to elucidate their possible correlation with environmental factors, by means of multivariate quantitative analysis. Two data sets were subjected to the Two-way Indicator Species Analysis (TWINSPAN), the community similarity analysis and the Detrended Correspondence Analysis (DCA) and Canonical Correspondence Analysis (CCA). The distribution pattern of Stipa purpurea steppe showed obvious geographical heterogeneity in different regions and some homogeneity in the same region. And the altitude, longitude and latitude were the three major environmental factors affecting Stipa purpurea steppe’s distribution.     

Latitudinal pattern in species diversity and its response to global warming in permafrost wetlands in the Great Hing’an Mountains, China

Permafrost wetlands are one of the most sensitive plant communities in response to global warming. Global warming could induce natural plant communities to shift into cooler climate zones, or extirpate. To understand how plant communities in permafrost wetlands are affected by global warming, we examined the patterns of plant species diversity in the 24 permafrost wetlands in the Great Hing’an Mountains along a latitudinal gradient. This gradient was characterized by a northward decline in mean annual temperature (Δ = 3.5°C) and mean annual precipitation (Δ = 38.7 mm). Our results indicated that latitudinal patterns in species diversity existed in the permafrost wetlands. The numbers of family, genus and species, the Gleason index and Shannon-Wiener index for shrubs decreased linearly with decreasing latitude, but increased for herbaceous plants. The latitudinal patterns in species diversity had influenced strongly by temperature. Simple linear regression yielded about 2 decreases in shrub number and 9 increases in herbaceous species number with an increase of mean annual temperature by 1°C, with 0.33 decreases in shrub diversity and 0.29 increases in herbaceous species diversity. If temperature warms 3.7°C by 2100, herbaceous plants might increase in the permafrost wetlands, with species number increasing 48% or 6 times and species diversity increasing 40% or 2 times; and some shrub species might decrease and even disappear in part of the areas with lower latitude, with species number decreasing 50–100% and species diversity decreasing 69–100%. The permafrost wetlands in the Great Hing’an Mountains might continue degenerating and shift northward with global warming over the next century.     

Numerical simulation of municipal solid waste combustion in a novel two-stage reciprocating incinerator

A mathematical model was presented in this paper for the combustion of municipal solid waste in a novel two-stage reciprocating grate furnace. Numerical simulations were performed to predict the temperature, the flow and the species distributions in the furnace, with practical operational conditions taken into account. The calculated results agree well with the test data, and the burning behavior of municipal solid waste in the novel two-stage reciprocating incinerator can be demonstrated well. The thickness of waste bed, the initial moisture content, the excessive air coefficient and the secondary air are the major factors that influence the combustion process. If the initial moisture content of waste is high, both the heat value of waste and the temperature inside incinerator are low, and less oxygen is necessary for combustion. The air supply rate and the primary air distribution along the grate should be adjusted according to the initial moisture content of the waste. A reasonable bed thickness and an adequate excessive air coefficient can keep a higher temperature, promote the burnout of combustibles, and consequently reduce the emission of dioxin pollutants. When the total air supply is constant, reducing primary air and introducing secondary air properly can enhance turbulence and mixing, prolong the residence time of flue gas, and promote the complete combustion of combustibles. This study provides an important reference for optimizing the design and operation of municipal solid wastes furnace.     

Digestion of frozen/thawed food waste in the hybrid anaerobic solid-liquid system

The hybrid anaerobic solid-liquid (HASL) system, which is a modified two-phase anaerobic digester, is to be used in an industrial scale operation to minimize disposal of food waste at incineration plants in Singapore. The aim of the present research was to evaluate freezing/thawing of food waste as a pre-treatment for its anaerobic digestion in the HASL system. The hydrolytic and fermentation processes in the acidogenic reactor were enhanced when food waste was frozen for 24h at -20 degrees C and then thawed for 12h at 25 degrees C (experiment) in comparison with fresh food waste (control). The highest dissolved COD concentrations in the leachate from the acidogenic reactors were 16.9g/l on day 3 in the control and 18.9g/l on day 1 in the experiment. The highest VFA concentrations in the leachate from the acidogenic reactors were 11.7g/l on day 3 in the control and 17.0g/l on day 1 in the experiment. The same volume of methane was produced during 12 days in the control and 7 days in the experiment. It gave the opportunity to diminish operational time of batch process by 42%. The effect of freezing/thawing of food waste as pre-treatment for its anaerobic digestion in the HASL system was comparable with that of thermal pre-treatment of food waste at 150 degrees C for 1h. However, estimation of energy required either to heat the suspended food waste to 150 degrees C or to freeze the same quantity of food waste to -20 degrees C showed that freezing pre-treatment consumes about 3 times less energy than thermal pre-treatment.