The co-processing of wastes in cement production has become an irreversible trend worldwide. However, secondary pollution particularly the air pollution has rarely been investigated despite it may compromise the environmental benefits of waste utilization. In this study, we collected the atmospheric particulate matter (PM10) around a cement plant in Changping district in Beijing, China, which co-processes hazardous wastes and municipal sewage sludge, and investigated the characteristics of trace elements, inorganic and organic species in the samples. The results show that volatile elements (Zn, As, Se, Sc, Cd, Sb and Pb) that are abundant in the wastes can be highly enriched in PM10 compared with local soil, reflecting the influences from cement production. The water-soluble species were generally dominated by organics, which were moderately oxidized with an average oxygen-to-carbon atomic ratio (O/C) of 0.25 and an organic mass-to-organic carbon (OM/OC) ratio of 1.49. In addition, single particle imaging analyses revealed eight types of aerosol particles: S-rich, K-rich, Na-rich, fly ash, mineral, organic, metal and soot. Furthermore, the single particle analysis suggests that the metals released from the cement production may act as catalysts to promote the heterogeneous formations of sulfate and other secondary organic species. Overall, as a preliminary yet pioneering study, our findings highlight the possibly important but understudied influences of solid waste treatment processes on local air quality and haze formation. (C) 2018 Elsevier Ltd. All rights reserved.

Municipal sewage sludge is abundant and rich in phosphorus, making it a promising alternative phosphorus reserve. A good knowledge of the phosphorus transformation during pyrolysis will underlie the industrial phosphorus recycling and reclamation of sewage sludge. This work first advanced a novel calcium oxide (CaO)-enhancement phosphorus-recycling technique based on pyrolysis of sewage sludge, by regulating the transformation of phosphorus in sewage sludge during pyrolysis through the CaO addition. The obtained results indicated that CaO addition promoted the formation of hydroxylapatite, which is a desirable phosphorus species for plant growth. The factors of pyrolysis temperature and inherent composition of sewage sludge both influenced the fraction of hydroxylapatite during pyrolysis. An increase in pyrolysis temperature and a sludge with a high content of ash and a low content of volatile matters potentially promoted the transformation of P from organic phosphorus to the inorganic species during pyrolysis with the addition of CaO, particularly for the formation of hydroxylapatite. Increasing CaO addition significantly increased the fraction of hydroxylapatite in the obtained char, and the maximum content of 25 wt % hydroxylapatite over total phosphorus was attained. This enhanced transformation of hydroxylapatite may be potentially attributed to the interaction between CaO and the polyphosphate with the aid of the inherent minerals that appeared to benefit the immobilization of phosphorus during sludge pyrolysis. As the formation of hydroxylapatite was enhanced, this facile technology of CaO-enhancement sewage sludge pyrolysis could be used for the direct recycling of P as well as the disposal of sewage sludge. © Copyright 2018 American Chemical Society.

Alkaline earth metals (AEMs) aggregated in sludge minerals influence the pyrolysis characteristics and product distribution. Sewage sludge pyrolysis behaviors driven by AEMs were first investigated using advanced thermogravimetry sequentially combined with Fourier transform infrared spectroscopy and mass spectrometry (TG-FTIR-MS). The AEMs represented by MgO and CaO affected the release of volatile products in different ways during sludge pyrolysis. Over 440 °C, CaO and MgO additions both enhanced total absorbance of pyrolytic volatiles, while the enhancement coming from CaO was stronger. Both additions reduced the release order of alkanes and olefins by varying degrees. The degree of reduction with MgO was more significant than that with CaO, while CaO addition promoted the release of CH4, C4H8 and C5H10 over 490 °C with respect to MgO. The addition of MgO more severely suppressed the release of pollutants including NH3, HCN, NO2, H2S, CH3SH, COS, SO2 and nitrogen-derived aromatics than that of CaO. The catalytic effect induced by both species was evidenced by the related pyrolysis kinetics. The attained results revealed that AEM-containing minerals are promising candidates for pollution control during sludge pyrolysis for value-added products recovery. © 2018 Elsevier Ltd

The effect of calcium hydroxide (Ca(OH)(2)), a promising additive to control the pollutants released during sludge pyrolysis, on the pyrolysis behavior and kinetics of sewage sludge was investigated in detail in this study. The obtained thermograms of Ca(OH)(2)-blended sludge showed that the addition of Ca(OH)(2) influenced the thermogravimetric characteristics of sludge, especially in the temperature range of 340-700 degrees C where the decomposition of Ca(OH)(2) happens. An increasing addition of Ca(OH)(2) improved the pyrolysis conversion of sludge at temperatures of more than 600 degrees C, which was verified by the increase of the process heat flow. Importantly, the transformation of elements in sludge was promoted, resulting in a lesser content of impurities, which existed mostly in the thermally stable forms, in the remaining char. Kinetic analysis revealed that the pyrolysis behavior of sludge was influenced by the addition of Ca(OH)(2) and reaction temperature. At low temperatures, Ca(OH)(2) acted as the source of nuclei required for the establishment of reaction interface and then induced the secondary cracking of the pyrolytic compounds in the sludge matrix when the reaction came to high temperatures. A retrofitted kinetic model, overcoming the drawback faced by most Arrhenius-derived models that the integral of temperature-induced item was resolved by approximation, is developed and exhibits superiority in describing the reaction characteristics of sludge pyrolysis.