The nitrogen conversions in relation to NH3 and HCN were investigated during microwave pyrolysis of sewage sludge. The nitrogen distributions and evolution of nitrogen functionalities in the char, tar, and gas fractions were conducted. The results suggested that the thermal cracking of protein in sludge produced three important intermediate compounds, including the amine-N, heterocyclic-N, and nitrile-N compounds. The deamination of amine-N compounds resulted from labile proteins cracking led to the formation of NH3 (about 7.5% of SS-N) between 300 and 500 °C. The cracking of nitrile-N and heterocyclic-N compounds in the tars from the dehydrogenation and polymerization of amine-N generated HCN (6.6%) from 500 to 800 °C, respectively. Moreover, the ring-opening of heterocyclic-N in the char and tar contributed to the release of NH3 accounting for about 18.3% of SS-N with the temperature increasing from 500 to 800 °C. Specifically, the thermal cracking of amine-N, heterocyclic-N and nitrile-N compounds contributed to above 80% of the total (HCN+NH3) productions. Consequently, it might be able to reduce the HCN and NH3 emissions through controlling the three intermediates production at the temperature of 500-800 °C.

Previous evaluations of model simulations of the cloud and water vapor feedbacks in response to El Niño warming have singled out two common biases in models from phase 3 of the Coupled Model Intercomparison Project (CMIP3): an underestimate of the negative feedback from the shortwave cloud radiative forcing (SWCRF) and an overestimate of the positive feedback from the greenhouse effect of water vapor. Here, the authors check whether these two biases are alleviated in the CMIP5 models. While encouraging improvements are found, particularly in the simulation of the negative SWCRF feedback, the biases in the simulation of these two feedbacks remain prevalent and significant. It is shown that bias in the SWCRF feedback correlates well with biases in the corresponding feedbacks from precipitation, large-scale circulation, and longwave radiative forcing of clouds (LWCRF). By dividing CMIP5 models into two categories-high score models (HSM) and low score models (LSM)-based on their individual skills of simulating the SWCRF feedback, the authors further find that ocean-atmosphere coupling generally lowers the score of the simulated feedbacks of water vapor and clouds but that the LSM is more affected by the coupling than the HSM. They also find that the SWCRF feedback is simulated better in the models that have a more realistic zonal extent of the equatorial cold tongue, suggesting that the continuing existence of an excessive cold tongue is a key factor behind the persistence of the feedback biases in models.

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China is the world's largest CO2 emitting country and coal-fired thermal power generation accounted for over 50% of total electricity generation in China in 2015. This study reports the changes in power generation efficiency of coal-fired thermal power plants in China from 2009 to 2011 and how the differences in the production scale of the power plants and regional heterogeneity affect the power generation efficiency. We propose a metafrontier data envelopment analysis (DEA) decomposition framework to investigate the sources of inefficiency in power generation. The results suggest that on average, power generation efficiency of the large-scale power plants is 13% higher than that of the small-scale power plants. Although operational inefficiency is the main source of inefficiency in eastern and central China, the technology gap-the differences in the quality of coal consumed for electricity production and in the equipment of the power plants among the regions is the main source of inefficiency in western China. This study uses the results of the framework to discuss the scrapping policies for the coal-fired thermal power plants in China. For large-scale power plants in western China, the components of inefficiency vary and thus policymakers should consider scrapping the thermal power plants based not only on the level of inefficiency but also on its components.

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The sulfur distributions and evolution of sulfur-containing compounds in the char, tar and gas fractions were investigated during the microwave and conventional pyrolysis of sewage sludge. Increased accumulation of sulfur in the char and less production of HS were obtained from microwave pyrolysis at higher temperatures (500-800 °C). Three similar conversion pathways were identified for the formation of HS during microwave and conventional pyrolysis. The cracking of unstable mercaptan structure in the sludge contributed to the release of HS below 300 °C. The decomposition of aliphatic-S compounds in the tars led to the formation of HS (300-500 °C). The thermal decomposition of aromatic-S compounds in the tars generated HS from 500 to 800 °C. However, the secondary decomposition of thiophene-S compounds took place only in conventional pyrolysis above 700 °C. Comparing the HS contributions from microwave and conventional pyrolysis, the significant increase of HS yields in conventional pyrolysis was mainly attributed to the decomposition of aromatic-S (increasing by 10.4%) and thiophene-S compounds (11.3%). Further investigation on the inhibition mechanism of HS formation during microwave pyrolysis confirmed that, with the special heating characteristics and relative shorter residence time, microwave pyrolysis promoted the retention of HS on CaO and inhibited the secondary cracking of thiophene-S compounds at higher temperatures.