Promoting potential direct interspecies electron transfer (DIET) and methanogenesis with nitrogen and zinc doped carbon quantum dots.

Although it has been demonstrated that one-dimensional, two-dimensional, and three-dimensional carbon nanomaterials can improve the CH4 production of anaerobic digestion (AD), the effect of zero-dimensional carbon nanomaterials on AD have not been reported. To expand the application of carbon nanomaterials in AD, the effect of zero-dimensional carbon nanomaterials-carbon quantum dots (CDs) on various feedstocks (c.a. cellulose, glucose, ethanol, and vinegar residue) were investigated in this study. Results have shown that CH4 yield from ethanol was increased by 24.59% (p = 0.396) after adding 5 g/L zinc doped carbon quantum dots (Zn-doped CDs) while that from vinegar residue was dramatically increased by 230% (p = 0.000) using 5 g/L nitrogen doped carbon quantum dots (N-doped CDs). In addition, photoluminescence demonstrated that CDs acted as a capacitor for transmitting and receiving electrons. Furthermore, co-occurrence network analysis revealed that Clostridiales might be used as a signal source to communicate with other species. This study firstly shifted the application of CDs from fluorescence to AD and manifested its positive impact on AD. In short, these findings provided a better understanding on the effects of CDs on different feedstocks of methanogenesis and revealed new evidence of stimulating methanogenesis via CDs.

Characterization of hydrothermal carbonization products (hydrochars and spent liquor) and their biomethane production performance.

To optimize the energy yield (EY) of food waste (FW) via hydrothermal carbonization (HTC), a response surface method was applied. Hydrochars and spent liquor were further conducted to evaluate their characterization and anaerobic digestion potential. Results found that optimal parameters for HTC of FW were suggested as temperature of 260 °C, reaction time of 4 h and moisture of 80%, with higher EY of 66.1%. Higher heating value, good combustion quality, lower H/C and O/C ratios indicated that hydrochar could be utilized as a safe solid fuel. Biochemical methane potential (BMP) experiment showed that spent liquor and hydrochars could be used as feedstocks for anaerobic digestion. Interestingly, hydrochars added in the spent liquor could promote the specific methane yield, which was 2.53 times higher than no addition of hydrochars. The finding of this study could provide useful information for HTC of FW and the utilization of hydrochars and spent liquor.

A geographical location prediction method based on continuous time series Markov model.

Trajectory data uploaded by mobile devices is growing quickly. It represents the movement of an individual or a device based on the longitude and latitude coordinates collected by GPS. The location based service has a broad application prospect in the real world. As the traditional location prediction models which are based on the discrete state sequence cannot predict the locations in real time, we propose a Continuous Time Series Markov Model (CTS-MM) to solve this problem. The method takes the Gaussian Mixed Model (GMM) to simulate the posterior probability of a location in the continuous time series. The probability calculation method and state transition model of the Hidden Markov Model (HMM) are improved to get the precise location prediction. The experimental results on GeoLife data show that CTS-MM performs better for location prediction in exact minute than traditional location prediction models.