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In this study, eight different submerged aquatic species were screened by batch biochemical methane potential and anaerobic degradability tests to identify a promising/suitable feedstock. Kinetics of the best-screened substrate were studied in a mesophilic semi-continuous experiment. The aquatic species Myriophyllum aquaticum, Egeria densa and Potamogeton perfoliatus showed relatively higher methane yields of over 400 NmL/g-VS (volatile solids). Semi-continuous operation was carried out by feeding E. densa for over 400 days. The achieved results were 33%–53% chemical oxygen demand (COD) reduction and methane yield of 126–231 NmL/g-VS with a short hydraulic retention time (HRT). Additionally, the NH4+ and PO43− releases from the biomass to water were found to be low (18%–27% and 2.5%–3.9%) throughout the experiment. Hydrolysis was the limiting step in the digestion of E. densa, regardless of changes in HRT (15–45 days). The acid-phase model indicated that the hydrolysis rate constant (kh) of E. densa was 0.058 one/day, which was one third lower the kh value of food waste, but quite similar to cow manure.

In view of the precursory characteristic point of limestone failure under uniaxial compression, the underlying mechanisms are not sufficiently clear. Experimental studies examining the acoustic emission (AE) characteristics of the complete limestone failure process have been carried out under uniaxial compression. The experimental results, including accumulative AE counts, the curve of stress and strain, AE rate and stress-time, AE energy rate and stress-time, AE amplitude-time, and AE frequency- time were obtained in detail. The experimental results clearly indicate that AE activities of the samples were generated during the entire process of uniaxial compression. Flowever, the abnormal AE activities appeared in the late stage of the unstable crack propagation phase. These parameters, such as the AE rate, AE energy rate, AE amplitudes, and AE frequencies, were observed to decrease sharply after a relatively quiet period. Flowever, the accumulative AE counts remained at nearly constant values. Stress passed through the quiet period quickly before the peak stress, where the AE activities were enhanced. The AE rate increased suddenly and AE energy rate rose rapidly when the stress reached the peak stress of the samples. As a consequence, the relatively quiet period could be used as the precursory information of rock failure, and the starting point of a relatively quiet period could be predicted as a precursory characteristic point of rock failure. The start point of the relatively quiet period was approximately located in the range of 88 to 98 % of the peak stress. [ABSTRACT FROM AUTHOR]

In this study, eight different submerged aquatic species were screened by batch biochemical methane potential and anaerobic degradability tests to identify a promising/suitable feedstock. Kinetics of the best-screened substrate were studied in a mesophilic semi-continuous experiment. The aquatic species Myriophyllum aquaticum, Egeria densa and Potamogeton perfoliatus showed relatively higher methane yields of over 400 NmL/g-VS (volatile solids). Semi-continuous operation was carried out by feeding E. densa for over 400 days. The achieved results were 33%-53% chemical oxygen demand (COD) reduction and methane yield of 126-231 NmL/g-VS with a short hydraulic retention time (HRT). Additionally, the NH4+ and PO43- releases from the biomass to water were found to be low (18%-27% and 2.5%-3.9%) throughout the experiment. Hydrolysis was the limiting step in the digestion of E. densa, regardless of changes in HRT (15-45 days). The acid-phase model indicated that the hydrolysis rate constant (kh) of E. densa was 0.058 one/day, which was one third lower the kh value of food waste, but quite similar to cow manure. [ABSTRACT FROM AUTHOR]