Characterization of aerobic granular sludge of different sizes for nitrogen and phosphorus removal.

Granular size plays a key role in the performance of the aerobic granular sludge (AGS). As the diameter of the granule increases, stratification may begin to appear due to the increase in mass transfer resistance. Aerobic granules harvested from a lab-scale anaerobic-aerobic sequencing batch reactor (AO-SBR) were classified into three categories according to their size: (a) 0.15-0.28 mm, (b) 0.28-0.45 mm and (c) larger than 0.45 mm. In this study, the categories were called small-size, medium-size and large-size granules, respectively. A fraction of the different forms of phosphate and denitrification efficiency was investigated in each category. Results show that small-size granules present much more easily mobile phosphorus than other granules. Moreover, the denitrification performance has been tested by using dumping and trickling patterns for COD and NO3--N feeding. The results demonstrated that the large-size granules exhibit poor denitrification rates, as opposed to the medium-size granules. Therefore, medium-size granules, with a size of 0.28-0.45 mm, are regarded as the most suitable granular size for AGS in this experiment from the perspective of denitrification and phosphorus removal.

[Analysis of Respirogram Characteristics of Filamentous Bulking Caused by Low Dissolved Oxygen].

The current research on filamentous bulking focuses on the effluent quality and the settling properties but the reports on the microbial physiology under filamentous bulking conditions are seldom. In this study, the variations in the respirogram of microorganisms and affinity coefficient during filamentous bulking were explored in a sequence batch reactor. Low dissolved oxygen, regarded as the typical reason for filamentous bulking, was applied as the stimulation method. The results showed that microorganisms entered the physiological adaptation stage in the early period of low DO. The following properties were observed in the system:① a sudden increase in the endogenous specific oxygen uptake rate (SOURe) of activated sludge, ② an abrupt decrease in the specific oxygen uptake rate (SOURn) of autotrophic bacteria, ③ a rapid increase after a slight decline in the specific oxygen uptake rate (SOURc) of heterotrophic bacteria and a sudden increase in the oxygen affinity coefficient (KO). However, maintaining the low DO levels would deteriorate the effluent quality and sedimentation properties, but the SOURn and SOURc could recover to higher levels after a while and the COD affinity coefficient (KS) and KO would decrease gradually. In low DO conditions, a sufficient hydraulic retention time will benefit the effluent quality from a theoretical point of view. Moreover, microorganisms could adapt to low DO conditions, which verifies the feasibility of "low oxygen aeration theory" from the respiration and kinetic parameters. The results from this study provide a theoretical support for energy savings of sewage treatment plant operations.

[Endogenous respiration process analysis of heterotrophic biomass and autotrophic biomass based on respiration map ].

The endogenous process is an important metabolic part of the activated sludge, and the understanding of this process is still unclear. Characteristics of endogenous respiration for heterotrophic bacteria and autotrophic nitrifiers were analyzed using respirogram. Results showed that both heterotrophic and autotrophic bacteria entered the stage of endogenous respiration at almost the same time, but heterotrophic bacteria first entered the stage of dormancy i. e. , they were easier to recover a higher proportion of biomass during the dormancy stage, indicating that heterotrophic bacteria exhibited strong environmental adaptability. Autotrophic bacteria were, however, quite different. This finding confirmed that autotrophic bacteria were more vulnerable from the viewpoint of endogenous respiration. In addition, the study also found that the increase of endogenous respiration rate ratio reflected the decreased sludge activity. And the proportion of endogenous respiration was an important parameter to characterize the activity of activated sludge, which can be used as a quantitative index for the health status of activated sludge. The findings further deepened the understanding of endogenous respiration process and provided a theoretical basis for the operation and management of wastewater treatment plants.

Investigation of individual heterozygosity correlated to growth traits in Tongshan Black-boned goat.

Ten single nucleotide polymorphisms were used for genotyping of 176 Tongshan Black-boned goats, which are Chinese indigenous goat colony for meat production. The average individual heterozygosity was 0.292. To assess the correlations between individual heterozygosity and growth in Tongshan Black-boned goat individuals, and the potential of using individual heterozygosity as an indicator of growth, the data of growth traits, including body weight, height at withers, body length, chest girth and cannon circumference, were collected. Significant correlations were observed between individual heterozygosity and body weight, height at withers, body length, heart girth, cannon circumference (P < 0.05). All the significant regression showed positive slope with R square values ranged from 0.0251 to 0.0368. These data suggests that individual heterozygosity is positively correlated with growth traits in Tongshan Black-boned goat individuals and associative overdominance may affect Tongshan Black-boned goat growth significantly. Therefore it is possible to use individual heterozygosity as an indicator of growth. Our results also provide a strong support to the overdominance hypothesis.