[Effect of Different Temperatures on the Performance of Autotrophic Nitrogen Removal and Microbial Community from Swine Wastewater].

Four laboratory-scale autotrophic nitrogen removal bioreactors were implemented to investigate performance differences and microbial mechanisms under different temperatures (30, 25, 20, and 15℃). The results showed that the reactor performance under 30℃ was higher than others. When the temperature decreased from 30℃ to 25℃, total nitrogen removal efficiency reduced from 73% to 66%, and total nitrogen removal rate from 2.29 kg·(m3·d)-1 to 1.72 kg·(m3·d)-1. The morphology and particle size of the sludge did not change significantly (SMD:from 80.85 µm to 79.95 µm). When the temperature was 20℃, the total nitrogen removal efficiency reduced to 42%, the total nitrogen removal rate reduced to 1.18 kg·(m3·d)-1, and the sludge disintegration phenomenon occurred with particle size reduction (SMD:63.21 µm). When the temperature was 15℃, the total nitrogen removal efficiency reduced to 37%, and the total nitrogen removal rate got as low as 1.00 kg·(m3·d)-1. In addition to that, the reactor operation was difficult. The analysis of microbial community structure showed that the influence of temperature on anaerobic ammonia oxidizing bacteria is greater than that on ammonia oxidizing bacteria. This sensitivity to temperature of the anaerobic ammonia oxidizing bacteria was the main reason for the decreased performance under low temperature conditions.

The Enrichment of Microbial Community for Accumulating Polyhydroxyalkanoates Using Propionate-Rich Waste.

Polyhydroxyalkanoates (PHAs) are promising alternatives to plastics since they have similar properties to polyolefin but are biodegradable and biocompatible. Recently, the conversion of propionate wastewater to PHAs by undefined mixed microbial cultures becomes attractive. However, how microbial community changes remains unclear during the enrichment step, which is critical for a robust PHA-producing system. In this study, PHA-accumulating cultures were enriched under feast/famine condition using propionate-rich substrates. Our results showed that during the first 2 h of the enrichment, dissolved oxygen of cultures increased remarkably until saturation, and amounts of C, N, and chemical oxygen demand of cultures decreased significantly to a very low level. High-throughput sequencing revealed that bacterial populations affiliated with Alphaproteobacteria and Bacteroidetes dominated the cultures enriched. Most of these dominant populations contributed to the conversion of short-chain fatty acids to PHAs. Being fed with the substrate rich in propionate but without nitrogen, the cultures enriched could accumulate nearly 27% PHAs at 72 h with higher content of hydroxyvalerate. Our work reveals the process in which environmental microbes responded to propionate-rich condition and shifted to populations for accumulating PHAs; it also will be helpful to develop an efficient PHA-producing system using propionate-rich waste.