Nitrogen Removal and N₂O Accumulation during Hydrogenotrophic Denitrification: Influence of Environmental Factors and Microbial Community Characteristics

Hydrogenotrophic denitrification is regarded as an efficient alternative technology of removing nitrogen from nitrate-polluted water that has insufficient organics material. However, the biochemical process underlying this method has not been completely characterized, particularly with regard to the generation and reduction of nitrous oxide (N₂O). In this study, the effects of key environmental factors on hydrogenotrophic denitrification and N₂O accumulation were investigated in a series of batch tests. The results show that nitrogen removal was efficient with a specific denitrification rate of 0.66 kg N/(kg MLSS·d), and almost no N₂O accumulation was observed when the dissolved hydrogen (DH) concentration was approximately 0.40 mg/L, the temperature was 30 °C, and the pH was 7.0. The reduction of nitrate was significantly affected by the pH, temperature, inorganic carbon (IC) content, and DH concentration. A considerable accumulation of N₂O was only observed when the pH decreased to 6.0 and the temperature decreased to 15 °C, where little N₂O accumulated under various IC and DH concentrations. To determine the microbial community structure, the hydrogenotrophic denitrifying enrichment culture was analyzed by Illumina high-throughput sequencing, and the dominant species were found to belong to the genera <i>Paracoccus</i> (26.1%), <i>Azoarcus</i> (24.8%), <i>Acetoanaerobium</i> (11.4%), <i>Labrenzia</i> (7.4%), and <i>Dysgonomonas</i> (6.0%)

Architecture and Performance of Raspberry-like Colloidal Particle Clusters via Self-Assembly of in Situ Generated Janus Particles

Uniform raspberry-like poly­(vinylidene fluoride)/polystyrene (PVDF/PS) complex colloidal particle clusters (CCPCs) with PVDF seed particles protruding outward are fabricated by a novel and one-step approach: soap-free seeded emulsion polymerization following single-electron transfer radical polymerization (SET-RP) mechanism. The driving force from different hydrophobicity values between PVDF and PS induces the self-assembly of the first formed Janus particles, which can be caught because of the relatively low rate of SET-RP, and then Pickering emulsion polymerization performs continuously because of the presence of the unreacted St monomers to form the CCPCs. In contrast, the raspberry-like CCPCs cannot be achieved via a relatively high rate of conventional radical polymerization. In addition, the static water contact angle of the latex nanocoating prepared with the obtained raspberry-like CCPCs is 169.6° and remains at 155° after ultraviolet (UV) irradiation for 6 h. Therefore, it is expected to lead to superhydrophobic and anti-UV functional coatings

Table_1_Effects of fertilizer reduction coupled with straw returning on soil fertility, wheat root endophytic bacteria, and the occurrence of wheat crown rot.DOC

Excessive fertilization is associated with nutrient loss, soil compaction, and weak plant resistance. Straw returning can increase soil fertility with a consequent reduction in fertilizer, but the effects of fertilizer reduction coupled with straw returning on crop endophytic microbes and crop disease are poorly understood. Therefore, using metagenomic sequencing methods we investigated the responses of soil fertility, diversity, the function of root endophytic bacteria, and the occurrence of wheat crown rot due to the application of fertilizer (no, moderate and excessive fertilizer) coupled with or without straw returning after 7 years of treatments. The results showed that, after excessive fertilization, the wheat crown rot became severe, registering a disease index of 23. Compared with excessive fertilization, moderate fertilization coupled with straw returning significantly reduced the incidence of wheat crown rot, the disease index was reduced by 38.50%, and the richness and diversity of endophytic bacteria were increased by 61.20 and 11.93%, respectively, but the soil fertility was not significantly affected. In addition, moderate fertilization coupled with straw returning changed the community structure of endophytic bacteria and increased the relative abundance of carbohydrate metabolism and nitrogen fixation-related genes by 4.72 and 9.32%, respectively. Our results indicated that fertilizer reduction coupled with straw returning reduced the occurrence of wheat crown rot, increased the diversity of endophytic bacteria, and changed the community structure and function of endophytic bacteria, which will provide a better understanding of the interaction of fertilization coupled with straw returning, endophytic bacteria and wheat crown rot.</p