Effect of exogenous N-acyl-homoserine lactones on the anammox process at 15 ℃: Nitrogen removal performance, gene expression and metagenomics analysis.

In this study, C6-HSL and C8-HSL were separately introduced into anammox biofilm reactors to facilitate the anammox performance at 15 ℃. After operation 138 d, total nitrogen removal efficiencies in reactors with amendment C6-HSL or C8-HSL at 15 ℃ reached 76.2% and 74.6%, respectively. Content of extracellular polymeric substances increased by 19.8%, 67.7% and 121.2% in control group, C6-HSL and C8-HSL addition group, respectively. Genes associated with nitrogen removal (i.e., hzo, hzsB, nirS, and ccsB) showed higher expression level at amendment C6-HSL or C8-HSL group. Metagenomics analysis found that amendment of C6-HSL or C8-HL resulted in an increased abundance of genes related to the tricarboxylic acid cycle, amino sugar and nucleotide sugar metabolism, and also genes associated with amino acid biosynthesis pathways. Overall, amendment C6-HSL or C8-HSL had been confirmed as the effective method to improve the performance of anammox bioreactor at 15 ℃.

N-acyl-l-homoserine lactones release and microbial community changes in response to operation temperature in an anammox biofilm reactor.

A 1 L lab-scale anaerobic ammonium oxidation (anammox) biofilm reactor with nitrogen loading rate of 0.11 g/L d was run for 110 days with the operation temperature declining from 36 °C to 15 °C. The total inorganic nitrogen removal efficiency showed a reduction from 80% to 66%, when the temperature declined from 36 °C to 15 °C. N-acyl-l-homoserine lactones (AHLs) concentrations, especially C8-HSL and C6-HSL, declined in both water and biomass phases, and this decline indicated that the quorum sensing weakened. Microbial community analysis revealed that Candidatus Kuenenia was the predominant anammox bacteria during the entire operating period. The abundance of Candidatus Kuenenia increased from 1.43% to 22.89% when the temperature decreasing from 36 °C to 15 °C. The correlation between microbial genus and AHLs was complicated. Overall, the temperature decrease weakened the quorum sensing so that the nitrogen removal performance deteriorated, and increasing the anammox activity might be an efficient way to improve performance.

[Effects of Mesophilic Anaerobic Digestion and Thermophilic Anaerobic Digestion on the Risk and Stability of Heavy Metals in Sludge].

Anaerobic digestion is widely used for sewage sludge stabilization. Different anaerobic digestion methods have different impacts on the speciation and stability of heavy metals in sludge. This study investigated the response of the speciation and stability of heavy metals in sludge to the treatment of mesophilic anaerobic digestion-mechanical dewatering and thermal hydrolysis pre-treatment-thermophilic anaerobic digestion. The results showed that the process of mesophilic anaerobic digestion increased the contents of Cd, Cr, Cu, Ni, and Zn in the sludge, increasing its contamination level and potential ecological risks. In contrast, the thermophilic anaerobic digestion process increased the contents of Cd, Cr, and Pb in the sludge, reducing the level of heavy metal contamination and potential ecological risks. It was found that the main contaminated metals were Cd and Zn in Plant N and Cd in Plant S. Cd has the highest risk factor and is the highest risk contributor to the potential ecological risk of all the types of sludge. The sum of reducible and the exchangeable fractions of Cd, Ni, Pb, and Zn reduced, and the residual fraction of Cd, Cr, Cu, and Ni decreased after mesophilic anaerobic digestion. This indicated that the process of mesophilic anaerobic digestion changed the proportion of potential toxicity and steady state of the heavy metals into direct toxicity. After thermophilic anaerobic digestion, the exchangeable proportion of Cd, Cr, Cu, Pb, and Zn decreased, and the steady state of Cd, Cr, Cu, Ni, Pb, and Zn decreased. After the thermophilic anaerobic digestion process, the proportions of bio-availability and mobility of heavy metals therefore decreased, and the proportions of steady state also reduced. The potential toxicity increased.

Response of nitrogen removal performance, functional genes abundances and N-acyl-homoserine lactones release to carminic acid of anammox biomass.

Carminic acid (CA) can serve as a redox mediator and influence the electron transfer process. CA dosages of 0-5 mg/L were added to anaerobic ammonia oxidation (anammox) biomass. The results illustrated that CA not only reduced the inorganic nitrogen removal efficiency, but also decreased the nitrogen removal rate. The deterioration of nitrogen removal performance was due to the excess production of nitrate-nitrogen. The concentration of extracellular polymeric substances showed a decrease together with a decline in N-acyl-homoserine lactones release. CA addition decreased the activity of anammox bacteria while increasing the nitrifying potential. Quantitative reverse transcription polymerase chain reaction showed a decrease in anammox functional genes (nirS, hzo, and hzsB) and promotion of the expression of the nxrB gene, which corresponded with a decrease in anammox bacteria activity and the improvement of nitrifying potential. As a result, CA should not be added to anammox biomass.

Study on the Pyrolysis Kinetics and Mechanisms of the Tread Compounds of Silica-Filled Discarded Car Tires.

The disposal of used automobile tires is a major waste concern. Simply stacking tires and allowing them to decompose will harbor breeding mosquitoes that spread viruses, whereas burning them will release acidic and toxic gases. Therefore, one viable option is pyrolysis, where elevated temperatures are used to facilitate the decomposition of a material. However, the lack of theoretical support for pyrolysis technology limits the development of the pyrolysis industry when it comes to discarded tires. The purpose of this research is to put forward a brand-new multi-kinetic research method for studying materials with complex components through the discussion of various kinetic research methods. The characteristic of this kinetic research method is that it is a relatively complete theoretical system and can accurately calculate the three kinetic factors considered during the pyrolysis of multicomponent materials. The results show that the multi-kinetic research method can obtain the kinetic equation and reaction mechanism for the pyrolysis of tires with high accuracy. The pyrolysis process of this compound was divided into two stages, Reaction I and II, where the kinetic equation of Reaction I was f ( α ) = 0.2473 α - 3.0473 , with an activation energy of 155.26 kJ/mol and a pre-exponential factor of 5.88 × 109/min. Meanwhile, the kinetic equation of Reaction II was f ( α ) = 0.4142 ( 1 - α ) [ - ln ( 1 - α ) ] - 1.4143 , while its activation energy was 315.40 kJ/mol and its pre-exponential factor was 7.86 × 1017/min. Furthermore, based on the results of the research analysis, the reaction principles corresponding to Reaction I and Reaction II in the pyrolysis process of this compound were established.

Insight into the short-term effect of fulvic acid on nitrogen removal performance and N-acylated-L-homoserine lactones (AHLs) release in the anammox system.

Fulvic acid (FA) can serve as electron shuttles between bacteria and electron acceptors. It explored the short-term effect of FA dose on nitrogen removal performance and N-acylated-L-homoserine lactones (AHLs) release change in the anaerobic ammonium oxidation (anammox) system. The results demonstrated that the total inorganic nitrogen removal efficiency increased with the FA dosages from 0.5 mM to 1 mM. FA addition improved anammox bacteria activity, together with extracellular polymeric substances production. FA addition from 0.5 mM to 1 mM stimulated AHLs release in both water and biomass phases, which indicated that the quorum sensing could be improved. These findings revealed that the addition of FA could improve quorum sensing and then enhance nitrogen removal performance.