The treatment of solvent recovery raffinate by aerobic granular sludge in a pilot-scale sequencing batch reactor

Modeling nitrogen removal performance based on novel microbial activity indicators in WWTP by machine learning and biological interpretation

Modeling the pollutant removal performance of wastewater treatment plants (WWTPs) plays a crucial role in regulating their operation, mitigating effluent anomalies and reducing operating costs. Pollutants removal in WWTPs is closely related to microbial activity. However, there is extremely limited knowledge on the models accurately characterizing pollutants removal performance by microbial activity indicators. This study proposed a novel specific oxygen uptake rate (SOURATP) with adenosine triphosphate (ATP) as biomass. Firstly, it was found that SOURATP and total nitrogen (TN) removal rate showed similar fluctuated trends, and their correlation was stronger than that of TN removal rate and common SOURMLSS with mixed liquor suspended solids (MLSS) as biomass. Then, support vector regressor (SVR), K-nearest neighbor regressor (KNR), linear regressor (LR), and random forest (RF) models were developed to predict TN removal rate only with microbial activity as features. Models utilizing the novel SOURATP resulted in better performance than those based on SOURMLSS. A model fusion (MF) algorithm based on the above four models was proposed to enhance the accuracy with lower root mean square error (RMSE) of 2.25 mg/L/h and explained 75% of the variation in the test data with SOURATP as features as opposed to other base learners. Furthermore, the interpretation of predictive results was explored through microbial community structure and metabolic pathway. Strong correlations were found between SOURATP and the proportion of nitrifiers in aerobic pool, as well as between heterotrophic bacteria respiratory activity (SOURATP_HB) and the proportion of denitrifies in anoxic pool. SOURATP also displayed consistent positive responses with most key enzymes in Embden-Meyerhof-Parnas pathway (EMP), tricarboxylic acid cycle (TCA) and oxidative phosphorylation cycle. In this study, SOURATP provides a reliable indication of the composition and metabolic activity of nitrogen removal bacteria, revealing the potential reasons underlying the accurate predictive result of nitrogen removal rates based on novel microbial activity indicators. This study offers new insights for the prediction and further optimization operation of WWTPs from the perspective of microbial activity regulation.

Stability of aerobic granular sludge in a pilot scale sequencing batch reactor enhanced by granular particle size control

Aerobic granulation was successfully achieved in a pilot scale sequencing batch reactor within 40 days. Then, stability of different particle size granules was explored according to their activity and resistance to ultrasonic crushing. Different particle size granules (0.3-0.6 mm, 0.6-1 mm, 1-1.43 mm, 1.43-2 mm, 2-3 mm and 3-4 mm) were exposed under different ultrasonic power separately. It was found that the granules with 2-3 mm always had the maximum granulation rates after ultrasonic crushing. Meanwhile, activity data showed that the 2-3 mm granules had the lowest specific oxygen utilization rates, which indicated that they were easier to maintain stability as the increase of their particle sizes was the slowest. So, 500 mL mixed liquid of the reactor were taken out and sieved to obtain the 2-3 mm granules, which were subsequently returned to the reactor to increase their proportion. Through the manual regulation, the proportion of 2-3 mm granules kept increasing which gradually became dominant in the reactor. Under the strategy of 86 days of operation, the aerobic granules were regular and compact, which had good removal effects of the real wastewater. The results indicated that the stability of the system could be greatly enhanced by the method, which provided a new strategy to maintain the granular stability.

Storage of aerobic granular sludge embedded in agar and its reactivation by real wastewater

Aerobic granular sludge (AGS) was preserved using an agar embedding method to maintain its stability. No obvious damage was imposed on the granular appearance during 30 days of cold and dry storage, but the granular microstructure had an uneven surface with a large number of holes. The results were consistent with the extinction of microbial communities and the monitored consumption of extracellular polymeric substances, in which granular specific oxygen utilization rate and mixed liquor volatile suspended solids/mixed liquor suspended solids ratio, respectively, decreased by 72.4% and 62.5% during storage. A mass conversation calculation indicated that the loss of granular mass was 1.6393 g. An offensive odour was smelled during storage, and the results indicated that a material transformation and mitigation were involved between AGS and the gas phase. Although the granular structure was destroyed to a certain extent, no obvious damage was imposed on the granular skeleton during storage. After it was aerated again after a feeding with real wastewater, the residual skeleton served as a carrier for the rapid proliferation of microorganisms, and good granular properties were obtained after 11 days of reactivation.

Exploiting Quorum Sensing Interfering Strategies in Gram-Negative Bacteria for the Enhancement of Environmental Applications

Quorum sensing (QS) is a widespread intercellular form of communication to coordinate physiological processes and cooperative activities of bacteria at the population level, and it depends on the production, secretion, and detection of small diffusible autoinducers, such as acyl-homoserine lactones (AHLs), auto-inducing oligo-peptides (AIPs) and autoinducer 2. In this review, the function of QS autoinducers of gram-negative bacteria in different aspects of wastewater treatment systems is examined. Based on research primarily performed over the past 10 years, QS involvement in the formation of biofilm and aerobic granules and changes of the microbial community and degradation/transformation pathways is discussed. In particular, the QS pathway in the role of bacterial infections and disease prevention in aquaculture is addressed. Interference of QS autoinducer-regulated pathways is considered potential treatment for a variety of environmentally related problems. This review is expected to serve as a stepping stone for further study and development strategies based on the mediation of QS-regulated pathways to enhance applications in both wastewater treatment systems and aquaculture.