Water-lifting and aeration system improves water quality of drinking water reservoirs: Biological mechanism and field application.

Reservoirs have been served as the major source of drinking water for dozens of years. The water quality safety of large and medium reservoirs increasingly becomes the focus of public concern. Field test has proved that water-lifting and aeration system (WLAS) is a piece of effective equipment for in situ control and improvement of water quality. However, its intrinsic bioremediation mechanism, especially for nitrogen removal, still lacks in-depth investigation. Hence, the dynamic changes in water quality parameters, carbon source metabolism, species compositions and co-occurrence patterns of microbial communities were systematically studied in Jinpen Reservoir within a whole WLAS running cycle. The WLAS operation could efficiently reduce organic carbon (19.77%), nitrogen (21.55%) and phosphorus (65.60%), respectively. Biolog analysis revealed that the microbial metabolic capacities were enhanced via WLAS operation, especially in bottom water. High-throughput sequencing demonstrated that WLAS operation altered the diversity and distributions of microbial communities in the source water. The most dominant genus accountable for aerobic denitrification was identified as Dechloromonas. Furthermore, network analysis revealed that microorganisms interacted more closely through WLAS operation. Oxidation-reduction potential (ORP) and total nitrogen (TN) were regarded as the two main physicochemical parameters influencing microbial community structures, as confirmed by redundancy analysis (RDA) and Mantel test. Overall, the results will provide a scientific basis and an effective way for strengthening the in-situ bioremediation of micro-polluted source water.

Effects of artificially induced complete mixing on dissolved organic matter in a stratified source water reservoir.

Naturally complete mixing promotes the spontaneous redistribution of dissolved oxygen (DO), representing an ideal state for maintaining good water quality, and conducive to the biomineralization of organic matter. Water lifting aerators (WLAs) can extend the periods of complete mixing and increase the initial mixing temperature. To evaluate the influence of artificial-induced continuously mixing on dissolved organic matter (DOM) removal performance, the variations of DOM concentrations, optical characteristic, environmental factors were studied after approaching the total mixing status via WLAs operation. During this process, the dissolved organic carbon reduced by 39.18%, whereas the permanganate index decreased by 20.47%. The optical properties indicate that the DOM became more endogenous and its molecular weight decreased. Based on the results of the Biolog EcoPlates, the microorganisms were maintained at a relatively high metabolic activity in the early stage of induced mixing when the mixing temperature was relatively high, whereas DOM declined at a high rate. With the continuous decrease in the water temperature, both the metabolic capacity and the diversity of aerobic microorganisms significantly decreased, and the rate of organic matter mineralization slowed down. The results of this study demonstrate that the artificial induced mixing largely enhanced the removal DOM performance by providing a long period of aerobic conditions and higher initial temperature.

[Temporal and Spatial Evolution of Storm Runoff and Water Quality Assessment in Jinpen Reservoir].

To explore the temporal and spatial intrusion process of runoffs and the response of water quality during the flood season in the Jinpen Reservoir (JPR) in Xi'an. Continuous in-situ monitoring was carried out on the water quality indexes (WQI) from the upstream river channel to the reservoir of two runoffs in early August and mid-September 2019. The single factor WQI and comprehensive WQI were used to assess the water quality vertically. Different inflow conditions of rain storm runoffs evolved into different intrusions. The initial inflow of the two runoffs was small, the runoff experienced a full-section intrusion, bottom intrusion, and mid-intrusion process along the way; the position of mid-intrusion in reservoir changed from 545-565 m at the beginning of the runoff to 535-580 m at the end in early August, and developed from 540-575 m of mid-intrusion to 575 m below the bottom of the intrusion in mid-September. The continuous inflow weakened the thermal stratification structure and replenished the DO in the reservoir. Meanwhile, mass particulate pollutants sank into the reservoir, and vertically, the nutrients of middle and bottom parts were higher than at the surface. The single factor WQI showed that the TP and permanganate index values of underflow location increased to some extent, and both exceeded the class Ⅲ water quality standard of surface water at the end. The comprehensive WQI showed that the middle layer of runoff was moderately polluted in early August, while the bottom layer was heavily polluted due to the dual effects of anaerobic and particle deposition, and reached the peak after one week of runoff, while the bottom intrusion of below 575 m directly caused heavy pollution in the middle layer, and bottom layer was medium polluted due to the supplement of dissolved oxygen in mid-September. The discharge of the spillway tunnel and the intake of stratified water could effectively guarantee the safety of the water supply during the flood season.