Zizhen Zhou

Nitrogen Removal from Micro-Polluted Reservoir Water by Indigenous Aerobic Denitrifiers

Treatment of micro-polluted source water is receiving increasing attention because of environmental awareness on a global level. We isolated and identified aerobic denitrifying bacteria Zoogloea sp. N299, Acinetobacter sp. G107, and Acinetobacter sp. 81Y and used these to remediate samples of their native source water. We first domesticated the isolated strains in the source water, and the 48-h nitrate removal rates of strains N299, G107, and 81Y reached 33.69%, 28.28%, and 22.86%, respectively, with no nitrite accumulation. We then conducted a source-water remediation experiment and cultured the domesticated strains (each at a dry cell weight concentration of 0.4 ppm) together in a sample of source water at 20–26 °C and a dissolved oxygen concentration of 3–7 mg/L for 60 days. The nitrate concentration of the system decreased from 1.57 ± 0.02 to 0.42 ± 0.01 mg/L and that of a control system decreased from 1.63 ± 0.02 to 1.30 ± 0.01 mg/L, each with no nitrite accumulation. Total nitrogen of the bacterial system changed from 2.31 ± 0.12 to 1.09 ± 0.01 mg/L, while that of the control system changed from 2.51 ± 0.13 to 1.72 ± 0.06 mg/L. The densities of aerobic denitrification bacteria in the experimental and control systems ranged from 2.8 × 104 to 2 × 107 cfu/mL and from 7.75 × 103 to 5.5 × 105 cfu/mL, respectively. The permanganate index in the experimental and control systems decreased from 5.94 ± 0.12 to 3.10 ± 0.08 mg/L and from 6.02 ± 0.13 to 3.61 ± 0.11 mg/L, respectively, over the course of the experiment. Next, we supplemented samples of the experimental and control systems with additional bacteria or additional source water and cultivated the systems for another 35 days. The additional bacteria did little to improve the water quality. The additional source water provided supplemental carbon and brought the nitrate removal rate in the experimental system to 16.97%, while that in the control system reached only 3.01%, with no nitrite accumulation in either system. Our results show that aerobic denitrifying bacteria remain highly active after domestication and demonstrate the applicability of such organisms in the bioremediation of oligotrophic ecosystems.

Sediment pollution characteristics and in situ control in a deep drinking water reservoir

Sediment pollution characteristics, in situ sediment release potential, and in situ inhibition of sediment release were investigated in a drinking water reservoir. Results showed that organic carbon (OC), total nitrogen (TN), and total phosphorus (TP) in sediments increased from the reservoir mouth to the main reservoir. Fraction analysis indicated that nitrogen in ion exchangeable form and NaOH-extractable P (Fe/Al-P) accounted for 43% and 26% of TN and TP in sediments of the main reservoir. The Risk Assessment Code for metal elements showed that Fe and Mn posed high to very high risk. The results of the in situ reactor experiment in the main reservoir showed the same trends as those observed in the natural state of the reservoir in 2011 and 2012; the maximum concentrations of total OC, TN, TP, Fe, and Mn reached 4.42mg/L, 3.33mg/L, 0.22mg/L, 2.56mg/L, and 0.61mg/L, respectively. An in situ sediment release inhibition technology, the water-lifting aerator, was utilized in the reservoir. The results of operating the water-lifting aerator indicated that sediment release was successfully inhibited and that OC, TN, TP, Fe, and Mn in surface sediment could be reduced by 13.25%, 15.23%, 14.10%, 5.32%, and 3.94%, respectively.

The Effects of Storm Runoff on Water Quality and the Coping Strategy of a Deep Canyon-Shaped Source Water Reservoir in China

Storm runoff events in the flooding season affect the water quality of reservoirs and increase risks to the water supply, but coping strategies have seldom been reported. The phenomenon of turbid current intrusion resulting in water turbidity and anoxic conditions reappearing after storm runoff, resulting in the deterioration of water quality, was observed in the flooding season in the deep canyon-shaped Heihe Reservoir. The objective of this work was to elucidate the effects of storm runoff on the Heihe Reservoir water quality and find a coping strategy. In this study, an intensive sampling campaign measuring water temperature, dissolved oxygen, turbidity, nutrients, and metals were conducted in the reservoir over a period of two years, and the water-lifting aerators were improved to achieve single aeration and a full layer of mixing and oxygenation functions using different volumes of gas. The operation of the improved water-lifting aerators mixed the reservoir three months ahead of the natural mixing time, and good water quality was maintained during the induced mixing period, thereby extending the good water quality period. The results can provide an effective coping strategy to improve the water quality of a source water reservoir and ensure the safety of drinking water.

Brief Introduction to the Selected Chinese Reservoirs

Reservoirs are artificially formed in the bed of a river by building a dam, which intercepts the runoff. They have narrow surface but great depth, and the water level changes significantly during flooding. The mean depth of Chinese reservoirs is around 20–50 m.

Destratification and oxygenation efficiency of a water-lifting aerator system in a deep reservoir: Implications for optimal operation

Thermal stratification is a common phenomenon in lakes and reservoirs and has a significant influence on water quality dynamics. Heihe Reservoir is a canyon-shaped reservoir in Shaanxi Province with strong thermal stratification. Therefore, eight water-lifting aerators (WLAs) were installed in this reservoir, which could overcome thermal stratification and increase oxygenation with gas flows between 20 and 50m3/hr, and oxygenate the hypolimnion with gas flows less than 20m3/hr. To examine the destratification efficiency of the WLA system, we used a three-dimensional hydrodynamic module based on MIKE 3 to simulate the thermal structure of Heihe Reservoir and compared the simulations with measured data. Results showed that operation of the WLA system promoted water mixing and effectively oxygenated the hypolimnion. Through the established energy utilization assessment method, the energy utilization efficiency of the WLA system was between 5.36% and 7.30%, indicating the capability of the technique for destratification in such a large reservoir. When the surface water temperature dropped to the theoretical mixed water temperature calculated by the energy utilization assessment method, reducing gas flow could save energy. This would prevent anaerobic conditions from occurring in the bottom water and maintain good water quality in Heihe Reservoir.

Impact of Contaminated Sediment on the Water Quality of Typical Reservoirs

The sediment in reservoirs is mainly derived from the sedimentation of suspended grains, such as organic particles and inorganic minerals, carried by runoff scouring from vegetation. There are three parts in this chapter: (1) Effects of pollutants released from sediment on water quality; (2) Effects of metals released from sediment on water quality; (3) Algal blooms and their impact on water quality. The decrease of the oxidation–reduction potential (ORP) in a multiphase interface under anaerobic conditions resulted in the increase of soluble ferrous hydroxide. Phosphate combining with iron hydroxide in sediment is released to interstitial water and then diffused into the overlying water. In addition, the metabolism of microbes resulted in the decrease of the ORP in anaerobic conditions, promoting the release of soluble iron in sediment and then causing the huge release of phosphorus. The release of endogenous phosphorus from sediment under anaerobic conditions resulted in the significant increase of PO4 3− in the overlying water. The release of phosphorus from sediment depends on the conditions of the ORP.

Overview of Reservoir Sediment Contamination

The concentration of inorganic phosphorus (IP) in the surface sediment of each of the studied reservoirs ranged from 208.8 to 636.7 mg/kg. The concentration of Fe/Al-P in the surface sediment in the four reservoirs ranged from 82.1 to 216.7 mg/kg, and the average value was 129.6 mg/kg, accounting for 11.54–18.1 % of the sediment total phosphorus (STP) content. The highest proportion of IP is observed in Yuqiao Reservoir, and Jinpen Reservoir had the lowest proportion. In addition, the results indicated that the Ca–P concentrations of the four reservoir sediments are in the range 180.7–303.4 mg/kg, with an average value of 247.1 mg/kg, accounting for 22.33–37.1 % of the STP. The content of organic phosphorus (OP) in the reservoir surface sediment is in the range 64.2–201.8 mg/kg, accounting for 9.85–18.52 % of STP content. The ion exchange nitrogen (IE-N) content (mg/kg) in reservoirs is significantly different. The IE-N content of Shibianyu Reservoir is much higher than that of other reservoirs, accounting for 18.35 % of the total nitrogen (TN). The IE-N in the studied reservoirs accounted for 15.33–18.35 % of the TN. IE-N exists in three different speciations: the concentration of ammonia is much higher than that of nitrate and nitrite, and the concentration of nitrite is the lowest. The cloning and sequencing results showed that microorganisms were made up of ten major categories, including shaped bacillus, Chloroflexi, Verrucomicrobia, Bacteroides, Acidobacteria, thick wall bacteria, actinomycetes, Gemmatimonadetes, Nitrospirae, and Planctomycetes, in the Jinpen Reservoir sediments.

Characteristics of Pollutants Released from Reservoir Sediments

Nitrogen is not only a basic constituent element of life, but it is also one of the key elements causing eutrophication. It has an important effect on nutritional status and water quality in lakes and reservoirs. Inorganic nitrogen, including ammonia (NH4 +) and nitrate (NO3 −), often occurs following nitrification and denitrification reactions in a multiphase interface with the change of dissolved oxygen (DO) and redox. In addition, the extent of heavy metals is diffused from sediments to overlying water. It may cause potential harm to the water quality of the reservoir. This chapter is separated into two parts: (1) The release of nitrogen and phosphorus from sediment is investigated in typical Chinese reservoirs; (2) The release of metals from sediment is investigated in typical Chinese reservoirs.