|Place of Conferral||中国科学院大学|
|Keyword||微藻 生物膜 硫酸盐 重金属 Rab反应器|
Gold is an important strategic and financial reserve resource. Due to its scarcity, stable nature and noble features, gold has become necessary in life to some extent. However, the difficulty of gold mining and smelting has increased due to the increasing social demand, which cause the associated environmental problems, especially the discharge of wastewater and waste slag. Jiaodong region in Shandong province is recognized as the main source of gold production in China. The process of gold smelting could generate large amounts of waste acid, raffinate and cyanide containing wastewater, most of which are acidic and contain high concentration of sulfate and heavy metals. However, the current techniques for gold smelting wastewater treatment have many problems, such as high cost, hardly meet the wastewater discharge standards, and low reuse rate of reclaimed water, etc. Nonetheless, generally the wastewater in the smelting area is usually the mixed wastewater of smelting wastewater and domestic wastewater. The mixed wastewater contains large amounts of pollutants including carbon, nitrogen and phosphorus, which greatly improves the biodegradability of the wastewater in such area. Therefore, it is particularly important to develop new treatment techniques for gold smelting wastewater treatment and realize the utilization of wastewater resources.
Microalgae, a group of primary organisms, which are capable of performing photosynthesis and can be used in many fields including food and health care industries, cosmetics industries, animal feed industries, bioenergy, carbon sequestration, wastewater treatment and so on. Generally, wastewater often contains large amount of carbon, nitrogen, phosphorus, sulfur and other nutrients, which are necessary for the growth of microalgae. Meanwhile, microalgae have strong ability in absorbing heavy metal ions. Therefore, wastewater treatment by microalgae can realize both environmental protection and the cultivation of microalgae biomass. It is significant to investigate treating gold smelting wastewater using microalgae by studying the growth of microalgae in relatively extreme water environment, the performance of wastewater treatment, and the subsequent direct use of microalgae for industrial wastewater and polluted water treatment and the restoration.
Our study was carried out using two different microalgae cultivation systems, which were the suspended microalgae cultivated by bubble column and the algal biofilm cultivated by the Rotating Algal Biofilm (RAB) reactor created by our lab. The wastewater around the gold smelting area in Yantai region has high concentrations of sulfate and heavy metals such as nickel, zinc, cobalt, chromium. Aiming at the features above, the growth of microalgae in the synthetic wastewater containing high concentration of sulfide and sulfate was evaluated. The results indicated that the growth of suspended algal cells were completely inhibited at high concentration of sulfide, but showed the best growth performance at 1g/L SO42-, pH of 9 and hydraulic retention time (HRT) of 10 days. The suspended microalgae cultivation system showed the best TN and COD removal efficiency, which are 84% and 99% respectively. However, the removal performance of TP and SO42- were poor. The TP concentration of the effluents was even higher than that of the influents, and the SO42- removal efficiency of most conditions were around 20%. What’s more, the cell waste problem happened in the continuous suspended culture mode.
The treatment performance of the acidic high sulfate (1g/L, 2g/L, 4g/L) synthetic wastewater treated by the algal biofilm was studied particularly using the RAB reactor. The long-term operation status of the RAB reactor in this water environment was also monitored. The results showed that the algal biofilm in RAB reactor had a sulfate removal efficiency of 46% and a removal rate of 0.56g/L-day. The removal performances of the algal biofilm on ammonia, TP and COD in the acidic synthetic wastewater were excellent, with the removal rate up to 82.64%, 99.69% and 98.90%, respectively. The sulfur content in the biomass were detected by inductively coupled plasma spectrometry (ICP-MS). The results showed that the biomass sulfur content increased with the increase of SO42- concentrations, indicating that the algal biofilm could effectively absorb sulfate in the synthetic wastewater system. The variation of the microbial community of the algal biofilms treating the acidic sulfur-containing synthetic wastewater was characterized by high-throughput sequencing technology. The results showed that the algal biofilms in RAB reactor had a high species richness of microbial communities, including various cyanobacteria, green algae, diatoms and acid reducing bacteria, etc. The work further studied the sulfur removal mechanism of microalgae, which laid a foundation for the subsequent research on the treatment of gold smelting wastewater by microalgae.
The adsorption performance of nickel (Ni (II)), zinc (Zn (II)), cobalt (Co (II)) and chromium (Cr (II)) by suspended microalgae and algal biofilm was studied. Within the typical concentration range of industrial wastewater, the four metal ions (nickel, zinc, cobalt and chromium) were prepared to reach a concentration of 81.75mg/L, 0.292mg/L, 99mg/L and 25mg/L, respectively. The adsorption performance of microalgae on heavy metal ions increased with the increase of the biomass loading, with the removal efficiencies of nickel, zinc, cobalt and chromium of almost 100%. What’s more, the algal biofilm showed better adsorption performance of nickel, zinc and chromium than the suspended microalgae. The fluorescence confocal microscopy results showed that the content of EPS in microalgae biofilms was much higher than that in suspended microalgae, which was the reason for the better adsorption performance of microalgae biofilms on heavy metals than that of suspended microalgae. The kinetic parameters of metal adsorption followed the pseudo-second order kinetics, and the adsorption behavior could be interpreted by the Freundlich isotherm model. Furthermore, take nickel as the model metal ion, the growth performances of the suspended microalgae and algal biofilm cultivated in the water environment with different nickel concentrations (0, 10, 100, 1000, 5000 mg/L) and different pH (5, 7, 9) were studied. The adsorption mechanism of heavy metal ions by microalgae were also studied. The results showed that compared to suspended microalgae, the algal biofilm can tolerate a nickel concentration as high as 5000 mg/L. The nickel removal efficiency could reach to 90% at the initial nickel concentration of 100-1000 mg/L and the algal biofilm could realize the growth in such environment. The SYTOX Green dye analytical method was used to distinguish the membrane-damaged cells from the intact cells in the biomass of suspended microalgae and algal biofilm after adsorption of nickel. The results showed that the amount of intact cells in the algal biofilm was higher than that in suspended microalgae, which was contributed to the protection by large amounts of EPS in algal biofilm.
The growth of algal biofilm and pollutant removal performances in RAB reactors were studied in synthetic wastewater with sulfate concentration of 1000 mg/L and nickel concentration of 80 mg/L. The results showed that the algal biofilm could grow and removal nutrients in the synthetic high sulfate and heavy meatal containing wastewater. The existence of nickel could affect the sulfate removal performance by the algal biofilm to some extent.
The research showed that compared with the traditional suspended microalgae cultivation system, the biofilm cultivation system based on RAB reactors had better tolerance of high concentration sulfate environment and high concentration of heavy metals environment, and showed good growth performance in the synthetic wastewater with both the high concentration sulfate and heavy metals, succeding in removing pollutants in water. The results are significant for the further study of utilizing microalgae in the treatment of wastewater in mining smelting area.
|MOST Discipline Catalogue||工学|
|周浩媛. 微藻对高硫酸盐及重金属模拟废水的处理与机理研究[D]. 中国科学院大学. 周浩媛,2019.|
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