[Removal Efficiency and Mechanism of Ammonia Nitrogen in a Low Temperature Groundwater Purification Process].

To explore the mechanism and efficiency of ammonia nitrogen removal, a pilot-scale biofilter for the simultaneous removal of high concentrations of iron, manganese, and ammonia nitrogen[Fe(Ⅱ) 11.9-14.8 mg·L-1, Mn(Ⅱ) 1.1-1.5mg·L-1, and NH4+-N 1.1-3.2 mg·L-1] from low temperature(5-6℃) groundwater was operated in a water supply plant in Northeast China. Results indicated excellent performance for ammonia nitrogen removal during the initial start-up stage. According to theoretical analysis and experimental verification, TNloss was driven by the adsorption of ammonia nitrogen by iron oxides, and the conversion of ammonia nitrogen into nitrate nitrogen occurred via biological nitrification. When the concentration of ammonia nitrogen increased, due to limited adsorption sites, the adsorption capacity of iron oxides remained stable at approximately 1 mg·L-1. For the same period, the amount of ammonia nitrogen removal via oxidation continued to increase, with higher quantities removed in the upper filter layer than in the lower filter layer. Dissolved oxygen(DO) is the limiting factor in the further increase in the removal of ammonia nitrogen by oxidation. With an increase in the filtration rate, the adsorption time of ammonia nitrogen by iron oxides was shortened, and the adsorption amount was reduced. Meanwhile, the shortening of EBCT reduced the ammonia nitrogen removed by nitrification under the action of nitrifying bacteria in the unit volume of the filter material. Based on these findings, it is recommended that the thickness of the filter layer should be increased to improve ammonia nitrogen removal performance.

[Effect of Filter Speed and Water Quality on Ammonia Removal in Groundwater Containing Iron, Manganese, and Ammonia at Low Temperature].

In a groundwater plant we carried out a process operation test of biological removal of iron and manganese nitrification coupled with completely autotrophic ammonium removal over nitrite (CANON) (Fe(Ⅱ) 2.91-6.35 mg·L-1, Mn(Ⅱ) 0.47-0.98 mg·L-1, NH4+-N 1.15-2.26 mg·L-1) at low temperature (6-8℃), to explore the effects of filter speed and water quality on ammonia nitrogen removal. The results showed that the mature low-temperature biological filter column, which had been out of service for one month, was cultured for 40 days at a filtration rate of 2 m·h-1 and successfully started. In this process, when the water inlet concentration remained the same, the improved filter speed would reduce the efficiency of ammonia nitrogen capture by the filter column, increase the concentration of ammonia nitrogen in the depth of the filter layer, and improve the efficiency of ammonia nitrogen ions capture by anaerobic ammonia oxidation bacteria (AnAOB) in the depth of the filter layer, so that the ammonia nitrogen removed by CANON in the water increased, while the ammonia nitrogen removed by nitrification decreased. When the filter speed remained unchanged, the concentration of ammonia nitrogen in water was increased to make the ammonia nitrogen with higher concentration enter the filter layer, which increased the concentration of ammonia nitrogen in the zone where ammonia nitrogen and nitrous nitrogen coexist, and improved the net catching efficiency of AnAOB on ammonia nitrogen ions in the filter layer, thus resulting in an increase in ammonia nitrogen removed by CANON.

[Low Temperature Ammonia Nitrogen Removal from an Iron, Manganese, and Ammonia Groundwater Purification Process with Different Concentrations of Iron and Manganese].

In a groundwater plant, removal of iron, manganese, and ammonia nitrogen was performed via a purification process using a filter column at a low temperature (5-6℃). Iron, manganese and ammonia [Fe(Ⅱ) 0-19.26 mg·L-1, Mn(Ⅱ) 0.52-2.05 mg·L-1, and NH4+-N 0.37-2.59 mg·L-1] were analyzed to explore the ammonia nitrogen removal efficiency under different iron and manganese concentrations. The results showed that when the concentration of manganese in the inlet water was maintained at approximately 0.6 mg·L-1 and the concentration of ferrous iron in the inlet water was increased, with the increase of iron oxides in the filter layer, the ratio of ammonia nitrogen removed by adsorption of iron oxides increased, while the ratio of ammonia nitrogen removed by nitrification will decreased and adsorption preceded nitrification. When the concentration of ferrous iron in the water was maintained at approximately 8 mg·L-1and 11 mg·L-1, and the concentration of manganese in the water was increased, the proportion of ammonia nitrogen removed by adsorption did not increase with the increase of manganese oxide, and the removal route of ammonia nitrogen hardly changed. This is because less manganese oxides were formed 20 cm before the filter layer, which had little effect on the ammonia nitrogen adsorbed in this range. The production area of manganese oxides was concentrated below 20 cm of the filter layer, and most ammonia nitrogen was removed by adsorption and nitrification before this area, and the manganese oxides in this area did not adsorb ammonia nitrogen.

[Identification of the meiotic events in grasshopper spermatogenesis].

The grasshoppers are ideal materials to study various meiotic stages of spermatogenesis due to their easy availability, fairly large chromosomes, and fewer numbers of chromosomes. It is easy to make temporary squash preparation of grasshopper testes; however, it is usually difficult for the beginners to differentiate between stages of meiosis. In view of this, we demonstrated the method of identification of meiotic stages by chromosome number and chromosome conformation, taking spermatogonial meiosis of Locusta migratoria manilensis as an example. We described briefly the mitosis of spermatogonia and the spermatogenesis of this species as well.