[Study the effect of insecticides commonly used locally on the bacteria of economic importance in the soil]

This study aims to identify the effect of different concentrations of insecticides the common dorspan and decis on the total number of Nitrosomonas, Nitrobacter and cellulose degradation bacteria in the soil during the winter and spring of the agricultural season 2012/2013 has been selected for two insecticide fixed rates [half - the same - twice] concentration, was treated soil with two insecticide both individually and prescribed for each concentration of insecticide using spraying machine 10-liter, with a smaple treatmen without. Results insecticides showed its effect on bacterial groups, and has been associated it effect by quantity additive concentration, dropped the numbers of Nitrosomonas, Nitrobacter and cellulose degradation at twice and provided for it, that continued period of time after soil treatment to make sure their influence in general and not because of decline amount of the required nitrogen for the decompose of organic carbon, while it did not affect half concentration of two insecticides on the numbers of Nitrosomonas and degradation of cellulose bacteria, it returned to increase in recent weeks indicating the biodecomposition of insecticide and there is no inhibitory effect of this concentration on the two groups. For Nitrobacter, the numbers decreased in the half concentration of two insecticides in recent weeks after increase it in the first few weeks but dorspan returned to the increase in the last week which shows the cumulative effect of Decis, while dorspan decline the numbers by decreasing the amount of the insecticide and the occurrence of biodecomposition and there is no accumulative effect of this insecticides. Comparing insecticides show that the effect of high concentrations of two insecticides similar on the number of economically important groups, while differed effect the half concentration on Nitrobacter for Nitrosomonas and degradation of celluiose bacteria, which were similar in this concentration too Through statistical analysis shows that there is a highly significant of the interaction between the type of insecticide and concentration, and the insecticide depends on the concentration to show the impact on the numbers of Nitrification and cellulose degradation bacteria at the level of of significance 0.05

Analysis of microbial diversity of nitrifying bacteria by terminal restriction fragment length polymorphism / 生物工程学报

We analyzed the microbial diversity and quantity of nitrifying bacteria in the enrichment reactor by Terminal Restriction Fragment Length Polymorphism (T_RFLP), a cultured-independent molecular technique. The result indicated that nitrobacteria enriched the best, and the diversity index decreased 62.80% compared with the initial data. Nitrobacteria were predominant in the reactor. Meanwhile, we studied the microbial diversity before and after adding Nitrobacteria into shrimp ponds, and analyzed several major bacterial species that existed stably in the pond. According to the analysis by T_RFLP program, species including Brevibacillus brevis, Microbacterium lactium, Azoarcus indigens and Bordetella holmesii were the dominant bacteria in the ponds.

Effect of osmotic pressure on nitrification / 生物工程学报

The effect of osmotic pressure on nitrification was investigated in the internal-loop air-lift nitrifying reactor. When influent ammonia concentration is kept at 420mg x L(-1) and influent osmotic pressure is increased from 4.3 to 18.8 x 10(5) Pa, the ammonia conversion of the nitrifying bioreactor is maintained between 93% and 100%. After influent osmotic pressure is further increased to 19.2 x 10(5)Pa, the ammonia conversion goes down to 69.2%. The influence of osmotic pressure on nitrification takes place without any alarm and the critical osmotic pressure is between 18.8 x 10(5) and 19.2 x 10(5) Pa. During osmotic stress, the nitrifying bacterial populations in the activated sludge become simplified, the cell size becomes smaller, the inner membrane becomes less and some unknown inclusion particles are formed. The cell structure is restored as soon as the osmotic pressure is removed. Addition of potassium is able to relieve the effect of osmotic pressure on nitrification. The nitrifying activity of the activated sludge is stimulated by the osmotic stress, and the specific ammonia conversion is increased from 0.083 kg x kg(-1) x d(-1) to 0.509 kg x kg(-1) x d(-1) and 2.569 kg x kg(-1) x d(-1), respectively.

Operation performance of membrane nitrification bioreactor for ammonia-containing wastewater / 生物工程学报

The operation performance of membrane nitrification bioreactor to treat ammonia-containing wastewater as well as the capabilities of separation and filtration of polypropylene membrane modules were tested. The removal efficiency of ammonia was kept higher than 95% when the hydraulic retention time was set at 1 day, the influent concentration was increased up to 80 mmol (NH4+ -N) x L(-1) and the volume loading rate was increased up to 1.12 kg (NH4+ -N) x m(-3) x d(-1). The biomass in the reactor was accumulated from 5 g x L(-1) to 10 g x L(-1) within 50 days, which indicated that polypropylene membrane modules were efficient in retaining biomass. The biomass attached to the membrane also contributed to the conversion of ammonia and nitrite. When the hydraulic pressure was lower than 80cm, the increase of hydraulic pressure improved the permeation of membrane. However, when the hydraulic pressure was beyond 80cm, the increase of hydraulic pressure did not significantly improve the permeation of membrane. The permeate flux was the highest 2.51 (L x m (-2) x h(-1)) but the resistance was the lowest (2.63 x 10(-5)) m(-1) when the hydraulic pressure was about 20 cm. The results showed that the membrane nitrification bioreactor could be run normally without extra energy input.

Ammonification and nitrification of biuret in soils at different moisture levels

In laboratory experiments under three moisture levels [50, 200 and 400% whc] with sandy, sandy loam and clay loam soils, the ammonification and subsequent nitrification of 200 ppm biuret-N was studied. Ammonification was more rapid in heavy than in light textured soils. Mineralization percentages of biuret-N were 25, 27 and 30.2 at 400% whc, in sandy, sandy loam and clay loam soil, respectively, and most mineralized-N was in the form of NH4 +. The corresponding figures at 50% whc were 15, 16 and 21% and most nitrogen was in the NO3 form. NO-2-N accumulated in considerable amount only at 200% whc, and persisted longer in soils which reflect the relative sensitivity of Nitrobacter to anaerobic conditions. Whc, of 400%, inhibited both Nitrosomonas and Nitrobacter and no NO-2 or NO-3 was detected in the soils. Biuret, by itself, at 200 ppm-N had no effect on nitrifying bacteria