Selective inhibition of nitrite oxidation by chlorate dosing in aerobic granules

Partial nitrification was successfully achieved with addition of 5mM KClO(3) in the aerobic granules system. Batch tests demonstrated that KClO(3) selectively inhibited nitrite-oxidizing bacteria (NOB) but not ammonia-oxidizing bacteria (AOB). During stable partial nitrification, the influent pH was kept at 7.8-8.2, while the DO and temperature were not controlled in the SBR. When the NH(4)-N and COD levels were kept at 100mg/l and 400mg/l in the influent, the NH(4)-N and COD removal efficiencies reached 98.93% and 78.65%, respectively. The NO(2)-N accounted for 92.95% of the NO(χ)-N (NO(2)-N+NO(3)-N) in the effluent. Furthermore, about 90% of the chlorate was reduced to nontoxic chloride, thus it would not cause environmental problem. SEM showed that the main composition of the aerobic granules was bacilli and coccus bacteria. FISH analysis revealed that AOB became the dominant nitrifying bacteria, whereas NOB were detected only in low abundance. Chlorate could be used to control the development and maintenance of aerobic granules sludge for partial nitrification.     

Modeling the decay of ammonium oxidizing bacteria

A bench-scale sequencing batch reactor was used to study factors affecting the endogenous decay of the ammonium oxidizing biomass (AOB) in different operating conditions. AOB decay was very sensitive to oxygen concentration, and increased up to 0.4 d⁻¹ for oxygen concentration of 7 mg O₂ L⁻¹. The decay in anaerobic conditions was shown to be very low (0.03 d⁻¹) when compared to literature data.The effect of nitrite and nitrate on AOB decay was also studied. The correlation was quite weak suggesting that both nitrate and nitrite absence had little impact on decay which is contrary to what is typically assumed in some of the existing process models. A simple expression for the decay of AOB was proposed, calibrated and validated using the results of batch kinetic tests and of the continuous sequencing batch reactor monitoring.     

Effects of carbon dioxide deficiency and metal toxicity on biological oxygen demand

In this study, the effects of carbon dioxide (CO₂) deficiency on the biological growth under respirometric conditions, first‐ and second‐order biological oxygen demand (BOD) progressions using two different BOD measurement techniques and metal toxicity effects on the respirometric BOD are investigated. The effects of CO₂ deficiency in the growth of bacteria and related effects on the first‐ and second‐stage BOD progressions are investigated using various media with respirometers in comparison with the BOD dilution method. CO₂ deficiency causes significant retardations on the growth of bacteria and the second‐stage respirometric BOD values are suppressed. CO₂ seems to be an essential nutrient for the growth of microorganisms and for the oxygen uptake progressing rates. HgCl₂, HgSO₄, CuSO₄, K₂Cr₂O₇, ZnSO4 and Al₂(SO₄)₃ inorganic metal compounds cause significant retardations in the respirometric BOD values obtained from a synthetic autotrophic medium. Effects are found to be dependent on the applied concentrations of these chemicals in the medium.     

温度对两种固定化硝化菌硝化反应的影响

通过包埋固定化硝化菌颗粒和生物接触氧化法在不同温度条件下的硝化反应速率测定试验,发现在28℃时两个反应器均达到最大硝化速率,分别为40 mgN/(L.h)和31 mgN/(L.h);温度降至8℃时,硝化速率分别为18 mgN/(L.h)和8 mgN/(L.h),包埋固定化硝化菌在低温条件下显示出明显的优势。温度为20~32℃时,包埋硝化菌处理高氨氮废水很容易形成亚硝酸型硝化。     

Characterization and Treatment of Leachates from Hong Kong Landfill Sites

Development of a large landfill site in the North-Eastern New Territories of Hong Kong, which will receive 25 million m³ of wastes during a life of about 13 years, must include the provision of a scheme to manage leachates which will arise in the tropical climate of the region.
The paper presents detailed results from a study commissioned by the Environmental Protection Department of the Hong Kong Government, to characterize and treat leachates generated by landfills in Hong Kong, in order to design a suitable management scheme. Field and laboratory trials which were carried out during 1989 showed that, although leachates from Hong Kong landfills have some specific characteristics (e.g. concentrations of amm.N to 5000 mg/l), they can be treated to high standards by aerobic biological processes.
As a result of these studies, a scheme has been designed which will provide a high degree of environmental protection in respect of leachate, as the landfill is developed.     

同步短程硝化反硝化研究

分析了现有短程硝化反硝化工艺处理高浓度氨氮废水所存在的问题,试验利用序批式反应器(SBR)的内部水力特性对其进行改造,以畜禽养殖废水为研究对象,从宏观上创造同步硝化反硝化(SND)条件,并实现了同一反应器内短程硝化反硝化的同步进行,改造后系统pH值下降速度减缓,反硝化效率提高,最终出水的亚硝酸盐和硝酸盐浓度分别降低了39%和38%。     

Enhancing nitrification in vertical flow constructed wetland utilizing a passive air pump

Nitrification of simulated secondary effluent solution using a variant of the vertical flow bed constructed wetland was studied. In this system oxygen required for the nitrification process is supplied by a passive air pump. The passive air pump is based on a fill and draw cycle, where oxygen depleted air is removed from the system while fresh air is introduced. Each volume of effluent drained is displaced by an equal volume of fresh air. Spatial and temporal oxygen distribution in the system as a function of drained effluent volume was investigated. Experimental results of nitrification and the corresponding oxygen consumption show good agreement with theoretical calculations based on physico–chemical considerations. Observations show that while oxygen distribution within the media was found to be non-uniform at the beginning of each cycle, it approached more uniform distribution with time. The latter resulted mainly from diffusion of oxygen in the gaseous phase.     

Specific activity of nitrobacter through attachment on granular media

This work represents one stage in the optimization of biological nitrification by attached culture.The utilization of columns packed with fine granular media, such as Biolite, and sterile conditions has enabled the overall nitrite oxidation rates of the pure strain Nitrobacter winogradskyi serotype agilis in attached culture to be measured.The utilization of methods for counting attached bacteria, combined with measurements of the oxygen consumption, has enabled the specific respiratory activity of Nitrobacter in attached culture to be determined and a comparison to be made with the values observed with free cultures.The results obtained show a great increase in the nitrite oxidation rate and a 130% increase in the respiratory activities specific to attached bacteria in comparison with free cells.     

Transformation of calcium cyanamide and its inhibitory effect on urea nitrification in some tropical soils

Transformation of calcium cyanamide and its inhibitory effect on urea nitrification was studied in some tropical soils. Three soils, from Onne, Mokwa and Samaru, representing different agro-climatological zones of Nigeria were incubated with calcium cyanamide, urea or a mixture of both for eight weeks at 30 °C and at field capacity moisture content. The recovery of inorganic N (NH ₄ ⁺ plus NO ₂ ^- plus NO ₃ ^- )from calcium cyanamide varied from 64% to 87% in different soils. Most of the inorganic N accumulated was in NH ₄ ⁺ form. Nitrification of the accumulated NH ₄ ⁺ in all the soils was slow.Urea (75 mg N kg^–1 soil) was completely nitrified within a week in the Samaru and Mokwa soils whereas in the Onne soil the rate of nitrification was slow. Addition of CaCN₂ at the rate of 10 mg N kg^–1 soil generally delayed ammonification of urea and nitrification was severely inhibited in all the soils. Addition of CaCN₂ at the rate of 20 mg N kg^–1 soil further reduced the ammonification of urea and completely inhibited the nitrification. High recovery of inorganic N from calcium cyanamide and its effective reduction of nitrification of urea make it suitable source of N for plants in the tropics, provided it is managed to avoid phyto-toxicity.     

Urea,ammonium sulfate and dicyandiamide transformations in Costa Rican soils

The transformations of urea, ammonium sulfate and dicyandiamide (DCD) were studied in an Inceptisol and three Andisols from Costa Rica, considering the influence of temperature and DCD as a nitrification inhibitor.Nitrification was very slow with or without DCD in the strongly acid Inceptisol. A higher urea dose resulting in higher pH was well nitrified without DCD and appreciably retarded by DCD.In Andisols nitrification was retarded as long as a higher DCD level existed. Higher temperatures accelerated the DCD-breakdown and were followed by a quicker nitrification. The decomposition of DCD was slower compared with the Inceptisol. According to these experiments DCD is suitable as a nitrification inhibitor in tropical soils.