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1.
The aim of the study was to investigate the nutrient removal rate of three wastewater protozoan isolates. The study was carried out in a laboratory-scale batch reactor for a period of 120 h. in a four batch study. Aliquot samples were withdrawn from the reactor every 24 h. for the analysis of phosphate, nitrate, nitrite, ammonia, chemical oxygen demand, dissolved oxygen and pH, using standard methods. The results obtained in the different batches among the three isolates showed PO4 2? removal rate ranging from 0.04 to 0.52 mg-PO4 2?/L/h. while NO3 ? nitrate removal rates ranged from 0.08 to 0.16 mg-NO3 ?/L /h. Also NO2- and NH3 rates were observed to range between 0.022 and 0.087 mg-NO2 ?/L /h. 0.05 and 0.16 mg-NH3 ?/L /h, respectively. For the physicochemical parameters, there was no observed COD decrease; rather there was an increase and this was irrespective of isolates and experimental batches. However, dissolved oxygen concentration decreased drastically (below 1 mg/L) at the end of each batch while pH show a decrease after an initial 24 h. period and thereafter increased. This trend was also irrespective of isolates and experimental batches. Overall, the study has been able to show the effect of the test isolates on nutrient removal rates and other physicochemical parameters (COD, DO and pH) in activated sludge mixed liquor.  相似文献   

2.
The kinetics of Mn(II) oxidation by the bacterium Leptothrix discophora SS1 was investigated in this research. Cells were grown in a minimal mineral salts medium in which chemical speciation was well defined. Mn(II) oxidation was observed in a bioreactor under controlled conditions with pH, O2, and temperature regulation. Mn(II) oxidation experiments were performed at cell concentrations between 24 mg/L and 35 mg/L, over a pH range from 6 to 8.5, between temperatures of 10°C and 40°C, over a dissolved oxygen range of 0 to 8.05 mg/L, and with L. discophora SS1 cells that were grown in the presence of Cu concentrations ranging from zero to 0.1 μM. Mn(II) oxidation rates were determined when the cultures grew to stationary phase and were found to be directly proportional to O2 and cell concentrations over the ranges investigated. The optimum pH for Mn(II) oxidation was approximately 7.5, and the optimum temperature was 30°C. A Cu level as low as 0.02 μM was found to inhibit the growth rate and yield of L. discophora SS1 observed in shake flasks, while Cu levels between 0.02 and 0.1 μM stimulated the Mn(II) oxidation rate observed in bioreactors. An overall rate law for Mn(II) oxidation by L. discophora as a function of pH, temperature, dissolved oxygen concentration (D.O.), and Cu concentration is proposed. At circumneutral pH, the rate of biologically mediated Mn(II) oxidation is likely to exceed homogeneous abiotic Mn(II) oxidation at relatively low (≈μg/L) concentrations of Mn oxidizing bacteria.  相似文献   

3.
For treating oily sludge, wet peroxide oxidation (WPO) and catalytic wet oxidation (CWO) were investigated. The CWO experiment was carried out in a 0.5?L batch reactor using FeCl3 as catalyst. By using WPO, the effects of reaction parameters such as residence time, temperature, H2O2 excess, and initial COD were investigated. The results demonstrated that >80?% chemical oxygen demand (COD) was removed by CWO and >90?% COD was removed by WPO. Significantly, more of COD could be removed from the oily sludge by adding H2O2 in small doses. In conclusion, WPO was much more effective in the removal of organic compounds from oily sludge.  相似文献   

4.
Landfill leachate treatment was investigated using two anaerobic/aerobic sequencing batch reactors inoculated with suspended growth-activated sludge (ASBR) and aerobic granular sludge (GSBR). The total ammonium nitrogen (TAN) concentration in the GSBR influent was as high as 1200 mg/L with an average TAN removal efficiency of 99.7%. However, the ASBR treatment did not show a consistent performance in TAN removal. The TAN removal efficiency decreased with increasing ammonium concentration in the influent. Aerobic granular sludge was found to be more resistant to free ammonia (FA). In the GSBR, nitrification was partially inhibited at FA concentration from 48 to 57 mg/L, which was two times more than the FA concentration that inhibited nitrification in the ASBR. Low chemical oxygen demand removal efficiencies were obtained in both reactors, which was associated with the refractory organic content of the leachate used in this study. This resulted in poor phosphorous removal in both treatments. The results prove that aerobic granular sludge is a robust method as compared to suspended-activated sludge to treat leachate containing high levels of TAN and FA.  相似文献   

5.
《Applied Geochemistry》2001,16(9-10):1241-1249
A two-column reactor was designed to remove dissolved As and Cd from contaminated water. The reactor functions by equilibrating the targeted water with CO2 and directing it via saturated flow through a column of crushed siderite. This results in siderite dissolution and an increase in dissolved Fe(II). The feedwater is then directed into the top of a second, aerated column of crushed limestone, where it passes by unsaturated flow. The Fe2+ ion oxidizes quickly to Fe3+ and precipitates as Fe(III) oxyhydroxide, which is an effective sorbent of AsO43−. The aeration that occurs in the second column also removes dissolved CO2 from the feedwater. This causes precipitation of Ca and Cd carbonates. Together, the two processes reduce As and Cd concentrations from 1 and 3 mg/l, respectively, to below detection (respectively <0.005 and <0.01 mg/l). A time-limited reduction in Cr concentration also occurred. Much of the As was removed in the first column of the reactor, because Fe(III) oxyhydroxides also formed there. This was due to oxidation of Fe(II) by Cr(VI) and other oxidants present in the input wastewater. Although As is removed in the reactor columns by a sorption mechanism, the sorbent responsible, Fe(III) oxyhydroxide, is continuously produced during the operation of the reactor. Thus, unlike attenuation in a system with a fixed amount of sorbent, breakthrough of the As contaminant should never occur.  相似文献   

6.
Exposure to high concentration of nitrate through drinking water poses a threat to human health and environment. Electrocoagulation (EC) is an alternative water treatment process that involves electrogeneration of coagulant agents. In the present study, EC was exerted for the nitrate removal in a batch reactor using aluminum and iron anodes simultaneously. The effects of the main parameters including electrical current, initial pH, NaCl dosage, initial nitrate concentration and presence of turbidity on NO3 ? removal were investigated. NO2 ? as a by-product was monitored during electrolysis, and nitrate–nitrite index was calculated. The results indicated that optimum condition was pH of 5, 300 mA electrical current, 100 mg/L NaCl and electrolysis time of 40 min, under which removal efficiency was 81.5 %. Nitrite anion was generated during electrolysis of nitrate solution which increases nitrate–nitrite index at the first reaction time, and it was eliminated after 20-min electrolysis time. Reaction kinetic of nitrate removal in the absence and presence of turbidity was first-order and zero-order, respectively.  相似文献   

7.
Passive treatment systems for mine drainage use no energy other than gravity, but they require greater area than active treatment systems. Researchers are considering “hybrid” systems that have passive and active components for increased efficiency, especially where space limitations render passive-only technology ineffective. Flow-through reactor field experiments were conducted at two large net-alkaline anthracite mine discharges in central Pennsylvania. Assuming an Fe removal rate of 20 g m−2 day−1 and Fe loading from field data, 3.6 × 103 and 3.0 × 104 m2 oxidation ponds would be required for the passive treatment of Site 21 and Packer 5 discharges, respectively. However, only a small area is available at each site. This paper demonstrates aeration to drive off CO2, increase pH, and increase Fe(II) oxidation rates, enabling treatment within a small area compared to passive treatment methods, and introduces a geochemical model to accurately predict these rates as well as semi-passive treatment system sizing parameters. Both net-alkaline discharges were suboxic with a pH of ≈5.7, Fe(II) concentration of ≈16 mg L−1, and low Mn and Al concentrations. Flow rates were ≈4000 L min−1 at Site 21 and 15,000 L min−1 at Packer 5. Three-h aeration experiments with flow rates scaled to a 14-L reactor resulted in pH increases from 5.7 to greater than 7, temperature increases from 12 to 22 °C, dissolved O2 increases to saturation with respect to the atmosphere, and Fe(II) concentration decreases from 16 to <0.05 mg L−1. A 17,000-L pilot-scale reactor at Site 21 produced similar results although aeration was not as complete as in the smaller reactor. Two non-aerated experiments at Site 21 with 13 and 25-h run times resulted in pH changes of ?0.2 and Fe(II) concentration decreases of less than 3 mg L−1.  相似文献   

8.
Hydroxylamine, a very important intermediate in nitrification, has a direct relationship with the production of nitrous oxide in biological wastewater treatment processes. The spectrophotometric method taking ferric ammonium sulfate and 1, 10-phenanthroline as the oxidant and the chromogenic agent, respectively, was used to determine the concentration of hydroxylamine in biological wastewater treatment processes. The impacts of nitrite, nitrate, orthophosphate, calcium ion and trace elements on the method were examined. The results indicated that the spectrophotometric method can be used for the determination of hydroxylamine in biological wastewater treatment processes. The correlation was significant in the range of 0.02–1.00 mg N/L (y = 1.5078x ? 0.0132, R 2 = 0.9991), and the range varied to 0.05–1.00 mg N/L when nitrite and orthophosphate presented. Nitrate, calcium ion and trace elements did not interfere with the determination of hydroxylamine nitrogen. When the concentrations of nitrite nitrogen in the samples were lower than 15.00 mg/L, nitrite had a minor interference on the method. The impacts of orthophosphate on the method were complex. When the concentrations of hydroxylamine nitrogen were higher than 0.10 mg/L, the interference of orthophosphate on the method can be ignored. However, when the concentrations of hydroxylamine nitrogen in the samples were lower than 0.10 mg/L, orthophosphate had significant impacts on the determination, and a numerical method proposed can eliminate the interference of orthophosphate. The spectrophotometric method can determine the concentration of hydroxylamine in biological wastewater treatment processes quickly and conveniently and was helpful to understand the function of NH2OH in N2O production in biological wastewater treatment processes.  相似文献   

9.
Removal of Congo red from textile wastewater by ozonation   总被引：7，自引：6，他引：1  
Congo red, which has a complex molecular structure with various diazo aromatic groups, is widely used in textile industry as an anionic dye. The purpose of this study was to investigate the degradation of Congo red in laboratory solution which had the chemical properties of the rinse waters of textile manufacturing dye-houses and the samples with Congo red alone wastewater by ozonation and to optimize the reaction parameters such as pH and time which influence the efficiencies of total organic carbon, total kjeldahl nitrogen and chemical oxygen demand removal. Ozonation of Congo red dye were carried out in a semi-batch reactor with constant ozone flow rate and concentration of 23 mL/sec and 13.6 mg/L, respectively. Decolorization was complete within a few minutes of ozonation possibly due to the cleavage of chromophore groups. It was observed that its structural destruction occurs predominantly at higher pHs. The reduction of chemical oxygen demand and destruction of the dye was more than 60 % and 42 %, respectively. Total kjeldahl nitrogen removal was accompanied by slight changes in nitrogen oxides. It can be deduced from the experimental results that: (a) the mineralization is very weak; (b) the reaction follows the indirect mechanism; i.e., the interaction of hydroxyl radicals with the dye and (c) the nitrification is rather predominant. Biological oxygen demand is declined in simulated alkalic and neutral samples respectively. At 13.6 mg O3/L, the biological oxygen demand levels were significantly enhanced. This might be attributable to the enhancement of its biodegradation at alkaline pHs.  相似文献   

10.
One of the technologies used for wastewater nitrogen removal consists in simultaneous nitrification–denitrification. The low microbial growth rate and the low availability of organic material for the denitrification stage make it necessary to study new operational conditions and the use of microbial supports. The aim of this study was to evaluate the operational behavior of a simultaneous nitrification–denitrification process in a sequential batch reactor utilizing zeolite as a biomass support and step-feed strategy. Two reactors of 2 L were used, one with zeolite and another without zeolite, both operated at constant temperature (31 °C), varying nitrogen loading rate (NLR) from 0.041 to 0.113 kg total Kjeldahl nitrogen (TKN/m3/day). After 209 days, removals higher than 86 and 96 % in nitrogen compounds and organic matter were obtained, respectively. There was not accumulation of nitrate and nitrite in any case; this means that there was a simultaneous nitrification–denitrification in the reactors. The incorporation of zeolite in the system held higher concentration of biomass in the reactor; this led to reduce start-up to 21 days and to improve 11.31 % removal kinetic. The use of a step-feed strategy prevents events of inhibition by substrate, even duplicating tolerance to higher NLR for the same operation time.  相似文献   

11.
In this study, the performance of moving-bed biofilm sequencing batch reactor in operating the anaerobic/anoxic/oxic (A2O) process for treatment of wastewaters containing nitrogen and phosphorous was evaluated. For this purpose, a pilot system with two bench-scale sequencing batch reactors with a total volume of 30 L and functional volume of 10 L was used. The installation was elaborated using plexiglass, in which 60% of the functional volume consisted of PVC suspended carriers (Kaldnes K3) with a specific surface area of 560 m2/m3. The independent variables used in this study were hydraulic retention time (HRT) (1.5, 2, 2.5, 3, and 3.5 h) and the initial organic load (300, 500, 800, 1000 mg O2/L). The results showed impressive performance in the case of an initial organic load of 300 mg O2/L and HRT of 3 h with maximum removal of COD and TN, respectively, by 95.1 and 89.8%. In the case of an initial organic load of 1000 mg O2/L and HRT of 3.5 h, the maximum total phosphorus removal was 72.3%. Therefore, according to the analysis of data obtained by different HRTs, it was revealed that the system of A2O has greater efficiency in removing organic matter from wastewater in the shortest possible time.  相似文献   

12.
Low- and high-concentration nitric wastewater can induce stable nitrite accumulation and realize the nitrification system, with the nitrite accumulation rate between 50% and 90%. In the low-concentration nitrite nitrification system, the average FA concentrations during the period of stable nitrite accumulation remained at 7 to 10 mg/L. In the high-concentration nitrite nitrification system, the nitrogen oxidation activity will not be affected by biomass, the nitrite oxidation activity is related to the system biomass, it is recommended to be measured by FA/MLSS. Keeping the FA sludge load below 0.1 is the precondition of making good nitrite accumulation and nitrogen degradation rate. Nitrite oxidation bacteria cannot be totally eliminated or washed out from the system.  相似文献   

13.
In the present work, a continuous catalytic wet peroxide oxidation fixed bed reactor was employed to treat a simulated wastewater sample with malachite green dye, as a contaminant. Natural perlite particle-supported nano-Fe3O4 catalyst was used as a fixed bed inside a reactor, and it was immobilized by a persistent magnetic field. The range of (perlite) particle sizes was from 100 to 1000 nm. The effects of various operating parameters, including temperature of the reactor, pH, initial hydrogen peroxide concentration and initial dye concentration, were investigated on the percentage removal of malachite green dye. Load of catalyst of 2 g and volumetric flow rate of 1 L/h were selected for all the tests. Maximum malachite green degradation was 99.5 ± 0.3%. This removal percentage was attained at temperature of 80 °C, pH = 6, initial dye concentration of 6 mg/L and initial hydrogen peroxide concentration of 100 mg/L. The process was isotherm, and the catalyst showed high catalytic activity in the steady-state condition. The loss of catalyst was less than 0.3%.  相似文献   

14.
Sulfate-reducing bacteria (SRB) are ubiquitous in anoxic environments where they couple the oxidation of organic compounds to the production of hydrogen sulfide. This can be problematic for various industries including oil production where reservoir “souring” (the generation of H2S) requires corrective actions. Nitrate or nitrite injection into sour oil fields can promote SRB control by stimulating organotrophic nitrate- or nitrite-reducing bacteria (O-NRB) that out-compete SRB for electron donors (biocompetitive exclusion), and/or by lithotrophic nitrate- or nitrite-reducing sulfide oxidizing bacteria (NR-SOB) that remove H2S directly. Sulfur and oxygen isotope ratios of sulfide and sulfate were monitored in batch cultures and sulfidic bioreactors to evaluate mitigation of SRB activities by nitrate or nitrite injection. Sulfate reduction in batch cultures of Desulfovibrio sp. strain Lac15 indicated typical Rayleigh-type fractionation of sulfur isotopes during bacterial sulfate reduction (BSR) with lactate, whereas oxygen isotope ratios in unreacted sulfate remained constant. Sulfur isotope fractionation in batch cultures of the NR-SOB Thiomicrospira sp. strain CVO was minimal during the oxidation of sulfide to sulfate, which had δ18OSO4 values similar to that of the water-oxygen. Treating an up-flow bioreactor with increasing doses of nitrate to eliminate sulfide resulted in changes in sulfur isotope ratios of sulfate and sulfide but very little variation in oxygen isotope ratios of sulfate. These observations were similar to results obtained from SRB-only, but different from those of NR-SOB-only pure culture control experiments. This suggests that biocompetitive exclusion of SRB took place in the nitrate-injected bioreactor. In two replicate bioreactors treated with nitrite, less pronounced sulfur isotope fractionation and a slight decrease in δ18OSO4 were observed. This indicated that NR-SOB played a minor role during dosing with low nitrite and that biocompetitive exclusion was the major process. The results demonstrate that stable isotope data can contribute unique information for understanding complex microbial processes in nitrate- and sulfate-reducing systems, and offer important information for the management of H2S problems in oil reservoirs and elsewhere.  相似文献   

15.
Estuaries act as an organic matter and nutrient filter in the transition between the land, rivers and the ocean. In the past, high nutrient and organic carbon load and low oxygen concentration made the Elbe River estuary (NW Europe) a sink for dissolved inorganic nitrogen. A recent reduction in loads and subsequent recovery of the estuary changed its biogeochemical function, so that nitrate is no longer removed on its transition towards the coastal North Sea. Nowadays in the estuary, nitrification appears to be a significant nitrate source. To quantify nitrification and determine actively nitrifying regions in the estuary, we measured the concentrations of ammonium, nitrite and nitrate, the dual stable isotopes of nitrate and net nitrification rates in the estuary on five cruises from August 2012 to August 2013. The nitrate concentration increased markedly downstream of the port of Hamburg in summer and spring, accompanied by a decrease of nitrate isotope values that was clearest in summer exactly at the location where nitrate concentration started to increase. Ammonium and nitrite peaked in the Hamburg port region (up to 18 and 8 μmol L?1, respectively), and nitrification rates in this region were up to 7 μmol L?1 day?1. Our data show that coupled re-mineralization and nitrification are significant internal nitrate sources that almost double the estuary’s summer nitrate concentration. Furthermore, we find that the port of Hamburg is a hot spot of nitrification, whereas the maximum turbidity zone (MTZ) only plays a subordinate role in turnover of nitrate.  相似文献   

16.
Enrichment of molybdenum (Mo) in reducing sediments due to authigenic fixation in anoxic interstitial waters could provide an indicator of hypoxic conditions that integrates over substantial temporal extents. Sediments maintained under controlled dissolved oxygen (DO) conditions showed elevated concentrations of Mo when exposed to low DO concentrations. Mo accumulation was linearly related to time of exposure in treatments below 2.8 mg O2/L, with less or no accumulation at higher concentrations. Rates of accumulation were independent of DO concentration below 2.8 mg/L. Accumulation occurred at DO concentrations higher than those limiting accumulation in field settings, with rates in the lowest treatments similar to those in sediments of deep basins with restricted circulation and low DO concentrations.  相似文献   

17.
百花湖水体氮的空间分布研究   总被引：2，自引：1，他引：1  
初步探讨了百花湖水体中氮的空间分布特征,并分析了氮及溶解氧(DO)的相关性。对8个站位的表层、4m、8m及12m水体中总氮、氨氮、硝酸盐氮、亚硝酸盐氮及溶解氧进行了测定。结果表明,百花湖水体中总氮的平均含量为1.18mg/L,氨氮的平均含量为0.144mg/L,硝酸盐氮的平均含量为0.20mg/L,亚硝酸盐氮的平均含量为0.018mg/L。百花湖入湖口附近的1号采样点总氮、氨氮和硝酸盐氮的平均浓度都较其它采样点高。分析表明百花湖中DO浓度与硝酸盐氮和亚硝酸盐氮呈负相关,相关系数分别为-0.629、-0.724。   相似文献   

18.
In this work, a new process called advanced reduction process (ARP) was used for nitrate removal from water. This ARP process combines sodium dithionite as reducing agent with ultraviolet irradiation using medium pressure lamps (UV-M) as an activating method. Experimental results showed that UV-M/S2O4 2? process achieved almost complete removal of nitrate from aqueous solutions containing 25 mg NO3 ?/L using stoichiometric dose of dithionite of 68.8 mg/L at neutral pH conditions. Analysis of final products and material balance confirmed that NO3 ? ions were reduced to ammonium with formation of nitrite as intermediates in addition to the formation of small amounts of volatile species, mainly ammonia and nitrogen gas. Effects of certain experimental parameters including dithionite dose, initial pH, initial nitrate concentration, and UV light source on the kinetics and efficiency of nitrate reduction were evaluated. Increasing dithionite dose augmented the rate of nitrate reduction and enhanced the efficiency of ARP process. Dithionite doses higher than stoichiometric ratios led to complete removal of nitrate in shorter reaction time. UV-M/S2O4 2? process was found to be effective only under neutral pH or alkaline conditions, and its removal efficiency is negligible in acidic medium (pH < 4). Irradiation with UV-M was more effective than low pressure or narrow band lamps. These results can be attributed to the contribution of several mechanisms for nitrate reduction to ammonium. These include the following: direct photolysis, chemical reduction of nitrate dithionite, and mediated reduction of nitrate by free reducing radicals.  相似文献   

19.
本文通过两组不同水镁石-苯酚投料比的实验,研究固体沉淀物与水质变化的关系。实验显示,水镁石解离出的Mg2+与苯酚降解的中间产物能形成难溶盐,并发生沉淀分离,促进含苯酚废水臭氧化降解的效率。当苯酚的初始浓度为47 g/L,初始碳镁原子比(C/Mg)为30时,经3小时充分臭氧化曝气后,投加的水镁石全部耗尽。XRD、TG/DSC结果显示新形成的沉淀物为草酸镁。反应终点的pH值在4以下,TOC去除率为40%。当体系的初始C/Mg(原子比)为1,苯酚的初始浓度为1.5 g/L时,同样的臭氧化曝气过程体系残留的沉淀物仍是水镁石。反应终点的pH值在10左右,TOC去除率为92.8%。研究证明,苯酚臭氧化过程也是体系酸化的过程,至少在高C/Mg比条件下新生的质子能与水镁石解离出的羟基中和,水镁石解离出的Mg2+可与草酸根结合沉淀出草酸镁。  相似文献   

20.
《Geochimica et cosmochimica acta》1999,63(19-20):3301-3310
The weathering rate of sedimentary organic matter in the continental surficial environment is poorly constrained despite its importance to the geochemical carbon cycle. During this weathering, complete oxidation to carbon dioxide is normally assumed, but there is little proof that this actually occurs. Knowledge of the rate and mechanisms of sedimentary organic matter weathering is important because it is one of the major controls on atmospheric oxygen level through geologic time.We have determined the aqueous oxidation rates of pyrite-free bituminous coal at 24° and 50°C by using a dual-cell flow-through method. Coal was used as an example of sedimentary organic matter because of the difficulty in obtaining pyrite-free kerogen for laboratory study. The aqueous oxidation rate obtained in the present study for air-saturated water (270 μM O2) was found to be on the order of 2 × 10−12 mol O2/m2/s at 25°C, which is fast compared to other geologic processes such as tectonic uplift and exposure through erosion. The reaction order with respect to oxygen level is 0.5 on a several thousand hour time scale for both 24° and 50°C experiments. Activation energies, determined under 24° and 50°C conditions, were ≈40 kJ/mol O2 indicating that the oxidation reaction is surface reaction controlled.The oxygen consumption rate obtained in this study is two to three orders of magnitude smaller than that for pyrite oxidation in water, but still rapid on a geologic time scale. Aqueous coal oxidation results in the formation of dissolved CO2, dissolved organic carbon (DOC), and solid oxidation products, which are all quantitatively significant reaction products.  相似文献   

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