Improving the performance of sequencing batch reactor (SBR) by the addition of zeolite powder

Two types of operation means "SBR reactor alone (control reactor)" and "adding zeolite powder into SBR reactor (test reactor)" were used to treat municipal wastewater. The test results revealed that zeolite powder addition could improve the activity of the activated sludge. It was investigated the specific oxygen utilization rate (SOUR) of the tested zeolite sludge were about double times that of the control activated sludge, and the nitrification rate and settling property of zeolite-activated sludge were both improved. Due to the combination of zeolite adsorption for NH(4)(+)-N and enhanced simultaneous nitrification and de-nitrification (SND), a higher nitrogen removal was observed in test reactor compared to the control reactor, and the addition of zeolite powder is helpful to inhabit sludge bulking. In addition, through long-term parallel shock load test, it was found that the zeolite powder addition could enhance the ability of activated sludge in resisting the shock load of organics and ammonium. Compared to the control activated sludge, zeolite powder added activated sludge could remove COD, NH(4)(+)-N, TN and TP significantly in a shorter cycle time. At the same operational time period, the test SBR could treat wastewater quantity 1.22 times that treated in control SBR.     

Tertiary treatment of textile wastewater with combined media biological aerated filter (CMBAF) at different hydraulic loadings and dissolved oxygen concentrations

An up-flow biological aerated filter packed with two layers media was employed for tertiary treatment of textile wastewater secondary effluent. Under steady state conditions, good performance of the reactor was achieved and the average COD, NH(4)(+)-N and total nitrogen (TN) in the effluent were 31, 2 and 8mg/L, respectively. For a fixed dissolved oxygen (DO) concentration, an increase of hydraulic loading resulted in a decrease in substrate removal. With the increase of hydraulic loadings from 0.13 to 0.78m(3)/(m(2)h), the removal efficiencies of COD, NH(4)(+)-N and TN all decreased, which dropped from 52 to 38%, from 90 to 68% and from 45 to 33%, respectively. In addition, the results also confirmed that the increase of COD and NH(4)(+)-N removal efficiencies resulted from the increase of DO concentrations, but this variation trend was not observed for TN removal. With the increase of DO concentrations from 2.4 to 6.1mg/L, the removal efficiencies of COD and NH(4)(+)-N were 39-53% and 64-88%, whenas TN removal efficiencies increased from 39 to 42% and then dropped to 35%.     

Study on nitrogen removal enhanced by shunt distributing wastewater in a constructed subsurface infiltration system under intermittent operation mode

Subsurface wastewater infiltration system is an efficient and economic technology in treating small scattered sewage. The removal rates are generally satisfactory in terms of COD, BOD(5), TP and SS removal; while nitrogen removal is deficient in most of the present operating SWIS due to the different requirements for the presence of oxygen for nitrification and denitrification processes. To study the enhanced nitrogen removal technologies, two pilot subsurface wastewater infiltration systems were constructed in a village in Shenyang, China. The filled matrix was a mixture of 5% activated sludge, 65% brown soil and 30% coal slag in volume ratio for both systems. Intermittent operation mode was applied in to supply sufficient oxygen to accomplish the nitrification; meanwhile sewage was supplemented as the carbon source to the lower part in to denitrify. The constructed subsurface wastewater infiltration systems worked successfully under wetting-drying ratio of 1:1 with hydraulic loading of 0.081 m(3)/(m(2)d) for over 4 months. Carbon source was supplemented with shunt ratio of 1:1 and shunt position at the depth of 0.5m. The experimental results showed that intermittent operation mode and carbon source supplementation could significantly enhance the nitrogen removal efficiency with little influence on COD and TP removal. The average removal efficiencies for NH(3)-N and TN were 87.7 ± 1.4 and 70.1 ± 1.0%, increased by 12.5 ± 1.0 and 8.6 ± 0.7%, respectively.     

Landfill leachate treatment with a novel process: anaerobic ammonium oxidation (Anammox) combined with soil infiltration system

A novel combined process was proposed to treat municipal landfill leachate with high concentrations of ammonium and organics. This process consisted of a partial nitritation reactor (PNR), an anaerobic ammonium oxidation (Anammox) reactor (AR) and two underground soil infiltration systems (USIS-1 and USIS-2). Based on the optimum operating conditions obtained from batch tests of individual unit, the combined process was continuously operated on a bench scale for 166 days. Partial nitritation was performed in a fixed bio-film reactor (PNR, working volume=12 L). Ammonium nitrogen-loading rate (Nv) and DO were combined to monitor partial nitritation, and at T=30+/-1 degrees C, Nv=0.27-1.2 kg/(m3.d), DO=0.8-2.3 mg/L, the ratios of nitrite nitrogen (NO2--N) to ammonium nitrogen (NH4+-N) were successfully kept close to 1.0-1.3 in the effluent. Nitrate nitrogen (NO3--N) less than 43 mg/L was observed. The effluent of PNR was ideally suited as influent of AR. Sixty-nine percent CODcr from the raw leachate was degraded in the PNR. Anammox was carried out in a fixed bio-film reactor (AR, working volume=36 L). At T=30+/-1 degrees C, Nv=0.06-0.11 kg/(m3.d), about 60% NH4+-N and 64% NO2--N in the influent of AR were simultaneously removed. Inhibition of high-strength NO2--N (up to 1011 mg/L) should be responsible for the low removal rate of nitrogen. About 35% aquatic humic substance (AHS) was degraded in the AR. With the same working volume (200 L), USIS-1 and USIS-2 were alternately performed to treat the effluent from AR at one cycle of about 30 days. At hydraulic loading rate (HLR)=0.02-0.04 m3/m3.d, pollutant loading rates (PLR)=NH4+-N相似文献   

Spatio-temporal dynamics of nutrients in the upper Han River basin, China

The upper Han River basin with an area of approximately 95,000 km(2), is the water source area of the Middle Route of China's South to North Water Transfer Project. Thus, water quality in the basin's river network is of great importance. Nutrients including dissolved inorganic nitrogen (DIN), NO(3)(-)-N, NH(4)(+)-N, and dissolved phosphorus (DP) were analyzed in 41 sites during the period of 2005-2006. Cluster analysis (CA), analysis of variance (ANOVA) and general linear models (GLM) were performed to explore their spatio-temporal variations in the basin. The results revealed that the DIN, NO(3)(-)-N and NH(4)(+)-N increased over the 2 year study period, and their concentrations in the wet season was higher than those in the dry season. The seasonal variation in nitrogen was strongly associated with seasonal pattern of precipitation and there was a negative relationship between DP concentration and river flow. Cluster analysis indicated high nutrient contents in the urban and agricultural production areas. The research will help articulate water resource management strategy for the interbasin water transfer project.     

Influence of alkalinity on the stabilization of municipal solid waste in anaerobic simulated bioreactor

Four simulated landfill anaerobic bioreactors were performed to investigate the influence of alkalinity on the anaerobic treatment of municipal solid waste (MSW). Leachate was recirculated in all the four reactors. One reactor was operated without alkalinization. The other three were operated under alkaline conditions. Na(2)CO(3), NaHCO(3) and NaOH were added to leachate in the second, third and fourth reactor, respectively. Experimental results showed that CO(3)(2-) and HCO(3)(-) addition had a more pronounced effect on MSW stabilization while the effect of addition of OH(-) was weak. The concentration of COD, BOD(5), total nitrogen (TN), ammonium nitrogen (NH(4)(+)-N) and nitrate nitrogen (NO(3)(-)-N), etc. in leachate significantly reduced in four reactors. The removal efficiencies were 90.56%, 92.21%, 92.74% and 90.29% for COD, 66.45%, 72.38%, 68.62% and 68.44% for NO(3)(-)-N, and 96.5%, 98.75%, 97.75% and 98% for NO(2)(-)-N in the control, Na(2)CO(3), NaHCO(3) and OH(-) added reactors, respectively. The final BOD(5)/COD was 0.262, 0.104, 0.124, and 0.143, and pH was 7.13, 7.28, 7.42, and 7.24 for control, Na(2)CO(3) added, NaHCO(3) added, and OH(-) added reactor, respectively. Therefore, alkalinity addition had positive effect on the stabilization of MSW.     

2-Chlorophenol consumption and its effect on the nitrifying sludge

The kinetic behavior of a nitrifying sludge exposed to 2-chlorophenol (2-CP) was evaluated in batch culture. The assays were performed using a stabilized nitrifying sludge. In control assays with (mg L(-1)): NH(4)(+)-N (100) and NaHCO(3)(-)-C (250), the substrates were consumed in 8h, the ammonium consumption efficiency was 99% and the NO(3)(-) yield higher than 0.9. When 5mg 2-CP-C L(-1) was added, it was transformed into an unidentified intermediate and the nitrifying efficiency decreased to 10%. Ammonium specific consumption rate diminished 95%, but the NO(3)(-) yield remained higher than 0.9. The biomass previously exposed to 2-CP was newly suspended with NH(4)(+)-N or NO(2)(-)-N in order to evaluate the ammonium and nitrite oxidizing processes. The consumption efficiencies and NO(3)(-) yields were similar to those obtained in control assays. However, the total time required for ammonium and nitrite consumption increased to 120 and 42 h, respectively. Specific consumption rates for NH(4)(+)-N and NO(2)(-)-N decreased by 95% and 83% respectively, compared to control assays. Thus, the previous contact to 2-CP had more influence on ammonium oxidizing process than the nitrite oxidizing process. These are the first evidences where a nitrifying sludge exposed to 2-CP are reported.     

Chemical denitrification of water by zero-valent magnesium powder

A laboratory-scale study was conducted in batch mode to investigate the feasibility of using zero-valent magnesium (Mg(0)), for removal of nitrate from aqueous solution. Reaction pH, dose of Mg(0), initial nitrate concentration and temperature were considered variable parameters during the study. Strong acidic condition enhanced nitrate reduction and in absence of external proton addition, reaction pH increased rapidly above ten and insignificant nitrate removal (7-16%) was achieved. At Mg(0):NO(3)(-)-N molar ratio of 5.8 and controlled reaction pH of 2, 84% denitrification efficiency was achieved (initial NO(3)(-)-N 50 mg/L) under ambient temperature and pressure and total nitrogen removal was 70% with 3.2% and 10% conversion of initial NO(3)(-)-N to NO(2)(-)-N and NH(4)(+)-N, respectively. The reaction was first order with respect to nitrate concentration. Nitrate removal rate decreased with solution pH and increased linearly with Mg(0) dose. Nitrate removal was coupled with 96-100% removal of dissolved oxygen and 85-90% generation of soluble Mg(2+) ion. An activation energy (E(a)) of nitrate reduction over the temperature range of 10-50 degrees C was observed as 17.7 kJ mol(-1).     

新型生态膜＋活性炭深度处理深圳某小区生活污水的研究

通过对新型生态膜反应器处理生活污水的试验研究,考察了不同水力停留时间（HRT）对反应器中去除CODer、NH,-N、TP污染物效果的影响。通过实验表明,在实际工况下,控制HRT为最佳工况状态,CODcr、NH3-N、TP的去除率分别达到80％、78％、65％以上,出水浓度可达到30mg／L、5mg／L、1mg／以下。出水水质达到国家标准《城镇污水处理厂污染物排放标准》（GB18918—2002）一级A标准要求。     

Ion exchange uptake of ammonium in wastewater from a Sewage Treatment Plant by zeolitic materials from fly ash

The potential value of zeolitic materials (ZM) obtained from a hazardous waste, such as coal fly ash, for the retention of NH(4)(+) present in liquid effluents from a Sewage Treatment Plant (STP) is studied. A wastewater sample was taken from an STP in Zaragoza (Spain) after conventional treatment at the Plant. The water was treated with different amounts of three ZM: NaP1 zeolite, K-F zeolite and K-Chabazite/K-Phillipsite zeolites all of them in powdered and granulated state. The wastewater was treated by two kinds of processes: continuous stirring batch experiments with powdered ZM, and fixed packed bed of granulated ZM in a column. The powdered materials reduced about 80% of NH(4)(+) from wastewater, even in the presence of Ca(2+), which competes with NH(4)(+) for the cation exchange sites in zeolites. Around 70% of NH(4)(+) reduction was achieved with granulated materials. In both cases, moderate ZM/wastewater ratios had to be used to achieve those results, with K-zeolites slightly less effective in NH(4)(+) retention.     

Zeolite synthesis from paper sludge ash at low temperature (90 degrees C) with addition of diatomite

Paper sludge ash was partially converted into zeolites by reaction with 3M NaOH solution at 90 degrees C for 24 h. The paper sludge ash had a low abundance of Si and significant Ca content, due to the presence of calcite that was used as a paper filler. Diatomite was added to the NaOH solution to increase its Si content in order to synthesize zeolites with high cation exchange capacity. Diatomite residue was filtered from solution before addition of ash. The original ash without addition of diatomite yielded hydroxysodalite with a cation exchange capacity ca. 50 cmol/kg. Addition of Si to the solution yielded Na-P1 (zeolite-P) with a higher cation exchange capacity (ca. 130 cmol/kg). The observed concentrations of Si and Al in the solution during the reaction explain the crystallization of these two phases. The reaction products were tested for their capacity for PO(4)(3-) removal from solution as a function of Ca(2+) content, suggesting the formation of an insoluble Ca-phosphate salt. The product with Na-P1 exhibits the ability to remove NH(4)(+) as well as PO(4)(3-) from solution in concentrations sufficient for application in water purification. Both NH(4)(+) and PO(4)(3-) removal showed little variation with pH between 5 and 9. Alternative processing methods of zeolite synthesis, including the addition of ash to an unfiltered Si-NaOH solution and addition of a dry ash/diatomite mixture to NaOH solution, were tested. The third process yielded materials with lower cation exchange capacity due to formation of hydroxysodalite. The second process results in a product with relatively high cation exchange capacity, and reduces the number of processing steps necessary for zeolite synthesis.     

Application of struvite precipitation in treating ammonium nitrogen from semiconductor wastewater

Struvite precipitation was applied to the removal of NH(4)-N in semiconductor wastewater. Batch experiments were conducted to examine the effects of final pH, magnesium and orthophosphate dosages and the initial influent concentrations of NH(4)-N and F on the removals of NH(4)-N and PO(4)-P by forming struvite deposits. pH was an important parameter in the simultaneous removals of ammonium nitrogen and orthophosphate. In struvite precipitation, the amount of orthophosphate in the solution affected NH(4)-N removal much more than that of magnesium ions in some cases. It was revealed that the low and high initial concentrations of NH(4)-N and F inhibited NH(4)-N and PO(4)-P removal efficiencies in struvite precipitation, respectively. We also evaluated field-scale treatment plant incorporated by struvite precipitation process. On semiconductor wastewater with an NH(4)-N concentration of 155 mg/L, the results obtained showed that the incorporation of the struvite precipitation process brought about a high NH(4)-N removal efficiency of over 89% on average.     

Effect of different N fertilizer forms on antioxidant capacity and grain yield of rice growing under Cd stress

Cadmium contamination in soil has become a serious issue in sustainable agriculture production and food safety. A pot experiment was conducted to study the influence of four N fertilizer forms on grain yield, Cd concentration in plant tissues and oxidative stress under two Cd levels (0 and 100 mg Cd kg(-1)soil). The results showed that both N form and Cd stress affected grain yield, with urea-N and NH(4)(+)-N treatments having significantly higher grain yields, and Cd addition reducing yield. NO(3)(-)-N and NH(4)(+)-N treated plants had the highest and lowest Cd concentration in plant tissues, respectively. Urea-N and NH(4)(+)-N treatments had significantly higher N accumulation in plant tissues than other two N treatments. Cd addition caused a significant increase in leaf superoxide dismutase (SOD) and peroxidase (POD) activities for all N treatments, except for NO(3)(-)-N treatment, with urea-N and NH(4)(+)-N treated plants having more increase than organic-N treated ones. The results indicated that growth inhibition, yield reduction and Cd uptake of rice plants in response to Cd addition varied with the N fertilizer form.     

Removal of organic pollutants from 2,2',5,5'-tetrachlorobenzidine (TCB) industrial wastewater by micro-electrochemical oxidation and air-stripping

A feasible method for treatment of the wastewater from the two-staged neutralization in 2,2',5,5'-tetrachlorobenzidine (TCB) manufacturing processes, a refractory dye intermediate effluents, based on combined micro-electrochemical oxidation or iron-chipping filtration (ICF) and air-stripping reactor (ASR), was developed. On conditions of HRT 1h, pH 3.0 in ICF and HRT 38 h, gas-liquid ratio 15, pH 6.0-8.65, temperature 26 degrees C in ASR, the overall COD, color, TCB and NH(4)(+)-N removal were 96.8%, 91%, 87.61% and 62%, respectively, during the treatment of TCB wastewater from the two-staged neutralization dissolved by methanol. The averaged 18.3%, 81.7% of the total degraded COD, 35.2%, 64.8% of TCB were carried out in ICF and ASR, respectively. NH(4)(+)-N removal was finished mainly in ASR. The experimental results indicated that the combined micro-electrochemical oxidation and air-stripping process performed good treatment of COD, color, TCB and NH(4)(+)-N removal in TCB wastewater from the two-staged neutralization dissolved by ethanol or acetone, came up the discharge standard in China. But the TCB wastewater from the two-staged neutralization dissolved by methanol should be deeply treated before discharged.     

Ammonium exchange in aqueous solution using Chinese natural clinoptilolite and modified zeolite

In this study, the Chinese natural clinoptilolite (sample 1) was fused with sodium hydroxide prior to hydrothermal reaction, and it was transformed to modified zeolite Na-Y (sample 2). The uptake of ammonium ion from aqueous solutions in the concentration range 50-250 mg NH(4)(+)/l on to the two samples was compared and the equilibrium isotherms have been got. The influence of other cations present in water upon the ammonia uptake was also determined. The cations studied were potassium, calcium and magnesium. In all cases the anionic counterion present was chloride. The results showed that sample 2 exhibited much higher uptake capacity compared with sample 1. At the initial concentration of 250 mg NH(4)(+)/l, the ammonium ion uptake value of sample 2 was 19.29 mg NH(4)(+)g(-1) adsorbent, while sample 1 was only 10.49 mg NH(4)(+)g(-1) adsorbent. For the natural clinoptilolite, the effect of the metal ions suggested an order of preference K(+)>Ca(2+)>Mg(2+). These contrasted with the modified zeolite, where the order appeared to be Mg(2+)>Ca(2+)>K(+).     

Bioelectricity generation and microcystins removal in a blue-green algae powered microbial fuel cell

Bioelectricity production from blue-green algae was examined in a single chamber tubular microbial fuel cell (MFC). The blue-green algae powered MFC produced a maximum power density of 11 4 mW/m(2) at a current density of 0.55 mA/m(2). Coupled with the bioenergy generation, high removal efficiencies of chemical oxygen demand (COD) and nitrogen were also achieved in MFCs. Over 78.9% of total chemical oxygen demand (TCOD), 80.0% of soluble chemical oxygen demand (SCOD), 91.0% of total nitrogen (total-N) and 96.8% ammonium-nitrogen (NH(3)-N) were removed under closed circuit conditions in 12 days, which were much more effective than those under open circuit and anaerobic reactor conditions. Most importantly, the MFC showed great ability to remove microcystins released from blue-green algae. Over 90.7% of MC-RR and 91.1% of MC-LR were removed under closed circuit conditions (500Ω). This study showed that the MFC could provide a potential means for electricity production from blue-green algae coupling algae toxins removal.     

Simultaneous removal of phenol, ammonium and thiocyanate from coke wastewater by aerobic biodegradation

A laboratory-scale activated sludge plant composed of a 20 L volume aerobic reactor followed by a 12 L volume settling tank and operating at 35 degrees C was used to study the biodegradation of coke wastewater. The concentrations of ammonium nitrogen (NH(4)(+) -N), phenols, chemical oxygen demand (COD) and thiocyanate (SCN(-)) in the wastewater ranged between 504 and 2,340, 110 and 350, 807 and 3,275 and 185 and 370 mg/L, respectively. The study was undertaken with and without the addition of bicarbonate. The addition of this inorganic carbon source was necessary to favour nitrification, as the alkalinity of the wastewater was very low. Maximum removal efficiencies of 75%, 98% and 90% were obtained for COD, phenols and thyocianates, respectively, without the addition of bicarbonate. The concentration of ammonia increased in the effluent due to both the formation of NH(4)(+) as a result of SCN(-) biodegradation and to organic nitrogen oxidation. A maximum nitrification efficiency of 71% was achieved when bicarbonate was added, the removals of COD and phenols being almost similar to those obtained in the absence of nitrification. Batch experiments were performed to study the influence of pH and alkalinity on the biodegradation of phenols and thiocyanate.     

Nitrogen removal in the bioreactor landfill system with intermittent aeration at the top of landfilled waste

High ammonia concentration of recycled landfill leachate makes it very difficult to treat. In this work, a vertical aerobic/anoxic/anaerobic lab-scale bioreactor landfill system, which was constructed by intermittent aeration at the top of landfilled waste, as a bioreactor for in situ nitrogen removal was investigated during waste stabilization. Intermittent aeration at the top of landfilled waste might stimulate the growth of nitrifying bacteria and denitrifying bacteria in the top and middle layers of waste. The nitrifying bacteria population for the landfill bioreactor with intermittent aeration system reached between 10(6) and 10(8) cells/dry g waste, although it decreased 2 orders of magnitude on day 30, due to the inhibitory effect of the acid environment and high organic matter in the landfilled waste. The denitrifying bacteria population increased by between 4 and 13 orders of magnitude compared with conventional anaerobic landfilled waste layers. Leachate NO(3)(-)-N concentration was very low in both two experimental landfill reactors. After 105 days operation, leachate NH(4)(+)-N and TN concentrations for the landfill reactor with intermittent aeration system dropped to 186 and 289 mg/l, respectively, while they were still kept above 1000 mg/l for the landfill reactor without intermittent aerobic system. In addition, there is an increase in the rate of waste stabilization as well as an increase of 12% in the total waste settlement for the landfill reactor with intermittent aeration system.     

Nitritation and denitritation of ammonium-rich wastewater using fluidized-bed biofilm reactors

Fluidized-bed biofilm nitritation and denitritation reactors (FBBNR and FBBDR) were operated to eliminate the high concentrations of nitrogen by nitritation and denitritation process. The dissolved oxygen (DO) concentration was varied from 1.5 to 2.5 g/m(3) at the top of the reactor throughout the experiment. NH(4)-N conversion and NO(2)-N accumulation in the nitritation reactor effluent was over 90 and 65%, respectively. The average NH(4)-N removal efficiency was 99.2 and 90.1% at the NLR of 0.9 and 1.2 kg NH(4)-N/m(3)day, respectively. Increasing the NLR from 1.1 to 1.2 kg NH(4)-N/m(3)day decreased the NH(4)-N elimination approximately two-fold while NH(4)-N conversion to NO(2)-N differences were negligible. The NO(2)-N/NO(x)-N ratios corresponded to 0.74, 0.73, 0.72, and 0.69, respectively, indicating the occurrence of partial nitrification. An average free ammonia concentration in the FBBNR was high enough to inhibit nitrite oxidizers selectively, and it seems to be a determining factor for NO(2)-N accumulation in the process. In the FBBDR, the NO(x)-N (NO(2)-N+NO(3)-N) concentrations supplied were between 227 and 330 mg N/l (NLR was between 0.08 and 0.4 kg/m(3)day) and the influent flow was increased as long as the total nitrogen removal was close to 90%. The NO(2)-N and NO(3)-N concentrations in the effluent were 3.0 and 0.9 mg/l at 0.08 kg/m(3)day loading rate. About 98% removal of NO(x)-N was achieved at the lowest NLR in the FBBDR. The FBBDR exhibited high nitrogen removal up to the NLR of 0.25 kg/m(3)day. The NO(x)-N effluent concentration never exceeded 15 mg/l. The total nitrogen removal efficiency in the FBBRs was higher than 93% at 21+/-1 degrees C.     

Study of the aerobic biodegradation of coke wastewater in a two and three-step activated sludge process

A laboratory-scale biological plant composed of two aerobic reactors operating at 35 degrees C was used to study the biodegradation of coke wastewater. The main pollutants to be removed are organic matter, especially phenols, thiocyanate and ammonium nitrogen. The concentrations of the main pollutants in the wastewater during the study ranged between 922 and 1,980 mg COD/L, 133 and 293 mg phenol/L, 176 and 362 mg SCN/L and 123 and 296 mg NH(4)(+)-N/L. The biodegradation of these pollutants was studied employing different hydraulic residence times (HRT) and final effluent recycling ratios in order to minimize inhibition phenomena attributable to the high concentrations of pollutants. During the optimisation of the operating conditions, the removal of COD, phenols and thiocyanate was carried out in the first reactor and the nitrification of ammonium took place in the second. The best results were obtained when operating at an HRT of 98 h in the first reactor and 86 h in the second reactor, employing a recycling ratio of 2. The maximum removal efficiencies obtained were 90.7, 98.9, 98.6 and 99.9% for COD, phenols, thiocyanate and NH(4)(+)-N, respectively. In order to remove nitrate, an additional reactor was also implemented to carry out the denitrification process, adding methanol as an external carbon source. Very high removal efficiencies (up to 99.2%) were achieved.