Formaldehyde and urea removal in a denitrifying granular sludge blanket reactor

Simultaneous formaldehyde biodegradation, urea hydrolysis and denitrification in anoxic batch assays and in a continuous laboratory anoxic reactor were investigated. In batch assays, the initial formaldehyde biodegradation rate was around 0.7 g CH(2)Og VSS(-1)d(-1) and independent of the urea concentration (90- 370 mg N-NH(2)CONH(2)l(-1)). Urea was completely hydrolyzed to ammonium in the presence of 430 mg l(-1) formaldehyde and complete denitrification took place in all cases (125 mg N-NO(-)(3)l(-1)). Formaldehyde removal efficiencies above 99.5% were obtained in a lab-scale denitrifying upflow sludge blanket reactor at organic loading rates between 0.37 and 2.96 kg CODm(-3)d(-1) (625-5000 mg CH(2)Ol(-1)). The urea loading rate was increased from 0.06 to 0.44 kg Nm(-3)d(-1) (100-800 mg N-NH(2)CONH(2)l(-1)) and hydrolysis to ammonium was around 77.5% at all loading rates. The denitrification process was always almost complete (100-800 mg N-NO(3)(-)l(-1)), due to the high COD/N ratio of 6.7 in the influent. A minimum value of 3.5 was found to be required for full denitrification. The composition of the biogas indicated that denitrification and methanogenesis occurred simultaneously in the same unit. A good granulation of the sludge was observed.     

Anoxic treatment of phenolic wastewater in sequencing batch reactor

Studies were conducted on the anoxic phenol removal using granular denitrifying sludge in sequencing batch reactor at different cycle lengths and influent phenol concentrations. Results showed that removal exceeded 80% up to an influent phenol concentration of 1050 mg/l at 6 h cycle length, which corresponded to 6.4 kg COD/m3/d. Beyond this, there was a steep decrease in phenol and COD removal efficiencies. This was accompanied by an increase in nitrite concentration in the effluent. On an average, 1 g nitrate-N was consumed per 3.4 g phenol COD removal. Fraction of COD available for sludge growth was calculated to be 11%.     

Phenol biodegradation and its effect on the nitrification process

Phenol biodegradation under aerobic conditions and its effect on the nitrification process were studied, first in batch assays and then in an activated sludge reactor. In batch assays, phenol was completely biodegraded at concentrations ranging from 100 to 2500 mg l(-1). Phenol was inhibitory to the nitrification process, showing more inhibition at higher initial phenol concentrations. At initial phenol concentrations above 1000 mg l(-1), the level of nitrification decreased. In the activated sludge reactor, the applied ammonium loading rate was maintained at 140 mg N-NH(4)(+)l(-1)d(-1) (350 mg N-NH(4)(+)l(-1)) during the operation time. However, the applied organic loading rate was increased stepwise from 30 to 2700 mg COD l(-1)d(-1) by increasing the phenol concentration from 35 up to 2800 mg l(-1). High phenol removal efficiencies, above 99.9%, were maintained at all the applied organic loading rates. Ammonium removal was also very high during the operation period, around 99.8%, indicating that there was no inhibition of nitrification by phenol.     

Simultaneous urea hydrolysis, formaldehyde removal and denitrification in a multifed upflow filter under anoxic and anaerobic conditions

A multifed upflow filter (MUF), working under anoxic or anaerobic conditions, coupled with an aerobic biofilm airlift suspension (BAS) reactor was operated in order to treat a wastewater with high formaldehyde (up to 1.5 g L-1) and urea (up to 0.46 g L-1) concentrations. In the MUF, formaldehyde removal, denitrification and urea hydrolysis took place simultaneously. The MUF was operated at 37 degrees C, at a hydraulic retention time (HRT) ranging from 1 to 0.3 d. An organic loading rate (OLR) of 0.5 kg-formaldehyde m-3 d-1 was efficiently eliminated during anaerobic operation and transformed into methane, while a much higher OLR (up to 2 kg-formaldehyde m-3 d-1) was oxidised under anoxic conditions by the nitrite or nitrate from the nitrifying airlift. However, only 80% of urea was hydrolysed to ammonia in an anoxic environment while complete conversion occurred under anaerobic conditions. Moreover, formaldehyde concentrations higher than 50 mg L-1 provoked a loss of efficiency of urea hydrolysis, decreasing to 10% at formaldehyde concentrations above 300 mg L-1. Methane production rate during the anaerobic stage was adversely affected by accumulations of formaldehyde in the reactor causing lower formaldehyde removal efficiency. However, denitrification proceeded properly even at a formaldehyde concentration of 700 mg L-1 in the reactor, although nitrous oxide appears in the off-gas. The COD/N ratios required for complete nitrite and nitrate denitrification with formaldehyde were estimated at 2.1 and 3.5 kg-COD/kg-N, respectively.     

Coupled BAS and anoxic USB system to remove urea and formaldehyde from wastewater

Wastewater containing formaldehyde and urea was treated using a coupled system consisting of a biofilm airlift suspension (BAS) reactor and an anoxic upflow sludge blanket (USB) reactor. The anoxic USB reactor was used to carry out denitrification and urea hydrolysis, while the BAS reactor was used to carry out nitrification. In a first step, individual experiments were carried out to investigate the effects of both compounds on the nitrifying and denitrifying biomass. The BAS reactor was fed with a synthetic medium containing 500 mg N-NH4(+)l(-1) and 100mg N-urea l(-1), that were added continuously to this medium. Neither urea hydrolysis nor inhibition of nitrification was observed. Nitrification efficiency decreased when formaldehyde was fed during shocks at concentrations of 40, 80 and 120 mg C-formaldehyde l(-1). The anoxic USB reactor was fed with a synthetic medium containing nitrate, formaldehyde and urea. Concentrations of formaldehyde in the reactor of 100-120 mg C-formaldehyde l(-1) caused a decrease in the denitrification and urea hydrolysis rates. In a second step, the coupled system was operated at recycling ratios (R) of 3 and 9. Fed C/N ratios of 0.58, 1.0 and 1.5 g C-formaldehyde g(-1) N-NH4(+) were used for every recycling ratio. The maximum nitrogen removal percentages were achieved at a C/N ratio of 1.0 g C-formaldehyde g(-1) N-NH4(+) for both recycling ratios. A fed C/N ratio of 1.5 g C-formaldehyde g(-1) N-NH4(+) caused a decrease in the efficiency of the system with respect to nitrogen removal, due to the presence of formaldehyde in the BAS reactor, which decreased the nitrification. Formaldehyde was completely removed in the BAS reactor and a heterotrophic layer formed around the nitrifying biofilm.     

NOx monitoring of a simultaneous nitrifying-denitrifying (SND) activated sludge plant at different oxidation reduction potentials

Simultaneous nitrification-denitrification (SND) allows biological nitrogen removal in a single reactor without separation of the two processes in time or space but requires adapted control strategies (anoxic/aerobic conditions). In this study, the formation of gaseous nitric oxide (NO(G)) and nitrogen dioxide (NO(2G)) was monitored for SND in relation to the oxidation-reduction potential (ORP) and nitrogen removal in a lab batch reactor and a pilot membrane bio-reactor (MBR). In addition hospital wastewater (COD/N(tot)>6:1) was treated on site for 1 year. The highest total nitrogen removal rates of max 90% were reached at 220-240mV ORP (given as E(h)) with corresponding maximal NO(G) emissions rates of 0.9microgg(-1)VSSh(-1). The maximal emission rates of NO(2G) (0.2microgg(-1)VSSh(-1)) were reached at the same ORP level and the NO(2G) emissions correlated to the nitrite accumulation in the activated sludge up to 5mgl(-1)NO(2L)-N. It was shown that this correlation was due to biological production and not due to pH-dependent chemical conversion. Therefore, NO(2G) can be used as additional control loop for ORP-controlled SND systems to avoid the inhibition of denitrification and high nitrite concentrations in the plant effluent.     

Kinetics of denitrification reactions in single sludge systems

This paper reports denitrification studies performed using the anoxic reactor of a laboratory scale anoxic-aerobic plant as a batch reactor of variable volume. This was achieved by adding to the anoxic reactor a supplementary flow of nitrate after the shut down of the recirculation line and the interruption of the hydraulic connection to the aerobic reactor. By operating in this way, in a relatively short time, it is possible to get a number of experimental data sufficient to describe the biological process kinetics. The system is extremely flexible and gives kinetic data in short times for different experimental conditions. In fact, it is possible to operate at different COD/NO₃-N ratios simply by changing the influent wastewater flowrate to the anoxic reactor. Two series of tests were performed: in the first series (use of endogenous carbon) a supplementary flow of nitrate was fed to the anoxic reactor while the wastewater influent flow was interrupted; in the second series (use of internal carbon) the influent wastewater flow was fed during the addition of nitrate. The importance of the carbonaceous substrate nature on the denitrification rate was also verified. Data analysis was performed by utilizing the integral method procedure and a zero order kinetics referring to both the substrates COD and nitrate nitrogen was considered. A satisfactory agreement between predicted and experimental data was found. Values obtained for k_D range from 0.07 mg NO₃-N/mg VSS·d, at which the carbon source is mostly endogenous, to 0.25 mg NO₃-N/mg VSS·d, at which the carbon source consists mainly of readily biodegradable COD. Intermediate values occur when the readily biodegradable COD is limiting and denitrification takes place by utilizing the slowly biodegradable one.     

Simultaneous methanogenesis and denitrification of pretreated effluents from a fish canning industry

A lab-scale hybrid upflow sludge bed-filter (USBF) reactor was employed to carry out methanogenesis and denitrification of the effluent from an anaerobic industrial reactor (EAIR) in a fish canning industry. The reactor was initially inoculated with methanogenic sludge and there were two different operational steps. During the first step (Step I: days 1-61), the methanogenic process was carried out at organic loading rates (OLR) of 1.0-1.25 g COD l-1 d-1 reaching COD removal percentages of 80%. During the second step (Step II: days 62-109) nitrate was added as KNO3 to the industrial effluent and the OLR was varied between 1.0 and 1.25 g COD l-1 d-1. Two different nitrogen loads of 0.10 and 0.22 g NO3(-)-N l-1 d-1 were applied and these led to nitrogen removal percentages of around 100% in both cases and COD removal percentages of around 80%. Carbon to nitrogen ratio (C:N) in the influent was maintained at 2.0 and eventually it was increased to 3.0, by means of glucose addition, to control the denitrification process. From these results it is possible to establish that wastewater produced in a fish canning industry can be used as a carbon source for denitrification and that denitrifying microorganisms were present in the initially methanogenic sludge. Biomass productions of 0.23 and 0.61 g VSS:g TOC fed for Steps I and II, respectively, were calculated from carbon global balances, showing an increase in biomass growth due to denitrification.     

Nitrous oxide production in high-loading biological nitrogen removal process under low COD/N ratio condition

Effects of influent COD/N ratio on N2O emission from a biological nitrogen removal process with intermittent aeration, supplied with high-strength wastewater, were investigated with laboratory-scale bioreactors. Furthermore, the mechanism of N2O production in the bioreactor supplied with low COD/N ratio wastewater was studied using 15N tracer method, measuring of reduction rates in denitrification pathway, and conducting batch experiments under denitrifying condition. In steady-state operation, 20-30% of influent nitrogen was emitted as N2O in the bioreactors with influent COD/N ratio less than 3.5. A 15N tracer study showed that this N2O originated from denitrification in anoxic phase. However, N2O reduction capacity of denitrifiers was always larger than NO3(-)-N or NO2(-)-N reduction capacity. It was suggested that a high N2O emission rate under low COD/N ratio operations was mainly due to endogenous denitrification with NO2(-)-N in the later part of anoxic phase. This NO2(-)-N build-up was attributed to the difference between NO3(-)-N and NO2(-)-N reduction capacities, which was the feature observed only in low COD/N ratio operations.     

SMSBR去除焦化废水中有机物及氮的特性

选用一体化膜—序批式生物反应器 (SubmergedMembraneSequencingBatchReac tor ,简称SMSBR)处理焦化废水 ,考察了能否通过膜分离的强化作用提高生物处理系统对焦化废水的处理效果 ,使出水COD达到新的排放标准 ( <10 0mg/L) ,并提高脱氮效率。研究结果表明 :在HRT为 32 .7h ,平均COD容积负荷为 0 .4 5kg/ (m3·d)的条件下 ,出水COD可以稳定在 10 0mg/L以下 (平均为 86.4mg/L) ;要使COD达到新的排放标准 ,进水COD容积负荷应低于 0 .67kg/ (m3·d) (该负荷下出水COD在 10 0mg/L上下波动 ,平均为 10 6.3mg/L) ;好氧段存在明显的反硝化现象 ,使COD的去除得到强化 ;在保证系统温度、碱度、溶解氧和不受进水COD负荷冲击的情况下 ,出水NH3-N可低于 1mg/L ,但泥龄太长所产生的微生物代谢产物抑制了硝化反应过程中的硝酸盐细菌 ,使好氧段出水NO2 -N/NOx-N平均为 91.1% ,因此系统获得极其稳定高效的短程硝化作用 ,有利于进一步脱氮 ;按“缺氧 1—好氧—缺氧 2”方式运行时 ,若“缺氧 2”的HRT>8.4 4h ,可实现 81.34 %的反硝化率 (外加碳源 :COD/N为 2 .1g/g) ,平均TN去除率为 87.2 % ,最高达 90 .2 %。     

Organic removal by denitritation and methanogenesis and nitrogen removal by nitritation from landfill leachate

A system consisting of a two-stage UASB and anoxic-oxic reactor was used to enhance COD and nitrogen removal from landfill leachate. To improve denitrification efficiency, the raw leachate with recycled final effluent was pumped into the first-stage UASB (UASB1) to carry out simultaneous denitrification and methanogenesis. The results over 180 d show that the maximum organic removal rate in UASB1 and UASB2 was 12.5 and 8.5 kgCODm(-3)d(-1) in the oxic zone of the A/O reactor, respectively. The COD and biochemical oxygen demand (BOD5) removal efficiency of the system was 80-92% and about 99%, respectively. Without controlling temperature (17-30 degrees C) and dissolved oxygen (0.5-4.0 mgL(-1)), the maximum NH4+-N removal rate was 0.68 kg NH4+-Nm(-3)d(-1), and about 99% of NH4+-N removal was obtained by nearly complete nitritation. The 81-93% total nitrogen removal was obtained by complete denitrification in the UASB1 and in the anoxic zone of the A/O reactor. Fluorescence in situ hybridization (FISH) analysis of the sludge samples from A/O reactor showed that ammonia oxidizing bacteria (AOB) consisted 4% of the eubacterium, while nitrite oxidizing bacteria (NOB) counted less than 0.2% of that. The study shows that the main factors achieving and maintaining nitritation are a proper range of free ammonia concentration obtained by dilution recycled final effluent that inhibits NOB but not AOB; effective control on aeration time by indication of "ammonia valley" on pH profile; and highly efficient denitrification and its reproducing alkalinity to result in pH above 8.5.     

Biological removal of phenol from strong wastewaters using a novel MSBR

In this study, the performance of a moving-bed sequencing batch reactor (MSBR) that removes phenol from wastewater is presented. The effects of phenol concentration (50-3325 mg L⁻¹), filling time (0-4 h) and aerating time (4-18 h) on the performance of the MSBR are given in terms of phenol and COD removal efficiencies. Moreover, the effect of the moving media on the overall performance of the reactor is also determined. The reactor can completely remove phenol and COD at inlet concentrations up to 3000 mg phenol L⁻¹ (6780 mg COD L⁻¹), which was the inhibition concentration, and with a 24-h cycle time. The filling time range tested here did not significantly affect phenol or COD removal. The optimum hydraulic retention time (HRT) for the MSBR is 40 h and the critical phenol loading rate is 83.4 g phenol m⁻³ h⁻¹, which gives a phenol removal efficiency of 99%. The reactor can also withstand shock loads from slug feeding. The moving bed contribution to phenol and COD removal efficiencies was up to 28.1 and 34.7%, respectively, at the phenol loading rate of 83.4 g m⁻³ h⁻¹. The findings of this investigation suggest that MSBR can be a robust and promising process for effectively treating wastewaters containing inhibitor or recalcitrant compounds in industrial settings.     

Biomass characteristics in three sequencing batch reactors treating a wastewater containing synthetic organic chemicals

The physical and biochemical characteristics of the biomass in three lab-scale sequencing batch reactors (SBR) treating a synthetic wastewater at a 20-day target solids retention time (SRT) were investigated. The synthetic wastewater feed contained biogenic compounds and 22 organic priming compounds, chosen to represent a wide variety of chemical structures with different N, P and S functional groups. At a two-day hydraulic retention time (HRT), the oxidation-reduction potential (ORP) cycled between -100 (anoxic) and 100 mV (aerobic) in the anoxic/aerobic SBR, while it remained in a range of 126+/-18 and 249+/-18 mV in the aerobic sequencing batch biofilm reactor (SBBR) and the aerobic SBR reactor, respectively. A granular activated sludge with excellent settleability (SVI=98+/-31 L mg(-1)) developed only in the anoxic/aerobic SBR, compared to a bulky sludge with poor settling characteristics in the aerobic SBR and SBBR. While all reactors had very good COD removal (>90%) and displayed nitrification, substantial nitrogen removal (74%) was only achieved in the anoxic/aerobic SBR. During the entire operational period, benzoate, theophylline and 4-chlorophenol were completely removed in all reactors. In contrast, effluent 3-nitrobenzoate was recorded when its influent concentration was increased to 5 mg L(-1) and dropped only to below 1 mg L(-1) after 300 days of operation. The competent (active) biomass fractions for these compounds were between 0.04% and 5.52% of the total biomass inferred from substrate-specific microbial enumerations. The measured competent biomass fractions for 4-chlorophenol and 3-nitrobenzoate degradation were significantly lower than the influent COD fractions of these compounds. Correspondent to the highest competent biomass fraction for benzoate degradation among the test SOCs, benzoate oxidation could be quantified with an extant respirometric technique, with the highest specific oxygen uptake rate (SOUR(benzoate), 0.026 g O2 h(-1) g(-1) XCOD) in the anoxic/aerobic SBR. These combined results suggest that operating SBRs with alternative anoxic/aerobic cycles might facilitate the formation of granular sludge with good settleability, and retain comparable removal of nitrogen and synthetic organic compounds. Hence, the practice of anoxic/aerobic cycling should be considered in wastewater treatment systems whenever possible.     

Biofilm growth and characteristics in an alternating pumped sequencing batch biofilm reactor (APSBBR)

A novel biofilm reactor-alternating pumped sequencing batch biofilm reactor (APSBBR)-was developed to treat synthetic dairy wastewater at a volumetric chemical oxygen demand (COD) loading rate of 487 g COD m(-3) d(-1) and an areal loading rate of 5.4 g COD m(-2) d(-1). This biofilm reactor comprised two tanks, Tanks 1 and 2, with two identical plastic biofilm modules in each tank. The maximum volume of bulk fluid in the two-tank reactor was the volume of one tank. The APSBBR was operated as a sequencing batch biofilm reactor with five operational phases-fill (25 min), anoxic (9 h), aerobic (9 h), settle (6 h) and draw (5 min). The fill, anoxic, settle and draw phases occurred in Tank 1. In the aerobic phase, the wastewater was circulated between the two tanks with centrifugal pumps and aeration was mainly achieved through oxygen absorption by micro-organisms in the biofilms when they were exposed to the air. In this paper, the biofilm growth and characteristics in the APSBBR were studied in a 98-day laboratory-scale experiment. During the course of the study, it was found that the biofilm thickness (delta) in Tank 1 ranged from 1.2 to 7.2 mm and that in Tank 2 from 0.5 to 2.2 mm; the biofilm growth against time (t) can be simulated as delta=0.07t0.99 (R2 = 0.97, P = 0.002) in Tank 1 and delta = 0.08t0.66 (R2 = 0.81, P = 0.04) in Tank 2. The biomass yield coefficient, Y, was 0.18 g volatile solids (VS) g(-1) COD removal. The biofilm density in both tanks, X, decreased as the biofilm thickness increased and can be correlated to the biofilm thickness, delta .     

Effect of specific gas loading rate on thermophilic (55 degrees C) acidifying (pH 6) and sulfate reducing granular sludge reactors

The effect of the specific gas loading rate on the acidifying, sulfate reducing and sulfur removal capacity of thermophilic (55 degrees C; pH 6.0) granular sludge bed reactors treating partly acidified wastewater was investigated. A comparison was made between a regular UASB reactor and a UASB reactor continuously sparged with N(2) at a specific gas loading rate of 30 m(3)m(-2)d(-1). Both UASB reactors (upflow velocity 1.0 mh(-1), hydraulic retention time about 5h) were fed a synthetic wastewater containing starch, sucrose, lactate, propionate and acetate and a low sulfate concentration (COD/SO(4)(2-) ratio of 10) at volumetric organic loading rates (OLR) ranging from 4.0 to 49.8 gCODl(-1) reactord(-1). Immediately after imposing an OLR of 25 gCODl(-1) reactord(-1), the acidification and sulfate reduction efficiency dropped to 80% and 30%, respectively, in the UASB reactor. Both efficiencies recovered slowly to 100% during the course of the experiment. In the N(2) sparged reactor, both the acidification and sulfate reduction efficiency remained 100% following the OLR increase to 25 gCODl(-1) reactord(-1). However, the sulfate reduction efficiency gradually decreased to about 20% at the end of the experiment. The biogas (CO(2) and CH(4)) production rate in the UASB was very low, i.e. <3l biogasl(-1) reactorday(-1), resulting in negligible amounts (<20%) of H(2)S stripped from the reactor liquid. The total H(2)S concentration of the N(2) sparged UASB reactor effluent was always below 25 mgl(-1), but incomplete sulfate reduction kept the maximal H(2)S stripping efficiency below 70%.     

Treatment of anaerobically pre-treated domestic sewage by a rotating biological contactor.

The performance of a rotating biological contactor (RBC) for the post-treatment of the effluent of an up-flow anaerobic sludge blanket (UASB) was the subject of this study. Different hydraulic and organic loading rates have been investigated. The removal efficiencies of COD(total), COD(suspended), COD(colloidal) and COD(soluble) increased at a higher hydraulic retention time (HRT) and a lower influent organic loading rate. The results obtained indicated that a two-stage RBC reactor at an HRT of 10 h and an organic loading rate of 6.4g COD m(-2) d(-1) represents an effective post-treatment process. Most COD(suspended) and COD(colloidal) were removed in the first stage while nitrification proceeded in the second stage. The overall nitrification efficiency was 92% at an ammonia loading rate of 1.1 gm(-2) d(-1). Total E. coli removal at HRTs of 10, 5 and 2.5h were 99.5%, 99.0% and 89.0%. respectively. The major part of suspended E. coli ( >4.4 microm) was removed by sedimentation or by adsorption in the biofilm of the first stage of RBC (99.66%). However, E. coli in the colloidal fraction (<4.4 to >0.45 microm) was eliminated in the second stage of RBC (99.78%). A comparison of the performance of a one-stage versus two-stage RBC system, operated at the same total loading rate, revealed an improvement in the effluent quality of the two-stage effluent as compared to the one-stage effluent. The two stages RBC were used to examine the effect of hydraulic shock loads on reactor performance in terms of COD, nitrification and E. coli removal.     

The nature of the carbon source rules the competition between PAO and denitrifiers in systems for simultaneous biological nitrogen and phosphorus removal

The presence of nitrate in the theoretical anaerobic reactor of a municipal WWTP aiming at simultaneous C, N and P removal usually leads to Enhanced Biological Phosphorus Removal (EBPR) failure due to the competition between PAO and denitrifiers for organic substrate. This problem was studied in a continuous anaerobic-anoxic-aerobic (A²/O) pilot plant (146 L) operating with good removal performance and a PAO-enriched sludge (72%). Nitrate presence in the initially anaerobic reactor was studied by switching the operation of the plant to an anoxic-aerobic configuration. When the influent COD composition was a mixture of different carbon sources (acetic acid, propionic acid and sucrose) the system was surprisingly able to maintain EBPR, even with internal recycle ratios up to ten times the influent flow rate and COD limiting conditions. However, the utilisation of sucrose as sole carbon source resulted in a fast EBPR failure. Batch tests with different nitrate concentrations (0-40 mg L⁻¹) were performed in order to gain insight into the competition for the carbon source in terms of P-release or denitrification rates and P-release/C-uptake ratio. Surprisingly, no inhibitory or detrimental effect on EBPR performance due to nitrate was observed. A model based on ASM2d but considering two step nitrification and denitrification was developed and experimentally validated. Simulation studies showed that anaerobic VFA availability is critical to maintain EBPR activity.     

Chemolithotrophic denitrification with elemental sulfur for groundwater treatment

Denitrification for the treatment of nitrates in wastewater typically relies on organic electron donating substrates. However, for groundwater treatment, inorganic compounds such as elemental sulfur (S0) are being considered as alternative electron donors in order to overcome concerns that residual organics can cause biofouling. In this study, a packed-bed bioreactor supplied with S0:limestone granules (1:1, v/v) was started up utilizing a chemolithotrophic denitrifying enrichment culture in the form of biofilm granules that was pre-cultivated on thiosulfate. The granular enrichment culture enabled a rapid start-up of the bioreactor. A nearly complete removal of nitrate (7.3 mM) was NO3- attained by the bioreactor at nitrate loading rates of up to 21.6 mmol/(L(reactor)d). With lower influent concentrations (1.3 mM nitrate) comparable to those found in contaminated groundwater, high nitrate loads of 18.1 mmol/(L(reactor)d) were achieved with an average nitrate removal efficiency of 95.9%. The recovery of nitrogen as benign N2 gas was nearly stoichiometric. The concentration of undesirable products from S0-based denitrification such as nitrite and sulfide were low. Comparison of bioreactor results with batch kinetic studies revealed that denitrification rates were dependent on the surface area of the added S0. The surface area normalized denitrification rate was determined to be 26.4 mmol /(m2 S0 d).     

Treatment of easily degradable wastewater in a stirred anaerobic sequencing batch biofilm reactor

The main objectives of this study were to evaluate the performance of an anaerobic sequencing batch reactor when subjected to a progressive increase of influent glucose concentration and to estimate the kinetic parameters of glucose degradation. The reactor was initially operated in 8-h cycles, treating glucose in concentrations of 500, 1000 and 2000 mg l(-1). No glucose was detected in the effluent under these three conditions. The reactor showed operating stability when treating a glucose concentration of approximately 500 mg l(-1), with filtered chemical oxygen demand (COD) removal efficiencies varying from 93% to 97%. Operational instability occurred in the operation with glucose concentrations of approximately 1000 and 2000 mg l(-1), caused mainly by a production of extracellular polymeric substances (EPS), which led to hydrodynamic and mass transfer problems in the reactor. The mean volatile acid concentration values in the effluent were approximately 159+/-72 and 374+/-92 mg l(-1), respectively. A first-order model was adjusted to glucose concentration profiles and a modified model, including a residual concentration of substrate, was adjusted to COD temporal profiles. To check the formation of EPS, the reactor was operated in 3-h cycles with concentrations of 500 and 1000 mg l(-1). The purpose of this step was to discover if the production of EPS resulted from the biomass's exposure to a low concentration of substrate over a long period of time. Thus, it was hypothesized that a reduction of the time cycle would also reduce the exposure to low concentrations. However, this hypothesis could not be confirmed because large amounts of EPS were formed already under the first operational condition, using approximately 500 mg l(-1) of glucose in the influent, thus indicating the fallacy of the hypothesis. The production of EPS proved to depend on the organic volumetric load applied to the reactor.     

Kinetic modelling of nitrogen and organics removal in vertical and horizontal flow wetlands

This paper provides a comparative evaluation of the kinetic models that were developed to describe the biodegradation of nitrogen and organics removal in wetland systems. Reaction kinetics that were considered in the model development included first order kinetics, Monod and multiple Monod kinetics; these kinetics were combined with continuous-stirred tank reactor (CSTR) or plug flow pattern to produce equations to link inlet and outlet concentrations of each key pollutants across a single wetland. Using three statistical parameters, a critical evaluation of five potential models was made for vertical and horizontal flow wetlands. The results recommended the models that were developed based on Monod models, for predicting the removal of nitrogen and organics in a vertical and horizontal flow wetland system. No clear correlation was observed between influent BOD/COD values and kinetic coefficients of BOD₅ in VF and HF wetlands, illustrating that the removal of biodegradable organics was insensitive to the nature of organic matter. Higher effluent COD/TN values coincided with greater denitrification kinetic coefficients, signifying the dependency of denitrification on the availability of COD in VF wetland systems. In contrast, the trend was opposite in HF wetlands, indicating that availability of NO₃-N was the main limiting step for nitrogen removal. Overall, the results suggested the possible application of the developed alternative predictive models, for understanding the complex biodegradation routes of nitrogen and organics removal in VF and HF wetland systems.