Phenol removal in packed bed reactor under denitrifying conditions

Detailed studies on the efficiency of phenol degradation by a biofilm in an anaerobic packed bed reactor were carried out. The efficiency of phenol degradation depended on both the concentration of phenol in the medium and the phenol load in anaerobic packed bed reactor. Increasing phenol concentrations from 200 to 1,250 mg l(-1) and retention time (Tr)= 12 h were paralleled by increasing efficiency of the process, which reached a maximum value of 1,390 mg l(-1) day(-1) at 700 mg phenol l(-1). The highest concentration of phenol used inhibited growth by approximately 95%. When the phenol load in medium containing 200, 300, 400 and 500 mg l(-1) was increased through a shortening of the retention time (Tr from 24 to 2 h) a maximum efficiency of phenol degradation of 2,200 mg l(-1) day(-1) was obtained at Tr=4 h and phenol concentrations in the medium of 200 mg l(-1). Phenol in concentrations from 300 to 500 mg l(-1) was fully degraded at Tr>9 h and phenol load reaching 530-1330 mg l(-1) day(-1) for the individual concentrations. The post-denitrification effluent leaving packed bed reactor in spite of the absence or even trace amounts of phenol in it requires further purification.     

Biodegradation of pyridine by an isolated bacterial consortium/strain and bio-augmentation of strain into activated sludge to enhance pyridine biodegradation

Pyridine and pyridine based products are of major concern as environmental pollutants due to their recalcitrant, persistent, toxic and teratogenic nature. In this study, we describe biodegradation of pyridine by an isolated consortium/strain under aerobic condition. Batch experiment results reveal that at lower initial pyridine concentrations (1-20 mg l(-1)), almost complete degradation was observed whereas at higher concentration (30-50 mg l(-1)), the degradation efficiency was dropped significantly. This may be due to inhibitory effect of pyridine at higher concentrations. The value of decay and yield coefficient was also determined. Furthermore, the bio-augmentation of isolated consortium/strain into the activated sludge consortium in different quantity has been also done and the effect of bio-augmentation on degradation has been studied. The results reveal that as the quantity of bio-augmentation increases, the degradation of pyridine increases. At 25% bio-augmentation, complete degradation of 20 mg l(-1) of pyridine can be achieved within 96 h of incubation. Thus, the study concluded that the bio-augmentation of the isolated consortium/strain into the sludge enhances the pyridine degradation efficiency of the biomass.     

Enhanced biodegradation of hexachlorocyclohexane in upflow anaerobic sludge blanket reactor using methanol as an electron donor

Anaerobic dechlorination of technical grade hexachlorocyclohexane (THCH) was studied in a continuous upflow anaerobic sludge blanket (UASB) reactor with methanol as a supplementary substrate and electron donor. A reactor without methanol served as the experimental control. The inlet feed concentration of THCH in both the experimental and the control UASB reactor was 100 mg l(-1). After 60 days of continuous operation, the removal of THCH was >99% in the methanol-supplemented reactor as compared to 20-35% in the control reactor. THCH was completely dechlorinated in the methanol fed reactor at 48 h HRT after 2 months of continuous operation. This period was also accompanied by increase in biomass in the reactor, which was not observed in the experimental control. Batch studies using other supplementary substrates as well as electron donors namely acetate, butyrate, formate and ethanol showed lower % dechlorination (<85%) and dechlorination rates (<3 mg g(-1)d(-1)) as compared to methanol (98%, 5 mg g(-1)d(-1)). The optimum concentration of methanol required, for stable dechlorination of THCH (100 mg l(-1)) in the UASB reactor, was found to be 500 mg l(-1). Results indicate that addition of methanol as electron donor enhances dechlorination of THCH at high inlet concentration, and is also required for stable UASB reactor performance.     

Anoxic-oxic activated-sludge of cyanides and phenols

The anoxic-oxic activated-sludge process has been evaluated in a laboratory investigation as a means for effective treatment of cyanide-laden wastewaters, with phenols used as the organic carbon sources for denitrification reactions. The performance of the process was evaluated at different levels of feed cyanide concentration and mean cell residence time (MCRT). The results obtained indicate that the phenolic compounds used can be effectively used as the organic carbon sources to promote denitrification reactions. The effects of cyanide inhibition on overall TOC removal can be alleviated at longer MCRTs. Between 1.2 and 2.2 g TOC can be utilized per gram NO(2) + NO(3) (-) -N removed in the anoxic chamber depending on the prevailing MCRT. Microbial oxidation of cyanide and thiocyanate which yields ammonia is the main mechanism responsible for the removal of cyanide and thiocyanate observed in the anoxic-oxic activated-sludge process. Excellent removal efficiencies have been observed with feed concentrations up to 60 mg CN(-)/L and 100 mg SCN(-)/L Frequent exposure of autotrophic and aerobic cyanideutilizing microbes does not impede their activities in the oxic environment. Good nitrification and denitrification efficiencies are attainable in the anoxic-oxic activated-sludge process in the presence of high feed cyanide and thiocyanate concentrations, provided that MCRT is maintained at a desirable level. As a result, the microbial degradation of cyanide and thiocyanate in conjunction with nitrification and denitrification to produce innocuous nitrogen gas is feasible in the anoxic-oxic activated-sludge process.     

Effect of a static magnetic field on formaldehyde biodegradation in wastewater by activated sludge

The aim of this study was to determine the impact of a static magnetic field (MF) of 7 mT on formaldehyde (FA) biodegradation by activated sludge in synthetic wastewater. The MF had a positive effect on activated sludge biomass growth and dehydrogenase activity. The influence of the MF on the degradation process was observed with a FA concentration of 2400-2880 mg/l. Decreases in FA concentration and chemical oxygen demand (COD) were greater, by 30% and 26% respectively, than those in the control sample. At initial FA concentrations in raw wastewater of 2400 and 2880 mg/l, a decrease in the wastewater biodegradation efficiency was observed. This resulted in an increase of the ecotoxicity of the effluent to Daphnia magna. The value of the sludge biotic index (SBI) was dependent on the FA concentration in raw wastewater and the induction of the MF.     

Effect of hexavalent chromium on the activated sludge process and on the sludge protozoan community

The objectives of this study were the determination of chromium effects to the performance of an activated sludge unit and the investigation of the response of the activated sludge protozoan community to Cr(VI). Two bench scale activated sludge reactors were supplied with synthetic sewage containing Cr(VI), at concentrations from 1 up to 50 mg L(-1). Protozoan species were identified and were related to the system efficiency. Variations in the abundance and diversity of the protozoan species were observed under various chromium concentrations. High removal rates of organics and nutrients were observed after the acclimatization of the activated sludge, which were related to the initial chromium(VI) concentration. Chromium(VI) removal efficiency was high in all cases. The protistan community was affected by the influent chromium content. Dominance of sessile species was observed in the reactor receiving 5 mg L(-1) influent chromium, whereas co-dominance of sessile and carnivorous species was observed in the reactors receiving higher chromium concentrations.     

Influence of phenol on cultures of acetate-fed aerobic granular sludge

AIMS: This paper attempts to investigate the inhibition of phenol on the acetate utilization in acetate-fed aerobic granular sludge culture. METHODS AND RESULTS: Acetate-fed aerobic granules with a mean diameter of 1.0 mm were predeveloped in a column sequencing aerobic sludge blanket reactor. The present study looked into the utilization kinetics of acetate by acetate-fed aerobic granules in the presence of different phenol concentrations ranging from 0 mg l(-1) to 50 mg l(-1). For this purpose, batch experiments were conducted at 25 degrees C, while the initial biomass and acetate concentrations were in a range of 109-186 mg mixed liquor suspended solids (MLSS) l(-1) and 185-300 mg acetate-chemical oxygen demand (COD) l(-1). Results showed that the utilization of acetate in the presence of phenol was subject to a zero-order reaction kinetics. The relative phenol concentration in terms of the ratio of initial phenol concentration (C(p)) to initial biomass concentration (X(0)) was used to describe the real inhibitory strength of phenol imposed on acetate-fed aerobic granules. When the C(p)/X(0) ratio increased from 0 to 0.19 mg phenol mg(-1) MLSS, the zero-order reaction rate constant of acetate dropped from 1.15 mg l(-1) min(-1) to 0.38 mg l(-1) min(-1), and a similar trend was also observed in specific oxygen utilization rate. As compared to the control test without addition of phenol, the acetate-COD removal efficiency was reduced by nearly 50% at a C(p)/X(0) value of 0.19 mg phenol mg(-1) MLSS. It was found that biodegradation of phenol was negligible in acetate-fed aerobic granular sludge batch culture. CONCLUSIONS: It appears that phenol can seriously repress the utilization of acetate in the acetate-fed aerobic granular sludge batch cultures. A simple zero-order reaction model could adequately describe the utilization of acetate by acetate-fed aerobic granules in the presence of phenol. SIGNIFICANCE AND IMPACT OF THE STUDY: It is expected that this study would lead to a better understanding of the behaviour of acetate-fed aerobic granules in the presence of inhibitory organic compounds.     

Anaerobic biodegradation of a petrochemical waste-water using biomass support particles

During the anaerobic biodegradation of effluent from a dimethyl terephthalate (DMT) manufacturing plant, reduction in chemical oxygen demand (COD) degradation and biogas formation was observed after the waste-water concentration exceeded 25% of added feed COD. This condition reverted back to normal after 25–30 days when the DMT waste-water concentration in the feed was brought down to a non-toxic level. However, the above effects were observed only after the concentration of DMT waste-water reached more than 75% of added feed COD when biomass support particles (BSP) were augmented to the system. In the BSP system, a biomass concentration of up to 7000 mg/l was retained and the sludge retention time increased to > 200 days compared to 2200 mg/l and 8–10 days, respectively, in the system without BSP (control). Formaldehyde in the waste-water was found to be responsible for the observed toxicity. The BSP system was found to resist formaldehyde toxicity of up to 375 mg/l as against 125 mg/l in the control system. Moreover, the BSP system recovered from the toxicity much faster (15 days) than the control (25–30 days). The advantages of the BSP system in anaerobic treatment of DMT waste-water are discussed. Correspondence to: C. Ramakrishna     

Biosorption of copper(II) ions onto powdered waste sludge in a completely mixed fed-batch reactor: estimation of design parameters

Biosorption of Cu(II) ions onto pre-treated powdered waste sludge (PWS) was investigated using a fed-batch operated completely mixed reactor. Fed-batch adsorption experiments were performed by varying the feed flow rate ( 0.075-0.325 l h(-1)), feed copper (II) ion concentrations (50-300 mg l(-1)) and the amount of adsorbent (1-6 g PWS) using fed-batch operation. Breakthrough curves describing the variations of effluent copper ion concentrations with time were determined for different operating conditions. Percent copper ion removals from the aqueous phase decreased, but the biosorbed (solid phase) copper ion concentrations increased with increasing the feed flow rate and Cu(II) concentration. A modified Bohart-Adams equation was used to determine the biosorption capacity of PWS and the rate constant for Cu(II) ion biosorption. Adsorption rate constant in fed-batch operation was an order of magnitude larger than those obtained in adsorption columns because of elimination of mass transfer limitations encountered in the column operations while the biosorption capacity of PWS was comparable with powdered activated (PAC) in column operations. Therefore, a completely mixed reactor operated in fed-batch mode was proven to be more advantageous as compared to adsorption columns due to better contact between the phases yielding faster adsorption rates.     

Performance evaluation of an anoxic/oxic activated sludge system: effects of mean cell residence time and anoxic hydraulic retention time

A laboratory investigation has been undertaken to asses the effects of two operating parameters, mean cell residence time (MCRT) and anoxic hydraulic retention time (HRT), on the performance of an anoxic/oxic activated sludge system. The performance of the system was evaluated in terms of its COD, nitrogen, and biomass characteristics. An activated sludge system is capable of producing a better effluent, in terms of COD and nitrogen characteristics, when it is operated in an anoxic/oxic fashion. A longer MCRT and an adequate anoxic HRT are desirable in the operation of an anoxic/oxic activated sludge system. For the wastewater used in this investigation, the anoxic/oxic unit was capable of producing an effluent with the following characteristics when it was operated at MCRT = 20 days, total system HRT = 10 h, and anoxic HRT = 3-5 h: COD = 15 mg/L; VSS = 10 mg/L; TKN = 1.30 mg/L; NH(3) - N = 0.60 mg/L; and NO(2) + NO(3) - N = 5.0 mg/L. A uniform distribution of biomass is achievable in an anoxic/oxic activated sludge system because of the intensive recirculation/convection maintained. The provision of an anoxic zone in the aeration tank promotes a rapid adsorption of feed COD into the biomass without an immediate utilization for cell synthesis. This, in turn, results in a high microbial activity and a lower observed biomass yield in the system. A tertiary treatment efficiency is achievable in an anoxic/oxic activated sludge system with only secondary treatment operations and costs. A conventional activated sludge system can be easily upgraded by converting to the anoxic/oxic operation with minor process modifications.     

Microbial adaptation to biodegradation of tert-butyl alcohol in a sequencing batch reactor

This study demonstrates the utility of the sequencing batch reactor (SBR) to adapt microorganisms towards biological removal of tert-butyl alcohol (TBA). The reactor was inoculated with activated sludge and fed with TBA as the sole carbon source. Start-of-cycle TBA concentrations were initially set at 100 mgL(-1) with a cycle time of 24 h and a volumetric exchange ratio of 50% to maintain a TBA loading rate of not more than 100 mgL(-1)d(-1). Step increases in TBA loading rates up to 600 mgL(-1)d(-1) were achieved by first raising the start-of-cycle TBA concentration to 150 mgL(-1) on day 90 and subsequently by reducing the cycle time from 24 to 12, 8 and 6h on days 100, 121 and 199, respectively. This acclimation strategy favored the retention of increasingly higher densities of well-adapted microbial populations in the reactor. The increases in TBA loading produced better settling biomass and higher biomass concentrations with higher specific TBA biodegradation rates. Effluent TBA concentrations were consistently below the detection limit of 25 microgL(-1). The use of progressively shorter cycle times created selection pressures that fostered the self-immobilization of the reactor microorganisms into aerobic granules which first appeared on day 125. Specific TBA biodegradation rates in the granules followed the Haldane model for substrate inhibition, and peaked at 13.8 mgTBAgVSS(-1)h(-1) at a TBA concentration of 300 mgL(-1). Denaturing gradient gel electrophoresis (DGGE) analysis of PCR-amplified 16S rRNA genes from granules sampled between days 220 and 247 confirmed the existence of a highly stable microbial community with members belonging to the alpha, beta and delta subdivisions of Proteobacteria and the Cytophaga-Flavobacteria-Bacteroides (CFB) group.     

Distribution and change of microbial activity in combined UASB and AFB reactors for wastewater treatment

A thermophilic upflow anaerobic sludge blanket (UASB) reactor was combined with a mesophilic aerobic fluidized bed (AFB) reactor for treatment of a medium strength wastewater with 2,700?mg COD?l^?1. The COD removal efficiency reached 75% with a removal rate of 0.2 g COD?l^?1 h^?1 at an overall hydraulic retention time 14 hours. The distribution of microbial activity and its change with hydraulic retention time in the two reactors were investigated by measuring ATP concentration in the reactors and specific ATP content of the biomass. In the UASB reactor, the difference in specific ATP was significant between the sludge bed and blanket solution (0.02?mg ATP g VS^?1 versus 0.85?mg ATP g VS^?1) even though the ATP concentrations in these two zones were similar. A great pH gradient up to 4 was developed along the UASB reactor. Since a high ATP or biological activity in the blanket solution could only be maintained in a narrow pH range from 6.5 to 7.5, the sludge granules showed a high pH tolerance and buffering capacity up to pH 11. The suspended biomass in AFB reactor had a higher specific ATP than the biomass fixed in polyurethane carriers (1.6?mg ATP g VS^?1 versus 1.1?mg ATP g VS^?1), which implies a starvation status of the immobilized cells due to mass transfer limitation. The aerobes had to work under starvation conditions in this polishing reactor. The anaerobic biomass brought into AFB reactor contributed to an increase in suspended solids, but not the COD removal because of its fast deactivation under aerobic conditions. A second order kinetic model was proposed for ATP decline of the anaerobes. The results on distribution of microbial activity in the two reactors as well as its change with hydraulic retention time lead to further performance improvement of the combined anaerobic/aerobic reactor system.     

Toxic effects of thiol-reactive compounds on anaerobic biomass

The objective of this study was to characterize the toxic effects of three well known thiol-reactive electrophilic compounds, N-ethylmaleimide (NEM), pentachlorophenol (PCP) and 1-chloro-2,4-dinitrobenzene (CDNB) on anaerobic biotransformation process. The work was part of a larger investigation on potassium efflux as a possible response mechanism of anaerobic microorganisms to the presence of thiol-reactive organic compounds and the interference of such compounds on the reductive dehalogenation process. Using anaerobic toxicity assay (ATA) and granular anaerobic biomass from a full-scale upflow anaerobic sludge blanket (UASB) reactor, inhibitory concentrations of these compounds that reduced the microbial activity of granular biomass to 50% of a control (IC50) were determined to be 592, 0.97, and 450 mg/l for NEM, PCP, and CDNB, respectively. Toxicity of NEM was also tested on anaerobic biomass from a municipal wastewater treatment plant digester and slightly lower IC50 of 532 mg/l was obtained. The results presented here indicate that anaerobic biomass can acclimate to the three thiol-reactive compounds studied and recover from inhibition as long as the toxicant concentration is below a threshold level. That threshold concentration was found to be 500 mg/l for NEM on biomass from the municipal digester, 1 mg/l for PCP, and 500 mg/l for CDNB, both on granular biomass. Granular anaerobic biomass showed recovery even at NEM concentrations of 1000 mg/l.     

Kinetic parameters of continuous cultures of Bacillus thermoleovorans sp. A2 degrading phenol at 65 degrees C

In this paper, we report on the kinetics of phenol degradation and cell growth in continuous cultures of suspended cells of Bacillus thermoleovorans sp. A2 at 65 degrees C. A high yield coefficient of Y(x/s)=0.84 g cell dry weight g(-1) phenol was measured at a dilution rate of 0.5 h(-1). At the same dilution rate the coefficient for maintenance metabolism (m(s)) was determined to be 0.045 g phenol g(-1) cell dry weight h(-1). The maximal growth rate (wash-out) determined at a phenol inlet concentration of 188 mg l(-1) was 0.9 h(-1). Up to 7 g phenol l(-1) per day were degraded in a continuously operated 2-l stirred tank reactor with suspended cells (feed concentration 660 mg l(-1)). Additionally, yield coefficients for oxygen and ammonium are reported.     

Effect of long-term cobalt deprivation on methanol degradation in a methanogenic granular sludge bioreactor

The effect of the trace metal cobalt on the conversion of methanol in an upflow anaerobic sludge bed (UASB) reactor was investigated by studying the effect of cobalt deprivation from the influent on the reactor efficiency and the sludge characteristics. A UASB reactor (30 degrees C; pH 7) was operated for 261 days at a 12-h hydraulic retention time (HRT). The loading rate was increased stepwise from 2.6 g chemical oxygen demand (COD) x L reactor(-1) x d(-1) to 7.8 g COD x L reactor(-1) x d(-1). Cobalt deprivation had a strong impact on the methanogenic activity of the sludge. In batch tests, the methanogenic activity of the sludge with methanol as the substrate increased 5.3 (day 28) and 2.1 (day 257) times by addition of 840 nM of cobalt. The sludge had an apparent K(m) for cobalt of 948 nM after 28 days of operation and 442 nM at the end of the run. Cobalt deprivation during 54 days of operation led to a methanol conversion efficiency of only 55%. Continuous addition of cobalt (330 nM) for 33 days improved the methanol removal efficiency to 100%. In this period of cobalt dosing, the cobalt concentration in the sludge increased 2.7 times up to 32 microg x g TSS(-1). Upon omission of the cobalt addition, cobalt washed-out at a stable rate of 0.1 microg x g VSS(-1) x d(-1). At the end of the run, the cobalt concentration of the sludge was similar to that of the seed sludge.     

Influence of 2,4-dinitrophenol on the characteristics of activated sludge in batch reactors

The response of activated sludge characteristics to the presence of 2,4-dinitrophenol (dNP) in batch cultures was investigated in this study. The sludge yield slightly decreased with an increase in dNP concentration. At 10 mg l(-1), or lower, dNP significantly reduced sludge yield and relative specific growth rates (mu/mu0), but didn't substantially affect its relative specific chemical oxygen demand removal rate (q/q0). Presence of dNP at 1-20 mg l(-1) increased the specific oxygen uptake rate of activated sludge, and slightly changed its hydrophobicity. An analysis on inhibition indicated that the reduction in sludge yield in the presence of dNP was mainly attributed to the significant decreased sludge growth, rather than the reduced substrate degradation.     

High rate treatment of terephthalic acid production wastewater in a two-stage anaerobic bioreactor

The feasibility was studied of anaerobic treatment of wastewater generated during purified terephthalic acid (PTA) production in two-stage upflow anaerobic sludge blanket (UASB) reactor system. The artificial influent of the system contained the main organic substrates of PTA-wastewater: acetate, benzoate, and terephthalate. Three parallel operated reactors were used for the second stage, and seeded with a suspended terephthalate degrading culture, with and without additional methanogenic granular sludge (two different types). The first stage UASB-reactor was seeded with methanogenic granular sludge. Reactors were operated at 37 degrees C and pH 7. During the first 300 days of operation a clear distinction between the biomass grown in both reactor stages was obtained. In the first stage, acetate and benzoate were degraded at a volumetric loading rate of 40 g-COD/L . day at a COD-removal efficiency of 95% within the first 25 days of operation. No degradation of terephthalate was obtained in the first stage during the first 300 days of operation despite operation of the reactor at a decreased volumetric loading rate with acetate and benzoate of 9 g-COD/L . day from day 150. Batch incubation of biomass from the reactor with terephthalate showed that the lag-phase prior to terephthalate degradation remained largely unchanged, indicating that no net growth of terephthalate degrading biomass occurred in the first stage reactor. From day 300, however, terephthalate degradation was observed in the first stage, and the biomass in this reactor could successfully be enriched with terephthalate degrading biomass, resulting in terephthalate removal capacities of 15 g-COD/L . day. Even though no single reason could be identified why (suddenly) terephthalate degradation was obtained after such a long period of operation, it is suggested that the solid retention time as well the prevailing reactor concentrations acetate and benzoate may have played an important role. From day 1 of operation, terephthalate was degraded in the second stage. In presence of methanogenic granular biomass, high terephthalate removal capacities were obtained in these reactors (15 g-COD/L . day) after approximately 125 days of operation. From the results obtained it is concluded that terephthalate degradation is the bottleneck during anaerobic treatment of PTA-wastewater. Pre-removal of acetate and benzoate in staged bioreactor reduces the lag-phase prior to terephthalate degradation in latter stages, and enables high rate treatment of PTA-wastewater.     

Aggregation of immobilized activated sludge cells into aerobically grown microbial granules for the aerobic biodegradation of phenol

AIMS: The aim of this study is to evaluate the utility of aerobically grown microbial granules for the biological treatment of phenol-containing wastewater. METHODS AND RESULTS: A column-type sequential aerobic sludge blanket reactor was inoculated with activated sludge and fed with phenol as the sole carbon source, at a rate of 1.5 g phenol l-1 d-1. Aerobically grown microbial granules first appeared on day 9 of reactor operation and quickly grew to displace the seed flocs as the dominant form of biomass in the reactor. These granules were compact and regular in appearance, and consisted of bacterial rods and cocci and fungi embedded in an extracellular polymeric matrix. The granules had a mean size of 0.52 mm, a sludge volume index of 40 ml g-1 and a specific oxygen utilization rate of 110 mg oxygen g VSS-1 h-1 (VSS stands for volatile suspended solids). Specific phenol degradation rates increased with phenol concentration from 0 to 500 mg phenol l-1, peaked at 1.4 g phenol g VSS-1 d-1, and declined with further increases in phenol concentration as substrate inhibition effects became important. CONCLUSIONS: Aerobically grown microbial granules were successfully cultivated in a reactor maintained at a loading rate of 1.5 g phenol l-1 d-1. The granules exhibited a high tolerance towards phenol. Significant rates of phenol degradation were attained at phenol concentrations as high as 2 g l-1. SIGNIFICANCE AND IMPACT OF THE STUDY: This is the first study to demonstrate the ability of aerobically grown microbial granules to degrade phenol. These granules appear to represent an excellent immobilization strategy for microorganisms to biologically remove phenol and other toxic chemicals in high-strength industrial wastewaters.     

para-Chlorophenol inhibition on COD, nitrogen and phosphate removal from synthetic wastewater in a sequencing batch reactor

COD, nitrogen, phosphate and para-chlorophenol (4-chlorophenol, 4-CP) removal from synthetic wastewater was investigated using a four-step sequencing batch reactor (SBR) at different sludge ages and initial para-chlorophenol (4-CP) concentrations. The nutrient removal process consisted of anaerobic, oxic, anoxic and oxic phases with hydraulic residence times (HRT) of 1/3/1/1 h and a settling phase of 0.75 h. A Box-Wilson statistical experiment design was used considering the sludge age (5-25 days) and 4-CP concentration (0-400 mg l(-1)) as independent variables. Variations of percent COD, NH4-N, PO4-P and 4-CP removals with sludge age and initial 4-CP concentration were investigated. Percent nutrient removals increased with increasing sludge age and decreasing 4-CP concentrations. Low nutrient removals were obtained at high initial 4-CP concentrations especially at low sludge ages. However, high sludge ages partially overcome the adverse effects of 4-CP and resulted in high nutrient removals. COD, NH4-N, PO4-P and 4-CP removals were 76%, 72%, 26% and 34% at a sludge age of 25 days and initial 4-CP concentration of 200 mg l(-1). Sludge volume index (SVI) also decreased with increasing sludge age and decreasing 4-CP concentrations. An SVI value of 104 ml g(-1) was obtained at a sludge age of 25 days and initial 4-CP of 200 mg l(-1).     

Behavior of microbial communities developed in the presence/reduced level of soluble microbial products

Soluble microbial products (SMP) are organics produced by microorganisms as they degrade substrates. The available literature does not reveal how SMP affect and regulate microbial activities. In this study, we monitored variations in pH, dissolved oxygen concentration, soluble biological and chemical oxygen demands (sBOD₅ and sCOD) as a measure of microbial activity in synthetic wastewater. Aerobic degradation tests were carried out under the following conditions: aeration, 1,500 cm³ /min; initial sBOD₅, 515±5 mg/l; initial sCOD, 859±6 mg/l; initial biomass concentration (defined as mixed liquor suspended solids), 1,200±25 mg/l; sludge retention time, 24 h; and temperature, 20±1°C. The study involved non-acclimated biomass (R0 flora), biomass developed in the presence of SMP (R1 flora), and biomass developed in reduced level of SMP (R2 flora). We also determined which of these flora produced more refractory SMP. The results showed that R2 flora utilized the synthetic feed more quickly, and produced less refractory organic matter than R0 and R1 flora. The production of more refractory organics by R0 and R1 flora shows that not all the biomass was active. R1 flora degraded the substrates irregularly, suggesting that some microbes were dependent on the metabolic products of those that could utilize the feed components. These results show that production of SMP also depends on the prior substrates and on the ability of the flora to respond to changes in substrate composition.