Denitrification of high concentrations of nitrites and nitrates in synthetic medium with different sources of organic carbon. III. Methanol

The denitrification of nitrites and nitrates (1000 mg N/l) in medium containing methanol as a source of organic carbon was studied. Continuous cultures of mixed population of autochtonic microflora from bottom sludge of nitrogenous wastewater reservoir were set up in a chemostat-type column and packed bed reactor. The efficiency of denitrification of nitrates in packed bed reactor was 506.7 mg N/l/h whereas denitrification of nitrites was from 8.7 to 16.0 mg N/l/h depending on the granulation of the filing material. In the latter case 83% nitrogen was removed from the medium. One of the factors causing low efficiency of denitrification of nitrites is excessive alkalization of the medium in the bed. The use of a three-step bed with adjusted pH resulted in complete denitrification of nitrites with efficiency 60 mg N/l/h. The bacteria inside the bed were dominated by Paracoccus denitrificans and by Pseudomonas aeruginosa when nitrates were present. The sensitivity of P. denitrificans to high concentrations of nitrites seems to be the second factor contributing to low efficiency of denitrification with methanol as organic substrate.     

Empirical model for the autotrophic biodegradation of thiocyanate in an activated sludge reactor

AIMS: The aim of this investigation was to develop an empirical model for the autotrophic biodegradation of thiocyanate using an activated sludge reactor. METHODS AND RESULTS: The methods used for this purpose included the use of a laboratory scale activated sludge reactor unit using thiocyante feed concentrations from 200 to 550 mg x l(-1). Reactor effluent concentrations of <1 mg x l(-1) thiocyanate were consistently achieved for the entire duration of the investigation at a hydraulic retention time of 8 h, solids (biomass) retention of 18 h and biomass (dry weight) concentrations ranging from 2 to 4 g x l(-1). A biomass specific degradation rate factor was used to relate thiocyanate degradation in the reactor to the prevailing biomass and thiocyanate feed concentrations. A maximum biomass specific degradation rate of 16 mg(-1) x g(-1) x h(-1) (mg thiocyanate consumed per gram biomass per hour) was achieved at a thiocyanate feed concentration of 550 mg x l(-1). The overall yield coefficient was found to be 0.086 (biomass dry weight produced per mass of thiocyanate consumed). CONCLUSION: Using the results generated by this investigation, an empirical model was developed, based on thiocyanate feed concentration and reactor biomass concentration, to calculate the required absolute hydraulic retention time at which a single-stage continuously stirred tank activated sludge reactor could be operated in order to achieve an effluent concentration of <1 mg x l(-1). The use of an empirical model rather than a mechanistic-based kinetic model was proposed due to the low prevailing thiocyanate concentrations in the reactor. SIGNIFICANCE AND IMPACT OF THE STUDY: These results represent the first empirical model, based on a comprehensive data set, that could be used for the design of thiocyanate-degrading activated sludge systems.     

Enhanced selection of an anaerobic pentachlorophenol-degrading consortium

A rapid enrichment approach based on a pentachlorophenol (PCP) feeding strategy which linked the PCP loading rate to methane production was applied to an upflow anaerobic sludge bed reactor inoculated with anaerobic sludge. Due to this strategy, over a 140-day experimental period the PCP volumetric load increased from 2 to 65 mg L(R)(-1) day(-1) with a near zero effluent concentration of PCP. Dechlorination dynamics featured sequential appearance of 3,4,5-chlorophenol, 3,5-chloro- phenol, and 3-chlorophenol in the reactor effluent. Profiling of the reactor population by denaturing gradient gel electrophoresis (DGGE) revealed a correlation between the appearance of dechlorination intermediates and bands on the DGGE profile. Nucleotide sequencing of newly detected 16S rDNA fragments suggested the proliferation of Clostridium and Syntrophobacter/Syntrophomonas spp. in the reactor during PCP degradation. Published by John Wiley & Sons, Inc.     

Biodegradation of high phenol containing synthetic wastewater by an aerobic fixed bed reactor

The continuous aerobic degradation of phenol, mixed with readily degradable synthetic wastewater was studied over a period of 400 days at 25+/-5 degrees C temperature in a fixed bed biofilm reactor using 'Liapor' clay beads as packing material. The phenol concentration added to the reactor ranged from 0.19 to 5.17g/l and was achieved by a gradual increase of phenol in wastewater, thus adapting the microbial flora to high contaminant concentrations. A maximal removal rate of 2.92g phenol/(ld) at a hydraulic retention time (HRT) of 0.95 days and a total organic loading rate (OLR) of 15.3g COD/(ld) with a phenol concentration of 4.9g/l was observed. However, this was not a stable rate at such high phenol loading. At the end of reactor operation on day 405, the phenol removal rate was 2.3g/(ld) at a influent phenol concentration of 4.9g/l. There were no phenol intermediates present in the reactor, as evident from corresponding COD, phenol removal and the absence of fatty acids. Omission of organic nitrogen compounds or of urea in influent feed was not favourable for optimal phenol removal. The phenol degradation profile that was studied in shake flasks indicated that the presence of a acetate which represent as an intermediate of phenol degradation retarded the phenol degradation. The highest phenol degradation rate observed in batch assays was 3.54g/(ld).     

Evaluation of straw as a biofilm carrier in the methanogenic stage of two-stage anaerobic digestion of crop residues

Straw was evaluated as a biofilm carrier in the methanogenic stage of the two-stage anaerobic digestion of crop residues. Three reactor configurations were studied, a straw-packed-bed reactor, a glass packed-bed reactor and a reactor containing suspended plastic carriers. The reactor with the packed straw bed showed the best results. It had the highest methane production, 5.4 11(-1) d(-1), and the chemical oxygen demand (COD) removal ranged from 73-50% at organic loading rates from 2.4-25 g COD l(-1) d(-1). The degradation pattern of volatile fatty acids showed that the degradation of propionate and longer-chain fatty acids was limiting at higher organic loading rates. A stable effluent pH showed that the packed-bed reactors had good ability to withstand the variations in load and volatile fatty acid concentrations that can occur in the two-stage process. The conclusion is that straw would work very well in the intended application. A further benefit is that straw is a common agricultural waste product and requires only limited resources concerning handling and cost.     

Adaptation of anaerobic ammonium-oxidising consortium to synthetic coke-ovens wastewater

A consortium with autotrophic anaerobic ammonium oxidising (AAAO) activity was developed from municipal sludge, and its ability to remove high ammonium concentrations in a toxic wastewater such as coke ovens wastewater is presented here. The enriched AAAO consortium was acclimatised to a synthetic coke ovens wastewater to establish anaerobic ammonium oxidation (AAO) activity. Phenol was the main carbon component of the synthetic wastewater whereby it was added stepwise from 50+/-10 to 550+/-10 mg l(-1) into an anammox enrichment medium. Ammonium-N removal was initially impaired; however, it gradually recovered. After 15 months of further selection and enrichment, the ammonium removal rate reached 62+/-2 mg NH(4)(+)-N l(-1) day(-1), i.e. 1.5 times the rate in the original AAAO reactor. The new consortium demonstrated higher ammonium and nitrite removal rates, even under phenol perturbation (up to 330+/-10 mg l(-1)). It is therefore concluded that the AAO activity in the consortium was resistant to high phenol and has potential for treating coke-ovens wastewater.     

Continuous anaerobic phenol degradation using an adapted mixed culture

A mixed culture derived from cow dung and sewage sludge and adapted to phenol was used for anaerobic phenol degradation. The phenol degradation rate depended on the period of adaptation of the mixed culture to phenol. In the continuous process, a higher degradation rate (2500 mg.1^-1 d^-1) and better reactor stability was achieved with a granular activated-carbon-packed bed reactor than with a stirred tank reactor.The authors are with the Department of Biochemical Engineering & Biotechnology, Indian Institute of Technology, Delhi Hauz Khas, New Delhi, India.     

Effect of various sources of organic carbon and high nitrite and nitrate concentrations on the selection of denitrifying bacteria. II. Continuous cultures in packed bed reactors

The effect of different organic compounds, nitrites and nitrates at the concentration of 1,000 mg N/l on the quantitative and strain-specific selection of denitrifying bacteria was determined in anaerobic packed bed reactors. Both the source of carbon and nitrogen form influenced strain specificity and the frequency of occurrence of denitrifying bacteria. The frequency of denitrifying bacteria within packed bed reactor ranged in different media from 11% (glucose and nitrates) to 100% (methanol and ethanol with nitrates). A single species selection was observed in the presence of nitrites within packed bed reactor: Pseudomonas aeruginosa in medium with acetate. Pseudomonas stutzeri in medium with ethanol, Pseudomonas mendocina in medium with methanol and Pseudomonas fluorescens in medium with glucose. When nitrates were present in packed bed reactor, the dominating bacteria were: P. stutzeri in medium with acetate, P. fluorescens in medium with ethanol, Paracoccus denitrificans in medium with methanol and Alcaligenes faecalis in medium with glucose.     

Biodegradation of pentachlorophenol in a continuous anaerobic reactor augmented with Desulfitobacterium frappieri PCP-1.

In this work, a strain of anaerobic pentachlorophenol (PCP) degrader, Desulfitobacterium frappieri PCP-1, was used to augment a mixed bacterial community of an anaerobic upflow sludge bed reactor degrading PCP. To estimate the efficiency of augmentation, the population of PCP-1 in the reactor was enumerated by a competitive PCR technique. The PCP-1 strain appeared to compete well with other microorganisms of the mixed bacterial community, with its population increasing from 10(6) to 10(10) cells/g of volatile suspended solids within a period of 70 days. Proliferation of strain PCP-1 allowed for a substantial increase of the volumetric PCP load from 5 to 80 mg/liter of reaction volume/day. A PCP removal efficiency of 99% and a dechlorination efficiency of not less than 90.5% were observed throughout the experiment, with 3-Cl-phenol and phenol being observable dechlorination intermediates.     

Biodegradation of tech-hexachlorocyclohexane in a upflow anaerobic sludge blanket (UASB) reactor

Biodegradability of technical grade hexachlorocyclohexane (tech-HCH) was studied in an upflow anaerobic sludge blanket reactor (UASB) under continuous mode of operation in concentration range of 100-200 mg/l and constant HRT of 48 h. At steady state operation more than 85% removal of tech-HCH (upto 175 mg/l concentration) and complete disappearance of beta-HCH was observed. Kinetic constants in terms of maximum specific tech-HCH utilization rate (k) and half saturation velocity constant (K(L)) were found to be 11.88 mg/g/day and 8.11 mg/g/day, respectively. The tech-HCH degrading seed preparation, UASB reactor startup and degradation in continuous mode of operation of the reactor is presented in this paper.     

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.     

Performance of an UASB reactor treating synthetic wastewater at low-temperature using cold-adapted seed slurry

The present study is an attempt to investigate if a long-term acclimation of digester contents to low-temperatures would improve wastewater treatment at low-temperatures similar to mesophilic ranges. The feasibility of low-temperature (15 °C) anaerobic treatment of synthetic wastewater in an upflow anaerobic sludge blanket reactor was studied using inoculum from a cattle manure digester adapted to 15 °C. The effect of varying hydraulic retention time was studied by decreasing the retention time from 7 days to 1 day. Under a constant temperature of 15 °C with a hydraulic retention time of 1 day and a corresponding loading rate of 7.2 g-chemical oxygen demand (COD)/l/day, 90–95% removal efficiency was achieved. The methane production of 250 l/kg-COD removed at standard temperature pressure (STP) is a major highlight of the study complementing the high treatment efficiency achieved. Loading rates >5 g-COD/l/day was accompanied by increase in effluent volatile fatty acids (VFA) concentrations. Due to the presence of a high concentration of active granular sludge in the lower compartment of the reactor, 80% reduction of COD occurred within the granular bed of the reactor. Treatment of low strength wastewater for a short period showed 70–75% removal efficiencies with methane yield of 300 l/kg-COD removed. Specific methanogenic activity profiles of the anaerobic biomass revealed low-temperature (15 °C) optima, indicating selection of cold-active microorganisms during the acclimation process. The SMA assays also indicate the development of a putatively psychrophilic acetoclastic methanogenic community and biogas analysis showed 75% efficiency in energy recovery as methane.     

Slaughterhouse wastewater treatment: evaluation of a new three-phase separation system in a UASB reactor.

The anaerobic treatment of the wastewater from the meat processing industry was studied using a 7.2 1 UASB reactor. The reactor was equipped with an unconventional configuration of the three-phase separation system. The effluent was characterized in terms of pH (6.3-6.6), chemical oxygen demand (COD) (2,000-6,000 mg l(-1)), biochemical oxygen demand BOD5 (1,300-2,300 mg 1(-1)), fats (40-600 mg l(-1)) and total suspended solids (TSS) (850-6,300 mg l(-1)) The reactor operated continuously throughout 80 days with hydraulic retention time of 14, 18 and 22 h. The wastewater from Rezende Industrial was collected after it had gone through pretreatment (screening, flotation and equalization). COD, BOD and TSS reductions and the biogas production rate were the parameters considered in analyzing the efficiency of the process. The average production of biogas was 111 day(-1) (STP) for the three experimental runs. COD removal varied from 77% to 91% while BOD removal was 95%. The removal of total suspended solids varied from 81% to 86%. This fact supports optimal efficiency of the proposed three-phase separation system as well as the possibility of applying it to the treatment of industrial effluents.     

Immobilized white-rot fungal biodegradation of phenol and chlorinated phenol in trickling packed-bed reactors by employing sequencing batch operation

The biodegradation of phenol and 2,4,6-trichlorophenol (2,4,6-TCP) by immobilized white-rot fungal cultures was studied in pinewood chip and foam glass bead-packed trickling reactors. The reactors were operated in sequencing batch format. Removal efficiency increased over time and elevated influent phenol and 2,4,6-TCP (800 and 85 mg l(-1)) concentrations were removed by greater than 98% in 24-30 h batch cycles. Comparable performance between the packing materials was shown. Increased lignin peroxidase (LiP) activity was detected with the introduction of the compounds and optimum activity corresponded to optimum removal periods. Higher LiP activity (16.7-19 Ul(-1)) was detected in glass bead-packed reactor compared to wood chip reactor (0.2-5 Ul(-1)). The presence of Mn(2+) in the wood material possibly effected elevated manganese peroxidase (MnP) activity (0.3-5.8 Ul(-1)) compared to low to negligible activity in the glass bead reactor. Reactor performances are discussed in relation to sequencing batch operation and nutrient requirements necessary to induce and sustain fungal enzyme activity in inert vs. organic material packed systems.     

Biodegradation of Pentachlorophenol in a Continuous Anaerobic Reactor Augmented with Desulfitobacterium frappieri PCP-1

In this work, a strain of anaerobic pentachlorophenol (PCP) degrader, Desulfitobacterium frappieri PCP-1, was used to augment a mixed bacterial community of an anaerobic upflow sludge bed reactor degrading PCP. To estimate the efficiency of augmentation, the population of PCP-1 in the reactor was enumerated by a competitive PCR technique. The PCP-1 strain appeared to compete well with other microorganisms of the mixed bacterial community, with its population increasing from 10⁶ to 10¹⁰ cells/g of volatile suspended solids within a period of 70 days. Proliferation of strain PCP-1 allowed for a substantial increase of the volumetric PCP load from 5 to 80 mg/liter of reaction volume/day. A PCP removal efficiency of 99% and a dechlorination efficiency of not less than 90.5% were observed throughout the experiment, with 3-Cl-phenol and phenol being observable dechlorination intermediates.     

Experimental studies and mathematical modeling of an up-flow biofilm reactor treating mustard oil rich wastewater

Bioremediation of lipid-rich model wastewater was investigated in a packed bed biofilm reactor (anaerobic filter). A detailed study was conducted about the influence of fatty acid concentration on biomethanation of the high-fat liquid effluent of edible oil refineries. The biochemical methane potential (BMP) of the liquid waste was reported and maximum cumulative methane production at the exit of the reactor is estimated to be 785 ml CH₄ (STP)/(g VSS added). The effects of hydraulic retention time (HRT), organic loading rate (OLR) and bed porosity on the cold gas efficiency or energy efficiency of the bioconversion process were also investigated. Results revealed that the maximum cold gas efficiency of the process is 42% when the total organic load is 2.1 g COD/l at HRT of 3.33 days. Classical substrate uninhibited Monod model is used to generate the differential system equations which can predict the reactor behavior satisfactorily.     

Impact of liquid-to-gas hydrogen mass transfer on substrate conversion efficiency of an upflow anaerobic sludge bed and filter reactor

Efficient anaerobic degradation may be completed only under low levels of dissolved hydrogen in the liquid surrounding the microorganisms. This restraint can be intensified by the limitations of liquid-to-gas H₂ mass transfer, which results in H₂ accumulation in the bulk liquid of the reactor. Dissolved hydrogen proved to be an interesting parameter for reactor monitoring by showing a good correlation with short-chain volatile fatty acid concentration, namely propionate, which was not the case for the H₂ partial pressure. Biogas recycle was performed in a upflow anaerobic sludge bed and filter reactor. The effects of varying the ratio of recycled-to-produced gas from 2:1 (9 l/l reactor per day) to 8:1 (85 l/l reactor per day) were studied. By increasing the liquid—gas interface with biogas recycling, the dissolved hydrogen concentration could be lowered from 1.1 to 0.4 μ . Accordingly, the H₂ sursaturation factor was also reduced, leading to an important improvement of the H₂ mass transfer rate, which reached 20.86 h⁻¹ (±9.79) at a 8:1 gas recycling ratio, compared to 0.72 h⁻¹ (±0.24) for the control experiment. Gas recycling also lowered the propionate concentration from 655 to 288 mg l⁻¹ and improved the soluble chemical oxygen demand removal by 10–15%. The main problem encountered was the shorter solid retention time, which could lead to undesirable biomass washout at high gas recycling ratio. This could be circumvented by improving the reactor design to reduce the turbulence within the biomass bed.     

Conversion of cereal residues into biogas in a rumen-derived process

A recently developed high-rate, two-phase process, which employs rumen microorganisms for efficient acidogenesis, was tested for anaerobic degradation of barley straw, rye straw, and maize stover. Under conditions similar to those of the rumen and loading rates varying between 9.8 and 26.0 g of organic matter/I/day in the first phase (acidogenic reactor), total fibre degradation efficiencies ranged between 42% and 57%, irrespective of the loading rate applied. Average specific production of volatile fatty acids and biogas/g volatile solid digested in the acidogenic reactor varied between 6.9 and 11.2 mmol and 0.10 and 0.25 l, respectively.The effect of varying solid retention times on the extent of degradation of barley straw was examined. Changing of retention times in the range of 60 to 156 h had no effect on degradation efficiency, but a decrease in efficiency was observed at retention times below 60 h.By connecting the acidogenic reactor in series to an Upflow Anaerobic Sludge Blanket (UASB) methanogenic reactor the volatile fatty acids were converted into biogas. Average methane contents of the gases produced in the acidogenic reactor and in the UASB reactor were 30±3% and 78±3%, respectively.     

Continuous adsorption and recovery of Cr(VI) in different types of reactors

This study reports the results of experiments on continuous adsorption and desorption of Cr(VI) ions by a chemically modified and polysulfone-immobilized biomass of the fungus Rhizopus nigricans. A fixed quantity of polymer-entrapped biomass beads corresponding to 2 g of dry biomass powder was employed in packed bed, fluidized bed, and stirred tank reactor for monitoring the continuous removal and recovery of Cr(VI) ions from aqueous solution and synthetic chrome plating effluent. Parameters such as flow rate (5, 10 and 15 mL/min), inlet concentration of Cr(VI) ions (50, 100, 150 and 250 mg/L) and the depth of biosorbent packing (22.8, 11.2 and 4.9 cm) were evaluated for the packed bed reactor. The breakthrough time and the adsorption rates in the packed bed column were found to decrease with increasing flow rate and higher Cr inlet concentrations and to increase with higher depths of sorbent packing. To have a comparative analysis of Cr adsorption efficiency in different types of reactors, the fluidized bed reactor and stirred tank reactor were operated using the same quantities of biosorbent material. For the fluidized bed reactor, Cr(VI) solution of 100 mg/L was pumped at 5 mL/min and fluidized by compressed air at a flow rate of 0.5 kg/cm.(2) The stirred tank reactor had a working volume of 200 mL capacity and the inlet/outlet flow rate was 5 mL/min. The maximum removal efficiency (mg Cr/g biomass) was obtained for the stirred tank reactor (159.26), followed by the fluidized reactor (153.04) and packed bed reactor (123.33). In comparison to the adsorption rate from pure chromate solution, approximately 16% reduction was monitored for synthetic chrome plating effluent in the packed bed. Continuous desorption of bound Cr ions from the reactors was effective with 0.01 N Na(2)CO(3) and nearly 80-94% recoveries have been obtained for all the reactors.     

Development of a novel process for the biological conversion of H2S and methanethiol to elemental sulfur

The feasibility of anaerobic treatment of wastewater containing methanethiol (MT), an extremely volatile and malodorous sulfur compound, was investigated in lab-scale bioreactors. Inoculum biomass originating from full-scale anaerobic wastewater treatment facilities was used. Several sludges, tested for their ability to degrade MT, revealed the presence of organisms capable of metabolizing MT as their sole source of energy. Furthermore, batch tests were executed to gain a better understanding of the inhibition potential of MT. It was found that increasing MT concentrations affected acetotrophic organisms more dramatically than methylotrophic organisms. Continuous reactor experiments, using two lab-scale upflow anaerobic sludge bed (UASB) reactors (R1 and R2), aimed to determine the maximal MT load and the effect of elevated sulfide concentrations on MT conversion. Both reactors were operated at a hydraulic retention time (HRT) of about 7 hours, a temperature of 30 degrees C, and a pH of between 7.3 and 7.6. At the highest influent MT concentration applied, 14 mM in R1, corresponding to a volumetric loading rate of about 50 mM MT per day, 87% of the organic sulfur was recovered as hydrogen sulfide (12.2 mM) and the remainder as volatile organic sulfur compounds (VOSCs). Upon decreasing the HRT to 3.5 to 4.0 h at a constant MT loading rate, the sulfide concentration in the reactor decreased to 8 mM and MT conversion efficiency increased to values near 100%. MT conversion was apparently inhibited by the high sulfide concentrations in the reactor. The specific MT degradation rate, as determined after 120 days of operation in R1, was 2.83 +/- 0.27 mmol MT g VSS(-1) day(-1). During biological desulfurization of liquid hydrocarbon phases, such as with liquefied petroleum gas (LPG), the combined removal of hydrogen sulfide and MT is desired. In R2, the simultaneous addition of sodium sulfide and MT was therefore studied and the effect of elevated sulfide concentrations was investigated. The addition of sodium sulfide resulted in enhanced disintegration of sludge granules, causing significant washout of biomass. Additional acetate, added to stimulate growth of methanogenic bacteria to promote granulation, was hardly converted at the termination of the experimental period.