Competitive reaction kinetics of sulfate-reducing bacteria and methanogenic bacteria in anaerobic filters

A kinetic model for the anaerobic filter (AF) that takes into account the mass fractions of sulfate-reducing bacteria (SRB) (f(SRB)) and methanogenic bacteria (MB) (f(MB)) and an inhibiting effect of H(2)S on bacterial groups is proposed. When the acetate-fed AFs were maintained at the low organic loading rate of 2.5kg COD/m(3)d, variations of the influent COD/SO(4)(2-) ratio (0.5-3.0) does not materially affect the acetate removal efficiency (all varying between 98.1% and 99.7%). With an increase in influent COD/SO(4)(2-) ratio, both the biofilm thickness and the specific substrate utilization rate decreased slightly but f(SRB) decreased markedly. The estimated results of f(SRB) and f(MB) showed that SRB out-competed MB for bacterial growth if the influent COD/SO(4)(2-) ratio was maintained at less than 1.3, whereas MB out-competed SRB for bacterial growth if the influent COD/SO(4)(2-) ratio was maintained at greater than 2.0. The specific substrate utilization rate of SRB (0.19-0.24mg acetate/mg VSSd) was lower than that of MB (0.31-0.59mg acetate/mg VSSd). The estimated kinetic parameters disclosed that the affinity of acetate to MB was higher and unionized H(2)S imposed a greater inhibiting effect on MB. The model simulation results (acetate and sulfate removal) agreed well with the experimental results.     

Effect of influent COD/SO4(2-) ratios on mesophilic anaerobic reactor biomass populations: physico-chemical and microbiological properties

The competitive and syntrophic interactions between different anaerobic bacterial trophic groups in sulphate limited expanded granular sludge bed (EGSB) reactors was investigated. The outcome of competition between the sulphate-reducing, methanogenic and syntrophic populations after development in reactors at varying influent COD/SO4 (2-) ratios was examined in batch activity tests with the inclusion of specific sulphate reducing bacteria (SRB) and methane producing archaea (MPA) inhibitors. SRB species could not out-compete MPA species for acetate at influent COD/SO4 (2-) ratios as low as 2. The SRB were seen to play a more significant role in the conversion of hydrogen but did not become completely dominant. HMPA were responsible for hydrogen utilization at an influent COD/SO4 (2-) ratio of 16, and were still dominant when the ratio was reduced to 4. It was only when the COD/SO4 (2-) ratio was reduced to 2 that the HSRB assumed a more influential role. SRB species were significant in the degradation of propionate at all COD/SO4 (2-) ratios applied. Sludge samples were analysed by scanning electron microscopy (SEM), granule size distribution and fluorescent in situ hybridization (FISH), combined with confocal laser scanning microscopy (CLSM), to monitor any changes in granule morphology under the various COD/SO4 (2-) ratios imposed during the reactor trial. In situ hybridization with domain- and species-specific oligonucleotide probes demonstrated a layered architecture with an outer layer harboring mainly Eubacterial cells and an inner layer dominated by Archaeal species.     

Specific biogas production and role of packing medium in the treatment of rubber thread manufacturing industry wastewater

Wastewater from three rubber thread manufacturing industries collected from three different sampling points was characterised. The acidic wastewater (pH = 3.6 to 4.7) contains high levels of COD, BOD, nitrogen and zinc. The average COD:N:P ratio was 100:3.8:0.4 whereas the BOD:N:P ratio was 100:4.5:0.4 with more than sufficient amounts of N and P for anaerobic digestion using the up-flow anaerobic filter. The specific biogas yield ranged between 0.250 to 0.069 l CH₄/g COD added when the organic loading rate was altered from 2.0 to 14.0 g COD/l/d respectively. The biogas production rate and the biogas yield rate increased from 8.2 to 42.7 l/d and 0.97 to 1.50 l CH₄/l/d respectively, for the same organic loading rate. The N and P utilised ranged between 1.53 to 1.20 and 0.3 to 0.26 mg per 100 mg COD consumed respectively when the organic loading rate was increased from 2.0 to 14.0 g COD/l/d. The optimum COD:N:P ratio obtained for steady state operation of the up-flow anaerobic filter in this study for the rubber thread manufacturing wastewater was 100:1.3:0.3. Attached biomass was responsible for the removal of more than 70% of the COD in the wastewater when PU foam was used as the packing media.     

Effect of molybdate on methanogenic and sulfidogenic activity of biomass

The effect of molybdate, a sulfate analog, on the total methanogenic activity (TMA) and total sulfidogenic activity (TSA) of biomass metabolizing synthetic sucrose based substrate containing sulfate was investigated in batch assays. In Phase I of the study, TMA and TSA were assessed twice for four feed changes at a chemical oxygen demand to sulfate (COD/SO(4)(2-)) ratio of 3.5. In Phase II, long-term experiments were conducted for 10-13 feed changes with varying chemical oxygen demand (COD) concentration, sulfate concentration, COD/SO(4)(2-) ratio, molybdate dose and biomass with different growth histories. Assays with 3mM molybdate showed TSA inhibition over 85%. Dose dependency was observed for sulfate concentration, COD/SO(4)(2-) ratio, and biomass history. The minimum concentration that gave over 93% TSA inhibition was 0.25 mM. However, intermediate concentrations of molybdate inhibited methane producing bacteria (MPB) activity. TMA stimulation was observed at 0.75-2.0 mM molybdate.     

Performance of an anaerobic bioreactor with biomass recycling, continuously removing COD and sulphate from industrial wastes

A 30-l anaerobic bioreactor with biomass recycling was used to provide a continuous reduction in sulphate and a continuous COD removal from wastewater, which consisted of the effluent from an industrial pig fattening farm, enriched with technical FeSO(4) x 7H(2)O, a waste product from ferrous metallurgy. The concentrations of sulphate and COD in the wastewater amounted to 2.73 g l(-1) and 3.15 g l(-1), respectively. The HRT (hydraulic retention time) of 10-1.7d produced an extent of sulphate and COD reduction which totalled 98% and 88%, respectively. When the HRT was further shortened, the efficiency of reduction in sulphate and COD decreased. The maximum removal rate constants for both the pollutants, calculated by means of a modified Stover-Kincannon model, were 80.9 g COD l(-1)d(-1) and 41.8 g SO(4)(2-)l(-1)d(-1), the values of the saturation constants being 91.582 g COD l(-1)d(-1) and 42.398 g SO(4)(2-)l(-1)d(-1).     

Effect of influent COD/N ratio on biological nitrogen removal (BNR) from high-strength ammonium industrial wastewater

The effect of influent COD/N ratio on biological nitrogen removal (BNR) from high-strength ammonium industrial wastewater was investigated. Experiments were conducted in a modified Ludzack–Ettinger pilot-plant configuration for 365 days. Total nitrification of an influent concentration of 1200 mg NH₄⁺–N l⁻¹ was obtained in this period. Influent COD/N ratios between 0.71 and 3.4 g COD g N⁻¹ were tested by varying the nitrogen loading rate (NLR) supplied to the pilot plant. An exponential decrease of nitrification rate was observed when the influent COD/N ratio increased.

The experimental COD/N ratio for denitrification was 7.1±0.8 g COD g N⁻¹ while the stoichiometric ratio was 4.2 g COD g N⁻¹. This difference is attributable to the oxidation of organic matter in the anoxic reactor with the oxygen of the internal recycle. The influence of influent COD/N ratio on the treatment of high-strength ammonium industrial wastewater can be quantified with these results. The influence of COD/N ratio should be one of the main parameters in the design of biological nitrogen removal processes in industrial wastewater treatment.     

Co-degradation of resorcinol and catechol in an UASB reactor

Co-degradation of resorcinol and catechol was studied in a catechol acclimated up flow anaerobic sludge blanket (UASB) reactor. Synthetic binary aqueous solution having a total concentration of 1000 mg/L with the resorcinol/catechol (R/C) ratio of 1/19, 1/9, 3/17, 1/4, 1/3, 3/7, 2/3 and then 1/3 was fed at various time intervals to the UASB reactor with a fixed organic loading rate of 5.7 kg COD/m(3) d and hydraulic retention time of 8h. The reactor was operated over a period of 145 days after its acclimation with catechol bearing synthetic wastewater at a constant feed rate of 1.2 L/h. When the resorcinol concentration was increased to have a R/C ratio of 1/4, the COD removal efficiency and the biogas production increased to the maximum levels. Pseudo steady state condition for COD removal was achieved at each of the stepped-up loading condition. An increase in the R/C ratio above 1/4 in the binary feed solution led to a decrease in the COD removal efficiency and the biogas production rate.     

Decolourisation of a synthetic textile effluent using a bacterial consortium

In the present study we examined the performance of a thermoalkalophilic bacterial consortium, where the predominant strain was Bacillus sp. SF, in the degradation of Reactive Black 5 (RB5). We used a reactor working in continuous mode and investigated the effects of pH, hydraulic retention time (HRT) and several added salts on colour and chemical oxygen demand (COD) reductions. For the chosen operational conditions (pH 9, 55 degrees C and HRT of 12 h) the efficiencies achieved were 91.2 +/- 0.8 % for colour removal and 81.2% for COD removal. The system tolerated, with no significant decrease in colour removal efficiency, 30 g/L Na(2)SO(4), Na(2)CO(3) or NaCl. The latter two salts, however, led to a reduction in COD removal of 30% and 50%, respectively. The system proved to be very effective in the decolourisation of C.I. RB5 under alkaline conditions and at a comparatively high temperature.     

Evaluation of a static granular bed reactor using a chemical oxygen demand balance and mathematical modeling

In order to evaluate the static granular bed reactor (SGBR), a chemical oxygen demand (COD) balance was used along with a mathematical model. The SGBR was operated with an organic loading rate (OLR) ranging from 0.8 to 5.5 kg/m³ day at 24 °C. The average COD removal efficiency was 87.4%, and the removal efficiencies of COD, carbohydrates, and proteins increased with an OLR, while the lipids removal efficiency was not a function of an OLR. From the results of the COD balance, the yield of biomass increased with an OLR. The SGBR was modeled using the general transport equation considering advection, diffusion, and degradation by microorganisms, and the first-order reaction rate constant was 0.0166/day. The simulation results were in excellent agreement with experimental data. In addition, the SGBR model provided mechanistic insight into why the COD removal efficiency in the SGBR is proportional to an OLR.     

Experimental study of the anaerobic urban wastewater treatment in a submerged hollow-fibre membrane bioreactor at pilot scale

The aim of this study was to assess the effect of several operational variables on both biological and separation process performance in a submerged anaerobic membrane bioreactor pilot plant that treats urban wastewater. The pilot plant is equipped with two industrial hollow-fibre ultrafiltration membrane modules (PURON? Koch Membrane Systems, 30 m2 of filtration surface each). It was operated under mesophilic conditions (at 33 °C), 70 days of SRT, and variable HRT ranging from 20 to 6h. The effects of the influent COD/SO?-S ratio (ranging from 2 to 12) and the MLTS concentration (ranging from 6 to 22 g L?1) were also analysed. The main performance results were about 87% of COD removal, effluent VFA below 20 mg L?1 and biogas methane concentrations over 55% v/v. Methane yield was strongly affected by the influent COD/SO?-S ratio. No irreversible fouling problems were detected, even for MLTS concentrations above 22 g L?1.     

Effect of COD/N ratio and salinity on the performance of sequencing batch reactors

The effects of COD/N ratio (3-6) and salt concentration (0.5-2%) on organics and nitrogen removal efficiencies in three bench top sequencing batch reactors (SBRs) with synthetic wastewater and one SBR with fish market wastewater were investigated under different operating schedules. The solids retention time (SRT, 20-100 days) and aeration time (4-10h) was also varied to monitor the performance. For synthetic wastewater, chemical oxygen demand (COD) removal efficiencies were consistently greater than 95%, irrespective of changes in COD/N ratio, aeration time and salt concentrations. Increasing the salt concentrations decreased the nitrification efficiency, while high COD/N ratio's favored better nitrogen removal (>90%). The treatment of real saline wastewater ( approximately 3.2%) from a fish market showed high COD (>80%) and nitrogen (>40%) removal efficiencies despite high loading rate and COD/N fluctuations, which is due to the acclimatization of the biomass within the SBR.     

Enzymatic iodination of polypeptides with 125I to high specific activity

1. Lactoperoxidase was extracted from cow milk by a simplified method starting with batch-wise adsorption onto GM-Sephadex-50. It was then purified by (NH4)2SO4 precipitation and isoelectric focusing. This product had an A412 nm/A280 nm ratio of 0.8-0.9. 2. Lactoperoxidase together with H2O2 could oxidize carrier-free Na125I to "active iodine" with efficiency to iodinate proteins to high specific activity. 3. Polypeptide hormones radioiodinated by this technique retained their immunological reactivity and were used in radioimmunoassays with good results.     

Microbial sulfate reduction with acetate: process performance and composition of the bacterial communities in the reactor at different salinity levels

Microbial sulfate reduction with acetate as carbon source and electron donor was investigated at salinity levels between 0.53 and 1.48%. The experiment was carried out in a 2.3-1 upflow anaerobic sludge blanket reactor inoculated with granular methanogenic sludge. A pH of 8.3, a temperature of 32 +/- 1 degrees C and a chemical oxygen demand (COD)/SO4(2-)-S ratio of 2 were maintained in the reactor throughout the experiment. Sulfate reduction and the composition of the dominant bacterial communities in the reactor were monitored. The results showed that a maximal conversion rate for SO4(2-)-S of 14 g l(-1) day(-1) and a conversion efficiency of more than 90% were obtained at a salinity level of 1.26-1.39%. A further increase in the salinity level led to reactor instability. Denaturant gradient gel electrophoresis of 16S rDNA fragments amplified by PCR from total bacterial DNA extracted from the inoculum and reactor sludge showed that salinity level had an impact on the composition of the bacterial communities in the reactor. However, no clear relationship was found between reactor performance and the composition of the dominant bacterial communities in the reactor.     

Control of COD/N ratio for nutrient removal in a modified membrane bioreactor (MBR) treating high strength wastewater

A modified membrane bioreactor (MBR) system has been developed to evaluate the efficiency of nutrient removal in treating synthetic high strength water. This study examined the effect of influent COD/N ratio on this system. Results showed that above 95.0% removal efficiencies of organic matter were achieved; indicating COD removal was irrespective of COD/N ratio. The average removal efficiencies of total nitrogen (TN) and phosphate (PO(4)(3-)-P) with a COD/N ratio of 9.3 were the highest at 90.6% and 90.5%, respectively. Furthermore, TN removal was primarily based on simultaneous nitrification and denitrification (SND) process occurred in the aerobic zone. Decreased COD/N ratios to 7.0 and 5.3, TN removal efficiencies in steady-states were 69.3% and 71.2%, respectively. Both aerobic SND and conventional biological nitrification/denitrification contributed to nitrogen removal and the latter played dominant effect. PO(4)(3-)-P-release and uptake process ceased in steady-states of COD/N 7.0 and 5.3, which decreased its removal efficiency significantly.     

Enhanced nitrogen removal in single‐chamber microbial fuel cells with increased gas diffusion areas

Single‐chamber microbial fuel cells (MFCs) with nitrifiers pre‐enriched at the air cathodes have previously been demonstrated as a passive strategy for integrating nitrogen removal into current‐generating bioelectrochemical systems. To further define system design parameters for this strategy, we investigated in this study the effects of oxygen diffusion area and COD/N ratio in continuous‐flow reactors. Doubling the gas diffusion area by adding an additional air cathode or a diffusion cloth significantly increased the ammonia and COD removal rates (by up to 115% and 39%), ammonia removal efficiency (by up to 134%), the cell voltage and cathode potentials, and the power densities (by a factor of approximately 2). When the COD/N ratio was lowered from 13 to 3, we found up to 244% higher ammonia removal rate but at least 19% lower ammonia removal efficiency. An increase of COD removal rate by up to 27% was also found when the COD/N ratio was lowered from 11 to 3. The Coulombic efficiency was not affected by the additional air cathode, but decreased by an average of 11% with the addition of a diffusion cloth. Ammonia removal by assimilation was also estimated to understand the ammonia removal mechanism in these systems. These results showed that the doubling of gas diffusion area enhanced N and COD removal rates without compromising electrochemical performance. Biotechnol. Bioeng. 2013; 110: 785–791. © 2012 Wiley Periodicals, Inc.     

Dyestuff wastewater treatment using chemical oxidation,physical adsorption and fixed bed biofilm process

Fenton’s oxidation and activated carbon adsorption were examined as pretreatment processes for dyestuff wastewater having high salinity, colour, and non-biodegradable organic concentrations. In this work, each wastewater stream produced by individual production processes was classified as streams R1, R2, and R3. The stream having a value of BOD₅/COD lower than 0.4 was pretreated by Fenton’s oxidation or activated carbon adsorption to increase the ratio of BOD₅/COD which indicates biodegradability. For Fenton’s oxidation with one stream having a value of BOD₅/COD lower than 0.4, the optimal reaction pH was 3.0 and the minimum dosing concentration (mg l⁻¹) of H₂O₂:FeSO₄·7H₂O was 700:3500. Stream R3, which consisted mainly of methanol was efficiently treated by activated carbon adsorption. The ratio of BOD₅/COD was also increased to 0.432 and 0.31 from 0.06 in Fenton’s oxidation and activated carbon adsorption, respectively. A biological treatment system using a fixed bed reactor was also investigated to enhance biological treatment efficiency at various hydraulic retention times, pretreatment conditions by Fenton’s reagent and salt concentrations by dyestuff wastewater. In addition, the efficiency of Fenton’s oxidation as a post-treatment system was also investigated to present a total treatment process of dyestuff wastewater. As the influent COD and salinity were increased, the effluent SS and COD were consequently increased. However, as the microorganisms became adapted to the changed influent condition, the treatment efficiency of the fixed bed reactor quickly recovered under the high COD and salinity since the microorganisms were well adapted to toxic influent conditions. A wastewater treatment process consisting of chemical oxidation, activated carbon adsorption, fixed bed biofilm process and Fenton’s oxidation as a post-treatment system can be useful to treat dyestuff wastewater having high salinity, colour, and non-biodegradable organic concentration.     

Effect of organic loading rate on the stability, operational parameters and performance of a secondary upflow anaerobic sludge bed reactor treating piggery waste

A study of anaerobic digestion of piggery wastewater was carried out in a laboratory-scale sludge bed reactor as a secondary treatment. The effect of organic volumetric loading rates (BV) in the range of 1.0-8.1 g TCOD/ld on the process performance was evaluated. The best results were obtained at BV equal to or lower than 4 g TCOD/ld. At higher BV values, the removal efficiency of the process decreased suddenly. A linear relationship was found between the effluent SCOD and the TVFA/alkalinity ratio (P). A relationship was found among the different operational variables (BV , removal efficiency, effluent soluble COD, soluble COD removal rate (R), retention factor (phi), specific microbial growth rate (mu), methane production rate per volume of reactor and per volume of waste treated--QM and qM, respectively) and the corresponding regression equations were obtained. An increase of BV determined a decrease of removal efficiency, phi and qM and an increase of effluent soluble COD, mu, R and QM. The value of the maximum specific microbial growth rate (muM) determined through the equation that correlated BV and mu was found to be 0.19 d(-1). This value was of the same magnitude as those reported in other works of anaerobic digestion of piggery waste.     

Denitrification of wastewater containing high nitrate and calcium concentrations

The removal of nitrate from rinse wastewater generated in the stainless steel manufacturing process by denitrification in a sequential batch reactor (SBR) was studied. Two different inocula from wastewater treatment plants were tested. The use of an inoculum previously acclimated to high nitrate concentrations led to complete denitrification in 6h (denitrification rate: 22.8mg NO(3)(-)-N/gVSSh), using methanol as carbon source for a COD/N ratio of 4 and for a content of calcium in the wastewater of 150mg/L. Higher calcium concentrations led to a decrease in the biomass growth rate and in the denitrification rate. The optimum COD/N ratio was found to be 3.4, achieving 98% nitrate removal in 7h at a maximum rate of 30.4mg NO(3)(-)-N/gVSSh and very low residual COD in the effluent.     

The effect of landfill age on municipal leachate composition

The influence of municipal landfill age on temporal changes in municipal leachate quality on the basis of elaboration of 4 years monitoring of leachate from landfill in Wysieka near Bartoszyce (Poland) is presented in this study. In leachate, concentrations of organic compounds (COD, BOD(5)), nutrients (nitrogen, phosphorus), mineral compounds, heavy metals and BTEX were investigated. It was shown that the principal pollutants in leachate were organics and ammonia - as landfill age increased, organics concentration (COD) in leachate decreased from 1,800 mg COD/l in the second year of landfill exploitation to 610 mg COD/l in the sixth year of exploitation and increase of ammonia nitrogen concentration from 98 mg N(NH)/l to 364 mg N(NH4) /l was observed. Fluctuation of other indexes (phosphorus, chlorides, calcium, magnesium, sulfate, dissolved solids, heavy metals, BTEX) depended rather on season of the year (seasonal variations) than landfill age. Moreover, the obtained data indicate that despite of short landfill's lifetime some parameters e.g. high pH (on average 7.84), low COD concentration (<2,000 mg COD/l), low BOD(5)/COD ratio (<0.4) and low heavy metal concentration, indicated that the landfill was characterized by methanogenic conditions already at the beginning of the monitoring period.     

Performance evaluation of a mesophilic anaerobic fluidized-bed reactor treating wastewater derived from the production of proteins from extracted sunflower flour

A study of the anaerobic digestion of wastewater derived from the production of protein isolates from extracted sunflower flour was carried out in a laboratory-scale, mesophilic (35 degrees C) fluidized-bed reactor with saponite as bacterial support. Chemical oxygen demand (COD) removal efficiencies in the range of 98.3-80.0% were achieved in the reactor at organic loading rates (OLR) of between 0.6 and 9.3 g COD/I d, hydraulic retention times (HRT) of between 20.0 and 1.1 d and average feed COD concentration of 10.6 g/l. Eighty percent of feed COD could be removed up to OLR of 9.3 g COD/l d. The yield coefficient of methane production was 0.33 l of methane (at STP) per gram of COD removed and was virtually independent of the OLR applied. Because the buffering capacity of the experimental system was maintained at favorable levels with excess total alkalinity present at all loadings, the rate of methanogenesis was not affected by loading. The experimental data indicated that a total alkalinity in the range of 2,000-2,460 mg/l as CaCO3 was sufficient to prevent the pH from dropping to below 7.0 for OLR of up to 9.3 g COD/l d. The volatile fatty acid (VFA) levels and the VFA/alkalinity ratio were lower than the suggested limits for digester failure (0.3-0.4) for OLR and HRT up to 9.3 g COD/l d and 1.1 d, respectively. For a HRT of 0.87 d (OLR of 12.1 g COD/l d) the start of acidification was observed in the reactor.