Upflow Sludge Blanket Research Articles

Characterization of Denitrifying Granular Sludge Treating Soft Groundwater in an Upflow Sludge-Blanket Reactor.

Nitrate removal from soft groundwater using ethanol as a carbon source in an upflow sludge-blanket reactor containing denitrifying granular sludge was investigated. At a hydraulic retention time of 0.83 h, influent nitrate was increased stepwise from 20 to 145 mg N/l (volumetric loading rates (VLRs), 0.60 to 4.2 g N/l/d, respectively) and sludge was periodically wasted to maintain a sludge bed of about 2 3 the liquid volume. Complete nitrate removal was achieved at influent nitrate concentrations up to 75 mg N/l(2.1 g N/l/d). MLSS increased from 20 g/l at a VLR of 0.6 g N/l/d to 51 g/l at a VLR of 1.9 g N/l/d, above which it decreased. VSS increased from 11 g/l to a maximum of 25 g/l at a VLR of 2.1 g N/l/d. Settling velocities showed the same trend with maximum values in a VLR range of 1.5 to 2.1 g N/l/d. However, granule size, calcium and magnesium contents of the granular sludge and protein, carbohydrate and nucleic acid contents of extracellular polymers decreased steadily with an increase in VLR throughout the range of testing. Within the VLR range of 0.6 to 2.1 g N/l/d, corresponding to complete nitrate removal and efficient sludge retention, the granular sludge had a high calcium content of 24 to 22%, magnesium ranged from only 0.7 to 0.1%, proteins from 3.2 to 1.3%, carbohydrates from 4.2 to 1.4%, and nucleic acids from 0.34 to 0.05% of the sludge dry weight. These results suggest an optimum operational VLR in terms of nitrate removal and sludge retention of about 2 g N/l/d.

Anaerobic treatability of leachate: a comparative evaluation for three different reactor systems

In this study landfill leachate from two young municipal landfill sites were treated in three bench-scale systems including anaerobic sequencing batch reactors (ASBR), anaerobic hybrid bed filter (AHBF) and upflow sludge blanket reactor (UASBR) at mesophilic conditions. The experimental studies have been conducted at variable influent leachate CODs of 1900–19000 mg.l–1 and hydraulic retention times (HRT) of 10 to 1.5 days and solid retention times (SRT) of 40 to 10 days in ASBRs. Influent leachate concentrations and HRT's of AHBF were varied in the range of 4000 to 15000 mg.l–1 and 5.1 to 0.9 days, respectively. Anaerobic treatability studies have been performed for about 20 months using 3.5 year old landfill leachate for ASBR and AHBF. The anaerobic treatability of the second leachate which was only two years old was investigated in the lab-scale UASBR for about 4 months. The influent CODs of the UASBR were varied from 9000 to 25000 mg.l–1. HRTs ranged from 1.7 to 2.35 days in the same period. COD removals were in the range of 92 to 94% at the related operating conditions. The steady-state performance data of anaerobic reactors fit quite well to the linearized second-order multicomponent substrate removal kinetic model with a correlation of more than 98%.

Denitrification of greenhouse leachates in an upflow sludge blanket reactor

Biological denitrification of greenhouse leachates was investigated in laboratory scale upflow sludge blanket (USB) reactors. Two simulative solutions, representing greenhouse leachates at “high concentration” (200 mg/L NO3––N and 140 mg/L PO43–) and “low concentration” (120 mg/L NO3––N and 15 mg/L PO43–) ranges were used in the experiments. Ethanol was added as the carbon and electron source for bacterial metabolism. The USB reactor successfully removed 99% of the nitrate at retention times from 1 hour to 10 minutes. Nitrogen removal rates reached 16.7 g NO3––N/L · d for the “low concentration” reactor and 26.8 g NO3––N/L · d for the “high concentration” reactor. Due to the large increase in alkalinity resulting from the denitrification, precipitation of calcium compounds occurred which resulted in sludge with good settling characteristics (SVI=6.5 to 8 ml/g). The mineral fraction of the granular sludge was higher than 50%. High concentrations of biomass (100g/L TSS and 40 g/L VSS) were also observed. From the mineral analysis of the granular sludge, the main precipitating compound in the “low concentration” reactor was identified as calcium carbonate. In the “high concentration” reactor, the mineral analysis did not give a clear answer as to the composition of the precipitating compound. Using theoretical Ksp values together with the remaining soluble concentrations of calcium, phosphate and pH in the effluent, amorphous Ca3(PO4)2 was suggested as the main precipitating compound. The calcium phosphate rich sludge was shown to be unstable and dissolved when the influent concentrations were changed. Modeling the biological and chemical processes in the reactor was done using AQUASIM modified to include chemical systems. When experimental Ksp values were used, the model gave good agreement with reactor results.

Denitrification in a Carbon and Nitrogen Removal System for Leachate Treatment: Performance of a Upflow Sludge Blanket (USB) Reactor

The performance of a bench scale upflow sludge bed (USB) denitrifying reactor was evaluated in order to integrate it into a C and N removal system for Sanitary Landfill Leachate. The raw leachate used presented COD and NH4-N average values of 30000 mg/l and 1000 mg/l, respectively. The complete system comprises in addition an UASB reactor and a nitrifying RBC. A portion of the aerobic reactor effluent was recycled into the denitrification stage and some raw leachate was also added as an additional C source. In order to obtain operating parameters the denitrifying reactor was operated alone. Sludge from an aerobic reactor (RBC) treating raw leachate was used as inoculum. Shortly after the start up, good granulation of the sludge bed was observed. Using raw leachate and UASB outlet as carbon sources with COD/NO3-N ratios of 4 and 12, respectively, denitrification efficiencies of about 90% were reached. A sludge yield of 0.16 gVSS/gCODremoved was obtained operating with raw leachate. For the anoxic reactor operating in the complete system, denitrification efficiencies of 90% were also achieved. A nitrogen gas recycle was a successful way to avoid frequently observed sludge bed rising problems.

Post-Treatment of Effluents from Anaerobic Reactor Treating Domestic Sewage by Dissolved-Air Flotation

This paper presents the results of a study performed with a lab-scale dissolved-air flotation (LSDAF) unit fed with previously coagulated effluent from a pilot scale up-flow anerobic sludge blanket (UASB) reactor treating domestic sewage. Physical operational conditions for coagulation (rapid mix) and flocculation/flotation were maintained constant. Chemical (FeCl3) dosages ranged from 30 to 110 mg.l−1. The effect of pH was also verified in the range of 5.1 to 7.6 for each dosage. Best results were achieved for 65 mg.l−1 of FeCl3 and pH values between 5.3 and 6.1. For these conditions, the removal efficiencies obtained in the LSDAF unit were: between 87% and 91% for chemical oxygen demand (COD), between 95% and 96% for total phosphate (TP), 94% for total suspended solids (TSS), between 96% and 97% for turbidity (TU), between 90% and 93% for apparent color (AC) and more than 96% for sulfide (S). For the UASB-DAF system, global efficiencies would be around 98% for COD, 98% for TP, 98.4% for TSS, 99.3% for TU and 98% for AC. The stripped gases treatment is desirable.

New and Broader Applications of Anaerobic Digestion

The general performance of anaerobic digesters and the diversity of wastes that these can treat have been increasing steadily during the last decade as a result of new reactor designs, operating conditions, or the use of specialized microbial consortia. This article illustrates a few examples of new or broader applications of anaerobic digestion to the treatment of sewage, slurries, industrial wastewater, and solid wastes. In the case of domestic sewage, the sustainability of the overall process is much improved by the adoption of an anaerobic pretreatment step, for example, an upflow sludge blanket (USB) reactor. New methods for nutrient removal need to be coupled with anaerobic digestion. These may include, for example, anaerobic ammonium oxidation (anammox) and chemical P precipitation. In terms of industrial wastewaters, new additives are being developed that help the anaerobic sludge deal with unbalanced or toxic wastewaters. Engineering of anaerobic sludge granules is a new area of research that serves the purpose of expanding and rechanneling the catabolic capabilities of the sludge and of shortening the length of the adaptation period of the microbial consortia to xenobiotics. New biotechnologies are also being marketed for the anaerobic removal of sulfate and heavy metals in liquid and gaseous wastes. The new ‘high-solids’ fermentation technology used to treat solid wastes in industrialized regions is being expanded to suit specific needs of regions with other priorities such as the presence of nonbiocompatible solid wastes or the occurrence of fuel shortage.

Maintainability of Denitrifying Granular Sludge in Soft to Marginally Hard Waters in an Upflow Sludge-Blanket Reactor

The maintainability of denitrifying granular sludge in a bench scale reactor treating soft groundwater with low nitrate (21 mg N l−1) was investigated. With influent alkalinity at 180 mg CaCO3 l−1, a calcium addition to a relatively low total hardness of 120 mg CaCO3 l−1 and an influent pH of 8.5, generation of mineral precipitation needed for production of a heavy granular sludge with good settling characteristics was achieved. Bed biomass concentration increased with increasing granule mineral content due to improved retention. With reduced mineral precipitation at a lower influent pH of 7.9, an increase in volumetric loading rate was also shown to be effective in cultivating biomass in a manageable granular sludge.

Denitrification in a carbon and nitrogen removal system for leachate treatment: Performance of a upflow sludge blanket (USB) reactor

The performance of a bench scale upflow sludge bed (USB) denitrifying reactor was evaluated in order to integrate it into a C and N removal system for Sanitary Landfill Leachate. The raw leachate used presented COD and NH 4 -N average values of 30000 mg/l and 1000 mg/l, respectively. The complete system comprises in addition an UASB reactor and a nitrifying RBC. A portion of the aerobic reactor effluent was recycled into the denitrification stage and some raw leachate was also added as an additional C source. In order to obtain operating parameters the denitrifying reactor was operated alone. Sludge from an aerobic reactor (RBC) treating raw leachate was used as inoculum. Shortly after the start up, good granulation of the sludge bed was observed. Using raw leachate and UASB outlet as carbon sources with COD/NO 3 -N ratios of 4 and 12, respectively, denitrification efficiencies of about 90% were reached. A sludge yield of 0.16 gVSS/gCOD removed was obtained operating with raw leachate. For the anoxic reactor operating in the complete system, denitrification efficiencies of 90% were also achieved. A nitrogen gas recycle was a successful way to avoid frequently observed sludge bed rising problems.

Post-treatment of effluents from anaerobic reactor treating domestic sewage by dissolved-air flotation

This paper presents the results of a study performed with a lab-scale dissolved-air flotation (LSDAF) unit fed with previously coagulated effluent from a pilot scale up-flow anerobic sludge blanket (UASB) reactor treating domestic sewage. Physical operational conditions for coagulation (rapid mix) and flocculation/flotation were maintained constant. Chemical (FeCl 3 ) dosages ranged from 30 to 110 mg.l −1 . The effect of pH was also verified in the range of 5.1 to 7.6 for each dosage. Best results were achieved for 65 mg.l −1 of FeCl 3 and pH values between 5.3 and 6.1. For these conditions, the removal efficiencies obtained in the LSDAF unit were: between 87% and 91% for chemical oxygen demand (COD), between 95% and 96% for total phosphate (TP), 94% for total suspended solids (TSS), between 96% and 97% for turbidity (TU), between 90% and 93% for apparent color (AC) and more than 96% for sulfide (S). For the UASB-DAF system, global efficiencies would be around 98% for COD, 98% for TP, 98.4% for TSS, 99.3% for TU and 98% for AC. The stripped gases treatment is desirable.

The effect of heavy metals on a thermophilic methanogenic upflow sludge blanket reactor

Copper, nickel, zinc and lead were added to the feed of the methanogenic stage of a two-phase thermophilic anaerobic digester, which had an overall hydraulic retention time of 10·5 h. Each metal was added for a period of 30 h. A period of 7 days was used between the metal dosing as a recovery phase. All the metals caused a reduction in the chemical oxygen demand removal which was reversed when the metal dosing ceased. Nickel and lead had the greatest impact. Lead also had the greatest effect on biogas production and, on the basis of the volatile fatty acid production, appeared to act immediately on acidogenesis and more slowly on the methanogenic bacteria. Metal speciation, using a sequential extraction technique, showed that sludges in reactors being directly dosed with metals fixed the ions at sites with relatively weak binding, whereas sludges in secondary digesters used sites which bound the metals strongly. Lead was an exception to this, always being bound in the relatively weak, adsorbed state.

Domestic wastewater treatment using a UASB reactor

The performance of a pilot-scale (55-l) upflow sludge blanket (UASB) reactor treating municipal sewage without any supplementary heating was examined in a 200-day trial. The flow rate to the digester was kept constant, giving a hydraulic retention time of 7.6 h. Although there were some variations in the strength of the sewage, after the initial 18 days the loading rate was maintained at about 1.21 kg COD/m 3 day. A pregranulated sludge was used as the inoculum, but the start-up period was still long; about 90 days. The total volatile fatty acid:alkalinity ratio was initially high, indicating an element of instability in the digester. However, as more alkalinity was added to the incoming sewage, the ratio fell below the critical value. Once this had been achieved, the digestion process stabilised and achieved a COD removal efficiency averaging 85% and a specific gas yield of 0.34 m 3 methane/kg COD removed.

Biological nutrient removal from a phosphorus-rich pre-fermented industrial wastewater

The objective of this work was to demonstrate the feasibility and to quantify the maximum extent of enhanced biological phosphorus (bio-P) removal from a phosphorus-rich (60 to 100 mg P/L) wastewater originating from a cheese factory (2100 mg total COD/L; 57 mg total TKN-N/L). An existing wastewater treatment plant at the industrial site consisted of an anaerobic equalization tank followed by an anaerobic upflow sludge blanket (UASB) and aerated lagoons. In a bench-scale sequencing batch reactor, bio-P removal was better achieved by treating the effluent from the equalization tank in which a high level of volatile fatty acids were produced (1230 mg as HAc/L) rather than the effluent from the UASB. The effluent orthophosphates concentration reached as low as 5 mg P/L. An intracellular polyphosphates content in the biomass greater than 5% (g P/g MLVSS) was observed which demonstrated without doubt that bio-P removal, and not just normal metabolic phosphorus accumulation, took place. Optimizing industrial bio-P removal should consider prior acidogenesis of the influent wastewater, acetate or chemical addition, and an efficient control over effluent suspended solids.

Biological nutrient removal from a phosphorus-rich pre-fermented industrial wastewater

The objective of this work was to demonstrate the feasibility and to quantify the maximum extent of enhanced biological phosphorus (bio-P) removal from a phosphorus-rich (60 to 100 mg P/L) wastewater originating from a cheese factory (2100 mg total COD/L; 57 mg total TKN-N/L). An existing wastewater treatment plant at the industrial site consisted of an anaerobic equalization tank followed by an anaerobic upflow sludge blanket (UASB) and aerated lagoons. In a bench-scale sequencing batch reactor, bio-P removal was better achieved by treating the effluent from the equalization tank in which a high level of volatile fatty acids were produced ( 1230 mg as HAUL) rather than the effluent from the UASB. The effluent orthophosphates concentration reached as low as 5 mg P/L. An intracellular polyphosphates content in the biomass greater than 5% (g P/g MLVSS) was observed which demonstrated without doubt that bio-P removal, and not just normal metabolic phosphorus accumulation, took place. Optimizing industrial bio-P removal should consider prior acidogenesis of the influent wastewater, acetate or chemical addition, and an efficient control over effluent suspended solids.

An examination of the structure of UASB granules

Sonication, staining and the analysis of extracellular polymers (ECP) were used to examine the structure of granules from pilot-scale and laboratory-scale anaerobic upflow sludge blanket reactors. The pilot-scale unit was part of the SERC Anaerobic Facility which was treating the liquors from the manufacture of instant coffee. The laboratory-scale reactors used a chemically defined substrate. The results showed that, although the strength of the granules from the pilot-plant, as measured by the effect of sonication, varied with time, the variations could not be related to the microbial composition of the granules. However, it was found that the granules tended to become weaker as the organic load increased and the ECP from weak granules had a lower polysaccharide content. The effect of inhibitory agents (pyrogallol and coffee oil) on granule structure was also examined. These studies showed that the effect was to reduce the strength of the granules.

Application of Sulfate-Reducing and Sulfide-Oxidizing Bacterial Symbiosis for Wastewater Treatment

Abstract This investigation attempted to advance the state of the art of the process which utilizes the symbiotic relationship between the sulfate-reducing bacteria (SRB) and sulfide oxidizing bacteria (SOB) for degradation of organic matter present in wastewater. Major emphasis has been on the development of the desired microbial system without any external seed and comparative evaluation of the two types of multistage reversing flow bioreactor (MRB) systems. Biological vessels (BVs) in the MRB systems simulate conditions which correspond to configurations described as upflow sludge blanket and stationary fixed film. Two bench-scale models – one designed to achieve self granulation of sludge (SGS), and the second designed to promote growth of SRB/SOB on additional nonreactive surface – were set up and operated over a period of 4 months. Domestic wastewater supplemented with organic matter from sugar cane molasses was used as feed to develop the desired microbial population. Several visual and microscopic observations confirmed the presence of a significant number of SRB and SOB in all the biological vessels. Results indicated that it is possible to develop SGS and a microbial population of SRB and SOB which could attach to the nonreactive surface without any external seeding. Domestic wastewater could serve as a source of these organisms. Immobilized growth conditions and suspended growth conditions in BVs yield similar results in terms of organic matter utilization. The empirical formula for MRB biomass can be expressed as C11O12H36N5S.

Denitrification by a mixture of bacterial strains derived from an upflow sludge blanket reactor, following entrapment in sol-gel glass

Whole cell extracts of a bacterial mixture grown in an upflow sludge blanket reactor used for drinking water denitrification, were successfully entrapped into sol-gel glass, and afterwards air dried. The sol-gel complex was able to reduce sodium nitrate and nitrite solutions. Compared with free whole cell extract, the sol-gel complex required twice as much time for nitrate and nitrite reduction. This study is the first successful attempt to entrap denitrifier reductases for experimental denitrification into sol-gel glass. Denitrifying enzymes entrapped into sol-gel glass matrix, can be used several times without significant loss in specificity, but gradual loss in reactivity occurs, probably due to electron donor depletion.

Anaerobic Digestion of Starch Particulates in an Upflow Sludge Blanket Filter Reactor

The effect of starch particulates in wastewater on an anaerobic upflow sludge blanket filter (UBF) reactor was evaluated at 37°C and pH 7.0–7.5 over a period of 415 days, during which the volumetric chemical oxygen demand (COD) loading was increased from 3 kg.m−3.d−1 to 50 kg.m−3.d−1. The initial organic substrate was a mixture of sucrose and starch. Upon reaching the constant loading rate of 10 kg-COD.m−3.d−1, starch gradually replaced sucrose in the wastewater and eventually became the sole substrate at loading rates of 10 kg-COD.m−3.d−1 and higher. Results showed that, despite the insoluble nature of the starch, only about 1.2% of starch in wastewater remained unhydrolyzed and about 5.9% became soluble COD in the effluent for loading rates up to 40 kg-COD.m−3.d−1. Of the COD removed, 86.1% was converted to methane and the rest was presumably converted to biomass with a sludge yield of 0.10 kg-VSS.kg-COD−1. The suspended solids in the effluent were mostly composed of the washed-out biomass, the amount of which increased with loading rate, because of the turbulence generated by the increased gas production and the insufficient depth of the reactor. There was no accumulation of starch in the reactor throughout this study. The starch-degrading granules had a higher methanogenic activity than granules in the previous studies degrading soluble carbohydrates. The bacterial populations of acidogens, syntrophic acetogens, and methanogens, were about 108–109 per ml.

Precipitation potential as a major factor in the formation of granular sludge in an upflow sludge-blanket reactor for denitrification of drinking water.

The effects of the chemical composition of water on granular sludge formation and characteristics in a denitrifying upflow sludge-blanket (USB) reactor were studied. Denitrification of drinking water showed different biomass sludge characteristics when the reactor was fed with groundwater as opposed to surface water USB reactors fed with groundwater produced granules with good settling characteristics, SVI (sludge volume index) values lower than 30 ml/g, and high reactor biomass concentrations (20-25 g/l), while surface-water-fed reactors exhibited lower biomass concentrations (10-15 g/l) due to poor settling characteristics (SVI values of 50-90 ml/g). Sludge granules from the reactor fed with surface water had a low mineral content of between 10% and 20% as compared to a mineral content of 25%-50% in the groundwater reactor. The larger mineral content in the groundwater-fed reactor was due to a greater precipitation potential, i.e. higher concentrations of calcium and alkalinity present in groundwater combined with the release of alkalinity and subsequent increase in pH caused by biological denitrification. Verification for this phenomenon was established by enriching surface water with calcium and alkalinity, which increased the reactor's precipitation potential from 15 mg/l to 40 mg/l (as CaCO3). The granules obtained from the reactor fed with enriched surface water had a high mineral content of between 40% and 50% and very low SVI values, contributing to improved granule-settling characteristics and reactor stability.

Primary fermentation of soluble and particulate organic matter for wastewater treatment

A new reactor based on upflow sludge blanket technology (USB) for fermentation of both the particulate and soluble fractions of domestic wastewater is presented. The process is fed with the total wastewater flow, and carries out suspended solids (SS) retention, fermentation and clarification of the fermented effluent in a single reactor. The study was carried out using pilot scale reactors, under six different operating conditions with regards to hydraulic load (hydraulic retention time, HRT, varying between 1.1 and 4.3 hours) and at a constant temperature (20 ± 1°C). With regards to primary treatment, the process has been shown to ensure low SS residuals in the fermented effluent under all operating conditions tested. Very low residuals, with an average below 50 mg SS/l, were obtained with an upflow velocity of between 0.75 and 0.9 m/h. These trials have also highlighted the important role played by the adsorption of particulate organic matter on the biological flocs of the sludge blanket in the elimination of SS. Fermentation efficiencies are superior to those of existing fermenters, the results clearly proving that a majority of the volatile fatty acids produced originate from the soluble fraction of the wastewater. Under the optimum conditions tested, with an HRT = 2.8 hours, 0.17 mg HAc/mg total COD are produced, over 60% of which is generated by the fermentation of the influent soluble organic matter. Under these operating conditions, maximum solubilisation of the particulate fraction has been estimated at 0.13 mg of filtered COD/mg particulate COD (total COD-filtered COD).

Inhibitory effects in the thermophilic anaerobic treatment of a simulated coffee wastewater

Abstract The performance of a thermophilic upflow sludge blanket reactor, which was operated at an organic loading rate of 4 kg COD m‐3 d‐1 and a hydraulic retention time of 12 hours, was examined at a range of potassium:calcium ion ratios. The results confirmed that, at 55°C, the addition o f potassium ions caused an appreciable reduction in the gas production. The results also showed that, under the conditions examined, there was an optimum potassium: calcium ratio of 8–12.