Upflow Velocity Research Articles

Influence of Process Parameters on the Characteristics of Struvite Pellets

With an ever-increasing demand for phosphate-based fertilizer, new sustainable sources of phosphorus are warranted. Recent technologies have successfully demonstrated the possibility of recovering phosphorus from wastewater-treatment plants as struvite, which is also a ready-made, slow-release fertilizer. However, process parameters that influence the operation of crystallizers and production of good-quality struvite pellets have yet to be fully understood. This paper discusses the influence of process parameters on the characteristics of struvite pellets. Among the various process parameters, upflow velocity and flow patterns in the crystallizer were found to influence the size and shape of the pellets. In the range (1.5–7.1) tested, supersaturation ratio did not appear to influence the crushing strength of the pellets formed. Midsized pellets, in the 2.0–2.5-mm range, exhibited the highest crushing strengths. Higher magnesium concentration in the crystallizer was able to increase the crushing strength of struvite pellets by as much as 15–27%.

Characteristics of denitrifying granular sludge grown on nitrite medium in an upflow sludge blanket (USB) reactor

While inoculating pre-acclimatized floccular sludge, nitrite-denitrifying granular sludge was obtained after approximately 40 days of cultivation in a 10 L upflow sludge blanket (USB) reactor. The nitrite removal efficiency was approximately 95% when the nitrite concentration was 50 mg L(-1)at an influent flow rate of 20 L h(-1). The nitrite granular sludge had several notable features including good settleability (110 m h(-1)), high ash content (79%), and high density (1.248 g cm(-3)). The mixed liquor suspended solids (MLSS) of the sludge bed remained at 130.04 g L(-1), at a hydraulic upflow velocity of 2 m h(-1). These interesting characteristics were attributed to a high effluent pH (9.7) caused by the release of alkalinity during the nitrite denitrification process. The surfaces of the granules were dominated by cocci bacteria with a diameter of approximately 3 μm, which could be classified as Nitrosomonas-like species based on our analysis of 16 S rDNA sequences.

Sulfide oxidation in fluidized bed bioreactor using nylon support material

A continuous fluidized bed bioreactor (FBBR) with nylon support particles was used to treat synthetic sulfide wastewater at different hydraulic retention time of 25, 50 and 75 min and upflow velocity of 14, 17 and 20 m/hr. The effects of upflow velocity, hydraulic retention time and reactor operation time on sulfide oxidation rate were studied using statistical model. Mixed culture obtained from the activated sludge, taken from tannery effluent treatment plant, was used as a source for microorganisms. The diameter and density of the nylon particles were 2–3 mm and 1140 kg/m3, respectively. Experiments were carried out in the reactor at a temperature of (30 ± 2)°C, at a fixed bed height of 16 cm after the formation of biofilm on the surface of support particles. Biofilm thickness reached (42 ± 3) μm after 15 days from reactor start-up. The sulfide oxidation, sulfate and sulfur formation is examined at all hydraulic retention times and upflow velocities. The results indicated that almost 90%–92% sulfide oxidation was achieved at all hydraulic retention times. Statistical model could explain 94% of the variability and analysis of variance showed that upflow velocity and hydraulic retention time slightly affected the sulfide oxidation rate. The highest sulfide oxidation of 92% with 70% sulfur was obtained at hydraulic retention time of 75 min and upflow velocity of 14 m/hr.

Flow pattern analysis of a full-scale expanded granular sludge bed-type reactor under different organic loading rates

The hydraulic characteristics of a lab-scale and a full-scale (275m3) expanded granular sludge bed (EGSB)-type reactor under different organic loading rates varying from 10kgCODm−3d−1 to 45kgCODm−3d−1 were investigated. A modified combined model composed of two completely mixing regions and a plug flow region was sufficient for simulating the flow pattern of a full-scale EGSB-type reactor. Moreover, the outputs fitted the measured tracer distribution results well. The simplified model structure was in very good agreement with the physical structure of a full-scale EGSB-type reactor. The upflow (liquid+gas) velocity, high concentration of granular sludge, and gas hold-up effect may contribute to the generation of dead spaces (maximum of 19.5%). The bed expansion characteristics indicated that the sludge bed of the EGSB-type reactor performed as a suspended bed, in which the bed expansion was controlled between 20% and 30%, rather than the usually considered expanded bed.

Clear Detection of Chromospheric Evaporation Upflows with High Spatial/Temporal Resolution by Hinode XRT

We find clear evidence for typical chromospheric evaporation associated with small transient brightenings, using the data from the X-ray Telescope (XRT) onboard Hinode. We found 13 events, each having a pair of evaporation upflows arising almost symmetrically from both foot points of a magnetic loop. These facts strongly support the standard flare model based on the magnetic reconnection. The apparent upflow velocities of three of the events are ≈ 500 km s−1, while those of the other events are ≈ 100 km s−1. This is the first clear direct detection of evaporating upflow motion in soft X-ray images from Hinode/XRT; such images were obtained with high cadence (≈ 60 s) and high spatial resolution (1 arcsec).

SPECTROSCOPIC ANALYSIS OF INTERACTION BETWEEN AN EXTREME-ULTRAVIOLET IMAGING TELESCOPE WAVE AND A CORONAL UPFLOW REGION

We report a spectroscopic analysis of an EIT wave event that occurred in active region 11081 on 2010 June 12 and was associated with an M2.0 class flare. The wave propagated near circularly. The south-eastern part of the wave front passed over an upflow region nearby a magnetic bipole. Using EIS raster observations for this region, we studied the properties of plasma dynamics in the wave front, as well as the interaction between the wave and the upflow region. We found a weak blueshift for the Fe XII {\lambda}195.12 and Fe XIII {\lambda}202.04 lines in the wave front. The local velocity along the solar surface, which is deduced from the line of sight velocity in the wave front and the projection effect, is much lower than the typical propagation speed of the wave. A more interesting finding is that the upflow and non-thermal velocities in the upflow region are suddenly diminished after the transit of the wave front. This implies a significant change of magnetic field orientation when the wave passed. As the lines in the upflow region are redirected, the velocity along the line of sight is diminished as a result. We suggest that this scenario is more in accordance with what was proposed in the field-line stretching model of EIT waves.

Optimization of petroleum refinery effluent treatment in a UASB reactor using response surface methodology

An upflow anaerobic sludge blanket (UASB) bioreactor was successfully used for the treatment of petroleum refinery effluent. Before optimization, chemical oxygen demand (COD) removal was 81% at a constant organic loading rate (OLR) of 0.4kg/m3d and a hydraulic retention time (HRT) of 48h. The rate of biogas production was 559mL/h at an HRT of 40h and an influent COD of 1000mg/L. Response surface methodology (RSM) was applied to predict the behaviors of influent COD, upflow velocity (Vup) and HRT in the bioreactor. RSM showed that the best models for COD removal and biogas production rate were the reduced quadratic and cubic models, respectively. The optimum region, identified based on two critical responses, was an influent COD of 630mg/L, a Vup of 0.27m/h, and an HRT of 21.4h. This resulted in a 76.3% COD removal efficiency and a 0.25Lbiogas/Lfeedd biogas production rate.

Effect of upflow velocity on the performance of an inclined plate membrane bioreactor treating municipal wastewater

An inclined plate membrane bioreactor (iPMBR) was introduced to meet the challenge of handling high mixed liquor suspended solids when operating at long sludge retention times. During the first 407 days of operation, the iPMBR was able to rezone more sludge (1.5-10.5 times greater) in its upstream, anoxic tank compared to its downstream, aerobic tank. This could extend membrane filtration by diverting most of the sludge from the aerobic zone. During this period, the upflow velocities through the inclined plates of the anoxic tank ranged from 2.3 x 10(-4) to 7.7 x 10(-4) m/s. After Day 407, the operating conditions were changed to determine whether the iPMBR would fail to create a sludge concentration difference between its two tanks. When the upflow velocity was increased to 1.8 x 10(-3) m/s, the sludge concentration difference between the two zones was removed. This indicated that the upflow velocity had increased sufficiently to overcome the settling velocities of most flocs, resulting in more solids being carried from the anoxic to the aerobic tank. For the configuration of this iPMBR, operating at flow rates where the upflow velocity through the inclined plates was less than 1.0 x 10(-3) m/s would be necessary to keep a significant sludge concentration difference between its two zones.

고율 혐기성 공정과 아질산-아탈질을 연계한 수산물가공폐수의 질소제거

Objectives: Organic matter and nitrogen were removed using the EGSB process, a high-rate anaerobic process, in combination with a nitritation-denitritation process, in order to ensure the stable treatment of seafood processing wastewater. Methods: The upflow velocity of an EGGS reactor was operated at 10 m/hr for maximal organics removal efficiency. For removal of nitrogen from seafood processing wastewater a nitritation-denitriation process was applied Results: The efficiency of the EGSB process showed that it has an 80% or more organic matter (CODcr) removal efficiency with an HRT of six hours or more at influent loadings of 17.34 kgCOD/<TEX>$m^3$</TEX>/day or less. The methane product for TCODcr removal was 0.23-0.38 <TEX>$m^3CH_4$</TEX>/kgCODrem., which was similar to the theoretical generation of STP-state methane, 0.35 <TEX>$m^3CH_4$</TEX>/kgTCODrem. In the nitritation-denitritation process, the nitritation conversion rate to <TEX>$NH_4^+$</TEX>-N concentration was 82% to 87%, 72% to 81% and 64% to 69% when HRT was 24 hr, 21 hr and 18 hr, respectively. In the denitritation process, the ratio of SCOD consumption to NOx-N removal ranged from 2.347 to 2.587. It was 2.472 on average. Conclusions: The optimal HRT for stable processing of seafood processing wastewater is six hours or more. The ratio of nitrite to total NOx-N was 82% to 96%, which indicates that nitrite accounts for the largest portion of the product.

Effect of upflow velocity and hydraulic retention time in anaerobic fluidized-bed reactors used for hydrogen production

The present study evaluated the influence of upflow velocity ( V up) applied to an anaerobic fluidized-bed reactor used for hydrogen production. For comparison, two reactors were used with different velocities: 1.24 cm s −1 (R124) and 1.88 cm s −1 (R188). Expanded clay was used as a support material for immobilization along with synthetic wastewater containing glucose as the main carbon source (5000 mg L −1). The reactor R124, which operated at the minimum fluidization velocity (1.24 cm s −1), had the best values for hydrogen production. The maximum hydrogen production rate was 2.21 L h −1 L −1 for a hydraulic retention time (HRT) of 1 h, while the best hydrogen yield was 2.55 mol H 2 mol −1 glucose for an HRT of 2 h. The hydrogen content in the biogas was around 40.53–67.57%. A high amount of ethanol was produced, suggesting that a metabolic pathway via ethanol was preferable. In general, the reactor under the minimum velocity fluidization (R124) presented a greater production of hydrogen than R188 showing that should have a limit point in V up till the hydrogen production is maximized.

INFLUENCE OF VELOCITY GRADIENT ON OPTIMISATION OF THE AGGREGATION PROCESS AND PHYSICAL PROPERTIES OF FORMED AGGREGATES: Part 1. Inline high density suspension (IHDS) aggregation process

INFLUENCE OF VELOCITY GRADIENT ON OPTIMISATION OF THE AGGREGATION PROCESS AND PHYSICAL PROPERTIES OF FORMED AGGREGATES: Part 1. Inline high density suspension (IHDS) aggregation processThis paper deals with optimisation and acceleration of the clarification process. It was established that both these objectives are closely inter-related and can be accomplished by the formation of aggregates with a high agitation intensity until the flocculation optimum is reached. This is a new method of formation of aggregates which is called the Inline High Density Suspension (IHDS) formation process. Further, under the IHDS process the aggregates are formed with a single root-mean-square velocity gradientG&gt;&gt; 50 s-1. It was also established that the process of formation of aggregates (expressed by residual e of the observed determinant) passes through a minimum. This minimum is considered to be the flocculation optimum. Furthermore, the agitation intensity (G) was found to be the inherent means influencing compactness and thereby density of the aggregates formed. This proves the vital role of agitation intensity on the morphological and physical properties of aggregates formed. The resultant aggregates formed by the IHDS process are very compact, dense and homogeneous in their size, shape, volume and inner structure. Last but not least, the IHDS process applied to the HR-CSAV type sludge blanket clarifier facilitated its high attainable upflow velocity above of 25 m h-1.

Influence of hydraulic retention time on fouling in a UASB coupled with an external ultrafiltration membrane treating synthetic municipal wastewater

This paper evaluates the effect of hydraulic retention time (HRT) 1 1 HRT: hydraulic retention time. on anaerobic membrane bioreactor (AnMBR) 2 2 AnMBR: anaerobic membrane bioreactor. performance, biopolymeric substances production and fouling; also, struvite precipitation is analyzed based on solubility product equation. A lab-scale UASB reactor coupled with an ultrafiltration (UF) 3 3 UF: ultrafiltration. membrane was operated under three different HRTs (4, 8 and 12 h) and fed with synthetic municipal wastewater in two experimental blocks: in the first one, phosphate was supplemented to the influent and in the second one, no phosphate was added. Results show that biopolymeric substances concentration in UASB effluent increased with HRT reduction, probably due to the higher shear forces occurring inside the UASB reactor at lower HRTs, as well as higher upflow velocities and washout conditions. Consequently, chemical oxygen demand (COD) 4 4 COD: chemical oxygen demand. removal decreased slightly at HRT of 4 h (81% vs. 89%). Increase in specific fouling cake resistance and decrease in particle size were also a consequence of HRT reduction. These results indicate that AnMBR (UASB-UF) operation at HRT lower than 4 h has an adverse effect on its performance and fouling. Though struvite components were found in UASB effluent, precipitation analysis showed that they were undersaturated, so it is presumed that struvite precipitation did not occur.

Treatment of slaughterhouse wastewater in upflow anaerobic sludge blanket reactor

The performance of an upflow anaerobic sludge blanket (UASB) reactor operated at ambient temperature (20.9-25.2°C) was analysed for the treatment of slaughterhouse wastewater previously pre-treated for solid separation. The experimental work was carried out in a reactor with 15 L effective volume. Four organic loads were applied and the process performance was evaluated. The COD removal rate increased with the load rise from 4 to 15 kg COD.m(-3).d(-1). Removal efficiencies of 90% were obtained with a load of 15 kg COD.m(-3).d(-1). The entrapment of suspended solids in the sludge blanket was greater in proportion during the first two stages due to the low upflow velocities used when loads of 4 and 7 kg COD.m(-3).d(-1) were evaluated. This phenomenon did not affect the structure of the biological grains or their methanogenic activity. More than 50% of the organic nitrogen was degraded, causing a 3% increase of ammonia concentration. The concentrations of the volatile fatty acids were not high and the wastewater alkalinity was enough to prevent acidification. The yield coefficient of methane production increased with the load rise, reaching 0.266 m(3)/kg COD(removed) at 15 kg COD.m(-3).d(-1) organic load. The UASB reactor is a good option for the biological treatment of pre-treated slaughterhouse wastewater. However, additional treatment is required in order to accomplish the water quality requirements in discharges to water bodies.

Anaerobic Digestion of Domestic Wastewater: The Role of Alkalinity in the Rate and Extent of Digestion

For an anaerobic baffled reactor (ABR) treating domestic wastewater, the major variables affecting the rate and extent of digestion are the organic loading/residence time, the upflow velocity and the pH/alkalinity characteristics of the wastewater. In this study, an ABR was operated at two different flow rates; in Phase A, a higher loading rate of 0.74 kgCOD/m3.d was employed, while in Phase B, the loading rate was reduced to 0.40 kgCOD/m3.d. At the higher organic loading rate, significantly higher solids accumulation rates per kgCOD treated were obtained, and it was estimated that only 30% of the influent COD was converted to CH4. At the lower loading rate the estimated conversion to methane was 60%. The most probable cause for the poor COD removal was failure of stable anaerobic microbial consortia to establish under the relatively high selection pressure experienced at the high loading rate, due to washout of anaerobic species. It was concluded that low wastewater alkalinity (240 mgCaCO3/l) characteristic of the KwaZulu-Natal East Coast region resulted in low compartment pH values and associated inhibition of microbial activity, causing slower digestion of organics, and greater washout, particularly of methanogenic organisms, at higher up-flow velocities. The implication was that critical value for up-flow velocity, above which washout of anaerobic species occurs, depends on the organic loading and the prevailing pH and alkalinity. This has implications for the stability of any anaerobic system, and the extent of treatment of the effluent, specifically, that low wastewater alkalinity has the potential to significantly affect reactor design in any anaerobic system.

Treatment of poultry slaughterhouse wastewater in upflow anaerobic filter under low upflow velocity

The wastewater discharged by poultry slaughterhouse industries are characterized mainly by high biochemical oxygen demand, high suspended solids and complex mixture of fats, proteins and fibers requiring systematic treatment prior to disposal. In this study, the performance of an upflow anaerobic filter reactor for treating Indian poultry slaughterhouse wastewater under low upflow velocity of 1.38 m/day at mesophilic temperature (29-35 °C) was investigated. The reactor was inoculated with anaerobic non-granular sludge from an anaerobic reactor treating the poultry slaughterhouse wastewater. The reactor took 147 days for complete start-up with removal efficiencies of total chemical oxygen demand and soluble chemical oxygen demand of 70 and 79 % respectively. The maximum total chemical oxygen demand removal efficiency of 78 % was achieved at an organic loading rate of 10.05 kg/m3/day and at an hydraulic retention time of 12 h. The average methane content varied between 46 and 56 % and methane yield at maximum removal efficiency was 0.24 m3 CH4/kg CODremoved·day. Sludge granules of 1–2 mm were observed in between the packing media. Scanning electron microscope analysis revealed that sludge granules are composed of clumps of Methanosarcina clustered with less intertwined Methanosaeta fibre of granules. The lower velocity used in this study has achieved better performance of the reactor by creating active microbial formation with stable pH upto an organic loading rate of 14.3 kg/m3/day. This has proved that the poultry slaughterhouse wastewater can be treated using anaerobic filter reactor under low upflow velocity.

Evaluation of Mixing and Performance of Lab-Scale Upflow Anaerobic Sludge Blanket Reactors Treating Domestic Wastewater

The effects of varying hydraulic retention time (HRT) and associated upflow velocity on mixing and reactor performance were evaluated in five lab-scale upflow anaerobic sludge blanket (UASB) reactors treating real domestic wastewater. The mixing and transport studies were carried out with the help of tracer experiments at various HRTs using a pulse tracer input. A number of existing models were assessed for the analysis of the time series of observed tracer concentrations. The plug-flow reactor (PFR) model with two-zone dispersion better simulated the time series of tracer concentrations at all HRTs than other models, such as single compartment dispersion, completely mixed flow reactors (CMFRs) in series, and a combination of CMFR and PFR. The dispersion coefficients obtained from the two-zone dispersion model correlated well with the dispersion analysis expression for flow in a circular cylinder, and the correlation can be used for the prediction of dispersion in a UASB reactor. The analysis of reactor performance data indicated that reduction of dispersion owing to decrease in the upflow velocity resulted in increased sulfidogenic activity in the reactor. This was attributed to the inability of the sulfate reducers to colonize in the reactor at high upflow velocity and mixing condition.

Fermentative hydrogen production from fresh leachate in batch and continuous bioreactors

This research for the first time investigated hydrogen production from the fresh leachate originated from municipal solid wastes. We found that fermentation of the leachate generated H 2 and was very much enhanced in the presence of extra phosphate in the batch reactor. The continuous expanded granular sludge bed (EGSB) reactor started to generate H 2 at day 20 and continued to 176 days with 120 mg/l of extra phosphate present. The highest chemical oxygen demand (COD) removal efficiency (66.9%) was achieved at liquid up-flow velocity of 3.7 m/h and hydraulic retention time of 12 h. Under proposed optimal operation conditions, the mean H 2 production rate reached up to 2155 ml/(l day). We also found that over 80% liquid metabolites were acetic acid and ethanol, suggesting the ethanol-type fermentation was dominant in the bioreactor. These findings indicate that the fresh leachate can be used as the source for continuous hydrogen production.

Improvement performance of Al-Wathba settling tank by a computational fluid dynamics model

Improvement performance of Al-Wathba settling tank by a computational fluid dynamics modelAn investigation has been carried out using the FLUENT Computational Fluid Dynamics (CFD) software, which uses the finite-volume method to determine whether it is feasible to improve the capacity and quality of the clarifier at the Al-Wathba Water Treatment Works (Iraq) by some relatively inexpensive means. Simulations were carried out with two dimensional, radially symmetric models, representing the existing configuration as well as a number of proposed modifications involving baffles and additional clarified water off-takes. A convection-diffusion equation, which is extended to incorporate the sedimentation of sludge flocs in the field of gravity, governs the mass transfer in the clarifier. The standardk-ε turbulence model is used to compute the turbulent motion, and our CFD model accounts for buoyancy flow. The sludge settling velocity was measured as a function of the concentration, and we have used the double-exponential settling velocity function to describe its dependence on the concentration. The CFD model is validated using measured concentration profiles. The results were evaluated on the basis of the simulated profiles of vertical up-flow velocity in the body of the clarifier.

Parameters affecting steady-state floc blanket performance

A laboratory-scale reactor was used to simulate a water treatment process sequence of rapid mix, hydraulic flocculation, upflow clarification with a floc blanket, and lamellar sedimentation to accomplish removal of colloidal particles. This study focused on variables affecting performance of the floc blanket including: provision of hydraulic flocculation, raw water turbidity, coagulant dose, upflow velocity through the floc blanket, and bulk density and solids concentrations of the floc blanket. An upflow clarifier velocity between 1.0 and 1.3 mm s -1 produced the best floc blanket performance for turbidities studied between 10 and 200 NTU while an upflow velocity between 0.6 and 0.8 mm s -1 produced the best floc blanket performance at 500 NTU. The results show that overall particle removal efficiency improved with increasing hydraulic flocculator residence time and energy dissipation rate. Particle removal efficiency improved with increasing floc blanket depth for floc blanket depths between 15 and 75 cm. Lamellar sedimentation with a capture velocity of 0.12 mm s -1 is a key component in improving clarifier performance when utilizing a floc blanket.

Technical and experimental evaluation of an innovative decentralized technology for the municipal wastewater treatment in the city of Rome

The present paper shows the results obtained through an experimental activity carried out on a pilot-scale plant using an innovative technology which couples the granular aerobic sludge with the sequencing batch process. Treatment efficiency and operation costs were evaluated in order to assess feasibility of this new technology for the upgrading of the existing continuous flow activated sludge treatment plant located in Casal Monastero, a decentralized area of the City of Rome. During start-up (about 3 months), the granular aerobic sludge was developed by controlling the dissolved oxygen concentration, the value of pH and the up-flow velocity. Besides, the influent organic loading was progressively increased starting from 0.1 kg/m³ d up to 0.9 kg/m³ d. In order to improve nitrogen removal, an anoxic phase was temporary added to the operative cycle. Complete development of the granular sludge determined an appreciable improvement of the denitrification process which allowed to eliminate the anoxic phase. At regime conditions, the plant was operated with 3 daily cycles, each one of 8 h. The new system showed a reduced sludge production (of about 20-35%) as compared to the existing plant, along with high removal efficiency of both Chemical Oxygen Demand (COD) and nitrogen. However, the operation was discontinuous and strictly related to the strength of the granular sludge. Therefore, a careful monitoring is recommended in order to control operation and performance of this new system.