Modeling the liquid flow in up-flow anaerobic sludge blanket reactors

By means of stimulus-response experiments an Li(+) tracer, models for the fluid flow in a 30-m(3) UASB reactor, used for the anaerobic treatment of wastewater, were tested. From the model with the best fit it could be derived that both the sludge bed and the sludge blanket can be described as perfectly mixed tank reactors with short-circuiting flows; the settler volume acts like a plug-flow region.Apart from the volumes of the different flow regions, two parameters are necessary and sufficient to describe the fluid flow in a well functioning UASB reactor, i.e., the short-circuiting flow over the sludge bed and the short-circuiting flow over the sludge blanket. The volumes could be measured accurately.The short-circuiting flow over the sludge bed is a linear function of the sludge bed height. When the optimal height of the sludge bed is defined as the height for which the short-circuiting flows are as small as possible, a bed-height of 3.5-4 m is sufficient (for superficial gas velocities between 1 and 1.5 m/h). This is in contradiction to the results of other authors. The short-circuiting flows over the sludge bed and the sludge blanket were also influenced by the superficial gas velocity.     

An integral dynamic model for the UASB reactor

In this article a dynamic model of a continuous working UASB reactor is described. It results from the integration of the fluid flow pattern in the reactor, the kinetic behavior of the bacteria (where inhibition and limitation were taken into account), and the mass transport phenomena between different compartments and different phases. The mathematical equations underlying the model and describing the important mechanisms were programmed and prepared for computations and simulations by computer. The settler efficiency has to be over 99% to prevent the reactor from wash-out. When the settler efficiency is over 99%, the total sludge content of the reactor increases steadily, so the reactor is hardly ever in a steady state. This implies dynamic modeling. The model is able to predict the various observable and nonobservable or difficult to observe state variables, e.g., the sludge bed height, the sludge blanket concentration, the short-circuiting flows over bed and blanket, and the effluent COD concentration as a function of the hydrodynamic load, COD load, pH, and settler efficiency. The optimal pH value is between 6.0 and 8.0; fatty acid shock loadings are difficult to handle outside this optimal pH range.     

升流厌氧污泥层反应器动力学模型

用碘离子作示踪剂,采用矩形脉冲示踪法测定升流厌氧污泥层(UASB)反应器的流动分布。建立了申级返混加沟流模型。模型简单,能够反映反应器流动分布,具有较强的拟合能力和良好的适用性。运用流动模型和Monod方程,建立了UASB反应器稳态模型,并对模型参数进行了估计。通过灵敏度分析,进水基质浓度S。,废水流量Q,最大比基质降解速率,μmax 对出水基质浓度有较大影响。在稳态模型的基础上又建立了UASB反应器动态模态,利用此模型,对出水基质浓度序列Se,和产气量序列Qg进行计算预测,平均偏差分别5．40％和7．46％,标准偏差分别为7．02％和9．66％。     

Biogas production from supernatant of hydrothermally treated municipal sludge by upflow anaerobic sludge blanket reactor

The supernatant of hydrothermally treated sludge was treated by an upflow anaerobic sludge blanket (UASB) reactor for a 550-days running test. The hydrothermal parameter was 170 °C for 60 min. An mesophilic 8.6 L UASB reactor was seeded with floc sludge. The final organic loading rate (OLR) could reach 18 kg COD/m³ d. At the initial stage running for 189 days, the feed supernatant was diluted, and the OLR reached 11 kg COD/m³ d. After 218 days, the reactor achieved a high OLR, and the supernatant was pumped into the reactor without dilution. The influent COD fluctuated from 20,000 to 30,000 mg/L and the COD removal rate remained at approximately 70%. After 150 days, granular sludge was observed. The energy balance calculation show that heating 1.0 kg sludge needs 0.34 MJ of energy, whereas biogas energy from the supernatant of the heated sludge is 0.43 MJ.     

Use of the upflow sludge blanket (USB) reactor concept for biological wastewater treatment,especially for anaerobic treatment

In recent years considerable effort has been made in the Netherlands toward the development of a more sophisticated anaerobic treatment process, suitable for treating low a strength wastes and for applications at liquid detention times of 3–4 hr. The efforts have resulted in new type of upflow anaerobic sludge blanket (UASB) process, which in recent 6 m³ pilot-plant experiments has shown to be capable of handling organic space loads of 15–40 kg chemical oxygen demand (COD)·m^?3/day at 3–8 hr liquid detention times. In the first 200 m³ full-scale plant of the UASB concept, organic space loadings of up to 16 kg COD·m^?3/day could be treated satisfactorily at a detention times of 4 hr, using sugar beet waste as feed. The main results obtained with the process in the laboratory as well as in 6 m³ pilot plant and 200 m³ full-scale experiments are presented and evaluated in this paper. Special attention is given to the main operating characteristics of the UASB reactor concept. Moreover, some preliminary results are presented of laboratory experiments concerning the use of the USB reactor concept for denitrification as well as for the acid formation step in anaerobic treatment. For both purposes the process looks feasible because very satisfactory results with respect to denitrification and acid formation can be achieved at very high hydraulic loads (12 day^?1) and high organic loading rates, i.e., 20 kg COD·m^?3/day in the denitrification and 60–80 kg COD·m^?3/day in the acid formation experiments.     

Anaerobic digestion of cheese whey using an upflow anaerobic sludge blanket reactor: III. Sludge and substrate profiles

Anaerobic treatment of cheese whey using a 17·5 litre upflow anaerobic sludge blanket reactor was investigated in the laboratory over a range of influent concentration from 4·5 to 38·1 g COD litre⁻¹ at a constant hydraulic retention time of 5 days. The results indicated that two sludge distribution regions, a sludge bed and a sludge blanket, as well as two distinct reaction phases, acidogenic and methanogenic, were formed. However, as the substrate loading was increased, the acidogenic region extended into the methanogenic region in the upper portion of the reactor until the whole region was acidogenic, leading to the failure of the reactor.     

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

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

Rapid start-up and performance of denitrifying granular sludge in an upflow sludge blanket (USB) reactor treating high concentration nitrite wastewater

Denitrifying granular sludge reactor holds better nitrogen removal efficiency than other kinds of denitrifying reactors, while this reactor commonly needs seeding anaerobic granular sludge and longer period for start-up in practice, which restricted the application of denitrifying granular sludge reactor. This study presented a rapid and stable start-up method for denitrifying granular sludge. An upflow sludge blanket (USB) reactor with packings was established with flocculent activated sludge for treatment of high concentration nitrite wastewater. Results showed mature denitrifying granular sludge appeared only after 15 days with highest nitrogen removal rate of 5.844 kg N/(m³ day), which was much higher than that of compared anoxic sequencing batch reactor (ASBR). No significant nitrite inhibition occurred in USB and denitrification performance was mainly influenced by hydraulic retention time, influent C/N ratio and internal reflux ratio. Hydraulic shear force created by upflow fluid, shearing of gaseous products and stable microorganisms adhesion on the packings might be the reasons for rapid achievement of granular sludge. Compared to inoculated sludge and ASBR, remarkable microbial communitiy variations were detected in USB. The dominance of Proteobacteria and Bacteroidetes and enrichment of species Pseudomonas_stutzeri should be responsible for the excellent denitrification performance, which further verified the feasibility of start-up method.     

Capacities and limits of three different technologies for the biological treatment of leachate from solid waste landfill sites

Leachate from a municipal waste landfill site was treated using an activated sludge bioreactor, a fluidized bed biofilm reactor and a packed-bed column reactor (trickling filter). The leachate contained high organic matter (2.0–2.6 g/l of COD), high ammonium (300–700 mg/l) and sulphide (200–800 mg/l) concentrations, as well as low metal concentrations. The continuously operating reactors were employed to study the effects of TOC loading on the removal of TOC as well as on the nitrification and denitrification processes. Among the three biological treatment technologies investigated, the fluidized bed biofilm reactor was best with respect to removing ammonia and TOC. More than 90% of TOC and 99% of ammonia were removed when TOC loading was less than 0.5 kg/m³ × d. At a TOC loading of 4 kg/m³ × d, the removal of TOC and ammonia was 80% and 99%, respectively. In contrast, the treatment of leachate with the packed-bed reactor was successful in TOC removing only at TOC loading less than 0.3 kg/m³ × d (TOC elimination decreased from 86% at 0.06 kg/m³ × d to 60% at 0.3 kg/m³ × d). However, the reactor was active in nitrification even at a higher TOC loading (more than a 98% ammonia elimination at a TOC loading of 0.5 kg/m³ × d). Leachate was processed in the activated sludge reactor when TOC loading was less than 0.5 kg/m³ × d (with a removal of TOC and ammonia up to 83% and 99%, respectively). The activated sludge reactor was also effective in TOC removal at a higher TOC loading (e.g. a 74% TOC removal at a TOC loading of 1 kg/m³ × d), but for ammonia elimination, the activity continuously decreased (less than 60% ammonia removal at a TOC loading of 1 kg/m³ × d). Overloading in the activated sludge system was indicated by a high concentration of ammonia and nitrite in the effluent. In the packed bed reactor, overloading was characterized by a progressively incomplete TOC removal. No significant overloading was found in the fluidized bed reactor up to a TOC loading of 4 kg/m³ × d.     

Design,Construction, and Starting-up of an Anaerobic Reactor for the Stabilisation,Handling, and Disposal of Excess Biological Sludge Generated in a Wastewater Treatment Plant

Design, construction, and starting-up of an upflow anaerobic sludge blanket reactor was carried out. This system was proposed for excess sludge stabilisation, particularly that generated at an activated sludge wastewater treatment facility installed in a sugarcane mill. The upflow anaerobic sludge blanket (UASB) reactor built, had a working volume of 22.3 m³and a hydraulic residence time of 22 days. Methane production was at a maximum of 79% volume with an average of 60% for this treatment. For starting up the anaerobic reactor, a suitable inoculum from a neighboring plant was used. As the waste characteristics in both plants were different, an acclimation procedure was followed to achieve granulation. Control and stability of anaerobic reactions were monitored with alkalinity data, using the so-called ‘alfa alkalinity’ to try to keep its value at around 0.4. Once pseudosteady-state conditions were reached (chemical oxygen demand reduction and methane-rich biogas production within ±10 percent), the organic load was steadily increased up to feeding 100% excess sludge. The UASB reactor used to stabilise the excess biomass generated a sludge with a much lower volume than that originally fed. Its design ensured adequate hydraulic flow and biogas production with a high methane content. The bacteria were attached constituting spheres and very minor maintenance operations were required.     

Improvement of the anaerobic treatment of potato processing wastewater in a UASB reactor by co-digestion with glycerol

The effect of three different types of glycerol on the performance of up-flow anaerobic sludge blanket (UASB) reactors treating potato processing wastewater was investigated. High COD removal efficiencies were obtained in both control and supplemented UASB reactors (around 85%). By adding 2 ml glycerol product per liter of raw wastewater, the biogas production could be increased by 0.74 l biogas ml⁻¹ glycerol product, which leads to energy values in the range of 810–1270 kWh_electric per m³ product. Moreover, a better in-reactor biomass yield was observed for the supplemented UASB reactor (0.012 g VSS g⁻¹ COD_removed) compared to the UASB control (0.002 g VSS g⁻¹ COD_removed), which suggests a positive effect of glycerol on the sludge blanket growth.     

Effect of hydraulic residence time on microbial sulfide production in an upflow sludge blanket denitrification reactor fed with methanol

Summary In the combined ion exchange/biological denitrification process for nitrate removal from ground water anion exchange resins are regenerated in a closed circuit by way of an upflow sludge blanket denitrification reactor. The regenerant (a concentrated sodium bicarbonate solution) is recirculated through the ion exchanger in the r generation mode and the denitrification reactor. In the closed system sulfate accumulates to very high concentrations. For that reason it was examined under what process conditions sulfate reduction occurs in an upflow sludge blanket denitrification reactor, when the influent contains high sulfate concentrations (5.45 g SO ₄ ^2- /l) and high sodium bicarbonate concentrations (19.8 g NaHCO₃/l) in addition to nitrate and methanol. It appeared that at a hydraulic residence time of 5 h sulfide production started, when the nitrate loading rate was 20% of the denitrification reactor capacity and methanol was added in excess. The excess of methanol was converted into acetate after nitrate was depleted. Conversion of methanol into acetate was a function of the hydraulic residence time. At hydraulic residence times above 8 h this conversion was complete. Also in batch experiments it was observed that excess of methanol was converted into acetate, and that sulfate reduction started when nitrate was depleted. From all experiments it is clear that, provided that methanol is added in good relation to the quantity of nitrate that has to be denitrified, acetate will not be produced and sulfate reduction will not occur in the denitrification reactor, even in the presence of very high sulfate concentrations.     

Treatment of poultry slaughterhouse wastewater in hybrid upflow anaerobic sludge blanket reactor packed with pleated poly vinyl chloride rings

In this study, the performance of 5.4 L hybrid upflow anaerobic sludge blanket (HUASB) reactor for treating poultry slaughterhouse wastewater under mesophilic conditions (29-35 °C), was investigated. After starting-up, the reactor was loaded up to an OLR of 19 kg COD/m³ d and achieved varied TCOD and SCOD removal efficiencies of 70-86% and 80-92%, respectively. The biogas was varied between 1.1 and 5.2 m³/m³ d with the maximum methane content of 72%. The maximum methane yield was 0.32 m³/kg COD_removed at an OLR of 9.27 kg COD/m³ d. Black matured granules of size between 2.5 and 5 mm were observed at the end of 225 d operation. RTD study showed the flow behavior was in mixed regime at the end of performance study. Step wise polynomial regression analysis was fitted well. Methanobacterium and Methanosaeta bacteria were dominant at the end of start-up whereas Methanosarcina, Cocci and rods were predominant at the end of performance studies.     

Two-stage anaerobic digestion of tomato, cucumber, common reed and grass silage in leach-bed reactors and upflow anaerobic sludge blanket reactors

Anaerobic digestion of tomato, cucumber, common reed and grass silage was studied in four separate two-stage reactor configuration consisting of leach bed reactor (LBR) and upflow anaerobic sludge blanket reactor (UASB). LBR studies showed that COD solubilization for cucumber and grass silage was higher (50%) than tomato (35%) and common reed (15%). Results also showed that 31-39% of initial TKN present in tomato and cucumber was solubilized in the leachates and 47-54% of the solubilized TKN was converted to NH₄-N. The corresponding values for common reed and grass silage were 38-50% and 18-36%, respectively. Biomethanation of the leachates in UASB reactors resulted in methane yields of 0.03-0.14 m³ CH₄ kg⁻¹VS_fed for the studied crop materials. Thus, high COD solubilization, high nitrogen mineralization and solubilization rates were feasible during anaerobic digestion of lignocellulosic materials in a two-stage LBR-UASB reactor system.     

Two-stage anaerobic treatment of dairy wastewater using HUASB with PUF and PVC carrier

In the present study, an attempt has been made to treat dairy wastewater entirely via anaerobic treatment over a period of 215 days, using two-stage Hybrid Upflow Anaerobic Sludge Blanket (HUASB) reactors, which offer the advantages associated both with fixed film and upflow sludge blanket treatments. A HUASB with polyurethane foam cubes was used for stage I, and a HUASB utilizing PVC-cut rings was used for stage II. The output from stage I was used as the input for stage II. The two-stage reactor was operated at an organic loading rate that varied from 10.7 to 21.4 kg COD m³/d for a period of 215 days, including the start-up period. The ideal organic loading rate for the two-stage reactor was 19.2 kg COD/m³/d. A further 21.4 kg COD m³/d increase in the organic loading rate resulted in the souring of the reactor function in stage I, which consequently reduced the overall reactor performance. Combined COD removal during the stable operation period (10.7 to 19.2 kg COD m³/d) occurred in a range between 97 and 99%. The methane content in the biogas varied from 65 to 70% in stage I, and from 63 to 66% in stage II. The two-stage anaerobic treatment using HUASB with PUF and PVC described in this work is expected to constitute a better alternative for the complete treatment of dairy wastewater than high-rate anaerobic, anaerobic/aerobic, and two-phase anaerobic treatment methods.     

Thermophilic treatment of bulk drug pharmaceutical industrial wastewaters by using hybrid up flow anaerobic sludge blanket reactor

The hybrid up flow anaerobic sludge blanket reactor was evaluated for efficacy in reduction of chemical oxygen demand (COD) and biochemical oxygen demand (BOD) of bulk drug pharmaceutical wastewater under different operational conditions. The start-up of the reactor feed came entirely with glucose, applied at an organic loading rate (OLR) 1 kg COD/m³ d. Then the reactor was studied at different OLRs ranging from 2 to 11 kg COD/m³ d with pharmaceutical wastewater. The optimum OLR was found to be 9 kg COD/m³ d, where we found 65–75% COD and 80–94% of BOD reduction with biogas production containing 60–70% of methane and specific methanogenic activity was 320 ml CH₄/g-VSS d. By the characterization studies of effluent using GC–MS, the hazardous compounds like phenol, l,2-methoxy phenol, 2,4,6-trichloro phenol, dibutyl phthalate, 1-bromo naphthalene, carbamazepine and antipyrine were present. After the treatment, these compounds degraded almost completely except carbamazepine. Thermophilic methanothrix and methanosaetae like bacteria are present in the granular sludge.     

Mechanical shear contributes to granule formation resulting in quick start-up and stability of a hybrid anammox reactor

It appears that if suspended biomass washout can be reduced effectively, granule formation will be fastened in fluidized bed. Quicker reactor start-up can be anticipated especially for those system keeping slow growth bacteria such as anammox. A hybrid reactor combined fixed-bed with nonwoven fabrics as biomass carrier and fluidized bed with slow speed mechanical stirring was therefore developed, and its nitrogen removal performances was evaluated experimentally. Only in 38 days, the total nitrogen removal rate (NRR) reached to 1.9 kg(N) m⁻³ day⁻¹ and then doubled within 17 days, with total nitrogen removal efficiency kept above 70%. After 180 days reactor operating, the NRR reached a maximum value of 6.6 kg(N) m⁻³ day⁻¹ and the specific anammox activity was gradually constant in 0.32 kg(N) kg(VSS)⁻¹ day⁻¹. Biomass attached on nonwoven fabrics could additionally improve reactor nitrogen removal by 8%. The dominant size of granular sludge reached to 0.78 mm with stirring speed adjusted from 30 to 80 rpm and the hydraulic retention time (HRT) from 8 to 1.5 h during the whole operating time. Scanning electron microscope observation showed especially compact structure of granular sludge. A 70% of anammox bacteria percentage was identified by fluorescence in situ hybridization analysis.     

Reactivation of effluent granular sludge from a high-rate Anammox reactor after storage

In this study, effluent sludge from a high-rate Anammox reactor was used to re-start new Anammox reactors for the reactivation of Anammox granular sludge. Different start-up strategies were evaluated in six upflow anaerobic sludge blanket (UASB) reactors (R₁–R₆) for their effect on nitrogen removal performance. Maximal nitrogen removal rates (NRRs) greater than 20 kg N/m³/day were obtained in reactors R₃–R₅, which were seeded with mixed Anammox sludge previously stored for approximately 6 months and 1 month. A modified Boltzmann model describing the evolution of the NRR fit the experimental data well. An amount of sludge added to the UASB reactor or decreasing the loading rate proved effective in relieving the substrate inhibition and increasing the NRR. The modified Stover–Kincannon model fit the nitrogen removal data in the Anammox reactors well, and the simulation results showed that the Anammox process has great nitrogen removal potential. The observed inhibition in the Anammox reactors may have been caused by high levels of free ammonia. The sludge used to seed the reactors did not settle well; sludge flotation was observed even after the reactors were operated for a long time at a floating upward velocity (F_s) of greater than 100 m/h. The settling sludge, however, exhibited good settling properties. Scanning electron microscopy showed that the Anammox granules consisted mainly of spherical and elliptical bacteria with abundant filaments on their surface. Hollows in the granules were also present, which may have contributed to sludge floatation.     

Nitrogen removal performance of a hybrid anammox reactor

The anaerobic ammonium oxidation (anammox) process has attracted considerable attention in recent years as an alternative to conventional nitrogen removal technologies. In this study, an innovative hybrid reactor combining fluidized and fixed beds for anammox treatment was developed. The fluidized bed was mechanically stirred and the gaseous product could be rapidly released from the anammox sludge to prevent washout of the sludge caused by floatation. The fixed bed comprising a non-woven biomass carrier could efficiently catch sludge to reduce washout. During the operation, nitrogen loading rates to the reactor were increased to 27.3 kg N/m³/d, with total nitrogen removal efficiencies of 75%. The biomass concentration in the fluidized bed reached 26-g VSS/L. Anammox granules were observed in the reactors, with settling velocities and sludge volumetric index of 27.3 ± 6.5 m/h and 23 mL/g, respectively. Quantification of extracellular polymeric substances revealed the anammox granules contained a significant amount of extracellular proteins.     

Thermophilic anaerobic treatment of sulphur rich forest industry wastewater

Thermophilic anaerobic treatment of sulphur-rich paper mill wastewater (0.8-3.1 gCOD/l, 340–850 mgSO₄/l; COD:SO₄ 3.4-5.3) was studied in three laboratory-scale, upflow anaerobic sludge blanket (UASB) reactors and in bioassays. The reactors were inoculated with non-adapted thermophilic granular sludge. In the bioassays, no inhibition of the inoculum was detected and about 62% COD removal (sulphide stripped) was obtained. About 70 to 80% of the removed COD was methanised. In the reactors, up to 60–74% COD removal (effluent sulphide stripped) was obtained at loading rates up to 10–30 kgCOD/m³d and hydraulic retention times down to 6 to 2 hours. The effluent total sulphide was up to 150–250 mg/l. Sulphide inhibition could not be confirmed from the reactor performances. The results from bioassays suggested that both the inoculum and sludge from the UASB reactor used acetate mainly for methane production, while sulphide was produced from hydrogen or its precursors.