Two-stage Upflow Anaerobic Sludge Blanket Research Articles

Anaerobic wastewater treatment of concentrated sewage using a two-stage upflow anaerobic sludge blanket- anaerobic filter system

A two-stage pilot-scale upflow anaerobic sludge blanket – anaerobic filter (UASB-AF) reactors system treating concentrated domestic sewage was operated at 23°C and at hydraulic retention times (HRT) of 15 and 4 h, respectively. Excess sludge from the downstream AF stage was returned to the upstream UASB reactor. The aim was to obtain higher sludge retention time (SRT) in the UASB reactor for better methanization of suspended COD. The UASB-AF system removed 55% and 65% of the total COD (CODtot) and suspended COD (CODss), respectively. The calculated SRT in the UASB reactor ranged from 20–35 days. The AF reactor removed the washed out sludge from the first stage reactor with average CODss removal efficiency of 55%. The volatile fatty acids concentration in the effluent of the AF was 39 mg COD/L compared with 78 mg COD/L measured for the influent. The slightly higher CODtot removal efficiency obtained in this study compared with a single stage UASB reactor was achieved at 17% reduction in the total volume.

Advanced landfill leachate treatment using a two-stage UASB-SBR system at low temperature

A two-stage upflow anaerobic sludge blanket (UASB) and sequencing batch reactor (SBR) system was introduced to treat landfill leachate for advanced removal of COD and nitrogen at low temperature. In order to improve the total nitrogen (TN) removal efficiency and to reduce the COD requirement for denitrification, the raw leachate with recycled SBR nitrification supernatant was pumped into the first-stage UASB (UASB1) to achieve simultaneous denitrification and methanogenesis. The results showed that UASB1 played an important role in COD removal and UASB2 and SBR further enhanced the nutrient removal efficiency. When the organic loading rates of UASB1, UASB2 and SBR were 11.95, 1.63 and 1.29 kg COD/(m 3·day), respectively, the total COD removal efficiency of the whole system reached 96.7%. The SBR acted as the real undertaker for NH 4 +-N removal due to aerobic nitrification. The system obtained about 99.7% of NH 4 +-N removal efficiency at relatively low temperature (14.9–10.9°C). More than 98.3% TN was removed through complete denitrification in UASB1 and SBR. In addition, temperature had a significant effect on the rates of nitrification and denitrification rather than the removal of TN and NH 4 +-N once the complete nitrification and denitrification were achieved.

Palm oil mill effluent treatment using a two-stage microbial fuel cells system integrated with immobilized biological aerated filters

An integrated system of two-stage microbial fuel cells (MFCs) and immobilized biological aerated filters (I-BAFs) was used to treat palm oil mill effluent (POME) at laboratory scale. By replacing the conventional two-stage up-flow anaerobic sludge blanket (UASB) with a newly proposed upflow membrane-less microbial fuel cell (UML-MFC) in the integrated system, significant improvements on NH(3)-N removal were observed and direct electricity generation implemented in both MFC1 and MFC2. Moreover, the coupled iron-carbon micro-electrolysis in the cathode of MFC2 further enhanced treatment efficiency of organic compounds. The I-BAFs played a major role in further removal of NH(3)-N and COD. For influent COD and NH(3)-N of 10,000 and 125 mg/L, respectively, the final effluents COD and NH(3)-N were below 350 and 8 mg/L, with removal rates higher than 96.5% and 93.6%. The GC-MS analysis indicated that most of the contaminants were satisfactorily biodegraded by the integrated system.

Nitrogen removal via nitrite from municipal landfill leachate

A system consisting of a two-stage up-flow anaerobic sludge blanket (UASB), an anoxic/aerobic (A/O) reactor and a sequencing batch reactor (SBR), was used to treat landfill leachate. During operation, denitrification and methanogenesis took place simultaneously in the first stage UASB, and the effluent chemical oxygen demand (COD) was further removed in the second stage UASB. Then the denitrification of nitrite and nitrate in the returned sludge by using the residual COD was accomplished in the A/O reactor, and ammonia was removed via nitrite in it. Last but not least, the residual ammonia was removed in SBR as well as nitrite and nitrate which were produced by nitrification. The results over 120 d (60 d for phase I and 60 d for phase II) were as follows: when the total nitrogen (TN) concentration of influent leachate was about 2500 mg/L and the ammonia nitrogen concentration was about 2000 mg/L, the short-cut nitrification with 85%-90% nitrite accumulation was achieved stably in the A/O reactor. The TN and ammonia nitrogen removal efficiencies of the system were 98% and 97%, respectively. The residual ammonia, nitrite and nitrate produced during nitrification in the A/O reactor could be washed out almost completely in SBR. The TN and ammonia nitrogen concentrations of final effluent were about 39 mg/L and 12 mg/L, respectively.

Integrated treatment of olive mill wastewater (OMW) by the combination of Fenton's reaction and anaerobic treatment

The use of an integrated treatment scheme consisting of wet hydrogen peroxide catalytic oxidation (WHPCO) followed by two-stage upflow anaerobic sludge blanket (UASB) reactor (10 l each) for the treatment of olive mill wastewater was the subject of this study. The diluted wastewater (1:1) was pre-treated using Fenton's reaction. Optimum operating conditions namely, pH, H 2O 2 dose, Fe +2, COD:H 2O 2 ratio and Fe +2:H 2O 2 ratio were determined. The UASB reactor was fed continuously with the pre-treated wastewater. The hydraulic retention time was kept constant at 48 h (24 h for each stage). The conventional parameters such as COD, BOD, TOC, TKN, TP, TSS, oil and grease, and total phenols were determined. The concentrations of polyphenolic compounds in raw wastewater and effluents of each treatment step were measured using HPLC. The results indicated a good quality final effluent. Residual concentrations of individual organic compounds ranged from 0.432 mg l −1 for ρ-hydroxy-benzaldhyde to 3.273 mg l −1 for cinnamic acid.

Acid resistance of methanogenic bacteria in a two-stage anaerobic process treating high concentration methanol wastewater

In this study, the two-stage upflow anaerobic sludge blanket (UASB) system and batch experiments were employed to evaluate the performance of anaerobic digestion for the treatment of high concentration methanol wastewater. The acid resistance of granular sludge and methanogenic bacteria and their metabolizing activity were investigated. The results show that the pH of the first UASB changed from 4.9 to 5.8 and 5.5 to 6.2 for the second reactor. Apparently, these were not the advisable pH levels that common methanogenic bacteria could accept. The methanogenic bacteria of the system, viz. Methanosarcina barkeri, had some acid resistance and could still degrade methanol at pH 5.0. If the methanogenic bacteria were trained further, their acid resistance would be improved somewhat. Granular sludge of the system could protect the methanogenic bacteria within its body against the impact of the acidic environment and make them degrade methanol at pH 4.5. The performance of granular sludge was attributed to its structure, bacteria species, and the distribution of bacterium inside the granule.

High rate treatment of terephthalic acid production wastewater in a two‐stage anaerobic bioreactor

The feasibility was studied of anaerobic treatment of wastewater generated during purified terephthalic acid (PTA) production in two-stage upflow anaerobic sludge blanket (UASB) reactor system. The artificial influent of the system contained the main organic substrates of PTA-wastewater: acetate, benzoate, and terephthalate. Three parallel operated reactors were used for the second stage, and seeded with a suspended terephthalate degrading culture, with and without additional methanogenic granular sludge (two different types). The first stage UASB-reactor was seeded with methanogenic granular sludge. Reactors were operated at 37 degrees C and pH 7. During the first 300 days of operation a clear distinction between the biomass grown in both reactor stages was obtained. In the first stage, acetate and benzoate were degraded at a volumetric loading rate of 40 g-COD/L . day at a COD-removal efficiency of 95% within the first 25 days of operation. No degradation of terephthalate was obtained in the first stage during the first 300 days of operation despite operation of the reactor at a decreased volumetric loading rate with acetate and benzoate of 9 g-COD/L . day from day 150. Batch incubation of biomass from the reactor with terephthalate showed that the lag-phase prior to terephthalate degradation remained largely unchanged, indicating that no net growth of terephthalate degrading biomass occurred in the first stage reactor. From day 300, however, terephthalate degradation was observed in the first stage, and the biomass in this reactor could successfully be enriched with terephthalate degrading biomass, resulting in terephthalate removal capacities of 15 g-COD/L . day. Even though no single reason could be identified why (suddenly) terephthalate degradation was obtained after such a long period of operation, it is suggested that the solid retention time as well the prevailing reactor concentrations acetate and benzoate may have played an important role. From day 1 of operation, terephthalate was degraded in the second stage. In presence of methanogenic granular biomass, high terephthalate removal capacities were obtained in these reactors (15 g-COD/L . day) after approximately 125 days of operation. From the results obtained it is concluded that terephthalate degradation is the bottleneck during anaerobic treatment of PTA-wastewater. Pre-removal of acetate and benzoate in staged bioreactor reduces the lag-phase prior to terephthalate degradation in latter stages, and enables high rate treatment of PTA-wastewater.

Anaerobic/aerobic treatment of municipal landfill leachate in sequential two-stage up-flow anaerobic sludge blanket reactor (UASB)/completely stirred tank reactor (CSTR) systems

The treatability of leachate produced from the lab-scale simulated reactor treating food wastes was investigated in a two-stage sequential up-flow anaerobic sludge blanket reactor (UASB)/aerobic completely stirred tank reactor (CSTR). Experiments were performed in two UASB reactors and a CSTR reactor having effective volumes of 2.5 and 9 l, respectively. The hydraulic retention times in anaerobic and aerobic stages were 1.25 and 4.5 days, respectively, through 42 days at a constant flow rate of 21. After the start-up period, the COD concentration of leachate was steadily increased from 5400 to 20,000 mg/l. OLRs were increased from 4.3 to 16 kg/m3 per day by increasing the COD concentrations from 5400 to 20,000 mg/l. The effluent of the first anaerobic UASB reactor (Run1) was used as the influent of the second UASB reactor (Run2), while the effluent of the second UASB reactor was used as the influent of the aerobic CSTR reactor (Run3). COD removal efficiencies of the first UASB reactor and in the whole system (two steps UASB + CSTR) were 58, 62, 65, 72, 74, 79% and 96, 96.8, 97.3, 98, 98 and 98%, respectively. As the OLR increased from 4.3 to 16 kg/m3 per day, the COD removal efficiency reached a maximum of 80%. NH4-N removal efficiency was approximately 99.6% after the aerobic stage. The maximum methane percentages of the first and second UASB reactors were 64 and 43%, respectively.

The inhibitory effects and removal of dieldrin in continuous upflow anaerobic sludge blanket reactors

The inhibitory effects and removal efficiency of dieldrin (DLD) in anaerobic reactors were investigated. Anaerobic toxicity assay (ATA) experiments conducted in batch reactors revealed that 30 mg/l DLD had inhibitory effects on the unacclimated mixed anaerobic cultures. Continuous reactor experiments performed in a lab-scale two-stage upflow anaerobic sludge blanket (UASB) reactor system which was fed with ethanol as the sole carbon source, indicated that anaerobic granular cultures could be successfully acclimated to DLD. Chemical oxygen demand (COD) removal efficiencies were 88–92% for the two-stage system. The influent DLD concentration of 10 mg/l was removed by 44–86% and 86–94% in the second stage and overall UASB system, respectively. Biosorption of DLD on granular anaerobic biomass was found to be a significant mechanism for DLD removal in the UASB system. The maximum DLD loading rate and minimum HRT achievable for the first stage UASB reactor were 0.5 mg/l day (76 μg DLD/g VSS.day) and 10 h, respectively, which resulted in the overall COD removal efficiency of 85%.

The inhibitory effects of lindane in batch and upflow anaerobic sludge blanket reactors.

In this study, the inhibitory effects of lindane (LIN) on originally unacclimated mixed anaerobic cultures were investigated by anaerobic toxicity assay (ATA) experiments. ATA experiments revealed that 10 mg/l LIN exerted inhibitory effects on anaerobic cultures, which was recoverable. Continuous reactor experiments conducted to determine the inhibitory effects of LIN and the maximum LIN loading rate achievable in two-stage upflow anaerobic sludge blanket (UASB) reactors indicated that anaerobic granular cultures were successfully acclimated to 30 mg/l LIN. The maximum LIN loading rate and minimum hydraulic retention time (HRT) possible for the UASB system were 10 mg/l day and 18 h, respectively, which resulted in the overall chemical oxygen demand (COD) removal efficiency of 89%.

Methane fermentation of coastal mud sediment by a two-stage upflow anaerobic sludge blanket (UASB) reactor system.

The removal of organic matter from a coastal mud sediment was carried out by a methane fermentation process under anaerobic conditions. In a batch acidogenic fermentation, the addition of vitamins containing thiamine, nicotinic acid and biotin dramatically enhanced acetate production from the mud sediment (200 g wet wt l(-1) artificial sea water), yielding 77 mM acetate after 6 days, which corresponded to 77% of the organic matter in the mud sediment, measured on the basis of chemical oxygen demand. Thereafter, the two-fold diluted, post-acidogenic fermentation liquor (PAF liquor) was continuously treated at 2.4x original dilution rate day(-1) for 30 days, using an upflow anaerobic sludge blanket methanogenic reactor containing the acclimated methanogenic sludge from the mud sediment. Acetate, 42 mM in the PAF liquor, was converted to methane at a maximum methane production rate of 96 mmol l(-1) day(-1); and 87.5% of the acetate and 88.7% of the total organic carbon in the PAF liquor were removed. Moreover, an efficient treatment of the mud sediment was carried out by a semi-continuous, two-stage reactor system, where the culture broth was circulated between acidogenic and methanogenic reactors. This two-stage reactor system gave a stable operation at 4-day intervals for one treatment period, yielding 112 mmol methane from the wet mud in the PAF liquor (278 g l(-1)).

Anaerobic biotransformation and methane generation potential of cheese whey in batch and UASB reactors

Anaerobic treatability and methane generation potential of cheese whey were determined in batch reactors. Furthermore, the effect of nutrient and trace metal supplementation on the batch anaerobic treatment, and the high-rate anaerobic treatability of cheese whey in upflow anaerobic sludge blanket (UASB) reactors were investigated. To this purpose biochemical methane potential experiments were conducted and single- and two-stage UASB reactors with granular cultures were operated. In UASB experiments significance of process staging, operational parameters such as hydraulic retention time (HRT), influent chemical oxygen demand (COD) concentration and loading rate were also investigated. The results revealed that nutrient and trace metal supplementation is vital for the anaerobic treatment of cheese whey; the anaerobic methane generation for the cheese whey studied was found to be 424 ml CH 4/g COD (23.4 l CH 4/l cheese whey); undiluted cheese whey could be treated anaerobically at relatively short HRT values (2.06–4.95 days) without any significant stability problems; HRT values as low as 2–3 days can be used for the anaerobic treatment of cheese whey, with a COD removal efficiency of 95–97% at influent COD concentration of 42 700±141–55 100±283 mg/l.

Anaerobic biotransformation of four3-carbon compounds (acrolein, acrylic acid, allyl alcohol and n-propanol) in UASB reactors

Anaerobic biotransformation of the 3-carbon compounds, namely acrolein, acrylic acid, allyl alcohol, and n-propanol was investigated in upflow anaerobic sludge blanket (UASB) reactors containing granular cultures. The toxic effects of acrolein, acrylic acid, and allyl alcohol on an acetate-enriched Methanosarcina culture were determined. Furthermore, process staging, effect of operational parameters such as influent concentration, F/ M ratio and loading rate were also considered. Acrolein, acrylic acid, and allyl alcohol were found to be inhibitory to acetate-enriched Methanosarcina cultures starting from the concentrations of 20, 60, and 3000 mg/l, respectively. Inhibition is defined as the reduction in the activity (in terms of gas production rate) of a batch reactor relative to its activity before the addition of the test chemical. The results of UASB experiments revealed that granular cultures could be acclimated to utilize acrolein, acrylic acid, allyl alcohol, and n-propanol as the sole substrates. Acrolein concentrations up to 300 mg/l were treated with 90% efficiency. In a single-stage UASB reactor, acrylic acid biotransformation and chemical oxygen demand (COD) removal efficiencies of 95–99 and 45%, respectively, were achieved at an influent concentration of 3000 mg/l. The low COD removal was due to persistence of acetic and propionic acids, as intermediates of acrylic acid. When a two-stage UASB system was employed at the same acrylic acid influent concentration, the COD removal efficiency increased to 97%. At an F/ M ratio of 0.027 g COD/g biomass-day, 1000 mg/l of influent allyl alcohol was removed at an efficiency of about 85% after 30 days of acclimation in a single-stage UASB reactor. n-Propanol was biotransformed to mainly propionic acid with more than 99% efficiency at an influent concentration and F/ M ratio of 3000 mg/l and 0.27 g COD/g biomass-day, respectively, in a single-stage UASB reactor. But the COD removal did not exceed 68% because of the propionic acid persistence. However, a two-stage UASB system improved the COD removal to 99% for the same n-propanol influent concentration of 3000 mg/l.

Anaerobic treatment of palm oil mill effluent in a two-stage up-flow anaerobic sludge blanket (UASB) system

A high rate anaerobic treatment of palm oil mill effluent (POME) was achieved in a two-stage up-flow anaerobic sludge blanket (UASB) reactor. The acidogenic reactor acclimated rapidly to the wastewater and was tolerant to a suspended solids (SS) concentration of 5.4 g l −1 in the influent wastewater. Loading was gradually increased over a period of 100 days resulting in a satisfactory hydrolysis and acidification giving a maximum rate of acid production of 4.1 g l −1 d −1 acetic acid at a loading rate of 16.6 g l −1 d −1 COD at a hydraulic retention time of 0.9 days. An increase in alkalinity throughout the acclimatization maintained the effluent from the reactor at around pH 5.8. The methanogenic reactor was initially fed on dilutions of the effluent from the first stage reactor after pH adjustment. The loading was gradually increased, and then stepwise, to 60 g l −1 d −1 COD at which point COD removal efficiency had declined significantly and an accumulation of long-chain volatile fatty acids was observed. It was concluded that the reactor could work efficiently up to loadings of 30 g 1 −1 d −1 COD, whilst producing a good methane yield and a COD reduction of greater than 90%. Effluent recirculation alleviated the need for alkali additions to the feed of the methanogenic reactor and a direct coupling of the two reactors was achieved towards the end of the experimental run of 175 days. Both reactors showed granule formation with distinct morphological characteristics; these were observed to be formed after 80 days in the acidogenic reactor and after 110 days in the methanogenic reactor.