Extracellular polymeric substances (EPS) in upflow anaerobic sludge blanket (UASB) reactors operated under high salinity conditions

Considering the importance of stable and well-functioning granular sludge in anaerobic high-rate reactors, a series of experiments were conducted to determine the production and composition of EPS in high sodium concentration wastewaters pertaining to anaerobic granule properties. The UASB reactors were fed with either fully acidified substrate (FAS) consisting of an acetate medium (reactor R1) or partly acidified substrate (PAS) consisting of acetate, gelatine and starch medium (reactors R2, R3, and R4). For EPS extraction, the cation exchange resin (CER) method was used. Strength and particle size distribution were determined by assessing the formation of fines sludge under conditions of high shear rate and by laser diffraction, respectively. Batch tests were performed in 0.25 L bottles to study Ca²⁺ leaching from anaerobic granular sludge when incubated in 20 g Na⁺/L in the absence of feeding for 30 days. Results show a steady increase in the bulk liquid Ca²⁺ concentration during the incubation period. UASB reactor results show that the amounts of extracted proteins were higher from reactors R2 and R3, fed with PAS compared to the sludge samples from reactor R1, fed with FAS. Strikingly, the amount of extracted proteins also increased for all reactor sludges, irrespective of the Na⁺ concentration applied in the feed, i.e. 10 or 20 gNa⁺/L. PAS grown granular sludges showed an important increase in particle size during the operation of the UASB reactors. Results also show that, addition of 1 gCa²⁺/L to the high salinity wastewater increases the granules' strength.     

Pre-acidification in anaerobic sludge bed process treating brewery wastewater

The effect of pre-acidification on anaerobic granule bed processes treating brewery wastewater was the focus of a comparison study employing two configurations, (a) a single stage upflow anaerobic sludge bed (UASB) and (b) an upflow acidification reactor in series with a methanogenic UASB. The pre-acidification reactor achieved 20±4% SCOD removal and 0.08±0.003 L of methane produced per gram of SCOD removal at a hydraulic retention time (HRT) of 0.75–4 h. Butyric acid was not detected and short chain fatty acids (SCFAs) were mainly acetic and propionic acids. The acidification ratio was about 0.42±0.02 g SCFAs as COD/g of influent COD.

Both systems’ critical loading rate to achieve 80% COD removal was established at 34–39 kg COD/m³ of total sludge bed volume per day. SCOD removal efficiency of 90±3% was achieved by both systems at an organic loading rate of 25±1 kg COD/m³ of total sludge bed volume per day, indicating that the installation of an acidification reactor had no effect in terms of the maximum granular activity, biomass granulation and the settleability of granules. At an organic loading rate of 67 kg COD/m³ of total sludge bed volume per day at an HRT of 1 h, the series system outperformed the single UASB by a removal of 62 compared to 57%.     

Enrichment of acetogenic bacteria in high rate anaerobic reactors under mesophilic and thermophilic conditions

The objective of the current study was to expand the knowledge of the role of acetogenic Bacteria in high rate anaerobic digesters. To this end, acetogens were enriched by supplying a variety of acetogenic growth supportive substrates to two laboratory scale high rate upflow anaerobic sludge bed (UASB) reactors operated at 37 °C (R1) and 55 °C (R2). The reactors were initially fed a glucose/acetate influent. Having achieved high operational performance and granular sludge development and activity, both reactors were changed to homoacetogenic bacterial substrates on day 373 of the trial. The reactors were initially fed with sodium vanillate as a sole substrate. Although % COD removal indicated that the 55 °C reactor out performed the 37 °C reactor, effluent acetate levels from R2 were generally higher than from R1, reaching values as high as 5023 mg l⁻¹. Homoacetogenic activity in both reactors was confirmed on day 419 by specific acetogenic activity (SAA) measurement, with higher values obtained for R2 than R1.Sodium formate was introduced as sole substrate to both reactors on day 464. It was found that formate supported acetogenic activity at both temperatures. By the end of the trial, no specific methanogenic activity (SMA) was observed against acetate and propionate indicating that the methane produced was solely by hydrogenotrophic Archaea. Higher SMA and SAA values against H₂/CO₂ suggested development of a formate utilising acetogenic population growing in syntrophy with hydrogenotrophic methanogens. Throughout the formate trial, the mesophilic reactor performed better overall than the thermophilic reactor.     

Effect of anaerobic reactor process configuration on useful energy production

The effect of reactor process configuration on anaerobic production of useful energy (hydrogen and methane) from a complex substrate was investigated for the following reactor systems: suspended growth, two-phase mixed, two-stage mixed, upflow anaerobic sludge blanket (UASB) reactor, and two-phase UASB. The mixed two-phase and two-stage configurations yielded the highest specific energy productions of 13.3 and 13.4 kJ/g COD fed, respectively. Reactor process configuration influenced microbial pathways in acidogenic reactors in that butyrate was the predominant volatile acid in phased configurations, whereas acetate was predominant in the staged configuration. The UASB reactor achieved the highest average daily energy production per reactor volume of 101 kJ/L reactor-d. All reactor configurations achieved high COD removals on the order of 99%. However, hydrogen represented only 3% of the total energy produced by the two-phase mixed and two-phase UASB configurations. Theoretical analysis revealed that the maximum specific energy production by the two-phase suspended-growth configuration is only 9% higher than that for a single-stage mixed reactor. Consequently, the production of hydrogen from complex substrates in these process configurations does not seem to be justifiable solely from an energy point of view. Instead, it is suggested that phased anaerobic systems should be considered primarily for improved process stability whereas resultant hydrogen production is of secondary benefit.     

Effects of ferric iron on the anaerobic treatment and microbial biodiversity in a coupled microbial electrolysis cell (MEC) – Anaerobic reactor

Adding Fe(III) into a MEC – anaerobic reactor enhanced the degradation of organic matters. To clarify the respective effects of combining Fe(III) dosage and a MEC and Fe(III) dosage only on strengthening anaerobic digestion, three anaerobic reactors were operated in parallel: a MEC – anaerobic reactor with dosing Fe(OH)₃ (R1), an anaerobic reactor with dosing Fe(OH)₃ (R2) and a common anaerobic reactor (R3). With increasing influent COD from 1500 to 4000 mg/L, the COD removal in R1 was maintained at 88.3% under a voltage of 0.8 V, which was higher than that in reactor R2 and R3. When the power was cut off, the COD removal in R1 decreased by 5.9%. The addition of Fe(OH)₃ enhanced both anaerobic digestion and anodic oxidation, resulting in the effective mineralization of volatile fatty acids (VFAs). The reduced Fe(II) combined with electric field resulted more extracellular polymeric substances (EPS) production. Quantitative real – time PCR showed a higher abundance of bacteria in the anodic biofilm and R1. Pyrosequencing and denaturing gradient gel electrophoresis (DGGE) analysis revealed that the dominant bacteria and archaea communities were richer and more abundant in the anode biofilm and R1.     

Enhanced granulation by natural ionic polymer additives in UASB reactor treating low-strength wastewater

Effect of natural ionic polymer additives on granulation in lab-scale UASB reactors treating low-strength synthetic wastewater (COD 750-850 mg/L) was examined. The organic loading rate was 1.477+/-0.118 kgCOD/m3/day. Under identical conditions four similar reactors were operated in parallel with the following additives: control with no additive, anionic part of Reetha (Sapindus trifoliata) extract, cationic part of Reetha extract, and Chitosan. By the end of the study period, Chitosan as an additive produced largest granules with mean size of 0.15 mm closely followed by the cationic fraction of the Reetha extract with mean size of 0.144 mm, and anionic fractions of the Reetha extract with 0.139 mm. Control reactor with no additives had the smallest size granules with mean size of 0.128 mm. The fraction of granules in the sludge bed of size >0.1 mm showed similar trend. The largest granule size observed in the reactors with additives was 4-5mm as compared to 2 mm in the control reactor. Cationic polymers were more effective additives for enhancing sludge granulation. Exo-cellular protein, lipid, sugar and total polymer increased with granulation in the reactors. A COD removal efficiency of 95-98% was achieved in all the reactors.     

Anaerobic biodegradability and treatment of grey water in upflow anaerobic sludge blanket (UASB) reactor

Feasibility of grey water treatment in an upflow anaerobic sludge blanket (UASB) reactor operated at different hydraulic retention time (HRT) of 16, 10 and 6h and controlled temperature of 30 degrees C was investigated. Moreover, the maximum anaerobic biodegradability without inoculum addition and maximum removal of chemical oxygen demand (COD) fractions in grey water were determined in batch experiments. High values of maximum anaerobic biodegradability (76%) and maximum COD removal in the UASB reactor (84%) were achieved. The results showed that the colloidal COD had the highest maximum anaerobic biodegradability (86%) and the suspended and dissolved COD had similar maximum anaerobic biodegradability of 70%. Furthermore, the results of the UASB reactor demonstrated that a total COD removal of 52-64% was obtained at HRT between 6 and 16 h. The UASB reactor removed 22-30% and 15-21% of total nitrogen and total phosphorous in the grey water, respectively, mainly due to the removal of particulate nutrients. The characteristics of the sludge in the UASB reactor confirmed that the reactor had a stable performance. The minimum sludge residence time and the maximum specific methanogenic activity of the sludge ranged between 27 and 93 days and 0.18 and 0.28 kg COD/(kg VS d).     

Characteristics of sludge developed under different loading conditions during UASB reactor start-up and granulation

Sludge characteristics available inside the reactor are of vital importance to maximize advantages of UASB reactor. The organic loading rate and sludge loading rate applied during start-up are among the important parameters to govern the sludge characteristics. Effects of these loading rates on the characteristics of the sludge developed are evaluated in six laboratory scale UASB reactors. The sludge characteristics considered are VSS/SS ratio of the sludge, sludge volume index, specific gravity, settling velocity and metal contents of the sludge developed under different loading rates. The experimental results indicate that, for developing good characteristics sludge, during primary start-up from flocculent inoculum sludge, organic loading rate and sludge loading rate should be in the range of 2.0-4.5 kg COD/m3 d and 0.1-0.25 kg COD/kg VSS d, respectively (chemical oxygen demand, COD). Proper sludge granulation and higher COD removal efficiency will be achieved by these loading rates.     

Accelerated start-up and enhanced granulation in upflow anaerobic sludge blanket reactors

In the present study, the effects of a cationic polymer on reactor start-up and granule development were evaluated. A control reactor R1 was operated without adding polymer, while the other five reactors designated R2, R3, R4, R5 and R6 were operated with different polymer concentrations of 20, 40, 80, 160 and 320 mg/L, respectively. Experimental results demonstrated that adding the polymer at a concentration of 80 mg/L markedly accelerated the start-up time. The time required to reach stable treatment at an organic loading rate (OLR) of 4 g COD/L.d was reduced by approximately 50% in R4 as compared with the control reactor. The same reactor with 80 mg/L polymer was able to achieve an OLR of 12 g COD/L.d after 59 days of operation, while R1, R2, R3, R5 and R6 achieved the same loading rate at much longer period of 104, 80, 69, 63 and 69 days, respectively. Comparing with the control reactor, the start-up time of R4 was shortened markedly by about 43% at this OLR, while other reactors also recorded varying degree of shortening. Monitoring on granule development showed that the granule formation was accelerated by 30% from the use of the appropriate dosage of polymer. Subsequent granules characterization indicated that the granules developed in R4 with 80 mg/L polymer exhibited the best settleability, strength and methanogenic activity at all OLRs. The organic loading capacities of reactors were also increased by the polymer addition. The maximum organic loading of the control reactor was 24 g COD/L.d, while the polymer-assisted reactor added with 80 mg/L polymer attained a markedly increased organic loading of 40 g COD/L.d. The laboratory results obtained demonstrated that adding the cationic polymer could result in shortening of start-up time and enhancement of granulation, which in turn lead to improvement in organics removal efficiency and loading capacity of the UASB system.     

Performance of UASB reactor treating leachate from acidogenic fermenter in the two-phase anaerobic digestion of food waste

This study was conducted to investigate the performance of the upflow anaerobic sludge blanket (UASB) reactor treating leachate from acidogenic fermenter in the two-phase anaerobic digestion of food waste. The chemical oxygen demand (COD) removal efficiency was consistently over 96% up to the loading rates of 15.8 g COD/l d. The methane production rate increased to 5.51/l d. Of all the COD removed, 92% was converted to methane and the remaining presumably to biomass. At loading rates over 18.7 g COD/l d, the COD removal efficiency decreased due to sludge flotation and washout in the reactor, which resulted from short HRT of less than 10.6 h. The residual propionate concentration was the highest among the volatile fatty acids (VFA) in the effluent. The specific methanogenic activity (SMA) analysis showed that the VFA-degrading activity of granule was the highest for butyrate, and the lowest for propionate. Typical granules were found to be mainly composed of microcolonies of Methanosaeta. The size distribution of sludge particles indicated that partially granulated sludge could maintain the original structure of granular sludge and continue to gain size in the UASB reactor treating leachate from acidogenic fermenter.     

Tannery effluent as a carbon source for biological sulphate reduction

Tannery effluent was assessed as a carbon source for biological sulphate reduction in a pilot-scale upflow anaerobic sludge blanket (UASB), stirred tank reactor (STR) and trench reactor (TR). Sulphate removals of between 60-80% were obtained in all three reactors at total sulphate feed levels of up to 1800 mg l(-1). Sulphate removal in the TR (400-500 mg SO4 l(-1) day(-1)) and UASB (up to 600 mg SO4 l(-1) day(-1)) were higher than those obtained in the STR (250 mg SO4 l(1) day(-1)). A change in operation mode from a UASB to a STR had a large impact on chemical oxygen demand (COD) removal efficiencies. COD removal rates decreased by 25% from 600-700 mg COD l(-1) day(-1) to 200-600 mg COD l(-1) day(-1). The TR had an average COD removal rate of 500 mg COD l(-1) day(-1). Large quantities of sulphide were produced in the reactors (up to 1500 mg l(-1)). However due to the elevated pH in the reactor, only a small amount was in the form of H2S and thus the odour problem normally associated with biological sulphate reduction was not present.     

Anaerobic sludge granulation

This paper reviews different theories on anaerobic sludge granulation in UASB-reactors that have been proposed during the past two decades. The initial stages of the formation of anaerobic granules follow the same principles as biofilm formation of bacteria on solid surfaces. There exist strong evidence that inert carriers play an important positive role in granulation. Most researchers conclude that Methanosaeta concilii is a key organism in granulation. Only the Cape Town Hypothesis presumes that an autotrophic hydrogenotrophic organism, i.e., Methanobacterium strain AZ, growing under conditions of high H(2)-pressures, is the key organism in granulation. Many authors focus on the initial stage of granulation, and only a few contributions discuss the latter stages in granulation: granule maturation and multiplication. Granule enhancing factors in the latter stages predominantly rely on manipulation of the selection pressure, through which selectively heavier sludge particles are retained in the UASB reactor.     

Electricity assisted anaerobic treatment of salinity wastewater and its effects on microbial communities

High salinity wastewater is often difficult to treat using common anaerobic technologies. Considering that high conductivity of salinity wastewater may enhance electrodes reaction to accelerate the decomposition of volatile fatty acids produced in anaerobic digestion, a pair of electrodes was packed into an anaerobic reactor (R1) with the aim to enhance the treatment of salinity wastewater. With increasing the salt concentration (NaCl) gradually from 0 to 50 g/L in 137 days' operation, COD removal in this reactor under the voltage for the electrodes of 1.2 V was well maintained at 93%, while the COD removal in a reference anaerobic reactor without electrodes (R2) decreased to 53%. When the voltage for R1 was cut off, about 10% COD removal was declined, which was still 30 percentage points higher than that in R2. The electrodes enhanced the biodegradation of volatile fatty acids, especially propionate. Fluorescence in situ hybridization analysis confirmed that the relative abundance of propionate-utilizing bacteria in R1 was significantly higher than that in R2. PCR-DGGE analysis of bacteria and archaea domains indicated that the electric field stimulation effectively enriched salt-adapted microorganisms during the treatment.     

Anaerobic sewage treatment in a one-stage UASB reactor and a combined UASB-Digester system

The treatment of sewage at 15 degrees C was investigated in a one-stage upflow anaerobic sludge blanket (UASB) reactor and a UASB-Digester system. The latter consists of a UASB reactor complemented with a digester for mutual sewage treatment and sludge stabilisation. The UASB reactor was operated at a hydraulic retention time of 6h and a controlled temperature of 15 degrees C, the average sewage temperature during wintertime of some Middle East countries. The digester was operated at 35 degrees C. The UASB-Digester system provided significantly (significance level 5%) higher COD removal efficiencies than the one-stage UASB reactor. The achieved removal efficiencies in the UASB-Digester system and the one-stage UASB reactor for total, suspended, colloidal and dissolved COD were 66%, 87%, 44% and 30%, and 44%, 73%, 3% and 5% for both systems, respectively. The stability values of the wasted sludge from the one-stage UASB reactor and the UASB-Digester system were, respectively, 0.47 and 0.36g CH(4)-COD/g COD. Therefore, the anaerobic sewage treatment at low temperature in a UASB-Digester system is promising.     

双区厌氧反应器的开发与试验研究

设计了双区厌氧反应器:下部污泥膨胀区在强水力作用下,消除了UASB的配水问题,加强了传质和预处理能力,刺激了厌氧微生物的生长和颗粒化进程;上部精处理区颗粒污泥生长条件好.实现了2.3倍的UASB反应器容积负荷.现场毒性试验表明:双区厌氧反应器比IC反应器受毒恢复更快.     

Removal of residual dissolved methane gas in an upflow anaerobic sludge blanket reactor treating low-strength wastewater at low temperature with degassing membrane

In this study, we investigated the efficiency of dissolved methane (D-CH₄) collection by degasification from the effluent of a bench-scale upflow anaerobic sludge blanket (UASB) reactor treating synthetic wastewater. A hollow-fiber degassing membrane module was used for degasification. This module was connected to the liquid outlet of the UASB reactor. After chemical oxygen demand (COD) removal efficiency of the UASB reactor became stable, D-CH₄ discharged from the UASB reactor was collected. Under 35 °C and a hydraulic retention time (HRT) of 10 h, average D-CH₄ concentration could be reduced from 63 mg COD L⁻¹ to 15 mg COD L⁻¹; this, in turn, resulted in an increase in total methane (CH₄) recovery efficiency from 89% to 97%. Furthermore, we investigated the effects of temperature and HRT of the UASB reactor on degasification efficiency. Average D-CH₄ concentration was as high as 104 mg COD L⁻¹ at 15 °C because of the higher solubility of CH₄ gas in liquid; the average D-CH₄ concentration was reduced to 14 mg COD L⁻¹ by degasification. Accordingly, total CH₄ recovery efficiency increased from 71% to 97% at 15 °C as a result of degasification. Moreover, degasification tended to cause an increase in particulate COD removal efficiency. The UASB reactor was operated at the same COD loading rate, but different wastewater feed rates and HRTs. Although average D-CH₄ concentration in the UASB reactor was almost unchanged (ca. 70 mg COD L⁻¹) regardless of the HRT value, the CH₄ discharge rate from the UASB reactor increased because of an increase in the wastewater feed rate. Because the D-CH₄ concentration could be reduced down to 12 ± 1 mg COD L⁻¹ by degasification at an HRT of 6.7 h, the CH₄ recovery rate was 1.5 times higher under degasification than under normal operation.     

Cultivation of anaerobic granular sludge in UASB reactors with aerobic activated sludge as seed

Methanogenic bacteria of 10⁸ g SS⁻¹ in the activated sludges from an aeration tank treating sewage and from a secondary sedimentation tank of an activated sludge plant treating textile dyeing wastewater were enumerated by the Most Probable Number (MPN) technique. By using the two activated sludges as the seed material, anaerobic granular sludges were obtained at 35°C in two lab-UASB reactors having volumes of 29 and 481, and treating a glucose molasses solution of 1000–3500 mg COD 1⁻¹ and citrate wastewater of 20,000–36,000 mg COD 1⁻¹ respectively. The characteristics of granulation using the activated sludge as the seed were similar to those using digested sewage sludge as the seed. It is shown that activated sludge is readily available seed material for an anaerobic reactor. The growth of methanogenic bacteria in the activated sludge can be attributed to the existence of some anaerobic nuclei in the activated sludge flocs. The factors for the cultivation of granular sludge by using the activated sludge are also discussed.     

颗粒活性炭加速厌氧反应器污泥颗粒化的研究

为克服厌氧反应器启动慢和启动难的问题,以UASB反应器为代表,向反应器内投加颗粒活性炭以加快厌氧污泥颗粒化进程,并采用扫描电子显微镜观察颗粒污泥的生长情况.结果表明,在试验的第64天即完成了厌氧污泥颗粒化的全部过程,培养出的颗粒污泥具有厌氧颗粒污泥的基本特征和典型的生化特性,并对啤酒废水有很好的处理效果.可见,投加颗粒活性炭可加速厌氧污泥颗粒化进程,并能有效维持厌氧反应器的稳定运行.     

Effect of process configuration and substrate complexity on the performance of anaerobic processes

The roles of substrate complexity (molecular size of the substrate) and process configuration in anaerobic wastewater treatment were investigated to determine optimal methanogenic technology parameters. Five substrates (glucose, propionate, butyrate, ethanol, and lactate) plus a mixed waste (60% carbohydrate, 34% protein, and 6% lipids) were studied under five reactor configurations: batch-fed single-stage continuous stirred tank reactor (CSTR), continuously fed single-stage CSTR, two-phase CSTR, two-stage CSTR, and single-stage upflow anaerobic sludge blanket (UASB). The substrate feed concentration was 20,000 mg/L as COD. The solids retention time (SRT) and hydraulic retention time (HRT) in the CSTR reactors were 20 d, while HRT in the UASB was 2 d. All reactors were operated for at least 60 d (equal to 3SRT). Substrate complexity was observed to be less significant under two-phase, two-stage and UASB reactor configurations. Two-phase CSTR, two-stage CSTR, and single-stage UASB configurations yielded the lowest effluent chemical oxygen demands (130-550, 60-700, and 50-250 mg/L, respectively). The highest effluent chemical oxygen demands were detected when feeding glucose, propionate, and lactate to continuously fed single-stage CSTRs (10, 400, 9900, and 4700 mg/L COD, respectively) and to batch-fed single-stage CSTRs (11, 200, 2500, and 2700 mg/L COD, respectively). Ironically, the one stage CSTR--most commonly utilized in the field--was the worst possible reactor configuration.     

Anaerobic treatment of municipal wastewater at ambient temperature: Analysis of archaeal community structure and recovery of dissolved methane

Anaerobic treatment is an attractive option for the biological treatment of municipal wastewater. In this study, municipal wastewater was anaerobically treated with a bench-scale upflow anaerobic sludge blanket (UASB) reactor at temperatures from 6 to 31 °C for 18 months to investigate total chemical oxygen demand (COD) removal efficiency, archaeal community structure, and dissolved methane (D-CH₄) recovery efficiency. The COD removal efficiency was more than 50% in summer and below 40% in winter with no evolution of biogas. Analysis of the archaeal community structures of the granular sludge from the UASB using 16S rRNA gene-cloning indicated that after microorganisms had adapted to low temperatures, the archaeal community had a lower diversity and the relative abundance of acetoclastic methanogens decreased together with an increase in hydrogenotrophic methanogens. D-CH₄, which was detected in the UASB effluent throughout the operation, could be collected with a degassing membrane. The ratio of the collection to recovery rates was 60% in summer and 100% in winter. For anaerobic treatment of municipal wastewater at lower temperatures, hydrogenotrophic methanogens play an important role in COD removal and D-CH₄ can be collected to reduce greenhouse gas emissions and avoid wastage of energy resources.