Anaerobic Sludge Granulation Research Articles

Comparative study on the effect of various pretreatment methods on the enrichment of hydrogen producing bacteria in anaerobic granulated sludge from brewery wastewater

Five pretreatment methods, namely chemical, acid, heat-shock, freezing and thawing, and base, were evaluated for the enrichment of hydrogen-producing bacteria in anaerobic granulated sludge, which will be subsequently used as seed in biological hydrogen production. All the pretreatments showed positive effects towards improving hydrogen (H2) generation by the microbial population with higher hydrogen production yield and COD removal efficiency as compared to control. The granulated sludge pretreated by heat-shock showed maximum accumulated H2 (19.48mLg−1-COD), COD removal efficiency (62%), and biomass concentration (22.5 gL−1).

The Simultaneous Removal of Carbon and Nitrogen from the Anaerobically Pretreated Distillery Wastewater in an Anaerobic Expanded Granule Sludge Bed (EGSB) Reactor

The simultaneous removal of carbon and nitrogen of the anaerobically pretreated distillery wastewater with nitrate, nitrite and ammonia addition was investigated in an expanded granule sludge bed (EGSB) reactor inoculated with methanogenic granule sludge. The experiment showed the COD removal efficiency decreased with the nitrogen loading increasing. Moreover, denitrifiers out-compete methanogens for the utilization of organics gradually, and COD removed by methanogenesis decreased to only 20% by measuring the amount of CH4 produced at low C/N ratios of 2, 3 and 4. Nitrate reduction to ammonium didn’t occur whatever the C/N ratio under anaerobic conditions. At high C/N ratios of 10 and 8, little total Kjeldahl nitrogen (TKN) was removed. However, 30%-50% of TKN entering the reactor was removed at lower C/N ratios of 2, 3 and 4 suggesting the removal of ammonium. At a lower C/N ratio of 2, the nitrite and the nitrate accumulation were observed and TKN removal decreased gradually due to their inhibition. The result suggested that the nitrate and ammonium simultaneous removal occurred through a coupling of nitrate reduction to nitrite by denitrification and then nitrite reduction to nitrogen gas by both denitrification and Anammox at a proper C/N ratio in an anaerobic EGSB reactor.

Biohydrogen production from desugared molasses (DM) using thermophilic mixed cultures immobilized on heat treated anaerobic sludge granules

Hydrogen production from desugared molasses (DM) was investigated in both batch and continuous reactors using thermophilic mixed cultures enriched from digested manure by load shock (loading with DM concentration of 50.1 g-sugar/L) to suppress methanogens. H 2 gas, free of methane, was produced during batch cultivations, at different (DM) concentrations ranging from 1.5 g-sugars/L to 50.1 g-sugars/L. The highest yield of 237 ml-H 2/g-sugar was achieved during the DM batch fermentation at concentration of 2.1 g-sugars/L, whereafter the yield decreased with increasing DM concentration. The enriched hydrogen producing mixed culture achieved from the 16.7 g-sugars/L DM batch cultivation was immobilized on heat treated anaerobic sludge granules in an up-flow anaerobic sludge blanket (UASB) reactor. The UASB reactor, operated at a hydraulic retention time (HRT) of 24 h fed with 16.7 g-sugars/L DM showed good performance with a satisfactory hydrogen yield of 269.5 ml-H 2/g-sugar and rate of 4500 ml H 2/l⋅d. Fluorescent in situ hybridization (FISH) analysis of the microbial community of sludge from batch fermentation and the UASB-granules after 54 days of operation, was dominated by Thermoanaerobacterium spp., which are key players in fermentative hydrogen production of DM under thermophilic conditions. Furthermore, the granules in the UASB reactor were also significantly containing Thermoanaerobacterium spp. and phylum Firmecutes (most Clotridium, Bacillus and Desulfobacterium) and Thermoanaerobacterium thermosaccharolyticum with a relative abundance of 36%, 27%, and 10% of total microorganisms, respectively. This study shows that hydrogen production could be efficiently facilitated by using anaerobic granules as a carrier, where microbes from mixed culture enriched in the DM batch cultivation were immobilized on, in an UASB reactor.

Study on Granulation of Anaerobic Sludge in UASB Reactor Adding Cationic Polymer Treating Low Strength Wastewater at Room Temperature

Effect of cationic polymer on granulation and COD removal efficiency in lab scale UASB reactors was examined, treating low-strength wastewater (COD 300-500mg l-1) at room temperature. It was shown that cationic polymer was more effective for enhancing sludge granulation and COD removal efficiency as compared to the control experiment (without additives). After day 166 of operation, the amount of granules size above 0.5mm accounted for 32.1% of total sludge, higher than that of control experiment (19.3%). At 1.03 kg COD m-3 d-1 of OLR and 9.8 h of HRT, the effluent VFA had a maximum value of 168mg l-1 and 240mg l-1 in Reactor A and B respectively. The polymer-amended reactor took 36days to receive 1.44 kg COD m-3 d-1 of OLR at the 7.8 h of HRT, shorter than the control reactor (54days). The two reactors obtained above 80% in COD removal efficiency. It is shown that UASB reactor can also achieve higher COD removal treating low strength wastewater at room temperature.

Comparison of anoxic granulation in USB reactors with various inocula

AbstractAnoxic granulation process with four different inocula was monitored in a laboratory post-denitrification up-flow sludge bed (USB) reactor. Wastewater containing 20 mg L−1 NO3-N and methanol as an organic carbon source was used. Gradual increase of mass volumetric loading (B v) and hydraulic loading (γ) resulted in spontaneous granulation of anoxic biomass both from flocculant activated sludge and from anaerobic granulated sludge. With flocculant activated sludge as the inoculum, anoxic granules sedimentation properties and maximum loadings of the USB reactor depended on the sludge volume index (SVI) of the inoculum. B v,max achieved in the USB reactor with flocculant inoculum from a municipal wastewater treatment plant (SVI = 208 mL g−1) was only 4.2 kg of COD per m3 per day and 0.7 kg of NO3-N per m3 per day. B v,max using flocculant inoculum from an industrial wastewater treatment plant (SVI = 170 mL g−1) was 8.1 kg of COD per m3 per day and 1.35 kg of NO3-N per m3 per day. With anaerobic granulated inoculum (SVI range 8–11 mL g−1), markedly higher loadings in the USB reactor and lower SVI values of anoxic granulated biomass were achieved. Values of B v,max were in the range of 16.1–22.4 kg of COD per m3 per day and of 2.7–3.7 kg of NO3-N per m3 per day (depending on the inoculum and the granulation procedure). It was proved that anaerobic granulated sludge is not just an inoculum, it is also a carrier for new denitrification biomass.

Denitrification in USB reactor with granulated biomass

Denitrification of low concentrations of NO 3–N (20 mg L −1), with methanol as an organic carbon source (COD:NO 3–N = 6) in laboratory upflow sludge bed reactor (USB), was tested as a possibility for wastewater post-treatment. By gradual increase of volumetric loading (Bv) and hydraulic loading ( γ), anoxic biomass spontaneously granulated out even from flocculate activated sludge and from anaerobic granulated sludge as well. Anaerobic granulated biomass derived from high-rate anaerobic IC reactor was a far better inoculum for anoxic granulation and for denitrification in the USB reactor. The maximum level of Bv and γ was remarkably higher with the use of anaerobic granulated inoculum, (19–22 kg COD m −3 d −1; 3.2–3.7 kg NO 3–N m −3 d −1; 2.8–3.2 m 3 m −2 h −1; SVI = 15 mL g −1) in comparison to inoculum from flocculate activated sludge (4.2–8.1 kg COD m −3 d −1; 0.7–1.4 kg NO 3–N m −3 d −1; 0.7–1.15 m 3 m −2 h −1; SVI = 40–95 mL g −1).

Cultivation of low-temperature (15°C), anaerobic, wastewater treatment granules

Anaerobic sludge granules underpin high-rate waste-to-energy bioreactors. Granulation is a microbiological phenomenon involving the self-immobilization of several trophic groups. Low-temperature anaerobic digestion of wastes is of intense interest because of the economic advantages of unheated bioenergy production technologies. However, low-temperature granulation of anaerobic sludge has not yet been demonstrated. The aims of this study were to (i) investigate the feasibility of anaerobic sludge granulation in cold (15 degrees C) bioreactors and (ii) observe the development of methanogenic activity and microbial community structure in developing cold granules. One mesophilic (R1; 37 degrees C) and two low-temperature (R2 and R3, 15 degrees C) laboratory-scale, expanded granular sludge bed bioreactors were seeded with crushed (diameter <0.4 mm) granules and were fed a glucose-based wastewater for 194 days. Bioreactor performance was assessed by chemical oxygen demand removal, biogas production, granule growth and temporal methanogenic activity. Granulation was observed in R2 and R3 (up to 33% of the sludge). Elevated hydrogenotrophic methanogenesis was observed in psychrophilically cultivated biomass, but acetoclastic methanogenic activity was also retained. Denaturing gradient gel electrophoresis of archaeal 16S rRNA gene fragments indicated that a distinct community was associated with developing and mature granules in the low-temperature (LT) bioreactors. Granulation was observed at 15 degrees C in anaerobic bioreactors and was associated with H(2)/CO(2)-mediated methanogenesis and distinct community structure development. Granulation underpins high-rate anaerobic waste treatment bioreactors. Most LT bioreactor trials have employed mesophilic seed sludge, and granulation <20 degrees C was not previously documented.

Influence of low pH (6, 5 and 4) on nutrient dynamics and characteristics of acidifying sulfate reducing granular sludge

The effect of a low pH (6, 5 and 4) on macro- and micronutrient dynamics in anaerobic sludge granules was investigated in batch leaching experiments and thermophilic (55 °C) Upflow Anaerobic Sludge Bed (UASB) reactors. The UASB reactors were fed with sucrose and sulfate at an organic loading rate of 3.5 g COD (l reactor d) −1 and a COD/SO 4 2− ratio of 9 or 3.5 over a period of 520 days at pH 6 and 270 days at pH 5 and 4. Decreasing the pH led to increased solubilisation of metals from the sludge in the leaching experiments within 48 h. For many metals (Co, Ni, Fe, Zn and Al), the difference between pH 6 and 5 was very small. For the three pH values investigated, the degree of leaching was the highest for the macronutrients K, Ca and Mg while for the other micronutrients leaching decreased in the following order: Mn > Ni ≈ Co ≈ Fe > Al ≈ Zn ≈ Cu. In the continuously operating UASB reactors, most metals leached from the sludge granules except for Co at pH 6, Al at pH 6 and 5 and Cu and Zn at all three pH values investigated. At the end of the UASB reactor runs, the sludge granules were almost deprived of Fe and Mn both at pH 5 and 4. Despite the significant changes in the inorganic composition of the sludge granules, the granular form of the sludge was kept at the different pH values and sulfate loading rates applied, and no significant washout occurred, though the granules’ strength decreased at pH 5 and 4. The colour of the granules changed gradually from black to grey during the operation at pH 6 and to a pale yellow during the operation at pH 5 and 4.

Research of Toxic Mechanism on Anaerobic Digestion by Lead

Abstract The paper analyzes the influence of lead toxicity by anaerobic granule sludge inhibition and recovering experiments. The result shows that there are different inhibition types at different lead contents. Higher lead content leads to more inhibition granular sludge, and at the same time, the time of gas recovery is different. Lower lead content per microorganism results in sooner sludge recovery. Microorganisms have a good ability to resist lead toxicity.

Temporal microbial diversity changes in solvent-degrading anaerobic granular sludge from low-temperature (15 °C) wastewater treatment bioreactors

Anaerobic sludge granules were obtained from laboratory-scale anaerobic bioreactors used to treat pharmaceutical-like (methanol-, acetone- and propanol-contaminated) wastewater under low-temperature conditions (15 °C). The microbial diversity and diversity changes of the sludge samples were ascertained by applying 16S rRNA gene cloning and terminal restriction fragment length polymorphism (TRFLP) analyses, respectively, and using sludge samples from the inoculum, throughout and at the conclusion of the bioreactor trial. Data from genetic fingerprinting correlated well with those from physiological activity assays of the reactor biomass. Specifically, for example, TRFLP profiles indicated the dominance of hydrogenotrophic methanogens within the archaeal community, thus supporting the findings of specific methanogenic activity measurements. TRFLP data supported the hypothesis that the deviation between the replicated reactors, in terms of treatment efficiency, was associated with succession within the microbial communities present, and indicated that community development was linked to both operating temperature and wastewater composition. Fluorescence in situ hybridization (FISH) was also applied, to quantitatively assess the abundance of selected microbial groups, and revealed the underestimation of the abundance Methanosarcina by gene cloning analysis and demonstrated the spatial arrangement of these organisms within the architecture of the low-temperature solvent-degrading anaerobic biofilms.

Biosorption and biodegradation of pentachlorophenol (PCP) in an upflow anaerobic sludge blanket (UASB) reactor

In order to understand the fate of PCP in upflow anaerobic sludge blanket reactor (UASB) more completely, the sorption and biodegradation of pentachlorophenol (PCP) by anaerobic sludge granules were investigated. The anaerobic granular sludge degrading PCP was formed in UASB reactor, which was seeded with anaerobic sludge acclimated by chlorophenols. At the hydraulic retention time (HRT) of 20-22 h, and PCP loading rate of 200-220 mg l(-1) d(-1), UASB reactor exhibited good performance in treating wastewater which containing 170-180 mg l(-1) PCP and the PCP removal rate of 99.5% was achieved. Sequential appearance of tetra-, tri-, di-, and mono-chlorophenol was observed in the reactor effluent after 20 mg l(-1) PCP introduction. Sorption and desorption of PCP on the anaerobic sludge granules were all fitted to the Freundlich isotherm equation. Sorption of PCP was partly irreversible. The Freundlich equation could describe the behavior of PCP amount sorbed by granular sludge in anaerobic reactor reasonably well. The results demonstrated that the main mechanism leading to removal of PCP on anaerobic granular sludge was biodegradation, not sorption or volatization.

Cultivation, granulation and characteristics of anaerobic ammonium-oxidizing sludge in sequencing batch reactor

Anaerobic sequencing batch reactor (SBR) was started-up by inoculating the nitrifying activated sludge. After an operation of 72 d, the bioreactor reached at steady state with ammonia and nitrite removal percentages higher than 95%. During operation, the sludge granulated in the reactor. The morphology and internal structure of sludge granules changed conspicuously, the density increased while the color changed from khaki to red. The average granular diameter grew from 1.2 to 3.69 mm, and its settling velocity accelerated from 107.68 to 118.49 m/h. Sludge granulation improved the tolerance to hydraulic shock loading, and reduced sludge washout (TSS &amp;lt; 0.028 g/L). The dominant bacterial communities (filamentous and cocci) in nitrifying activated sludge were replaced by irregular shaped ANAMMOX bacterial species gradually. An increase of ANAMMOX rate was achieved with the increasing granular diameter. SBR is a useful reactor to cultivate ANAMMOX granular sludge, while granular ANAMMOX sludge thus developed can be used as seeding sludge in a pilot-scale or full scale wastewater treatment plant.

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.

Feasibility studies on the treatment of dairy wastewaters with upflow anaerobic sludge blanket reactors

The feasibility of using upflow anaerobic sludge blanket (UASB) reactors for the treatment of dairy wastewaters was explored. Two types of UASBs were used––one operating on anaerobic sludge granules developed by us from digested cowdung slurry (DCDS) and the other on the granules obtained from the reactors of M/s EID Parry treating sugar industry wastewaters. The reactors were operated at HRT of 3 and 12 h and on COD loading rates ranging from 2.4 kg per m 3 of digester volume, per day to 13.5 kg m −3 d −1. At the 3 h HRT, the maximum COD reduction in the DCDS-seeded and the industrial sludge-seeded reactors was 95.6% and 96.3%, respectively, better than at 12 h HRT (90% and 92%, respectively). In both the reactors, the maximum, the second best, and the third best COD reduction occurred at the loading rates of 10.8, 8.6 and 7.2 kg m 3 d −1, respectively. At loading rates higher than 10.8 kg, the reactor performance dropped precipitously. Whereas in the first few months the reactors operating on sludge from EID Parry achieved better biodegradation of the waste, compared to the reactors operated on DCDS, the performance of the latter gradually improved and matched with the performance of the former.

Biohydrogen production using an up-flow anaerobic sludge blanket reactor

Sewage sludge was acclimated to establish H 2-producing enrichment cultures for converting sucrose (20 g COD/l ) into H 2 in an up-flow anaerobic sludge blanket (UASB) reactor. The operating hydraulic retention times (HRTs) were 24– 4 h . The experimental results indicated that this UASB system could be used for hydrogen production. The hydrogen productivity was HRT dependent and nearly constant at the HRT of 8– 20 h . However, it drastically decreased at an HRT of 4 or 24 h . The hydrogen production rate (HPR) and specific HPR peaked at the HRT of 8 h and drastically decreased at all other HRTs. At an HRT of 8 h , the average granular diameter peaked at 0.43 mm and each gram of biomass produced 53.5 mmol H 2/ day with a hydrogen gas content of 42.4% (v/v). Butyrate and acetate were the main fermentation volatile fatty acids. The anaerobic granule sludge kinetic constants were endogenous decay coefficient (K d ) 0.1 day −1 and yield coefficient (Y g ) 0.1 g VSS/g COD . The mean cell retention time was 22.2 h and the excess sludge discharge rate was 3.24 l/day .

Characterization of microbial community in granular sludge treating brewery wastewater

The diversity and distribution of microbes within brewery-degrading anaerobic sludge granules were studied using various molecular techniques. Molecular cloning of small-subunit rRNA gene sequences indicated that all archaeal clones were affiliated with Methanosaeta concillii (>99% sequence similarity), and the bacterial clones were mostly affiliated with a not-yet-cultured Clostridium cluster (48 out of 99 clones) in the low G+C gram-positive group, Xanthomonas spp. in the γ-subclass of Proteobacteria (30 clones), and Desulfovibrio spp. (16 clones) in the δ-subclass of Proteobacteria. Slot-blot hybridization indicated that archaeal cells from the Methanomicrobiales (58.4% of total rRNA), Methanobacterials (3.3%) and Methanococcales (1.0%) accounted for 62.4% of the total community rRNA. The rest of the microbial populations were the clostridial cluster (27.3% of total rRNA) and Desulfovibrio spp. (9.4%). Fluorescence in-situ hybridization with domain and group-specific oligonucleotide probes further revealed a multi-layer granular architecture. On the surface layer, the hydrolytic clostridial species and hydrogenotrophic Methanobacteriales were the predominant. In the middle layer, mostly H 2-producing acetogens from the δ- Proteobacteria (i.e., Desulfovibrio spp.), hydrogenotrophic Methanobacteriales and aceticlastic Methanosaeta were observed to presumably form a syntrophic association. Finally, the center core consisted of microcolonies of Methanosaeta cells.

New and Broader Applications of Anaerobic Digestion

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

Influence of organic volumetric loading rate, nutrient balance and alkalinity: COD ratio on the anaerobic sludge granulation of an UASB reactor treating sugar cane molasses

Using sugar cane molasses (a byproduct of the sugar industry) as substrate an experimental work was carried out with the aim to obtain a granulated anaerobic sludge at controlled conditions of alkalinity and micronutrients. The experiment was carried out in a laboratory-scale-upflow anaerobic sludge blanket (UASB) reactor of 16.51 capacity. The substrate concentration was adjusted at a COD value of 3750 mgl −1 by addition of tap water. The ratios of Alkalinity:COD, N:COD and P:COD were maintained at 1.06, 0.018 and 0.0028 respectively. Under such conditions the production of spherical granules was observed after thirty days of operation. The average diameter of the granules grew progressively with the increase of the organic volumetric loading (Bv) achieving a maximum average value of 3.1 mm at the 90th day of operation and remained constant furtherly in spite of the increase of Bv. It was found that after the granules formation the addition of nutrients could be suspended while the Alkalinity: COD ratio could be reduced to 0.4 without changes on the process performance.

Surface charge and extracellular polymer of sludge in the anaerobic degradation process

Changes of surface charge and extracellular polymer (ECP) content were investigated in batch experiments for three anaerobic sludges, each of which had been enriched at 35°C and pH 639-7.3 for more than 40 batches using propionate, butyrate and glucose, individually, as the sole substrate. Results showed that both ECP and the negative surface charge were dependent on the growth phase of microorganisms. They increased at the beginning of all batches when the microorganisms were in the prolific-growth phase, having high substrate concentration and food-to-microorganisms ratio. Both later gradually returned to their initial levels when the microorganisms were in the declined-growth phase, as the substrate became depleted. The negative surface charge increased linearly with the total-ECP content in all series with slopes of 0.0187, 0.0212 and 0.0157 meq/mg-total-ECP for sludge degrading propionate, butyrate and glucose, respectively. The change of surface charge for the first two sludges was mainly due to the increase of proteinaceous fraction of ECP; but, for glucose-degrading sludge, that could be due to the increases of both proteinaceous and carbohydrate fractions of ECP. The negative-charged nature of anaerobic sludge implies that cations should be able to promote granulation of anaerobic sludge.

Yields of Biomass and Extracellular Polymers in Four Anaerobic Sludges

Extracellular polymers (ECP) are responsible for the flocculation of activated sludge as well as the granulation of anaerobic sludge. In this study, the biomass and ECP yields of four anaerobic sludge were examined. The sludges were enriched by using acetate, propionate, butyrate and glucose, respectively, as the sole substrate. Throughout the enrichment process, which lasted up to 73 cycles, the sludge samples were analyzed for their volatile suspended solids (VSS) as well as ECP's protein (ECPp) and carbohydrate (ECPc) contents. Under steady-state condition, the net yields of biomass, ECPp and ECPc were measured for the conversion of each individual substrate to methane and carbon dioxide. Furthermore, the corresponding yields for the acetogenesis of propionate and butyrate, and the acidogenesis of glucose, were also estimated, based on the stoichiometry of the degradation reactions. Results show that acidogenesis of glucose produced more ECPp and ECPc than acetogenesis and methanogenesis. This explains the reported observations that carbohydrate-degrading sludge produced better granules than the acid-degrading sludge.