Development Of Granular Sludge Research Articles

Aerobic granular sludge development using diatomite for low-strength wastewater treatment

This paper presents an assessment of the start-up performance of aerobic granular sludge (AGS) for the treatment of low-strength (chemical oxygen demand, COD < 200mg/L) domestic wastewater by the application of a diatomite carrier. The feasibility was evaluated in terms of the start-up period and stability of the aerobic granules as well as COD and phosphate removal efficiencies. A single pilot-scale sequencing batch reactor (SBR) was used and operated separately for the control granulation and granulation with diatomite. Complete granulation (granulation rate ≥ 90%) was achieved within 20days for the case of diatomite with an average influent COD concentration of 184mg/L. In comparison, control granulation required 85days to accomplish the same feat with a higher average influent COD concentration (253mg/L). The presence of diatomite solidifies the core of the granules and enhances physical stability. AGS with diatomite recorded the strength and sludge volume index of 18 IC and 53mL/g suspended solids (SS) which is superior to control AGS without diatomite (19.3 IC, 81mL/g SS). Quick start-up and achievement of stable granules lead to an efficient COD (89%) and phosphate removal (74%) in 50days of bioreactor operation. Interestingly, this study revealed that diatomite has some special mechanism in enhancing the removal of both COD and phosphate. Also, diatomite has a significant influence on microbial diversity. The result of this research implies that the advanced development of granular sludge by using diatomite can provide promising low-strength wastewater treatment.

Forming aerobic granulation in SBR technology at the laboratory

Transplanting and application of aerobic granulation in SBR technology have been developed since 1970. In recent years, this technology has been extensively researched with different substances such as glucose, acetate, ethanol, molasses, sugar, starch, phenol, phthalic acid, chloroanilines, tert-butyl alcohol, and synthetic wastewater. This article describes the process of formation and development of aerobic granulation with acetate at the laboratory in Vietnam. Activated sludge for the study was obtained from Yen So (Hanoi) wastewater treatment plant with MLSS 900-1200 mg/l. The research was carried out on two reactors of the same SBR technology with 0.110 m in diameter and 1 m in height, water level height 0.8 m, working volume of 2.5 l with respective names of A and B. The reactors were sequentially operated 6 cycles/day, each cycle was divided into 4 periods, lasting 4 hours: 1-2 mins of influent filling, 180 mins of aeration, 20-30 mins of settling, and 10-15 mins of effluent. The input wastewater for model A was wastewater with low strength has OLR from 1.0-1.2 kg COD/m3.day. The input wastewater for model B was wastewater with high strength has OLR from 2.7-3.0 kg COD/m3.day, time for research was 120 days. The result showed that the formation and development of granular sludge in model A were very difficult. Meanwhile, granular sludge was formed and developed after 30-45 days of experimentation in model B

Isolation and characterization of a strain with high microbial attachment in aerobic granular sludge

Aerobic granule is a special microbial aggregate associated with biofilm structure. The formation of aerobic granular sludge is primarily depending on its bacterial community and relevant microbiological properties. In this experiment, a strain with high microbial attachment was isolated from aerobic granular sludge, and the detailed characteristics were examined. Its high attachment ability could reach 2.34 (OD600nm), while other low attachment values were only around 0.06-0.32, which indicated a big variation among the different bacteria. The strain exhibited a very special morphology with many fibric fingers under SEM observation. A distinctive behaviour was to form a spherical particle by themselves, which would be very beneficial for the formation and development of granular sludge. The EPS measurement showed that its PN content was higher than low attachment bacteria, and 3D-EEM confirmed that there were some different components. Based on the 16S rRNA analysis, it was identified to mostly belong to Stenotrophomonas. Its augmentation to particle sludge cultivation demonstrated that the strain could significantly promote the formation of aerobic granule. Conclusively, it was strongly suggested that it might be used as a good and potential model strain or chassis organism for the aerobic granular sludge formation and development.

Effect of steel slag in recycling waste activated sludge to produce anaerobic granular sludge

The amount of waste activated sludge (WAS) has grown dramatically in China. WAS is considered as a problematic and hazardous waste, which should be disposed in a safe and sustainable manner. In order to recycle WAS to an anaerobic granular sludge (AnGS) process for anaerobic digestion, Fe powder and steel slags (rusty and clean slags) were used to enhance the granulation process. The results demonstrated that both rusty and clean slags encouraged the development of granular sludge. Adding 10 g/L clean slags could increase AnGS granulation rate by 37%. In the presence of clean slags, extracellular polymeric substances (EPS) concentration in granules increased noticeably to 715 mg/g mixed liquor suspended solids (MLSS). High throughput sequencing analysis exhibited more diversity and higher abundance of functional microbial communities in the batch bottle with 10 g/L clean slags. This study suggested that adding clean slags at 10 g/L dosage was a sustainable and effective method for the sludge granulation.

Strategies of anaerobic sludge granulation in an EGSB reactor

Anaerobic sludge granulation was evaluated in an expanded granular sludge bed (EGSB) reactor based on the increases in the specific organic loading rate (SOLR). The effect of precursor substances (calcium chloride, sodium chloride, and tannin) on the development of granular sludge was also investigated in batch reactors. The reactors were fed with synthetic sewage and operated in mesophilic conditions. The EGSB was operated with a variable hydraulic retention time (HRT) and the batch reactors, with cycles of 8 h and 16 h. The increase of SOLR from 17.4 ± 7.4 to 104.6 ± 66.7 mgCOD gVSS-1 d-1 in the EGSB resulted in an increase on the average granules diameter from 344.3 to 1583.3 μm. These conditions also favored the reduction rates of chemical oxygen demand (COD) and volatile fatty acids (VFAs) concentration in the reactor. When the upflow velocity suffered an abrupt increase (from 0.06 L h-1 to 0.25 L h-1), the granules size began to decrease and lose their settleability characteristics. Considering this, it is proposed to start the biomass granulation process without effluent recirculation, and, after the granules reach the desired size and settleability capacity, the normal operation of EGSB reactor starts. The results showed that calcium chloride was more efficient for granulation. CaCl2 addition can be performed only during the reactor's start-up, improving granulation and reducing start-up time. Thus, these results have practical implications as granules maintenance is the key to the proper EGSB operation.

Effect of Static Magnetic Field on the Efficiency of Granular Sludge Development for Pharmaceutical Wastewater Treatment

The effect of static magnetic field (SMF) on the development of granular sludge was evaluated in sequential batch reactor (SBR) system under alternating aerobic and anaerobic condition fed with pharmaceutical wastewater which is categorized as a high strength wastewater. The magnetic field intensity used in this research was 20 mT and compared with the control system without magnetic field exposure. The results showed that sludge granulation was enhanced significantly in the presence of magnetic field which made the reaction time for granulation process faster compared with that of the control. Matured, dense and compact granules with diameter of 6.5 ± 1.0 mm with maximum size reaching up to 8.9 mm were developed with good settling velocity of 76.92 m/h. Magnetic field could stimulated EPS production by accumulating iron, calcium and magnesium compounds in the sludge. The contents of total EPS in R2 (with SMF) were 28.5 mg/gVSS, while in R1 (without SMF) were 21.7 mg/gVSS. The magnetic field system was efficiently treated COD, TP, orthophosphate, TN, nitrate and nitrite with over 90% removal from pharmaceutical wastewater. The application of magnetic field is then helpful and reliable for accelerating the granulation process and is capable in treating the pharmaceutical wastewater

Bioaccumulation of metals and granular sludge development in a newly-inoculated high rate anaerobic reactor

For treatment of wastewater from soft drink production, a full scale (546 m3) expanded granular sludge bed (EGSB) reactor was inoculated with granular sludge previously used to treat wastewater from paper and food processing industries. During startup and subsequent phases, there were significant changes observed in granule composition, performance, and population distribution. Microbial, compositional and functional development of granular sludge during a six month time period immediately following inoculation was investigated. Reaction kinetics and fluorescence in situ hybridization (FISH) analysis were used to describe population dynamics and evolution of methanogens and fermentative microbes within the granules. Bioaccumulation of elements was quantified and analyzed statistically with respect to operational parameters; calcium and sulfate deficiencies in the new wastewater likely contributed to granule disintegration and eventual reactor failure. Second generation granules formed from the novel conditions exhibited characteristics from multiple granulation models.

Granulation and microbial community dynamics in the chitosan-supplemented anaerobic treatment of wastewater polluted with organic solvents

The effect of chitosan on the development of granular sludge in upflow anaerobic sludge blanket reactors (UASB) when treating wastewater polluted with the organic solvents ethanol, ethyl acetate, and 1-ethoxy-2-propanol was evaluated. Three UASB reactors were operated for 219 days at ambient temperature with an organic loading rate (OLR) of between 0.3 kg COD m−3 d−1 and 20 kg COD m−3 d−1. One reactor was operated without the addition of chitosan, while the other two were operated with the addition of chitosan doses of 2.4 mg gVSS−1 two times. The three reactors were all able to treat the OLR tested with COD removal efficiencies greater than 90%. However, the time required to reach stable operation was considerably reduced in the chitosan-assisted reactors. The development of granules in the reactors with chitosan was accelerated and granules larger than 2000 μm were only observed in these reactors. In addition, these granules exhibited better physicochemical characteristics: the mean particle diameter (540 and 613 μm) was approximately two times greater than in the control reactor (300 μm), and the settling velocities exceeded 35 m h−1. The extracellular polymeric substances (EPS) in the reactors with the chitosan was found to be higher than in the control reactor. The protein-EPS content has been correlated with the granule size. The analyses of the microbial communities, performed through denaturing gradient gel electrophoresis and high-throughput sequencing, revealed that the syntrophic microorganisms belonging to genus Geobacter and the hydrogenotrophic methanogen Methanocorpusculum labreanum were predominant in the granules. Other methanogens like Methanosaeta species were found earlier in the chitosan-assisted reactors than in the control reactor.

Comparison of an anaerobic feed and split anaerobic–aerobic feed on granular sludge development, performance and ecology

The retrofitting of existing wastewater sequencing batch reactors (SBRs) to select for rapid-settling aerobic granular sludge (AGS) over floc-based conventional activated sludge (CAS), could be a viable option to decrease reactor cycle time and increase hydraulic capacity. Successful CAS-to-AGS conversion has previously been shown to be highly dependent on having a dedicated anaerobic feed, which presents additional engineering challenges when retrofitting SBRs. In this study we compared the performance of a split anaerobic–aerobic (An–Aer) feed with that of a traditional dedicated anaerobic feed regarding AGS formation and stability, nitrogen removal performance and microbial ecology. Using pilot trials, we showed that AGS could be established and maintained when using a split An–Aer feed at low organic loading rates analogous to that of a parallel full-scale conventional SBR. Additionally, we showed that AGS start-up time and nitrogen removal performance were comparable under a split An–Aer feed and dedicated anaerobic feed. Microbial ecology characterisations based on whole-of-community 16S rRNA profiles and targeted analysis of functional genes specific for nitrifying and denitrifying microorganisms, showed that the two different feed strategies had only subtle impacts on both the overall community composition and functional ecology. A much greater divergence in microbial ecology was seen when comparing AGS with CAS. Data presented here will be of value to those planning to retrofit existing CAS-based SBRs to operate with AGS and demonstrates the viability of using a more cost-effective split An–Aer feed configuration over a dedicated anaerobic feed.

Enhancement of sludge granulation in hydrolytic acidogenesis by denitrification.

Acidogenesis is an important pretreatment process for various industrial wastewater treatments. Granular sludge is an efficient form of a microbial community in anaerobic methanogenic reactors, such as upflow anaerobic sludge blanket (UASB), but it is hard to develop in the acidogenic process due to the short hydraulic retention times (HRTs) of acidogenesis. In this study, nitrate was added into an acidogenic reactor as an electron acceptor to enhance electron exchange between acidogenic and denitrifying bacteria to accelerate sludge growth in the acidogenesis process. The results showed that it developed solid and mature granular sludge with a mean size of 410 ± 35 μm over 84 days of operation. Comparatively, the sludge in a no-nitrate acidogenic reactor showed a flocculent appearance with a mean size of 110 ± 18 μm. Analysis of the microbial community indicated that denitrifying bacteria interwoven with propionate-oxidizing bacteria were distributed in the outer granule layer, which provided an ideal shield for susceptible microorganisms inside the granules. This microbial structure was favorable for the development of granular sludge and made the system possible to respond well to shocks in the operation.

Characteristics of methanogenic granules grown on glucose in an upflow anaerobic sludge blanket reactor

The development of granular sludge is the key factor for successful operation of the upflow anaerobic sludge blanket (UASB) reactors. This paper deals with the changes in physico-chemical and microbial characteristics while transforming anaerobically digested sludge to granular sludge grown on glucose in an UASB reactor. The bench scale reactor was operated at 35 ± 2 °C for a period of 120 days at an organic loading rates (OLR) varying from 1.5 to 15 kg [COD] m−3 d−1. Results demonstrated that a good quality, well settling granular sludge was cultivated and retained in the reactor. The specific methanogenic activity (SMA) of sludge granules increased linearly with the increasing age of the sludge as well as OLR. X-ray diffraction (XRD), Energy dispersive X-ray analysis (EDXA) and Inductive coupled plasma mass spectrometer (ICP-MS) analysis showed that considerable constitutional change occurred during the operation period. The results indicated that silicon and aluminium may have played a crucial role in the formation of the aggregates of sludge. Na, Mg, K and Ca were the major constituents in the sludge and the changes in concentration may be ascribed to the formation of compounds with minor concentrations of P, Co and Fe, which is thought to be responsible for the formation of stable granules. Fourier transform infra-red spectroscopy (FTIR) spectral analysis confirmed accumulation of volatile fatty acids, mineral matter and other aliphatic components in the granular sludge. Scanning electron microscope microphotographs demonstrated that granulation can be accomplished successfully by gradually increasing the OLR.

Partial nitritation of landfill leachate with varying influent composition under intermittent aeration conditions

The start-up and operation of a partial nitritation sequencing batch reactor for the treatment of landfill leachate were carried out on intermittent aeration mode. Partial nitrite accumulation was established in 15 days after the mode was changed from continuous aeration to intermittent aeration. Despite the varying influent composition, partial nitritation could be maintained by adjusting the hydraulic retention time (HRT) and the air flow rate. An increase in the air flow rate together with a decrease in air off duration can improve the partial nitritation capacity and eventually result in the development of granular sludge with fine diameters. A nitrogen loading rate of 0.71±0.14kg/m3/d and a COD removal rate of 2.21±0.13kg/m3/d were achieved under the conditions of an air flow rate of 19.36±1.71m3 air/m3/h and an air on/off duration of 1.5min/0.7 min. When the ratio of total air flux (TAF) to the influent loading rate (ILR) was controlled at the range of 163–256m3air/kgCOD, a stable effluent NO3−–N/NOx−–N (NO2−–N plus NO3−–N) ratio below 13% was achieved. Interestingly, the effluent pH was found to be a good indicator of the effluent NO2−–N/NH4+–N ratio, which is an essential parameter for a subsequent anaerobic ammonium oxidation (Anammox) reactor.

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 A rchaea. Higher SMA and SAA values against H 2/CO 2 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.

Development of granular sludge for textile wastewater treatment

Microbial granular sludge that is capable to treat textile wastewater in a single reactor under intermittent anaerobic and aerobic conditions was developed in this study. The granules were cultivated using mixed sewage and textile mill sludge in combination with anaerobic granules collected from an anaerobic sludge blanket reactor as seed. The granules were developed in a single sequential batch reactor (SBR) system under alternating anaerobic and aerobic condition fed with synthetic textile wastewater. The characteristics of the microbial granular sludge were monitored throughout the study period. During this period, the average size of the granules increased from 0.02 ± 0.01 mm to 2.3 ± 1.0 mm and the average settling velocity increased from 9.9 ± 0.7 m h −1 to 80 ± 8 m h −1. This resulted in an increased biomass concentration (from 2.9 ± 0.8 g L −1 to 7.3 ± 0.9 g L −1) and mean cell residence time (from 1.4 days to 8.3 days). The strength of the granules, expressed as the integrity coefficient also improved. The sequential batch reactor system demonstrated good removal of COD and ammonia of 94% and 95%, respectively, at the end of the study. However, only 62% of color removal was observed. The findings of this study show that granular sludge could be developed in a single reactor with an intermittent anaerobic–aerobic reaction phase and is capable in treating the textile wastewater.

Anaerobic co-digestion of surplus yeast and wastewater to increase energy recovery in breweries

Surplus yeast is a residue produced during brewery process, which presents high contents of organic matter. Biogas production from yeast could significantly contribute to bioenergy production in breweries, via biogas generation. Co-digestion of surplus yeast and brewery wastewater in a single treatment step would simplify the technical and economical requirements for the transformation of both residues into biogas. The feasibility of such co-digestion process was studied by means of batch tests and a lab-scale UASB reactor operation. The effect of applying three pre-treatments (thermal, chemical and mechanical) to the surplus yeast was also studied. Results showed that co-digestion of yeast and brewery wastewater is feasible, since no negative effects of the joint digestion were observed. Pre-treatments tested in this research produced no significant improvements on biogas yield or digestion rates. Even though no negative effects were observed when digesting wastewater and yeast in a UASB reactor after 70 days, long-term studies would be needed in order to detect potential negative effects over granular sludge development, sometimes observed during the treatment of some wastewaters containing suspended solids.

Possible role of denitrification on aerobic granular sludge formation in sequencing batch reactor

The aim of this work was to evaluate and quantify the influence of denitrification of nitrate on the aerobic granular sludge development. Two parallel sequencing batch reactors (SBRs) were fed with synthetic wastewater, the first reactor (R1) receiving nitrate at a fixed concentration whereas the second reactor (R2) did not receive any external source of nitrate. Both systems were working at the same operational conditions with a low specific air velocity (0.07 cm s −1), a relatively low and acceptable oxygen concentration (1.8 ± 0.8 mg L −1) and without significant biomass selection pressure (minimal velocity 0.4 m h −1). The results showed that the sludge settling properties of R1 were comparable to granular sludge (settling velocity ≈ 10.6 m h −1, SVI 5 ≈ 13–30 mL g −1, SVI 30 ≈ 11–28 mL g −1 and SVI 5/SVI 30 ratio ≈ 1.05–1.1). In the opposition, biomass of the reactor R2 reveals more traditional properties. Nitrogen measurements revealed that a significant denitrification (up to 80% of fed nitrate) occurred in R1 in the core of aggregates, as aerobic condition was maintained in the bulk. After the mean particle size was reduced from 250 to 125 μm by an increase of mechanical stirring rate, it was shown that denitrification decreased from 80% to 20%. These parallel experiments definitively proved that the presence of nitrate in SBRs can assist the densification of the biological aggregates in aerobic condition. The presence of nitrate (commonly provided by nitrification) should be considered as a possible factor which helps to maintain the granulation process.

Influence of external circulation on sludge characteristics during start-up of internal circulation reactor

The start-up of external circulation — added internal circulation (IC) reactor was finished in 26 d, 32 d fewer than that of IC reactor. To evaluate the influence of the added external circulation on the development of granular sludge, the characteristics of the granular sludge taken from the two tested laboratory-scale reactors during start-up were studied. The results show that the added external circulation can enhance biomass granulation, accelerate granule development and improve sludge characteristics. At the end of start-up, the granular size of sludge in external circulation-added IC reactor greatly increases with a size distribution much better than that of sludge in IC reactor. The granular sludge originated from external circulation — added IC reactor contains more extracellular polymers and has a greater settling velocity than that from IC reactor. Methanogenic activity of the granular sludge from the external circulation — added IC reactor started 26 d ago reaches 358.23 mL · g−1 · d−1, 1.66 and 1.20 times as great as that of the sludge from the IC reactor started 26 d and 58 d ago respectively.

Granular sludge formation in upflow anaerobic sludge blanket (UASB) reactors

The state of the art for upflow anaerobic sludge blanket (UASB) reactors is discussed, focusing on the microbiology of immobilized anaerobic bacteria and the mechanism of granule formation. The development of granular sludge is the key factor for successful operation of the UASB reactors. Criteria for determining if granular sludge has developed in a UASB reactor is given based on the densities and diameters of the granular sludge. The shape and composition of granular sludge can vary significantly. Granules typically have a spherical form with a diameter from 0.14 to 5 mm. The inorganic mineral content varies from 10 to 90% of the dry weight of the granules, depending on the wastewater composition etc. The main components of the ash are calcium, potassium, and iron. The extracellular polymers in the granular sludge are important for the structure and maintenance of granules, while the inorganic composition seems to be of less importance. The extracellular polymer content varies between 0.6 and 20% of the volatile suspended solids and consists mainly of protein and polysaccharides. Both Methanosaeta spp. (formerly Methanothrix) and Methanosarcina spp. have been identified as important aceticlastic methanogens for the initial granulation and development of granular sludge. Immunological methods have been used to identify other methanogens in the granules. The results have showed that, besides the aceticlastic methanogens Methanosaeta spp. and Methanosarcina spp., hydrogen and formate utilizing bacteria are also present, e.g., Methanobacterium formicicum, Methanobacterium thermoautotrophicum, and Methanobrevibacter spp. Microcolonies of syntrophic bacteria are often observed in the granules, and the significant electron transfer in these microcolonies occurs through interspecies hydrogen transfer. The internal organization of the various groups of bacteria in the granules depends on the wastewater composition and the dominating metabolic pathways in the granules. Internal organization is observed in granules where such an arrangement is beneficial for an optimal degradation of the wastewater. A four-step model is given for the initial development of granular sludge. (c) 1996 John Wiley & Sons, Inc.

Advanced start up of UASB reactors by adding of water absorbing polymer

We have developed a new approach to enhance granulation by adding water absorbing polymer (WAP) particles into the inoculated digested sludge. In this study, the effect of adding WAP on formation of anaerobic granular sludge was evaluated in lab-scale UASB reactors using two typical synthetic wastewater, i.e. glucose or volatile fatty acid (VFA) mixture solution. In addition, side by side with the lab-scale experiment, a pilot-scale experiment using the VFA mixture was carried out to evaluate the availability of accelerated start-up by adding WAP. The development of granular sludge was significantly enhanced by adding WAP. Granules developed on glucose and VFAs had high methanogenic activities and good settleability. From results of lab-scale experiment, the recommended dosage of WAP was about 750 mg/l of reactor volume. The results, pilot-scale experiment, indicated the availability of accelerated start-up by adding WAP.

Advanced start up of UASB reactors by adding of water absorbing polymer

We have developed a new approach to enhance granulation by adding water absorbing polymer (WAP) particles into the inoculated digested sludge. In this study, the effect of adding WAP on formation of anaerobic granular sludge was evaluated in lab-scale UASB reactors using two typical synthetic wastewater, i.e. glucose or volatile fatty acid (VFA) mixture solution. In addition, side by side with the lab-scale experiment, a pilot-scale experiment using the VFA mixture was carried out to evaluate the availability of accelerated start-up by adding WAP. The development of granular sludge was significantly enhanced by adding WAP. Granules developed on glucose and VFAs had high methanogenic activities and good settleability. From results of lab-scale experiment, the recommended dosage of WAP was about 750 mg/l of reactor volume. The results, pilot-scale experiment, indicated the availability of accelerated start-up by adding WAP.