Anaerobic Sludge Granulation Research Articles

Effect of pH on 17 beta-estradiol adsorption by anaerobic granule sludge combined with iron

Effect of pH on 17 beta-estradiol adsorption by anaerobic granule sludge combined with iron

Fast anaerobic sludge granulation at elevated salinity

It is commonly accepted that high salt concentrations negatively affect microbial activity in biological wastewater treatment reactors such as upflow anaerobic sludge blanket (UASB) reactors. Microbial aggregation in such reactors is equally important. It is well documented that anaerobic granules, when exposed to high salinity become weak and disintegrate, causing wash-out, operational problems and decreasing process performance. In this research, the possibility of microbial granule formation from dispersed biomass was investigated at salinity levels of 5 and 20 g Na+/L. High removal efficiencies of soluble influent organics were achieved at both salinity levels and this was accompanied by fast and robust formation of microbial granules. The process was found to be stable for the entire operational period of 217 days. As far as we know this is the first time it has been demonstrated that stable granule formation is possible at a salinity level as high as 20 g Na+/L. Methanosaeta was identified as the dominant methanogen at both salinity levels. Streptococcus spp. and bacteria belonging to the family Lachnospiraceae were identified as the dominant microbial population at 5 and 20 and g Na+/L, respectively.

Bacterial and archaeal community distribution and stabilization of anaerobic sludge in a strengthen circulation anaerobic (SCA) reactor for municipal wastewater treatment

In this study, a SCA reactor was employed for municipal wastewater treatment at a mesophilic temperature (30°C) under different hydraulic retention times (HRT) and upflow velocities (Vup) to investigate granule sludge stability and spatial microbial distribution. The stable COD removal efficiency readied at HRT of 15, 12, 9 and 6h, and Vup ranging from 0.6 to 5.9mh−1. EPS fraction analysis of granule sludge shows that municipal wastewater was mainly attributed to the enrichment influence of polysaccharide and tightly bound-EPS. SEM images exhibited that the stability and floating of anaerobic granular sludge may be promoted in the primary three-phase separator area because the channels of the granules was clogged by EPS. The SMA and high-throughput sequencing analysis indicated acetoclastic methanogens and hydrogenotrophic methanogens played an important role in formation and maintenance of the anaerobic granule sludge in low and high organic load rate operation conditions.

Insights into sludge granulation during anaerobic treatment of high-strength leachate via a full-scale IC reactor with external circulation system

In this study, a full-scale internal circulation (IC) reactor coupled with an external circulation system was developed to treat high-strength leachate from a municipal solid waste (MSW) incineration plant, in which anaerobic sludge granulation was intensively investigated. Results showed that the IC reactor achieved excellent treatment performance under high organic loading rates (OLR) of 21.06–25.16kg chemical oxygen demand (COD)/(m3∙day). The COD removal efficiency and biogas yield respectively reached 89.4%–93.4% and 0.42–0.50m3/kgCOD. The formation of extracellular polymeric substances (EPS) was closely associated with sludge granulation. Protein was the dominant component in sludge EPS, and its content was remarkably increased from 21.6 to 99.7mg/g Volatile Suspended Solid (VSS) during the reactor operation. The sludge Zeta potential and hydrophobicity positively correlated with the protein/polysaccharide ratio in EPS, and they were respectively increased from −26.2mV and 30.35% to −10.6mV and 78.67%, which was beneficial to microbial aggregation. Three-dimensional fluorescence spectroscopy (3D-EEM) and Fourier transform infrared spectroscopy (FT-IR) analysis further indicated the importance of protein-like EPS substances in the sludge granulation. Moreover, it was also found that the secondary structures of EPS proteins varied during the reactor operation.

The impact of pretreatment and inoculum to substrate ratio on methane potential of organic wastes from various origins

Biochemical methane potentials (BMP) of two different substrates from macroalgae (MA) and market place wastes (MPW) were investigated using anaerobic granulated sludge from food industry with different ratios of substrate to inoculum (S/X). The substrates were used as MA only, MPW only, MA–MPW mixture, pretreated MA, and pretreated MA–MPW mixture. Research involved investigation of the effects of parameters such as temperature (35, 45, and 55 °C), substrate to inoculum ratio (S/X = 0.5, 2.0, 4.0, and 6.0 as g VSsubstrate/g VSinoculum), and the type of pretreatment (by microwave, thermal, and ultrasonic) on BMP. BMP assays were performed for all substrates. The highest cumulative biogas production (and BMP) were obtained for MA only at an S/X ratio of 4.0 g VS/g VS as 357 Lbiogas/kg VS (197 L CH4/kg VS) and 33 Lbiogas/kg VS (17 L CH4/kg VS), respectively, at 35 and 55 °C. For pretreated substrates, the highest cumulative biogas production and BMP were observed as 287 Lbiogas/kg VS and 146 L CH4/kg VS using pretreated macroalgae at 35 °C. Results suggested that MA only and MA–MPW mixtures are suitable substrates for biogas production. It is also concluded that any type of pretreatment has adverse effects on biogas and methane productions.

Influence, equilibrium, thermodynamic and kinetic investigations on adsorption of 17beta-estradiol by anaerobic granule sludge

Influence, equilibrium, thermodynamic and kinetic investigations on adsorption of 17beta-estradiol by anaerobic granule sludge

Influence of fluid dynamics on anaerobic digestion of food waste for biogas production

ABSTRACTTo enhance the stability and efficiency of an anaerobic process, the influences of fluid dynamics on the performance of anaerobic digestion and sludge granulation were investigated using computational fluid dynamics (CFD). Four different propeller speeds (20, 60, 100, 140 r/min) were adopted for anaerobic digestion of food waste in a 30 L continuously stirred tank reactor (CSTR). Experimental results indicated that the methane yield increased with increasing the propeller speed within the experimental range. Results from CFD simulation and sludge granulation showed that the optimum propeller speed for anaerobic digestion was 100 r/min. Lower propeller speed (20 r/min) inhibited mass transfer and resulted in the failure of anaerobic digestion, while higher propeller speed (140 r/min) would lead to higher energy loss and system instability. Under this condition, anaerobic digestion could work effectively with higher efficiency of mass transfer which facilitated sludge granulation and biogas production. The corresponding mean liquid velocity and shear strain rate were 0.082 m/s and 10.48 s−1, respectively. Moreover, compact granular sludge could be formed, with lower energy consumption. CFD was successfully used to study the influence of fluid dynamics on the anaerobic digestion process. The key parameters of the optimum mixing condition for anaerobic digestion of food waste in a 30 L CSTR including liquid velocity and shear strain rate were obtained using CFD, which were of paramount significance for the scale-up of the bioreactor. This study provided a new way for the optimization and scale-up of the anaerobic digestion process in CSTR based on the fluid dynamics analysis.

Reductive Transformation of p-chloronitrobenzene in the upflow anaerobic sludge blanket reactor coupled with microbial electrolysis cell: performance and microbial community

A microbial electrolysis cell (MEC) combined with an upflow anaerobic sludge blanket (UASB) reactor was operated to degrade p-chloronitrobenzenes (p-ClNB) effectively. The results indicated that p-ClNB was transformed to p-chloroaniline (p-ClAn) and then reduced via dechlorination pathways. In the MEC-UASB coupled system, p-ClNB, p-ClAn removal efficiency and dechlorination efficiency reached 99.63±0.37%, 40.39±9.26% and 32.16±8.12%, respectively, which was significantly improved in comparison with the control UASB system. In addition, the coupled system could maintain appropriate pH and promote anaerobic sludge granulation to exert a positive effect on reductive transformation of p-ClNB. PCR-DGGE experiment and 454 pyrophosphate sequencing analysis indicated that applied voltage would significantly influence the succession of microbial community and promote oriented enrichment of the functional bacteria, which could be the underlying reasons for the improved performance. This study demonstrated that MEC-UASB coupled system had a promising application prospect to remove the recalcitrant pollutants effectively.

Biological Pretreatment of Chicken Feather and Biogas Production from Total Broth.

Chicken feathers are available in large quantities around the world causing environmental challenges. The feathers are composed of keratin that is a recalcitrant protein and is hard to degrade. In this work, chicken feathers were aerobically pretreated for 2-8days at total solid concentrations of 5, 10, and 20% by Bacillus sp. C4, a bacterium that produces both α- and β-keratinases. Then, the liquid fraction (feather hydrolysate) as well as the total broth (liquid and solid fraction of pretreated feathers) was used as substrates for biogas production using anaerobic sludge or bacteria granules as inoculum. The biological pretreatment of feather waste was productive; about 75% of feather was converted to soluble crude protein after 8days of degradation at initial feather concentration of 5%. Bacteria granules performed better during anaerobic digestion of untreated feathers, resulting in approximately two times more methane yield (i.e., 199mlCH4/gVS compared to 105mlCH4/gVS when sludge was used). Pretreatment improved methane yield by 292 and 105% when sludge and granules were used on the hydrolysate. Bacteria granules worked effectively on the total broth, yielded 445mlCH4/gVS methane, which is 124% more than that obtained with the same type of inoculum from untreated feather.

Treatment of decentralized molasses wastewater using anaerobic baffled reactor

The anaerobic baffled reactor (ABR) was used to remove carbonaceous organic pollutants from decentralized molasses wastewater in the study. The anaerobic chambers were inoculated with anaerobic granule sludge. The ABR was studied regarding the hydraulic retention time, the pH, and gas production velocity. After the ABR was seeded with sludge, the organic loading rate was increased gradually from 1.5 to 3.6 kg/m3 d. The average chemical oxygen demand (COD) removal efficiency was about 90% and it was attributed to the high resistance of COD and hydraulic shock loads. The COD removal efficiency and the gas production velocity of the first chamber were the highest compared with other chambers. In addition, the volatile suspended solids to total suspended solids ratio of the first chamber was maximum.

Role of sludge volume index in anaerobic sludge granulation in a hybrid anaerobic reactor

This work focuses on microbial granulation in hybrid anaerobic reactors (HAR). Five HARs were used in two sets of experiments and all were seeded with the same inoculum. The volume of inoculum added was 10%, 20%, 30%, 40% and 50% in the first and 13%, 15%, 18%, 23%, and 27% in the second set of experiment. The volume of inocula added affects the sludge volume index, which in the present study proves to be important parameter for granulation. The results suggest that if SVI during the reactor start-up is kept between 150 and 210, reactors were able to form granules. Outside this range in the present set-up, no granulation was observed due to increased biomass wash-out, causing decreased SRT. Higher methane production was achieved in reactors with good granulation. The DGGE profiles show that the non-granulating systems had lesser diversity, due to increased wash out. Archaeal profile gave better correlation for granulation. Granulating reactors were rich in aceticlastic methanogens over hydrogen utilizing groups, especially Methanosaetaceae. Both Methanosarcina and Methanosaeta are required for better granulation as confirmed quantitatively. Bacterial profile of granulating reactors were rich in acetogens. SEM (Scanning electron microscopy) pictures show that granules are dominated by Methanosaeta-like microbes. Thus, the sludge characteristics at the start-up are of vital importance as they influence the sludge quality developed during the reactor operation and also the microbial communities retained.

Anaerobic Treatment of Palm Oil Mill Effluent in Pilot-Scale Anaerobic EGSB Reactor.

Large volumes of untreated palm oil mill effluent (POME) pose threat to aquatic environment due to the presence of very high organic content. The present investigation involved two pilot-scale anaerobic expanded granular sludge bed (EGSB) reactors, continuously operated for 1 year to treat POME. Setting HRT at 9.8 d, the anaerobic EGSB reactors reduced COD from 71179 mg/L to 12341 mg/L and recycled half of sludge by a dissolved air flotation (DAF). The average effluent COD was 3587 mg/L with the consistent COD removal efficiency of 94.89%. Adding cationic polymer (PAM) dose of 30 mg/L to DAF unit and recycling its half of sludge caused granulation of anaerobic sludge. Bacilli and small coccid bacteria were the dominant microbial species of the reactor. The reactor produced 27.65 m3 of biogas per m3 of POME which was utilized for electricity generation.

Application of Novel Amino-Functionalized NZVI@SiO2 Nanoparticles to Enhance Anaerobic Granular Sludge Removal of 2,4,6-Trichlorophenol.

A novel amino-functionalized silica-coated nanoscale zerovalent iron (NZVI@SiO2-NH2) was successfully synthesized by using one-step liquid-phase method with the surface functionalization of nanoscale zerovalent iron (NZVI) to enhance degradation of chlorinated organic contaminants from anaerobic microbial system. NZVI@SiO2-NH2 nanoparticles were synthesized under optimal conditions with the uniform core-shell structure (80–100 nm), high loading of amino functionality (~0.9 wt%), and relatively large specific surface area (126.3 m2/g). The result demonstrated that well-dispersed NZVI@SiO2-NH2 nanoparticle with nFe0-core and amino-functional silicon shell can effectively remove 2,4,6-trichlorophenol (2,4,6-TCP) in the neutral condition, much higher than that of NZVI. Besides, the surface-modified nanoparticles (NZVI@SiO2-NH2) in anaerobic granule sludge system also showed a positive effect to promote anaerobic biodechlorination system. More than 94.6% of 2,4,6-TCP was removed from the combined NZVI@SiO2-NH2-anaerobic granular sludge system during the anaerobic dechlorination processes. Moreover, adding the appropriate concentration of NZVI@SiO2-NH2 in anaerobic granular sludge treatment system can decrease the toxicity of 2,4,6-TCP to anaerobic microorganisms and improved the cumulative amount of methane production and electron transport system activity. The results from this study clearly demonstrated that the NZVI@SiO2-NH2/anaerobic granular sludge system could become an effective and promising technology for the removal of chlorophenols in industrial wastewater.

Comparison of Mg2+- and Ca2+-enhancing anaerobic granulation in an expanded granular sludge-bed reactor

The mechanisms responsible for the fast granulation of anaerobic sludge caused by Mg2+ and Ca2+ addition was examined in four lab-scale expanded granular sludge bed (EGSB) reactors. Results indicated that both Mg2+ and Ca2+ accelerated the sludge-granulation process and increased the amount of polysaccharides and proteins in the sludge. Energy dispersive x-ray spectrometry (EDX) analysis revealed that, in a mature granule, both Mg2+ and Ca2+ composed as phosphate and calcium was distributed primarily in the periphery of the granule, while magnesium distributed mainly in the interior. The addition of Mg2+ was more favorable for the nuclei formation, whereas the addition of Ca2+ was more favorable for subgranule growth and maintaining the granules' rigid structure. Results showed that the addition of Mg2+ in the nuclei formation stage and Ca2+ in the granule-growth stage accelerated granulation more than adding only one of them in the granulation process.

English

Optimization of up-flow anaerobic sludge blanket (UASB) reactor operation for treatment of a composite fermentation and distillation wastewater was achieved using a locally available thickened municipal sludge instead of imported commercial anaerobic granulated sludge. Over the first 12 days, a fed batch start-up operation was maintained and anaerobic stable sludge granules with 11.2% of extra cellular polymers (ECP) were successfully developed and further used for long-term continuous operation. Two types of granules were developed within the reactor but with very different characteristics. Granules grown in the bottom part of UASB reactor were more compact and tense than those that occurred in the upper part. The latter were fragile, irregular in shape and with much lower methanogenic activities. Bottom granules were dominated by both Methanosarcina spp. and Methanosaeta spp. whereas upper granules harbored only Methanosarcina spp. During continuous anaerobic treatment of composite fermentation and distillation wastewater with organic load of 24 g.l-1 of chemical oxygen demand (COD), a removal efficiency of up to 84% was achieved. Moreover, biogas was produced with a production rate of o.52 m3/Kg COD removed.   Key words: Composite wastewater, up-flow anaerobic sludge blanket (UASB), anaerobic biological treatment, biogas, granulated anaerobic sludge, industrial wastewater.

Performance of a hybrid anaerobic-contact oxidation biofilm baffled reactor for the treatment of decentralized molasses wastewater

A novel hybrid anaerobic-contact oxidation biofilm baffled reactor (HAOBR) was developed to simultaneously remove nitrogenous and carbonaceous organic pollutants from decentralized molasses wastewater in the study. The study was based on the inoculation of anaerobic granule sludge in anaerobic compartments and the installation of combination filler in aerobic compartments. The performance of reactor system was studied regarding the hydraulic retention time (HRT), microbial characteristics and the gas water ratio (GWR). When the HRT was 24h and the GWR was 20:1, total ammonia and chemical oxygen demand (COD) of the effluent were reduced by 99% and 91.8%, respectively. The reactor performed stably for treating decentralized molasses wastewater. The good performance of the reactor can be attributed to the high resistance of COD and hydraulic shock loads. In addition, the high solid retention time of contact oxidation biofilm contributed to stable performance of the reactor.

Responses of anaerobic granule and flocculent sludge to ceria nanoparticles and toxic mechanisms

Effects of CeO2-NPs on anaerobic fermentation were investigated from the processes of acidification and methanation with anaerobic granule sludge and anaerobic flocculent sludge as the targets. Results showed that acidification process was more sensitive to CeO2-NPs than methanation process. Both types of sludge produced less short-chain fatty acid compared to the control, with a reduction of 15-19% for the flocculent sludge at the dosage of 5, 50 and 150 mg CeO2-NPs/g-VSS, and a reduction of 35% for the granular sludge at 150 mg CeO2-NPs/g-VSS. CeO2-NPs caused no inhibition to methanation process. Most of CeO2-NPs distributed on the surface of sludge as revealed by fluorescence labeled CeO2-NPs. The toxicity of CeO2-NPs to anaerobic sludge did not result from reactive oxygen species. Physical penetration and membrane reduction may be important toxic mechanisms.

Effects of stirring strategies on the sludge granulation in anaerobic CSTR reactor

The anaerobic sludge granulation was studied in two laboratory-scale continuous-flow stirred tank reactors (CSTRs), which treating synthetic glucose wastewaters under a mesophilic constant temperature of 35 ± 1°C. Different stirring strategies were employed in the two CSTRs. Magnetic stirring at a rotation speed of 140 rpm was used in CSTR1 and axial continuous agitation at a speed of 90 rpm in CSTR2. It was observed that highly activated granular sludge formed in CSTR2, but flocculent sludge still remained in CSTR1 after about 45 days’ cultivation. Liquid circulation analysis of the two stirring modes displayed that the overall circulation in CSTR2 was more uniform. Furthermore, calculation results proved that the hydraulic shear force produced in CSTR2 was more suitable for granules formation than it in CSTR1, and granules did form in the CSTR2. Therefore, it could be concluded that in the laboratory-scale CSTR, stirring strategy played a key role in sludge granulation. On the other hand, scanning electron microscope images of granular sludge displayed that filamentous bacterial dominated in the outer layer and bacilli surrounded by lots of extracellular polymeric substances in the inner layer. Both of these are beneficial to promote the granules formation and maintenance.

Granulation of anaerobic sludge in the sulfate-reducing up-flow sludge bed (SRUSB) of SANI® process

This study reports on anaerobic sludge granulation in a laboratory-scale sulfate-reducing up-flow sludge bed (SRUSB) in a novel sulfate reduction, autotrophic denitrification and nitrification integrated (SANI(®)) process for treatment of saline sewage. Granulation occurred in 30 d and reached full development in 90 d. The sulfate-reducing granules grew up to around 1 mm after 90 d with 21 mL/g SVI5 (sludge volume index measured after 5 min) and the biomass concentration reached 29 g/L after 4 months' operation. The reactor removed 89% chemical oxygen demand (COD) and reduced 75% sulfate within 1 h of hydraulic retention time, under a COD loading rate of up to 6.4 kg COD/(m(3) · d).

Flocculation, Anaerobic and Microaerobic Treatment Process of Normal Temperature Low Concentration Domestic Sewage

Domestic sewage was treated by adopting flocculation, anaerobic and microaerobic combined process under normal temperature. The result demonstrates: total hydraulic retention time is 5.5h (chemical flocculation 1.0h, UASB reactor 2.0h and MUSB reactor 2.5h). UASB reactor can achieve anaerobic sludge granulation under normal temperature and is fairly feasible for low concentration domestic sewage treatment. Compared with single stage UASB reactor, hydraulic retention time of flocculation-UASB combined technique reduces from 4h to 2h. COD removal rate rises from 45% to 50%-60% and suspended COD is mainly removed. DO of microaerobic MUSB technique after anaerobic treatment is 0.2mg/L-0.5mg/L with air and water ratio of 1:1. Effluent quality is stable, in accordance with first standard of Synthetical Draining Standard of Sewage, GB8978—1996.