Anaerobic Sludge Granulation Research Articles

Application of Recycled Filling to Improve the Purification Performance of Confectionery Wastewater in a Vertical Anaerobic Labyrinth Flow Bioreactor

Anaerobic wastewater treatment is, in many cases, a justified alternative to typical activated sludge processes, from a technological, economic, and ecological point of view. The optimisation of fermentation reactors is primarily concerned with increasing the biodegradation of organic compounds and biogas production, as well as improving efficiency in the removal of nitrogen and phosphorus compounds. The aim of the research was to determine the impact of using low-cost recycled filling on the efficiency of treating real confectionery wastewater in a vertical anaerobic labyrinth flow bioreactor. The experiments focused on selecting the organic loading rate that would allow for the effective biodegradation and removal of pollutants, as well as the efficient production of biomethane. It was found that the tested reactor can operate efficiently at a maximum organic loading rate (OLR) of 7.0–8.0 g of chemical oxygen demand (COD)/L·d. In this OLR range, high efficiency was guaranteed for both wastewater treatment and biogas production. However, increasing the OLR value to 8.0 g COD/L·d had a significant negative effect on the methane (CH4) content in the biogas. The most efficient variants achieved a biodegradation efficiency of around 90% of the organic compounds, a CH4 content of over 70% in the biogas, and a biogas yield of over 400 L/kg of COD removed. A significant influence of the applied OLR on the ratio of free organic acids (FOS) to total alkaline capacity (TAC) and pH was observed, as well as a strong correlation of these indicators with the specific biogas yield and CH4 content. The application of a solution based on the use of a hybrid system of anaerobic granulated sludge and an anaerobic filter resulted in an efficient treatment process and an almost complete elimination of suspensions from the wastewater.

Formation/characterization of humin-mediated anaerobic granular sludge and enhanced methanogenic performance

This study presents a novel method for accelerating the granulation of methanogenic anaerobic granular sludge (AnGS) in an upflow anaerobic sludge blanket (UASB) reactor using solid-phase humin (HM). The results demonstrated that HM-mediated AnGS (HM-AnGS) formed rapidly within 50 days. The increase in particle size, settling velocity and mechanical strength was attributed to the rapid granulation of the HM-AnGS. The maximum methane yield of the HM-AnGS was 5-fold higher than that of the control group. This is consistent with the findings, which showed that HM-AnGS had 3.2–3.4 times more methyl-coenzyme M reductase (Mcr) activity and 2.4–2.9 times more adenosine triphosphate (ATP) than control groups. Molecular analyses indicate that HM most likely accelerated interspecies electron transfer (IET) in HM-AnGS (e.g., from Enterococcus to Methanosaeta). Furthermore, the HM-AnGS was effective in recovering energy from actual slaughterhouse wastewater.

Methane Production from Poly(lactic Acid) (PLA) and Polyhydroxybutyrate (PHB) Biodegradable Plastics with Anaerobic Granulated Sludge

- In this study, using Methanosarcina barkeri DSM 800 and Methanococcus vannielii DSM 1224 methanogenic bacteria under mesophilic (38 ± 1oC) and thermophilic (58 ± 1oC) conditions in anaerobic granulated sludge taken from Pakmaya Yeast Factory in Izmir, Turkey; Methane production from biodegradable plastics with poly(lactic acid) (PLA) and polyhydroxybutyrate (PHB) was investigated. Effect of different operating parameters, increasing biodegradation times (from 10 days to 500 days), different inoculumsubstrate ratios (ISRs) (16, 8, 4, 2, 1) and increasing biochemical methane potential (BMP) times (between 10 day and 500 days) for the production of methane gas from PLA and PHB biodegradable plastics in anaerobic granular sludge waste; Methanosarcina barkeri DSM 800 and Methanococcus vannielii DSM 1224 methanogenic bacteria were operated during the anaerobic digestion process under anaerobic conditions at mesophilic (38 ± 1oC) and thermophilic (58 ± 1oC) experimental temperatures. PLA biodegradable plastics were operated at optimum pH=7.6. PHB biodegradable plastics were carried out at optimum pH=8.1. Predicting the biodegradation behavior of PLA and PHB biodegradable plastics with BMP tests; It is found that the ISR parameter plays a very important role. This study showed that temperature plays a key role in the aging of microorganisms (Methanosarcina barkeri DSM 800 and Methanococcus vannielii DSM 1224 methanogenic bacteria) during anaerobic digestion, the degradation of bioplastic materials (PLA and PHB) and the degradation of their natural properties. The increase in temperature from mesophilic conditions to thermophilic conditions increased the activities of methanogenic bacteria such as Methanosarcina barkeri DSM 800 and Methanococcus vannielii DSM 1224. The maximum cumulative CH4(g) production was measured at 630 NL CH4 / kgVS for PHB biodegradable plastics in anaerobic granulated sludge with inoculum culture (the mixture of Methanosarcina barkeri DSM 800 and Methanococcus vannielii DSM 1224 methanogenic bacteria), at ISR=16 value, after 100 days, at pH=8.1 and at 58±1oC, respectively. The maximum 97% biodegradation efficiency was observed for PHB biodegradable plastics after 100 days, at pH=8.1 and at 58 ± 1oC thermophilic conditions, respectively.

Effects of pharmaceuticals compounds and calcium on granulation, microbiology, and performance of anaerobic granular sludge systems.

Granular sludge is a promising biotechnology to treat sewage contaminated with pharmaceuticals due to its increased toxicity resistance. In this context, this study evaluated the potential of Ca2+ as a granulation precursor and how pharmaceutical compounds (loratadine, prednisone, fluconazole, fenofibrate, betamethasone, 17α-ethinyl estradiol, and ketoprofen) affect granulation. Continuous and intermittent dosages of Ca2+ in the presence and absence of pharmaceuticals were evaluated. The results showed that intermittent addition of Ca2+ reduces the time for anaerobic sludge granulation, and pharmaceuticals presence did not impair granulation. 10% of the granules presented mean diameters greater than 2.11 mm within 93 days with intermittent Ca2+ dosage in the pharmaceuticals' presence. In contrast, no granules higher than 2.0 mm were observed with no precursor addition. The pharmaceuticals' toxicity may have created a stress condition for the microbial community, contributing to more EPS production and a greater potential for granulation. It was also verified that pharmaceuticals' presence did not decrease organic matter, total alkalinity, and volatile fatty acids removals. The 16S rRNA gene analysis revealed taxa resistance to recalcitrant compounds when pharmaceuticals were added. Besides, the efficiency of a granular sludge bioreactor (EGSB) was evaluated for pharmaceuticals removal, and betamethasone, fenofibrate, and prednisone were effectively removed.

The Role of Extracellular Polymeric Substances in the Toxicity Response of Anaerobic Granule Sludge to Different Metal Oxide Nanoparticles.

Wastewater treatment plants (WWTP) are regarded as the last barriers for the release of incompletely separated and recycled nanoparticles (NPs) into the environment. Despite the importance and ubiquity of microbial extracellular polymeric substances (EPSs) in the complex wastewater matrix, the interaction between NPs and EPSs of anaerobic microflora involved in wastewater treatment and the resultant impact on the biomass metabolomics are unclear. Thus, the impacts of different metal oxide (TiO2, ZnO, and CuO) NPs on functional bacteria in anaerobic granular sludge (AGS) and the possible toxicity mechanisms were investigated. In particular, the binding quality, enhanced resistance mechanism, and chemical fractional contribution of EPSs from AGS against the nanotoxicity of different NPs was assessed. The results showed that CuO NPs caused the most severe inhibition towards acetoclastic and hydrogenotrophic methanogens, followed by ZnO NPs, whereas TiO2 NPs caused no inhibition to methanogenesis. Excessive EPS production, especially the protein-like substances, was an effective strategy for reducing certain NPs’ toxicity by immobilizing NPs away from AGS cells, whereas the metabolism restriction on inner microorganisms of AGS induced by CuO NPs can deteriorate the protective role of EPS, indicating that the roles of EPS may not be amenable to generalizations. Further investigations with lactate dehydrogenase (LDH) and reactive oxygen species (ROS) assays indicated that there are greatly essential differences between the toxicity mechanisms of metal NPs to AGS, which varied depending on the NPs’ type and dosage. In addition, dynamic changes in the responses of EPS content to different NPs can result in a significant shift in methanogenic and acidogenic microbial communities. Thus, the production and composition of EPSs will be a key factor in determining the fate and potential effect of NPs in the complex biological matrix. In conclusion, this study broadens the understanding of the inhibition mechanisms of metal oxide NPs on the AGS process, and the influence of EPSs on the fate, behavior, and toxicity of NPs.

Calcium migration inside anaerobic granular sludge: Evidence from calcium carbonate precipitation pattern

Calcification of anaerobic granule sludge caused the decrease of reactor deactivation has been focused in paper industry for decades, the mechanism of calcium immigration is still in curiosity. In this study, evidences relevant to the calcium immigration involving surface adherence, crystallite size and precipitation pattern were analyzed in a calcified granule. Crystal larger than 2 µm would be sterically stuck in the channel and calcium transfer occurred through serial deposition and resolution. Ca2+ diffusion in the confined channel through Ostwald ripening was in consisted with the Liesegang rings pattern. Thus, a hypothetical mechanism of calcium migration was proposed used to understand the calcium-precipitation control strategy in granule-based anaerobic reactor. The findings of this study are referable for the regulation of mineral precipitation during granule-based wastewater treatment system.

Effects of reflux ratio on the anaerobic sludge and microbial social behaviors in an expanded granular sludge bed reactor: From the perspective of acyl-homoserine lactones-mediated quorum sensing

Performance of anaerobic sludge and microbial social behaviors in an expanded granular sludge bed (EGSB) were evaluated by increasing reflux ratio from 50% to 500% stage by stage, with a constant influent chemical oxygen demand (COD) of 5500 mg/L at hydraulic retention time 12 h. The results indicated that the reflux ratio of 100% − 200% was more favorable for the EGSB with a methane production of 2.4 m3/m3·d. It was found that acyl-homoserine lactones (AHLs)-mediated quorum sensing (QS) could balance various microbial populations in the anaerobic digestion process. C4-HSL and C8-HSL were identified as the specific AHLs in enhancing granulation of anaerobic sludge by stimulating protein secretion into extracellular polymeric substances (EPS). 3-oxo-C6-HSL and 3-oxo-C14-HSL were verified for the enhancement of methanogenesis. The present study showed a novel perspective on the performance of EGSB with reflux ratios based on the AHLs-mediated QS.

Granulation and response of anaerobic granular sludge to allicin stress while treating allicin-containing wastewater

In order to treat allicin-containing wastewater with antimicrobial characteristic, anaerobic granular sludge (AnGS) under allicin stress was cultivated, which completely granulated on day 143 in the up-flow anaerobic sludge bed (UASB). The mature allicin-tolerant AnGS had a granule size of 0.356–2.000 mm with an excellent settleability, and the chemical oxygen demand (COD) removal efficiency reached 93.26 %. Moreover, the tightly-bound extracellular polymeric substances (TB-EPS) and extracellular protein (PN) enchanted the formation and tolerance of AnGS under the allicin environment. Meanwhile, the short-chain N-acylhomoserine lactones (AHLs) including C4-HSL, C6-HSL and C8-HSL were utilized by quorum sensing (QS) to regulate EPS production during AnGS formation process, while the long-chain AHLs including C10-HSL, C12-HSL and C14-HSL had a positive effect towards the allicin stress. In addition, Acinetobacter and Petrimonas were observed to be the dominant allicin resistant genera, which along with the EPS producers of Comamonas and Thauera enhanced the AnGS tolerance. These results confirmed that the AHL-mediated QS regulated EPS production and the growth of functional bacteria involved in allicin-tolerant AnGS formation. This provides useful information for AnGS application in treating allicin-containing wastewater.

Role of magnetite in methanogenic degradation of different substances

For better understanding the role of magnetite in methanation of different substrates, two up-flow anaerobic sludge bed reactors (RM with magnetite; RS with silica) were built using acetate (stage I), propionate + butyrate (stage II), and sucrose (stage III) as the substrates, respectively. RM reactor showed better COD removal efficiency and adaptability to different substrate impacts. More extracellular polymeric substances (EPS) were produced for anaerobic sludge granulation, and the sludge in RM had better intensity, hydrophobicity and electroactivity compared with those in RS. Interestingly, magnetite had different promoting effects on methanogenic degradation of different substrates, and magnetite facilitated different syntrophic partners, like Desulfovibrio, Smithella, unidentified Clostridiates and Methanosaeta in different stages. The strengthening factor of biogas production from sucrose was the highest (1.23 ± 0.03), and analysis of key enzyme activities indicated that the potential magnetite-induced direct interspecies electron transfer (DIET) improved the process between the glycolysis, oxidation of pyruvate and CO2-dependent methanogenesis.

Development of granular sludge coupling n-DAMO and Anammox in membrane granular sludge reactor for high rate nitrogen removal

The integration of nitrate/nitrite dependent anaerobic methane oxidation (n-DAMO) and anaerobic ammonium oxidation (Anammox) provides sustainable solution to simultaneously remove nitrate, nitrite and ammonium. This study demonstrated the sludge granulation process coupling n-DAMO and Anammox from mixed inoculum including river sediment, return activated sludge and crushed anaerobic granule sludge in a novel membrane granular sludge reactor (MGSR). Flocculent biomass gradually turned into compact aggregates and retained as granular sludge with an average diameter of 2.2 mm in MGSR after 684 days’ operation. When steady state with a hydraulic retention time of 1.19 days was reached, the MGSR achieved a nitrogen removal rate of 1.77 g N L−1 d−1. Granules with density of 1.043 g mL−1, settling velocity of 72 m h−1 and sludge volume index of 22 mL g−1 leaded to excellent biomass retention (42 g VSS L−1). Pyrosequencing analysis revealed that two dominant microbial groups, n-DAMO archaea and Anammox bacteria, in the microbial community of the granule were enriched to 31.09% and 12.45%. Fluorescence in situ hybridization revealed a homogenous distribution of n-DAMO archaea and Anammox bacteria throughout the granule. The granular sludge coupling n-DAMO and Anammox microorganisms provides significant potential for high rate nitrogen removal from wastewater.

Microbial Community Drivers in Anaerobic Granulation at High Salinity.

In the recent years anaerobic sludge granulation at elevated salinities in upflow anaerobic sludge blanket (UASB) reactors has been investigated in few engineering based studies, never addressing the microbial community structural role in driving aggregation and keeping granules stability. In this study, the combination of different techniques was applied in order to follow the microbial community members and their structural dynamics in granules formed at low (5 g/L Na+) and high (20 g/L Na+) salinity conditions. Experiments were carried out in four UASB reactors fed with synthetic wastewater, using two experimental set-ups. By applying 16S rRNA gene analysis, the comparison of granules grown at low and high salinity showed that acetotrophic Methanosaeta harundinacea was the dominant methanogen at both salinities, while the dominant bacteria changed. At 5 g/L Na+, cocci chains of Streptoccoccus were developing, while at 20 g/L Na+ members of the family Defluviitaleaceae formed long filaments. By means of Fluorescence in Situ Hybridization (FISH) and Scanning Electron Microscopy (SEM), it was shown that aggregation of Methanosaeta in compact clusters and the formation of filaments of Streptoccoccus and Defluviitaleaceae during the digestion time were the main drivers for the granulation at low and high salinity. Interestingly, when the complex protein substrate (tryptone) in the synthetic wastewater was substituted with single amino acids (proline, leucine and glutamic acid), granules at high salinity (20 g/L Na+) were not formed. This corresponded to a decrease of Methanosaeta relative abundance and a lack of compact clustering, together with disappearance of Defluviitaleaceae and consequent absence of bacterial filaments within the dispersed biomass. In these conditions, a biofilm was growing on the glass wall of the reactor instead, highlighting that a complex protein substrate such as tryptone can contribute to granules formation at elevated salinity.

Characterization of sulfate-reducing bacteria anaerobic sludge granulation enhanced by chitosan

Two laboratory-scale up-flow anaerobic sludge granules reactors were operated as control reactor (R1) and chitosan (CTS) addition reactor (R2) to investigate the effect of the addition of CTS on the granulation process of sulfate-reducing bacteria (SRB) anaerobic sludge. Granular sludge with the diameter greater than 0.5 mm was selected to calculate the granulation percentage, and the remaining sludge was considered as flocculent sludge in this paper. The results showed that the granulation percentage in the two reactors were stabilized to 47.3% and 64.2%, respectively. The sizes of sludge granules in R2 were mainly between 0.5 and 1.5 mm with the average pore diameter of 91.6 nm and the porosity of 57.1% while the granules in the same particle size in R1 were 41.5 nm and 46.1%, respectively. It demonstrated that CTS was an appropriate additive which can enhance the formation of SRB granule sludge with better pore structure. The granular sludge with CTS exhibited excellent physical performance and more extracellular polymeric substances, especially for protein (PN). In addition, computational fluid dynamics (CFD) simulation was conducted to illustrate the hydrodynamic characteristics of granules with Kozeny-Carman model. With a higher porosity, the permeability of the granules fed with CTS was considerably increased. Moreover, the model also indicated that the permeability and convection changed significantly with Reynolds numbers (Re) of the external flow field for a given type of the porous structure.

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.

Optimization of Biosorption Conditions for Surfactant Induced Decolorization by Anaerobic Sludge Granules

AbstractThe sorption of Remazol Black B (RBB) by dried anaerobic sludge granules (ASG) was examined in this study. The biosorption process was monitored based on the statistical optimization data of the batch reactor studies. In the factorial tests, 36 different tests were established by considering the variables such as temperature (25°C, 50°C), pH (1, 3, 5), dye concentration (100, 150, 200 mg/L) and cationic surfactant concentration (0, 0.5 mM). Also, it was intended to investigate the effect of cationic surfactant dodecyl trimethylammonium bromide (DTAB) on decolorization of the anionic dye RBB by ASG. The sorption isotherms and kinetics were determined for RBB removal. The biosorption of RBB was fitted with Langmuir isotherm and pseudo-second-order kinetic models. The oppositely charged dye and surfactant molecules interacted electrostatically. These electrostatic interactions improved the dye biosorption properties of ASG. Our results indicate that a surfactant can be used as an inducer in the treatment of dye-contaminated water. This is the first paper combining factorial experiment design and surfactant-accelerated decolorization to achieve more effective biosorption conditions.

Effective Anaerobic Bio-Treatment of Fresh Leachate From Municipal Solid Waste Incineration Plant by Full-Scale Internal Circulation Reactor

This study aimed to investigate the effectiveness of the full-scale internal circulation (IC) reactor in biodegrading of municipal solid waste (MSW) fresh leachate under mesophilic conditions, where the anaerobic process stability, biogas yield, and sludge granulation were intensively investigated. The effects of operational parameters on the influent organic loading rate (OLR), chemical oxygen demand (COD) removal efficiency, alkalinity (ALK), pH, volatile fatty acids (VFAs) accumulation, and effluent recirculation were also studied. The results showed that the reactor operated stably and effectively. The COD removal efficiency and biogas yield could be maintained at (92.8 ± 2.0)% and (0.47 ± 0.05) m3/kg CODremoval, respectively, with the influent OLR (24.5 ± 0.9) kg COD/(m3 d) and hydraulic retention time (HRT) 2.7d during the stable operation phase. Meanwhile, this study demonstrated that 1.5–3.0 m/h would be the optimal Vup for the reactor, corresponding to the effluent recirculation of 32.5–78.0 m3/h. Moreover, it was found that the content of extracellular polymeric substances (EPS) in the anaerobic sludge increased from 50.3 to 140.7 mg/g volatile suspended solids (VSS), and the sludge had good granular performance during the reactor operation.

Anaerobic granule sludge formation and perchlorate reduction in an upflow anaerobic sludge blanket (UASB) reactor

It is a novel biological method to reduce high concentration of perchlorate using an upflow anaerobic sludge blanket reactor with perchlorate granular sludge. A high perchlorate loading rate of 9.96 g/(L·d) was achieved in the UASB reactor with the perchlorate reduction rate of 84.7%. The perchlorate granular sludge wet density, mechanical strength and VSS/SS of the mature perchlorate granular sludge were 1.2516 g/cm3, 97.18% and 0.45, respectively. 16S rDNA gene amplicon sequencing indicated that the first abundant bacteria among all of the detected bacteria were Sulfurovum, Methyloversatilis and Sulfurospirillum for floccular anaerobic sludge, denitrifying granular sludge and perchlorate reduction granular sludge, respectively. The perchlorate reduction rate was compared with prediction of the first-order substrate removal models, second-order substrate removal models and the Stover–Kincannon substrate removal models with the correlation coefficient 0.9300, 0.9988 and 0.9995, respectively. These models may be used in predicting the behavior or design of the perchlorate reduction.

Technological Solution of Biogas Output Increasing at Grain Distillery Spent Wash Fermentation

Background. Distillery spent wash is the main waste of the alcohol industry. This is highly concentrated wastewater, which is characterized by high chemical oxygen demand (COD) values – up to 60–120 g O 2 /dm 3 – and low pH values – up to 3.7. It makes its processing a complicated task. One of the methods of its utilization is anaerobic fermentation with the production of biogas. Inert carriers for microorganism immobilization or granulation are used to intensify the process of anaerobic treatment and increase sludge concentration. Due to the high concentration of anaerobic microorganisms in granules, compared to the number of microorganisms in free-floating active sludge, the process of methanogenesis is more intensive with a high yield of biogas and a decrease in COD. Objective. To determine the possible centres of anaerobic sludge granulation in highly concentrated waste of alcohol production to increase biogas output in the process of waste treatment. Method s . Activated carbon, modified carbon on which surface calcium ions were precipitated, FeCl 3 , silica gel based sorbent, talc based sorbent were used to form pellets as the centres of microorganism accumulation. Results. Pellets have not been formed with the use of activated carbon; modified carbon with calcium ions; silica gel based sorbent and ferrum compounds. Pellets of activated sludge were received with the use of talc based sorbent – formation of initial biofilm on a carrier was observed on the third day of fermentation and then it was growing in pellets. Conclusions. It was demonstrated that for highly concentrated waste effluents of a distillery (grain distillery spent wash), which after co-fermentation with poultry manure contain volatile fatty acids in concentration 800–2000 mg/dm 3 , it is needed to use sorbents to receive microorganism pellets as a centre of granulation. Sorbents must contain donors and proton acceptors. It was established that the use of granular activated sludge for the distillery waste purification improves the efficiency of COD and Biochemical Oxygen Demand removal by 15–17%, increases biogas output by 26 ± 2% and biogas methane content by 8 ± 1%.

Role of biochar in the granulation of anaerobic sludge and improvement of electron transfer characteristics

For improving the formation of anaerobic sludge granulation and its electron transfer characteristics, two up-flow anaerobic sludge blanket (UASB) reactors (R1 with 4 g/L biochar; R2 without biochar) were built in this study. With the addition of biochar, the lag time of methanogenesis was shortened by 28.6%, and the strengthening factor of COD removal rate reached 1.6. At the same time, the conductivity of granular sludge in R1 (23.29 ± 0.99 μS/cm) was 2-fold of that in R2, and the integrity coefficient and hydrophobicity of granular sludge were improved significantly. According to the results of microbial community succession and electron transfer characteristics, the added biochar not only favors the anaerobic sludge granulation working as an inert core, but also facilitates the selective enrichment of potential direct interspecies electron transfer (DIET) partners such as Methanothrix and Geobacter spp. for enhancing the DIET process.

Chlorpyrifos and 3,5,6-trichloro-2-pyridinol degradation in zero valent iron coupled anaerobic system: Performances and mechanisms

Pesticide contaminants, such as chlorpyrifos (CP) and its more toxic metabolite 3,5,6-trichloro-2-pyridinol (TCP) in farmland drainage have attracted extensive concerns around the world, and are in urgent need of treatment. In this work, three groups of anaerobic reactors packed with zero valent iron (mono-ZVI system), ZVI coupled with anaerobic sludge (coupled system) and anaerobic sludge (mono-cell system) were continuously operated to investigate their performances on CP, TCP and chemical oxygen demand (COD) removal, as well as the reaction mechanisms of ZVI coupling with anaerobic microorganisms. Results showed that the removal efficiencies of CP and COD in coupled system were both around 95%. The corresponding results were 80% and 82% in mono-cell system, and the unstable values in mono-ZVI system were around 86% and 70%. The TCP residual concentration was the lowest in coupled system. The results of X-ray photoelectron spectrometer (XPS) and the photo images of ZVI at the end of reaction implied that the presence of sludge and the interaction between microorganisms and ZVI protected iron shavings from excessive corrosion. Moreover, the addition of ZVI promoted the electron transfer in the anaerobic system, which was proved by the higher value of electron transport system (ETS) activity and Cytochrome C (Cyt C) content of sludge with 250 mg (g h)−1 and 20.71 nmol L−1 in coupled system, compared to 200 mg (g h)−1 and 17.56 nmol L−1 in mono-cell system. The improvement of extracellular polymeric substances (EPS) and anaerobic sludge granulation in the coupled system were on account of the existence of ZVI. It was obvious that the key enzymes and microbial species functioned in COD, CP and TCP degradation were enriched in coupled system.

Characterization of sulfate-reducing bacteria anaerobic granular sludge and granulometric analysis with grey relation

We constructed a bench-scale up-flow anaerobic sludge reactor to systematically investigate the physicochemical characteristics of sulfate-reducing bacteria (SRB) anaerobic granular sludge and evaluate the granular size by a grey relational analysis. Results indicated that the granulation proportion was improved from 17.9% to 68.7% with the sulfate reduction efficiency larger than 90% under gradually shortened hydraulic retention time (HRT) and increased organic loading. Larger SRB granule sludge showed a higher specific gravity and settling velocity. The seed sludge was negatively charged, and the surface charge decreased with the incremental granular diameter. The maximal hydrophobicity and granulation proportion were 69.9% and 42.4%, respectively, for the granular diameter ranging from 1.5 to 2.5 mm. Extracellular polymeric substance (EPS) of the sludge exhibited the highest ratio of protein to polysaccharide (PN/PS) for the granular diameter in the range of 0.5 to 1.5mm. Based on the grey relational analysis of the SRB anaerobic sludge granulation, the correlation degree of the inherent influencing factors was PN/PS>surface charge> hydrophobicity. The theoretical evaluation would be conducive to granulation control during the potential application.