Start-up of a thermophilic upflow anaerobic sludge bed (UASB) reactor with mesophilic granular sludge

Long-term enrichment of anaerobic propionate-oxidizing consortia: Syntrophic culture development and growth optimization

Propionate is a quantitatively important methanogenic intermediate in anaerobic digesters and only limited number of microbes can utilize it under syntrophic association with methanogens. The syntrophic propionate oxidizing bacterias are known to be slow growers due to the low energy yield. Thus, propionate get accumulated frequently in anaerobic digesters and it negatively affect digester performance. In this study, propionate degrading consortia from four different seeding sources were enriched in sequential bath mode in two phases; first adaption phase with 1 g/L of propionate concentration and later, high-strength phase with 3 g/L. From 16s rRNA gene based metagenomics analysis of the former phase, four syntrophic microbial groups, Syntrophaceae, Syntrophomonadaceae, Methanobacterium and Methanosaeta were found to be dominant with complete degradation of propionate. The substrate accelerated microbial shifts were observed at high-strength phase with significant decrease of Syntrophaceae up to 26.9 %. Using Response Surface Methodology, pH 6.8-6.9 and temperature 34.5-34.9 °C were found to be optimum growth conditions for the propionate degradation culture. Observed results could be useful to improve degradation efficiencies and obtained enriched culture can be used to recover propionate-accumulated digesters by bio-augmentation.

Novel start-up process for the efficient degradation of high COD wastewater with up-flow anaerobic sludge blanket technology and a modified internal circulation reactor

To avoid wastage of water resources and operating cost increases caused by the traditional start-up process of large amounts of dilution influent chemical oxygen demand (COD), a novel start-up process (NSP) was developed and verified with water hyacinth juice (WHJ) on an up-flow anaerobic sludge blanket (UASB) and modified internal circulation (MIC) reactor. Results show that UASB and MIC reactors were started successfully and that the MIC reactor exhibited a superior performance. The NSP time of the MIC reactor (46 days) was less than that of the UASB reactor (52 days), although the start-up organic loading rate (OLR) of the MIC reactor was higher than that of the UASB reactor. Interestingly, high-throughput sequencing analysis indicated that the reactor configuration significantly impacted the microbial diversity, however, the UASB and MIC reactors had similar predominant methanogens: Methanosaeta and Methanosarcina. Therefore, acetoclastic methanogenesis is the primary pathway of methane formation during WHJ treatment.

Temperature susceptibility of a mesophilic anaerobic membrane bioreactor treating saline phenol-containing wastewater

This study examined the temperature susceptibility of a continuous-flow lab-scale anaerobic membrane bioreactor (AnMBR) to temperature shifts from 35 °C to 55 °C and its bioconversion robustness treating synthetic phenolic wastewater at 16 gNa^+.L^-1. During the experiment, the mesophilic reactor was subjected to stepwise temperature increases by 5 °C. The phenol conversion rates of the AnMBR decreased from 3.16 at 35 °C to 2.10 mgPh^.gVSS^-1.d^-1 at 45 °C, and further decreased to 1.63 mgPh^.gVSS^-1.d^-1 at 50 °C. At 55 °C, phenol conversion rate stabilized at 1.53 mgPh^.gVSS^-1.d^-1 whereas COD removal efficiency was 38% compared to 95.5% at 45 °C and 99.8% at 35 °C. Interestingly, it was found that the phenol degradation process was less susceptible for the upward temperature shifts than the methanogenic process. The temperature increase implied twenty-one operational taxonomic units from the reactor's microbial community with significant differential abundance between mesophilic and thermophilic operation, and eleven of them are known to be involved in aromatic compounds degradation. Reaching the upper-temperature limits for mesophilic operation was associated with the decrease in microbial abundance of the phyla Firmicutes and Proteobacteria, which are linked to syntrophic phenol degradation. It was also found that the particle size decreased from 89.4 μm at 35 °C to 21.0 μm at 55 °C. The accumulation of small particles and higher content of soluble microbial protein-like substances led to increased transmembrane pressure which negatively affected the filtration performance. Our findings indicated that at high salinity a mesophilic AnMBR can tolerate a temperature up to 45 °C without being limited in the phenol conversion capacity.

State of the art on granular sludge by using bibliometric analysis

With rapid industrialization and urbanization in the nineteenth century, the activated sludge process (ASP) has experienced significant steps forward in the face of greater awareness of and sensitivity toward water-related environmental problems. Compared with conventional flocculent ASP, the major advantages of granular sludge are characterized by space saving and resource recovery, where the methane and hydrogen recovery in anaerobic granular and 50% more space saving, 30-50% of energy consumption reduction, 75% of footprint cutting, and even alginate recovery in aerobic granular. Numerous engineers and scientists have made great efforts to explore the superiority over the last 40 years. Therefore, a bibliometric analysis was desired to trace the global trends of granular sludge research from 1992 to 2016 indexed in the SCI-EXPANDED. Articles were published in 276 journals across 44 subject categories spanning 1420 institutes across 68 countries. Bioresource Technology (293, 11.9%), Water Research (235, 9.6%), and Applied Microbiology and Biotechnology (127, 5.2%) dominated in top three journals. The Engineering (991, 40.3%), China (906, 36.9%), and Harbin Inst Technol, China (114, 4.6%) were the most productive subject category, country, and institution, respectively. The hotspot is the emerging techniques depended on granular reactors in response to the desired removal requirements and bio-energy production (primarily in anaerobic granular sludge). In view of advanced and novel bio-analytical methods, the characteristics, functions, and mechanisms for microbial granular were further revealed in improving and innovating the granulation techniques. Therefore, a promising technique armed with strengthened treatment efficiency and efficient resource and bio-energy recovery can be achieved.

Transition of municipal sludge anaerobic digestion from mesophilic to thermophilic and long-term performance evaluation

Strategies for the transition of municipal sludge anaerobic digestion from mesophilic to thermophilic were assessed and the long-term stability and performance of thermophilic digesters operated at a solids retention time of 30days were evaluated. Transition from 36°C to 53.3°C at a rate of 3°C/day resulted in fluctuation of the daily gas and volatile fatty acids (VFAs) production. Steady-state was reached within 35days from the onset of temperature increase. Transitions from either 36 or 53.3°C to 60°C resulted in relatively stable daily gas production, but VFAs remained at very high levels (in excess of 5000mg COD/L) and methane production was lower than that of the mesophilic reactor. It was concluded that in order to achieve high VS and COD destruction and methane production, the temperature of continuous-flow, suspended growth digesters fed with mixed municipal sludge should be kept below 60°C.

Performance and energy economics of mesophilic and thermophilic digestion in anaerobic hybrid reactor treating coal wastewater

Two anaerobic hybrid AHRs (AHR), mesophilic (35 °C) and thermophilic (55 °C) were operated with coal wastewater at different hydraulic retention times (HRT) ranging from 3-0.5 to 3.12-0.6d with organic loading rates (OLR) of 1.12-6.72 g L(-1) d(-1). Synthetic coal wastewater with an average chemical oxygen demand (COD) of 2240 mg L(-1) and phenolics concentration of 752 mg L(-1) was used as substrate. At each HRT, the thermophilic AHR gave a better performance, measured in terms of phenolics/COD removal and gas production. The specific methane yield was also higher for thermophilic AHR at each HRT compared to mesophilic one. The volatile fatty acid concentration in the effluent increased with the lowering of HRT. The Stover-Kincannon model was applicable at both temperatures and showed higher substrate utilization in thermophilic AHR. Energy economic study of the AHRs revealed that 11,938 MJ d(-1) more energy can be generated using thermophilic AHR than mesophilic.

Development of thermophilic methanogenic sludge in compartmentalized upflow reactors

The characteristics and development of thermophilic anaerobic sludge in upflow staged sludge bed (USSB) reactors were studied. The compartmentalized reactors were inoculated with partially crushed mesophilic granular sludge and then fed with either a mixture of volatile fatty acids (VFA) or a mixture of sucrose and VFA. The staged degradation of the soluble substrate in the various compartments led to a clear segregation of specific types of biomass along the height of the reactor, particularly in reactors fed with the sucrose-VFA mixture. Both the biological as well as the physical properties of the cultivated sludge were affected by the fraction of nonacidified substrate. The sludge in the first compartment of the reactor treating the sucrose-VFA mixture was whitish and fluffy, most likely resulting from the development of acidifying bacteria. Sludge granules which developed in the top part of this reactor possessed the highest acetogenic and methanogenic activity and the highest granule strength as well. The experiments also revealed that the conversion of the sucrose-VFA mixture into methane gradually deteriorated at prolonged operation at high organic loading rates (50 to 100 g COD x L(-1) x day(-1)). Stable long-term performance of a reactor can only be achieved by preserving the sludge segregation along the height of the reactor. In the reactor fed solely with the VFA mixture little formation of granular sludge occurred. In this reactor, large differences in sludge characteristics were also observed along the reactor height. Li(+)-tracer experiments indicated that the hydraulic regime in the USSB reactor is best characterized by a series of at least five completely mixed reactors. The formation of granular sludge was found to influence the liquid flow pattern.

Potentials of anaerobic membrane bioreactors to overcome treatment limitations induced by industrial wastewaters

This review presents a comprehensive summary on applications of anaerobic membrane bioreactor (AnMBR) technology for industrial wastewaters in view of different aspects including treatability and filterability. AnMBRs present an attractive option for the treatment of industrial wastewaters at extreme conditions, such as high salinity, high temperature, high suspended solids concentrations, and toxicity that hamper granulation and retention of biomass or reduce the biological activity. So far, most of the research has been conducted at laboratory scale; however, also a number of full-scale AnMBR systems is currently being operated worldwide. Membrane fouling, a multivariable process, is still a research quest that requires further investigation. In fact, membrane fouling and flux decline present the most important reasons that hamper the wide-spread application of full-scale reactors. This paper addresses a detailed assessment and discussion on treatability and filterability of industrial wastewaters in both lab- and full-scale AnMBR applications, the encountered problems and future opportunities.

UASB performance and microbial adaptation during a transition from mesophilic to thermophilic treatment of palm oil mill effluent

The treatment of palm oil mill effluent (POME) by an upflow anaerobic sludge bed (UASB) at organic loading rates (OLR) between 2.2 and 9.5 g COD l(-1) day(-1) was achieved by acclimatizing the mesophilic (37 °C) microbial seed to the thermophilic temperature (57 °C) by a series of stepwise temperature shifts. The UASB produced up to 13.2 l biogas d(-1) with methane content on an average of 76%. The COD removal efficiency ranged between 76 and 86%. Microbial diversity of granules from the UASB reactor was also investigated. The PCR-based DGGE analysis showed that the bacterial population profiles significantly changed with the temperature transition from mesophilic to thermophilic conditions. In addition, the results suggested that even though the thermophilic temperature of 57 °C was suitable for a number of hydrolytic, acidogenic and acetogenic bacteria, it may not be suitable for some Methanosaeta species acclimatized from 37 °C. Specifically, the bands associated with Methanosaeta thermophila PT and Methanosaeta harundinacea can be detected during the four consecutive operation phases of 37 °C, 42 °C, 47 °C and 52 °C, but their corresponding bands were found to fade out at 57 °C. The DGGE analysis predicted that the temperature transition can result in significant methanogenic biomass washout at 57 °C.

High-calorific biogas production by selective CO₂ retention at autogenerated biogas pressures up to 20 bar

Autogenerative high pressure digestion (AHPD) is a novel configuration of anaerobic digestion, in which micro-organisms produce autogenerated biogas pressures up to 90 bar with >90% CH(4)-content in a single step reactor. (1) The less than 10% CO(2)-content was postulated to be resulting from proportionally more CO(2) dissolution relative to CH(4) at increasing pressure. However, at 90 bar of total pressure Henry's law also predicts dissolution of 81% of produced CH(4). Therefore, in the present research we studied whether CO(2) can be selectively retained in solution at moderately high pressures up to 20 bar, aiming to produce high-calorific biogas with >90% methane. Experiments were performed in an 8 L closed fed-batch pressure digester fed with acetate as the substrate. Experimental results confirmed CH(4) distribution over gas and liquid phase according to Henry's law, but the CO(2)-content of the biogas was only 1-2%, at pH 7, that is, much lower than expected. By varying the ratio between acid neutralizing capacity (ANC) and total inorganic carbon (TIC(produced)) of the substrate between 0 and 1, the biogas CO(2)-content could be controlled independently of pressure. However, by decreasing the ANC relative to the TIC(produced) CO(2) accumulation in the aqueous medium caused acidification to pH 5, but remarkably, acetic acid was still converted into CH(4) at a rate comparable to neutral conditions.

Integrated application of upflow anaerobic sludge blanket reactor for the treatment of wastewaters

The UASB process among other treatment methods has been recognized as a core method of an advanced technology for environmental protection. This paper highlights the treatment of seven types of wastewaters i.e. palm oil mill effluent (POME), distillery wastewater, slaughterhouse wastewater, piggery wastewater, dairy wastewater, fishery wastewater and municipal wastewater (black and gray) by UASB process. The purpose of this study is to explore the pollution load of these wastewaters and their treatment potential use in upflow anaerobic sludge blanket process. The general characterization of wastewater, treatment in UASB reactor with operational parameters and reactor performance in terms of COD removal and biogas production are thoroughly discussed in the paper. The concrete data illustrates the reactor configuration, thus giving maximum awareness about upflow anaerobic sludge blanket reactor for further research. The future aspects for research needs are also outlined.

Performance of a sulfide-oxidizing expanded-bed reactor supplied with dissolved oxygen

The performance of a new sulfide-oxidizing, expanded-bed bioreactor is described. To stimulate the formation of well-settleable sulfur sludge, which comprises active sulfide-oxidizing bacterial biomass and elemental sulfur, the aeration of the liquid phase and the oxidation of sulfide to elemental sulfur are spatially separated. The liquid phase is aerated in a vessel and subsequently recirculated to the sulfide-oxidizing bioreactor. In this manner, turbulencies due to aeration of the liquid phase in the bioreactor are avoided. It appeared that, under autotrophic conditions, almost all biomass present in the reactor will be immobilized within the sulfur sludge which consists mainly of elemental sulfur (92%) and biomass (2.5%). The particles formed have a diameter of up to 3 mm and can easily be grinded down. Within time, the sulfur sludge obtained excellent settling properties; e.g., after 50 days of operation, 90% of the sludge settles down at a velocity above 25 m h(-1) while 10% of the sludge had a sedimentation velocity higher than 108 m h(-1). Because the biomass is retained in the reactor, higher sulfide loading rates may be applied than to a conventional "free-cell" suspension. The maximum sulfide-loading rate reached was 14 g HS(-) L(-1) d(-1), whereas for a free-cell suspension a maximum loading rate of 6 g HS(-) L(-1) d(-1) was found. At higher loading rates, the upward velocities of the aerated suspension became too high so that sulfur sludge accumulated in the settling zone on top of the reactor. When the influent was supplemented with volatile fatty acids, heterotrophic sulfur and sulfate reducing bacteria, and possibly also (facultatively) heterotrophic Thiobacilli, accumulated within the sludge. This led to a serious deterioration of the system; i.e., the sulfur formed was increasingly reduced to sulfide, and also the formation rate of sulfur sludge declined. (c) 1997 John Wiley & Sons, Inc.

Mesophilic and thermophilic anaerobic digestion of biologically pretreated abattoir wastewaters in an upflow anaerobic filter

The hydrolysis pretreatment of abattoir wastewaters (AW), rich in organic suspended solids (fats and protein) was studied in static and stirred batch reactors without aeration in the presence of natural microbial population acclimated in a storage tank of AW. Microbial analysis showed that the major populations which contribute to the pretreatment of AW belong to the genera Bacillus. Contrary to the static pretreatment, the stirred conditions favoured the hydrolysis and solubilization of 80% of suspended matter into soluble pollution. The pretreated AW, in continuous stirred tank reactor (CSTR) at a hydraulic retention time (HRT) of 2 days, was fed to an upflow anaerobic filter (UAF) at an HRT of 2 days. The performance of anaerobic digestion of biologically pretreated AW was examined under mesophilic (37 degrees C) and thermophilic (55 degrees C) conditions. The shifting from a mesophilic to a thermophilic environment in the UAF was carried out with a short start-up of thermophilic condition. The UAF ran at organic loading rates (OLRs) ranging from 0.9 to 6g COD/Ld in mesophilic conditions and at OLRs from 0.9 to 9 g COD/Ld in thermophilic conditions. COD removal efficiencies of 80-90% were achieved for OLRs up to 4.5 g COD/Ld in mesophilic conditions, while the highest OLRs i.e. 9 g COD/Ld led to efficiencies of 70-72% in thermophilic conditions. The biogas yield in thermophilic conditions was about 0.32-0.45 L biogas/g of COD removed for OLRs up to 4.5 g COD/Ld. For similar OLR, the UAF in mesophilic conditions showed lower percentage of methanization. Mesophilic anaerobic digestion has been shown to destroy pathogens partially, whereas the thermophilic process was more efficient in the removal of indicator microorganisms and pathogenic bacteria at different organic loading rates.

Anaerobic treatment of poultry mortality in a temperature-phased leachbed-UASB system

Anaerobic digestion has been proposed as an alternative to the conventional disposal methods of burial, incineration, rendering and aerobic composting. A temperature-phased system consisting of one UASB (at 55 degrees C) and three leach-bed reactors (at ambient temperatures) was tested for its efficiencies in treating poultry mortality. The thermophilic UASB was difficult to start-up. It also showed signs of inhibited methanogenesis. Chemical parameters such as long chain fatty acids, volatile fatty acids and ammonia concentrations were all very high for the thermophilic UASB. Lowering its temperature to 35 degrees C enhanced its stability and improved its performances. Lowering the pH of the 55 degrees C UASB also improved its chemical oxygen demand (COD) reduction efficiency as well as its methane production rate. The results were compared to that of another similar system where the UASB reactor was maintained at 35 degrees C instead of at 55 degrees C.

Thermophilic anaerobic digestion of source-sorted organic fraction of household municipal solid waste: start-up procedure for continuously stirred tank reactor

Two feeding strategies for start-up of continuously stirred tank reactors (CSTR) treating source-sorted organic fraction of household municipal solid waste (SS-OFMSW) at 55 degrees C were evaluated. Two reactors were started up separately with a limited amount of initial inoculum (i.e. 10% of the final volume of 3.5l) and operated in a fed batch mode until the reactors were filled (30 days). A reference reactor was filled up with 3.5l of inoculum and fed at a constant rate (11.4 g volatile solids (VS)/d). Loading at progressively increasing rate (from 1.7 to 15 gVS/d), as calculated based on an activated biomass concept, showed superior process performance compared to a fixed feed rate (5.7 gVS/d). Methane yield of 0.32 m(3)/kg VS was produced during the start-up in reactor filled at progressively increasing rate and was comparable to the reference reactor. On the contrary, significant inhibition due to volatile fatty acid (VFA) build-up, mainly due to butyrate, was noticed in the reactor filled at constant rate. Thus, low initial and progressive increasing inoculum loading rate could be used as a strategy for a successful start-up of CSTR treating SS-OFMSW as it allowed a gradual acclimation of the biomass. Lab-scale results were further reaffirmed from the start-up of a full-scale plant (7000 m(3) total capacity) which was supplied with inoculum corresponding to approx. 16% of final volume and operated in a fed batch mode until the reactors were filled (58 days). Stable biogas production with low VFA (<3 g/L; based on titration method) were noticed during the start-up period when fed at progressively increasing rate. Thus, a controlled and reliable start-up procedure was found essential, which could allow rapid process stabilization and time to focus on other technical aspects of plant operation. In addition, the influence of substrate to inoculum amount (1.5-30% TS) and temperature (5-65 degrees C) on anaerobic degradation and methane production of SS-OFMSW was investigated in batch assays as a protocol for start-up procedure.

Anaerobic treatment of phenol in wastewater under thermophilic condition

Over 99% of phenol was effectively degraded in an upflow anaerobic sludge blanket (UASB) reactor at 55 degrees C with 40 h of hydraulic retention time (HRT) for a wastewater containing 630 mg/L of phenol, corresponding to 1500 mg/L of chemical oxygen demand (COD) and a loading rate of 0.9 g-COD/L/d. The maximum specific methanogenic activity (SMA) of the phenol-degrading sludge was 0.09 g-CH4-COD/g-volatile suspended solids (VSS)/d. Based on 16S rDNA analysis, a total of 21 operational taxonomy units (OTUs) were found in the sludge, of which eight (42.6% of the total population) were related to the sequences in the GenBank with similarity of over 97%, and 13 (79.6%) were affiliated with the known thermophilic species. Additional SMA data and phylogenetic analysis suggest that the degradation pathway of phenol for thermophilic sludge was likely via caproate, instead of benzoate as for the mesophilic sludge.

Strategies for changing temperature from mesophilic to thermophilic conditions in anaerobic CSTR reactors treating sewage sludge

Thermophilic anaerobic digestion presents an advantageous way for stabilization of sludge from wastewater treatment plants. Two different strategies for changing operational process temperature from mesophilic (37 degrees C) to thermophilic (55 degrees C) were tested using two continuous flow stirred tank reactors operated at constant organic loading rate of 1.38 g VS/l reactor/day and hydraulic retention time of 20 days. In reactor A, the temperature was increased step-wise: 37 degrees C-->42 degrees C-->47 degrees C-->51 degrees C-->55 degrees C. While in reactor B, the temperature was changed in one-step, from 37 degrees C to the desired temperature of 55 degrees C, The results showed that the overall adaptation of the process for the step-wise temperature increment took 70 days in total and a new change was applied when the process was stabilized as indicated by stable methane production and low volatile fatty acids concentrations. Although the one-step temperature increase caused a severe disturbance in all the process parameters, the system reached a new stable operation after only 30 days indicating that this strategy is the best in changing from mesophilic to thermophilic operation in anaerobic digestion plants.

Thermophilic biohydrogen production from glucose with trickling biofilter

Thermophilic H2 production from glucose was studied at 55-64 degrees C for 234 days using a continuous trickling biofilter reactor (TBR) packed with a fibrous support matrix. Important parameters investigated included pH, temperature, hydraulic retention time (HRT), and glucose concentration in the feed. The optimal pH and temperature were 5.5 and 60 degrees C, respectively. With decreasing HRT or increasing inlet glucose concentration, volumetric H2 production rate increased but the H2 production yield to glucose decreased gradually. The biogas composition was almost constant at 53 +/- 4% (v/v) of H2 and 47 +/- 4% (v/v) of CO2. No appreciable CH4 was detected when the reactor was under a normal operation. The carbon mass balance showed that, in addition to cell mass, lactate, n-butyrate, CO2, and acetate were major products that comprised more than 85% of the carbon consumed. The maximal volumetric H2 production rate and H2 yield to glucose were 1,050 +/- 63 mmol H2/l.d and 1.11 +/- 0.12 mol H2/mol glucose, respectively. These results indicate that the thermophilic TBR is superior to most suspended or immobilized reactor systems reported thus far. This is the first report on continuous H2 production by a thermophilic TBR system.

Perspectives for anaerobic digestion

The modern society generates large amounts of waste that represent a tremendous threat to the environment and human and animal health. To prevent and control this, a range of different waste treatment and disposal methods are used. The choice of method must always be based on maximum safety, minimum environmental impact and, as far as possible, on valorization of the waste and final recycling of the end products. One of the main trends of today's waste management policies is to reduce the stream of waste going to landfills and to recycle the organic material and the plant nutrients back to the soil. Anaerobic digestion (AD) is one way of achieving this goal and it will furthermore, reduce energy consumption or may even be net energy producing. This chapter aims at provide a basic understanding of the world in which anaerobic digestion is operating today. The newest process developments as well as future perspectives will be discussed.

Anaerobic granular sludge and biofilm reactors

The long retention time of the active biomass in the high-rate anaerobic digesters is the key factor for the successful application of the high rate anaerobic wastewater treatment. The long solids retention time is achieved due to the specific reactor configuration and it is enhanced by the immobilization of the biomass, which forms static biofilms, particle-supported biofilms, or granules depending on the reactor's operational conditions. The advantages of the high-rate anaerobic digestion over the conventional aerobic wastewater treatment methods has created a clear trend for the change of the role of the anaerobic digestion in the wastewater treatment plants from a pre-treatment method to the main biological treatment method. The application of staged high-rate anaerobic digesters has shown the larger potential among the recent developments in this direction. The most common high-rate anaerobic treatment systems based on anaerobic granular sludge and biofilm are described in this chapter. Emphasis is given to a) the Up-flow Anaerobic Sludge Blanket (UASB) systems, b) the main characteristics of the anaerobic granular sludge, and c) the factors that control the granulation process. Finally, the most innovative staged anaerobic digesters are also presented.

Aerobic waste activated sludge (WAS) for start-up seed of mesophilic and thermophilic anaerobic digestion

Since there are very limited numbers of thermophilic anaerobic digesters being operated, it is often difficult to start up a new one using sludge from an existing reactor as a seed. However, for obvious reasons it seems few attempts have been made to compare the start-up performance of thermophilic anaerobic digestion using different sources of seed sludges. The purpose of this study was to evaluate the start-up performance of anaerobic digestion using aerobic waste activated sludge (WAS) from a plant which has no anaerobic digesters and mesophilic anaerobic digested sludge (ADS) as the seed source at both mesophilic (35 degrees C) and thermophilic (55 degrees C) temperatures. In this study, two experiments were conducted. First, thermophilic anaerobic reactors were seeded with WAS (VSS = 4400 mg/L) and ADS (VSS = 14,500 mg/L) to investigate start-up performance with a feed of acetate as well as propionate. The results show that WAS started to produce CH4 soon after acetate feeding without a lag time, while ADS had a lag time of 10 days. When the feed was changed to propionate, WAS removed propionate down to below the detection limit of 10 mg/L, while ADS removed little propionate and produced little CH4. Second, in order to further compare the methanogenic activity of WAS and ADS, both mesophilic and thermophilic reactors were operated. WAS acclimated to anaerobic conditions shortly (< 5 days at both mesophilic and thermophilic) and after acclimating it produced more CH4 per unit amount of seeded VSS than ADS. WAS at mesophilic temperature biodegraded acetate at the same rate as for thermophilic. However WAS at mesophilic temperature biodegraded propionate at a much faster rate than at thermophilic. WAS as the seed source of anaerobic digestion resulted in much better performance than ADS at both mesophilic and thermophilic temperatures for both acetate and propionate metabolism.

In situ detection, isolation, and physiological properties of a thin filamentous microorganism abundant in methanogenic granular sludges: a novel isolate affiliated with a clone cluster, the green non-sulfur bacteria, subdivision I

We previously showed that very thin filamentous bacteria affiliated with the division green non-sulfur bacteria were abundant in the outermost layer of thermophilic methanogenic sludge granules fed with sucrose and several low-molecular-weight fatty acids (Y. Sekiguchi, Y. Kamagata, K. Nakamura, A. Ohashi, H. Harada, Appl. Environ. Microbiol. 65:1280-1288, 1999). Further 16S ribosomal DNA (rDNA) cloning-based analysis revealed that the microbes were classified within a unique clade, green non-sulfur bacteria (GNSB) subdivision I, which contains a number of 16S rDNA clone sequences from various environmental samples but no cultured representatives. To investigate their function in the community and physiological traits, we attempted to isolate the yet-to-be-cultured microbes from the original granular sludge. The first attempt at isolation from the granules was, however, not successful. In the other thermophilic reactor that had been treating fried soybean curd-manufacturing wastewater, we found filamentous microorganisms to outgrow, resulting in the formation of projection-like structures on the surface of granules, making the granules look like sea urchins. 16S rDNA-cloning analysis combined with fluorescent in situ hybridization revealed that the projections were comprised of the uncultured filamentous cells affiliated with the GNSB subdivision I and Methanothermobacter-like cells and the very ends of the projections were comprised solely of the filamentous cells. By using the tip of the projection as the inoculum for primary enrichment, a thermophilic, strictly anaerobic, filamentous bacterium, designated strain UNI-1, was successfully isolated with a medium supplemented with sucrose and yeast extract. The strain was a very slow growing bacterium which is capable of utilizing only a limited range of carbohydrates in the presence of yeast extract and produced hydrogen from these substrates. The growth was found to be significantly stimulated when the strain was cocultured with a hydrogen-utilizing methanogen, Methanothermobacter thermautotrophicus, suggesting that the strain is a sugar-fermenting bacterium, the growth of which is dependent on hydrogen consumers in the granules.

Cultivation and in situ detection of a thermophilic bacterium capable of oxidizing propionate in syntrophic association with hydrogenotrophic methanogens in a thermophilic methanogenic granular sludge

The thermophilic, anaerobic, propionate-oxidizing bacterial populations present in the methanogenic granular sludge in a thermophilic (55 degrees C) upflow anaerobic sludge blanket reactor were studied by cultivation and in situ hybridization analysis. For isolation of propionate-degrading microbes, primary enrichment was made with propionate as the sole energy source at 55 degrees C. After several attempts to purify the microbes, a thermophilic, syntrophic, propionate-oxidizing bacterium, designated strain SI, was isolated in both pure culture and coculture with Methanobacterium thermoautotrophicum. Under thermophilic (55 degrees C) conditions, strain SI oxidized propionate, ethanol, and lactate in coculture with M. thermoautotrophicum. In pure culture, the isolate was found to ferment pyruvate. 16S ribosomal DNA sequence analysis revealed that the strain was relatively close to members of the genus Desulfotomaculum, but it was only distantly related to any known species. To elucidate the abundance and spatial distribution of organisms of the strain SI type within the sludge granules, a 16S rRNA-targeted oligonucleotide probe specific for strain SI was developed and applied to thin sections of the granules. Fluorescence in situ hybridization combined with confocal laser scanning microscopy revealed that a number of rod-shaped cells were present in the middle and inner layers of the thermophilic granule sections and that they formed close associations with hydrogenotrophic methanogens. They accounted for approximately 1.1% of the total cells in the sludge. These results demonstrated that strain SI was one of the significant populations in the granular sludge and that it was responsible for propionate oxidation in the methanogenic granular sludge in the reactor.

Fluorescence in situ hybridization using 16S rRNA-targeted oligonucleotides reveals localization of methanogens and selected uncultured bacteria in mesophilic and thermophilic sludge granules

16S rRNA-targeted in situ hybridization combined with confocal laser scanning microscopy was used to elucidate the spatial distribution of microbes within two types of methanogenic granular sludge, mesophilic (35 degrees C) and thermophilic (55 degrees C), in upflow anaerobic sludge blanket reactors fed with sucrose-, acetate-, and propionate-based artificial wastewater. The spatial organization of the microbes was visualized in thin sections of the granules by using fluorescent oligonucleotide probes specific to several phylogenetic groups of microbes. In situ hybridization with archaeal- and bacterial-domain probes within granule sections clearly showed that both mesophilic and thermophilic granules had layered structures and that the outer layer harbored mainly bacterial cells while the inner layer consisted mainly of archaeal cells. Methanosaeta-, Methanobacterium-, Methanospirillum-, and Methanosarcina-like cells were detected with oligonucleotide probes specific for the different groups of methanogens, and they were found to be localized inside the granules, in both types of which dominant methanogens were members of the genus Methanosaeta. For specific detection of bacteria which were previously detected by whole-microbial-community 16S ribosomal DNA (rDNA)-cloning analysis (Y. Sekiguchi, Y. Kamagata, K. Syutsubo, A. Ohashi, H. Harada, and K. Nakamura, Microbiology 144:2655-2665, 1998) we designed probes specific for clonal 16S rDNAs related to unidentified green nonsulfur bacteria and clones related to Syntrophobacter species. The probe designed for the cluster closely related to Syntrophobacter species hybridized with coccoid cells in the inner layer of the mesophilic granule sections. The probe for the unidentified bacteria which were clustered with the green nonsulfur bacteria detected filamentous cells in the outermost layer of the thermophilic sludge granule sections. These results revealed the spatial organizations of methanogens and uncultivated bacteria and their in situ morphologies and metabolic functions in both mesophilic and thermophilic granular sludges.

Limitations of thermophilic anaerobic wastewater treatment and the consequences for process design

Thermophilic anaerobic digestion offers an attractive alternative for the treatment of medium- and high-strength wastewaters. However, literature reports reveal that thermophilic wastewater treatment systems are often more sensitive to environmental changes than the well-defined high-rate reactors at the mesophilic temperature range. Also, in many cases a poorer effluent quality is experienced while the carry over of suspended solids in the effluent is relatively high. In this paper recent achievements are discussed regarding the process stability of thermophilic anaerobic wastewater treatment systems. Laboratory experiments reveal a relatively low sensitivity to temperature changes if high-rate reactors with immobilized biomass are used. Other results show that if a staged process is applied, thermophilic reactors can be operated for prolonged periods of time under extreme loading conditions (80-100 kg chemical oxygen demand.m-3.day-1), while the concentrations of volatile fatty acids in the effluent remain at a low level.

Acetate treatment in 70 degrees C upflow anaerobic sludge-blanket (UASB) reactors: start-up with thermophilic inocula and the kinetics of the UASB sludges

This study focused on the use the thermophilic anaerobic granulae in the start-up of 70 degrees C acetate-fed upflow anaerobic sludge-blanket (UASB) reactors and the kinetics of granulae grown at 70 degrees C. In the UASB reactors, chemical oxygen demand removal commenced within 48 h of the start-up. The maximum reduction in chemical oxygen demand was 84% with the feed containing yeast and 71% without a yeast supplement. In the bioassays, the yeast-grown sludge converted 98% of the acetate consumed to methane as compared to 92% for the sludge grown without yeast. The highest initial specific methane production rate (mu-CH4) of the UASB sludges grown at 70 degrees C was 0.088 h(-1) at an acetate concentration of 4.6mM. The higher initial acetate concentration was found to prolong the lag-phase in methane production significantly and to decrease mu-CH4. The half-saturation constant (Ks), the inhibition constant (Ki), the inhibition response coefficient (n) and the mu-CH4-max, calculated according to a modified Haldane equation, were 1.5 mM, 2.8 mM, 0.8 and 0.28 h(-1), respectively. The prolonged starvation of the 70 degrees C sludge (15 days) decreased the mu-CH4 from about 0.022 h(-1) to 0.011 h(-1) and increased the lag phase in methane production from 6 h to 24 h as compared with non-starved sludge.

Granulation in thermophilic upflow anaerobic sludge blanket (UASB) reactors

The state of the art for thermophilic UASB reactors is discussed focusing on the start-up of UASB reactors, the influence of the waste water composition and temperature on the development and maintenance of thermophilic granules, and the microbial composition and structure of thermophilic granules.

Anaerobic digestion and wastewater treatment systems

Upflow Anaerobic Sludge Bed (UASB) wastewater (pre-)treatment systems represent a proven sustainable technology for a wide range of very different industrial effluents, including those containing toxic/inhibitory compounds. The process is also feasible for treatment of domestic wastewater with temperatures as low as 14-16 degrees C and likely even lower. Compared to conventional aerobic treatment systems the anaerobic treatment process merely offers advantages. This especially is true for the rate of start-up. The available insight in anaerobic sludge immobilization (i.e. granulation) and growth of granular anaerobic sludge in many respects suffices for practice. In anaerobic treatment the immobilization of balanced microbial communities is essential, because the concentration of intermediates then can be kept sufficiently low. So far ignored factors like the death and decay rate of organisms are of eminent importance for the quality of immobilized anaerobic sludge. Taking these factors into account, it can be shown that there does not exist any need for 'phase separation' when treating non- or slightly acidified wastewaters. Phase separation even is detrimental in case the acidogenic organisms are not removed from the effluent of the acidogenic reactor, because they deteriorate the settleability of granular sludge and also negatively affect the formation and growth of granular sludge. The growing insight in the role of factors like nutrients and trace elements, the effect of metabolic intermediates and end products opens excellent prospects for process control, e.g. for the anaerobic treatment of wastewaters containing mainly methanol. Anaerobic wastewater treatment can also profitably be applied in the thermophilic and psychrophilic temperature range. Moreover, thermophilic anaerobic sludge can be used under mesophilic conditions. The Expanded Granular Sludge Bed (EGSB) system particularly offers big practical potentials, e.g. for very low strength wastewaters (COD << 1 g/l) and at temperatures as low as 10 degrees C. In EGSB-systems virtually all the retained sludge is employed, while compared to UASB-systems also a substantially bigger fraction of the immobilized organisms (inside the granules) participates in the process, because an extraordinary high substrate affinity prevails in these systems. It looks necessary to reconsider theories for mass transfer in immobilized anaerobic biomass. Instead of phasing the digestion process, staging of the anaerobic reactors should be applied. In this way mixing up of the sludge can be significantly reduced and a plug flow is promoted. A staged process will provide a higher treatment efficiency and a higher process stability. This especially applies for thermophilic systems.

Effects of acetate, propionate, and butyrate on the thermophilic anaerobic degradation of propionate by methanogenic sludge and defined cultures

The effects of acetate, propionate, and butyrate on the anaerobic thermophilic conversion of propionate by methanogenic sludge and by enriched propionate-oxidizing bacteria in syntrophy with Methanobacterium thermoautotrophicum delta H were studied. The methanogenic sludge was cultivated in an upflow anaerobic sludge bed (UASB) reactor fed with propionate (35 mM) as the sole substrate for a period of 80 days. Propionate degradation was shown to be severely inhibited by the addition of 50 mM acetate to the influent of the UASB reactor. The inhibitory effect remained even when the acetate concentration in the effluent was below the level of detection. Recovery of propionate oxidation occurred only when acetate was omitted from the influent medium. Propionate degradation by the methanogenic sludge in the UASB reactor was not affected by the addition of an equimolar concentration (35 mM) of butyrate to the influent. However, butyrate had a strong inhibitory effect on the growth of the propionate-oxidizing enrichment culture. In that case, the conversion of propionate was almost completely inhibited at a butyrate concentration of 10 mM. However, addition of a butyrate-oxidizing enrichment culture abolished the inhibitory effect, and propionate oxidation was even stimulated. All experiments were conducted at pH 7.0 to 7.7. The thermophilic syntrophic culture showed a sensitivity to acetate and propionate similar to that of mesophilic cultures described in the literature. Additions of butyrate or acetate to the propionate medium had no effect on the hydrogen partial pressure in the biogas of an UASB reactor, nor was the hydrogen partial pressure in propionate-degrading cultures affected by the two acids.(ABSTRACT TRUNCATED AT 250 WORDS)