Short Start-up Period Research Articles

Deammonification process start-up after enrichment of anammox microorganisms from reject water in a moving-bed biofilm reactor

Deammonification via intermittent aeration in biofilm process for the treatment of sewage sludge digester supernatant (reject water) was started up using two opposite strategies. Two moving-bed biofilm reactors were operated for 2.5 years at 26 (±0.5)°C with spiked influent (and hence free ammonia (FA)) addition. In the first start-up strategy, an enrichment of anammox biomass was first established, followed by the development of nitrifying biomass in the system (R1). In contrast, the second strategy aimed at the enrichment of anammox organisms into a nitrifying biofilm (R2). The first strategy was most successful, reaching higher maximum total nitrogen (TN) removal rates over a shorter start-up period. For both reactors, increasing FA spiking frequency and increasing effluent concentrations of the anammox intermediate hydrazine correlated to decreasing aerobic nitrate production (nitritation). The bacterial consortium of aerobic and anaerobic ammonium oxidizing bacteria in the bioreactor was determined via denaturing gel gradient electrophoresis, polymerase chain reaction and pyrosequencing. In addition to a shorter start-up with a better TN removal rate, nitrite oxidizing bacteria (Nitrospira) were outcompeted by spiked ammonium feeding from R1.

Recycled paper mill effluent treatment in a modified anaerobic baffled reactor: start-up and steady-state performance

Start-up period is considered to be the most unstable and difficult stage in anaerobic process and usually takes a long time due to slow-degree adaptation of anaerobic microorganisms. In order to achieve a shorter start-up period, a novel modified anaerobic baffled reactor (MABR) has been developed in this study, where each modified baffle has its own characteristics (form/shape) to facilitate a treatment of recycled paper mill effluent (RPME). The results of physico-chemical characteristics showed that effluent from recycled paper mill consisted of 4328 mg L−1 chemical oxygen demand (COD), 669 mg L−1 biochemical oxygen demand and 501 mg L−1 volatile fatty acid. It also consisted of variety of heavy metals such as zinc, magnesium, iron and nickel at concentrations of 1.39, 12.19, 2.39 and 0.72 mg L−1, respectively. Performance of MABR during the start-up period showed that methane production reached 34.7% with COD removal of 85% at steady state. The result indicates that MABR was successfully operated during the start-up period in treating RPME within a period of less than 30 days.

High NH4+-N concentration wastewater treatment by shortcut nitrification–denitrification using a system of A/O inner loop fluidized bed biofilm reactors

In this experiment, a rapid mass-transfer inner loop fluidized bed biofilm reactor (ILFBBR) was employed to treat synthetic high ammonia nitrogen-containing (NH(4)(+)-N) wastewater by shortcut nitrification-denitrification. The reactor operation was stable after a short start-up period. Ammonia oxidizing bacteria (AOB) were predominant and 65% nitrite (NO(2)(-)-N/NO(x)(-)-N) levels were achieved. During the nitrification-denitrification period, the removal rates of NH(4)(+)-N and total nitrogen (TN) reached 94 and 82%, respectively. From the material balance, it was indicated that 87% of NH(4)(+)-N was removed by shortcut nitrification. The features of ILFBBR and the benefits of shortcut nitrification were combined in this experiment, and showed an excellent removal of NH(4)(+)-N from high-concentration NH(4)(+)-N wastewater.

Rapid start-up of a sulfidogenic biofilm reactor: overcoming low acetate consumption

BACKGROUND Sulfate-reducing fluidized bed reactors represent an alternative for the treatment of wastewaters that contain dissolved metals. However, the low acetate consumption achieved through sulfate reduction affects the organic matter removal efficiency. The aim of this present work was to develop a sulfidogenic biofilm able to consume acetate via sulfate reduction within a short start-up period (21 days). Three experiments were conducted in a down-flow fluidized bed reactor with different acetate/lactate proportions in the feed (50/50, 80/20 and 90/10). Reduction of the influent pH from 6.0 to 4.0 was also studied at the higher acetate content. RESULTS Organic matter oxidation efficiency was similar in the three experiments (∼67%), nonetheless the sulfate reduction rate was higher in the experiments with 80 and 90% acetate in the feed (744 and 730 mg L−1 d−1). Acetate oxidation via sulfate reduction was highest (39% of inlet) at the ratio 90/10, at which the biofilm specific sulfate reducing activity with acetate was 4.3 times higher than that developed at 50/50. Influent pH reduction to 4.0 was not detrimental to acetate consumption via sulfate reduction, which was 56%. Analysis of the biofilm through DGGE found a similar community in the three experiments and the presence of acetotrophic microorganisms affiliated to Desulfobacca acetoxidans. CONCLUSIONS Limiting the substrate (lactate) was an appropriate strategy to enrich acetate-consuming sulfate reducers and improve the low acetate removal efficiency that sulfate-reducing reactors face. © 2012 Society of Chemical Industry

Anaerobic ammonium oxidation improvement via a novel capsule bioreactor

This study developed a capsule bioreactor made from polyvinyl alcohol (PVA) to entrap anaerobic ammonium oxidation (ANAMMOX) bacteria for the removal of nitrogen from synthetic wastewater. Experimental results demonstrate that the ANAMMOX bacteria were entrapped inside the capsule and not washed out from the bioreactor. This method also avoids damaging the ANAMMOX bacteria during immobilization. The proposed bioreactor also has a shorter start-up period. The diffusion rate of ammonium and nitrite from the bulk solution through the capsule determined the rate of the ANAMMOX reaction. The optimal ratio of was approximately 1 for the bioreactor. In addition, the capsule protected the ANAMMOX bacteria from nitrite inhibition. The bioreactor achieved a high stable nitrogen removal rate (5.8 Kg-N m−3 day−1) at high nitrite levels (up to 600 mg-N L−1 in the influent). Therefore, the proposed capsule bioreactor has considerable potential for actual nitrogen removal applications.

Denitritation of a high-strength nitrite wastewater in a sequencing batch reactor using different organic carbon sources

The use of different carbon sources (ethanol, acid-fermented primary sludge centrate, acid-fermented secondary sludge centrate, glycerol and landfill leachate) in heterotrophic denitrification from nitrite (denitritation) was studied in a sequencing batch reactor, operated without pH control. Complete denitritation of a high-strength nitrite wastewater was achieved using these organic carbon sources with the exception of fermented secondary sludge centrate. Loading rates around 0.2gNL−1d−1 were obtained for glycerol, landfill leachate and ethanol after a short start-up period of 20 days. The maximum specific nitrite removal rate of 0.25gNg−1VSSd−1 was achieved for glycerol, while values between 0.13 and 0.17gNg−1VSSd−1 were obtained using ethanol, landfill leachate and fermented primary sludge centrate. The COD/N ratio consumed varied between 3.0 for ethanol and 8.8 for landfill leachate. The denitritation rates and the required COD/N ratio for each carbon source are reported for the first time – they can be used for the scale-up of the denitritation process.

Hidrogramas e sedimentogramas associados à erosão hídrica em solo cultivado com diferentes sequências culturais, com diferentes condições físicas na superfície

Estudos hidrossedimentológicos detalhados são de grande valia para o melhor entendimento e controle do processo de erosão hídrica e, por conseguinte, para se aprofundar a pesquisa no assunto e, assim, praticar a conservação do solo e da água de modo mais eficaz e duradouro. Considerando isso, realizou-se este trabalho com o objetivo de desenvolver hidrogramas (taxas instantâneas de descarga da enxurrada versus tempo) e sedimentogramas (concentrações instantâneas de sedimento na enxurrada e taxas instantâneas de perda de solo versus tempo) individualizados (cada repetição de tratamento), associados à erosão hídrica ocorrida em solo cultivado com diferentes sequências culturais (gramíneas e leguminosas de inverno e verão, implantadas em semeadura direta, nos modos de cultivo isolado e consorciado), com diferentes condições físicas na superfície (solo não mobilizado, solo recém-escarificado, solo previamente escarificado e solo recém-gradeado, com presença e ausência de crosta e de completa, pouca e nenhuma cobertura por resíduos culturais). O estudo foi desenvolvido em campo, na EEA/UFRGS, em Eldorado do Sul (RS), usando-se chuva simulada e um Argissolo Vermelho distrófico típico com textura franco-argiloarenosa na camada superficial e declividade média de 0,115 m m-1. No início da pesquisa esse solo encontrava-se bastante degradado. As chuvas simuladas (seis no total, sendo uma para cada teste de erosão) foram aplicadas com o aparelho simulador de braços rotativos, todas elas na intensidade planejada de 64 mm h-1 (neste trabalho usaram-se as intensidades observadas das chuvas, as quais variaram de 59,1 a 74,6 mm h-1) e com duração variando de 1 a 3 h (devido almejar-se atingir a condição de equilíbrio da enxurrada em todos os testes de erosão). Observou-se que os hidrogramas e sedimentogramas, de modo geral, resultaram coerentes com as condições das quais foram desenvolvidos. Assim, na maior parte das vezes, os hidrogramas diferenciaram-se mais entre os testes de erosão do que entre os tratamentos de sequência cultural, e o inverso ocorreu com os sedimentogramas. As superfícies de solo não mobilizadas e com pequena rugosidade e pouca cobertura, de modo geral, proporcionaram hidrogramas e sedimentogramas com menor tempo de partida e maior magnitude, independentemente da presença ou ausência de crosta e do tipo de sequência cultural. As superfícies de solo recém-mobilizadas e com média e grande rugosidade, de modo geral, proporcionaram hidrogramas e sedimentogramas com maior tempo de partida e menor magnitude, praticamente independentemente da cobertura e do tipo de sequência cultural. As superfícies de solo com completa cobertura tiveram suas enxurradas diminuídas e suas erosões eliminadas, independentemente da sua mobilização e do tipo de sequência cultural. A sequência cultural com teosinto proporcionou hidrogramas e sedimentogramas com os maiores tempos de partida e as menores magnitudes, seguida das com milho+feijão-miúdo e milheto, as quais diferenciaram pouco entre si. As repetições dos tratamentos proveram valores das taxas instantâneas de descarga da enxurrada que se pareceram mais e se distribuíram no tempo de modo mais uniforme do que os providos para as correspondentes concentrações instantâneas de sedimento e taxas instantâneas de perda de solo. Os dados obtidos foram valiosos no que diz respeito a poder entender melhor a variação comumente observada nos resultados de pesquisas de erosão hídrica realizadas em campo.

Bioaugmented sulfur-oxidizing denitrification system with Alcaligenes defragrans B21 for high nitrate containing wastewater treatment

The performance of enriched sludge augmented with the B21 strain of Alcaligenes defragrans was compared with that of enriched sludge, as well as with pure Alcaligenes defragrans B21, in the context of a sulfur-oxidizing denitrification (SOD) process. In synthetic wastewater treatment containing 100-1,000 mg NO3-N/L, the single strain-seeded system exhibited superior performance, featuring higher efficiency and a shorter startup period, provided nitrate loading rate was less than 0.2 kg NO3-N/m(3) per day. At nitrate loading rate of more than 0.5 kg NO3-N/m(3) per day, the bioaugmented sludge system showed higher resistance to shock loading than two other systems. However, no advantage of the bioaugmented system over the enriched sludge system without B21 strain was observed in overall efficiency of denitrification. Both the bioaugmented sludge and enriched sludge systems obtained stable denitrification performance of more than 80% at nitrate loading rate of up to 2 kg NO3-N/m(3) per day.

Pressures acting in counter-current spontaneous imbibition

Four water/oil and four oil/air linear counter-current spontaneous imbibition experiments were performed on Berea sandstone cores with permeabilities ranging from 0.065 to 1.094 μm 2. The cores were initially 100% saturated with non-wetting phase and all faces except one end were sealed. The experiments showed a clear frontal displacement mechanism. Capillary pressure was the driving force of the imbibition process. As well as viscous drag in both phases between the imbibition front and the open face, there is a significant opposing capillary back pressure associated with production of non-wetting phase at the open face. The location of the imbibition front, the overall changes in core saturation, and the pressure in the nonwetting phase in the dead end space ahead of the imbibition front, were monitored during the course of imbibition. The dead end pressure was essentially constant after a short start-up period. The distance advanced by the imbibition front was proportional to the square root of time. Based on the assumption that the properties of Berea sandstone of different permeabilities can be scaled, the experimental data were matched by numerical simulation to predict the saturation and pressure profiles, the saturation and capillary pressure at the imbibition front, and the capillary back pressure at the open face. The ratio of the capillary back pressure to the estimated capillary pressure at the imbibition front ranged from approximately 1/3 to 2/5, for oil displacing air, to approximately 1/9 to 1/4, for water displacing oil.

Development of microbial community structure and actvity in a high-rate anaerobic bioreactor at 18 °C

Anaerobic digestion in the psychrophilic (< 20 °C) or sub-mesophilic temperature range has recently been proven as an effective treatment option for the mineralization of a wide variety of problematic wastewaters. In this study, an expanded granular sludge bed- anaerobic filter (EGSB-AF) bioreactor was seeded with a full-scale, mesophilic sludge and employed to evaluate the long-term operational potential, and underlying microbial ecology, of this approach for the treatment of a medium-strength (5 g chemical oxygen demand [COD] l −1), synthetic, volatile fatty acid-based wastewater. Throughout the trial period of 625 days, extended intervals of consistently stable and efficient wastewater treatment were sustained. These results were highlighted by a short start-up period (21 d), low hydraulic retention times (4.88 h), high organic (up to 24.64 kg COD m −3 d −1), and volumetric loading rates (up to 4.92 m 3 m −3 d −1). A stable, well-settling granular sludge bed was maintained in the bioreactor for the majority of the trial; however, reduced treatment efficiency and biomass washout were observed at an imposed OLR of 36.96 kg COD m −3 d −1. The microbial biomass in the bioreactor was investigated using maximum specific methanogenic activity assays and polymerase chain reaction-denaturing gradient gel electrophoresis. A temporal succession of both the bacterial and archaeal populations was noted during the trial, compared to the seed sludge, in response to bioreactor operation at lower temperatures, loading rate increases and to VFA accumulation in the bioreactor. During the trial, an increased contribution of hydrogenotrophic methanogenesis as a pathway of methane production was observed, along with the overall emergence of a highly active psychrotolerent—though still mesophilic biomass.

A Pilot-Scale Rotating Drum Biotrickling Filter for Removing Gaseous Styrene

A new type of biofilter, the rotating drum biotrickling filter (RDBF) system, was developed and operated to remove styrene from waste gas stream. Porous polyurethane foam sheets were used as a packing material for the RDBF and a pure culture of the Gram-positive bacterium Brevibacillus sp. SP1 was as an inoculum. The reactor showed a short start-up period of 18 days. Once uniform biofilms were developed on the packing, a high and stable removal of styrene over 95 % was observed at an incoming concentration of 200 ppmv and a retention time of 0.5 min. The maximum elimination capacity was estimated to be 125 g/m3/hr. The outstanding performance was attributed to an efficient gas-liquid mass transfer and proper supply of nutrient solution to the packing during the rotation of the drum. However, this performance of the RDBF was not maintained longer than 7 days because of the clogging of the open pores in the polyurethane foam due to an excessive growth of the biofilms. This result indicates that the RDBF has great potential as a gas purification system if a proper method to control the biofilm growth is developed.

Enhancement of the performance of an anaerobic sequencing batch reactor treating low-strength wastewater through implementation of a variable stirring rate program

This work focuses on enhancement of the performance of an anaerobic sequencing batch reactor with a six-vertical-blade-disk-turbine impeller, containing granulated biomass treating low-strength synthetic wastewater, through a study of the feasibility of implementing a variable stirring rate program. The reactor was operated at 30ºC and a six-hour cycle was used to treat approximately 2.0 L of the synthetic substrate with a chemical oxygen demand (COD) of nearly 500 mg/L. Two different stirring rate program were implemented: a constant rate of 50 rpm and a variable rate consisting of 75 rpm for one hour, 50 rpm for four hours and 25 rpm for 0.5 hour. The last 0.5 hour of the cycle was used for the settling step. In both cases, a very short start-up period and unfiltered and filtered substrate removal efficiencies of 81% and 88%, respectively, were attained. However, use of the variable stirring rate enhanced efficiency of the reactor dynamics without impairing biomass morphology, thus resulting in a reduction in the total cycle time and a possible decrease in energy consumption. Additionally, a simplified model of the anaerobic metabolic activity, using apparent kinetic parameters, was proposed as a consecutive first-order kinetic model with substrate and total volatile acid residual concentrations in order to analyze how the variable stirring rate affects reactor performance.

Steady-state and transient-state performance of a biotrickling filter treating chlorobenzene-containing waste gas.

Biotrickling filter (BTF) technology was applied for the treatment of waste gas containing a mixture of chlorobenzene and 1,2-dichlorobenzene. An adapted microbial community was immobilised on a structured packing material. The strategy followed was to reach high removal efficiencies at initially low mass loading rates followed by an increase of the latter. This procedure was successful and resulted in a short start-up period of only 2 weeks. A 3-month operation under steady-state conditions showed good performance, with >95% removal efficiency at a mass loading rate of 1,800 g m(-3) day(-1). Dimensionless concentration profiles showed that the chlorobenzenes were simultaneously degraded. Low dissolved organic carbon of 15 mg l(-1) and stoichiometric chloride concentrations in the trickling liquid indicated complete mineralisation of the pollutant. Transient-state experiments with five times higher mass loading rates caused a decrease in the removal efficiency that recovered rapidly once the mass loading rate returned to its original steady-state level. A progressive increase of the mass loading rate in a long-term performance experiment showed that the removal efficiency could be kept stable between 95 and 99% at loads of up to 5,200 g m(-3) day(-1) over several days. Above this mass loading rate, the elimination capacity did not increase any further. These results demonstrated that with a well-adapted inoculum and optimal operation parameters, a BTF system with excellent performance and stability that efficiently removes a mixture of chlorobenzene vapours from air can be obtained.

The Team Nutrition Pilot Study: Lessons Learned from Implementing a Comprehensive School-Based Intervention

Team Nutrition (TN) is an educational and promotional initiative developed by the US Department of Agriculture to change children's eating behaviors through social marketing techniques. This article reports on the process evaluation of a TN pilot project targeting students in kindergarten to grade 4 and systematically documents the implementation experience. Even with a very short start-up period, schools implemented most components of this multichannel nutrition intervention and formed new, supportive relationships with local media and community partners. School teachers and administrators, along with foodservice professionals, generally expressed support for and satisfaction with TN, citing the positive experience and gains for students. The lessons learned from this study highlight the management and organizational issues involved in a comprehensive intervention. These include the importance of local coordinators to support and create a bridge between teachers and cafeteria staff and to forge links with key external partners. To function effectively, coordinators themselves may need training in coalition building and working with media. Relationships formed with parents, local businesses, other educational institutions, health organizations, and the media offer promise for helping to sustain nutrition education efforts. The TN process evaluation identified multiple ideas for pursuing these partnerships more successfully.

Influence of agitation rate on the performance of a stirred anaerobic sequencing batch reactor containing immobilized biomass

The present work reports on the influence of the mechanical agitation rates on the performance of a stirred anaerobic sequencing batch reactor containing immobilized biomass on polyurethane foam, as inert support, treating synthetic domestic wastewater. The reactor was operated at 30 degrees C and an 8-hour cycle was used to treat approximately 0.5 L of the synthetic substrate with a COD concentration of nearly 500 mg/L. The studied agitation rates ranged from no agitation to 750 rpm. The system attained non-filtered substrate removal efficiency greater than 83% when agitation was employed. A very short start-up period and good solid retention could be observed. The use of agitation increased the efficiency of the reactor and enabled reduction of the total cycle time. An empirical equation and a first-order kinetic model are proposed to analyze the influence of agitation rates on the reactor's performance.

Treatment of Domestic Sewage in Horizontal-Flow Anaerobic Immobilized Biomass (HAIB) Reactor

This paper focuses on the evaluation of the start-up period and the performance of a pilot-scale horizontal-flow anaerobic immobilized biomass (HAIB) reactor treating pre-screened domestic sewage. The pilot-scale HAIB reactor comprises a 14.5 cm internal diameter PVC tube 14.4 m long divided into five stages of 2.88 m each. Polyurethane foam cubic matrices with 1 cm sides were used as support for biomass immobilization. The reactor was operated at the mean hydraulic detention time of 4.3 hours and the experimental results presented refer to 15 weeks of operation at mean sewage temperature of 25°C and mean liquid flow rate of 20 l h−1. The mean chemical oxygen demand (COD) of the sewage, based on composed samples, was found to be 350 mg l−1. A short start-up period lasting nearly 8 weeks was observed by monitoring several parameters such as COD, biogas composition, methane concentration and total volatile acid (TVA) concentration. By the end of the start-up period onward, the effluent COD attained approximately constant values of 100 mg l−1 and 75 mg l−1 for non-filtered and filtered samples.

Performance of horizontal-flow anaerobic immobilized sludge (HAIS) reactor treating synthetic substrate subjected to decreasing COD to sulfate ratios

The performance of a bench-scale horizontal-flow anaerobic immobilized sludge (HAIS) reactor treating a synthetic substrate under increasing influent sulfate (SO42-) concentrations was investigated. The synthetic substrate was composed of glucose, methanol and ammonium acetate, besides bicarbonate and trace metal nutritional solution. The reactor was filled with polyurethane foam cubic matrices for biomass immobilization. Influent chemical oxygen demand (COD) was kept almost constant along the experiments (2162 ± 250 mg.l−1) while influent sulfate concentration was increased from 9 to 501 mg.l−1, resulting in COD/SO42- ratio of 249, 66, 19.7 and 4.3 in the four experimental phases tested. After a short start-up period, no significant variations in COD removal efficiency were observed for the COD to sulfate ratios evaluated. Although sulfate reduction was expected to interfere with the methanogenic process, detrimental effects on the overall reactor performance were not observed. Moreover, monitoring parameters indicated that the reactor achieved stable operational conditions immediately after short transient periods following the increase of influent sulfate concentrations. Microscopic analysis of the sludge within the reactor permitted to observe the presence of both methanogenic and sulfate reducing bacteria, indicating that syntrophism and not competition seemed to be the predominant relationship between these two groups under the COD to sulfate ratios assayed.

Performance of horizontal-flow anaerobic immobilized sludge (HAIS) reactor treating synthetic substrate subjected to decreasing COD to sulfate ratios

2−) concentrations was investigated. The synthetic substrate was composed of glucose, methanol and ammonium acetate, besides bicarbonate and trace metal nutritional solution. The reactor was filled with polyurethane foam cubic matrices for biomass immobilization. Influent chemical oxygen demand (COD) was kept almost constant along the experiments (2162 ± 250 mg.l−1) while influent sulfate concentration was increased from 9 to 501 mg.l−1 resulting in COD/SO42− ratio of 249, 66, 19.7 and 4.3 in the four experimental phases tested. After a short start-up period, no significant variations in COD removal efficiency were observed for the COD to sulfate ratios evaluated. Although sulfate reduction was expected to interfere with the methanogenic process, detrimental effects on the overall reactor performance were not observed. Moreover, monitoring parameters indicated that the reactor achieved stable operational conditions immediately after short transient periods following the increase of influent sulfate concentrations. Microscopic analysis of the sludge within the reactor permitted to observe the presence of both methanogenic and sulfate reducing bacteria, indicating that syntrophism and not competition seemed to be the predominant relationship between these two groups under the COD to sulfate ratios assayed.

Methanogenic population dynamics during start-up of anaerobic digesters treating municipal solid waste and biosolids.

An aggressive start-up strategy was used to initiate codigestion in two anaerobic, continuously mixed bench-top reactors at mesophilic (37 degrees C) and thermophilic (55 degrees C) conditions. The digesters were inoculated with mesophilic anaerobic sewage sludge and cattle manure and were fed a mixture of simulated municipal solid waste and biosolids in proportions that reflect U.S. production rates. The design organic loading rate was 3.1 kg volatile solids/m3/day and the retention time was 20 days. Ribosomal RNA-targeted oligonucleotide probes were used to determine the methanogenic community structure in the inocula and the digesters. Chemical analyses were performed to evaluate digester performance. The aggressive start-up strategy was successful for the thermophilic reactor, despite the use of a mesophilic inoculum. After a short start-up period (20 days), stable performance was observed with high gas production rates (1.52 m3/m3/day), high levels of methane in the biogas (59%), and substantial volatile solids (54%) and cellulose (58%) removals. In contrast, the mesophilic digester did not respond favorably to the start-up method. The concentrations of volatile fatty acids increased dramatically and pH control was difficult. After several weeks of operation, the mesophilic digester became more stable, but propionate levels remained very high. Methanogenic population dynamics correlated well with performance measures. Large fluctuations were observed in methanogenic population levels during the start-up period as volatile fatty acids accumulated and were subsequently consumed. Methanosaeta species were the most abundant methanogens in the inoculum, but their levels decreased rapidly as acetate built up. The increase in acetate levels was paralleled by an increase in Methanosarcina species abundance (up to 11.6 and 4.8% of total ribosomal RNA consisted of Methanosarcina species ribosomal RNA in mesophilic and thermophilic digesters, respectively). Methanobacteriaceae were the most abundant hydrogenotrophic methanogens in both digesters, but their levels were higher in the thermophilic digester.

Microbial colonization of polyurethane foam matrices in horizontal-flow anaerobic immobilized-sludge reactor

This paper presents the anaerobic biomass characterization and the bacterial framework inside polyurethane foam matrices taken from a horizontal-flow anaerobic immobilized-sludge (HAIS) reactor treating a glucose-based substrate. Ultrastructure polyurethane foam analyses carried out using scanning electron microscopy (SEM) in samples treated with hexamethyldisylazane showed three different patterns of biomass retention inside the polyurethane foam matrices: micro-granules ranging from 270 μm to 470 μm were entrapped in the porous medium thin multi-cellular films were attached to the inner surface, and individual cells adhered to the support. The use of SEM and epifluorescence microscopy permitted inferences to be made on the bacteriological composition of the immobilized sludge formed by different morphotypes (rods, cocci and filaments) and on the ecological significance of their framework inside the matrices. Polyurethane matrices were found to offer excellent conditions for anaerobic growth and retention, favoring the flux of substrate and products. Such outstanding characteristics were confirmed by the short start-up period observed during the operation of the HAIS reactor.