Formulation of a protocol to evaluate the aerobic granulation potential (AGP) of an inoculum.

This paper proposes and develops a protocol for measuring the aerobic granulation potential of sludge, aiming to provide an affordable and simple alternative that can facilitate the development of aerobic granulation technology. In this sense, the protocol comprises a set of parameters and considerations that interact to create a controlled environment and stimulate cell population clustering. All of this is done in the context of procedural simplicity, low cost, and the speed at which results are obtained. The protocol is essentially a three-stage method: preparation of the substrate, adaptation of the inoculum, and implementation of the protocol. Simple parameters were measured to evaluate the granulation process: SVI, settling velocity, and morphological parameters. The protocol was validated according to optimal ranges and criteria previously established in the literature. For this purpose, an activated sludge inoculum from a domestic wastewater treatment plant was submitted to the protocol, obtaining an optimal response of the biomass (SVI5 =13.90 mL g-1, settling velocity= 25,79 m h-1, Diameter > 0.2 mm) in a relatively short time (7 d). The results show that this protocol can constitute a tool for evaluation and decision-making using traditional laboratory equipment and is applicable at different scales.

Anaerobic Biodegradation of Biodiesel Industry Wastewater in Mesophilic and Thermophilic Fluidized Bed Reactors: Enhancing Treatment and Methane Recovery.

In the past few years, the extraction of value-added compounds from the anaerobic digestion of glycerol has been an option to add value to this waste because biodiesel production is increasing worldwide. The evolution of research on glycerol valorization by anaerobic digestion has reached the use of high-rate reactors. However, no study has evaluated glycerol digestion in an anaerobic fluidized bed reactor (AFBR), a configuration with potential advantages in methane production. Still, the best operating temperature for high-rate glycerol digestion remains unclear. To clarify these gaps, the present study aimed to compare glycerol digestion in mesophilic AFBR (30 °C) and thermophilic AFBR (55 °C). In both reactors, glycerol concentration was increased from 1.0 to 7.0 g L-1 at a fixed hydraulic retention time of 24 h, resulting in an increase at the organic loading rate from 1.2 to 7.6 kg COD m-3 day-1. Thermophilic digestion of glycerol achieved superior removals of organic matter (67.7-94.2%) and methane yield (330.8 mL CH4 g-1 COD) than the mesophilic digestion (48.6-93.0% and 266.6 mL CH4 g-1 COD). Additionally, the application of the kinetic model of substrate utilization (modified Stover-Kincannon model) indicated a higher substrate utilization coefficient in the thermophilic AFBR (23.09 g L-1 day-1) than the mesophilic AFBR (7.14 g L-1 day-1). Therefore, the application of glycerol concentrations higher than 7.0 g L-1 in thermophilic AFBR should be further investigated. Also, given only operational results, the application of the AFBR in the two-stage anaerobic digestion of glycerol is recommended.

Difference in the running biomechanics between preschoolers and adults.

BACKGROUND: High vertical loading rate is associated with a variety of running-related musculoskeletal injuries. There is evidence supporting that non-rearfoot footstrike pattern, greater cadence, and shorter stride length may reduce the vertical loading rate. These features appear to be common among preschoolers, who seem to experience lower running injury incidence, leading to a debate whether adults should accordingly modify their running form. OBJECTIVE: This study sought to compare the running biomechanics between preschoolers and adults. METHODS: Ten preschoolers (4.2±1.6 years) and ten adults (35.1±9.5 years) were recruited and ran overground with their usual shoes at a self-selected speed. Vertical average (VALR) and vertical instantaneous loading rate (VILR) were calculated based on the kinetic data. Footstrike pattern and spatiotemporal parameters were collected using a motion capture system. RESULTS: There was no difference in normalized VALR (p=0.48), VILR (p=0.48), running speed (p=0.85), and footstrike pattern (p=0.29) between the two groups. Preschoolers demonstrated greater cadence (p<0.001) and shorter normalized stride length (p=0.01). CONCLUSION: By comparing the kinetic and kinematic parameters between children and adults, our findings do not support the notion that adults should modify their running biomechanics according to the running characteristics in preschoolers for a lower injury risk.

Influence of earthworm presence and hydraulic loading rate on the performance of vertical flow constructed wetlands.

In order to know the behaviour and performance of a vertical flow constructed wetland (VF-CW) operating with earthworm, this study evaluated the earthworm presence linked to hydraulic loading rates applied for domestic wastewater treatment. Two VF-CW units (710 cm², 0.75 m deep, with sand as filter media and planted with Heliconia rostrata) operated with a variable hydraulic and organic loadings rates (200 mm d-1/123 g COD m-2 d-1; 280 mm d-1/186 g COD m-2 d-1; 160 mm d-1/94 g COD m-2 d-1). Although the efficiency of COD load removal was similar (around 70%) for both CWs, the efficiency of total nitrogen load removal was around 95% throughout the evaluated period. The nitrification-denitrification process was identified with and without the presence of earthworm. VF-CW with earthworms showed higher hydraulic conductivity values (from 0.11 to 0.14 m h-1) compared with the VF-CW wetland without earthworms (0.07-0.09 m h-1). This study showed that the use of earthworms in CWs can be associated mainly with a preventive measure of clogging, which requires measures to maintain earthworms inside the bed media. Additionally, the earthworm presence has an ingestion mechanism of organic and inorganic solid particles in wastewater which excretes them as finer particles.

Methane potential of fruit and vegetable waste: an evaluation of the semi-continuous anaerobic mono-digestion.

The anaerobic digestion (AD) of a high diversity blend of fruit and vegetable waste (FVW) generated in tropical conditions as a single substrate was performed. A continuously stirred tank reactor (CSTR) operated in semi-continuous regime was used for AD. The reactor performance was monitored with gradually increasing organic loading rates (OLRs) from 0.5 up to 5.0 gVS L-1 d-1. The biochemical methane potential (BMP) of FVW determined by batch bottles was 360 LN CH4 kgVS-1, with a biodegradability of 79%. A stable pH with an adequate level of buffering capacity was observed during the entire experiment. Methane yield indicated the best performance at an OLR of 3.0 gVS L-1 d-1, with 285 LN CH4 kgVS-1 added, reaching 79% of BMP. At an OLR over 3.0 gVS L-1 d-1 accumulation of volatile fatty acids (VFA) was detected; in particular, propionic acid was monitored, and a decreased methane yield was detected. Biogas production rate was 1.55 LN L-1 d-1 and showed linear increase according to increases in the OLR.

Controlling methane and hydrogen production from cheese whey in an EGSB reactor by changing the HRT.

This study assessed the effects of hydraulic retention time (HRT; 8 h-0.25 h) on simultaneous hydrogen and methane production from cheese whey (5000 mg carbohydrates/L) in a mesophilic (30 °C) expanded granular sludge bed (EGSB) reactor. Methane production was observed at HRTs from 4 to 0.25 h. The maximum methane yield (9.8 ± 1.9 mL CH4/g CODap, reported as milliliter CH4 per gram of COD applied) and methane production rate (461 ± 75 mL CH4/day Lreactor) occurred at HRTs of 4 h and 2 h, respectively. Hydrogen production increased as methane production decreased with decreasing HRT from 8 to 0.25 h. The maximum hydrogen yield of 3.2 ± 0.3 mL H2/g CODap (reported as mL H2 per gram of COD applied) and hydrogen production rate of 1951 ± 171 mL H2/day Lreactor were observed at the HRT of 0.25 h. The decrease in HRT from 8 to 0.25 h caused larger changes in the bacterial populations than the archaea populations. With the decrease in HRT (6 h-0.25 h), the Shannon diversity index decreased (3.02-2.87) for bacteria and increased (1.49-1.83) for archaea. The bacterial dominance increased (0.059-0.066) as the archaea dominance decreased (0.292-0.201) with the HRT decrease from 6 to 0.25 h.

Efeito da variação da carga orgânica volumétrica natural na produção de biogás a partir de dejeto suíno em diferentes tempos de retenção hidráulica / The effect of organic loading rate's natural variation on the biogas yields from swine manure digestion at different hydraulic retention time

RESUMO O estudo sobre reatores anaeróbios em laboratório prioriza o controle de determinados parâmetros que são de difícil controle em campo, o que dificulta o processo de scale-up. Entre os parâmetros está a carga orgânica volumétrica (COV). No caso do dejeto suíno, esse parâmetro pode sofrer alterações diárias em função das condições climáticas, das mudanças no manejo, da alimentação dos animais, entre outros. A fim de verificar o impacto dessa variação na produtividade de biogás, foi analisado o comportamento de um reator anaeróbio de mistura completa (CSTR) em dois diferentes tempos de retenção hidráulica (TRHs) - 20 e 30 dias - durante um período total de 180 dias. Os resultados demonstraram que a elevação da COV resulta em piora da eficiência de tratamento, bem como na produção de biogás. O ensaio com TRH de 20 dias obteve uma melhor resposta às alterações de carga orgânica.

ABSTRACT The study of anaerobic digesters at laboratory focuses on the control of certain parameters that are not so easy to control in the field, which makes it difficult to process scale-up. One example is the Organic Loading Rate. To swine manure, this parameter can change daily due to weather conditions, management practices, feeding and others. In order to verify the impact of this fluctuation on biogas yield, the behavior of a CSTR reactor was analyzed in two different Hydraulic Retention Times (20 and 30 days) for a total period of 180 days. The result demonstrated that the increase of OLR result in a decrease of treatment efficiency as well as biogas yields. The study with HRT of 20 days had a better response to changes in organic load.

USE OF 2-DIMENSIONAL SAGITTAL KINEMATIC VARIABLES TO ESTIMATE GROUND REACTION FORCE DURING RUNNING.

BACKGROUND: Variations in vertical loading rates have been associated with overuse injuries of the lower extremity; however, they are typically collected using 3-dimensional motion capture systems and in-ground force plates not available to most clinicians because of cost and space constraints. PURPOSE: The purpose of this study was to determine if kinetic measures commonly used to describe lower extremity loading characteristics could be estimated from step rate and specific sagittal plane kinematic variables captured using 2-dimensional motion analysis during treadmill running. STUDY DESIGN: Observational Study. METHODS: Ten high school cross-country runners (4 men and 6 women) voluntarily consented to participate in this study. Reflective markers were placed on each lower extremity over multiple anatomical landmarks. Participants were then asked to run on the instrumented treadmill at their preferred running speed. When the participants indicated they were in their typical running pattern, they continued to run at their preferred speed for a minimum of five minutes. After three minutes of running at their preferred running speed, the participant's step rate was counted and after running for four minutes, video and ground reaction force data were recorded for 60 sec. All running motion data were recorded using a single high-speed camera at 240 frames per second and ground reaction force data were sampled at 1000 Hz. RESULTS: Mean kinematic values between the left and right extremities for all 10 participants were not significantly different. Consequently, data for the left and right extremities were grouped for all further analyses. The stepwise forward regression to predict vertical ground reaction force resulted in a five-variable model (step rate and four kinematic variables) with R2 = 0.56. The stepwise forward regression to predict average loading rate also resulted in a five kinematic variable model with R2 = 0.51. CONCLUSIONS: Step rate and sagittal plane kinematic variables measured using a simplified 2-dimensional motion analysis approach with a single high-speed camera can provide the clinician with a reasonable estimate of ground reaction force kinetics during treadmill running. LEVEL OF EVIDENCE: 4, Controlled laboratory study.

Long-term performance of a UASB reactor treating acid mine drainage: effects of sulfate loading rate, hydraulic retention time, and COD/SO42- ratio.

Acid mine drainage (AMD) is among the most serious threats to water and the typical alkali-based treatment costs are high. This study's main objective was the establishment of a highly efficient biological process using an upflow anaerobic sludge blanket (UASB) reactor to treat AMD based on a shorter hydraulic retention time (HRT) and lower organic matter input. The process was evaluated for a long-term operation (739 days) in terms of the influence of HRT (14-24 h), metal addition, sulfate loading rate (0.5-2.6 g SO42- l-1 d-1), and the COD/SO42- ratio (0.67-1.0) using ethanol as the only electron donor at a pH of 4.0. Neutral effluent pH was achieved throughout the time apart from operational modifications. The reduction in HRT from 24 to 16 h and an increase in the sulfate loading rate (SLR) up to 2.25 g SO42- l-1 d-1 improved the sulfate removal to (92.1 ± 1.8)% with 80% chemical oxygen demand (COD) removal. However, the sulfate reduction was less than 80% when the HRT and SLR was changed to 14 h and 2.6 g SO42- l-1 d-1, respectively. The oxidation of organic matter by sulfate reduction was greater than 50% regardless of the conditions imposed but the use of ethanol to treat AMD was more efficient when either the HRT was 16 h (1.5 g SO42- l-1 d-1) in the presence of Fe, Zn, and Cu or the HRT was 14 h (2.6 g SO42- l-1 d-1) but the COD/SO42- ratio was reduced to 0.67. The fully optimized conditions of the UASB reactor were set at an HRT of 16 h, SLR of 1.5 g SO42- l-1 d-1, and a COD/SO42- ratio of 1.0.

Improving EGSB reactor performance for simultaneous bioenergy and organic acid production from cheese whey via continuous biological H2 production.

OBJECTIVES: To evaluate the influence of hydraulic retention time (HRT) and cheese whey (CW) substrate concentration (15 and 25 g lactose l-1) on the performance of EGSB reactors (R15 and R25, respectively) for H2 production. RESULTS: A decrease in the HRT from 8 to 4 h favored the H2 yield and H2 production rate (HPR) in R15, with maximum values of 0.86 ± 0.11 mmol H2 g COD-1 and 0.23 ± 0.024 l H2 h-1 l-1, respectively. H2 production in R25 was also favored at a HRT of 4 h, with maximum yield and HPR values of 0.64 ± 0.023 mmol H2 g COD-1 and 0.31 ± 0.032 l H2 h-1 l-1, respectively. The main metabolites produced were butyric, acetic and lactic acids. CONCLUSIONS: The EGSB reactor was evaluated as a viable acidogenic step in the two-stage anaerobic treatment of CW for the increase of COD removal efficiency and biomethane production.

Continuous Hydrogen Production from Agricultural Wastewaters at Thermophilic and Hyperthermophilic Temperatures.

The objective of this study was to investigate the effects of hydraulic retention time (HRT) (8 to 0.5 h) and temperature (55 to 75 °C) in two anaerobic fluidized bed reactors (AFBR) using cheese whey (AFBR-CW = 10,000 mg sugars L-1) and vinasse (AFBR-V = 10,000 mg COD L-1) as substrates. Decreasing the HRT to 0.5 h increased the hydrogen production rates in both reactors, with maximum values of 5.36 ± 0.81 L H2 h-1 L-1 in AFBR-CW and 0.71 ± 0.16 L H2 h-1 L-1 in AFBR-V. The optimal conditions for hydrogen production were the HRT of 4 h and temperature of 65 °C in AFBR-CW, observing maximum hydrogen yield (HY) of 5.51 ± 0.37 mmol H2 g COD-1. Still, the maximum HY in AFBR-V was 1.64 ± 0.22 mmol H2 g COD-1 at 4 h and 55 °C. However, increasing the temperature to 75 °C reduced the hydrogen production in both reactors. Methanol and butyric, acetic, and lactic acids were the main metabolites at temperatures of 55 and 65 °C, favoring the butyric and acetic metabolic pathways of hydrogen production. The increased productions of lactate, propionate, and methanol at 75 °C indicate that the hydrogen-producing bacteria in the thermophilic inoculum were inhibited under hyperthermophilic conditions.

Nitrogen transforming bacteria within a full-scale partially saturated vertical subsurface flow constructed wetland treating urban wastewater.

The aim of this study was to characterize the nitrogen transforming bacterial communities within a partially saturated vertical subsurface flow constructed wetland (VF) treating urban wastewater in southern Brazil. The VF had a surface area of 3144m2, and was divided into four wetland cells, out of which two were operated while the other two rested, alternating cycles of 30days. The nitrifying and denitrifying bacterial communities were characterized in wetland cell 3 (764m2 surface area) over a period of 12months by using the FISH technique. Samples were collected monthly (from Feb 2014 to Feb 2015) from different layers within the vertical profile, during operation and rest periods, comprising a total of 6 sampling campaigns while the cell was in operation and another 6 when the cell was at rest. This wetland cell operated with an average organic loading rate (OLR) of 4gCODm-2d-1 and a hydraulic loading rate of 24.5mmd-1. The rest periods of the wetland cell presented influences on the abundance of ammonia-oxidizing bacteria (AOB) (8% and 3% for feed and rest periods, respectively), and nitrite-oxidizing bacteria (NOB) (5% and 2% for feed and rest periods, respectively). However, there was no influence of the rest periods on the denitrifying bacteria. AOB were only identified in the top layer (AOB ß-proteobacteria) in both operational and rest periods. On the other hand, the NOB (Nistrospirae and Nitrospina gracilis) were identified in feed periods just in the top layer and during rest periods just in the intermediate layer. The denitrifying bacteria (Pseudomonas spp. and Thiobacillus denitrificans) were identified from the intermediate layer downwards, and remained stable in both periods. Based on the identified bacterial dynamics, the partially saturated VF wetland operated under low OLR enabled favorable conditions for simultaneous nitrification and denitrification.

Biomethane production from vinasse in upflow anaerobic sludge blanket reactors inoculated with granular sludge

ABSTRACT The main objective of this study was to evaluate the anaerobic conversion of vinasse into biomethane with gradual increase in organic loading rate (OLR) in two upflow anaerobic sludge blanket (UASB) reactors, R1 and R2, with volumes of 40.5 and 21.5 L in the mesophilic temperature range. The UASB reactors were operated for 230 days with a hydraulic detection time (HDT) of 2.8 d (R1) and 2.8-1.8 d (R2). The OLR values applied in the reactors were 0.2-7.5 g totalCOD (L d)−1 in R1 and 0.2-11.5 g totalCOD (L d)−1 in R2. The average total chemical oxygen demand (totalCOD) removal efficiencies ranged from 49% to 82% and the average conversion efficiencies of the removed totalCOD into methane were 48-58% in R1 and 39-65% in R2. The effluent recirculation was used for an OLR above 6 g totalCOD (L d)−1 in R1 and 8 gtotalCOD (L d)−1 in R2 and was able to maintain the pH of the influent in R1 and R2 in the range from 6.5 to 6.8. However, this caused a decrease for 53-39% in the conversion efficiency of the removed totalCOD into methane in R2 because of the increase in the recalcitrant COD in the influent. The largest methane yield values were 0.181 and 0.185 (L) CH4 (gtotal COD removed)−1 in R1 and R2, respectively. These values were attained after 140 days of operation with an OLR of 5.0-7.5 g totalCOD (L d)−1 and total COD removal efficiencies around 70 and 80%.

Biomethane production from vinasse in upflow anaerobic sludge blanket reactors inoculated with granular sludge

The main objective of this study was to evaluate the anaerobic conversion of vinasse into biomethane with gradual increase in organic loading rate (OLR) in two upflow anaerobic sludge blanket (UASB) reactors, R1 and R2, with volumes of 40.5 and 21.5 L in the mesophilic temperature range. The UASB reactors were operated for 230 days with a hydraulic detection time (HDT) of 2.8 d (R1) and 2.8-1.8 d (R2). The OLR values applied in the reactors were 0.2-7.5 g totalCOD (L d)1 in R1 and 0.2-11.5 g totalCOD (L d)1 in R2. The average total chemical oxygen demand (totalCOD) removal efficiencies ranged from 49% to 82% and the average conversion efficiencies of the removed totalCOD into methane were 48-58% in R1 and 39-65% in R2. The effluent recirculation was used for an OLR above 6 g totalCOD (L d)1 in R1 and 8 gtotalCOD (L d)1 in R2 and was able to maintain the pH of the influent in R1 and R2 in the range from 6.5 to 6.8. However, this caused a decrease for 53-39% in the conversion efficiency of the removed totalCOD into methane in R2 because of the increase in the recalcitrant COD in the influent. The largest methane yield values were 0.181 and 0.185 (L) CH4 (gtotal COD removed)1 in R1 and R2, respectively. These values were attained after 140 days of operation with an OLR of 5.0-7.5 g totalCOD (L d)1 and total COD removal efficiencies around 70 and 80%.(AU)

Biomethane production from vinasse in upflow anaerobic sludge blanket reactors inoculated with granular sludge.

The main objective of this study was to evaluate the anaerobic conversion of vinasse into biomethane with gradual increase in organic loading rate (OLR) in two upflow anaerobic sludge blanket (UASB) reactors, R1 and R2, with volumes of 40.5 and 21.5L in the mesophilic temperature range. The UASB reactors were operated for 230 days with a hydraulic detection time (HDT) of 2.8d (R1) and 2.8-1.8d (R2). The OLR values applied in the reactors were 0.2-7.5gtotalCOD (Ld)(-1) in R1 and 0.2-11.5gtotalCOD (Ld)(-1) in R2. The average total chemical oxygen demand (totalCOD) removal efficiencies ranged from 49% to 82% and the average conversion efficiencies of the removed totalCOD into methane were 48-58% in R1 and 39-65% in R2. The effluent recirculation was used for an OLR above 6gtotalCOD (Ld)(-1) in R1 and 8gtotalCOD (Ld)(-1) in R2 and was able to maintain the pH of the influent in R1 and R2 in the range from 6.5 to 6.8. However, this caused a decrease for 53-39% in the conversion efficiency of the removed totalCOD into methane in R2 because of the increase in the recalcitrant COD in the influent. The largest methane yield values were 0.181 and 0.185 (L) CH4 (gtotalCOD removed)(-1) in R1 and R2, respectively. These values were attained after 140 days of operation with an OLR of 5.0-7.5gtotalCOD (Ld)(-1) and totalCOD removal efficiencies around 70 and 80%.

Manganese and lead in dust fall accumulation in elementary schools near a ferromanganese alloy plant.

Previous studies have shown elevated airborne manganese (Mn) in villages adjacent to a Mn alloy production plant in Brazil and negative associations between biomarkers of Mn and children's cognition and behavior. Since small Mn particles may be carried for long distances, we measured manganese (Mn) and lead (Pb) dust fall accumulation in 15 elementary schools, located between 1.25 and 6.48km from the plant in the municipality of Simões Filho, Bahia, Brazil. Passive samplers (polyethylene Petri dishes) were set in interior and exterior environments. After 30 days, the samplers' content was solubilized with diluted nitric acid and Mn and Pb levels were analyzed by electrothermal absorption spectrometry. The overall geometric mean and range of Mn and Pb accumulation in dust fall (loading rates) were 1582µg Mn/m(2)/30 days (37-37,967) and 43.2µg Pb/m(2)/30 days (2.9-210.4). A logarithmic decrease in interior and exterior Mn loading rates was observed with distance from the ferro-manganese alloy plant. Multiple regression analyses of log-transformed Mn loading rate within the schools showed a positive association with Mn levels in outdoor dust, a negative association with distance from the plant; as well, wind direction (downwind>upwind) and school location (urban>rural) entered significantly into the model. For the interior school environments, located within a 2-km radius from the plant, loading rate was, on average, 190 times higher than the Mn levels reported by Gulson et al., (2014) in daycare centers in Sydney, Australia, using a similar method. Pb loading rates were not associated with distance from the plant and were lower than the rates observed in the same daycare centers in Sydney. Our findings suggest that a significant portion of the children in this town in Brazil may be exposed to airborne Mn at concentrations that may affect their neurodevelopment.

Análise comparativa dos efeitos da carga orgânica e do tempo de detenção hidráulica na digestão anaeróbia mesofílica de lodo adensado de estação de tratamento de esgoto / Comparison of organic loading rate and hydraulic retention time effects on the mesophilic anaerobic digestion of thickened waste activated sludge

RESUMO Esta pesquisa comparou o desempenho de um digestor anaeróbio de lodo sob diferentes estratégias operacionais. Foi avaliada a influência do aumento da carga orgânica volumétrica (COV) (OP I) e o efeito da redução do tempo de detenção hidráulica (TDH) (OP II e OP III) no processo anaeróbio. As cargas aplicadas variaram entre 0,5 e 4,5 kgSV.m-3.d-1 e o TDH foi reduzido de 15 a 5 dias. Produção de gás metano, degradação do material orgânico e a diversidade microbiana foram utilizadas para medição e comparação do desempenho do processo. Foram necessários períodos de aclimatação a cada nova COV aplicada o que levou às instabilidades na remoção de SV e DQO do lodo. A operação com TDH entre 7 e 5 dias apresentou as maiores eficiências de remoção de SV, superiores a 70%, o que influenciou positivamente na estabilidade do processo. As COV aplicadas de 2,5 e 3,5 kgSV.m-3.d-1 resultaram nas maiores produções de metano durante a OP I. Para TDH inferiores a sete dias a produção de CH4 foi prejudicada apesar da existência de microorganismos metanogênicos atuantes no digestor. Comparativamente, a estratégia de redução do TDH resultou em um melhor desempenho do sistema que a fixação da COV. Quanto menor o TDH aplicado, melhor os resultados obtidos na operação do digestor, sugerindo que a eficiência do processo é otimizada em sistemas de alta carga com operação em baixos tempos de detenção hidráulica.

ABSTRACT This study compared the performance of a pilot anaerobic sludge digester under different operating strategies. The influence of increasing organic loading rate - OLR (OP I) and the effect of hydraulic retention time - HRT reduction (OP II and OP III) in anaerobic process were evaluated. The applied loads ranged between 0.5 and 4.5 kgSV.m-3.d-1; HRT was reduced from 15 to 5 days. Production of methane, organic matter degradation and microbial diversity were used to measure and compare the system´s performance. Acclimation periods were taken for each new OLR applied, leading to instabilities in sludge VS and COD removals. The experimental time with HRT between 7 and 5 days showed the highest VS efficiency removals (higher than 70%), which positively influenced process stability. The applied OLR of 2.5 and 3.5 kgVS.m-3.d-1 resulted in higher yields of methane during OP I. CH4 production showed impaired with HRT lower than 7 days, although it was observed active methanogenic microorganisms in the digester. Comparatively, HRT reduction resulted in a better system performance than the increasing OLR approach. The lower HRT applied, the better the results obtained in the operation of the digester, suggesting that the process efficiency is optimized with high load operation at low hydraulic retention times.

The use of the carbon/nitrogen ratio and specific organic loading rate as tools for improving biohydrogen production in fixed-bed reactors.

This study assessed the effect of the carbon/nitrogen (C/N) ratio on the hydrogen production from sucrose-based synthetic wastewater in upflow fixed-bed anaerobic reactors. C/N ratios of 40, 90, 140, and 190 (g C/g N) were studied using sucrose and urea as the carbon and nitrogen sources, respectively. An optimum hydrogen yield of 3.5 mol H2 mol-1 sucrose was obtained for a C/N ratio of 137 by means of mathematical adjustment. For all C/N ratios, the sucrose removal efficiency reached values greater than 80% and was stable after the transient stage. However, biogas production was not stable at all C/N ratios as a consequence of the continuous decreasing of the specific organic loading rate (SOLR) when the biomass accumulated in the fixed-bed, causing the proliferation of H2-consuming microorganisms. It was found that the application of a constant SOLR of 6.0 g sucrose g-1 VSS d-1 stabilized the system.

Reator anaeróbio compartimentado para o tratamento de águas residuárias de suinocultura / Anaerobic baffled reactor for treatment of swine wastewater

A poluição da água e do solo causada pela suinocultura provoca impactos ambientais severos nas regiões produtoras. Uma alternativa eficiente para atenuar esse problema pode ser a utilização de reatores anaeróbios de alta taxa. Neste trabalho, avaliou-se o efeito das águas residuárias de suinocultura com concentrações de sólidos suspensos totais em torno de 6.000 mg.L−1 no desempenho do reator anaeróbio compartimentado, com três câmaras. O volume da primeira câmara foi de 210 L e da segunda e terceira de 160 L. O reator anaeróbio compartimentado foi submetido a tempos de detenção hidráulica de 56, 28 e 18 horas e a cargas orgânicas volumétricas de 5,0 a 10,1 g DQOtotal (L.d)−1. As maiores remoções de demanda química de oxigênio total, de 42 a 68%, e das produções volumétricas de metano, de 0,261 a 0,454 L CH4 (L reator d)−1, ocorreram na segunda câmara.

Water and soil pollution caused by the waste from the swine production causes severe environmental impacts in producing areas. An efficient alternative to reduce these impacts can be the use of high-rate anaerobic reactors. In this work, it was evaluated the effect of the swine wastewater with total suspended solids concentrations around 6.000 mg.L−1 in the anaerobic baffled reactor with three compartments. The volume of the first compartment was 210 L and of the second and third ones of 160 L. The anaerobic baffled reactor was submitted at hydraulic detention times of 56, 28 and 18 hours and to organic load rates of 5.0 to 10.1 g total COD (L.d)−1. The highest total COD removals, of 42 to 68%, and volumetric methane productions, of 0.261 to 0.454 L CH4 (L reactor d)−1, occurred in the second compartment.

Effect of temperature on the anaerobic digestion of palm oil mill effluent

Two continuous stirred tank reactors (CSTRs) each fed with palm oil mill effluent (POME), operated at 37ºC and 55ºC, respectively, were investigated for their performance under varies organic loading rates (OLRs). The 37ºC reactor operated successfully at a maximum OLR of 12.25 g[COD]/L/day and a hydraulic retention time (HRT) of 7 days. The 55ºC reactor operated successfully at the higher loading rate of 17.01 g[COD]/L/day and had a HRT of 5 days. The 37ºC reactor achieved a 71.10% reduction of chemical oxygen demand (COD), a biogas production rate of 3.73 L of gas/L[reactor]/day containing 71.04% methane, whereas the 55ºC reactor achieved a 70.32% reduction of COD, a biogas production rate of 4.66 L of gas/L[reactor]/day containing 69.53% methane. An OLR of 9.68 g[COD]/L/day, at a HRT of 7 days, was used to study the effects of changing the temperature by 3ºC increments. The reactor processes were reasonably stable during the increase from 37ºC to 43ºC and the decrease from 55ºC to 43ºC. When the temperature was increased from 37ºC to 46ºC, the total volatile fatty acid (TVFA) concentration and biogas production was 2,059 mg as acetic acid/L and 1.49 L of gas/L[reactor]/day at day 56, respectively. When the temperature was reduced from 55ºC to 40ºC, the TVFA concentration and biogas production was 2,368 mg as acetic acid/L and 2.01 L of gas/L[reactor]/day at day 102, respectively. By first reducing the OLR to 4.20 g[COD]/L/day then slowly increasing the OLR back to 9.68 g[COD]/L/day, both reactors were restored to stable conditions at 49ºC and 37ºC respectively. The initial 37ºC reactor became fully acclimatized at 55ºC with an efficiency similar to that when operated at the initial 37ºC whereas the 55ºC reactor also achieved stability at 37ºC but with a lower efficiency.