Total Volatile Acids Research Articles

Avaliação da composição química de fermentados alcoólicos de jabuticaba (myrciaria jabuticaba)

This work aimed to characterize the chemical composition of samples of alcoholic beverages fermented from jabuticaba produced in five successive crops. Up to 2005 most of the results didn't meet the current legal standards for wines and there was a negative correlation between parameters such as pH and volatile acidity, pH and total acidity, volatile acidity and alcohol content (p<0.01). The implementation of Good Manufacturing Practices and must sulfitation during the 2006 harvest lowered volatile acidity and more than 60% of the samples were in accordance with legislation. Also, a significant improvement in alcohol content was found (p<0.05)

Influence of organic shock loads in an ASBBR treating synthetic wastewater with different concentration levels

Safe application of the anaerobic sequencing biofilm batch reactor (ASBBR) still depends on deeper insight into its behavior when faced with common operational problems in wastewater treatments such as tolerance to abrupt variations in influent concentration, so called shock loads. To this end the current work shows the effect of organic shock loads on the performance of an ASBBR, with a useful volume of 5 L, containing 0.5-cm polyurethane cubes and operating at 30 °C with mechanical stirring of 500 rpm. In the assays 2 L of two types of synthetic wastewater were treated in 8-h cycles. Synthetic wastewater I was based on sucrose–amide–cellulose with concentration of 500 mg COD/L and synthetic wastewater II was based on volatile acids with concentration ranging from 500 to 2000 mg COD/L. Organic shock loads of 2–4 times the operation concentration were applied during one and two cycles. System efficiency was monitored before and after application of the perturbation. When operating with concentrations from 500 to 1000 mg COD/L and shock loads of 2–4 times the influent concentration during one or two cycles the system was able to regain stability after one cycle and the values of organic matter, total and intermediate volatile acids, bicarbonate alkalinity and pH were similar to those prior to the perturbations. At a concentration of 2000 mg COD/L the reactor appeared to be robust, regaining removal efficiencies similar to those prior to perturbation at shock loads twice the operation concentration lasting one cycle and stability was recovered after two cycles. However, for shock loads twice the operation concentration during two cycles and shock loads four times the operation concentration during one or two cycles filtered sample removal efficiency decreased to levels different from those prior to perturbation, on an average of 90–80%, approximately, yet the system managed to attain stability within two cycles after shock application. Therefore, this investigation envisions the potential of full scale application of this type of bioreactor which showed robustness to organic shock loads, despite discontinuous operation and the short times available for treating total wastewater volume.

Anaerobic sequencing batch biofilm reactor applied to automobile industry wastewater treatment: Volumetric loading rate and feed strategy effects

This paper presents a technological viability study of wastewater treatment in an automobile industry by an anaerobic sequencing batch biofilm reactor containing immobilized biomass (AnSBBR) with a draft tube. The reactor was operated in 8-h cycles, with agitation of 400 rpm, at 30 °C and treating 2.0 L wastewater per cycle. Initially the efficiency and stability of the reactor were studied when supplied with nutrients and alkalinity. Removal efficiency of 88% was obtained at volumetric loading rate (VLR) of 3.09 mg COD/L day. When VLR was increased to 6.19 mg COD/L day the system presented stable operation with reduction in efficiency of 71%. In a second stage the AnSBBR was operated treating wastewater in natura, i.e., without nutrients supplementation, only with alkalinity, thereby changing feed strategy. The first strategy consisted in feeding 2.0 L batch wise (10 min), the second in feeding 1.0 L of influent batch wise (10 min) and an additional 1.0 L fed-batch wise (4 h), both dewatering 2.0 L of the effluent in 10 min. The third one maintained 1.0 L of treated effluent in the reactor, without discharging, and 1.0 L of influent was fed fed-batch wise (4 h) with dewatering 1.0 L of the effluent in 10 min. For all implemented strategies (VLR of 1.40, 2.57 and 2.61 mg COD/L day) the system presented stability and removal efficiency of approximately 80%. These results show that the AnSBBR presents operational flexibility, as the influent can be fed according to industry availability. In industrial processes this is a considerable advantage, as the influent may be prone to variations. Moreover, for all the investigated conditions the kinetic parameters were obtained from fitting a first-order model to the profiles of organic matter, total volatile acids and methane concentrations. Analysis of the kinetic parameters showed that the best strategy is feeding 1.0 L of influent batchwise (10 min) and 1.0 L fed-batch wise (4 h) in 8-h cycle.

Viabilidade celular de Saccharomyces cerevisiae cultivada em associação com bactérias contaminantes da fermentação alcoólica

The aim of this project was to study the influence of the bacteria Bacillus and Lactobacillus, as well as their metabolic products to decrease the cellular viability of the yeast Saccharomyces cerevisiae. The bacteria Bacillus subtilis, Bacillus coagulans, Bacillus stearothermophilus, Lactobacillus fermentum and Lactobacillus plantarum were cultivated in association with yeast S. cerevisiae (strain Y-904) for 72 hours at 32 oC under agitation. The cellular viability, budding rate and population of S. Cerevisiae and the total acidity, volatile acidity and pH of culture medium were determined at 0, 24, 48 and 72 hours of incubation of the mixed culture. The bacteria cultures were treated by heat sterilization, antibacterial agent and irradiation. The results showed that only the more acidified culture medium, contaminated with active bacteria L. fermentum and B. subtilis, caused a reduction in the yeast cellular viability. Except for the bacteria B. subtilis treated for radiation, the other bacteria treated by the different procedures (heat, radiation and antibacterial) did not cause a reduction in the cellular viability of S. cerevisiae, indicating that the isolated presence of the cellular metabolic of these bacteria was not enough to reduce the percentage of the living yeast cells.

Changes in the quality of surimi made from thornback ray (Raja clavata, L. 1758) during frozen storage

Surimi was prepared from the thornback ray (Raja clavata L. 1758) and divided into two groups. The first group was prepared with 4% sorbitol, 4% sucrose and 0.3% sodium tripolyphosphate as a cryoprotectant, while surimi in second group was prepared with 8% sorbitol and 0.3% sodium tripolyphosphate. The frozen surimi samples were stored at −23.8±2°C for 6 months. The total volatile basic nitrogen (8.40 mg/100 g for group A, 6.30 mg/100 g for group B), trimethylamine nitrogen (2.55 mg/100 g for group A, 2.38 mg/100 g for group B), thiobarbituric acid (1.29 mg malondialdehyde/100 g for group A, 1.17 mg malondialdehyde/100 g for group B), and pH values (7.34 for group A, 6.98 for group B) of surimi increased during frozen storage but remained within the acceptable limits. Total psychrophilic aerobic bacteria counts and sensory evaluation points in both groups decreased during frozen storage. The results of this study showed that thornback ray was found to be suitable for surimi production and the surimis were still acceptable at the end of the 6-month storage period.

Molecular Monitoring of Microbial Population Dynamics During Operational Periods of Anaerobic Hybrid Reactor Treating Cassava Starch Wastewater

This study characterized the microbial community and population dynamics in an anaerobic hybrid reactor (AHR) treating cassava starch wastewater. Methanogens and nonmethanogens were followed during the start-up and operation of the reactor, and linked to operational and performance data. Biomass samples taken from the sludge bed and packed bed zones of the AHR at intervals throughout the operational period were examined by 16S rRNA fluorescence in situ hybridization (FISH). The start-up seed and the reactor biomass were sampled during the feeding of the wastewater with a chemical oxygen demand (COD) value of 8 g L(-1) and a hydraulic retention time (HRT) of 8 days. These samples were characterized by the predominance of cells with long-rod morphology similar to Methanosaeta spp. Following a sharp operational change, accomplished by increasing the COD concentration of the organic influent from 8 to 10 g L(-1) and reducing the HRT from 8 to 5 days, there was a doubling of the organic loading rate, a reduction of the COD removal efficiency, as well as decreased methane content in the biogas and an accumulation of total volatile acids in the reactor. Moreover, this operational change resulted in a significant population shift from long-rod Methanosaeta-like cells to tetrad-forming Methanosarcina-like cells. The distributions of microbial populations involved in different zones of the AHR were determined. The results showed that nonmethanogens became the predominant population in both sludge and the packed bed zone. However, the percentage of methanogens in the packed bed zone was higher than that in the sludge bed zone. This higher percentage of methanogens was likely caused by the fact that the packed bed zone provided a suitable environmental condition with an appropriate nutrient availability for methanogen growth.

Effects of feeding time and organic loading in an anaerobic sequencing batch biofilm reactor (ASBBR) treating diluted whey

An investigation was carried out on the performance of an anaerobic sequencing batch biofilm reactor (ASBBR) treating diluted cheese whey when submitted to different feed strategies and volumetric organic loads (VOL). Polyurethane foam cubes were used as support for biomass immobilization and stirring was provided by helix impellers. The reactor with a working volume of 3 L treated 2 L of wastewater in 8-h cycles at 500 rpm and 30 ∘ C . The organic loads applied were 2, 4, 8 and 12 gCOD L - 1 d - 1 , obtained by increasing the feed concentration. Alkalinity was supplemented at a ratio of 50% NaHCO 3 /COD. For each organic load applied three feed strategies were tested: (a) batch operation with 8-h cycle; (b) 2-h fed-batch operation followed by 6-h batch; and (c) 4-h fed-batch followed by 4-h batch. The 2-h fed-batch operation followed by 6-h batch presented the best results for the organic loads of 2 and 4 gCOD L - 1 d - 1 , whereas the 4-h fed-batch operation followed by 4-h batch presented results slightly inferior for the same organic loads and the best results at organic loads of 8 and 12 gCOD L - 1 d - 1 . The concentration of total volatile acids varied with fill time. For the higher fill times maximum concentrations were obtained at the end of the cycle. Moreover, no significant difference was detected in the maximum concentration of total volatile acids for any of the investigated conditions. However, the maximum values of propionic acid tended to decrease with increasing fill time considering the same organic load. Microbiological analyses revealed the presence of Methanosaeta-like structures and methanogenic hydrogenotrophic-like fluorescent bacilli. No Methanosarcina-like structures were observed in the samples.

Dry-cured ham quality and acceptability as affected by the preservation system used for retail sale

Dry-cured ham cuts and slices were stored at 4 ± 2 °C for 8 months under vacuum and modified atmosphere (20% CO 2 + 80% N 2), respectively. Instrumental colour and texture, pH, non-protein nitrogen, total volatile basic nitrogen, acidity, lipid oxidation, sensory profile and consumer acceptability and purchase satisfaction were measured throughout storage. The overall quality of vacuum-packaged dry-cured ham cuts showed limited changes. Significant changes of sensory attributes involved only loss of flavour. The overall acceptability assessed by both trained and consumer panels did not decrease significantly throughout storage and the willingness to purchase remained above 50%. Conversely, modified-atmosphere-packaged ham slices had intense and extensive changes affecting sensory quality, particularly in visual appearance, flavour loss, off-flavour formation, saltiness and rancidity. Some of these changes were related to oxidation caused by low pH due to the presence of carbon dioxide in the protective atmosphere. Acceptability was significantly lower from the 4th month of storage and willingness to purchase fell below 50% at the same time.

Desempenho de processo anaeróbio em dois estágios (reator compartimentado seguido de reator UASB) para tratamento de águas residuárias de suinocultura

Avaliou-se o efeito das águas residuárias de suinocultura com concentrações de sólidos suspensos totais em torno de 6.000 mg L-1 (DQOtotal variando de 7.557 a 11.640 mg L-1) no desempenho de processo anaeróbio em dois estágios compostos por reator compartimentado (ABR) e reator de fluxo ascendente com manta de lodo (UASB), instalados em série, em escala-piloto (volumes de 530 e 120 L, respectivamente), submetidos a tempos de detenção hidráulica (TDH) de 56 a 18 h no primeiro reator e de 13 a 4 h no segundo reator. As eficiências médias de remoção de DQOtotal variaram de 71,1 a 87,5% no reator ABR e de 41,5 a 50,1% no reator UASB, resultando em valores médios de 86,8 a 94,9% para o sistema de tratamento anaeróbio em dois estágios com carga orgânica volumétrica (COV), na faixa de 5,05 a 10,12 kg DQOtotal (m³ d)-1, no reator ABR, e de 2,83 a 9,63 kg DQOtotal (m³ d)-1, no reator UASB. As eficiências de remoção de SST e SSV foram da ordem de 95,6%. O teor de metano no biogás manteve-se acima de 70% para os dois reatores. A produção volumétrica de metano máxima de 0,755 m³ CH4 (m³ d)-1 ocorreu no reator 1, com COV de 10,12 kg DQOtotal (m³ d)-1 e TDH de 18 h. Os valores médios de pH variaram na faixa de 7,2 a 8,0 para os efluentes dos reatores 1 e 2. Os ácidos voláteis totais mantiveram-se estáveis com concentrações abaixo de 200 mg L-1. Com variações abruptas e acentuadas de concentrações de SST e DQOtotal do afluente, os reatores mantiveram as eficiências de remoção de DQO e sólidos suspensos, em torno de 70%, e a qualidade do biogás, com 80% de CH4.

Desempenho de reatores anaeróbios de fluxo ascendente com manta de lodo em dois estágios tratando águas residuárias de suinocultura

Avaliou-se o desempenho de dois reatores anaeróbios de fluxo ascendente com manta de lodo (UASB) em escala-piloto com volumes de 908 L e 188 L, instalados em série, alimentados com águas residuárias de suinocultura com concentrações médias de sólidos suspensos totais (SST) variando de 2.216 mg L-1 a 7.131 mg L-1 e submetidos a tempos de detenção hidráulica (TDH) de 62,3 e 31,1 h, no primeiro reator, e de 12,9 e 6,5 h, no segundo reator. As eficiências médias de remoção de DQOtotal variaram de 74,0% a 89,6% no Reator 1 e de 34,3% a 45,1% no Reator 2, resultando em valores médios de 86,6% a 93,1% para o sistema de tratamento em dois estágios com carga orgânica volumétrica (COV) na faixa de 3,40 a 14,44 kg DQOtotal m-3 reator d-1 no Reator 1. As concentrações de metano no biogás foram acima de 75% para o Reator 1 e de 80% para o Reator 2. Os valores médios de pH variaram na faixa de 6,9 a 8,2 para o efluente do Reator 1 e de 7,0 a 8,3 para o efluente do Reator 2. Os ácidos voláteis totais mantiveram-se estáveis com concentrações médias abaixo de 200 mg L-1. Esses resultados indicaram que as condições de carga orgânica, em termos de DQO e SSV, impostas ao sistema de tratamento anaeróbio em dois estágios, não foram limitantes para que houvesse o desenvolvimento de lodo com microbiota adaptada e com alta atividade, propiciando altas eficiências médias de remoção de matéria orgânica (86,6 a 93,1% para DQOtotal e 85,6 a 88,2% para SSV) e taxas de produção de metano de 0,156 a 0,289 m³ CH4 kg-1 de DQO removida.

Prediction of organic acids and other quality parameters of wine vinegar by near-infrared spectroscopy. A feasibility study

A method for quality control of wine vinegar has been developed based on near-infrared spectroscopy that can be applied to monitor processes or in quality control in vinegar industries. In vinegar production, stages such as on-line fermentation monitoring, dilution process and quality control of the final product are relevant and necessary. The aim of this study was to achieve and simplify these manufacturing stages through the determination of 14 parameters from a spectral measurement. Total acids, non-volatile and volatile acids, organic acids, l-proline, solids, ash and chloride in vinegar were determined by near-infrared spectroscopy. Different data pre-processing methods such as orthogonal signal correction, multiplicative scatter correction or column centering were used and the final multivariate methods were evaluated and compared. The calibration models were validated and prediction capacity studied in order to examine their practical applicability to the vinegar industry.

Full-Scale Application of a Dynamic Model for High-Rate Anaerobic Wastewater Treatment Systems

High-rate anaerobic treatment systems are becoming increasingly popular to treat industrial wastewater containing large amounts of organic matter in the form of carbohydrates or proteins. Mathematical models of these systems can serve as tools for equipment sizing, process design, control and optimization, plant operation, and operator training. Several models for these plants have been proposed which have been validated and tested on laboratory-scale systems. Information on full-scale application of these models is not readily available. In this paper, a model only previously validated on laboratory scale was applied at full scale. The model was used to predict the behavior of two full-scale plants of different designs treating brewery wastewater under dynamic conditions. Influent and effluent liquid streams and gas flows were sampled over a 4 and 10 day period for the two plants, respectively. Limited characterization to just total carbon in feed over only four days was sufficient to predict the gas production rate or total volatile organic acid concentration in the effluent of the methanogenic reactor. Elaborate measurements over 10 days of feed characteristics including organic acid concentrations were important in obtaining good full-scale predictions of all variables that were modeled. Apart from the operating variables, the key parameter that required re-estimation for the full-scale system was the solids retention time in the methanogenic stage.

A study of the natural biodegradation of two-phase olive mill solid waste during its storage in an evaporation pond

A study of the natural biodegradation of two-phase olive mill solid waste (OMSW) during its storage in an evaporation pond was carried out. This system is traditionally used as the final disposal of this waste or constitutes a previous stage before being processed by cogeneration or anaerobic digestion processes. A laboratory-scale pond with a total volume of 520 l was used. The experiment was carried out between December 2002 and August 2003 covering a total period of 269 days. During the experiment, the variations of temperature (outside and inside the pond), the effective volume of the OMSW in the pond, moisture content, total solids (TS), volatile solids (VS), the total chemical oxygen demand (TCOD), total volatile acids (TVA), pH and cumulative methane production as a function of the operation time were evaluated. The experimental results obtained showed that the characteristics of the two-phase OMSW in the pond were dependent on the time of operation and temperature. During the experiment, three periods were clearly observed and differentiated: (a) An initial period with a rapid reduction of moisture content and effective volume, with an increase of TS, VS and TCOD removals, a decrease of pH and an increase of TVA and methane production until day 21. (b) A second period of slow decrease of moisture content and effective volume, due to the decrease of the ambient temperature. This period took place between day 21 and days 120–150 of assay, and it was characterised by a slight change in the OMSW properties. (c) A third period where the characteristics of the waste in the pond changed considerably due to the increase of the temperature outside the pond. The methane gas production also showed an increase due to the increase of methanogenic activity with the increase of temperature. An empirical model to describe the changes of two-phase OMSW characteristics and methane production with the operation time was developed. The proposed model, based on the use of polynomial equations, took into account the influence of the temperature and fit adequately into the experimental results obtained. It was found that the pond could probably be used as preliminary treatment of two-phase OMSW before its anaerobic digestion process, because a maximum conversion of organic matter to TVA was obtained after an operation time of around 200 days.

Improving acidogenic performance in anaerobic degradation of solid organic waste using a rotational drum fermentation system

The effects of leachate from a methanogenic process on acidogenic performance of a solid recycle (SR) process by a rotational drum fermentation (RDF) system were evaluated under mesophilic condition and a hydraulic retention time (HRT) of 20 days. Two SR process configurations, SR1 and SR2, were evaluated, using fresh soybean meal or Okara as substrates. An apparent first-order hydrolysis rate constant of 5.0 × 10 −3/d for SR1 at pH values of 4.4 and 14.4 × 10 −3/d for SR2 at pH of 5.0, were obtained. The apparent volatile solids (VS) degradation ratio ranged from 9.6% to 19.4% and total volatile acid (as acetic acid) from 10.8 to 14.9 g/L. Occupying ratios for ionized volatile acid (VA) increased from 30.6% to 63.4% after recycling the leachate to process. However, occupying ratios of acetic acid decreased from 93.3% to 42.0% whereas propionic acid and butyric acid ratios increased in SR2. Integrating the VA production with the hydrolysis rate constants, it is clear that the recirculation of leachate considerably enhanced acidogenic performance of solid recycle process.

Determination of Quality Characteristics of Holothuria tubulosa, (Gmelin, 1788) in Turkish Sea (Aegean Region) Depending on Sun Drying Process Step Used in Turkey

ABSTRACT There are around 500 species of sea cucumber but few (around 10-17) are valuable commercially. In Turkey, an Aegean region species, Holothuria tubulosa, is collected by divers and kept alive until processed. Generally, Chinese methods and processing techniques of sea cucumbers are applied in Turkey. Processing steps in Turkey consist of cleaning, gutting, boiling, cooling, sun drying, packaging and storage. In this study, quality characteristics of Holothuria tubulosa were determined depending on a sun drying process step used in Turkey: water activity (aw) and microbial quality of the sea cucumber were determined during sun drying period at different air conditions (temperature, wind velocity, humidity). Proximate analysis (crude protein, crude fat, moisture, carbohydrate) and chemical quality control analyses (total volatile base-nitrogen, trimetylamine-nitrogen, and thiobarbituric acid reactive substances) were also determined before and after sun drying of Holothuria tubulosa. According to the results of analysis, no quality criteria reached the maximum acceptability limit for the product.

H 2 production through anaerobic mixed culture: effect of batch S0/ X0 and shock loading in CSTR

Biological production of H 2 has received considerable attention lately. The present study was undertaken to observe the effects of substrate/seeding ratios ( S 0/ X 0) on batch H 2 generation. The H 2-producing seeding spores were obtained from the heat treatment (88 °C for 12 h) of the compost from a grass composting facility. A dehydrated brewery mixture was used as feed substrate. The results indicate that the pattern of the cumulative H 2 production with time is similar to the growth curve with a typical lag, exponential and stationary phase; the results were successfully modeled with a modified Gompertz equation. It appears that maximum H 2 yield potential (27 ml g −1 COD added) occurs at an S 0/ X 0 ratio of about 4, whereas the maximum specific H 2 yield (205 ml g −1 VSS d −1) occurs at approximately S 0/ X 0 = 3. The S 0/ X 0 ratios higher than 4 would inhibit H 2 production. An attempt was made to waste a certain amount of reactor content and replaced it with fresh substrate in order to enhance H 2 production. After this medium replacement, the H 2 production was initially inhibited and the system then exhibited a long lag before it reached an active H 2 production stage. For a continuous-stirred tank-reactor (CSTR) system, the results of replacing 25% of the reactor content indicate that there is still a lag time before a sudden increase in H 2 production after the addition of the new substrate feed. The major low molecular weight acids identified are HAc and HBu with total volatile acids of about 6000–8000 mg l −1. The ratio of HAc/HBu in the present study is relatively constant (about 5) and appears not significantly affected by the medium replacement. The concentration of total alcohols is about 2000 mg l −1. All in all, the CSTR system is able to recover to its previous performance after such a dramatic 25% medium replacement.

Metals behaviors of MSWI bottom ash co-digested Anaerobically with MSW

Co-disposal of refuse and incinerator bottom ash used as a soil cover resource has been practiced for many countries including Taiwan. However, the baseline information of co-disposal was still not fully known. In order to obtain a clear result in a short term, laboratory scale anaerobic reactors have been developed to simulate the landfill site operation. The parameters chosen for assessment were pH, total organic carbon, alkalinity, volatile acids and heavy metals. Over the period of 200-day operation, the pH, alkalinity and gas production in the ash added reactors were found to increase as compared to the controlled ones. Soluble concentrations of heavy metals Cd, Cr, Cu, Pb, Ni and Zn in the four reactors appeared to fluctuate in the range of 0.02–2, 0.01–2.5, 0.01–0.3, 0.01–1, 0.01–1.2 and 0.01–1 mg l −1, respectively. These ranges of heavy metals concentration showed neither significant stimulatory nor inhibitory effects on the anaerobic digesters. Furthermore, the released alkali metals seemed to exert the beneficial effect on the anaerobic digesters within which the volatile acids were buffered by the increase of acids neutralizing capacity (ANC pH=7) of around 2 mequiv. g −1 leading to a suitable pH for the anaerobic environment. Thus, the gas production in the ash added reactors was finally recovered back to the initial yield of about 400 ml g −1 VS added day −1 as compared to that of control reactors remaining about 50–200 ml g −1 VS added day −1. Therefore, it was concluded that the ash addition in the ash/refuse ratio of 25/100 and 50/100 showed a beneficial effects through the increase of pH, alkalinity and gas production. These phenomena indicated that using bottom ash as a soil cover might obtain the potential positive effects on landfill practice.

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.

Kinetic modelling of the hydrolysis, acidogenic and methanogenic steps in the anaerobic digestion of two-phase olive pomace (TPOP)

A simplified kinetic model for studying the hydrolysis, acidogenic and methanogenic steps of the anaerobic digestion process of two-phase olive pomace (TPOP) was proposed on the basis of the experimental results obtained. The process was conducted in a laboratory-scale completely stirred tank reactor at mesophilic temperature (35 °C) operating at hydraulic retention times (HRT) in the range of 10–50 days. Hydrolysis and acidogenic steps prevailed at HRTs lower than 20 days, while the methanogenic step prevailed at higher HRT values. Four differential equations described the overall process. A first-order kinetics for hydrolysis of non-soluble organic matter and a Michaelis–Menten equation type for soluble organic matter decomposition, total volatile acids consumption and methane production. The following kinetic constants with their standard deviations were obtained for the above-mentioned anaerobic stages: (a) hydrolysis and solubilization of organic matter: k 1 (kinetic constant for non-soluble organic matter degradation): 0.054 ± 0.003 day −1; k 2 (maximum rate of soluble organic matter production): 4.2 ± 0.3 g soluble chemical oxygen demand (SCOD)/l day; k 3 (saturation constant): 9.8 ± 0.5 g SCOD/l; (b) acidogenesis: k 4 (maximum rate of soluble organic matter degradation): 3.6 ± 0.2 g SCOD/l day; k 5 (saturation constant): 10.2 ± 0.5 g SCOD/l; and (c) methanogenesis: k 6 (maximum rate of total volatile acids (TVA) consumption): 4.3 ± 0.2 g TVA-COD/l day; and k 7 (saturation constant): 3.1 ± 0.2 g TVA-COD/l. The kinetic constants obtained and the proposed equations were used to simulate the different steps of the anaerobic digestion process of TPOP and to obtain the theoretical values of non-soluble and soluble CODs, TVA and methane production. The small deviations obtained (equal or lower than 10%) between the theoretical and experimental values suggest that the parameters obtained represent and predict the activity of the different microorganism types involved in the overall anaerobic digestion process of this waste.

Influence of organic loading on an anaerobic sequencing biofilm batch reactor (ASBBR) as a function of cycle period and wastewater concentration

The effect of organic loading on the performance of a mechanically stirred anaerobic sequencing biofilm batch reactor (ASBBR) has been investigated, by varying influent concentration and cycle period. For microbial immobilization 1-cm polyurethane foam cubes were used. An agitation rate of 500 rpm and temperature of 30±2 °C were employed. Organic loading rates (OLR) of 1.5–6.0 g COD l −1 d −1 were applied to the 6.3-l reactor treating 2.0 l synthetic wastewater in 8 and 12-h batches and at concentrations of 500–2000 mg COD l −1, making it possible to analyze the effect of these two operation variables for the same organic loading range. Microbial immobilization on inert support maintained approximately 60 gTVS in the reactor. Filtered sample organic COD removal efficiencies ranged from 73 to 88% for organic loading up to 5.4 g COD l −1 d −1. For higher organic loading (influent concentration of 2000 mg COD l −1 and 8-h cycle) the system presented total volatile acids accumulation, which reduced organics removal efficiency down to 55%. In this way, ASBBR with immobilized biomass was shown to be efficient for organic removal at organic loading rates of up to 5.4 g COD l −1 d −1 and to be more stable to organic loading variations for 12-h cycles. This reactor might be an alternative to intermittent systems as it possesses greater operational flexibility. It might also be an alternative to batch systems suspended with microorganisms since it eliminates both the uncertainties regarding granulation and the time necessary for biomass sedimentation, hence reducing the total cycle period.