New strategy for a suitable fast stabilization of the biomethanization performance.

The start-up strategies for thermophilic anaerobic reactors usually consist of an initial mesophilic stage (35°C), with an approximate duration of 185 days, and a subsequent thermophilic stage (55°C), which normally requires around 60 days to achieve the system stabilizatio. During the first 8-10 days of the mesophilic stage, the reactor is not fed so that the inoculum, which is generally a mesophilic anaerobic sludge, may be adapted to the organic solid waste. Between mesophilic and thermophilic conditions the reactor is still not fed in an effort to prevent possible imbalances in the proces. As a consequence, the start-up and stabilization of the biomethanization performance described in the literature require, at least, around 245 days. In this sense, a new strategy for the start-up and stabilization phases is presented in this study. This approach allows an important reduction in the overall time necessary for these stages in an anaerobic continuous stirred tank reactor (CSTR) operated at thermophilic-dry conditions for treating the organic fraction of the municipal solid waste (OFMSW): 60 days versus 245 days of conventional strategies. The new strategy uses modified SEBAC technology to adapt an inoculum to the OFMSW and the operational conditions prior to seeding the CSTR.

New criteria to determine the destabilization of the acidogenic anaerobic co-digestion of organic fraction of municipal solid waste (OFMSW) with mixed sludge (MS).

Effect of hydraulic retention time (HRT) on bio-hydrogen production from co-digestion of organic fraction of municipal solid waste (OFMSW) and mixed sludge (MS) in dry thermophilic conditions (55°C and 20% total solids) was investigated. A decreasing sequence of six HRTs, from 2.9 to 0.8-days, was performed to evaluate the stability of the system and the influence of HRT on the organic matter solubilization, the daily hydrogen production (HP) and the specific hydrogen production (SHP). Best results were obtained operating at 1.2-days HRT: HP of 3.67L H2/Lreactor/day, SHP of 33.8mL H2/gVSadded and hydrogen percentage in biogas of 52.4%. However, HRTs lower than 1.2-days induce failure in the system due to an unbalance of the hydrolytic phase. This fact was corroborated through the evaluation of two indirect parameters, "non-solubilized carbon" (NSC) and "acidogenic substrate as carbon" (ASC), and the relationships of NSC/TOC and ASC/TOC.

Influence of total solids concentration on the anaerobic co-digestion of sugar beet by-products and livestock manures.

A series of batch anaerobic digestion assays were implemented to determine the influence of total solids concentration on the anaerobic digestion of sugar beet by-products and their co-digestion with two kind of livestock manures (pig and cow manures). The two total solid concentrations studied were 8% and 5%. Total solids contents above 8% were not evaluated because of the inappropriate rheological behaviour of sugar beet by-products at these concentrations. The best total solid content tested corresponded to 8%, achieving specific methane yields of 464.3 and 451.4mL/g VSadded for co-digestion with pig manure and cow manure respectively. These data were 1.5 times higher than that obtained for reactors operating with 5% total solids content. For individual digestion of sugar beet by-products, final methane yields operating at 8% were also higher than those measured at 5% total solids concentration. However, in these tests, a large delay in the start of biogas production was registered due to the inhibition caused by the accumulation of volatile fatty acids. No significant differences in the organic matter removal efficiencies were observed for the two total solids contents studied.

Effect of the pH influent conditions in fixed-film reactors for anaerobic thermophilic treatment of wine-distillery wastewater.

In anaerobic treatments, the pH conditions affect the efficacy and operation of the process. The main purpose of this research is to compare the effect of the pH influent on the performance of a high rate technology at laboratory scale, upflow anaerobic fixed-film reactor, treating distillery wastewater (wine vinasses) in thermophilic conditions. The results obtained shown that the pH influent influences the performance of the biodegradation process: the depurative efficiency is higher for the operation with alkaline influent. The operation with acid influent allows us to operate at organic loading rates (OLR) around 5.6 kgCOD/m3/d (hydraulic retention time: 1.5 days), maintaining total Chemical Oxygen Demand removals (CODr) of 77.2%; the operation with alkaline influent allows total CODr of 76.8% working at OLR around 10.5 kgCOD/m3/d. The greatest efficiency of substrate removal was 87.5% for OLR 3.2 kgCOD/m3/d and hydraulic retention time of 4.0 days operating with alkaline influent. Therefore, the operation with alkaline influent implicates senior levels of purifying efficiency for similar organic load rate.

High rate anaerobic thermophilic technologies for distillery wastewater treatment.

In this paper, performance of two high rate technologies, upflow anaerobic fixed-film reactor and fluidized bed laboratory-scale, treating distillery wastewater (wine vinasses) at anaerobic thermophilic conditions have been compared. The results obtained show that the stationary packed bed, with a corrugated plastic support, operated under stable conditions at organic loading rates (OLR0) around 20 kgCOD/m3/d, gives maximal total CODr of 76% at OLR0 of 6.29 kgCOD/m3/d; the fluidized bed reactor, operated on open pore sintered-glass media, gives total CODr of 96% at OLR0 of 5.88 kgCOD/m3/d. The anaerobic fluidized bed technology is more effective than the upflow anaerobic fixed-film technology due, fundamentally, to this technology favouring the transport of microbial cells from the bulk to the surface and enhancing the contact between the microorganism-substrate phases, In this sense, the stationary packed bed technology is adequate for the treatment of easily biodegradable wastewater, or for the cases where elevated percentages of CODr removal are not required, while the fluidized bed technology is especially suitable for treatment of hazardous wastes with recalcitrant compositions.

Enhancement in hydrogen production by thermophilic anaerobic co-digestion of organic fraction of municipal solid waste and sewage sludge--optimization of treatment conditions.

Batch dry-thermophilic anaerobic co-digestion (55°C) of organic fraction of municipal solid waste (OFMSW) and sewage sludge (SS) for hydrogen production was studied under several sludge combinations (primary sludge, PS; waste activated sludge, WAS; and mixed sludge, MS), TS concentrations (10-25%) and mixing ratios of OFMSW and SS (1:1, 2.5:1, 5:1, 10:1). The co-digestion of OFMSW and SS showed a 70% improvement in hydrogen production rate over the OFMSW fermentation only. The co-digestion of OFMSW with MS showed 47% and 115% higher hydrogen production potential as compared with OFMSW+PS and OFMSW+WAS, respectively. The maximum hydrogen yield of 51 mL H2/g VS consumed was observed at TS concentration of 20% and OFMSW to MS mixing ratio of 5:1, respectively. The acetic and butyric acids were the main acids in VFAs evolution; however, the higher butyric acid evolution indicated that the H2 fermentation was butyrate type fermentation.

Dry-thermophilic anaerobic digestion of simulated organic fraction of municipal solid waste: process modeling.

Solid retention time (SRT) is a very important operational variable in continuous and semicontinuous waste treatment processes since the organic matter removal efficiency--expressed in terms of percentage of Dissolved Organic Carbon (% DOC) or Volatile Solids (% VS) removed--and the biogas or methane production are closely related with the SRT imposed. Optimum SRT is depending on the waste characteristics and the microorganisms involved in the process and, hence, it should be determined specifically in each case. In this work a series of experiments were carried out to determine the effect of SRT, from 40 to 8 days, on the performance of the dry (30% Total Solids) thermophilic (55°C) anaerobic digestion of organic fraction of Municipal Solid Wastes (OFMSW) operating at semicontinuous regime of feeding. The experimental results show than 15days is the optimum SRT (the best between all proved) for this process. Besides, data of organic matter concentration and methane production versus SRT have been used to obtain the kinetic parameters of the kinetic model of Romero García (1991): the maximum specific growth rate of the microorganisms (µmax=0.580 days(-1)) and the fraction of substrate non-biodegradable (α=0.268).

Start-up of thermophilic-dry anaerobic digestion of OFMSW using adapted modified SEBAC inoculum.

The work presented here concerns the start-up and stabilization stages of a Continuous Stirred Tank Reactor (CSTR) semicontinuously fed for the treatment of the Organic Fraction of Municipal Solid Waste (OFMSW) through anaerobic digestion at thermophilic temperature range (55 degrees C) and dry conditions (30% Total Solids). The procedure reported involves two novel aspects with respect to other start-up and stabilization protocols reported in the literature. The novel aspects concern the adaptation of the inoculum to both the operating conditions (thermophilic and dry) and to the type of waste by employing a modified SEBAC (Sequential Batch Anaerobic Composting) system and, secondly, the direct start-up of the process in a thermophilic temperature regime and feeding of the system from the first day of operation. In this way a significant reduction in the start-up time and stabilization is achieved i.e. 110 days in comparison to 250 days for the processes reported by other authors for the same type of waste and digester. The system presents suitable operational conditions to stabilize the reactor at SRT of 35 days, with a maximum biogas production of 1.944 LR/L.d with a CH(4) and CO(2) percentage of 25.27% and 68.15%, respectively.

Anestesia-analgesia epidural con bupivacaina y fentanil en cirugía de hemiabdomen superior / Epidural anesthesia-analgesia with bupivacaina and fentanil in surgery of hemiabdomen superior

Muchas veces, en aras de ganar tiempo, los anestesiólogos optamos por las variantes de técnicas anestésicas generales en detrimento de las alternativas locorregionales. Así, dentro de la anestesia regional, la epidural no es un proceder nuevo, aunque en la actualidad está retomando su utilidad, sobre todo en relación con la posibilidad de tratar el dolor postoperatorio.Una de las ventajas capitales radica en su beneficio respecto a la función respiratoria, ya que después de la cirugía abdominal alta y torácica se produce una importante reducción en la capacidad vital y en la capacidad residual funcional.Con el bloqueo epidural la capacidad vital tiene tendencia a recuperar los valores normales, acorta la duración de la hipoxemia postoperatoria y disminuye la incidencia de infecciones respiratorias, atelectásia o de soporte ventilatorio mecánico