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.

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.

Fecal pollution in coastal marine sediments from a semi-enclosed deep embayment subjected to anthropogenic activities: an issue to be considered in environmental quality management frameworks development.

Sewage discharge is a major source of pollution in marine environments. Urban wastewaters can directly enter marine environments carrying pathogen organisms, organic loads, and nutrients. Because marine sediments can act as the ultimate fate of a wide range of pollutants, environmental quality assessment in this compartment can help to identify pollution problems in coastal areas. In the present study, characterization of surficial marine sediments allowed assessment of fecal pollution in a semi-enclosed deep embayment that is subjected to anthropogenic activities. Physicochemical parameters and fecal indicators presented a great spatial heterogeneity. Fecal coliform and Clostridium perfringens showed accumulation in an extensive area, not only in proximity to sewage discharge points, but also in sediments at 100 meters depth. Results included herein demonstrated that, in coastal areas, urban wastewater discharge can affect the whole ecosystem through accumulation of fecal matter in bottom sediments. Application of multivariate techniques provided useful information with applicability for management of coastal areas in such complex systems. Environmental implications of wastewater discharge in coastal areas indicate the need to implement and include sediment quality control strategies in legislative frameworks.

Sublethal and lethal toxicity in juvenile Senegal sole (Solea senegalensis) exposed to copper: a preliminary toxicity range-finding test.

Static bioassay test for acute toxicity of copper in Senegal sole juveniles (Solea senegalensis) was conducted. The 96h LC(50) value of metal was found to be 0.32mg/L Cu. The intensity of histological alterations was increased gradually with the copper concentration and the exposure time. Numerous aneurysms, hypertrophy, hyperplasia and fusion of the lamellar epithelium in gills and a disorganization of the hepatic parenchyma and vacuolization in liver were common lesions in S. senegalensis juveniles exposed to copper. The results of the study indicate the sensitivity of juvenile S. senegalensis to copper (II), the persistence of sublethal effects and histology as a tool capable of revealing the sublethal effects of heavy metals on the environment and aquatic biota.

Effect of the test media and toxicity of LAS on the growth of Isochrysis galbana.

In this paper, the toxicity of linear alkylbenzene sulfonate (LAS) was evaluated in the marine microalga Isochrysis galbana using data of growth inhibition toxicity tests at 96-h exposure time. Toxicity was examined in standard conditions and by means of the modification of two variables of the test media: (1) the dilution water and (2) the content of nutrients in the test medium. For this purpose, a total of 10 toxicity test were designed: five dilution waters, four natural marine waters and one synthetic seawater; each in two different nutritive conditions, saturated nutrient concentration (SC) by the addition of modified f/2 nutritive medium, and natural nutrient concentration (NC), i.e., without the addition of f/2. At threshold toxicity levels, the dilution waters used in the test and the nutrient concentrations did not affect the toxicity of LAS. At IC50 concentrations, the toxicity of LAS is influenced by both variables: under SC conditions, the toxic effect of LAS diminishes, obtaining in all the tests IC50 > 10 mg/L LAS. Under NC conditions, IC50 concentrations ranging between 3.15 and 9.26 mg/L LAS have been obtained.

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.

A set of marine microalgae bioassays for the evaluation of biological water quality in enclosure areas in south of Spain.

The aim of this study has been the identification of the nutritive status (oligotrophy end eutrophy) in four enclosure areas from Gulf of Cadiz (Southwest Iberian Peninsula-Europe) by means of a battery of water column toxicity tests. The test organisms were four marine microalgae which comprised a wide taxonomic range. Growth tests with receiving waters from the four study areas were carried out under two nutritive conditions; with and without additional nutrient-enriched medium. The results of both bioassays were used to define a new eutrophication index (I(E)). The I(E) index obtained presents a good correlation with the traditional physical-chemical parameters in the enclosure areas; nevertheless in open waters where the dilution processes are more important the results show less correlation.