Microbial dynamics in anaerobic digestion reactors for treating organic urban residues during the start-up process.

Anaerobic digestion of organic residues offers economic benefits via biogas production, still methane (CH4 ) yield relies on the development of a robust microbial consortia for adequate substrate degradation, among other factors. In this study, we monitor biogas production and changes in the microbial community composition in two semi-continuous stirred tank reactors during the setting process under mesophilic conditions (35°C) using a 16S rDNA high-throughput sequencing method. Reactors were initially inoculated with anaerobic granular sludge from a brewery wastewater treatment plant, and gradually fed organic urban residues (4·0 kg VS m-3  day-1 ) . The inocula and biomass samples showed changes related to adaptations of the community to urban organic wastes including a higher relative proportion of Clostridiales, with Ruminococcus spp. and Syntrophomonas spp. as recurrent species. Candidatus Cloacamonas spp. (Spirochaetes) also increased from ~2·2% in the inoculum to >10% in the reactor biomass. The new community consolidated the cellulose degradation and the propionate and amino acids fermentation processes. Acetoclastic methanogens were more abundant in the reactor, where Methanosaeta spp. was found as a key player. This study demonstrates a successful use of brewery treatment plant granular sludge to obtain a robust consortium for methane production from urban organic solid waste in Mexico. SIGNIFICANCE AND IMPACT OF THE STUDY: This study describes the selection of relevant bacteria and archaea in anaerobic digesters inoculated with anaerobic granular sludge from a brewery wastewater treatment plant. Generally, these sludge granules are used to inoculate reactors digesting organic urban wastes. Though, it is still not clearly understood how micro-organisms respond to substrate variations during the reactor start-up process. After feeding two reactors with organic urban residues, it was found that a broader potential for cellulose degradation was developed including Bacteroidetes, Firmicutes and Spirochaetes. These results clarify the bacterial processes behind new reactors establishment for treating organic wastes in urban areas.

Assessment of Fenton's reagent and ozonation as pre-treatments for increasing the biodegradability of aqueous diethanolamine solutions from an oil refinery gas sweetening process.

The aim of this work was to evaluate the efficiency of three chemical oxidation processes for increasing the biodegradability of aqueous diethanolamine solutions (aqueous DEA solutions), to be used as pre-treatments before a biological process. The raw aqueous DEA solution, sourced from a sour gas sweetening plant at a Mexican oil refinery, was first characterized by standardized physico-chemical methods. Then experiments were conducted on diluted aqueous DEA solutions to test the effects of Fenton's reagent, ozone and ozone-hydrogen peroxide on the removal of some physicochemical parameters of these solutions. Lastly, biodegradability tests based on Dissolved Organic Carbon Die Away OECD301-A, were carried out on a dilution of the raw aqueous DEA solution and on the treated aqueous DEA solutions, produced by applying the best experimental conditions determined during the aforementioned oxidation tests. Experimental results showed that for aqueous DEA solutions treated with Fenton's reagent, the best degradation rate (70%) was obtained at pH 2.8, with Fe(2+) and H(2)O(2) at doses of 1000 and 10,000 mg/L respectively. In the ozone process, the best degradation (60%) was observed in aqueous DEA solution (100 mg COD/L), using 100 mg O(3)/L at pH 5. In the ozone-hydrogen peroxide process, no COD or DOC removals were observed. The diluted spent diethanolamine solution showed its greatest increase in biodegradability after a reaction period of 28 days when treated with Fenton's reagent, but after only 15 days in the case of ozonation.

Electro-Fenton as a feasible advanced treatment process to produce reclaimed water.

The feasibility of the electro-Fenton process to generate simultaneously both of the Fenton's reagent species (Fe2+/H2O2), was assessed as a potentially more economical alternative to the classical Fenton's reaction to produce reclaimed water. An air-saturated combined wastewater (mixture of municipal and laboratory effluents) was treated in discontinuous and continuous reactors at pH = 3.5. The discontinuous reactor was a 2 L electrochemical laboratory cell fitted with concentric graphite and iron electrodes. The continuous reactor tests used a pilot treatment system comprising the aforementioned electrochemical cell, two clarifiers and one sand filter. Several tests were carried out at different conditions of reaction time (0-60 min) and electrical current values (0.2-1.0 A) in the discontinuous reactor. The best operating conditions were 60 min and 1 A without filtration of effluents. At these conditions, in discontinuous and continuous reactors with filtration, the COD, turbidity and color removal were 65-74.8%, 77-92.3% and 80-100%, respectively. Fecal and total coliforms, Escherichia coli, Shigella and Salmonella sp. were not detected at the end of the pilot treatment system. Electrogeneration of the Fenton's reagent is also economical; its cost is one-fifth the cost reported for Advanced Primary Treatment.

Removal of detergents by activated petroleum coke from a clarified wastewater treated for reuse.

The removal of detergents from clarified wastewaters by activated petroleum coke (CAPA) was assessed. These substances, owing to their foamy properties, constitute a problem for ammonia removal by the air stripping process that could be installed in a wastewater treatment train to produce reclaimed water. CAPA was evaluated as a more economical alternative than a commercial activated carbon. Experimental work was divided in three stages: 1) production and characterisation of materials; 2) pretreatment of raw wastewater through the Fenton's reagent or coagulation-flocculation process with Al2(SO4)3; and 3) adsorption and bio-adsorption tests of clarified effluents. These tests were carried out in the laboratory in discontinuous and continuous reactors, the former by the "point-by-point" technique, with and without a previous fixing of bacteria, and the latter by the Rapid Small Scale Column Test. Detergents content, color, COD and UV254nm were measured in raw and treated wastewaters. Results show that the best pretreatment for the adsorption process was coagulation-flocculation rather than Fenton's method. Oxidation by this process decreased the adsorptive properties of detergents. Biomass fixed on the CAPA particles significantly increased the UV254nm and COD removal efficiencies (20% and 170% respectively). The breakthrough curves showed that CAPA could attain the expected detergents removal efficiency (66%) for the alum effluent.

Performance of basaltic dust issued from an asphaltic plant as a flocculant additive for wastewater treatment.

The feasibility of using basaltic dust as a flocculant additive or coagulant aid for wastewater treatment was assessed in this research. The experimental study was divided into two stages: 1) physicochemical characterisation of the basaltic dust by applying standardised techniques, and 2) evaluation of this material as flocculant additive for the coagulation-flocculation of wastewater treated for reuse. Coagulation-flocculation experiments were carried out in the laboratory with a mixture of industrial and municipal wastewater samples collected from two points of the final discharge of the Mexico City sewerage system. Aluminium sulphate and lime were used as coagulants and the basaltic dust as flocculant additive, by applying the jar-test technique. The results of the corrosivity, reactivity, explosiveness, toxicity, inflammability and biological risk tests indicated that this material is classified as a non-hazardous waste (according to the Mexican legislation, NOM-052-ECOL-1993). The density, oxide content and particle size values of basaltic dust were similar to those reported for the flocculant additive denominated activated silica. The jar test results showed a positive effect of basaltic dust over the effluent and sludge qualities, to the extent that coagulant doses can be reduced 30% (from 150 mg/L to 110 mg/L of Al2(SO4)3).

Primary silver extraction with a high sulphur activated petroleum coke.

An extended study was performed to determine the mechanisms that are responsible for the significant silver extraction capacity of activated carbons prepared from a high-sulphur petroleum coke that is available as a waste material from Mexican petroleum refineries. Earlier studies had shown the feasibility of the production of these adsorbents but indicated that the mechanisms of metal adsorption in the present carbons are significantly different from what is classically accepted for commercial carbons. Therefore, selective titration, IR-spectroscopy and scanning electron microscopy of carbons were combined with adsorption experiments and the determination of electrochemical parameters of mixtures of carbon-AgNO3 solution to explain the fundamental reasons for the performance of the obtained carbons. This allowed us to determine the identity of the surface functional groups and to distinguish the effect of different activation processes. The experiments permitted us to explain why these activated carbons, which have a low specific area and lack classical surface functional groups, show such a high silver adsorption capacity.

Fenton's reagent and coagulation-flocculation as pretreatments of combined wastewater for reuse.

In Mexico City, drinking water is mainly produced from groundwater (70%). This practice has caused collateral problems such as Mexico City's soil sinking (5-30 cm/year). One of the most viable alternatives to palliate this problem is the treatment of wastewater for reuse in either irrigation or for groundwater artificial recharge. This paper presents the evaluation of two physicochemical pretreatment systems to treat the wastewater from the metropolitan area of the Mexican Valley that are conducted by two main sewage systems called Great Canal and Churubusco River. In this research two treatment processes were studied: 1) coagulation-flocculation and, 2) Fenton's reagent. For each one of these processes suggested, tests were performed with wastewater samples of the Great Canal and the Churubusco River mixed in a volume ratio of 1:1. In the case of the coagulation-flocculation process, additional experiments were performed to determine the optimal conditions by applying an experimental design technique. In this experimental design, six coagulant agents were considered (alum, ferric chloride, three coagulant reagents of polymeric kind with aluminium and a coagulant reagent of natural origin), and three flocculant agents (an anionic, a cationic, and a non ionic polymers). Concerning the application of the Fenton's reagent (Fe2+:H2O2), the experimental variables were the weight ratio of the ferrous iron and the hydrogen peroxide and the concentrations of these reagents. The pH value was controlled to be near to 4. For the best experimental conditions, the effluent of the Fenton's method showed similar physicochemical characteristics to the wastewater treated by coagulation-flocculation. Nevertheless, Fenton's reagent showed two very important advantages compared to the coagulation-flocculation process: a disinfecting effect and a lower production of residual sludges.

Characterisation and conditioning of Fenton sludges issued from wastewater treatment.

Characterisation tests were conducted to determine the feasibility of land application of the sludges produced in wastewater treatment by means of Fenton's Reagent. Physicochemical and microbiological parameters of Fenton sludges were compared to the values obtained for raw alum sludges. The Fenton sludges presented preferable characteristics such as the specific resistance to filtration (SRF), metals and pathogen content (fecal and tot al coliforms, helminth ova, and Salmonella sp.). The SRF ofthe Fenton sludges (1.55 x 10(13) m/kg) was 24% less than the alum sludge value (1.92 x 10(13) m/kg). The concentrations of fecal coliforms (0 MPN/g TS), Salmonella sp. (0 MPN/g TS), Helminth ova (22 HH/g TS) and metals correspond to the limits for biosolids of Class B for land application of the Mexican legislation. The Fenton reagent efficiently removes most of the pathogens, considered by the norms, by means of the combined action of the different stages that constitute this process. These results exhibit the Fenton reagent as a feasible treatment for generating sludges with characteristics of biosolids of Class B for land application. The preliminary results of conditioning tests show that Fenton sludges present better dewatering characteristics with regard to the alum sludge, for a dose of cationic polymer of 1 mg/g TS.

[The control of food hygiene during the world's fair in Seville (EXPO'92)]. / El control de la higiene alimentaria durante la Exposición Universal de Sevilla (EXPO'92).

EXPO'92 has been one of the most important mass events held in Spain during several decades. Given the size of the event and the very complex circumstances surrounding the fair, the public health services had to face a big challenge. Food-hygiene and food-safety services, in particular were organized so as to take advantage and put into practice a fully managerial approach. Relevant conclusions can be drawn from such an experience which may be valuable not only with regards to similar mass-events in the future, but also for improving food hygiene in the overall Spanish context. In this article, the positive results obtained in the field of food hygiene and food safety at EXPO'92 are directly related by the authors with the methodology which was applied, namely the hazard analysis and critical control points. It is concluded that the interinstitutional coordination achieved played a decisive role.