Liliana Borzacconi

Defining the biomethane potential (BMP) of solid organic wastes and energy crops: a proposed protocol for batch assays

The application of anaerobic digestion technology is growing worldwide because of its economic and environmental benefits. As a consequence, a number of studies and research activities dealing with the determination of the biogas potential of solid organic substrates have been carrying out in the recent years. Therefore, it is of particular importance to define a protocol for the determination of the ultimate methane potential for a given solid substrates. In fact, this parameter determines, to a certain extent, both design and economic details of a biogas plant. Furthermore, the definition of common units to be used in anaerobic assays is increasingly requested from the scientific and engineering community. This paper presents some guidelines for biomethane potential assays prepared by the Task Group for the Anaerobic Biodegradation, Activity and Inhibition Assays of the Anaerobic Digestion Specialist Group of the International Water Association. This is the first step for the definition of a standard protocol.

Integrated anaerobic treatment of dairy industrial wastewater and sludge.

Performance parameters were studied in an alternative full-scale dairy effluent treatment system comprising two anaerobic sludge-blanket reactors in parallel arrangement with upward flow, internal fat-separation by flotation, external lamella settler and floated material digester. Reactors were initially inoculated with flocculent sludge and granulated in a high-load stage. Using loading rates up to a maximum 5.5 kg COD/m(3) x d-hydraulic residence time of 17 hours- reactor efficiency was found to remain stable around 90% of COD. Average sludge digester efficiency using a loading rate of 3.5 kgVS/m(3) x d with a lipid content of 47% of COD amounted to 78% of VS (87% of lipid removal). LCFA inhibition as assayed using palmitate was found to depend not only on the palmitate concentration but also on the palmitate-to-biomass concentration ratio.

Application of anaerobic digestion to the treatment of agroindustrial effluents in Latin America

A 1994 survey of high rate anaerobic reactors employed in the treatment of agroindustrial effluents in Latin America is presented. Data including number, volume and type of reactors, their evolution with time and type of effluents are discussed. Latin America has an increasing and significant participation in the application of anaerobic treatment to agroindustrial effluents. In particular, the design parameters of already operating reactors and the impact of applying this technology to the most typical effluents are analyzed. The equivalent energy of biogas that can be produced through this technology is given.

Microbial communities from 20 different hydrogen-producing reactors studied by 454 pyrosequencing

To provide new insight into the dark fermentation process, a multi-lateral study was performed to study the microbiology of 20 different lab-scale bioreactors operated in four different countries (Brazil, Chile, Mexico, and Uruguay). Samples (29) were collected from bioreactors with different configurations, operation conditions, and performances. The microbial communities were analyzed using 16S rRNA genes 454 pyrosequencing. The results showed notably uneven communities with a high predominance of a particular genus. The phylum Firmicutes predominated in most of the samples, but the phyla Thermotogae or Proteobacteria dominated in a few samples. Genera from three physiological groups were detected: high-yield hydrogen producers (Clostridium, Kosmotoga, Enterobacter), fermenters with low-hydrogen yield (mostly from Veillonelaceae), and competitors (Lactobacillus). Inocula, reactor configurations, and substrates influence the microbial communities. This is the first joint effort that evaluates hydrogen-producing reactors and operational conditions from different countries and contributes to understand the dark fermentation process.

Microbial community composition and reactor performance during hydrogen production in a UASB reactor fed with raw cheese whey inoculated with compost.

This study investigated the microbial community developed in a UASB reactor for hydrogen production and correlated it to reactor performance. The reactor was inoculated with kitchen waste compost and fed with raw cheese whey at two organic loading rates, 20 gCOD/Ld and 30 gCOD/Ld. Hydrogen production was very variable, using an OLR of 30 gCOD/Ld averaged 1.0 LH(2)/Ld with no methane produced under these conditions. The hydrogen yield was also very variable and far from the theoretical. This low yield could be explained by selection of a mixed fermentative population with presence of hydrogen producing organisms (Clostridium, Ruminococcus and Enterobacter) and other non-hydrogen producing fermenters (Lactobacillus, Dialister and Prevotella). The molecular analysis of the raw cheese whey used for feeding revealed the presence of three predominant organisms that are affiliated with the genera Buttiauxella (a low-yield hydrogen producer) and Streptococcus (a lactic acid-producing fermenter). Although these organisms did not persist in the reactor, the continuous addition of these fermenters could decrease the reactors hydrogen yield.

Anaerobic-aerobic treatment of municipal solid waste leachate

This paper describes the organic matter removal from sanitary landfill leachate using an anaerobic reactor and an aerobic one as post-treatment. Average characteristics of the leachate from Montevideos sanitary landfill are: COD, 18500 mg l−1; BOD5, 10500 mg l−1; NH4-N, 1500 mg l−1; P, 17 mg l−1; pH, 8.0; Cr, 2.6 mg l−1; Fe, 41 mg l−1; Ca, 408mg l−1. A system composed of an anaerobic reactor (UASB) and an aerobic rotating biological contactor (RBC) was tested. The maximum load for the anaerobic step was 20 kgCOD m−3 d−1 (1.8 kgCOD kgVSS−1 d−1) for an HRT of 2 days, with COD removal efficiencies higher than 80%. RBC efficiency was 72% at the maximum loading rate of 15 gCOD m−2 d−1. During the experiences, changes occurred in the landfill leading to a leachate pH increase. Due to the high free ammonia concentrations of leachate, inhibition threshold values reported in the literature were reached in the UASB reactor. However, this inhibition could be reverted by adjusting the inlet pH. In order to investiga...

Modelling of an EGSB treating sugarcane vinasse using first-order variable kinetics

An expanded granular sludge bed (EGSB) anaerobic reactor treating sugar cane vinasse was modelled using a simple model with two steps (acidogenesis and methanogenesis), two populations, two substrates and completely mixed conditions. A first-order kinetic equation for both steps with time-variant kinetic coefficients was used. An observer system was used to estimate the evolution of kinetic constants over time. The model was validated by comparing methane flow predictions with experimental values. An estimation of evolution of populations of microorganisms was also performed. This approach allows calculation of specific kinetic constants that reflect biological activity of microorganisms. Variation of specific kinetic constants reflects the influence of the fraction of raw vinasse in the feed. High salt concentrations in the reactor may have inhibited the process.

Anaerobic treatment of yeast manufacturing wastewater in UASB reactors

Abstract This paper describes the behaviour of the wastewater of a yeast manufacturing plant, treated in UASB reactors. Test runs were made in a straight UASB, an UASB with recycle and a series combination of both. Maximum load attained is 10 KgCODm‐3d‐1 for an HRT of 36 hours. It was found out that the wastewater contains about 35% of soluble non biodegradable COD, under the study conditions imposed. The recycle reactor processed slightly higher loads, developing smaller and more even sized granules.

Sludge deterioration in a full scale UASB reactor after a pH drop working under low loading conditions

A full scale UASB reactor treating the effluent of a malting plant was operated during nearly two years. During 37 weeks of operation the reactor worked with a COD removal efficiency of 80% and a biogas production of nearly 300 m(3)/d with a methane content of 77%. After the start up and during these months of operation the volumetric organic load was 4 kgCOD/m(3).d and the specific organic load was between 0.2-0.4 kgCOD/kgVSS.d. The sludge SMA in this period was around 0.25 kgCOD/kg VSS.d. On week 37 as a result of a problem at the industrial process the pH in the reactor dropped to a value of 4.8. After pH recovering, the reactor worked with fluctuating COD values in the exit and showed a downward trend in the COD removal efficiency. On week 81 the presence of filaments in the granules was detected. High proportion of Chloroflexi filaments were detected by FISH in the sludge. Changes in the microbial population caused by the low pH probably destabilize the reactor performance. The presence of filamentous granules in the sludge and its further growing could be encouraged by the pH drop and the low specific organic load applied to the reactor. The low specific organic load was a consequence of the high VSS content in the UASB reactor, due to the lack of purges. The length of the filaments attached to the granules grew throughout time. In order to eliminate the sludge with poor settlement properties a recycle was applied to the reactor. As a consequence, low amount of granular sludge stayed in the reactor. At the end, COD concentration in the influent reached higher values than in normal operation; at the same time a complete sludge wash out occurred. On the other hand, using the same sludge (after the recycle implementation) in a bench scale reactor the good properties of the sludge were completely recovered.

Assessment on the performance of a series of two UASB reactors compared against one of the same total volume using Anaerobic Digestion Model No 1 (ADM1)

The ADM1 is applied to simulate the behaviour of an Upflow Anaerobic Sludge Blanket Reactor (UASB) treating blood powder (spray dried blood meal) wastewater. Considering a completely mixed liquid phase, the model is defined by a set of differential equations which can be numerically solved. Experimental data allows validating the output of the model which is then used for performing numerous simulations. A single reactor is compared to a series of two identical reactors of half the volume each. For the same total hydraulic retention time, the series reaches an outlet concentration 74% inferior to that of the single reactor. Furthermore, for the same total conversion the volume required by the series is 43% of that of the single reactor.