Thermophilic anaerobic digestion of winery effluents in a two-stage process and the effect of the feeding frequency on methane production.

This investigation evaluates a two-stage process to treat highly concentrated winery effluents, including a thermophilic methanogenic stage. The inoculum adaptation, the effect of the organic loading rates on both stages, and the methanogenic reactor's feeding frequency on the process performance were studied. An active thermophilic inoculum was obtained by a one-step temperature increase from 35 to 55 °C. The application of organic loads above 120 kg COD m-3 d-1 in the acidogenic stage ensured the highest acetic acid concentration, while methane production rates as high as 7.1 Nm3 CH4 m-3 d-1 and a yield of 348 L CH4 kg-1 COD were obtained in the thermophilic methanogenic stage using an organic loading rate of 29.9 kg COD m-3 d-1. However, a lower removal of organic matter was observed under that condition. Lower feeding frequencies improved methane productivity and yield, suggesting that this parameter is a useful process optimization tool.

Microbial community dynamics during aerobic granulation in a sequencing batch reactor (SBR).

Microorganisms in aerobic granules formed in sequencing batch reactors (SBR) remove contaminants, such as xenobiotics or dyes, from wastewater. The granules, however, are not stable over time, decreasing the removal of the pollutant. A better understanding of the granule formation and the dynamics of the microorganisms involved will help to optimize the removal of contaminants from wastewater in a SBR. Sequencing the 16S rRNA gene and internal transcribed spacer PCR amplicons revealed that during the acclimation phase the relative abundance of Acinetobacter reached 70.8%. At the start of the granulation phase the relative abundance of Agrobacterium reached 35.9% and that of Dipodascus 89.7% during the mature granule phase. Fluffy granules were detected on day 43. The granules with filamentous overgrowth were not stable and they lysed on day 46 resulting in biomass wash-out. It was found that the reactor operation strategy resulted in stable aerobic granules for 46 days. As the reactor operations remained the same from the mature granule phase to the end of the experiment, the disintegration of the granules after day 46 was due to changes in the microbial community structure and not by the reactor operation.

Microbial community structure in aerobic and fluffy granules formed in a sequencing batch reactor supplied with 4-chlorophenol at different settling times.

Toxic compounds, such as 4-chlorophenol (4-CP), which is a common pollutant in wastewater, are removed efficiently from sequencing batch reactors (SBRs) by microorganisms. The bacterial community in aerobic granules formed during the removal of 4-CP in a SBR was monitored for 63days. The SBR reactor was operated with a constant filling and withdrawal time of 7 and 8min and decreasing settling time (30, 5, 3 and 2min) to induce the formation of aerobic granules. During the acclimation period lasting 15days (30min settling time) had a strong effect on the bacterial community. From day 18 onwards, Sphingobium and Comamonadaceae were detected. Rhizobiaceae were dominant from day 24 to day 28 when stable aerobic granules were formed. At day 35, fluffy granules were formed, but the bacterial community structure did not change, despite the changes in the reactor operation to inhibit filamentous bacteria growth. This is the first report on changes in the bacterial community structure of aerobic and fluffy granules during granulation process in a reactor fed with 4-CP and the prediction of its metabolic pathways.

Microrespirometric determination of the effectiveness factor and biodegradation kinetics of aerobic granules degrading 4-chlorophenol as the sole carbon source.

In this study, a microrespirometric method was used, i.e., pulse respirometry in microreactors, to characterize mass transfer and biodegradation kinetics in aerobic granules. The experimental model was an aerobic granular sludge in a sequencing batch reactor (SBR) degrading synthetic wastewater containing 4-chlorophenol as the sole carbon source. After 15 days of acclimation, the SBR process degraded 4-chlorophenol at a removal rate of up to 0.9kg CODm(-3)d(-1), and the degradation kinetics were well described by the Haldane model. The microrespirometric method consisted of injecting pulses of 4-chlorophenol into the 24 wells of a microreactor system containing the SBR samples. From the respirograms obtained, the following five kinetic parameters were successfully determined during reactor operation: (i) Maximum specific oxygen uptake rate, (ii) substrate affinity constant, (iii) substrate inhibition constant, (iv) maximum specific growth rate, and (v) cell growth yield. Microrespirometry tests using granules and disaggregated granules allowed for the determination of apparent and intrinsic parameters, which in turn enabled the determination of the effectiveness factor of the granular sludge. It was concluded that this new high-throughput method has the potential to elucidate the complex biological and physicochemical processes of aerobic granular biosystems.

Characterization of oxygen transfer in a 24-well microbioreactor system and potential respirometric applications.

The assessment of microbial processes is often done in Microbioreactor systems (MBRs), which allow for parallel cultivation in multiple independent wells. MBRs often include dissolved oxygen sensors, which are convenient for process characterization through oxygen uptake rate and other respirometric determinations. In order to assess respirometric potential of MBRs, a complete assessment of the DO fluorescent quenching sensors was done, showing that they presented a typical error of 0.56%, a signal to noise ratio of 189, a response time from 5.7 to 7.2 s and no drift over a period of 24 h. Then, KLa in the MBR was measured with different cassette and cap designs, liquid volumes, agitation rates, gas flow rates, temperatures and ionic strengths. KLa ranged from 8 to 90 h(-1), with a standard deviation between replicates from 2.8 to 17.5%. From these results and a numerical simulation, it was shown that the MBR tested allow the determination of oxygen uptake rates in a range from 0.038 to 3390 mg L(-1) h(-1), with a determination error less than 15%. Besides OUR determination, it was concluded that the MBR tested is also a convenient tool for dynamic pulse respirometry methods, based on experimental confirmation with four different cultures.