Molecular Monitoring of Microbial Population Dynamics During Operational Periods of Anaerobic Hybrid Reactor Treating Cassava Starch Wastewater

Abstract

This study characterized the microbial community and population dynamics in an anaerobic hybrid reactor (AHR) treating cassava starch wastewater. Methanogens and nonmethanogens were followed during the start-up and operation of the reactor, and linked to operational and performance data. Biomass samples taken from the sludge bed and packed bed zones of the AHR at intervals throughout the operational period were examined by 16S rRNA fluorescence in situ hybridization (FISH). The start-up seed and the reactor biomass were sampled during the feeding of the wastewater with a chemical oxygen demand (COD) value of 8 g L(-1) and a hydraulic retention time (HRT) of 8 days. These samples were characterized by the predominance of cells with long-rod morphology similar to Methanosaeta spp. Following a sharp operational change, accomplished by increasing the COD concentration of the organic influent from 8 to 10 g L(-1) and reducing the HRT from 8 to 5 days, there was a doubling of the organic loading rate, a reduction of the COD removal efficiency, as well as decreased methane content in the biogas and an accumulation of total volatile acids in the reactor. Moreover, this operational change resulted in a significant population shift from long-rod Methanosaeta-like cells to tetrad-forming Methanosarcina-like cells. The distributions of microbial populations involved in different zones of the AHR were determined. The results showed that nonmethanogens became the predominant population in both sludge and the packed bed zone. However, the percentage of methanogens in the packed bed zone was higher than that in the sludge bed zone. This higher percentage of methanogens was likely caused by the fact that the packed bed zone provided a suitable environmental condition with an appropriate nutrient availability for methanogen growth.

Viability of rapid startup and operation of UASB reactors for the treatment of cassava wastewater in the semi‐arid region of northeastern Brazil

“…Methane yields were similar to those reported by Paixão et al and Boonapatcharoen et al who reported yields of 0.240 L CH 4 · g −1 COD removed and 0.220 L CH 4 · g −1 COD removed , however the authors used cassava wastewater loads of 5 g COD · L −1 · d −1 and 6 g COD · L −1 · d −1 with 4‐day of HRT. The present results seem more promising, since Paixão et al employed a two‐phase reactor and Boonapatcharoen et al used a single‐phase reactor, though with a 4 day HRT.…”

“…Treating cassava wastewater in a single‐phase hybrid reactor (37 °C), Boonapatcharoen et al found VFA/TA ratios ranging from 0.69 to 0.94, with COD removal efficiencies ranging from 84 to 94 % using OLR of 1 to 6 g COD · L −1 · d −1 , which are lower than those employed in the present investigation. The authors operated the reactor at 37 °C with the alkalinity buffer adjusted to 2.0 g · L −1 using sodium bicarbonate, however with a HRT of 8 to 4 days, much higher than that applied in the present study. Evaluating the stability of a single‐phase anaerobic reactor for the treatment of cassava wastewater, Dias et al report VFA/TA ratios of 0.298, 0.211, 0.265, and 0.776 respectively, using OLR of 1.28, 1.57, 2.68, and 2.93 g COD · L −1 · d −1 .…”

“…Usually startups range from 60 days [3,14] to 192 days. [26] In the present study, the rapid startup and operation of UASB reactors with no design modifications and short HRT were investigated for the treatment of wastewater from cassava flour processing in the Caatinga biome.…”

Characterization of sulfate-reducing bacteria dominated surface communities during start-up of a down-flow fluidized bed reactor

“…Several authors had pointed out that the composition of the microbial community influences the stability and performance of anaerobic reactors, hence the importance of understanding such communities as well as the interactions within, for the effective operation and improvement of the reactor's performance [10,11,18]. These microbial interactions are particularly important in biofilm reactors, and are greatly influenced by the ability of microorganisms to attach to the support at the operational conditions applied to the reactor.…”

Methane Production From Cassava Starch Wastewater in Packed-Bed Reactor and Continuous Flow

“…This reactor configuration also allows the operation without the need for recirculat ion or temperature conditioning, except in regions whose average temperatures are less than 25° (Peixoto et al, 2011). Another advantage of the system is that it can be used the support mean occupying only a part of the useful volu me of the reactor, which in relation to other configurations reduces costs (Boonapatcharoen et al, 2007;Peixoto et al, 2011).…”