Granulation and sludge bed stability in upflow anaerobic sludge bed reactors in relation to surface thermodynamics

Abstract

Adhesion of bacteria involved in anaerobic consortia was investigated in upflow anaerobic sludge bed reactors and was related to surface thermodynamics. The adhesion of hydrophilic cells appeared to be enhanced at a low liquid surface tension (␥ LV), while the adhesion of hydrophobic cells was favored at a high ␥ LV. Growth in protein-rich growth media resulted in low granular biomass yields; addition of polycations, such as poly-L-lysine and chitosan, increased the ␥ LV and the granular biomass yield. On the basis of the results of activity tests and microbial counts with wash-out cells, we identified two types of structured granules that were related to the influence of ␥ LV. In one type of granules, hydrophilic acidogens surrounded a more hydrophobic methanogenic association. These granules were selected at a low ␥ LV provided that carbohydrates were available as substrates. The other type of granules was selected at a high ␥ LV ; hydrophobic cells (i.e., methanogens) were predominant throughout these granules. The granules which had acidogens as solid-phase emulsifiers around a methanogenic association appeared to allow more stable reactor performance. Decreasing the ␥ LV in the reactor by adding trace amounts of a surfactant also increased reactor stability.

Physico-chemistry of initial microbial adhesive interactions – its mechanisms and methods for study

“…Coaggregation between microbial pairs has almost exclusively been studied in the oral ¢eld. Hence most examples on microbial coaggregation dealt with in this section originate from this domain, although there is increasing interest in developing degradative microbial communities through the formation of ordered microbial coaggregates [234]. Only recently have studies into oral microbial coaggregation taken a physicochemical approach, often complementary to biochemical and structural studies [122,235].…”

Effect of variation in the C/[N+P] ratio on anaerobic digestion

“…For the correct start-up of the anaerobic process, some authors have established an optimal value of around 300:5:1 for COD:N:P [12,13]. As regards the C:N:P ratio, the optimal balance is between 400:5:1 and 100:28:6 [14,15]. As these proportions are not found for the treatment of all types of wastes, one alternative is to mix different wastes (anaerobic co-digestion) to ensure that the substrate fed to the digester has an adequate ratio.…”

Enhancement of biomass retention in an EGSB reactor used to treat 1‐methoxy‐2‐propanol

“…12 Moreover, the use of chitosan can prevent washout of methanogens due to the formation of an elastic hydrophilic layer and a hydrophobic inner core. 13 Chitosan is also preferred because it is non-toxic, biodegradable, and environmentally friendly. The efficiency of chitosan for flocculation depends on several factors, such as the deacetylation degree (DD) and the molecular weight.…”