Spatial microbial distributions of nitrifiers and heterotrophs in mixed-population biofilms

Abstract

Spatial microbial distributions of nitrifiers and heterotrophs in undefined mixed‐population biofilms were experimentally investigated using a microslicer technique and correlated with nitrification efficiency of the biofilm system. The general stratification of different bacterial groups in the biofilm was simulated using a one‐dimensional (1‐D) mathematical biofilm accumulation model (BAM) and compared with the experimental results. Biofilms were cultured at three C : N ratios of feed solutions in a partially submerged rotating biological contactor (RBC). It was shown that the biofilms were vertically stratified (from biofilm surface to substratum). At C : N = 0, heterotrophs and nitrifiers coexisted in the outermost biofilm and heterotrophs dominated in the innermost biofilm. At C : N = 1.5, heterotrophs outcompeted nitrifiers for dissolved oxygen and space; thus, heterotrophs dominated in the outermost biofilm and nitrifiers were present only in the deeper biofilm. Nitrifiers and heterotrophs coexisted in the innermost biofilm. An increase in the influent C : N ratio resulted in stronger stratification of microbial species, as well as inhibition of nitrification. In batch experiments, NH4N utilization rate (R NH 4N) was almost the same at each substrate C : N ratio even though NH4 oxidizers were predominantly present in the deeper biofilm. The biofilm performance could not be sufficiently explained by the obtained microbial spatial distribution, suggesting that one‐dimensional description of microbial distribution was not good enough and three‐dimensional measurements of microbial spatial distribution is necessary. Total bacterial densities increased by a factor of 3–17 with biofilm depth. The metabolically active cell fraction decreased from 35 ± 13% in the outermost biofilm to 15 ± 4% in the innermost biofilm, presumably due to substrate limitation. The model predicted more pronounced stratification of nitrifiers and heterotrophs than the observed results. This discrepancy could be attributed to the real biofilms that were structurally heterogeneous (e.g., water channels), which could not be described by the one‐dimensional model. The results of this study clearly indicate the limitation of 1‐D biofilm models to describe the extent of stratification of nitrifiers and heterotrophs and suggest a 3‐D model is necessary. © 1996 John Wiley & Sons, Inc.

Nitrite Removal Performance and Community Structure of Nitrite-Oxidizing and Heterotrophic Bacteria Suffered with Organic Matter

“…However, when the ecosystem is supplied with organic carbon, the heterotrophic bacteria compete with the nitrifiers for ammonia and oxygen and are always the winner due to their faster growth rate. As a result, the nitrification efficiency is reduced in most cases [8,11,12].…”

“…Many studies have reported that the overgrowth of nitrifiers by heterotrophs resulted in a lower nitrifying capacity of the biofilm reactor with the supplement of organics [8,11,12]. However, in our experiment, the nitrite removal rate did not fall as the normal culture was supplied with sodium acetate, although both the total protein and community structure analyses indicated that the heterotrophic bacteria were the majority.…”

“…We attributed this unique phenomenon to three reasons. First, our system was suspension and underwent short-term incubation, so the nitrifiers did not suffer from oxygen transport limitation and dilution by heterotrophs, which were the main causes of nitrification retardance in the earlier studies [8,12,18]. Second, the NOB was able to utilize both nitrite and organic carbon as energy sources for growth.…”

Nitrifying, Denitrifying and Heterotrophic Biomass Present in Moving Bed-Reactor

“…SM presence can favor bacteria distribution with faster growth rate in upper biofilm layers (where substrate passage and microorganisms shedding is higher), while slow growing nitrifying bacteria, grow inside the biofilm, preventing their drag out from the reactor, thus, biofilm formed of heterotrophic bacteria may present a greater thickness than biofilms composed of autotrophic bacteria (Okabe et al,1996a). Bassin et al (2012) when analyzing biofilm on micrographs, observed that nitrifying biomass is significantly changed when effluent COD is reduced, it was also noticed that in some parts of its SM, biofilm detachment was registered when COD was diminished.…”

Eliminación de nutrientes mediante tratamientos biopelícula : corrientes actuales y necesidades de investigación

“…El control de la edad del fango en el reactor biológico, por tanto, es un parámetro importante en la operación de las depuradores. Normalmente los fangos aerobios granulares son más heterogéneos en relación a las bacterias que coexisten en su interior y a las micro-características morfológicas de la biopelícula (De Beer et al 1996) (Okabe et al 1996).…”