Hydrolysis and degradation of filtrated organic particulates in a biofilm reactor under anoxic and aerobic conditions

Abstract

Two experiments were performed in order to investigate the anoxic and the aerobic degradation of filtrated organic matter in a biofilter. In submerged lab. scale reactors with Biocarbone media as filter material, accumulated particulate organic matter from pre-settled wastewater served as the only carbon source for anoxic and aerobic degradation respectively. In order to utilise the accumulated organic matter, the bacteria in the biofilm had to produce extracellular hydrolytic enzymes for the hydrolysis process. In the first experiment with anoxic degradation, a significant denitrification occurred. The maximum nitrate removal rate, with particulate organic matter as carbon source, was found to 1 g NO3-N/ (m2d), declining exponentially as rA.NO3-N = 1.04 e −4t g NO3-N/(m2d) (t = days). A significant release of soluble organic matter (< 0.45 μm) and production of inorganic carbon to the bulk liquid was observed as an indication of hydrolysis taking place. The second experiment was designed as a series of on-line OUR batch experiments in a biofilm reactor with recirculation, in order to investigate further the degradation of particulate organic matter. After the biofilm had been starved in order to remove the original organic matter, particulate organic matter was added and the degradation kinetics recorded. The initial removal rate was high, rA.02 = 2.1 g O2/(m2d) though fast declining towards endogenous respiration. The respiration ratio between removed oxygen and produced carbon dioxide was declining from 1.3 to 1.0 g O2/g CO2 during the degradation of organic particulates. The respiration ratio during endogenous respiration was determined to be 0.7 g O2/g CO2 indicating a thorough mineralisation of biomass.

A simplified mixed-culture biofilm model

“…This hypothesis is supported by experimental results from Janning et al (1997). According to the assumptions underlying the model concept (assumption (5)) readily biodegradable organic matter from hydrolysis is modelled as being instantaneously transferred into the bulk liquid.…”

Endogenous model state and parameter estimation from an extensive batch experiment

“…In recent years an increasing interest in the modeling of the endogenous subprocess, in particular for activated sludge processes, has been developed (Beeftink et al, 1990;Dold et al, 1980;Droste, 1996;Horn and Hempel 1997;Janning et al, 1997;Keesman et al, 1998;Pirt, 1965;Ratsak et al, 1996;Spanjers, 1993;Sykes, 1991;Torrijos et al, 1994;Wentzel et al, 1992;Yuan and Stenstrom, 1996). In microbiological literature endogenous respiration is defined in terms of maintenance: it occurs when there is no observed substrate consumption and when maintenance ATP is obtained from biomass degradation.…”

Nitrogen Removal in Fixed-Bed Submerged Biofilters without Backwashing

“…Previous investigations have suggested that extracellular enzymes have to be released by the biofilm in order to hydrolyse the particulate organic matter (Larsen et al, 1994;Hu et al, 1996). Subsequent research (Janning et al, 1997;Janning et al, 1998) has shown that the hydrolysis process occurs as the only process with wastewater particulates and that only 10% of the particles accumulated on the biofilm was effectively hydrolysed in 12-hour long experiments. It may hi!…”