Development of Decay in Biofilms under Starvation Conditions—Rethinking of the Biomass Model

Abstract

The study investigates the decay of heterotrophic biomass in biofilms under starvation conditions based on measurements of the oxygen uptake rate (OUR). Original incentive was to understand the preservation of active biomass in SBR-trickling filter systems (SBR-TFS), treating event-based occurring, organically polluted stormwater. In comparison with activated sludge systems, the analyzed biofilm carrier of SBR trickling filters showed an astonishing low decay rate of 0.025 d−1, that allows the biocenosis to withstand long periods of starvation. In activated sludge modeling, biomass decay is regarded as first order kinetics with a 10 times higher constant decay rate (0.17–0.24 d−1, depending on the model used). In lab-scale OUR measurements, the degradation of biofilm layers led to wavy sequence of biomass activity. After long starvation, the initial decay rate (comparable to activated sludge model (ASM) approaches) dropped by a factor of 10. This much lower decay rate is supported by experiments comparing the maximum OUR in pilot-scale biofilm systems before and after longer starvation periods. These findings require rethinking of the approach of single-stage decay rate approach usually used in conventional activated sludge modelling, at least for the investigated conditions: the actual decay rate is apparently much lower than assumed, but is overshadowed by degradation of either cell-internal substrate and/or the ability to tap “ultra-slow” degradable chemical oxygen demand (COD) fractions. For the intended stormwater treatment, this allows the application of technical biofilm systems, even for long term dynamics of wastewater generation.

Modeling a Three-Stage Biological Trickling Filter Based on the A2O Process for Sewage Treatment

“…Biological trickling filters (BTFs) are a kind of artificial biological treatment technology developed using an intermittent sand filter and a contact filter based on the principle of soil self-purification and the practice of sewage irrigation [16]. The BTF is a new type of biofilm technology that integrates biodegradation and solid-liquid separation.…”

“…Tao et al [14] simulated the partial nitrification anammox (PN/A) process of moving bed biofilm reactor (MBBR) and integrated fixed-film activated sludge (IFAS). Cramer et al [16] investigated the decay of heterotrophic biomass in biofilms of trickling filters. To simulate the WWTP more effectively, the ASMs and ADMs are integrated into the software package that includes Biowin, Gps-x, West, and Sumo, among others.…”