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.
Highlights
Biological wastewater treatment is based on the accumulation of a complex consortium of microorganisms in suspended systems, as biofilms attached to carriers, or a combination of both
The decay rate of heterotrophic organism is graphically expressed as a logarithmical decrease of endogenous respiration for activated sludge system
As the used biofilm carrier were grown with a thick biofilm, it seems that the organism makes organic compounds inside the biofilm stepwise accessible as substrate
Summary
Biological wastewater treatment is based on the accumulation of a complex consortium of microorganisms in suspended systems (activated sludge), as biofilms attached to carriers (biofilm systems), or a combination of both. Provided optimal living conditions and substrate supply, the performance of those systems is mainly dependent on mass of metabolic active microorganisms. Long starvation conditions may lead to a significant decrease of performance due to biomass decay. This needs to be assessed when designing treatment technologies for those conditions. Bacteria (as the most relevant group for substrate metabolism in activated sludge and biofilm systems) apply various adaptation strategies to starvation. A reduction of the protein synthesizing system, the ribosomes, has been observed. This process, known as ribophagy is so far
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Disclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.