Performance of permeable media rotating reactors used for pretreatment of wastewaters

Biosolids recycling impact on biofilm extracellular enzyme activity and performance of hybrid rotating biological reactors

Biological processes for wastewater treatment is limited by extracellular enzyme activity (EEA) of the biofilm on polymeric substrates. The efficiency of biodegradation / biosorption mechanisms causing EEA and organic load removal in biofilms remains unknown. Our hypothesis was that the limiting step of biological process can be overcome by biostimulation and/or bioaugmentation of the return sludge in hybrid biofilm reactors, which leads to competition between suspended and attached bacteria and lower effective substrate to microrganism ratio. Therefore, we considered more active biosolids to perform best at enhancing reactor removal rate. To test this, the efficacy of recycling distinct bio-solids types considered to have different bacterial activity such as final effluent (FE), humus solids (HS) and recycle activated sludge (RAS) on performance improvements of rotating biofilm reactors (RBRs). These bio-solids were investigated under high organic loading rates (OLR) and solids loading rates (SLR) using pilot scale reactors receiving real municipal wastewaters. Controlled overloading of RBRs revealed that EEA improved with increasing OLR/SLR. High SLR (>3.3 kg Total Suspended Solids m^-2 d^-1) delayed and decreased the reduction of organic and inorganic removal rates in the biological processes which commonly occurs under high OLRs. This effect was more pronounced in the highest activity solids (RAS > HS > FE) suggesting the activity and function of bio-solids was critical to improve performance of RBRs. High OLR and SLR induced efficient denitrification and organics removal within the biofilm reactor at residence times of <5 min. Recycling active solids permitted EEA despite overloading which was critical to the performance of the RBRs.

Microbial extracellular enzyme activity affects performance in a full-scale modified activated sludge process

The rate-limiting step of wastewater treatment is the breakdown of polymers by extracellular enzyme activity (EEA). The efficacy of EEA on biomass from full scale conventional activated sludge (AS) and modified AS with bench scale and full scale rotating biofilm reactors (RBR) was compared. The maximum amino-peptidase EEA was 394 ± 34 μmolL^-1 min^-1 for the bench RBR which was 11.7 and 4.5 times greater than maximum α-glucosidase and phosphatase EEA in these reactors. At full scale the RBR gave ~4.6, 13.5 and 6.3 times the EEA for amino-peptidase, α-glucosidase and phosphatase (based on enzyme V_max) compared to the highest EEA in conventional AS biomass. Controlled overloading of the bench RBRs revealed that EEA increased with OLR up to 190 g tCOD m^-2d^-1 and further increases in OLR reduced the EEA. Pretreatment of wastewater by EEA in the RBR was linked to better performance of the modified activated sludge process. Maintaining high EEA of biofilms is critical for the design of high OLR wastewater treatment systems.

Abundance and Distribution of Enteric Bacteria and Viruses in Coastal and Estuarine Sediments-a Review

The long term survival of fecal indicator organisms (FIOs) and human pathogenic microorganisms in sediments is important from a water quality, human health and ecological perspective. Typically, both bacteria and viruses strongly associate with particulate matter present in freshwater, estuarine and marine environments. This association tends to be stronger in finer textured sediments and is strongly influenced by the type and quantity of clay minerals and organic matter present. Binding to particle surfaces promotes the persistence of bacteria in the environment by offering physical and chemical protection from biotic and abiotic stresses. How bacterial and viral viability and pathogenicity is influenced by surface attachment requires further study. Typically, long-term association with surfaces including sediments induces bacteria to enter a viable-but-non-culturable (VBNC) state. Inherent methodological challenges of quantifying VBNC bacteria may lead to the frequent under-reporting of their abundance in sediments. The implications of this in a quantitative risk assessment context remain unclear. Similarly, sediments can harbor significant amounts of enteric viruses, however, the factors regulating their persistence remains poorly understood. Quantification of viruses in sediment remains problematic due to our poor ability to recover intact viral particles from sediment surfaces (typically <10%), our inability to distinguish between infective and damaged (non-infective) viral particles, aggregation of viral particles, and inhibition during qPCR. This suggests that the true viral titre in sediments may be being vastly underestimated. In turn, this is limiting our ability to understand the fate and transport of viruses in sediments. Model systems (e.g., human cell culture) are also lacking for some key viruses, preventing our ability to evaluate the infectivity of viruses recovered from sediments (e.g., norovirus). The release of particle-bound bacteria and viruses into the water column during sediment resuspension also represents a risk to water quality. In conclusion, our poor process level understanding of viral/bacterial-sediment interactions combined with methodological challenges is limiting the accurate source apportionment and quantitative microbial risk assessment for pathogenic organisms associated with sediments in aquatic environments.