Abstract
The impact of using different plastic mesh in rotating biofilm reactors (RBRs) on the treatment performance, biofilm activity and viability under varying organic loading rates (OLRs) was investigated. Laboratory-scale RBRs treating real wastewater were operated under OLR loading conditions typical of pre-treatment processes. A fully-crossed, three-factorial design series of experiments was undertaken with low and high surface area mesh made from polyvinyl chloride (PVC) and polypropylene (PP) operated at low, medium, high and very high OLR. The maximum volumetric removal rate of 2.4kgsCODm3d−1 occurred at the high OLR, for low surface area mesh, irrespective of plastic used. The highest OLR at which nitrification could be attained was 35gsCODm−2d−1. The biofilm growth decreased under medium compared to low OLR on all mesh. This coincided with a ∼2 fold decrease in the microbial viability. Higher surface area mesh was important for high nitrification rates at medium OLR (p<0.05). In contrast the low surface area PVC and PP mesh was best at very high OLR (160gsCODm−2d−1 or ∼320gBOD5m−2d−1) for bulk organics removal (p<0.05). Therefore, lower surface area mesh is recommended for wastewater pre-treatments at high OLR, whilst high surface area mesh was best for elevated nitrification rates at medium OLR. The microbial activity and viability had a strong positive correlation with OLR (R2=0.92, p<0.001 and 0.81, p<0.001 respectively). The microbial activity and viability also positively correlated (R2=0.4, p<0.05 and 0.29, p<0.01 respectively) to the sCOD removal performance but not the ammonia removal in mesh RBRs. This confirms the importance of maintaining biofilm activity and viability for bulk organics removal in biofilm processes in wastewater treatment.
Highlights
Achieving more stringent effluent standards in conventional biological treatment is usually contingent on factors such as extended reactor retention times and aeration rates, both of which increase the cost of treatment
A rotating biofilm reactor (RBR) known as shaft mounted advanced reactor technology (SMART) has shown promise for high organic load treatment (Hoyland et al, 2010). These units are similar to rotating biological contactors (RBCs) but with an open architecture mesh comprised of fibres arranged in a high porosity mesh, which overcomes the limitations of RBC-like reactors under high load conditions (Chen et al, 2006; Hassard et al, 2014, 2015)
In order to minimise the cost of treatment and maximise value of existing assets, the SMART unit operates as a roughing biofilm, for
Summary
Achieving more stringent effluent standards in conventional biological treatment is usually contingent on factors such as extended reactor retention times and aeration rates, both of which increase the cost of treatment. A rotating biofilm reactor (RBR) known as shaft mounted advanced reactor technology (SMART) has shown promise for high organic load treatment (Hoyland et al, 2010). These units are similar to rotating biological contactors (RBCs) but with an open architecture mesh comprised of fibres arranged in a high porosity mesh, which overcomes the limitations of RBC-like reactors under high load conditions (Chen et al, 2006; Hassard et al, 2014, 2015). The microbial population is attached on a solid media, which allows greater flow rates, OLR and process stability than is possible in most suspended culture systems (Stephenson et al, 2013)
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