International Environmental Modelling and Software Society (iEMSs) 7th International Congress on Environmental Modelling and Software Daniel P. Ames, Nigel W.T. Quinn and Andrea E. Rizzoli (Eds.) http://www.iemss.org/society/index.php/iemss-2014-proceedings Modelling biofilm based technologies with activated sludge unit processes: A short cut to performance simulation? Noelle Jones 1,2 , Maebh Grace 1,2 , Eoghan Clifford 1,2 1 Civil Engineering, College of Engineering & Informatics, NUI Galway, University Road, Galway 2 Ryan Institute, NUI Galway n.jones2@nuigalway.ie eoghan.clifford@nuigalway.ie Abstract: Biofilm-based passive aeration systems (PAS) have attracted recent attention as alternative, energy efficient and low maintenance technologies in the wastewater sector. However the modelling of biofilm-based PAS offers unique challenges for modellers, particularly where new technologies are not easily simulated using existing commercial modelling software. However, if the modeller is concerned only with simulating "macro" plant performance (e.g. key effluent concentrations and cycle analysis) it may be possible to efficiently model these technologies using "surrogate" unit process systems (e.g. using an activated sludge process to model a biofilm process). The pumped flow biofilm reactor (PFBR); a batch biofilm technology, is a recent example of a PAS. As a relatively new technology a predictive model for the PFBR system has yet to be developed. Indeed for novel passive aeration systems in general, it can be time consuming and difficult to develop new models that accurately describe performance. This research investigates the potential for (1) modelling the PFBR (an example of a batch biofilm PAS) using previously developed, simple activated sludge based models (2) predicting effluent results and contaminant concentration changes (nitrogen and organic carbon) during individual treatment cycles using the activated sludge object, and (3) using the calibrated model to predict the optimal operational regimes. Keywords: Passive Aeration Systems, Pumped Flow Biofilm Reactor (PFBR), Wastewater Treatment Technology, Batch Biofilm Reactor, GPS-X, Dissolved Oxygen 1.1 Introduction Wastewater treatment plant modelling is a useful tool for performing plant capacity assessments and optimising plant performance. Such simulations can lead to improved plant performance, along with reduced energy and chemical costs. Devisscher et al., (2006) noted that mathematical modelling can optimise plant efficiencies resulting in reduced costs from aeration processes (between 10% and 20%) and chemical dosing (up to 30%). There are numerous methods and commercial wastewater simulators used to model wastewater treatment processes including ASIM, BioWin, STOAT, Aquasim etc. For this study, GPSX (Hydromantis Inc, Canada), was chosen, though other packages could also be used as many unit processes can be simulated using various software. The Pumped Flow Biofilm Reactor (PFBR) is a novel batch biofilm based technology and has been previously described (O’Reilly et al., 2008, O’Reilly et al, 2011). Briefly, the PFBR is a two reactor technology that employs a unique hydraulic regime and enables aerobic, anoxic and anaerobic conditions to be sequenced. Biofilm, growing on plastic media modules within the two reactors, is aerated passively as wastewater is moved alternately between the reactors during an aeration sequence. Thus as the two reactors empty and fill a number of times during a typical aeration sequence, the biofilm is exposed, in turn, to atmospheric air and wastewater. While the PFBR has many of the features of a sequencing batch reactor, due to its configuration, it presents a unique modelling challenge. As a batch reactor, wastewater is treated in discreet cycles, similarly to a sequencing batch reactor (SBR). The aim of this research was to investigate the use of surrogate unit process (an activated sludge SBR) to simulate effluent quality and individual cycle performance in a batch biofilm process (the