Shortcut nitrogen demonstration trial plant performance Aprilia Vellacott 1* , Andrew Tipping 2 , Nathali Christy 2 , James McLeod 2 , Johanna Gladman 2 , Jackie Moss 2 , Joel Segal, David Lynch 1 , Pusker Regmi 3 and Jose Jimenez 3 1 Jacobs (Australia), Melbourne, Australia 2 Melbourne Water Corporation, Melbourne, Australia 3 Brown & Caldwell, USA *To whom correspondence should be addressed. Email: aprilia.vellacott@jacobs.com ABSTRACT A 42,300GPD demonstration shortcut nitrogen removal plant, operated in anoxic/oxic mode with secondary clarification has operated since June 2017 at Melbourne Water’s WTP. There have been four key periods (I - IV) exhibiting a high level of NOB out-selection, indicated by either NAR (= NO2 - /NOx) greater than 0.3 or NOB:AOB activity ratio (determined through ex situ SNR testing) less than 0.5. Period I observed effluent NAR average 0.77, higher than the baseline NAR of 0.01 to 0.17. Periods II, III and IV showed a low ratio of NOB:AOB activity rates, with measured ratios of 0.13 to 0.43, significantly lower than observed plant baseline of approximately 1.0 and the theoretical ratio of 0.78. The most efficient trial period is the sub-period IV(b) with an average ‘COD efficiency’ of 4.2kgCOD/kgTN removed compared with baseline ASP MLE process (9.40 kgCOD/kgTN) and Baseline 2 from the demonstration plant (without NOB out-selection) with 8.4 kgCOD/kgTN. KEYWORDS Short Cut Nutrient Removal, Secondary Treatment, Nitrite Shunt, Effluent TN INTRODUCTION A 42,300GPD (160kL/day) demonstration shortcut nitrogen removal plant, operated in anoxic/oxic (A/O) mode with secondary clarification has operated since June 2017 at Melbourne Water’s Western Treatment Plant (WTP). WTP in Melbourne, Australia treats 140 MGD (530ML/d) sewage with a significant industrial load component. Melbourne Water is undertaking laboratory and demonstration-scale trials of short-cut nitrogen removal processes for implementation in an upcoming major secondary treatment capacity augmentation (Watson, 2016). Carbon diversion for energy recovery is already practiced at the WTP with methane capture from the anaerobic lagoons. Therefore, the objective of this trial is to demonstrate shortcut nitrogen removal to meet low effluent total nitrogen (TN) standards (<10mgN/L) at reduced carbon availability (influent COD:TKN ratio of <7) without adding any supplemental chemicals at temperatures ranging from 17 -25 deg C. A shortcut nitrogen demonstration plant was designed with extensive Biowin TM modelling (Regmi, 2016) and constructed comprising a primary sedimentation tank (used only when feed solids exceed design levels), bioreactor configured as A/O and secondary clarifiers. The plant operates with feed from a primary anaerobic lagoon (hydraulic residence time (HRT) 1.5–3 days). The primary anaerobic lagoon performance varies, providing a demonstration plant influent which displays a wide range of chemical oxygen demand (COD) and total suspended solids (TSS) quality. The plant was designed with nitrite-oxidising bacteria (NOB) out-selection selective pressures and control strategies identified in the WERF manual on 4531