ANN	Artificial Neural Network
ASM1	Activated Sludge Model N.1
ASM2	Activated Sludge Model N.2
ASM2d	Activated Sludge Model N.2d
AuC	Area under the Curve
$BO{D}_5$	Biochemical Oxygen Demand (mg/L)
BP	Back-propagation
BPTT	Back-propagation Through Time
BSM1	Benchmark Simulation Model N.1
BSM2	Benchmark Simulation Model N.2
$COD$	Chemical Oxygen Demand
DC	Default Control Scenario
DCPS	Default Control Prediction Structure
DCPS-NH	DCPS for $S_{NH,e}$
DCPS-NT	DCPS for $S_{Ntot,e}$
ECAPS	Effluent Concentration & Alarm Prediction System
FFNN	Feed-forward Neural Network
FG	LSTM’s Forget Gate
HC	Hierarchical Control scenario
HCNH	Hierarchical Control for Ammonium
HCNtot	Hierarchical Control for Total Nitrogen
HCPS	Hierarchical Control Prediction Structure
HCPS-NH	HCPS for $S_{NH,e}$
HCPS-NT	HCPS for $S_{Ntot,e}$
HP	Horizon of prediction
IG	LSTM’s Input Gate
IoT	Internet of Things
IWA	International Water Association
$K_{l}a$x	Oxygen transfer coefficient for tank x (day${}^{-1}$)
LSTM	Long-Short Term Memory
MAPE	Mean average percentage error
MLP	Multilayer perceptron
MPC	Model predictive control
MSE	Mean-squared error
OG	LSTM’s Output Gate
OL	Open Loop scenario
OLPS	Open Loop Prediction Structure
OLPS-NH	OLPS for $S_{NH,e}$
OLPS-NT	OLPS for $S_{Ntot,e}$
$P_d$	Detection probability
$P_{fa}$	False alarm probability
PI	Proportional integral controller
$q_{EC,x}$	External carbon flow rate at tank x (m${}^3$/day)
$Q_a$	Internal recirculation flow rate (m${}^3$/day)
$Q_e$	Effluent flow rate (m${}^3$/day)
$Q_{in}$	Influent flow rate (m${}^3$/day)
$Q_{po}$	Primary clarifier’s flow rate (m${}^3$/day)
$Q_r$	Sludge internal recycle flow rate (m${}^3$/day)
R	Correlation coefficient
$R^2$	Determination coefficient
RMSE	Root-mean-squared error
RNN	Recurrent neural network
ROC	Receiver operating characteristic
$S_{NH}$	Ammonium concentration (mg/L)
$S_{NH,e}$	Ammonium concentration in the effluent (mg/L)
$S_{Ntot}$	Total nitrogen concentration (mg/L)
$S_{Ntot,e}$	Total Nitrogen Concentration in the effluent (mg/L)
$S_{O,x}$	Dissolved oxygen concentrations at tank x (mg/L)
$S_{P,e}$	Total phosphorus concentration in the effluent (mg/L)
$SS$	Suspended solids (mg/L)
$T_{as}$	Environment temperature (°C)
$TKN$	Total Kjeldahl nitrogen (mg/L)
$TSS$	Total suspended solids (mg/L)
WL	Window length
WWTP	Wastewater treatment plant
${\widehat{y}}_t$	ANN-based soft sensor’s predictions
$\gamma$	Alarm Generator’s threshold (mg/L)
${\gamma }_{NH,e}$	$S_{NH,e}$ threshold (mg/L)
${\gamma }_{Ntot,e}$	$S_{Ntot,e}$ threshold (mg/L)