diff --git a/dependencies/asm3_class.js b/dependencies/asm3_class.js
index 93c7364..ce44f96 100644
--- a/dependencies/asm3_class.js
+++ b/dependencies/asm3_class.js
@@ -62,7 +62,6 @@ class ASM3 {
   }
 
   constructor() {
-    // S_O, S_I, S_S, S_NH, S_N2, S_NO, S_HCO, X_I, X_S, X_H, X_STO, X_A, X_TS
     this.stoi_matrix = this._initialise_stoi_matrix()
   }
 
@@ -96,7 +95,7 @@ class ASM3 {
   }
 
   compute_rates(state) { // computes reaction rates. state is optional
-
+    // state: S_O, S_I, S_S, S_NH, S_N2, S_NO, S_HCO, X_I, X_S, X_H, X_STO, X_A, X_TS
     const rates = Array(12);
     const [S_O, S_I, S_S, S_NH, S_N2, S_NO, S_HCO, X_I, X_S, X_H, X_STO, X_A, X_TS] = state;
     const { k_H, K_X, k_STO, nu_NO, K_O, K_NO, K_S, K_STO, mu_H_max, K_NH, K_HCO, b_H_O, b_H_NO, b_STO_O, b_STO_NO, mu_A_max, K_A_NH, K_A_O, K_A_HCO, b_A_O, b_A_NO } = this.kin_params;
@@ -123,6 +122,7 @@ class ASM3 {
   }
 
   compute_dC(state){ // compute changes in concentrations
+    // state: S_O, S_I, S_S, S_NH, S_N2, S_NO, S_HCO, X_I, X_S, X_H, X_STO, X_A, X_TS
     return math.multiply(this.stoi_matrix, this.compute_rates(state));
   }
 }
diff --git a/dependencies/reactor_class.js b/dependencies/reactor_class.js
index 04527e8..5863dd0 100644
--- a/dependencies/reactor_class.js
+++ b/dependencies/reactor_class.js
@@ -6,16 +6,34 @@ class Reactor_CSTR {
     constructor(initial_state){
         this.state = initial_state;
         this.asm = new ASM3();
+
+        this.Vl = 10.0; // fluid volume reactor [m3]
+        this.F = 1.0; // fluid debit [m3 d-1]
+        this.C_in = Array(13).fill(0.0); // composition influent
+        this.OTR = 1000.0; // oxygen transfer rate [g O2 d-1]
     }
 
     tick_fe(time_step){ // tick reactor state using forward Euler method
-        const delta = this.asm.compute_dC(this.state);
-        this.state = math.add(this.state, math.multiply(delta, time_step));
+        const r = this.asm.compute_dC(this.state);
+        const dC_in = math.multiply(this.C_in, this.F/this.Vl);
+        const dC_out = math.multiply(this.state, this.F/this.Vl);
+        const T_O = Array(13).fill(0.0);
+        T_O[0] = this.OTR;
+
+        const dC_total = math.multiply(math.add(dC_in, dC_out, r, T_O), time_step);
+
+        this.state = math.add(this.state, dC_total);
         return this.state;
     }
 }
 
 // testing stuff
-let state = [0.1, 0.1, 0.1, 0.1, 0.1, 0.1, 0.1, 0.1, 0.1, 0.1, 0.1, 0.1, 0.1];
-const Reactor = new Reactor_CSTR(state);
-console.log(Reactor.tick_fe(0.001));
\ No newline at end of file
+// state: S_O, S_I, S_S, S_NH, S_N2, S_NO, S_HCO, X_I, X_S, X_H, X_STO, X_A, X_TS
+let initial_state = [0.1, 0.1, 0.1, 0.1, 0.1, 0.1, 0.1, 0.1, 0.1, 0.1, 0.1, 0.1, 0.1];
+const Reactor = new Reactor_CSTR(initial_state);
+Reactor.C_in = [0.0, 30., 100., 16., 0., 0., 5., 25., 75., 30., 0., 0., 125.];
+N = 0;
+while (N < 15) {
+    console.log(Reactor.tick_fe(0.001));
+    N += 1;
+}
\ No newline at end of file