The 3D contour for the production rate is presented in Figure 2. The maximum rate obtained was 75.8 mL biogas
min–1 with 45 g VS · L–1 · d–1 of OLR and 25.0 % application of NaOH pretreatment concentration, whilst the
minimum observed at 20.52 mL · min–1 of biogas with 25 g g VS · L–1 · d–1 of OLR and 45.0 % of NaOH
(w/w).The contour of 70.00 mL · min–1 of production rate on the range of (44.25 to 45.00) g VS · L–1 · d–1 OLR,
constrained with (27.0 to 39.0) % NaOH can be seen from Figure 3.