2.2. Substrate
10 L of sludge were sampled from the bottom of the natural lagoon first settling tank, with help of a gaped can connected to a rope. The initial substrate moisture content was 30%. The sample was conserved at 4 °C before feeding the bioreactors (Tomei, Braguglia et Mininni) [8].
Sludge characteristics were measured in triplicates and were presented in Table 1. The sludge was introduced in the bioreactor with a rate of 16 g TS/l, (Arnaiz, Gutierrez et Lebrato) [9] and (Lastella, Testa et Cornacchia) [10].