Biomethanization of waste derived from strawberry processing: advantages of pretreatment

The strawberry-tasted food is one of the most demanded products in the modern society, generating more than one harvest per year even at unfavorable environmental conditions thanks to the growing into green-houses. The manufacturing of products derived from strawberry generates a high volume of organic waste which presents environmental problems in the generation areas, being compulsory to evaluate different technical management solutions. When the objective is to produce biogas through biomethanization, the anaerobic valorization of this residue is problematic due to the presence of lignin concentrated in the achenes, which entails the destabilization of the process. Improvement of the mesophilic anaerobic digestion process using a pre-treatment with sieving was evaluated at laboratory scale by comparing the anaerobic digestion of raw strawberry waste and pretreated waste. The results showed an enhancement of the stability for the pretreated waste, while biodegradability was found to be 90% in VS (total volatile solids). Moreover, the proposed pre-treatment led to a 36% improvement in methane production yield (230 versus 312 mLSTP CH4/g VSadded) (STP: 0 °C, 1 atm), gas with high caloric power. Additionally, the permitted OLR (Organic loading rate) was again considerably higher for the pretreated waste (5.3–2.8 versus 8.0–12.0 kg waste/m3 d), permitting to treat much more waste. Nevertheless, an inhibition phenomenon was observed for increasing loads, although it was stronger and occurred at lower loads of untreated waste.