Assessment of biogas and biofertilizer produced from anaerobic co-digestion of olive mill wastewater with municipal wastewater and cow dung

Morocco as a part of Mediterranean countries is threatened by the tremendous quantities dejected of different organic wastes. Without any treatment or management strategy, these wastes are dumped illegally in large quantities and can affect natural resources, especially soil and water. Recently, it seems that the anaerobic co-digestion method is one of the best processes available to treat organic wastes. The aim of this work is to investigate the reduction of toxicity after anaerobic co-digestion of three different mixture of organic waste based on olive mill wastewater (OMW), domestic wastewater (DW) and cow dung (CD)), in three bioreactors (B1: OMW+DW/B2: OMW+DW+CD/B3: OMW+CD). The efficiency of this process was evaluated through the digestates quality as bio-fertilizers using a phytotoxicity test, and their characterizations by Fourier-transform infrared spectroscopy (FTIR) and Scanning Electronic Microscopy SEM, and also the biogas yield during the anaerobic co-digestion process. The highest biogas volume was obtained from bioreactor B2 (476.69 mL CH4 g-1 VS); the mixture of the three wastes OMW, DW and CD (1/1/1). Phytotoxicity test indicated that anaerobic co-digestion process reduced slightly the phytotoxicity of substrates. The FTIR spectra and SEM images confirmed that the anaerobic co-digestion process successfully carried out by microstructural changes after the process. Principal component analysis (PCA), Spearman correlations and cluster analysis were combined between biogas produced and all physical–chemical and biological parameters, which indicated that these digestates are unstable. •Highest biogas yield was obtained from mixing the three wastes (OM, DW & CW).•Phytotoxicity was reduced slightly after anaerobic co-digestion in the three bioreactors.•FTIR and SEM analysis confirmed that anaerobic co-digestion carried out and the organic matter was converted.•Principal component analysis (PCA), Spearman correlations and cluster analysis indicated that digestates need further treatment before agronomic use.