Anaerobic co-digestion 1 Anaerobic digestion 1 Article 1 Chemical industry 1 Cost benefit analysis 1 Environmental problems 1 Hydraulic retention time 1 Mediterranean countries 1 Methane 1 Municipal sewage sludge 1 Municipal wastewater treatment 1 Olive mill wastewaters Olive oil 1 Petroleum industry 1 Phenols 1 Sewage sludge 1 Sludge digestion 1 Treatment and disposal 1 Wastewater disposal 1 Wastewater treatment 1 adsorption 1 anaerobic digestion 1 biogas 1 cost benefit analysis 1 filtration 1 hydraulic retention time 1 methane 1 municipal wastewater 1 olive mill wastewater 1 olive mill wastewater; sewage sludge; anaerobic digestion; polyphenolic compounds; municipal wastewater; cost–benefit analysis 1