An anaerobic digestion system at a municipal wastewater treatment plant requires 3.0 MW of heating in the coldest winter months. If the system produces typical biogas, and uses that biogas in an engine-generator operating in a cogeneration mode (with heat recovery from oil cooler, engine block cooling jacket, and exhaust), how many m3/d of biogas are necessary for digester heating during the coldest months at standard conditions of temperature and pressure? Note you will need to use some judgment as to the lower heating value of the biogas and the percent of biogas energy recovered as usable heat for digester heating.