The greatest increase in biogas production covered in this review was 227 ± 65% using enzymatic pre-treatment of lipid-rich dairy waste; however, it should be noted that several articles investigating pre-treatmentmethods which do not concern themselves with AD and biogas production have been reviewed.Regardless, there is evidence from these investigations that thesepre-treatment methods affect considerable substrate degradation,and are subsequently worth investigation as pre-treatment methods for AD substrates.