Pulp mill wastewater sediment reveals novel methanogenic and cellulolytic populations

► The diversity of saline, alkaline, and pulp mill wastewater-derived sediment was investigated. ► The archaea community was found to be dominating with Halobacteriaceae and methanogenic species. ► Novel species of order Methanomicrobiales is abundant in the methanogenic community. ► Novel GHF48 reveals to playing important roles in the anoxic treatment process.