Adsorption of ammonium from wastewaters by an almond kernel derived biochar modified by potassium hydroxide or dolomite and activated by steam

•Almond kernel was modified by KOH or dolomite and steam activated.•Adsorption of ammonium from wastewaters was studied.•Effects of ammonium concentration, contact time, solution pH were examined.•Structural, chemical and mineralogical analyses were conducted.•The adsorption mechanism was investigated.