A method of treating sewage sludge that has a solids concentration of about 18-35% by weight includes treating the sewage sludge with sodium hydroxide, potassium hydroxide, or a combination thereof to increase its pH to at least about 12, and treating the sewage sludge with calcium oxide. The treatment of the sewage sludge with the calcium oxide can take place before and/or during the treatment of the sludge with the sodium hydroxide, potassium hydroxide, or a combination thereof. The amount of calcium oxide used is about 0.05-0.8% by weight of the sewage sludge.