Primary sludge stabilisation with calcium hydroxide

We studied the effect of the addition of calcium hydroxide to primary raw sludges. Calcium hydroxide enhances ammonia release as well as proteins and fats hydrolysis from the sludge organic material during stabilisation process. Changes in the molecular composition of the sludge extractable lipids caused by calcium hydroxide suspension, analysed using gas chromatography interfaced to mass spectrometry detector, are discussed. Calcium hydroxide treatment selectively removes fatty acids from the sludge lipids, while it has little effect on removal and molecular assemblage of the stanol and sterol compounds during sludge stabilisation. Biogenic n-alkanes are minor components in the sludge lipids.