Influence of fat and oil type on the yield, physico-chemical properties, and microstructure of fat, oil, and grease (FOG) deposits

Water Res. 2017 Nov 1;124:308-319. doi: 10.1016/j.watres.2017.07.047. Epub 2017 Jul 21.


Fat, oil, and grease (FOG) deposit, in the form of calcium soap, was found to cause sanitary sewer overflows due to its adhesion on pipe walls. To address this problem, laboratory-prepared calcium soaps have been used to investigate the formation mechanisms of FOG deposits. However, the fats and oils previously utilized were limited and some soap characteristics were not examined. This research attempted to probe through the properties of calcium soaps prepared from calcium chloride and the fats and oils of chicken, pork, palm olein, soybean, olive, and coconut to further understand FOG formation and stability. Results revealed that FOG deposits may occur as smooth, paste-like material or coarse, semi-solid substance depending on their exposure to excess fat/oil and calcium. The smooth soaps with more excess fat/oil demonstrated high apparent viscosity and consistency index, while the coarse soaps with large levels of calcium signified higher melting endset. Moreover, a soap microstructure showing evident networks and lesser void area displayed higher heat and rheological stability, respectively. Overall, fats and oils with higher oleic to palmitic acid ratio such as palm olein oil, olive oil, chicken fat, and pork fat produced soaps with greater yield and degree of saponification. Hence, establishments and authorities should be alert in managing and monitoring these wastes. On the other hand, soybean oil high in linoleic acid and coconut oil high in lauric acid do not pose an immediate threat to the sewer system since they only produced soaps in small quantity. However, their soaps showed high melting endset which could pose a serious effect when accumulated at large amount. On the whole, the fatty acid profile of fats and oils, the presence of excess fat/oil, and calcium content mainly dictate the appearance, melting, rheology, and microstructure of calcium soaps. Their distinct properties can be used as criteria in predicting the condition and stability of FOG deposits.

Keywords: Calcium soaps; FOG deposit; Fatty acids; Melting; Microstructure; Rheology.

MeSH terms

  • Animals
  • Calcium
  • Fats*
  • Fatty Acids
  • Plant Oils*
  • Red Meat*
  • Sewage*
  • Swine


  • Fats
  • Fatty Acids
  • Plant Oils
  • Sewage
  • Calcium