Abstract

Fats, oils and greases (FOG) are common causes of sewer blockages. It is estimated that FOG is linked to between 30 and 70% of the blockages. This problem is experienced both in the UK and many other countries. Annually in the UK approximately £80 million is spent on maintenance with an estimated £15 million spent on problems directly relating to FOG.

There are significant gaps of knowledge in the water industry in relation to the composition and formation mechanisms of FOG. There was a study conducted in the US simultaneously to this study. This study had sample size significantly smaller but it showed similarities in proportions of fat and mineral content.

Fats typically account for almost 16% of solid accumulations (wet weight) and perhaps surprisingly that the largest proportion (55%) is water with the remaining 29% being other organic or inorganic material. It was assumed for a long time that the FOG was 100% fats.

Fatty acid profiles along a sewer mock‐up have shown that there is a change in concentrations of both oleic acid (C18:1) and palmitic acid (C16:0). Prior to entry oleic acid is the most abundant, whereas, post entry palmitic acid becomes the most concentrated acid. There are two possible mechanisms, either preferential accumulation of palmitic acid or in‐situ microbial conversion of oleic acid to palmitic acid. Clostridium sp. is responsible for a similar process in adipocere formation.

Reproducing FOG in laboratory microcosms was successful although this mechanism was not reproduced and concentration changes were not observed, suggesting that the in‐ sewer factors responsible for this process are yet to be identified.

Significant differences between melting points of solid accumulations were found when comparing different levels of water hardness. There was previous experience of this within the water industry, but until now no data existed to support the relationship. There are two clear populations; samples from regions with levels of water hardness above 200 mg/L CaCO₃ and those under 200 mg/L CaCO₃. Higher levels of water hardness were found to give higher melting points, likely to be a result of formation of hard soap.

Additional Notes

In collaboration with WRcPlc

This study was an ICASE studentship with sponsorship from the Engineering and Physical Science Research Council 

 

Course: Master of Philosophy - MPhil

Date Deposited: 2017-05-08

URI/permalink: https://library.port.ac.uk/dissert/dis12868.html