How do our sewers get blocked? And what is done to clear them?

Southern Water explain how fat, oil and grease cause issues in our sewage systems

Transcript

00:00Good morning and welcome to Bud's Farm again on a wet, horrible day.

00:08I'm Steve Williams, I'm the Network Protection Manager for Southern Water, and I run a small

00:15team of people that investigate all of the sewer blockages we have, from pollutions to

00:21developers putting concrete down the sewer, heating oil, all those sort of things that

00:26we really don't want in the sewer.

00:28A big part of my day-to-day work is dealing with the fat oil and grease we get from restaurants,

00:34commercial kitchens, takeaways, nursing homes, hospitals, schools, all that sort of thing

00:43that have a kitchen that cook food, prepare it and serve it, and more importantly, wash

00:49up afterwards.

00:51Now the fat oil and grease we're talking about is not your used cooking oil, because cooking

00:56oil can be recycled as it is, restaurants buy it in, they collect it and they return

01:01it to the supplier for a return on the used cooking oil.

01:05The fat oil and grease we're talking about is the stuff that comes from the preparation

01:10of food, so you have a nice clean establishment, you clean everything down, all the plates,

01:16cups, saucers, knives, forks, all the preparation pans are all washed up, and it's that process

01:24that gives us the fat oil and grease that comes into our sewers.

01:28Now when that gets into warm water, it stays fluid for a little while, when it gets into

01:34the sewers it cools down and sets around the whole diameter of the sewer.

01:40Now your average sewer is only about 4 inches or 100mm in diameter, so to fill that up with

01:47fat oil and grease actually prevents the sewer working properly so the sewage can't flow

01:52through.

01:53And then when you get a bit of rag, like we get from our lovely rag skips behind us, that

01:58then sticks to the fat oil and grease and causes a blockage, which we then have to go

02:03and unblock.

02:05So the fat oil and grease from restaurants, takeaways, pubs, clubs, hospitals, all of

02:12those food service establishments can be collected in grease management systems, which will be

02:18fat traps, grease recovery units, or it can be digested by dosing systems which break

02:24down the fat and keep it fluid.

02:27Now we've just done a tour around Bud's Farm, so we know that all of that fat oil and grease

02:32gets right through the system, can get removed, it will go through our anaerobic digestion

02:37system and produce gas and heat that we can reuse to power our site.

02:44The problem is that fat oil and grease from restaurants gets stuck in those sewers, causes

02:50blockages and potentially causes pollution, which we don't want, which everybody doesn't

02:56like the smell of, doesn't like the look of, so we're desperately trying to keep it out

03:00of the sewers.