I'm Anthony Keenan. So I'm the supervisor at the Tahuna
Wastewater Treatment Plant, I’ve been supervising for about three months.
Prior to that, an operator that includes standbys, various sampling,
troubleshooting. Prior to that as well, I was a trainee and I’ve been in the job
for five years. All right. So this is the Tahuna Wastewater
Treatment Plant in Dunedin and Dunedin’s
population is about 130,000 people. This plant has flows
from about three quarters of the city. We have the Green Island and Mosgeil plants
as well, taking the remainder of it and our daily flows at 25 to 30,000 cube. When it rains, though,
I mean we can get over 180 to 200,000 cubes. So this is a high rate
activated sludge plant, which is really short
retention time of 20 minutes. So this area is called HRAS, which
stands for high rate activated sludge. And the tank is divided into three spots. So there's the grit chamber, the aeration tank, and then sedimentation. So the grit chamber removes
all the rocks or stones that come through the screenings, and then the aeration tank provides
air for the microorganisms. And then that goes over a weir to be settled out to the clarifiers that is aided
by a bridge which has scrapers that helps moves and even out the sludge
just across the bed of the clarifier. And then we have the RAS pumps,
which circulates around the sludge that has settled down to the bottom of the tank
and that joins in with the influent. Once we get to, a set-point of mixed liquors, suspended solids, then the waste pump is activated. Then we have a secondary stage
through the BTFs, and then UV treatment. So this is UV, this is the tertiary treatment area. So it’s the last line of defense
before it gets taken out to sea, so basically
what we're aiming for here is to treat the last of the effluent
before it gets pumped out. So what we take care of is E.coli, fecal coliforms and enterococci. And so to achieve this, we have to have the most intensity
we can get out of the UV lamps. For our de-watering we have GBTs; Gravity Belt Thickeners,
and then it goes through a centrifuge which gets our solids
to about 35% dry solids. Then it gets stored into a hopper
where we can either burn it, Then it gets stored into a hopper
where we can either burn it, All right, so this here is the fluidised bed incinerator. So it burns at 800 degrees. So we put through about 17 tons of sludge
through that a day, aided by diesel to help
burn it through sand. And it's fluidised through air,
which aids the treatment of burning it. It goes up through the recuperater
and gets cooled down by a scrubber and the rest of the ash gets removed
and the supernatent flow goes back through the head of the plant. Or we can send it to landfill. Currently, we have a lime
to stabilize the sludge to get rid of the odors basically,
so we can place it at the landfill without too much disruption. So as an operator, we go through
quite a few of the readings; like plant flows, mixed liquors and UVTs. So basically just the water quality. And what it does
is it travels through the plant, just trying to make sure
that a lot of the BODs are getting treated and the solids are getting removed
from the waste and just trying to make sure
that we produce the best effluent
we possibly can to discharge out to sea. So we've got HRAS, which is sampling sedimentation aeration. And so we'll go in, we'll sample, we'll
check the probes are reading properly and do a few tests in the lab, and then
match it up with the current probes in there. So this is the lab. This is where we take all the samples
that we get from the inlet, from HRAS, from our biological trickling
filters and our UV system. So what we do, from HRAS the 30 minute settling in the columns. We test the lab papers
for the suspended solids by putting them through filter papers
and cooking them in the oven. Then we do a Ph, a temperature DO, and a conductivity test through the probes and then we do a UV test
through the spectrophotometer. And then we go through the microscope
and check out the life of the microorganisms
and the filamentous. Other areas like UV, so that's the last area
before the waste gets discharged. So this is daily. We go through and clean roughly about six
of these modules daily, and anything else. So lamps or ballast that needs to be
replaced will also be part of the tasks. You can see the caustic soda baths
where we dunk them in for about 10 minutes, hose them down,
then put it into the citric acid. Then we top up the gel and the grease. in the wipers
to make sure that they can clean when the auto wipers
come on. For de-watering, so that's when the solids get removed
from the waste. There is centrifuging and GBTs which is aiding the separation
of the water from the solids, and that gets loaded up into a hopper.
So the hopper can go three ways: It's either to the incinerator
to get burnt. What we usually do is while it's running,
we use the cooling sprays, which is on top. We pull them out to make sure
that we're getting a good flow through. And then during shutdown,
we clean out a lot of the pressure sensors, do a bit of greasing, and clean out
a lot of the filters that the ash is connected to. It's great. It's always full of challenges
because no day is the same. So you change around different departments
as well. It can be a bit frustrating with breakdowns, but it can also be great
as well to troubleshoot these breakdowns
and try to figure out what the problem is. It's quite a reward when you figure out an issue, especially
if you figure out a problem by yourself. But there's a lot of people around here
with a lot of knowledge and experience as well
that you can ask to help out. Other times,
you can get about 20 minds together to try and figure out an issue
and not get anywhere. But having that sort of unknown
is part of the challenge too. And if everything was easy,
then it'll be boring. So yeah, that's the great side of it. It's good that you get a good balance
between hands on work as well as admin work too, so we do a lot of readings. We're on the computer as well, ordering tubes. Yeah, there’s a fair bit of study as well, in there to exercise our minds,
you know, keep us up to scratch. Even things like microscope
observations. Pretty cool to see those bugs
floating around in there and eating away at the BODs.
