Pete’s May Report includes a detailed explanation of waste treatment at Mawson and Michael Peterson invents a new way to measure sea-ice thickness.

Pete’s May report

Pete’s May Report.

Hi all,
Month 3 and boy did it fly past.  Life here has been flat out but people often ask me how I fill in my days.  “Musn’t it get boring?” they ask.  Well in a word, no, there’s plenty to do and that’s after a day’s work, which is 5.5 days of the week.

Speaking of days, we only have a few hours of daylight left at present and in just over a week we'll lose the sun all together for 2 weeks.

The main work focus this month has been a full clean out of the WWTP (Waste Water Treatment Plant), otherwise known as the sewer farm.   A job that’s not been done fully for 3 years and still has a couple of days to go before we are finally finished.
Although it's a smelly job, it's not as smelly as you might think.  This is because most of what we are cleaning out is actually partially and fully treated sewage which doesn't have that raw sewage smell anyway.  Several of the people who assisted us with the clean commented on this fact.

To step back and start at the beginning and take in the entire sewerage system here at Mawson we need to first go back to the individual buildings on station.  Of the dozens of buildings at Mawson, only 9 are connected to the system.  Six of these buildings have their own individual holding tanks of varying sizes, the biggest being in the Red Shed where we all live and where the kitchen is located and this tank holds 2000L.  All of the tanks have float switches to activate their maceration pumps (maceration pumps chop up any solids as they pump it out).  These all have backup float switches to indicate high and low levels, obviously to let us know if a pump is not working and that the tank is full or a pump has not turned off for some reason and the tank is getting too low.  Like most things here everything mechanical has a back-up, or second pump, allowing us to change duties once a month, (swap from one pump to the next), giving us capacity for breakdowns.

All the sewage reaches the WWTP via site services, a series of pipe work connecting most buildings.  Generally this is a series of 5 above ground pipes, all well insulated, one obviously carrying sewage, the other 4 carrying potable water flow & return plus HHW (heating hot water to heat the station), flow & return.  All of this pipe work is heat traced and the sewer lines have the heat trace permanently on so they don’t freeze up as they are mostly sitting there with their contents stationary.  If the heat trace turns off for some reason then we get a page letting us know so we can attend to it before it does freeze up.

Via site services all the sewage ends up at the WWTP and gets deposited into the Flow Equalisation Tank, or holding tank where it is then pumped at a controlled rate into the Primary Sedimentation Tank.  This is where the treatment process really begins with most of the solids being settled out or eaten by anaerobic bacteria (these thrive in a no oxygen environment).  A thick crust forms on top of this tank, pretty much the same as it would on your old fashion septic tank back home.  At cleanout time this is one of the more labour intensive parts of the cleaning process.  Shovels and buckets are the only way to move this 400mm plus crust.  We happened to pick the coldest May day ever recorded at Mawson to do this, −34.5C.  Many thanks to Ian who had the outside job carrying the buckets to the sludge containers, an unpleasant job at the best of times, let alone in these very cold conditions.

From here the effluent, as it’s now called, is discharged to the Rotating Biological Contactor Disc Tank (locally known as the “Choky Wheel”).  This consists of a series of six sets of partially submerged discs, rotating through the effluent and the air.  Here we now have aerobic bacteria which thrive on oxygen and nutrients, nutrients being something sewage and effluent have stacks off.  These bacteria live on the surface of the discs and eat all the goodies up, resulting in the bulk of the solids and nutrients being removed from the sewage come effluent.  It then flows to the Clarifier Tank where any remaining solids and bacteria settle to the bottom where they are drawn off and returned to the start of the process into the Flow Equalisation Tank, seeding the incoming sewage with bacteria, starting and speeding up the treatment process.  The finished product then flows out of the top of the Clarifier Tank into the Retention Tank where it is pumped out and sent on its way to the outfall.

All up there is well over one week’s work involved in a major clean of the WWTP, at times a very messy and labour intensive job. 

Many thanks to all the people who assisted in this necessary but less than pleasant job.



Different methods of measuring the sea-ice thickness at Mawson

Two different methods of measuring the sea-ice thickness at Mawson are the brass bar and the Peterson gauge.

During winter, the surface of the sea freezes. This ice has to be measured to make sure that it is safe to travel on. Horseshoe Harbour started to freeze reasonably early this year and so it was time to start measuring.

Malcolm, Ian and Wayne did some preliminary measurements by drilling a 50mm hole through the ice and then dropping a brass bar, which has 2 cords attached to it, down the hole. One cord is attached to the centre of the bar and the other cord to one end of the bar. Once down the hole and by pulling on the centre cord the bar becomes horizontal and it is pulled up to the bottom of the ice. The centre cord is marked every 10cm to make measurements easy. Once the measurement is taken, the bar is lowered and by pulling on the end cord the bar becomes vertical and can be removed from the hole.
When this was described to me I thought that there must be an easier and quicker way of doing this and I came up with a basic idea of making a gauge with measurements on the side that can be lowered down the hole and the measurement read easily. I designed and made, on the run, a gauge out of 25mm copper pipe, 1.8 metres long with a pivoting bar at the bottom linked with a rod through to the top. When the rod is pushed down the bar, it is vertical and will go through the hole and when passed the thickness of the ice the rod is raised and the bar becomes horizontal. The gauge is then raised so that it meets the bottom of the ice and the ice thickness is read off the side.

With more measurements required, I ventured out onto the ice with my gauge accompanied by Malcolm and Mel hoping that the gauge would work. The first hole was drilled and I apprehensively lowered the gauge into the hole, raised the rod and lifted the gauge to the bottom of the ice and measured the ice thickness. The gauge was lowered slightly, the rod raised and the gauge removed from the hole. With a sigh of relief I thought “Success!”, but one hole was not a full test, so we drilled about a dozen more holes and the only minor problem experienced was that between holes the bar at the base froze, but this was overcome by giving it a tap to dislodge any ice before it was lowered into the next hole.

Measurements of the rate of growth of the fast ice at Mawson have been carried out intermittently since the mid to late 1950s. These measurements have now been formalised through an Australian Antarctic Science project. To analyse the variability each year and to add value to the long term data set, the same 4 locations at Mawson are measured each year on a weekly basis once the ice is safe to travel on.

At Mawson, 2 people are rostered every Wednesday to measure the ice thickness at the 4 study sites. This week it was Malcolm and my turn and what better opportunity for me than to give the final test for my gauge. The gauge worked perfectly and the measurements this week were: East Bay (1000mm), Harbour (1030mm), Kista Strait (970mm) and West Bay (970mm).

Both methods of measuring the sea-ice thickness work well and are favoured by different users.
Owing to the success of my gauge in measuring the ice thickness and its ease and speed of use, it is now being used by groups measuring the ice thickness on the GPS sea-ice route to Macey Island.

Michael Peterson