Pete’s May Report.
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.