Sewage treatment isn’t exactly what we would call a ‘sexy science’, but it is a job for a true environmentalist. I learned this when I spent about a week shadowing chemist Liz Falejczyk at the Sewerage Agency of Southern Marin (SASM) in the north San Francisco Bay area.
I arrived on Sunday and drove with Liz to her home in Sonoma County, which is way north of Marin – as we drove, we passed the SASM building (which is just north of the Golden Gate Bridge) and a lot of gorgeous farmland. I took the opportunity of arriving on a non-working day to visit the Armstrong Redwoods State Natural Reserve and take a look at all of the gorgeous trees. I had never seen redwoods before, so it was a huge treat.
Monday morning we woke up early and arrived at the plant just in time to see the sun rise. I got a tour of the entire grounds, beginning where the sewage enters the plant in a room that is referred to as the headworks. Just as the sewage plant was built in the lowest area in the valley so that most of the pipes can flow with gravity, the headworks are underground in the lowest point of the plant. Sewage is then screened to remove plastic and other non-processable items and pumped through another room up to ground level.
This is the room with all of the pumps. They look small in this photo but are actually huge!
The wastewater is then pumped up to settling tanks, which are open to the air of the plant and are where the solid and liquid waste streams diverge. Heavy solids, which are referred to at this point as primary sludge, settle to the bottom of the tank and grease floats on top – both are sloughed off and diverted to a solid waste stream. The water is diverted to an aeration tank, where microbes digest most of the remaining organic material and nutrients. As Liz and many others mentioned, “They do all the work for us!” Liquid is then pumped to the clarifiers, which house more microbes to eat up the remaining organic materials. From here, the water is chlorinated, dechlorinated, and released into deep-water channels in the SF Bay.
The solid waste stream is a little different. The sludge is concentrated through the removal of water and sent to solid digesters, which house many bacteria that can be found in human digestive systems. These digesters are heated to human body temperature and release methane gas, which is often used to generate electricity and can even power entire plants. The sludge is then removed and used as fertilizer for agriculture or alternate daily cover on the top of landfills.
After the tour, the rest of my day was spent doing projects for Liz and watching Nimisha, another biochemist in the lab, complete fish bioassays to test the water that exited the plant post-dechlorination. Tuesday and Wednesday were much the same – I toured several more treatment plants and found that although they all contain the same basic components, each plant has its own personality. One tiny wastewater plant that I visited was built completely vertically, on an area that had to be less than four acres. Another plant I visited was spread out as far as the eye could see and processed a huge volume of wastewater every day.
On Wednesday I was able to visit Caltest, an environmental laboratory that many wastewater treatment plants outsource some of their more specialized testing and quality control measures to. Although my tour of their facilities was quick, I came away envious of all of their cool toys and efficient lab setup. I was floored when I saw them using some of the techniques that I learned in my first semester of organic chemistry! Some stuff really is fundamental.
I had been interested in wastewater treatment for a long time before I went on this externship. When it was first posted to Reed’s website, several different people contacted me to let me know it was available and I applied right away. So what did I learn, considering that this externship that was practically designed for me?
As a final note and somewhat of a PSA:
This is just a small amount of the plastic and junk that gunks up pumps in wastewater treatment plants all over the country. Floss, cotton balls, condoms, tampons, and string are also major offenders. Please do not flush anything that is not waste or toilet paper down the toilet! Remember that toilets and sinks do not make things go away forever; like trash, they just take things to other places for other people to deal with. Don’t flush things that shouldn’t be flushed – our sewage systems will thank you.
For more information on the wastewater treatment process, please check out http://www.wef.org/Flash/gowiththeflow_english/theflow.htm