Visiting the EBMUD Wastewater Treatment Plant near Emeryville was a a fascinating experience. (Thank you EBMUD for helping train the next generation of environmental lawyers!) The facility services about 750,000 residents in the Berkeley Oakland area and sits right in the middle of the interchange of I-580, I-80, and the approach to the Oakland Bay Bridge Toll Plaza. The tour took us through the entire facility, including the on-site distillation plant that produces oxygen to help speed up decomposition of the sewage, the intake of the wastewater into the treatment plant, the 8 settling tanks, and the biosolid digesters that decompose the remaining sludge.
Among the interesting features of the facility – it is a net-zero energy user of PG&E power, oftentimes feeding electricity back into the grid! That is the result of the plant’s collection of methane gas produced by the sewage sludge digesters. The methane is fed into several diesel turbines and a gas turbine that can generate enough power to run the entire plant. So, not only does the facilitate reduce the GHG emission contribution to climate change (as measured on a carbon equivalent basis) but it actually eliminates (mostly) the need for electric power generated elsewhere (by the PG&E) to run the plant!
We also saw the intake pump house of the plant, a place where large objects are screened out to protect the pumps from damage. What kind of large objects?: pieces of lumber, cable, and lots of debris caught on those items. Plant workers even discovered an entire motorcycle caught in the screen once! They speculate that somebody must have opened up a manhole and dropped it into the sewer instead of bringing to the landfill. [The screens, by the way, are essentially grates with a 5-6 inch gap spaces, so an object would have to be pretty large to get stuck.] The intake system is also where a lot of other debris ends up getting removed. Among the top items (maybe the top item) to be removed from wastewater – “flushable” wipes. This has been reported in various media. “Flushable” wipes can be flushed into the sewer, but they do not decompose and simply get collected in the screening systems of wastewater treatment plants. What’s worse is that they not only increase the amount of debris that treatment plants have to remove before the wastewater can be treated, but because of the nature of the wipes (essentially cloth rags), they catch on or collect other debris, creating larger debris, such as the legendary “fatbergs” that have been reported about in recent years.
There was a particularly interesting machine that visibly helped settle the solids from the wastewater stream. The end result of the treatment process was a black biosolid that could be handled and had the consistency of clay or dough — in wastewater engineering parlance, a “cake.” The most disturbing aspect of our tour were probably the common usage of food and cooking terminology, invoking images that made some of us queasy: “wet weather primary sludge thickeners” (don’t remember this one at Thanksgiving when making turkey gravy), the biosolids cake, and even a “juicer” used for the high-COD wastes (chemical oxygen demand, wastes that have a high content of organic materials, from example wastes from slaughter houses or wineries) brought in by truck and designed to separate the waste liquid from the solid materials . . . yum. Yet, in spite of these metaphors and the images they evoked, we still managed to have lunch afterwards.
A final bit of trivia about the plant. It provides recycled water! I did not get a chance to ask how pure the water is, but in its current form it is usable for irrigation, toilet flushes, and industrial cooling. Sufficient purification can actually make recycled water suitable for human consumption and for specialized industrial processes, such as semiconductor manufacturing. Unfortunately, significant psychological barriers remain to getting people to drink such water (“toilet to tap”). I learned about the same issue in Singapore, when I took students to Singapore’s NEWater recycled water facility last year. The other challenge of greater recycled water utilization is the supply infrastructure – since recycled water needs to be kept separate from traditional potable water, a separate system would need to be constructed (though that would be unnecessary if recycled water were pure enough to be mixed with other potable water).
One other tidbit – if this information about wastewater treatment has (bad food pun coming) whetted your appetite for more information about sewage issues, I found episode 1 of the new Netflix documentary series “Inside Bill’s Brain” to be interesting. It is all about his project of addressing childhood mortality linked to contaminated water, which is in turn directly linked to the challenge of managing the sanitation needs of human populations. (Of course, the sanitation-public health connection is not new to people who work on environmental and/or human development issues in other parts of the world. But it was nice to see how somebody with lots of money was able to leverage that wealth to change the economic calculus of the marketplace and to help overcome the barriers to finding new solution for these issues.) Kudos to Bill on that.
I have experience in STP plant 2 year