We went to Venice Beach on Sunday with Norris’ friend Alvin from El Cerrito. Everyone is crazy at Venice Beach—the vendors, the performers, the attendants. And I understand why people are willing to suffer the infamous traffic of LA: this place can be a lot of fun. Above is a drum session on the beach.
The garden in front of the building by entrance “C” had the following sign. The Hyperion wastewater treatment plant has been in the business of cleaning waste to the best of their ability since 1925. These days some of the treated wastewater goes to a water reclamation facility and on to crops and the garden outside the plant.
Naturally, this was the largest digester plant we saw on our trip as this is the largest wastewater treatment plant west of the Mississippi (!!). The size of the plant was mind-boggling. And too big for any photo to do justice. To attempt to show the scale Norris stood next to the biogas storage tank. We found out about this plant the day of our tour. In less than an hour, our kind host, Nancy Carr, organized a tour for us. Throughout this trip we have been lucky that our hosts have been so flexible with our “winging-it” schedule.
Everything was pretty much the same here as in previous wastewater anaerobic digesters we have visited, just on a much bigger scale.
Except here the digesters were egg shaped. This is similar to the digesters in Boston though I never got a chance to visit them. There are some advantages to egg shaped digesters, though they seem only to be used for the largest municipalities. As of 2006, there were four wastewater treatment plants in the US producing Class A biosolids including Hyperion in LA. Class A biosolids are the highest pathogen reduction rating by the EPA and, in a nutshell, require temperatures to exceed 50˚C for several hours. Simple continuously fed and continuously wasted plants that we visited in Missoula and Tigard could not qualify for Class A biosolids because they cannot guarantee that newly added solids will remain in the digester for the required length of time. The city of Los Angeles has bought a farm outside the city where they can apply the biosolids. Meeting Class A biosolids means that the fertilizer can be applied to crops for human consumption, but LA only uses the crops for animal consumption.
Here is a view of one of the batteries of digesters. There are six digesters here. In total there are 20 digesters which look nearly identical on the outside. The sludge first passes to the 16 continuously fed digesters. They are operated thermophilically at 128˚F. The retention time is 12-14 days. Then the solids are passed to the 4 batch digesters where the solids are held thermophilically for 16 hours. This ensures that all the solids have been heated for a sufficient amount of time. The primary digester is stirred with an impeller while the batch digester is mixed by a pump. Each digester has a capacity of 2.5 million gallons.
This is the control unit at every digester. The brown pipe enables TWAS to enter (thickened waste activated sludge) and the right enables solids from the primary clarifier to enter at 3% TS. TWAS are solids from the secondary clarifier which have been centrifuged to 6% TS. The two feed streams alternate every few minutes.
The small tube on the left of this picture carries steam used to heat the digesters. The tube on the right carries the sludge to the batch digester. The batch digester is heated by a stream of steam injected into the influent of the batch digester. I asked if the steam killed the organisms. Michael replied that he guessed not since it seemed to be working just fine. The primary digester is also heated with steam. The steam flows down through vertical pipes inside the digester which inject the hot steam directly into the sludge.
Here is the side of a digester. The digesters are only supported by a lip that runs around the equator of the digesters. Michael explained this was to reduce conduction of heat away from the digester. The white insulation was not particularly warm so I guess the insulation did a pretty good job of keeping the digesters warm. We learned that ferrous chloride is used in the digestion process to reduce struvite and H2S production. (This should not be confused with ferric chloride used in the primary clarifiers.)
On top of the digesters was of course was a pressure relief and a vacuum relief valve. In the left, the massive biogas pipe can be seen.
Foam is alway a problem in the biogas line (though Michael could not recall any catastrophic problems). This massive orange pipe is a “Foam Separator.” Water is sprayed down from the top to remove the foam from the biogas.
The solids are passed over a bar screen separator (seen steaming) with 1/16″ slats. This removes any grit from the digestate. The grit falls down into a trough and is carried to a belt press (on the right) which squeezes out residual liquid.
The grit is dumped into trucks and hauled to dump sites. We saw pigeons pecking in the back of this dump truck.
Here is a top view of the belt press. The augers on the right (when in use) push the grit through the system of covered troughs seen in the left photo.
This process was a bit smelly. Michael said it was an older part of the facility. If we were to make a wastewater treatment plant we should make sure that the dewatering process is covered to reduce the smell. The white stack is for odor control. Sodium hydroxide and sodium hypochloride are used in this process. Michael also said that this post-digestion grit removal process (that we had not seen in other wastewater treatment plants) was the result of old equipment and, if we planned correctly, would not have to deal with.
The liquid from the grit removal process is further dewatered at 2,000g to 30-32% TS in centrifuges such as the orange one above, before the solids are sent to the biosolid loading ports for trucks to haul off to be land applied.
Uncompressed biogas is held in the tank on the left while compressed biogas is held on the right.
The biogas flares are hardly ever used, our guides explained.
The biogas is sent to the Department of Water and Power just down the street where it is converted to electricity. The electricity from the biogas supplies 80% of the electricity needed to run the wastewater plant.
We did not look much at the water treatment side of the plant as this was very similar to the other places we have visited and there was SO much to see on the solids processing side. We did learn that water only spends 17 hours at the plant from the time it enters the headworks to the time it leaves 5 miles out in the ocean.
12000 Vista del Mar, Playa del Rey
Los Angeles, CA