Just the fact that Kendal has its own wastewater treatment plant (shared with Crosslands and Cartmel) is quite unusual for a retirement community. Some features of it are unusual as well, and there are exciting plans for its future. I tuned into a recent Zoom presentation at Crosslands about our plant and our experiment in testing for Covid-19 in sewage, and I learned a lot. (It was recorded, so you can watch it on YouTube, using this link.)
The presentation was given by Heath Edelman and Seth Beaver. Heath worked on previous upgrades to Kendal’s wastewater treatment, and his company has been helping us with our Covid-19 testing program. Here, I will focus just on our current and future treatment processes, since I’ve already written about the Covid-19 testing here, here, and here.
How we get from sewage to clean water to irrigate our woods. Our current treatment process goes through seven steps, from raw sewage to clean water. The location of the various components is shown in the image below.
Here is the process through which the wastewater goes.
- Grinding/screening. The incoming raw sewage initially goes through a grinder that breaks it up into small bits. Then, it passes through a screen to remove trash: plastic bags, disposal plastic gloves, and whatever else we residents heedlessly flush away that won’t break down. An auger (in the sloping tube shown in the photo below) removes and cleans that trash, which is hauled away.
2. Bacterial breakdown. The wastewater flows into Pond #1, which is referred to as the Sequencing Batch Reactor (SBR). Here, bacteria break down the waste. The resulting sludge settles to the bottom, and a layer of clear water forms above it. The sludge is periodically dredged out and trucked away and the clear water is pumped to Pond #2, the “polishing” pond.
3. Polishing. In Pond #2, any remaining solids settle out, and the plants, algae, and small invertebrates in the pond help to remove any organic matter that can support growth.
4. Filtering. The water from Pond #2 is pumped through a filter in the small building next to Pond #1. Periodically, the filter is cleaned and the material it has collected is returned to Pond #1 for further breakdown.
5. Storage. The water now moves to Pond #3, which is a storage pond. Its function is to manage the water flow, providing water to the spray system and storing it when the spray system cannot be run. (More on that in a moment.)
6. Chlorination and final screening. The water moves through the small building at the west end of Pond #3, where a low level of chlorine is added to kill off any bacteria which might remain. There is also a “basket strainer” that removes things like leaves and maple seeds that may have fallen into the pond and could clog the sprinkler system.
7. Spray irrigation. In the final step the water is sprayed into the woods using our spray irrigation system. It will percolate down through the soil and ultimately rejoin the water table. We have 17 acres of woods, divided into 6 zones, that are used for spray irrigation. On any given day, the sprinklers in two zones may be active. There’s a limit to the soil’s ability to absorb water, so irrigation can’t be done on rainy days or immediately following heavy rains. The irrigated soil must also be monitored periodically to avoid buildup of components such as nitrates and phosphates.
What makes Kendal’s system unusual? There are at least two features of our system that make it somewhat unusual. One is its size: it is rare for a community of our size to have its own treatment facility. The EPA classifies as “small” any system that serves fewer than 10,000 people and handles less than 1 million gallons per day. Ours serves less than 1,000 people and handles an average of about 72,000 gallons per day, so ours is very small.
The other unusual feature is our spray irrigation. Most treatment plants simply release their water into the nearest stream or river. That water ends up in the ocean and never makes it back into the water table. It turns out that spray irrigation is more common in Chester County than in the rest of Pennsylvania, but even here it is relatively uncommon. A 1990 publication on spray irrigation that was put out by Chester County devotes several pages to the system at Kendal.
What’s all that new construction? Residents who frequent the gardens or the tennis court will have noticed a lot of construction activity just east of Pond #2. That is the location of two projects that will result in improvements to our wastewater treatment. The first, now complete and operating, is an “aerobic digester”. It receives sludge from Pond #1 and bubbles air through it. This encourages bacterial digestion and stabilizes the resulting material. Heath Edelman, in the Crosslands presentation, likened it to the composting process. After that, the remaining material is either trucked away or piped to the reed bed (see below) for additional digestion.
The second construction project, almost complete, is the renovation of our “reed bed”. Water from the aerobic digester will be cycled through these two sections of reeds. Microorganisms growing among the reeds and on their roots help to remove the organic matter from the water. Combined with the aerobic digester, this should significantly cut down on sludge accumulation in Pond #1, reducing the frequency with which it must be dredged.
We have had a reed bed for many years, but it never worked as designed because it was constantly flooded. The reeds need the opportunity to dry out somewhat from time to time, and that will now be possible because new controls have been installed to manage the water flow.
Our new reed bed has an innovative design involving a bed made from pellets of recycled glass instead of the usual sand. (For more on the benefits of this award-winning use of recycled glass, see this link.) If you visit the site of our reed bed now, the glass-pellet bed is dry and visible and there are no reeds yet. In September, the new reeds will be planted, the bed will be flooded, and operation will begin.
What does the future hold? Within the next few years, a major improvement to the treatment plant is planned. The current function of Pond #1 (the smelly one) will be taken over by an “activated sludge” treatment facility, possibly located east of Pond #2, above the new aerobic digester. There is also a possibility of eliminating Pond #3, leaving our “lake district” with just a single lake (Pond #2). The maintenance road to Crosslands could come through the present location of Pond #1, so it would not be necessary for traffic between the campuses to flow through the maintenance parking area. No firm decisions have been made on these possibilities, which are still several years away from implementation.
There is no public sewer system in the area that we could tie into, so we will continue to operate our own plant for the foreseeable future.
[Updated 9-21-20 to correct the description of the role of the aerobic digester. Thanks to Merritt Cleaver for pointing out the error.]