Septic System and ATU vs. Cesspools

[MarkP]

To be sure, preventing run-off into waterways is important, but it is all a matter of degree. If you flushed it there is water that will eventually make its way through the water cycle again. The difference between a proper septic tank and leach field and peeing in a stream is the sufficient residence time in the correct aerobic environment. The ATUs are necessary when you can't guarantee the required conditions so you build those conditions into the ATU. Given sufficient time, surface area, and distance from the water table the ATU will have no effect on the finished product.

I maintain an ATU on a property that has insufficient distance between a leach field and a well such that the ATU was required. There are a couple dozen "blankets" of what looks like furnace filter material hanging in a large coffin sized box over the septic tank. The separation of solids takes place in the septic tank. The clarified waste-water is then pumped through an array of sprinklers on top of the blankets. The box with the blankets in it then drains to the leach field through a diverter valve that allows the water to flow back into the septic tank if the level gets low enough. The pump is on a timer to pump every 20 minutes whether it needs it or not, so while the level in the tank goes up and down due to loading, the community of bacteria in the biomats gets dosed on a comfortable cycle that keeps them happy and productive. It's all about oxygen, surface area, and residence time. Same in a full scale wastewater treatment plant. There is a bar screen at the inlet to the plant. It is a vertical array of bars with an automated rake that snags the big stuff. The next step is a deep tank (grit chamber) where the heaviest small stuff (grit and sand) is encouraged to settle out. After that is the primary clarifier, a round tank with a merry go round affair in it that skims scum off the top and sludge off the bottom. The flow enters in the center at the bottom and overflows around the perimeter at the top. A very slow flow rate is maintained with little mixing so that whatever's gonna sink can do so and it gets left behind. Rather it sinks to the bottom and the sludge rakes collect it, but it goes no further. The clarified water is then sent to a biotower which is another cylindrical structure full of cleverly shaped plastic media with lots of surface area for water to coat and lots of hollow space for air to pass up through. Fans pull air up through as the water trickles downward. This creates a good environment for the bacteria to live fast and die young. The water then flows to the secondary clarifier where the exhausted and now starving bacteria die off and settle out, most of them. Again with the sludge rakes and scum skimmers. More steps follow such as UV and chlorine disinfection but letting it settle and letting the bacteria do their job is the main part of all waste water treatment systems.

The primary failure mode of waste water treatment in Hawaii and most other places is bypassing of this cycle due to excessive incoming flow due to rainwater getting into the waste water system.

All major waste water treatment systems ultimately send their effluent the same place where all other water goes, downhill to the ocean, large lake, or river. One could consider that you are doing the world a favor by pooping in the woods as long as you are covering your stuff with a few inches of dirt and as long as you are far enough from running water or the water table. A covered compost heap makes you a saint compared to most of the residents of Honolulu (Hmmm. Composting your waste on the 20th floor lanai of your Waikiki condo? It could work.) Even an uncovered compost heap is still better than a cesspool since both get the same amount of rain and the compost started with less water. By uncovered I mean no cover to keep the rain off. You would always cover the waste with a cover of compost.

[VancouverIslander]

We already have limits on building cesspools near public wells. Some areas should be off limits for them, like Kapoho where cesspools are close to popular snorkelling areas but for the most part I don't think they cause any appreciable harm in most of Puna's AG zoned subdivisions as there aren't a lot of wells since the groundwater sits so deep and catchment is so prevalent. I doubt Orchidland (for example) cesspool output causes any appreciable problems since it seeps through many miles of lava rock before it comes out possibly miles under the ocean. Low population densities also help in this regard. I certainly wouldn't lobby to change any regulations that harshly affect the lives and finances of so many people without proper study to determine if there is even a problem (I expect everyone, including residents, would accept that Kapoho has a waste management issue).

[MarkP]

The point of my novel above is that many people have unrealistic expectations about waste water "treatment". Even the big plants don't do anything about most chemical contaminants. All they really do is separate all that water from the waste. They then try to use up the dissolved nutrients that are in the water by providing a long residence time in a highly oxygenated environment. Ultimately all that water is dumped directly into the nearest ocean, lake, or river. It always is because there is nowhere else for it to go and the EPA is OK with that. So far in the description you should not be able to tell whether I am describing a domestic septic tank/leach field or Sand Island WWTP. The thing that the big municipal systems have going for them is that they have professionals operating them and EPA oversight to make people comply. If you are committed and knowlegeable you can do even better by not mixing the waste with water in the first place. If you don't flush with water then you would be hard pressed to do as badly as a multi-million dollar waste water plant that is bypassing even correcting for scale because you didn't intentionally make a nice runny soup.

It is kinda shocking but I have read of places where drinking water is drawn from the river upstream of a town, treated, and distributed. Wastewater is then treated and put back into the river downstream of the town. 20 miles away is another town. Same deal there. Between the treatment at the upstream wastewater plant, the resident time in the river, and the domestic water treatment, it meets all the required standards. Yum. It is however only a more compressed version of the water cycle we all learned in earth science class. We are spoiled here in Hawaii though. We really have excellent water resources compared to much of the mainland.