RIGGERJACK TALKS POO. Part I.
I like to go camping at a friend's family beach property on the Hood Canal. They have a cool old logging cabin they barged over, back when the Navy was buying up the land for the Bangor sub base. I spent a lot of time there as a teen. It's good to go back and reconnect with friends there.
About a decade back, I wanted to go fishing on one of those trips. Looking up the rulebook, I find the Hood Canal is closed for all fishing. I thought “Weird, but whatever, there must have been too much commercial fishing allowed.” But I talked to the friend's family, and they had all kinds of reasons why the fish weren't there. Navy. Or sometimes Navy, plus commercial overharvesting. And if you look at a map, you can see there's just not much else going on out there. It's a reasonable assumption.
But soon thereafter, I saw some story in the local paper about how scuba divers were seeing deep water fish moving to the near surface, because the oxygen levels below 30 feet were too low to sustain them.
So, I looked up what the Dept of Ecology had to say about this.
They had a nifty little PDF explaining that the problem was low dissolved O2 in the waters of the Puget Sound. That this problem was caused by Eutrophication. That bio-avalable nitrogen was leaching into the Puget Sound, feeding bacteria, which used up the oxygen.
Since bacteria can survive in lower O2 levels than fish can, these bacteria blooms were creating fish kills. Then the dead fish dropped down to feed more bacteria.
It was a 30+page document, (I wish I could still find it) and the really important message delivered on each page was how varied and diffused the sources of these nutrients were. Leaking septic systems, farm and lawn over-fertilization, wastewater processing etc.
The message was clear; we need general widespread regulation of all these sources to come to grips with this situation.
But about halfway thru, there was a graph of nutrient flows at the mouth of a river. It wasn't quite a visual representation of a square wave, but it was close.
I'm no expert, but I have never seen varied, diffused sources produce a graph that looked like a square wave. A square wave is indicative of a point source with an on/off switch. Looking at the caption the authors wrote something like the source of the nutrients were unknown, because the researchers weren't allowed to know the pumping schedule of the sewage processing plant just upstream.
Wow. That seems suspicious. That note and graph were at odds with everything else the PDF was talking about.
Well, I'm no marine biologist, or septic engineer. So I just had a little flag in my mind about sewage processing and O2 deprivation. Something seems off here.
But life is busy, and I have other things to direct my attention.
A few years later, the push to build a sewage processing plant for Freeland Wa was coming to a head. The county health dept was all for it, and pushing for a plant as a required part of WA state's urban planning updates.
At the same time, that health dept was taking measurements of Fecal Coliform on my local beaches, and pushing that this was evidence that maybe we needed a sewage processing plant. Or maybe just stop allowing the building of on-site septic systems, until a plant could be approved...
Now I was both suspicious (by nature, and because I already had a red flag here) and concerned, because now this could now directly affect me. I started to look into how wastewater is processed.
So let me go into some detail of how my septic system works.
I have a well, I pump water from the well, to the house, thru me, and into my septic system. We all understand how that works.
My waste enters my septic tank. My tank is set up for a 3 bedroom home, or up to 6 people. It is a 1500 gallon tank, divided into 2) 750 gallon chambers.
Part of drilling a well here is installing a water meter. We go thru about 75 gallons/day, but the regulatory number is 375 gallons per day/per well.
Using my numbers, waste goes to the primary chamber and processes for an average of 10 days, using the regulatory number and flushing all that water thru my septic system, yields 2 days' processing. So the more water I use, the less time waste spends in my septic tank. But it's somewhere in the range of 2-10 days, before going to the secondary chamber where is sits processing for another 2-10 days.
Let's talk about what is happening here. I have a tank with my waste and bacteria that feed on my waste. It operates at just above ground temperature, year round. It's a bacteria farm that I keep regularly fed. The secondary chamber is the bacteria farm that is only fed by the output of the primary chamber. This is where those bacteria go to starve. If the primary chamber is overfed, the secondary chamber processes the excess, but mainly this is a place to finish the anaerobic bacterial processing, and ensure that process goes to completion (ie that the anaerobic bacteria starve). This takes 4-20 days.
After the septic tank, effluent leaves the tank, goes thru a distribution box, gets separated out to the various drainfield pipes, and flows to my drainfield. The whole system operates at volume capacity. So if one were looking at this D-box, the flows would be very similar to the household flows. If nobody is using water in the house, there is no flow. If someone is showering, the flow here is similar to the flow down the drain. A few minutes after the shower stops, this flow stops. But the D-box splits that flow 5 ways, one for each trench in my drainfield. A shower turns into 5 trickles to 5 different trenches.
So each trench gets 15-75 gallons of effluent per day, with irregular dosing. What is happening is taking the output of the anaerobic bacteria farm, and regularly dosing a patch of dirt with it. The effluent flows thru the soil particles, leaving these particles covered in this nutrient rich fluid that has already been processed by anaerobic bacteria, creating an aerobic bacteria farm. In the industry, this is known as a bio-mat. It is the purpose of the drainfield to take the wastewater that has been thru the anaerobic farm, and the anaerobic killing fields, and put it thru aerobic bacteria, before the water drops down to the water table.
Again, I'm no expert, but my understanding is that in a properly functioning drainfield, bacteria and viruses are removed by the time the water drops 18 inches into the soil under my drainfield.
That's how I process my poo. It takes time and space, but very little effort or energy. I would certainly prefer that the system be modified for water and nutrient recovery, and there could be very simple changes to the system that would allow that. But I didn't install them. I didn't know enough at the time, and didn't have the resources to tackle this kind of challenge at the time I built my home.
Now let's compare how I process my poo, with how poo is processed at a sewage processing plant. Let's use Langley, WA as our example.
I'm choosing Langley because it is close to me, wealthy, and very proud of its sewage processing facility. They are a small marina community, and their property values are higher than average. If anyone in our culture has their poo together, these would be the people. Additionally, they are so proud of their system, they post their sewer plan online, so you can download it and follow along:
https://cms4files1.revize.com/langleywa ... cument.pdf
This is a 264 pg engineering document. I'll give pg numbers with appropriate quotes. (Bolded highlights are mine)
Executive summary page iii:
'As of December 2014, the sewer system had a total of approximately 450 sewer billing accounts. Of the 450 accounts, 111 are commercial, 4 are public facility, 37 are multifamily and 298 are residential. '
“Flow data for 2012 and 2013 show that flows have been very uniform over that period. The average flows for these years were 0.075 mgd and 0.065 mgd, respectively. The average maximum monthly flows were also very similar at 0.10 mgd and 0.09 mgd, well within the 0.15 mgd capacity. Maximum average influent BOD and TSS loads in 2013 were 263 lbs BOD/day
and 214 lbs TSS/day. “
5.1 PROCESS DESCRIPTION The existing WWTP was completed in 1992 and contains three basic wastewater treatment process steps: preliminary treatment, secondary treatment and disinfection. The treatment plant is designed to remove at least 85% of the BOD and suspended solids present in the incoming wastewater. The treatment units consist of a grit chamber, influent Parshall flume, 3/8-inch bar screen with screenings washer and compactor, two Sequencing Batch Reactors (SBR), and a chlorine contact chamber. At the headworks, wastewater from the grit chamber passes through a Parshall flume flow meter. Flow measurements for permit reporting and for analysis are based on the effluent flow meter, which is an ultra-sonic device. Following screening, wastewater flows by gravity to one of two SBR basins (171,600 gallons each). Both SBR basins are in service throughout the year. Flows alternate between the two SBRs; one processes wastewater while the other fills with wastewater. The SBR processes the wastewater in 5 to 6 cycles per day.
Each cycle includes fill, react (alternating aeration and anoxic mixing), settling, decant, and idle. Effluent is decanted from the top of the SBRs to one of two chlorine contact chambers for a contact time of at least one hour. Both contact chambers are usually in operation and are cleaned every 6 months. Each chamber can be isolated for cleaning or operation. Liquid chlorine is used for disinfection. Effluent flows by gravity from the chlorine chambers to the outfall line and eventually to the Saratoga Passage in Puget Sound. A plant flow diagram of the treatment facility is shown in Appendix D. Waste activated sludge is digested in two aerobic digesters. The digested sludge is dewatered on a belt filter press and then composted on site. The Class A compost is available for free to the community. A fee is charged if City personnel and equipment are used to load trucks with compost.
Table 5.1 on page 5-3 shows Langley's permit limitations. Note how well Langley conforms to these limits. This is not a barely functioning system, this is an exemplary example of such a system.
5.2 OUTFALL The effluent from the treatment plant is discharged through a 12 inch ductile iron effluent pipe extends 6,200 feet north through the City and to the treatment plan outfall to Saratoga Passage. The original 12 inch ductile iron outfall was extended 100 feet (to approximately 1,000 feet offshore) to a depth of 46 feet below mean lower low water by connection of a new high density polyethylene (HDPE) pipe. The last 43 feet of the 12 inch HDPE outfall contains ten 3 inch diffuser ports alternate locations on each side of the outfall at 40 feet below mean lower low water. The first six ports are 5 feet apart and the last three are 4 to 6 feet apart. The final diffuser port is in the end plate of the outfall diffuser section. This configuration ensures diffusion of treated effluent to minimize impact on water quality. Saratoga Passage is designated as a Class A marine water in the vicinity of the outfall. Characteristic uses include the following: fish migration; fish and shellfish rearing, spawning and harvesting; wildlife habitat; recreation; commerce and navigation. Saratoga Passage is considered an estuary for the purpose of assigning a mixing zone.
“Between 2009 and 2014, the influent TSS loading averaged 193 lbs/day and the maximum month average was 383 lbs/day. The design influent TSS loading for the plant is 425 lbs/day; 85% of design load is 361 lbs/day. The maximum month average daily load of 383 lbs/day of TSS exceeded 85% of the design capacity in June 2011 and was noted in the 2014 NPDES Permit. This maximum month coincided with an unusually high influent TSS daily peak load of 1,265 lbs/day. The peak load in June 2011 appears to be reflected in the effluent; the maximum month effluent load of 5.3 lbs/day for the five year period, and the maximum weekly effluent concentration of 8.6 mg/L both occurred in June 2011. Notably both the load and concentration are still very low relative to the permit limits and do not exceed expansion criteria. “
Read figure 5-4. see how much BOD5 is allowed, versus how little is actually being discharged?
Ok, that's enough engineering gibberish for now. There's lots more pages talking about just how well Langley conforms to standards. I have no dispute with any of their conclusions. If one is measuring by compliance, this is an exemplary, well designed and maintained system.
But let's take a closer look at what exactly they are talking about.
First, what is BOD5?
From https://www.graf.info/en/rainwater-harv ... -bod5.html
“Biological oxygen demand (BOD5)
The BOD55 indicates the amount of oxygen which bacteria and other micro organisms consume in a water sample during the period of 5 days at a temperature of 20 °C to degrade the water contents aerobically. BOD5 is thus an indirect measure of the sum of all biodegradable organic substances in the water. The BOD5 indicates how much dissolved oxygen (mg / l) is needed in a given time for the biological degradation of the organic wastewater constituents.
This value is an important parameter for the assessment of the degree of pollution that wastewater represents for the environment (receiving water). Since the wastewater contents in the receiving water are degraded by the bacteria therein, the oxygen is completely or partly drawn from the water. If the limit values are exceeded, creatures breathing oxygen (crabs, fish, etc.) may die.
So BOD5 isn't the complete BOD, rather it is the easily measured regulatory number. I don't know the relationship between BOD5, BOD90, and BOD, except BOD will be higher than BOD90, which will be higher than BOD5. I suspect BOD5 is probably at least 90% of BOD, but I haven't been able to confirm this. So for my purposes, I will use BOD5, but understand the real number is certainly higher than this.
But remember, Langley is well within standards, so let's look at oxygen levels in saltwater to see what this number means.
https://www.fondriest.com/environmental ... oxygen/#10
“The amount of dissolved oxygen needed varies from creature to creature. Bottom feeders, crabs, oysters and worms need minimal amounts of oxygen (1-6 mg/L), while shallow water fish need higher levels (4-15 mg/L)
Microbes such as bacteria and fungi also require dissolved oxygen. These organisms use DO to decompose organic material at the bottom of a body of water. Microbial decomposition is an important contributor to nutrient recycling. However, if there is an excess of decaying organic material (from dying algae and other organisms), in a body of water with infrequent or no turnover (also known as stratification), the oxygen at lower water levels will get used up quicker.”
“Dissolved oxygen enters water through the air or as a plant byproduct. From the air, oxygen can slowly diffuse across the water’s surface from the surrounding atmosphere, or be mixed in quickly through aeration, whether natural or man-made 7. The aeration of water can be caused by wind (creating waves), rapids, waterfalls, ground water discharge or other forms of running water. Man-made causes of aeration vary from an aquarium air pump to a hand-turned waterwheel to a large dam.
Dissolved oxygen is also produced as a waste product of photosynthesis from phytoplankton, algae, seaweed and other aquatic plants.”
“Saltwater fish and organisms have a higher tolerance for low dissolved oxygen concentrations as saltwater has a lower 100% air saturation than freshwater. In general, dissolved oxygen levels are about 20% less in seawater than in freshwater ³.
This does not mean that saltwater fish can live without dissolved oxygen completely. Striped bass, white perch and American shad need DO levels over 5 mg/L to grow and thrive ⁵. The red hake is also extremely sensitive to dissolved oxygen levels, abandoning its preferred habitat near the seafloor if concentrations fall below 4.2 mg/L ²⁹.
Consequences of Unusual DO Levels
If dissolved oxygen concentrations drop below a certain level, fish mortality rates will rise. Sensitive freshwater fish like salmon can’t even reproduce at levels below 6 mg/L ¹⁹. In the ocean, coastal fish begin to avoid areas where DO is below 3.7 mg/L, with specific species abandoning an area completely when levels fall below 3.5 mg/L ²⁹. Below 2.0 mg/L, invertebrates also leave and below 1 mg/L even benthic organisms show reduced growth and survival rates
“Fish kills are more common in eutrophic lakes: lakes with high concentrations of nutrients (particularly phosphorus and nitrogen) ⁴¹. High levels of nutrients fuel algae blooms, which can initially boost dissolved oxygen levels. But more algae means more plant respiration, drawing on DO, and when the algae die, bacterial decomposition spikes, using up most or all of the dissolved oxygen available. This creates an anoxic, or oxygen-depleted, environment where fish and other organisms cannot survive. Such nutrient levels can occur naturally, but are more often caused by pollution from fertilizer runoff or poorly treated wastewater ⁴¹. “
A dead zone is an area of water with little to no dissolved oxygen present. They are so named because aquatic organisms cannot survive there. Dead zones often occur near heavy human populations, such as estuaries and coastal areas off the Gulf of Mexico, the North Sea, the Baltic Sea, and the East China Sea. They can occur in large lakes and rivers as well, but are more well known in the oceanic context.
Hypoxic and anoxic zones around the world (photo credit: NASA)
These zones are usually a result of a fertilizer-fueled algae and phytoplankton growth boom. When the algae and phytoplankton die, the microbes at the seafloor use up the oxygen decomposing the organic matter ³¹. These anoxic conditions are usually stratified, occurring only in the lower layers of the water. While some fish and other organisms can escape, shellfish, young fish and eggs usually die ³².
Naturally occurring hypoxic (low oxygen) conditions are not considered dead zones. The local aquatic life (including benthic organisms) have adjusted to the recurring low-oxygen conditions, so the adverse effects of a dead zone (mass fish kills, sudden disappearance of aquatic organisms, and growth/development problems in fish and invertebrates) do not occur ³¹.
It's worth pausing over that map. Note where the dead zones are. Note where human population densities match up with dead zones, and where they don't. What pops into your mind, looking at that map?
I should mention that I did some work for NOAA back in the 90's. Their maps of dead zones looked very similar to this map.
“Estuary stratifications are based on salinity distributions. Because saltwater holds less dissolved oxygen than freshwater, this can affect aquatic organism distribution. The stronger the river flow, the higher the oxygen concentrations. This stratification can be horizontal, with DO levels dropping from inland to open ocean, or vertical, with the fresh, oxygenated river water floating over the low DO seawater “
OK, so let's review. What do we now know about Langley?
1. They have flows of 65-75k gal/day for 450 customers, 144-167 gallons per customer per day, even with groundwater infiltration.
2. Their influent BOD is 263 lbs per day and effluent is only 2.54 lbs/day average, with a high of 11 lbs/day. (99% BOD removal in processing!)
3. Their process takes 4 hours, rather than the 4-20 days mine does. And theirs involves adding oxygen and chlorine (better living through chemistry!). Odd, isn't it, that “treatment” means adding chlorine, and the appropriate treatment for chlorine seems to be saltwater...
4. They pump this 2.54 lbs of BOD to the seafloor, about 1000' offshore.
5. O2 levels drop as depth increases.
6. If O2 levels are low enough, bacteria are the only form of life.
7. If O2 levels drop, adult fish will leave if possible. But shellfish, young fish, and eggs will die.
8. The place Langley puts its wastewater is “is designated as a Class A marine water in the vicinity of the outfall. Characteristic uses include the following: fish migration; fish and shellfish rearing, spawning and harvesting; wildlife habitat; recreation; commerce and navigation. Saratoga Passage is considered an estuary for the purpose of assigning a mixing zone.” So this shouldn't be a problem...
So, I guess we should look at how 2.54 lbs/day of BOD5 affects seawater.
That's enough biological demand to drop nearly a quarter million liters of saltwater from a healthy 7mg/l to a deadly 2mg/l. Look at the charts to see the few life forms that survive at 2mg/l.
That's not BOD, that's only BOD5. The Dept of Ecology may not care about the remainder, but it doesn't stop killing because the government stopped counting.
Now, I'm not a marine biologist. I don't know what the normal O2 levels 1000' offshore are, let alone how far the O2 level needs to drop to start killing. I don't know the recharge rate of the waters of the Puget Sound. I don't know how human fecal BOD compares with the waste BOD rest of the life in the Puget Sound.
But pumping BOD to the seafloor in estuarian waters seems like a really, really bad idea. These are the waters that sealife reproduces in.
They say one should not poo where one eats. We seem hellbent on not being able to eat from this poo hole.
This story started with the Dept of Ecology, nearly a decade ago. They have been working on it since, so we should check their progress.
https://ecology.wa.gov/Water-Shorelines ... on-studies
It seems they are studying the problem.
If you look at the study, it looks like they are showing water quality problems in fairly remote inlets. But look closer.
James C. Scott of “Seeing Like a State” couldn't have put it any better, they are mapping:
“Predicted days of Noncompliance.”
Maybe that's eerily Orwellian only to my ears...
But if one plays around a bit with their model some odd features stand out. They only model specific cells. The relationship between Noncompliance and O2 is not linear. IDK what they are aiming for, but the red cells are sometimes predicted to drop below 1mg/l. Low enough to kill most bacteria, and everything else.
In layers, one can find “Marine Point Sources” Click it. This is a map of waste water treatment plants, WWTP for short.
Unfortunately I can't find a BOD point source number anywhere in this model, but the Carbon and Nitrogen loading numbers should give you an idea of the scale of the issue we are talking about. These seem to be permit numbers, not real world measurements.
Ok, so that's the basic science of fecal waste disposal, and an overview of how the city and state view the issue.
I don't have a STEM education, so I linked to sources. Those who do, please raise any points of contention, now. I'm open to the possibility that I have misunderstood something technical.
If one were to speak to a septic engineer, a public health official, or a marine biologist, they may disagree with my framing, but I don't think they could say I'm wrong about any of this.
I'll follow up with Poo part II when I write it up. In the meantime, I'm open to questions.