rainbow over Oyster Pond Falmouth
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The Scoop on Poop - Know Your Wastewater Options -
A video of the excellent Jan. 4, 2011 meeting at the Waquoit Bay National Estuarine Research Reserve

Nitrogen 101 - A primer on how nitrogen moves from our septic systems to estuaries

EPA Approval Letter of Oyster Pond TMDL for Total Nitrogen – May 5 2008

Final – Oyster Pond Embayment System Total Maximum Daily Loads for Total Nitrogen – Ma EOEA & DEP - Feb 7, 2008


Wastewater Management

Wastewater from septic systems is the primary source of nitrogen (71%) to Oyster Pond according to the Massachusetts Estuaries Report.  Removing this source will be the key to restoring Oyster Pond to a healthier ecosystem. 

There are many ways to treat wastewater – BUT what will be the most economical and efficient method?  That will be one of the questions that a consultant hired by the Town of Falmouth will answer when developing the Comprehensive Wastewater and Nutrient Management Plan (CWNMP) for Oyster Pond.  We may end up with a variety of treatments around the pond.  Below is a description of possible treatments that were considered for Oyster Pond..

Title V Septic Systems
Innovative Alternative Denitrifying Systems
Composting Toilets
Urine Diverting Toilets

The Sources
According to the Swiss Federal Institute for Environmental Science and Technology (EAWAG), human urine typically contributes about 80% of the nitrogen and 50% of the phosphorus in household wastewater, yet only around 1% of its volume.  Laundry cleaners, personal care products, dishwashing liquids and human feces contribute the remaining 20% of nitrogen.  This is a quandary that officials and environmentalists are starting to recognize as a problem – municipalities spend lots of money and effort to deliver clean drinking water to households and businesses and then that water is polluted by a relatively small amount of human waste.  With conventional sewering systems, this waste must then be collected, moved long distances and then treated at a central facility.  This is why some people are questioning the wisdom of centralized sewer systems and it has spurred a movement to look at alternative toilet technology.

Title V Septic Systems
Title V septic systems, are so called because they are regulated by Title 5 of the State Environmental Code.  They do an excellent job of removing pathogens from entering groundwater, but not nitrogen.  They only remove about 25% percent of the nitrogen effluent, which is about 40mg/l from an average household, from the septic system outflow.  Many members of the public are surprised to learn this and it is important to note that more frequent pumping of the septic tank will not make a difference to the amount of nitrogen emanating from your septic tank.   

diagram of septic system

How nitrogen moves from homes to estuaries. Organic nitrogen is collected in a septic tank, where organic N is decomposed to ammonium.  Ammonium moves to leaching fields where it is converted to nitrate.  This nitrate then moves easily to groundwater and within groundwater to estuaries.

Septic systems are comprised of three main components – the septic tank, distribution box and leaching field.  They are designed to use natural processes to break down the wastes and remove pathogens.  Most of the nitrogen in human waste is comprised of the organic form of nitrogen and urea.  Microbes in the septic tank convert this nitrogen into ammonium or NH4.  When the wastes move into the leaching field oxygen is made available to intercept and treat any remaining pathogens.  Microorganisms in this oxygen environment convert the ammonium to nitrate or NO3.  This has consequences for the fate of nitrogen in our environment, while ammonium sticks to soils and tends to stay put, nitrate moves easily through soils to enter the groundwater and then down to a receiving water body.  The Buzzards Bay National Estuary Program has any excellent slide show on the principals and design of septic system installation in Massachusetts.

Costs:

  • $8,000 - $15,000 depending on location
  • Operation and Maintenance – approximately $100 a year (pumped every 2 – 4 years)

Innovative and Alternative Systems – (I/A)s

Performance of alternative septic systems Powerpoint
An excellent review of I/N performance by Susan Rask of the Barnstable County Dept. of Health.

The realization in the 1990s that nitrogen from backyard septic systems was a major pollution source to water bodies, spurred the development of many Innovative and Alternative Systems (I/As).  (Discussion in this section will be limited to denitrifying I/A systems and not alternative toilets, such as composting and urine diversion, those are discussed in later sections.)  Currently, there are over 50 different I/A technologies approved for use in Massachusetts.

I/As can differ greatly in their design, but all have at least an additional step in the treatment process.  The waste is moved through an anoxic environment where yet more microbes convert nitrate into harmless nitrogen gas.  I/As systems vary in how they introduce this denitrifying step.  Since 1998, the Massachusetts Alternative Septic System Test Center (MASSTC) located in Sandwich, Massachusetts has evaluated the performance and cost effectiveness of over a dozen different systems.   Additional information can be found at the Barnstable County Alternative Septic System Technology Information Page.

FAST septic tank unit
Schematic of a FAST - Fixed Activated Sludge Treatment - unit. courtsey of the Barnstable County Department of Health and Environment, http://www.barnstablecountyhealth.org/

Research at this testing center and results from monitoring tests from systems in use, show mixed results in their performance.  To receive DEP approval, systems “shall achieve a total nitrogen concentration at discharge not to exceed 19 mg/l.”  DEP assumes that an approved I/A will reduce the total nitrogen concentration by 50% under the assumptions of Title V flows (110 gal/day per bedroom).  However, testing of alternative septic systems in use throughout Barnstable County found that they don’t always perform as well in operation.  Studies show they remove 50% of the nitrogen 70% of the time. 

There are possibly several reasons for this.  It could be the incoming nitrogen loads entering the systems vary greatly in N concentration.  If a household is parsimonious in their water use, their concentrations will be higher.  The state assumes incoming influent at 50mg/l, yet some households Total Nitrogen (TN) can be as high as 70 – 80 mg/l. Their systems may be working great, and taking out a lot of nitrogen, but not meet the 19mg/l target, since I/As are designed to remove a percentage of the influent.  There is also a problem with the seasonality of the load.  Many systems need six weeks to activate the microbes, if a system is only used during the summer months; it may not have enough “ramp up” time.  Additionally an I/A requires much more maintenance to operate than a conventional septic system, if the operator is not intermittently testing and adjusting the system, it may not perform as well.  

masstc center aerial view
Photo courtsey of the Barnstable County Department of Health and Environment, http://www.barnstablecountyhealth.org/

Annual O&M costs are much higher for I/As than Title Vs.  There are electrical costs for running the pumps, aerators, fans and other mechanical parts.  Mass DEP requires that owners of an I/A system have a maintenance contract with a licensed individual or company.  If the

Management Issues:
If individual denitrifying systems are used to meet TMDLs, there must be some mechanism to provide a level of confidence to the DEP that the systems are working as required.  How shall that happen?  Does the Town take on the role of operator for all of these individual systems, because as noted above, it is crucial these systems are monitored and tested to insure they are meeting the effluent limits?  If the Town does take on this role, what is the legal mechanism giving Town employees access to private property?  Perhaps the systems will be owned by the Town?  How many additional Town employees need to be hired to perform these duties?  These are just some of the questions and management issues that need to considered if the Town relies on I/As to meet TMDL limits.

Costs:

  • $ 24,000 to $28,000 depending on location
  • Operating Costs – extra 5 -6 KwH/day in electricity costs
  • Maintenance costs – every system must have a maintenance contract - costs $1,200 up to $3,200 in areas where TMDL compliance must be documented

 

Sewers

Only 3% of Falmouth homes are hooked up to the sewer.

Cluster/Satellite Systems

Alternative Toilets

Composting Toilets

One alternative to conventional sewers or denitrifying septic systems is composting toilets.  Composting toilets are self contained units that collect human wastes and through natural processes convert them into a compostable material. While the composting of human waste has occurred for thousands of years, it wasn’t until the 1960s when the first commercially designed toilet was developed in Scandinavia. 

Many people think a composting toilet is similar to an outhouse.  In fact, the “user interface” looks similar to conventional toilets, especially if a low flush model is used.  Since water is not being using to move wastes to the septic system, these systems use substantially less water.  The composting reactor chamber is typically in the basement but in some units it is self contained.

a compost toilet

A Compost Toilet
credit: Barnstable County Dept of Health & Environ.

 

 

There is a great variety in the designs, features and sizes of composting toilets, but all composting toilets share the following components:

  • a reactor chamber where wastes are collected and processed
  • an exhaust system to vent odors, provide oxygen and dry out the wastes.  Vent pipes to the unit can either be installed inside or outside of the house, but in colder climates if outside all exposed pipe must be insulated
  • a rotor to turn and aerate the compost
  • a door or drawer to remove the finished product
  • overflow area to handle excess liquids
  • addition of carbon to start and continue the biological processes, either with peat moss, sawdust, wood shavings or a “starter” culture provided by the manufacturer.  Some designs require that a scoop be added after every bowel movement.

 

 

 

Composting toilets rely on aerobic bacteria and fungi to naturally degrade and convert the wastes into compost.  Therefore, it is critical that any toilet follows these three principles to function properly:

  • oxygen is supplied to the collection area to maintain the processes
  • a proper balance is maintained between dry and wet media – if it is too wet, oxygen cannot reach the compost and anaerobic processes will occur instead, causing smells.
  • a warm enough environment is maintained, between 60 to 65 degrees, if the unit is used year around.  Below 55 degrees composting is slowed or stopped

Composting toilets are separated into two main categories “self-contained” units and “remote” or central systems.

Self-contained units
Self-contained units, as the name implies, are toilets with the reactor, rotor and drawer all contained into one unit.  The reactor sits directly under the toilet which raises the bowl up off the floor, requiring a foot stool to reach it.  Due to the limited capacity of the reactor, this type of toilet is best for a two or even a one person household, summer cottage, or seasonal vacation home.  This type of composter requires more frequent emptying and has a shorter storage time which in turn could mean that the wastes may not be fully composted by the time the reactor chamber is full.  It also does not lend itself to emptying by outside contractors without access to the main part of the house and without carrying the compost through the house.

All of these styles also have an emergency overflow hose that must be connected to a tank, leach pit or drywell to contain excess liquids.  Mass DEP requires that these excess flows be sent to a Title V septic tank.  Of course, diverting these wastes to a septic tank makes the amount of nitrogen released to the environment little different from a conventional septic.  This defeats the purpose of using the compost toilet in the first place.  Mass DEP’s two year storage requirement is also problematic for these smaller units.  The very low duty cycle that this implies for the septic system may be technically problematic and there is no monetary savings from not having a Title V system.

The advantage of a self-contained toilet is they are cheaper and easier to install – no new plumbing is needed though it still needs to be vented to the outside.  Disadvantages are that these toilets require a high level of maintenance by the home owners to insure the proper wet vs. dry balance is maintained.  Some designs use fans or a heater to dry out the moisture that some users complain can be noisy.

A schematic for compost toilets in a house

A general configuration for two compost toilets in a two story house
credit: Barnstable County Dept of Health & Environ.

Central composting systems
Remote or central composting systems are designed to handle larger loads and can accommodate more than one toilet.  The larger size allows for more variability in the waste flow and use.  The reactor chamber typically sits in the basement of a house and can be connected to multiple toilets.  The toilets themselves tend to look more like conventional toilets.  Toilets directly over the reactor can be “dry” style toilets.  Those without a direct vertical drop to the reactor must either be a “micro” flush, foam or vacuum toilet.  Micro flush or foam toilets use a minimal amount of water (a pint to 3 ounces of water compared to 1.6 gal in conventional low flush toilets).  These styles of toilets are a good option for users who want a toilet that appears and functions more like a traditional one. 

Some of these central systems are designed with a slope in the reactor chamber to prevent new wastes from interfering with the decomposition of older compost.  Accumulated wastes slide to the bottom of the chamber while newer products are introduced at the top.  Excess liquid waste is collected at the bottom level to evaporate or be collected in a tank similar to the self contained units, though some newer units maintain the composter at higher temps to evaporate liquids.  It is important that the system is designed to remove this excess water from the composting area as aerobic decomposition will not take place.  This is especially important for the foam and micro flush toilets that generate more liquids.  Some models require the owner to hand crank the rotor at least once a week to mix and aerate the compost, though some models offer an automated cranking system.

Installation Considerations
Central units are more expensive than self-contained units and also have additional installation costs.  Dry toilets must sit directly above the reactor and can be separated by several stories as long as there is a direct vertical drop to the composter.  The Phoenix composting toilet requires a 12 inch in diameter chute to connect the dry toilets.  Toilets in a household not directly over a composter must either be a micro-flush, foam or vacuum toilet.  It is critical that pipes connecting these toilets are properly installed.  Many manufacturers recommend that horizontal waste pipes not run over 20 feet or even 15 feet away from the tank.  The pipes must be angled at a slope between 45 degrees and 90 degrees.  Anything less will cause clogging.  It is also recommended that clean-out fittings and extra flush troughs be installed. 

Once the finished composted product is ready to be removed, it must be disposed of properly as it could still contain pathogens.  To be extra safe, some people use the compost only on their ornamental plants, not on anything they will be consumed.  Massachusetts state law requires that the end products be covered with a minimum of six inches of clean compacted soil, or be disposed of by a licensed septage hauler.  It is important to note that composting does not change the amount of nitrogen in human waste, it merely reduces the volume.  This is why DEP does not give credits to composting toilets as nitrogen removal systems. 

While the toilet wastes are captured in the compost tank, a Title 5 septic system is still needed to confine the greywater  -water from showers, laundry, dish washers – from a household.  The Massachusetts DEP has revised Title V regulations to allow new construction projects using compost toilets to downsize their septic systems to 60% of the dwelling's design flow.  It should be noted that these greywaters will still contain some nitrogen.  Studies are ongoing by the Barnstable County Board of Health to determine the nitrogen levels.

While composting toilets may offer an affordable alternative to centralized sewers, there are several caveats.  Manufacturers say many of the common problems with composting toilet use – odor, liquid build up and problems removing the finished product - are due to errors by the users.  Switching from a conventional toilet to a composting one requires education, commitment and responsibility on the part of the owner. 

 

Urine Diversion

Urine Diversion toilets are another type of toilet being considered as an alternative to sewering here in Falmouth.   Urine diversion (UD) toilets work just like the name says - they divert urine into a separate container, while feces can continue to be piped to a septic system along with the rest of a household’s waste waters from showers, laundry and dish washing. 

Most of the nutrients in our wastewater come from the urine.  While urine is only 1% of the wastewater volume, it contains 50% of the phosphorus and 80% nitrogen.  UD toilets were designed not only to capture this high amount of nutrients and keep them from polluting waterbodies, but also for resource recovery.   Phosphorus is one of the key ingredients in fertilizer needed for growing food crops.  With world-wide shortages of phosphorus predicted by the end of this century, urine may soon be reprocessed into “liquid gold”.  An average household of four can generate enough urine to fertilizer a 1/3 of an acre of crops annually.  

Capturing urine can also reduce the amount of hormones and pharmaceuticals coming out of our septic systems.  Two-thirds of these “Contaminants of Emerging Concern” (CECs) are excreted in urine.  CECs are receiving attention because though they are seen at very low levels in the environment, little is known about their potential impact to human and animal health.  Some of these chemicals are endocrine disrupters that can alter normal hormone functions and cause a variety of health effects.  Studies by the EPA found components of antidepressants and antihistamines in fish downstream from wastewater treatment plants.  Some CECs from wastewater effluent have been found in the groundwater and ponds here on Cape Cod.

From the outside, a UD toilet can look the same as a conventional toilet, until you lift the lid. Inside, the toilet bowl is split into two chambers.  The front smaller bowl captures the urine and diverts it to a storage tank while the larger bowl in the back carries the feces either to a septic system or a compost tank.   The storage tank can be located in the basement, outside next to the building or below ground, but must be built from plastic because urine is too corrosive to metal.  

The size of the storage tank depends on the household size and storage time. The average person produces a little less than half a gallon of urine a day.  UD toilets can be “dry” or use a small amount of water for flushing.   (One of the benefits of UDs is that they use much less water than even conventional low flush toilets.)  If a water flushing toilet is used, then the storage tank needs to be increased accordingly.

Though fitting an UD toilet into an existing house is less of a challenge than installing a compost toilet, they still need special consideration.  As fresh urine sits, crystals precipitate out of the urine. These crystals combine with hair, skin and paper particles to form a sludge that builds up especially quickly in slow moving sections of pipes, causing blockages.  This happens in both dry and water flush toilets.   To minimize this problem, pipes must be installed to decrease the time urine is in the pipes.   Pipes must be less than 33 feet in length with at least a 1% slope and between 2” to 3” in diameter without any sharp bends.  They also must be installed to allow access for a twice a year clean out of the crystal build up either with caustic soda, acetic acid or with an auger.  The storage tank and pipes need be pressured equally to minimize odors.

The use of UD toilets does require education and a cultural shift.  Men need to sit to urinate.  While in some models, children and some women have a hard time fitting on them.  One of the greatest challenges in using UD toilets is making sure feces do not end up in the urine side of the bowl.  Despite these challenges, UDs are being used at small and mid-level scale developments in Europe (Sweden, Switzerland), Latin America (Mexico), Asia (Nepal, China, Japan) and Africa (Ethiopia, South Africa).

The question remains however (as with compost toilets) how much nitrogen is there in the remaining household water coming from our septic systems?  Even if we remove urine -- the highest source of nitrogen in a household’s wastewater effluent, -- laundry detergents, dish washing soaps and personal care products still contain nitrogen.  Is just diverting urine from the household effluent enough to reach the removal requirements needed to clean up our bays? 

 


Oyster Pond Environmental Trust, Inc.
501(c) 3 non-profit organization
PO Box 496 • Woods Hole, MA 02543-0496