natural sewage treatment SOLAR.KnowledgePublications.com

natural sewage treatment
17 mar 1996
i've been reading two works by sherwood c. reed, a professional engineer
who lives and works in new hampshire. 

us epa design manual number 74, "subsurface flow constructed wetlands for
wastewater treatment" is available for about $12 from the small flows
clearinghouse at west virginia university at pob 6064, morgantown, wv,
26506-6064, (304) 293-4191 or (800) 624-8301. this clearinghouse is largely
government-supported, and i think they do a wonderful job.

here's a little quote:

  the proponents of subsurface inlet manifolds claim they are necessary
  to avoid the buildup of algal slimes on the rock surfaces and resulting
  clogging adjacent to a surface manifold. the disadvanatages of a subsurface
  manifold are the inabilitiy for future adjustment and the limited access
  for maintenance. in one case, a buried manifold became clogged with turtles
  which entered the piping system from the preliminary treatment lagoon and
  had to be removed. 
  
there is a lot of nice, simple math in this book, which explains how
to build a natural wastewater treatment system for a home or community.

you can tell what's inside _natural systems for waste management and treatment_
by the cover, which cleverly has a small piece of gravel embedded therein,
of a type that is used in the construction of artificial wetlands. mcgraw
hill, 1995, second edition, isbn 0-07-060982-9, 434 pages, about $55.

the back cover says: 

  here is your chance to learn about biologically-based systems for handling
  waste that are fast becoming the technology of choice in communities and
  municipalities across the united states... the new edition of this classic
  reference will introduce you to low-cost, low-energy methods of processing
  waste and wastewater naturally...

here are some quotes:

  serious interest in natural methods for waste treatment reemerged in the us
  following the passage of the clean water act of 1972... the major initial
  response was to assume that the "zero-discharge" mandate of the law could be
  obtained via a combination of mechanical treatment units capable of advanced
  wastewater treatment (awt). in theory, any specified level of water quality
  can be achieved via a combination of mechanical operations, however the
  energy requirements and high cost of this approach soon became apparent,
  and a search for alternatives was commenced...  

  ...as more and more systems were built... it was noticed that these natural
  systems... could usually be constructed and operated for less cost and with
  less energy... ...there were about 400 municipal land treatment systems
  using wastewater in the us in the early 70's. that number had grown to at
  least 1400 by the mid 1980's and is projected to pass 2000 by the year 2000. 

  stabilization ponds have been employed for treatment of wastewater for over
  3000 years... the most common type is the facultative pond. other terms
  commonly applied are oxidation pond, sewage lagoon, and photosynthetic pond.
  anaerobic fermentation occurs in the lower layer and aerobic stabilization
  occurs in the upper layer... a continuous ice layer on a facultative pond
  will lower performance [but a partial ice layer on a cold day might make a
  very nice solar reflector--np]... the occasional high concentration of
  suspended solids (ss) in the effluent... is the major disadvantage of pond
  systems. the solids are composed primarily of algae, not wastewater solids. 

  aquatic treatment is defined as the use of aquatic plants or animals as a
  component in a wastewater treatment system. in many parts of the world,
  wastewater is used for the production of fish... the floating aquatic plants
  with the greatest potential for wastewater treatment include water hyacinths,
  duckweeds, pennywort and water ferns... hyacinths are one of the most
  productive photosynthetic plants in the world. it has been estimated that
  10 plants could produce 600,000 more during an 8 month growing season and
  completely cover 0.4 ha (1 acre) of a natural freshwater surface. the rate
  can be even higher in wastewater ponds... the dense canopy of leaves shades
  the surface and prevents algal growth... the plant can survive and grow in
  anaerobic waters, since oxygen is transmitted from the leaves to the root
  mass. the attached biological growth on the root mass is similar to...
  rotating biological contactor (rbc) slimes. bacteria, fungi, predators,
  filter feeders and detritovores have been reported in large numbers on and
  among the plant roots... an effective mosquito control method is to stock
  each basin with gambusia or other small surface feeding fish that prey on
  the mosquito larvae... [other species include goldfish, frogs, grass shrimp,
  blue tilapia and japanese koi. the hyacinths are sometimes harvested and
  processed in a biogas digestor or used for animal feed...] 

  ...duckweeds are the smallest and simplest of the flowering plants and have
  one of the fastest reproduction rates... lemna sp. grown in wastewater
  effluent (at 27 c) doubles in frond numbers, and therefore area covered,
  every 4 days. [not surprisingly, ducks like to eat duckweed, a lot--np]
  ...duckweed can grow at least twice as fast as other vascular plants. the 
  plant is essentially all metabolically active cells, with very little
  structural fiber... duckweeds are more cold-tolerant than hyacinths, and are
  found throughout the world. in 1992 there were at least 15 operational
  wastewater treatment facilities designed specifically as duckweed systems...
  mosquito larvae will not be able to penetrate a fully developed duckweed
  mat, and are therefore not a problem... duckweed, like hyacinth, contains
  about 95% water... duckweed contains at least twice as much protein, fat,
  nitrogen and phosphorous as hyacinth. several nutritional studies have
  confirmed the value of duckweed as a food source for a variety of birds
  and amimals [footnote]... the harvested plants may be used directly in the
  wet state as poultry or animal feed. composting... is also feasible. 

  the aquatic animals that have been considered for use in wastewater treatment
  include daphnia, brine shrimp, and a wide variety of fish, clams, oysters
  and lobsters...  except for the predatory fish and the lobsters, the primary
  function of the other species is the removal of the suspended solids or
  algae. assumning that the animals are routinely harvested, this will in turn
  also improve nutrient removal... fish activity is highly dependent on
  temperature, and most of the species... with the exception of catfish...
  require relatively warm water... the final lightly loaded cells in
  wastewater pond systems can be used for fish culture if a market for the
  harvested fish exists. at present, federal and state health regulations
  prevent the sale of such fish for direct human consumption, even though
  microbiological studies have not detected any contamination... major markets
  for this harvested material would be bait fish, pet food or fertilizer. 

i'm just starting to read the section on wetlands, including those enclosed
by simple inexpensive commercial film greenhouses, and smaller on-site systems
for houses. i'll post more about that later, along with a few basic programs
that might help in designing these systems. 

nick