Pages: (HOME) 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24
Types of Sewage Treatment from a biological standpoint:
Sewage treatment processes of a biological nature calls upon
bacteria, plants and even animals. Nature has been treating raw sewage for
millions of years; everything sustains itself on the waste of other species.
Bacteria have naturally occurred to eat and live off of raw sewage, thus septic
tanks, cesspools can exist without the introduction of anything else.
Many of the biological sewage treatment options thus far are
not readily applicable for populations of millions, such as New York City and
Los Angeles. However these sewage treatment options do work for small
communities.
Space may at first appear to be a problem when it
comes to the Oceanic City platforms, the reality is beneath the main living
level (the top) there will be at least one level available providing as much
acreage as the surface (17 acres per platform).
It is possible if not desirable to design the top deck of
each platform with skylights in mind for the deck below. Light from above can
be directed, magnified and diffused below deck, coupled with what will be
abundant electrical power and the use of low watt, high candle power light
bulbs and careful selection of plants that grow best in low light conditions
the lower deck would be well suited for growing plants that not only treat
sewage run-off, but also serve other purposes, such as a source of cellulose
for paper, plastics, or as a source of material for alcohol production, or even
as a source of food for humans and livestock alike.
We will explore these below.
Constructed
Reed Bed Systems
Also known
as artificial wetland systems, Constructed reed bed systems are the reconstruction
of freshwater wetland ecosystems to treat wastewater. They are often used in
combination with other conventional treatment facilities, including septic
tanks. There are three basic types of wetland construction:
- Horizontal Flow -
wastewater is continually fed through an inlet / outlet gradient system
- Vertical Flow -
wastewater is applied in batch and allowed to drain each time
- Pond Systems - a
series of shallow ponds linked by a constructed wetland container
Most reed bed models are land-intensive, but they are highly
energy-efficient (requiring no energy for treatment processes) inexpensive to
build, low maintenance, productive, have minimal sludge generation, are
aesthetically appealing, and create valuable habitat for wildlife.
Solar
aquatic systems model the processes of wetland ecosystems in a controlled and
intensified environment. Anaerobically treated wastewater is passed through a
series of tanks in a greenhouse, using sequenced ecologies of specified aquatic
plants and animals to break down sewage. The resulting water is pure enough to
be used for non-drinking purposes and can be safely discharged into the
environment. Dr. John Todd of Ocean Arks International pioneered this
technology in a patented design called 'Living Machines'. He has now developed
this into the design of restorers, assemblies of engineered ecologies that can
be floated as a raft to treat sewage in constructed canals or lagoons.
Biogas
Plants
Biogas plants are being developed in the UK and Europe in
combination with conventional sewage plants to capture gas from sludge and
introduce it into the National Gas Pipeline. They are already used widely in
developing countries as complete sewage systems. In a biogas plant, sewage is
piped into a sealed container called a digester, where it ferments producing a
mixture of methane and carbon dioxide along with slurry. The anaerobic
conversion process destroys pathogens and renders the slurry harmless and
odorless, so it can be used directly on the land as a fertilizer. The methane is
piped directly out from the top of the digester.
Sewage:
A Valuable Resource
Ecologically designed sewage systems are a good example of
sustainable design. They are energy-efficient, inexpensive, effective and
environmentally friendly, and can be applied at any scale, from a single home
to a large city. Yet this technology fails to realize the full potential of
sewage as a resource. Although sewage contains contaminants, it also holds
nutrients that can be used to improve soil fertility, along with the ability to
produce natural gas. Technologies such as biogas plants that maximize sewage as
an energy and nutrient source need to be developed on a global scale. It's time
that sewage was viewed as a valuable resource, and not just a problem to be
treated.
http://www.sustainablebuild.co.uk/SustainableDesignSewage.html
A combination of solid retrieval for composting or soils,
along with the use of reed bed models used to grow as example Papyrus Cyperus
papyrus that has been used to make paper called papyrus. Aside from
papyrus, several other members of the genus Cyperus may actually have
been involved in the multiple uses Egyptians found for the plant. Its flowering
heads were linked to make garlands for the gods in gratitude. The pith of young
shoots was eaten both cooked and raw. Its woody root made bowls and other
utensils and was burned for fuel. From the stems were made reed boats (seen in
bas-reliefs of the Fourth Dynasty showing men cutting papyrus to build a boat;
similar boats are still made in the southern Sudan), sails, mats, cloth,
cordage, and sandals. In southern Africa the starchy rhizomes and culms are
eaten, raw or cooked, by humans. The culms are also used for building
materials. Livestock frequently grazes young shoots.
Hyacinth
Ponds (Experimental)
Raw sewage
was treated in a project conducted in San Diego using ponds of hyacinths. In
six 1/4-acre (0.1 ha) ponds, water hyacinths were grown in sewage water.
Bacteria, which lived in the plants' root hairs, broke down organic matter for
the plants' roots to absorb, and the hyacinths could also absorb heavy
dissolved metals, which conventional sewage treatments do not deal with.
This
method was highly effective with organic material, being able to reduce the BOD
measurement of household sewage by 147 parts per million after 36 h. BOD, which
means biological oxygen demand, measures the amount of oxygen consumed by
microorganisms in the sewage to decompose organic material. The measurement
represents the amount of organic matter in the sewage, and is given in parts of
oxygen per million parts of water/sewage (ppm). The sewage received by the
hyacinth ponds had a BOD of 158 ppm and left with a BOD of 11 ppm. After
conventional secondary treatment, the U.S. Environmental Protection Agency
allows a maximum BOD of 30 ppm.
Besides
performing a higher level of purification, hyacinth ponds are cheaper and
easier to maintain than conventional primary and secondary treatment, and they
can support other aquatic life as well, such as frogs, snails, and a turtle.
They require little aeration and no heating or stirring, and hyacinths can
thrive in heavily polluted waters. The number of plants in a pond can double in
two weeks.
In
fact, the tremendous growth rate became a problem. Every two weeks, half of the
plants in the ponds had to be harvested and shipped to landfills. Alternative
uses for these harvested plants were being investigated, and included
fertilizer, paper, and cattle feed. Another disadvantage of this method was its
climate dependence. Hyacinths cannot withstand frost, so while this method was
effective in San Diego's warm climate, it would not be practical in Canadian
winters. The main limitation of the hyacinth ponds was volume: They could treat
only 300,000 gallons (1.1 million L) of sewage per day, about 1/500th of the
approx. 150 million gallons (570 million L) of sewage produced daily by the
city. Larger ponds would be needed, but land area is very expensive. Mosquitoes
were also a major problem. Slow-moving, nutrient rich, protected waters bred
huge numbers of mosquitoes. The mosquito fish, a kind of guppy that eats
mosquitoes, was introduced into the ponds, but they did not survive.
Grass
Ponds (Experimental)
In
Beltsville, Maryland, the U.S. Agricultural Research Service conducted tests on
purifying sewage with grass in a method much like the one used in hyacinth
ponds.
Grass
was grown in shallow rectangular tanks over a layer of crushed rock, which
provided an anchor for the grass roots. Effluent from a lagoon (after solids
and most organic matter were removed) flowed slowly through these tanks and
filtered through the grass.
In
the tests, the grass absorbed 70% of the remaining nitrogen and 80% of the
remaining phosphorus.
The Grass pond method would be applied in the lower level of
the platforms where artificial and natural light could be used in tandem with
shade adapted grasses. The grass would be allowed to grow tall enough and
either act as pasture land for livestock, or could be cut and baled for use as
hay and straw.
If not used in that manner, then it could be grown and mowed
and the clippings used in composting to make new soil.
Recent research in South Korea indicates that rice paddies
may be used in the treatments of sewage water as well. Not only treating sewage
but also providing nutrients for rice that is a main staple for many cultures.
The potential for a mix of different plant biomes, such as
using hyacinth and papyrus for the initial treatment of black sewage water,
then using the semi-treated water for grass, rice and grain crops would provide
a wider range of applications. In essence hydroponics would be used where
instead of a soil an aggregate of rock or even meshes of cotton and other plant
fibers would be used.
'Living
Machines'
A concept that may prove to be the most useful for Oceanic
Platforms is the living machine.
Living Machines are a form of biological wastewater treatment designed to mimic the
cleansing functions of wetlands. They are intensive bioremediation
systems that can also produce beneficial by-products such as methane gas,
edible and ornamental plants, and fish. Aquatic and wetland plants, bacteria, algae, protozoa, plankton, snails, clams, fish and other
organisms are used in the system to provide specific cleansing or trophic
functions. In temperate climates, the system of tanks, pipes
and filters is housed in a greenhouse to raise the temperature, and thus the
rate of biological activity. The initial development of living machines is
generally credited to John Todd, and evolved out of the bioshelter
concept developed at the now-defunct New Alchemy Institute. Living Machine
is a trademarked term held by Living
Designs Group, LLC of Taos,
New Mexico. Living machines fall within the emerging discipline of ecological engineering, and many similar
systems are built in Europe without being dubbed “Living Machines.”
Design Theory
The
scale of living machines ranges from the backyard experiment to dependable public
works. Some living machines treat domestic wastewater
in small, ecologically-conscious
villages, such as Findhorn Community in Scotland ,
and some treat the mixed municipal wastewater for semi-urban areas, such as South Burlington, Vermont .
Each
system is designed to handle a certain volume of water per day, but the system
is also tailored for the qualities of the specific influent. For example, if
the influent contains high levels of heavy
metals, the living machine must be designed to include the proper biota
to accumulate the metals.
During the “spring cleaning” season, there may be high levels of bleach in the water.
This sudden concentration of a toxin is an example of a steep gradient.
- Steep gradients are
drastic changes in conditions throughout the system that challenge the ecosystem
to become resilient and stable.
A well-designed living machine requires little management, so managers may
intentionally create abrupt environmental or biochemical
changes to promote ecosystem self-regulation. This mimics nature’s power
and trains the ecosystem to adapt to influent variations.
- Designers seek to
increase the surface area of contact that biota have with the sewage to promote high
reaction rates. When organisms have ready access to the sewage, they can
treat it more thoroughly.
- The living machine is
cellular, as opposed too monolithic, in design. If influent volume or
makeup changes, new cells can be added or omitted without halting or
disturbing the ecosystem.
- Photosynthetic
plants and algae are important for oxygenating
water, providing a medium for biofilms,
sequestering heavy metals and many other services.
Species
diversity is a design goal that promotes complexity and resiliency in an ecosystem.
Functional redundancy (the presence of multiple species that provide the same
function) is an important example of the need for biodiversity. Snails and fish
filter sludge and act as diagnostics: when a toxic load enters, snails will
rise above the water level on the wall of the tank.
- The micro-ecosystem of
the living machine can be integrated with the macro-ecosystem just as ecosystems
fade into one another naturally. This connection is commonly made with an
outdoor constructed or natural wetland into which the effluent flows. Some
living machines are partially or completely open to the outdoors, and this
promotes interaction with the surrounding environment. [5]
The
above points are an incomplete synthesis of a paper by Todd and
Josephson.
Built Components
In
warm climates, living machines can be outdoors, as the temperature will sustain
sufficient biological activity throughout the winter. In temperate climates, a
greenhouse is used to keep water temperatures warm so that plants do not
winterize. In cold climates supplemental heating may also be necessary.
Living
machines use screens, biofilters, plumbing, large plastic tanks, reed beds,
rocks, fans, pumps and other mechanical devices. Every system is tailored to
the volume and makeup of the sewage. Some are stand-alone greenhouses, while
others are built into larger buildings.
John Todd
and James Shaw have a patent on a device called an "ecological fluidized
bed" which is essentially a pumice-filled tank with a concentric inner
tank that contains wetland plants. Pumps rapidly recirculate water to maximize
the filtration rate of this device.
Biological Processes
- The first step of the
process is an anaerobic settling tank. This closed anaerobic
tank serves as a pre-treatment to allow solids to fall out of suspension
and precipitate to the bottom of the reactor to reduce the turbidity of
the water. A variety of anaerobic bacteria are present in this tank; they
generate acids and ferment methane. This step may be unnecessary if the
influent has low levels of solids.
- Next, the sewage flows
through a biofilter of bark and humic materials.
This gives the influent its first filtration and reduces the odors
prevalent in anaerobic conditions.
- The mixture then moves
into a series of aerobic tanks. The first tank is a dark, closed-top aerobic
reactor that serves as a transitional step. The next tank is an open-top,
aerobic reactor that contains photosynthetic
algae that
fix oxygen
back into the formerly anoxic, turbid water. This provides oxygen and
organic food (dead algae) for biological metabolism
and respiration.
Microbial communities proliferate, and eventually must consume all of the photosynthetic
algae so that the algae do not choke out macrophytes in later steps.
- Many types of bacteria
immobilize pollutant minerals, but certain species of bacteria
are crucial to nutrient conversion. Specifically, Nitrosomonas
and Nitrobacter work in steps to nitrify
ammonia,
making it into nitrates, which are available for plant and microbial
uptake. These bacteria need calcium carbonate to catalyze
this reaction (Note: Biorock formation will collect calcium carbonate, there will not be a lack of this material in Oceanic Platforms), so managers must maintain sufficient calcium levels in the
water. Denitrifying bacteria such as Pseudomonas fluorescens convert nitrates
into gaseous nitrogen, which is volatilized
in these open aerobic tanks.
Denitrification is the most desirable sink for nitrogen in living
machines.
Protozoa have been shown to be capable of coliform and pathogen
suppression.
Microbial breakdown is the primary biological treatment of both the
conventional activated sludge process as well as these
aquatic ecosystem sludge reactors.
- Higher plants are
grown hydroponically
in the aerobic tanks and provide multiple services. The most common plant
used is water hyacinth (Eicchornia crassipies),
which has filamentous aquatic roots with a high specific area. These
feather-like roots provide a stable habitat for microbes,
and over time a bacterial biofilm builds up around the roots. Water hyacinth, bulrush and other macrophytes
sequester heavy metals. The bodies of these plants can be harvested and
burned, and the heavy metals can be chemically isolated to take them out
of the environment. Brassica juncea growing in waste streams has
been found to contain 60% of its dry weight in lead.
- Plankton
carries out multiple functions in the system with varying efficacy.
Zooplankton feed on extremely small (<25µm) particles. In juvenile
stages they feed on particles smaller than 1 µm.
Conventional waste treatment cannot process these fine suspended solids.
Although zooplanktons does consume these fine particles,
which are difficult for conventional treatment systems to process, the
placement of plankton in the system is more valuable as a trophic
link. Plankton can eat microbes, which are abundant in the system, and the plankton
is an ideal food for filter feeding fish and mollusks.
This food chain transfers biomass to higher trophic levels and increases
the diversity and complexity of the ecosystem. John Todd thinks, “Since zooplankton
can exchange the volume of a natural body of water several times per day
it is difficult to overstate their importance in ecological engineering.”
- According to Björn
Guterstam, another one of the most well-published and experienced ecological engineers, this theoretical
role has not been as successful in practice. He concedes that phytoplankton
populations have been limited by toxic and somewhat deoxidized water at
the bottom of tanks, as well as light limitations. Phytoplankton
are primary producers, which provide food for
larger zooplankton species, so the zooplankton
population drops with its photosynthetic
counterpart.
Because these principles have been implemented only on a small scale,
these systems have a lowered buffering capacity due to issues of scale and
separation from the macro ecosystem, even though genetic and functional
diversity is encouraged.
- Aquaculture
can take place in more dilute tanks downstream after the eutrophication-causing
contaminants have been ameliorated. Snails slide
along the tank walls and graze on slime and sludge buildup, cleaning the
tank. This self-regulation improves light penetration, which stimulates
photosynthetic forms of algae, bacteria and plankton. Filter feeders sift
through large volumes of water each day and consume the bacteria and
plankton that are small enough to pass through. Mollusks
such as mussels and snails, as well as some fish, are filter feeders. Detritus-feeding
fish consume larger particles of suspended biosolids.
Herbivorous fish are excluded from tanks where macrophytes carry out
useful functions (such as biofilm hosting), but when plants are eventually
harvested from the system, this plant tissue can be fed to a tank of
herbivorous fish for aquaculture production.
- A single Anodonta freshwater clam can filter as much as 40 liters/day of water, absorbing colloidal materials and other suspended solids at a removal rate of 99.5%. Many freshwater clams are in danger of extinction, in part because some have gills that perform poorly in polluted environments. Since some of these clams can sequester colloids from streams or lakes, this provides an ecosystem service by slowing the erosion of soil colloids.
We should note here that Oceanic Platforms would have better control over what goes into the raw sewage.Industrial sewage lines (Which will contain heavy metals and chemicals in the waster water) would be handled separately from the homes and living areas where human wastes, toilet paper and home cleaning solutions will be the main ingredients in the black sewage.
Oceanic City will need to control the products it uses, thus the cleaning chemicals will be biodegradable and ecologically safe. The sewage treatment processes above are designed or take into account urban chemicals in waste water of current cities.
Algae, kelps and sewage treatment:
Many marine environments are presently being disrupted by excess algae growth due to man’s dumping of nutrient rich sewage (although treated in part or in whole) making a case for the use of sewage water to grow species of algae for use by Oceanic City. Marine algae, as primary producers, are ecologically important, and economically have been used as food and medicines for centuries. Today, various species of marine algae provide not only food but also produce extracts such as agar, carrageen, and alginates. These extracts are used in numerous food, pharmaceutical, cosmetic, and industrial applications.
Industrial and other uses
- Fertilizer / soil
amendments
Miscellaneous species of Kelps (Brown algae), e.g. Laminaria, Macrocystis - Filters / Rubbing
compounds (polish) / Pest control (fleas)
Diatoms in the form of Diatomaceous earth (diatomite)
Unicellular freshwater Chlorophyta and other micro- and macroalgae.
Pages: (HOME) 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24