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What Are Aerobic Wastewater Treatment Systems and How Do They Work?
SAMCO
Typically used as a
secondary wastewater treatment method after the initial larger contaminants
have been settled and/or filtered out, biological wastewater treatment systems can
be efficient and economical technologies for breaking down and removing organic
contaminants from heavily organic-laden wastes, such as those produced in the
food and beverage, chemical manufacturing, oil and gas, and municipal
industries.
Anaerobic and
aerobic systems are two of the main types of biological wastewater treatment,
but this article will focus on “what aerobic wastewater treatment systems
are and how they work.”
What is aerobic wastewater treatment?
Aerobic wastewater
treatment systems use oxygen-feeding bacteria, protozoa, and other
specialty microbes to clean water (as opposed to anaerobic systems
that do not need oxygen).
These systems
optimize the naturally occurring process of microbial decomposition to break
down industrial wastewater contaminants so they can be removed.
The organic
contaminants these microorganisms decompose are often measured in biological
oxygen demand, or BOD, which refers to the amount of dissolved oxygen needed by
aerobic organisms to break down organic matter into smaller molecules.
High levels of BOD
indicate an elevated concentration of biodegradable material present in
the wastewater and can be caused by the introduction of pollutants such as
industrial discharges, domestic fecal wastes, or fertilizer runoff.
How do aerobic wastewater treatment systems work?
Because these
organisms require oxygen, aerobic systems require some means of
supplying oxygen to the biomass by adding wastewater treatment ponds
(which work by creating a large surface area for introducing air to the
wastewater) and/or by incorporating some type of mechanical aeration device to
introduce oxygen into the biomass.
Depending on the
chemical makeup of the wastewater in relation to the effluent
requirements, a biological wastewater treatment system might be composed
of several different processes and numerous types of microorganisms.
They will also
require specific operational procedures that will vary depending on the
environment needed to keep biomass growth rates optimal for the specific
microbial populations.
For example, it is
often required to monitor and adjust aeration to maintain a consistent dissolved
oxygen level to keep the system’s bacteria multiplying at the appropriate rate
to meet discharge requirements.
In addition to
dissolved oxygen, biological systems often need to be balanced for flow, load,
pH, temperature, and nutrients.
Balancing a combination
of system factors is where the biological treatment process can become very
complex.
Below are examples
of some common types of aerobic biological wastewater treatment
systems, including a brief description of how they function within an
industrial wastewater treatment regimen to give you an idea of the types of
technologies and systems that might benefit your industrial facility.
Activated sludge
Used widely used in
municipal applications, activated sludge processes occur when wastewaters from
the primary treatment phase enter an aeration tank.
After aeration in
the presence of suspended (freely floating) aerobic microorganisms, the organic
material is broken down and consumed, forming biological solids which
flocculate into larger clumps, or flocs.
The suspended flocs
enter a settling tank and are removed from the wastewater by sedimentation.
Recycling settled solids to the aeration tank controls levels of suspended
solids, while excess solids are wasted as sludge.
Activated sludge
treatment systems typically have larger space requirements and generate large
amounts of sludge, with associated disposal costs, but capital and maintenance costs are
relatively low, compared to other options.
Fixed-bed bioreactors, or FBBRs
These systems
consist of multiple-chambered tanks in which the chambers are packed tight with
porous ceramic, porous foam, and/or plastic media.
Wastewater then
passes through the immobilized bed of media. The media is engineered to have a
high enough surface area to encourage a robust biofilm formation with long
solids lifespan, resulting in low sludge formation and lowest sludge disposal
costs.
A well-engineered
fixed-bed bioreactor will allow wastewater to flow through the system without
channeling or plugging.
Chambers can be
aerobic and still have anoxic zones to achieve aerobic carbonaceous removal and
full anoxic denitrification at the same time.
More advanced
biological processes can be facilitated with these systems (for example,
nitrification, denitrification, desalination, sulfide-reduction, and anammox),
by having unique bacterial populations colonize the biofilm media in separate
tank chambers, which can be uniquely configured to treat your facility’s
specific wastewater constituents.
Moving bed bioreactors, or MBBRs
MBBRs typically
consist of aeration tanks filled with small moving polyethylene biofilm
carriers held within the vessel by media retention sieves.
Today the plastic
biofilm carriers come from many vendors in many sizes and shapes, are typically
half- to one-inch diameter cylinders or cubes and are designed to be suspended
with their immobilized biofilm throughout the bioreactor by aeration or
mechanical mixing.
Because of the
suspended moving bio-film carriers, MBBRs allow high BOD wastewaters to be
treated in a smaller area with no plugging.
MBBRs are typically
followed by a secondary clarifier, but no sludge is recycled to the process;
excess sludge settles, and a slurry removed by vacuum truck, or settled solids
are filter pressed and disposed as a solid waste.
Membrane bioreactors, or MBRs
MBRs are advanced
biological wastewater treatment technologies that combine conventional
suspended growth activated sludge with membrane filtration, rather than
sedimentation, to separate and recycle the suspended solids.
As a result, MBRs
operate with much higher mixed liquor suspended solids (MLSS) and longer solids
residence times (SRTs), producing a significantly smaller footprint with a much
higher quality effluent compared to conventional activated sludge.
MBRs primarily
target BOD and total suspended solids (TSS).
MBR system design
varies depending on the nature of the wastewater and the treatment goals, but a
typical MBR might consist of aerobic (or anaerobic) treatment tanks, an
aeration system, mixers, a membrane tank, a clean-in-place system, and either a
hollow fiber or flat sheet ultrafiltration membrane.
As a result of its
many parts and cleaning processes, MBRs are known for high capital, high
operating, and high maintenance costs.
Biological trickling filters
These filters work
by passing air or water through a media designed to collect a biofilm on its
surfaces.
The biofilm may be
composed of both aerobic and anaerobic bacteria which breakdown organic
contaminants in water or air. Some of the media used for these systems include
gravel, sand, foam, and ceramic materials.
The most popular
application of this technology is municipal wastewater treatment and air remediation
to remove H2S at municipal sewer plants, but they can be used in many
situations where odor control is important.
How SAMCO can help?
SAMCO has over 40
years’ experience custom-designing and manufacturing biological wastewater
treatment systems for a range of industries and applications, so please feel
free to reach out to us with your questions. Contact us
here to set up a consultation with an engineer or request
a quote. We can walk you through the steps for developing the proper
solution and realistic cost for your specific water treatment system needs.
To learn more about
the services and technologies that SAMCO offers, visit our page on wastewater
treatment solutions here.
At
SAMCO, we anticipate the needs of industry,
and respond with forward-thinking solutions. Our focus on industrial
applications began in 1987 with the founding of Northeast equipment supplier
and systems servicer CS Kimeric. Acquired from a Western New York soft water
provider with over 30 years in the business, CS Kimeric was established to
provide specialized service for industrial applications. Over the course of the
next decade, it became clear that industrial clients would benefit from working
with a partner capable of delivering comprehensive, concept-to-completion
solutions. In 1998, founder and CEO Richard Posa established SAMCO as an integrated
provider of design, fabrication, startup, and maintenance services.
Today,
SAMCO serves the process water needs of clients across the nation and globe
from its headquarters in Buffalo, New York. Leveraging the collective skills of
experienced chemical, civil, environmental, electrical, mechanical and process
engineers, chemists, and skilled tradesmen, SAMCO blends a culture of teamwork,
commitment and passion to help solve your unique industrial water treatment
needs.
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