Biofilms form when microorganisms like bacteria attach to a surface and produce an extracellular polymeric substance (EPS) that enables them to stick together. As more layers of microorganisms and EPS build up, they create a complex 3D structure. In wastewater treatment, microorganisms in biofilms absorb and break down organic matter, producing new cells, carbon dioxide, and water. This process removes organic compounds from wastewater as the microcolonies settle as sludge.

1. What is biofilm? How is it formed? Describe its role in removing organic
compounds from the waste water.
ANSWER: Biofilms are a collective of one or more types of microorganisms that
can grow on many different surfaces. Microorganisms that form biofilms
include bacteria, fungi and protists.
One common example of a biofilm is dental plaque, a slimy buildup of bacteria
that forms on the surfaces of teeth. Pond scum is another example. Biofilms have
been found growing on minerals and metals. They have been found underwater,
underground and above the ground. They can grow on plant tissues and animal
tissues, and on implanted medical devices such as catheters and pacemakers.
Biofilm formation begins when free-floating microorganisms such as bacteria
come in contact with an appropriate surface and begin to put down roots, so to
speak. This first step of attachment occurs when the microorganisms producea
gooey substance known as an extracellular polymeric substance(EPS). An EPS is
a network of sugars, proteins and nucleic acids (such as DNA). It enables the
microorganisms in a biofilm to stick together.
Attachment is followed by a period of growth. Further layers of microorganisms
and EPS build upon the first layers. Ultimately, they create a bulbous and complex
3D structure. Water channels crisscross biofilms and allow for the exchange of
nutrients and waste products. Multiple environmental conditions help determine
the extent to which a biofilm grows. These factors also determine whether it is
made of only a few layers of cells or significantly more. For instance,
microorganisms that producea large amount of EPS can grow into fairly thick
biofilms even if they do not have access to a lot of nutrients, he said. On the other
hand, for microorganisms that depend on oxygen, the amount available can limit
how much they can grow. Another environmental factor is the conceptof shear
stress. If you have a very high flow of water across a biofilm, like in a creek, the
biofilm is usually fairly thin. If you have a biofilm in slow flowing water, like in a
pond, it can become very thick.
Finally, the cells within a biofilm can leave the fold and establish themselves on a
new surface. Either a clump of cells breaks away, or individual cells burst out of
the biofilm and seek out a new home. This latter process is known as "seeding
dispersal".
The organic material present in wastewater includes detergents, pesticides, fats and
oils. In addition, many types of microorganisms, including bacteria, viruses,
protozoaand helminths, can be present in wastewater. Microorganisms in biomass
absorb organic matter and nutrients in their vicinity, which allows them to grow

2. and reproduceto form microcolonies. microorganisms oxidize the organic carbon
present in wastewater to producecarbondioxide, water and new cells These
microcolonies settle as sludge, which is then either removed or treated in a sludge
treatment process orreused in the process bybeing resuspended.
Describe the working principle of trickling filter of wastewatersystem.
ANSWER: Wastewater treatment through trickling filters (TFs)is among the
oldest and most well characterized treatment technologies. TFs generally comprise
a vessel packed with inert media (rocks, coke, lava, slag, gravel, polyurethane
foam, ceramic, sphagnum peat moss or plastic media). The distribution system is
used to sprinkle wastewater over filter media, and the wastewater trickles through
the filter media supporting biomass under the influence of gravitational force. A
biological slime layer grows on the media, and treatment is provided by the
microbes that absorb dissolved organic matter for their growth and reproduction as
the wastewater cascades randomly through the voids between the media. A
schematic of the entire process is shown in the figure below. TFs are suitable for
small- to medium-sized communities with a high filter loading rate and marked by
their ease of operation, self-cleaning capacity and efficient removal of ammonia.
However, additional treatment may be needed for the effluent to meet strict
discharge standards as it generates large amounts of sludge and a relatively high
incidence of clogging.

3. Fig: Schematic of a trickling typical trickling filter system.