What Is Screening in Water Treatment? A Complete Beginner’s Guide

Whether for a large city or a specialised industrial facility, every effective
wastewater treatment processbegins with a simple step. Before any complex
chemical or biological treatment can occur, you must first deal with the solid
objects that have found their way into the water. This essential first stage is
known as screening in water treatment.
Screening in water treatment is the physical barrier that stands between the
raw, incoming water and the delicate, expensive machinery of the plant. It stop
the large, troublesome particles from getting inside and causing problems for
the more advanced processes downstream. Even though it may seem like a
basic concept, this initial step plays an important role in water treatment. It is
evident to ensure the efficiency, longevity, as well as operational success of
the entire system.
Why Screening is the First Step
The primary purpose of screening in water treatment is protection. A
wastewater treatment plant is an interconnected system of pumps, pipes,
valves, and sensitive monitoring equipment. This machinery is designed to
handle water and suspended solids, not large debris.
Without an effective screening process, items like plastic bottles, rags, wood,
and other rubbish can enter the system. This can lead to catastrophic
blockages in pipes, damage to pump impellers, and fouling of sensors and
other treatment units.
By removing these solids at the beginning, screening in water treatment
completes many important purposes:
● It protects all downstream equipment from damage and blockages.
● It improves the reliability and operational efficiency of the entire plant.
● It reduces costly and inconvenient maintenance shutdowns.
As a result, a well-designed screening system will protect the rest of your
water treatment infrastructure.
The Different Levels of Screening

Screening is not a one-size-fits-all process. It is usually performed in stages,
using screens with smaller openings to remove different sizes of solid
material. There are three main screening levels:
● Coarse Screening
This is the very first stage that raw wastewater encounters. Coarse screens
are the heavy-duty protectors of the plant, commonly using a bar screen,
which is a series of parallel steel bars, to stop the largest debris.
● Fine Screening
After the largest items have been removed, the water flows onto the fine
screening stage. These screens use a wire mesh or perforated plates with
much smaller openings (1.5 mm to 6 mm) to grasp smaller suspended solids.
● Micro Screening
This is a more advanced stage reserved for applications requiring very clean
water. These screens use a very fine mesh, almost like a fabric, usually fitted
onto a rotating drum or disc to remove even very small particles.

The Importance of Design and Engineering
The selection and design of a screening system is a very important decision
that depends on several factors. It is crucial to consider the flow rate of the
water, the specific parts of the wastewater (for example, industrial wastewater
may have different types of solids than municipal wastewater), as well as the
requirements of the downstream treatment processes.
From inefficient solids removal to frequent blockages, choosing the wrong
type of screen or sizing it incorrectly can lead to operational problems. Choose
an expert water treatment solutions provider for advanced water treatment
plants.
At Alantech, we understand that every part of a wastewater treatment system
must work effeciently. Screening is the first and one of the most important
steps. Our expert tream design complete, integrated solutions. Our team of
engineers analyses your unique requirements to select and implement the
most appropriate screening technology for a efficient wastewater treatment
plant.
Conclusion
While it may be the simplest step in a complex process, screening in water
treatment is considered one of the most important. From a simple bar screen
to an advanced micro screen, each level plays a main role in the journey
towards clean water.
If you are planning a new wastewater treatment plant or looking to improve an
existing one, contact Alantech.

Frequently Asked Questions (FAQs)
Q1: What is the difference between screening and filtration?
A1: While both separate solids from liquids, the main difference between
screening and filtration is the size of the particles they remove. Screening is
the first stage and is used to remove larger, non-settlable solids. Filtration is a
more advanced process used later in the treatment cycle to remove much
finer, mostly microscopic, particles that screening cannot capture.
Q2: Are the bar screens and fine screens cleaned manually?
A2: The bar screens and fine screens can be cleaned manually, but in most
modern treatment plants, cleaning is automated. Mechanical rakes or cleaning

arms are set to operate on a timer or are triggered by sensors that detect
when the screen is becoming blocked. This automated process removes the
collected debris into a container for proper disposal.
Q3: Does every water treatment plant use all three types of screens?
A3: No. All wastewater treatment plants will use coarse screening, and the
vast majority will also use fine screening. Micro screening is a more
specialised process for better water quality. It is only used in situations where
a very high quality of effluent is required, such as for water reuse, or in
specific industrial applications.
Q4: Why is screening important for industrial wastewater?
A4: Screening is important for industrial wastewater as it can contain a wide
variety of specific solid materials related to the manufacturing process, such
as plastic pellets, textile fibres, or food processing waste. An effective,
custom-designed screening system is essential to remove these specific
solids early.