Filtration

Filtration is a useful way to separate solids from liquids or gases. It works by passing the mixture through a special material, called a filter, that lets the liquid or gas go through but keeps the solid particles back. The solid that stays on the filter is called the "oversize," and the liquid or gas that passes through is called the "filtrate."

This process is used in many everyday situations. For example, when you drain cooking water from pasta using a colander, you are filtering. Oil filtration is another important use, where impurities are removed from oil to keep machines running smoothly and for a longer time.

Filtration also happens in nature and in living things. Some animals, like the basking shark and baleen whales, are filter feeders, which means they eat by filtering small food particles from the water. Even tiny organisms, such as Vorticella, use filtration to get their food. Filters can also clean water, like in slow sand filters and trickling filters, which remove unwanted things from the water.

Physical processes

Filtration is a way to separate solid particles from fluids like liquids or gases by passing the mixture through a filter. The fluid goes through, but the solid particles, called oversize, stay behind. This process is used in many places, such as chemical engineering, where it helps separate different materials.

There are many methods of filtration, each suited for different purposes. For example, in labs, hot filtration keeps solutions warm to prevent crystals from forming, while cold filtration cools the solution quickly to make small crystals. Vacuum filtration uses suction to speed up the process, and gravity filtration lets the liquid flow down naturally. Filters can be made from different materials, like mesh or depth filters, which trap particles in various ways. Sometimes, special substances are added to help the filtration process work better.

Biological filtration

Biological filtration can happen inside living things or on materials that are being filtered. It helps remove solids, tiny drops, organic chemicals, and ions by processes like eating, sticking, or absorbing them. Because living things interact in complex ways, it is hard to know exactly how the filtration happens. At a tiny level, it might be due to enzymes inside individual organisms. The waste from some organisms can be broken down by others to create simple substances like water, carbon dioxide, and nitrogen.

In animals like mammals, reptiles, and birds, the kidneys help remove unwanted substances like urea through a process called renal filtration. This is part of excretion through urination. Even simple organisms like protozoa have ways to remove waste, such as using a contractile vacuole. Biofilms are communities of tiny living things that form slimy layers on surfaces, helping to clean water in places like rivers and in water treatment systems. Filter feeders, such as some protozoa, rotifers, and arthropods, get their food by filtering particles from water using special body parts like cilia or webs.

Main article: Renal physiology § Filtration

Main article: Biofilm

Main article: Filter feeders

Examples

Filtration is used in many everyday processes to separate solids from liquids or gases. For example, a coffee filter separates coffee grounds from the liquid coffee. HEPA filters in air conditioning remove tiny particles from the air to keep it clean.

Other examples include belt filters used in mining to extract valuable materials, air filters in cars and buildings to clean the air, and aquarium filters to keep water clean for fish. In laboratories, a Büchner funnel with filter paper is often used to separate solids from liquids during experiments.