Water Treatment Processes

Water treatment comprises a series of physical, chemical and biological operations designed to remove suspended solids, organic and inorganic contaminants, pathogens and micro-pollutants from surface water, groundwater and waste-streams. Conventional schemes begin with pretreatment to remove coarse debris and grit, followed by primary settlement to eliminate larger particles. Chemical coagulation and flocculation then destabilise colloidal matter, permitting its removal by sedimentation or filtration. Secondary treatment relies on aerobic or anaerobic bioprocesses—activated sludge, trickling filters, membrane bioreactors—to oxidise biodegradable organics and reduce nutrient loads. Tertiary polishing employs adsorption, membrane separations, ion exchange and disinfection to meet stringent standards for potable use or ecological discharge. Rapid advances in membrane science, advanced oxidation (UV, ozone, Fenton‐type reagents) and supercritical oxidation extend the reach of treatment to trace organics, pharmaceuticals, micro-plastics and recalcitrant industrial compounds. Across all scales—from decentralised point-of-use units to large desalination plants—energy efficiency, process intensification and life-cycle impacts guide the selection and integration of treatment steps to safeguard health, promote water reuse and protect aquatic ecosystems.

Research from Nature Portfolio

A new portable filtration unit constructed from inert polymer fibres and a biodegradable pore-forming agent has been demonstrated to remove ultrafine particles—including micro- and nanoplastics, bacterial cells and protozoan cysts—using a low-head pump or gravity feed. This “green” filter requires no chemical consumables, produces minimal waste and operates with energy consumption below 0.5 kWh m⁻³ while achieving ≥99 % removal of 0.1–1 µm contaminants under varied water chemistries.

Zeolite-cotton cloth, fabricated by in situ growth of a chabazite framework on cotton fibres, serves as a simple household component for heavy-metal removal. A small column packed with 10 g of this material reduced 1 000 ppm Cu²⁺, Cd²⁺ and Pb²⁺ solutions to below 5 ppb in a single pass and remained effective over 8 000 bed volumes without secondary discharges of silver from Ag-exchanged filters.

Biobased hydrogel composites combining carboxymethyl cellulose with graphene oxide sheets have been synthesised by one-step crosslinking. The resulting aerogel combines a mesoporous network (surface area ≈800 m² g⁻¹) with abundant oxygen functional groups and achieves >90 % removal of cationic dyes in under 30 minutes at neutral pH. Over ten adsorption–desorption cycles, >85 % of initial capacity is retained, demonstrating robust reusability.

Water Treatment Processes publication trend

The graph below shows the total number of articles in water treatment processes across all publications each year (not limited to Nature Index journals).

Technical terms

Coagulation: Addition of metal-salt coagulants to neutralise colloidal charges and form insoluble flocs for removal by sedimentation.

Flocculation: Gentle mixing to aggregate destabilised colloids into larger flocs that settle or filter readily.

Adsorption: Accumulation of dissolved species on the surface of a solid sorbent via chemical or physical interactions.

Membrane filtration: Separation by forcing water through a porous or dense polymeric barrier under pressure or concentration gradients.

Advanced oxidation: Generation of reactive radicals (e.g. •OH) by UV, ozone or Fenton chemistry to degrade recalcitrant organics.

Biofilm reactor: An enclosed system in which microorganisms attached to support media digest dissolved organic matter.

Life-cycle assessment (LCA): A systematic evaluation of environmental impacts associated with all stages of a product or process.

References

1. Filtration made green and easy. Nature Sustainability (2024).
2. Zeolite Cotton in Tube: A Simple Robust Household Water Treatment Filter for Heavy Metal Removal. Scientific Reports (2020).
3. Development of carboxymethyl cellulose-graphene oxide biobased composite for the removal of methylene blue cationic dye model contaminate from wastewater. Scientific Reports (2023).
4. Integrated Solution for As(III) Contamination in Water Based on Crystalline Porous Organic Salts. Advanced Science (2024).
5. Assessment of environmental sustainability of drinking water treatments for arsenic removal. Resources Conservation and Recycling (2024).
6. Coagulation of trace arsenic and cadmium from drinking water using titanium potassium oxalate. npj Clean Water (2023).