Wastewater Treatment Processes

Wastewater treatment encompasses a sequence of physical, chemical and biological steps designed to protect human health and the environment by removing suspended solids, organic load and nutrients from municipal and industrial effluents. Initial screening and grit removal prevent damage to downstream equipment by coarse debris and sand. Primary clarification uses sedimentation to extract settleable solids and floating grease. Secondary treatment most often employs microbial communities—either suspended (activated‐sludge, sequencing‐batch, aerated lagoons) or attached (trickling filters, biofilm reactors)—to biodegrade organic matter and convert nitrogenous compounds through nitrification and denitrification or via anaerobic ammonium oxidation (anammox). Anaerobic digestion of sludge reduces solids volume and generates biogas. Tertiary or advanced stages may include membrane separation (nanofiltration, reverse osmosis), ion exchange, chemical precipitation (struvite formation, metal hydroxide removal), advanced oxidation processes and disinfection. Recent emphasis falls on resource recovery—nutrient capture as fertiliser, energy generation as methane or hydrogen—and on minimising greenhouse‐gas emissions through process intensification and integrated control strategies.

Research from Nature Portfolio

Researchers have enriched a continuous‐flow bioreactor with a nitric oxide‐reducing community that converts NO directly to N₂ with minimal N₂O by‐product. By supplying nanomolar NO as the sole electron acceptor, the study demonstrated stable growth at toxic NO concentrations and identified two dominant, previously unknown taxa as key reducers. The work offers a blueprint for mitigating climate‐active gases in denitrifying systems and for harnessing NO respiration in engineered wastewater reactors.

Another advance couples on‐site electrochemical iron carbonates production with biogas upgrading, linking H₂S, CO₂ and NH₃ capture from biogas streams to sulfide and phosphate removal in raw wastewater and sludge. The electrochemical cell yields FeCO₃, which replaces imported iron salts in full‐scale plants, achieving comparable sulphide abatement while enhancing sludge settling and dewaterability. This integrated approach reduces supply‐chain risk, lowers costs and recovers high‐quality bioenergy in a circular urban water framework.

Foundational genome‐centric metagenomic analysis of anammox granules in a laboratory‐scale reactor has elucidated interspecies metabolic networks underpinning anaerobic ammonium oxidation. By reconstructing 17 draft genomes and mapping metatranscriptomes, the study revealed heterotrophic partners degrading extracellular peptides, recycling nitrate to nitrite and supplying alternative electron donors such as H₂, acetate and formate. These insights inform granular‐sludge design for energy‐efficient nitrogen removal.

Wastewater Treatment Processes publication trend

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

Technical terms

Anaerobic ammonium oxidation (anammox): A microbial process in which ammonium and nitrite are directly converted to dinitrogen gas under anoxic conditions.

Denitrification: Sequential microbial reduction of nitrate to nitrite, nitric oxide, nitrous oxide and ultimately nitrogen gas.

Nitric oxide (NO) reduction: Microbial respiration that uses NO as an electron acceptor, converting it to N₂ with minimal N₂O by-product.

Sulfide precipitation: Chemical removal of dissolved sulfide via reaction with metal ions (commonly iron) to form insoluble metal sulfides.

Struvite precipitation: Recovery of magnesium ammonium phosphate crystals (MgNH₄PO₄·6H₂O) from wastewater for simultaneous ammonium and phosphate removal.

Electrochemical cell: A reactor that uses applied current to drive redox reactions, such as in-situ generation of iron coagulants or oxidants for contaminant removal.

References

1. Overview of Methods and Processes Used in Wastewater Treatment.
2. Enrichment and characterization of a nitric oxide-reducing microbial community in a continuous bioreactor. Nature Microbiology (2023).
3. Integrated urban water management by coupling iron salt production and application with biogas upgrading. Nature Communications (2023).
4. Metabolic network analysis reveals microbial community interactions in anammox granules. Nature Communications (2017).
5. Strategies for ammonia recovery from wastewater: a review. Environmental Chemistry Letters (2024).
6. Net-zero carbon condition in wastewater treatment plants: A systematic review of mitigation strategies and challenges. Renewable and Sustainable Energy Reviews (2023).
7. A critical review of chemical uses in urban sewer systems. Water Research (2023).