WASTE WATER

Discover wastewater management and water analytics with PREI Instrumentation. Treatment transforms water that is no longer suitable for its original use into treated effluent suitable for environmental discharge or an appropriate reuse application, depending on the treatment achieved.

Effective wastewater management involves several stages that remove debris, separate solids, break down organic matter, and improve water quality. The exact process varies according to the plant’s design and treatment requirements.

PRE-TREATMENT PHASE

During pre-treatment, operators use bar screens to remove large debris, including branches, leaves, rubbish, cans, rags, plastic bottles, and nappies.

Grit chambers allow heavier materials, such as stones, sand, and glass, to settle. Where installed, equalisation basins help regulate incoming flows and provide temporary storage to manage variations in wastewater volume, including increased flows during storms.

Some plants also remove fats and grease during this stage. Aeration can help float these materials to the surface for removal, while other facilities address them during primary treatment.

PRIMARY TREATMENT PHASE

Following pre-treatment, wastewater enters primary clarifiers: large settling tanks where suspended solids separate from the water by gravity.

Mechanically driven scrapers collect settled material and direct it towards hoppers connected to sludge treatment equipment. Surface skimmers remove floating grease and oil that remain after pre-treatment.

Collected fats may undergo separate recovery or processing where suitable facilities are available. Removing these materials supports the subsequent stages of wastewater management.

SECONDARY TREATMENT PHASE

Secondary treatment uses microorganisms to break down organic matter in the wastewater. In activated sludge systems, aeration and mixing support this biological process.

Other treatment arrangements use biofilms, where microorganisms grow on surfaces and wastewater passes over them. Depending on the plant, biological treatment may involve filter beds, lagoons, constructed wetlands, reed beds, biological aerated filters, or membrane bioreactors.

These processes reduce organic pollution. Systems designed for nutrient removal can also reduce nitrogen and phosphorus through appropriate treatment stages.

In conventional activated sludge plants, the mixture then enters a secondary clarifier, where biological solids settle. Some settled sludge returns to the biological treatment stage to maintain the microbial population, while excess sludge is removed for further treatment. Membrane bioreactors use membranes to separate solids instead of relying on conventional secondary clarification.

SLUDGE TREATMENT PHASE

Sludge collected during primary and secondary treatment is processed separately from the liquid wastewater stream.

Treatment commonly includes thickening, stabilisation, and dewatering. Where anaerobic digestion is used, microorganisms break down organic material without oxygen, producing biogas containing methane. Facilities equipped for energy recovery can use this gas to help power plant operations.

Dewatering equipment, such as centrifuges, reduces the sludge’s water content and makes it easier to handle. Suitably treated biosolids may be used as a soil conditioner or fertiliser where their quality and applicable requirements permit. Other material requires an appropriate disposal route.

FINAL TREATMENT AND DISINFECTION

Depending on the plant’s design and required effluent quality, further treatment may remove remaining nutrients, suspended solids, and other contaminants.

Disinfection using chlorine, ozone, or ultraviolet light reduces harmful microorganisms before discharge or reuse. Returning treated wastewater to a drinking water supply requires additional treatment and verification appropriate to that purpose.

Water analytics supports wastewater management throughout these stages, helping operators monitor treatment performance and assess final effluent quality.