Wastewater treatment is the most common method used to recover purified water from wastewater or sewage. that treated water can be returned into the water cycle. Treated effluent creates an acceptable impact on the environment or it can be reused for different purposes.

There are two types of wastewater domestic and industrial. The wastewater is treated at suitable wastewater treatment plants (WWTP). For domestic wastewater (Municipal Wastewater), the treatment plant is known as a Sewage Treatment Plant(STP). Industrial wastewater treatment is in a mechanical wastewater treatment plant or a sewage treatment plant. Wastewater treatment is essential for the sanitation sector. Sanitation includes human waste and solid waste management as well as rainwater (drainage) management.

Wastewater generates from various sources, such as sanitary and domestic wastewater, commercial and institutional wastewater, manufacturing and industrial wastewater, construction wastewater, and stormwater.

Wastewater treatment removes contaminants from wastewater before it is discharged into a water body. Physical processes like sedimentation and filtration, chemical processes like precipitation, and biological processes like aerated lagoons or activated sludge systems are under this category.

Conventional wastewater treatment consists of combining physical, chemical, and biological processes and operations to remove solids, organic matter, and nutrients from wastewater. General terms used to describe different steps of wastewater treatment, in order of increasing treatment level, are preliminary, primary, secondary, tertiary, and advanced wastewater treatment.

Specifically, in the water industry, recover wastewater and turn it into a valuable source while limiting waste production. Water treatment facilities contribute significantly to the circular economy by creating clean water, fertilizers, renewable energy, and other functional bio-based materials. Water treatment facilities offer a unique potential to reduce energy needs, minimize costs, and improve renewable energy production by producing valuable resources from waste streams. These resources include water, energy, nutrients (phosphorus and nitrogen), and biosolids.

1. Biological Wastewater Treatment Systems

Biological wastewater treatment harnesses microorganisms to decompose dissolved and colloidal organic matter. Water Lanka Services provides design, engineering, and turnkey civil construction across Sri Lanka for:

• Anaerobic Treatment Plants: Upflow Anaerobic Sludge Blanket (UASB) and anaerobic digester plants for high-COD industrial wastewater (distilleries, breweries, dairy, food processing) with low sludge volume and biogas recovery.
• Aerobic Treatment Plants: Activated Sludge Process (ASP), Extended Aeration, Moving Bed Biofilm Reactors (MBBR), and Sequencing Batch Reactors (SBR) delivering rapid organic oxidation and CEA compliance.
• Construction of Aeration Tanks: Turnkey reinforced concrete (RCC) civil construction of aeration tanks with fine bubble membrane diffusers, Roots blowers, and jet aerators optimized for maximum oxygen transfer.
• Facultative Ponds & Lagoons: Cost-effective biological treatment ponds for agro-industrial estates, rubber, and palm processing facilities utilizing natural algae-bacteria symbiosis.

2. Chemical Water Treatment & pH Correction

Chemical treatment neutralizes charges, forms settleable flocs, and corrects hazardous pH ranges before biological treatment or discharge:

• Coagulants: Polyaluminium Chloride (PAC), Alum, and Ferric/Ferrous salts for rapid colloidal charge neutralization.
• Flocculants: High-molecular-weight Anionic (APAM) and Cationic (CPAM) polymers bridging particles into heavy flocs.
• pH Adjusters & pH Boosters: Caustic Soda (NaOH), Hydrated Lime, and Soda Ash dosing for raising acidic wastewater pH.
• Automated pH Correction Systems: Online pH sensor-controlled dosing skids maintaining effluent strictly within CEA's 6.0 - 8.5 standard.

3. Physical Water Treatment & Filtration Plants

Physical separation eliminates suspended matter, free oils, and turbidity through mechanical screening, gravity separation, and pressure filtration:

• Screening & Grit Traps: Coarse bar screens and fine rotary drum screens to prevent mechanical pump clogging.
• Oil-Water Separation & Flotation: API separators and Dissolved Air Flotation (DAF) units for grease and oil capture.
• Industrial Pressure Filters: Sand filters, multimedia filters, activated carbon filters, and FRP pressure vessels.