Chemical Dosing System

A chemical dosing system is a skid-mounted assembly that stores, meters, and injects process chemicals into a wastewater treatment stream at a precisely controlled flow rate. In effluent treatment plants (ETPs) and sewage treatment plants (STPs), four main dosing duties arise: pH correction using sulphuric acid, hydrochloric acid, or caustic soda (NaOH) to neutralise acidic or alkaline effluent before biological treatment; coagulation and flocculation using alum, ferric chloride (FeCl3), or polyaluminium chloride (PAC) to aggregate suspended solids ahead of clarification; disinfection using sodium hypochlorite (NaOCl) to achieve the residual chlorine required for treated effluent discharge; and nutrient dosing using urea and phosphoric acid to supplement nitrogen and phosphorus for biological treatment stages. Each of these duties is central to achieving the effluent quality required for CPCB/SPCB consent. For a complete overview of ETP process design, see our effluent treatment plant page at /effluent-treatment-plant-etp/.

A chemical dosing system comprises a day tank fabricated in HDPE, FRP, or SS316L depending on chemical compatibility, an agitator where slurry or powder dissolution is required, a high/low level switch for inventory management and spill prevention, a metering or dosing pump (peristaltic type for aggressive and viscous chemicals, electromagnetic diaphragm type for clean chemical service), a discharge check valve to prevent back-siphoning, a graduated calibration column on the suction side for field verification of delivery rate, and an inline static mixer at the injection point to achieve rapid, uniform chemical dispersion in the process stream. All components are mounted and pre-wired on a common GRP or painted MS skid frame, allowing the complete system to be lifted into position, connected to supply and process pipework, and commissioned with minimal site assembly time.

Chemical dosing systems are required at every ETP and STP where influent pH, coagulation, or disinfection control is part of the treatment process — in practice, this means virtually all industrial and municipal treatment plants. Major user industries include food and beverage (pH correction and coagulant dosing), pharmaceutical ETP (neutralisation of API and antibiotic effluent, see /etp-for-pharma/), textile (acid dosing for pH correction of high-alkalinity dye effluent), chemical manufacturing, and municipal sewage treatment plants (disinfection dosing, see /sewage-treatment-plant-stp/). Spans Envirotech supplies dosing systems as standalone equipment for retrofit into existing ETPs, or as integrated skid packages within new ETP/STP projects across India.