Chitosan Enhanced Sand Filtration (CESF) is a flow-through chemical water treatment technology that combines the use of polymers/flocculants (chitosan) with pressurized sand filtration capable of producing a continuous effluent turbidity of less than 5 ntu’s. Also known as Active Treatment System (ATS).
The process relies on a unique biopolymer called chitosan, a derivative of chitin. Chitosan is made from recycled crustacean shells. When added to storm water at dose rates of up to 1 part per million, chitosan agglomerates submicron suspended sediment and acts as a filter aid when the treated storm water is processed through a sand filtration unit.
The ATS process utilizes pumps, tanks, chitosan, a sand media filter and a computerized monitoring and data collection system to continuously reduce turbidity in construction storm water. Storm water is first pumped from its retention pond to the control system, where an initial dose of chitosan is added as a pretreatment measure. The storm water is then routed to settling ponds for bulk solids removal. From the ponds, pretreated storm water is pumped through the control system, where turbidity, pH and flow are measured. As the water passes through the control system, another dose of chitosan is added prior to sand filtration.
The effluent from the sand filter is routed to the control unit, where turbidity, pH and flow are measured again to ensure compliance with National Pollutant Discharge Elimination System (NPDES) permit requirements and water quality discharge standards. In the unlikely event that the effluent does not meet requirements, the control system automatically recirculates the water to the point of origin to be treated again.
The ATS system has a unique programmable logic controller (PLC) which is utilized to monitor influent and effluent water quality parameters. The PLC also monitors external factors such as pond level and rainfall data. System pumps, the chemical metering system and sand filtration unit are all controlled using a touch screen on the PLC. The control system is equipped with remote telemetry capable of transmitting operational data to a secure website or initiating operational alarm text messages to system technicians.