While some wastewater facilities adjust their phosphorus-control chemical dose based on flow or by setting a fixed dose rate, the ability to adjust quickly for loading changes can reduce chemical costs significantly.

Hach Company now offers the RTC101 phosphorus control system, providing real-time control of chemical dosing that helps maintain consistent phosphorus levels in effluent. The system is designed as a turnkey solution with instruments and technology that work together for accurate control of phosphorus levels to chemical savings.

"What makes the unit so efficient in optimizing phosphorus levels are its pre-programmed algorithms," says Bob Dabkowski, applications development manager. "It is designed to determine the exact loading of phosphorus in a facility's influent water, allowing for automatic dosing to what is needed.

"It's cruise control for chemical phosphorus removal. If you need to meet a phosphorus limit by dosing alum or ferric chloride, the system controls in real time exactly how much you need to dose in order to hit your effluent setpoint.

"In a typical application involving ferric addition, we measure the effluent phosphate leaving the plant and pull in a flow measurement from the SCADA system. Based on how much phosphate they want leaving the plant, our algorithms crunch the math every minute and tell the plant how much ferric chloride to dose.

"So if the effluent setpoint is 0.6 mg/L phosphate, that's what they type into the face of the controller. And it will ramp up and ramp down as the system changes. It's just like if you're going down the highway and set your cruise control for 55 mph."

The RTC101 can be used for open (feed forward) and closed loop (feed back) control of the chemical dose. The chemical feed pump is controlled continuously via a 4-20 mA signal or a dry contact relay.

Both outputs can be used together: if the dose determined by the controller is below the pump minimum flow rate, the system will switch from 4-20 mA control to relay control automatically. If the phosphate or flow input is disrupted, the unit automatically refers back to previously created profiles to ensure that effluent compliance is maintained until the signal is restored. 800/227-4224; www.hach.com.