A low cost automatic control system for conductivity of small scale wastewater treatment

This paper presents a design for a low cost 2-electrodes conductivity control system for small scale wastewater treatment system, such as that from etching process of printed circuit board. It involves the design of a conductivity sensing probe, its associated control circuitry and an actuation mechanism. The conductivity sensor applies a direct current to two electrodes and measures the potential voltage. The control circuitry computes the switching action of the actuation mechanism which acts in response to a specific level of conductivity. This control system determines whether the wastewater from the wastewater treatment system is clean enough to be discharged based on the water conductivity. Experimental result covered by this low cost conductivity control system ranges from 0.08 muS to 0.632 S and shows a switching voltage of 2.23 volts which corresponds to 20 muS, a requirement for treated water from small scale wastewater treatment system for etching process of printed circuit board. The wastewater is recycled when the water conductivity reaches above 20 muS while the wastewater is discharged otherwise.