It’ll produce waste water contains heavy metal ion, such as Fe3+、Hg2+、 Cd2+ 、Cu2+ 、Pb2+ 、Fe2+ 、Mn2+ 、Ni2+、Zn2+ 、Cr3+ 、Cr6+ , in industry of Electroplating, electronic, chemical , colored ion and steel industry, and photo laboratory, film factory, garbage incinerator， leather manufacturing, storage battery factory etc. this kind of waste water is not allowed to dispatch directly. According to different kinds of heavy metal ion and different containment of wastewater in different industry, the waste water is allowed to dispatch directly only if the residue volume of heavy metal ion meet national criterion (less than 0.01-0.5mg/L)
When we use the regular way of chemical dosing treatment to treat the waste water contains heavy metal ion, we can only get good treatment result only the heavy metal ion coagulant is very expensive, if the dosing chemical volume is not enough,we can not achieve expect result. Overdose will cause big waste of financial resourses, and it will cause effect to other water treatment equipment, even it will cause secondary pollution to water. So it is demanded that the water treatment chemicals should be optimum dosed and auto-controlled, make sure accurately test proper dosing volume and finish time of reaction.
During the treatment process of water water contains heavy metal ion, in order to judge accurately and reliably the proper dosing volume and finished time of reaction, the measurement ORP difference is must needed. Because of different pretreat water and different technology dispersivity of ORP electrode, and factors of temperature, pressure etc always make the ORP value moving in a display range, not a good steady ORP value.
Common ORP adjustment controller can not judge the ORP value in advance before the reaction of dosing, it can only control the dosing reaction mechnically and measure the ORP value. In this case, it may cause unqualified water quality or big waste of chemicals after the treatment, and actually it can not achieve automatic control water treatment.
However, there is a fact in treatment of wastewater contains heavy metal ion: although the ORP value is moving in a display range at the beginning of reaction, for same type of wastewater, the ORP measure value difference is fixed and can be measured before the dosing treatment and after the reaction of heavy metal.