Treating wastewater from electroplating plants

Treating wastewater. Improving environmental safety through development of low-waste technologies, efficient treatment equipment, resource recovery wastewater treatment are the priority directions of the modern industry.

Natural water resources are becoming a critical problem of today, because of outdated industrial water supply processes, poor state of wastewater treatment plants and old wastewater treatment technologies. They all lead to aggravation of the environmental situation. While towns and settlements suffer from the lack of fresh water, industrial plants dump polluted industrial wastewater into the water bodies. One of the biggest sources of pollution are galvanic electroplating facilities. Their insufficiently treated galvanic wastewater pollutes waterways with thousands of tons of highly toxic heavy metals such as zinc, nickel, chromium, and others annually, considerably complicating the environmental situation.

One of the most dangerous is the wastewater containing toxic hexavalent chromium. Hexavalent chromium damages natural environment, poisons water, further contaminates the ecosystem, disrupting the ecological balance.

In order to protect the biosphere from chromium compounds electroplating wastewater is treated with electrocoagulation method, which simultaneously reduces the hexavalent chromium and sediments it in the form of hydroxides. The electrogenerated sediment sludge has a stable form that does not leak into the environment during prolonged storage or when used as a secondary raw material in construction, metallurgy and roadworks. Still, electrocoagulation method is rarely used because of its technological complexity and high cost.

Considering the abovementioned problem of treatment galvanic plant wastewater and the continuing search for new and more effective approaches, GlobeCore designed the AVS vortex layer devices that are successfully operated in production lines in various industries at the moment.

The intensifying factors in vortex layer devices are:

• electrochemical factors, electromagnetic treatment with activation of substances;
• dispersed phase;
• geometric parameters and hydrodynamic factors that ensure intensive mixing of the processed media.

We conducted the experiment treating wastewater from an electroplating facility removing heavy metals with the AVS-100 (laboratory unit). The reducing agent used in the experiment was ferrous sulfate FeSO4. The reduction of trivalent and hexavalent chromium with the reagent was performed in an alkaline medium, introducing lime milk Ca(OH)2 into the water.

Because a reducing agent in an alkaline medium is iron(II) sulphate, there is no need to increase wastewater acidity. During the experiment, 10 mg of 10% iron sulfate solution was added into the  0.5 liters of wastewater.

The ferromagnetic particles for processing in the operating chamber of AVS were 20 mm long and 1.8 mm in diameter (total weight 200 g) The treatment duration was 3 seconds.

Table 1 shows the results of treating wastewater from an electroplating plant, removing heavy metals with the AVS-100 vortex layer device,  and comparing them with the maximum permissible concentrations according to the European Union standards.

Table 1

The results of removing heavy metals from electroplating wastewater with the AVS-100 vortex layer device.

The research leads to the following conclusions

1) Treating wastewater from electroplating facilities with the AVS-100 vortex layer device reduces the concentration of heavy metals to values ​​not exceeding the maximum permissible concentration for the European Union. A complete absence of nickel and hexavalent chromium in the treated water was achieved. It shows the future perspectives for vortex layer devices in countries with more stringent regulations for concentrations of hexavalent chromium and nickel.

2) The treatment of wastewater is instant and does not overuse the reagents.

3) Sediment settles quicker than when using stirring devices.