Comparison of Sludge Characteristics Obtained From Precipitation Treatment of Plating Wastewater

Electroplating wastewater from the printed circuit board manufacturing process contains organic and inorganic contaminants which are harmful to the environment. Metals of cancan include copper, lead, zinc, cadmium, nickel and chromium. Electroplating wastewater treatment alternatives include precipitation and sludge dewatering, ion exchange, reverse osmosis, and electrowinnirg. Due to economical feasibility and adaptability of the manufacturers, few methods have gained wide acceptance. One of the most common methods used by many manufacturers is precipitation and sludge dewatering. Conventional precipitation processes used for plating wastewater treatment concentrate wastewater contaminants in a sludge cake which, because of its Constituents, must be disposed of as a hazardous waste. Increasing costs of hazardous waste transportation and treatment have increased the cost of plating waste disposal. One way to decrease the disposal cost is to reduce the volume of sludge produced in waste treatment. Sludge volume reduction can be achieved through the use of more efficient chemicals, through improved predisposal sludge dewatering, and through waste minimization programs. Chemicals used in electroplating wastewater treatment have a great impact on sludge characteristics. Precipitate particle size and surface properties affect dewaterability of the sludge. The strength of the reducing agent determines the copper content of the sludge. Thus understanding the relationship between sludge characteristics and treatment chemistry is essential to minimizing sludge production. The amount of sludge produced, its dewaterability, and the copper content in the sludge obtained from wastewater treated with different chemicals and methods are studied and compared in this project to obtain a better understanding of the relationship between sludge characteristics and process chemistry. The wastewater used for this investigation was obtained from a local circuit board manufacturer. This wastewater was produced from the circuit board plating operation. Since the type of reducing agent used in the precipitation process has a major impact on the sludge characteristics, three types of reducing agents were used to treat the wastewater. These reducing agents were ferrous sulfate, sodium borohydride (VenMet solution) and dithiocarbamate (DTC-2000). The main objectives of this investigation were: 1. To compare sludge characteristics for alternative reducing agents. Sludge characteristics included dewaterability, sludge volume and copper content. 2. To compare cost of treatment