Biological activated carbon treatment is applied to a type of wastewater collected from plating industries. The water contains small amounts of refractory organic pollutants, such as anionic surfactants, small amounts of heavy metals, such as cupric and chromic ions, and large amounts of sodium salts. It is found that the thickness of biofilm formed around activated carbon particles increases with time, even though the existence of heavy metals is unfavorable to the growth of microorganisms. As a result, about 50% of organic substances are removed from the water. Present removals for the ionic species of copper and chromium are about 80% and 30%, respectively. Heavy metals are removed from the wastewater by uptake in the bodies of microorganisms, while organic substances are removed by biological decomposition and partly by adsorption.