Abstract
A rubber thread factory manufactures about 20 tonnes of thread daily, produces about 600 m³ of waste water. The raw waste water, although is mainly organic in nature, contains a significant amount of zinc ions, that is up to 300 ppm, which can effect a healthy therefore categorized as a hazardous waste. This heavy metal should be be effectively removed prior to biological treatment, because it can inhibits biological activity resulting inhibition of reducing COD value. By regulating addition of NaOH solution to reach pH above 10 can precipitate more than 99,0% of zinc ions, producing 607,2 mg of solid suspension per litre of waste. Because of the PH is to high, it must be neutralized with sulfuric acid, before it is flew to the waste treatment pond. The cost of chemical for wastewater treatment is Rp 4.930 per m³ of waste.
