Treatment of rinsing water from electroless nickel plating with a biologically active moving-bed sand filter

Abstract

The MERESAFIN (MEtal REmoval by SAnd Filter INoculation) process presented here was designed to combine the optimum conditions for more than one of the well-known processes of biological metal immobilisation like biosorption and bioprecipitation in a treatment system for industrial waste water. The approach makes use of a continuously operated moving-bed Astrasand® filter which has been inoculated with a mixed population of selected metal biosorbing, bioprecipitating and biodegrading bacteria. One of four pilot plants has been erected at a metal plating company in Vienna (A) to treat waste water from an electroless nickel plating line. In addition to several mg/L of nickel the rinsing water also contains organic acids and inorganic phosphates, which make conventional treatment difficult. Metal laden biomass is continuously removed from the sand grains in the filter and settled in a lamella separator. The thickened biosludge contained 2% of Ni (at only 2–5 mg/L in the feed water), which could be recycled in a shaft furnace. Regeneration of biofilms on the sand is achieved by dosing a cheap carbon source; all other nutrients are available from that specific waste water. For the removal of 0.8 mg/L of nickel the biofilms consumed 8 mg carbon/L and, in addition to 8 mg/L of dissolved oxygen, 3.4 mg NO 3–N/L as additional electron acceptor. The process was shown to be economically favourable over comparable conventional techniques of metal removal. A further advantage of the biological system is its ability to cleave organo-metal complexes (e.g. nickel lactate in the presented case), to degrade organic molecules like organic acids, surface active substances, etc., often present in industrial waste waters, or to reduce ammonium, nitrite and nitrate. Proposed areas of application comprise the final polishing of industrial and mining water, but also the full treatment of contaminated ground water or drainage water.