On-line environmental monitoring of electroplating chemicals

On-line environmental monitoring of electroplating chemicals

Pitney Bowes in Stamford,Connecticut, recycles the discharge streams from an electroplating process to a modern wastewater treatment plant which uses dual microfiltration units and an activated carbon system to meet the 1 ppm heavy metal discharge limits set by the state environmental regulatory body.

Pretreatment effluent contains copper and nickel, which need to be monitored constantly to document discharge compliance. This monitoring also allows corrective action to be taken if the treatment plant is not operating correctly.

The wastewater treatment plant handles 100gpm, with two microfiltration modules working in parallel to process discharges during periods of heavy flow loading. The process runs over a two or three-shift schedule up to six days a week.

As enforcement action could be initiated if discharged levels are exceeded, Pitney Bowes needs to monitor closely the copper and nickel levels in the finally discharged effluent continuously, often around-the-clock.

Any on-line monitoring needs to be very reliable. Government regulatory personnel can enter the plant at any time to review the analyzer's performance against their own grab samples.

Pitney Bowes consulted water instrumentation manufacturers Ionics, whose analyzers are developed for on-line situations that require high reliability.

Ionics provided their Digichem 3000 on-line wet chemical analyzer, specially tailored to the Pitney Bowes' requirements, to monitor the two parallel permeate streams. It would be required to operate unattended for up to 24 hours per day, six days per week.

The Digichem can be programmed to perform a number of classical wet chemical analyses including titrimetric, colourimetric and ion selective procedures. At Pitney Bowes, the Digichem uses the bathocuproine method for copper, the dimethylglyoxime analysis for nickel. The instrument performs volumetric dispensing of sample and reagents, similar to an analyst in the laboratory, followed by colourimetric measurements. It can house up to six dispensing modules.

The analyzer reportedly achieves a sensitivity of 0.02ppm for both copper and nickel in the 0 to 1 ppm range.

Digichem can be field programmed via simple keyboard commands if changes to the analysis are needed. Data for each of the two streams is output to a printer and a PLC to provide a real-time record and to alert the process operators in the event of a high load.

If the analysis produces readings above the 1 ppm set point, then alarms are actuated and the discharge diverted to a 7,500 gallon holding tank until the problem is located and resolved. Once resolved, the diverted discharge from the holding tank is reprocessed through the pre-treatment system and then the treatment plant.

Pitney Bowes comment that the analyzer's on-line feedback control has proven invaluable to the running of the plating water discharge system. Any analyzer downtime would affect the plating shop operation. Pitney Bowes have therefore established a set of actions for regular maintenance of the instrument, from weekly tube replacement to monthly cleaning of the reaction chamber burettes and overflow cups. This has paid good dividends. Only twice have they required manufacturer support to diagnose/repair a malfunction. There have been only four days of non-operation since installation.

Further details are available from Ionics Ltd, 3 Mercury Way, Mercury Park Estate, Trafford Park,Manchester M41. Tel: 0161 866 9337.