The Problem

A Metal Treatment company was under increasing pressure from their local water authority due to the quality of effluent being discharged from site. They were also faced with increased costs of sludge removal from site from treatment of various hazardous waste streams.

The Solution

Vale Water undertook an initial survey both of the effluent treatment and the waste neutralisation processes. The first step was to introduce a programme of continual improvement to the various stages of treatment.

The chemistry was amended to introduce a product from the “ValePac” series and combined this with a chelating agent to control the metal removal, principally zinc. An alternative polymer(“Valefloc” series) was then introduced at a new point in the treatment process, with dramatic results in terms of assisting in taking out effluent solids.

The second stage was to upgrade the neutralisation of the HCl stream contaminated with zinc. A recirculation loop was installed combined with a controlled addition of caustic soda to ensure that the required pH of 10.2/10.5 was achieved prior to processing through a filter press. The resultant zinc contaminated sludge going for land fill disposal to a licensed site.

The Result

In terms of final discharge the site now meets its discharge limits on all parameters including heavy metals and is no longer under threat of closure by the regulatory authorities.

The changes to the neutralisation stage means that it no longer presents a Health and Safety issue to the operators.

The Future

The final discharge water is now so clean that this year a further process is under evaluation so that the majority of the effluent water can be recycled.The plan will be to have a plant that can cope with a minimum of 60% recycling initially and then subject to agreement with customers on quality, may be increased in the future to recycling 100%.

It is estimated that this change could save the site in excess of £30K pa with the cost of water being a double charge to site, firstly as intake and then as effluent.