An international quarrying company was at serious risk of breaching its consent to discharge at a particular site, thereby compromising its ISO14001 Environmental Quality Assurance accreditation. Despite having substantial recent, purpose-built, settlement capacity for dirty water, winter operating conditions were causing problems with suspended solids, specifically with non-settling fines.
SNF, already supporting other sites in this company on dirty water and sludge matters, was invited to investigate the problem and to come up with a solution.
Site testwork was carried out. One-step treatment did not adequately deal with the non-settling fines. A suitable two-step treatment process, ensuring proper flocculation and settlement of the fines, was identified. Flow to treat was 20 litres/second.
SNF rapidly arranged supply of IBCs of both the pre-treatment coagulant, and of pre-prepared solutions of the necessary flocculant. Likewise, SNF organised hire supply to the site of the high-capacity dosing pumps required for each chemical.
Full-scale treatment of the quarry’s discharge was quickly implemented, and discharge quality was speedily brought back to be comfortably within consent.
The coagulant first used was known to have only a minimal impact on discharge pH, and so was used for safety in the first instance. Once discharge was reliably back within consent, an alternative coagulant could be tried. This alternative coagulant was cheaper, but was known to give a greater pH reduction than the first coagulant. Bench-top testwork, followed by full-scale trial, showed that this more economical coagulant could safely be used, while still keeping within pH consent. The alternative, more economical, coagulant was consequently used thereafter, allowing the site a useful economy in treatment costs.
The treatment regime, identified and supported throughout by SNF, kept the quarry well within consent. Lower rainfall in summer meant treatment could be suspended. Treatment was resumed at the beginning of following winter.