Bardon Aggregates keep it clean at Croft

Bardon Aggregates have stepped up their commitment to ensuring that water discharged from the treatment works at their Croft site in Leicester more than complies with Environmental Agency consent levels.

The challenge faced by the company is to ensure that the water used in washing the aggregate is treated effectively on site before discharge into the nearby river Soar. Historically, Croft Quarry has always ensured that it has fulfilled its environmental responsibilities with regard to water treatment by operating a flocculant dosing plant in conjunction with a settlement lagoon. Towards the end of 2003, however, Bardon invested in a Partech Turbi-Tech sensor and 7200 monitor to constantly monitor suspended solids and turbidity.

The company operate to a very tight solids discharge level of 30mg/litre, imposed by the Environment Agency, making continuous on-line monitoring the only way of guaranteeing that it does not break consent levels. Before the introduction of the Partech equipment, Bardon Aggregates did take regular samples for analysis, as did the Environment Agency. However, this did not provide a real-time picture. It also meant that control over flocculant dosing was inefficient.

The water-treatment plant has a typical waste water inflow of 50 litres/s and the flocculant dosing pump unit is set in accordance with this. Problems can arise when the flow increases, making it necessary to increase the speed of the dosing pump. Without access to real-time sampling results, changes to the dosing level may not be wholly accurate leading to over dosing or discharge levels being broken.

Using the Partech Turbi-Tech 2000LS and 7200 monitor, Bardon Aggregates have a constant indicator of the levels of suspended solids within the treatment lagoon. The self-cleaning Turbi-Tech instrument, which uses infrared 90° light scatter as its measuring principle, is suspended in the lagoon and connected to the 7200 monitor located adjacent to the sampling point. The 7200 monitor is designed for external locations and features a large character display that shows the measured value combined with a scrolling information bar showing output status.

The complete system is linked to the main control room at Croft Quarry, from where management have a constant overview of what is happening within the treatment plant with regard to the effectiveness of the flocculation process. The menu structure features set-up wizards that allow simple system configuration and routine calibration.

Partech Instruments, Charlestown, St Austell, Cornwall PL25 3NN; tel: (01726) 879800.