UV treatment plant: A winner on aggregate

CEMEX is one of the world’s leading cement producers and suppliers of building materials. Headquartered in Mexico it manufactures a range of building materials including cement, ready-mix concrete and aggregates. CEMEX UK provides a wide range of aggregates from decorative to high-PSV to limestone, rock armour and sand and gravel. Production uses considerable quantities of water and CEMEX UK plans carefully to ensure a balance between the need for raw materials and protecting the environment, including maximising the use of recycled materials. 

As part of the company’s sustainability policy, it looked at the water being used at its Kensworth Quarry in Bedfordshire. Although sometimes hard to believe, this area is classified as semi-arid, so CEMEX decided to find a source of water that would have the least environmental impact and, after discussions with Anglian Water, agreed to use final effluent from the nearby Houghton Regis wastewater treatment works. Whilst the final effluent meets the Environment Agency’s discharge consent, CEMEX had some concerns about microbiological contaminants. There was the concern that personnel could be exposed to pathogens such as coliforms and anti-biotic resistant bacteria; additionally, there were concerns about the possibility of microbiologically induced corrosion by sulphate reducing bacteria (SRBs), nitrate reducing bacteria (NRBs) and similar organisms.

atg UV carried out a pilot plant trial on the final effluent and demonstrated a better than 3 log (99.9%) reduction in all the target organisms as the table shows:

Pilot trial results

On the basis of these results, CEMEX UK asked atg UV to supply and install a UV treatment plant to disinfect 125m3/h of final effluent. This was achieved using a UV reactor fitted with eight 800W high output and low pressure amalgam UVLW lamps. The UV system, with its control panel, was constructed as a DFMA (Design For Manufacture and Assembly) project with all plant items installed in a standard ISO container. This allowed off-site testing and commissioning; all that was required on site was connection to the supply pump from the final effluent lagoon and an outlet connection to the distribution pipe.

The efficacy of UV disinfection is dependent on the dose (mJ/cm2) required to achieve a log reduction of the target microorganism e.g. 4 log reduction of SRBs (99.99% kill). In order to ensure disinfection performance, the atg UV solution for CEMEX UK used an independently 3rd party validated UV system, that was biometrically tested using the US NWRI (National Water Research Institute) Ultraviolet Disinfection Guidelines for Drinking Water and Water Reuse test protocols. 

NWRI validated systems are independently tested using live surrogate microorganisms and take into account critical design criteria such as reactor design, hydraulics, UVT and UV dose distribution. By providing an NWRI approved system, atg UV could guarantee the performance regarding the required bacterial log reduction for the CEMEX UK installation.      

Typically the lamp units and control panels will be shipped to site for installation by the main contractor’s mechanical and electrical installation subcontractors. With DFMA, manufacturing is carried out in controlled, clean and safe conditions away from the construction site. This means that there are no clashes with other subcontractors, no delays due to inclement weather or late deliveries, a significantly lower safety risk because of reduced craneage and testing prior to delivery. There are environmental benefits from DFMA, too: site traffic is reduced, which means lower carbon emissions and less noise. All in all, the future for DMFA in UV systems looks very bright indeed.