The awards aim to recognise and promote organisations who make an outstanding contribution to safety, the environment, sustainable development and other aspects of the process industries. 

Croda Chemicals manufacture speciality chemicals for the cosmetics industry.  They currently generate up to 1,000 m3/d of wastewater that is treated on site prior to discharge to watercourse.  The Company have recently been subjected to a tightening of their existing Environment Agency discharge consent. Also, as part of their IPPC application, they have a requirement to achieve water re-use wherever possible.  Consequently a tertiary treatment system was considered necessary to remove suspended solids (TSS) from the final effluent and thereby achieve improvement in effluent quality.

Aqua Enviro have had long-term involvement in optimising the performance of the Croda effluent treatment plant and were approached to undertake an assessment of the most appropriate tertiary treatment options.  The selected technology was required to:

• Achieve an effluent TSS concentration of <100 ppm and thus act as a pre-treatment stage prior to the implementation of membrane ultra filtration (UF).  This is intended to make water re-use economically feasible.
• Have a small footprint.
• Be able to cope with large variations in suspended solids loads
• Be a sustainable and robust solution and in particular not require the use of any chemicals 

Depth filtration appeared to be the most feasible treatment option but historically due to its susceptibility to blinding, its use has been restricted to wastewater with a low TSS concentration.  However, recent research has indicated that recycled glass media can perform well at a higher solids loading and that it has less propensity to blind compared to a traditional sand media.  As the concentration of final effluent solids from Croda is highly variable, Aqua Enviro proposed a novel two-stage process utilising two grades of crushed, recycled glass as media.  In view of the novel aspects of this proposal, pilot-trials were essential to prove the concept.  Funding was obtained from the Wastes and Resources Action Program (WRAP) to carry out both small and large scale pilot trials to determine the optimum filter configuration and provide the necessary data to design a full-scale system.

The pilot trials demonstrated that the optimum combination for solids removal was a two-stage filtration system using a medium grade recycled glass with a particle size of 0.5 to 1 mm in the first vessel and finer grade of recycled glass (0.2 to 1 mm) in the second vessel (appendix 1).  The trial showed that system removed the majority of the solids in the first filter whereas the second filter providing the polishing necessary to remove finer solid particles.  Solids loading rates were around 30% higher than comparable sand filters. 

In view of the success of the pilot-trials Croda Chemicals built and commissioned a full-scale plant in 2006, which has confirmed the preliminary results and is performing well with an average solids removal of 70% and at higher solids loadings 81% solids removal has been observed.  Successful implementation has meant that Croda Chemicals can now plan for the installation of a membrane system for water re-use.

The end-result is a treatment process that does not require chemical addition, has a small footprint and employs a high value, recycled product compared to the traditional sand media, which requires quarrying or dredging.  It has been estimated that the use of recycled glass will save 1.5 kg CO₂ for every m³ of wastewater treated.