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Thames Water have recently built a demonstrationscale biological n&ent-removal plant at Beckton sewage-treatment works to provide (a) operational experience of nutrient removal, and (b) accurate design and cost infoxmation. The paper (i) outlines the basic principles of biological nutrient removal, (ii) describes the plant layout at Beckton, and (iii) presents results from the first three months of o p t i o n . The plant has removed over 50% of both nitrogen and phosphorus present in the settled sewage but has not been able to meet consistently the most stringent standards proposed by the urban waste water treatment Directive. Periods of good performance are compared with periods of poor performance, and differences in operating conditions are highlighted. From these findings, steps to improve performance are indicated and w i l l be included in the future o p t i o n a l programme.

Ballasted flocculation is an efficient high-rate sedimentation process getting more attention as an advanced P removal technology for levels below 0.1 mg/L. The process is well-known yet only very few studies have investigated the interactions, within the matrix of wastewater, of coagulant, polymer and ballast, especially when it comes to polymer doses and types which are, in the industry, rather based on recommendations than scientific evidence. In this work, the impact of anionic and cationic polymers has been investigated on P removal and floc properties. Anionic polymers showed to be superior to cationic ones when it comes to P removal and doses even as low as 0.01 mg/L yield better results than coagulant alone. There appears to be a "best-case" floc size with which very good P removal (>90%) can be achieved and flocs of sufficient strength can be generated.