Plant description

The municipal WWTP at Hove serves a community of 28,000 population equivalents (PE). Primary treatment consists of fine screens, an aerated sand-trap and rectangular primary clarifiers (Figure 1). Secondary treatment is achieved by a conventional single-stage activated sludge system. Phosphorus is removed by simultaneous chemical precipitation. The excess sludge is aerobically digested, thickened by gravitation and mechanically dewatered; the sludge is then transported to a nearby facility for further treatment.

Figure 1. Layout of the WWTP Hove

Legend: 1. screw pump pit 2. main building 2.1. blower basement 3. fine screen 4. sandtrap 4.1. santdrap basement 5. sand silos 6. Prime sedimentation tank (PST) and stormwater 7. aeration 8. secondary sedimentation tanks 9. effluent 10. recirculation building 11. recirculation channel 12. sludge oxidation tanks (SOT) 12.1 SOT and PST basement 13. Thickener 14. FeCl3 tank 15. Sludge building 16. container lime milk 20. conveyor belts 21. gates

Table 1. Influent loading and effluent quality during 1996-2000: 280 measurements
* 95th percentile; ** Annual Mean

Goal

An alternative design approach explicitly incorporating uncertainty is herein proposed. The procedure is examined in an upgrade of a conventional WWTP towards stricter effluent standards on nutrients. The results suggest that the procedure can support the decision-making process under uncertainty conditions and that it can enhance the likelihood of meeting effluent standards without entailing above-normal capital investments.

Results

At WWTP Hove, this approach helped to reduce the dimensioning of the biological reactors by 21%. The analysis led to reducing the capital investment by 43%, producing savings of more than 1.2 million euro.