Walvis Bay Trickling Filter – Efficiency increase by changing stone filling to structured media

Background

The wastewater treatment plant in Walvis Bay, Namibia was supposed to be modified. It had three existing trickling filters filled with stone media but typical problems occurred such as ponding and clogging. Furthermore the customer was not satisfied with the performance of the plant. The decision was made to upgrade two of the three filters by replacing the fills. The third filter was decommissioned.

Design

The two filters were enhanced using cross flow structured fill media from ENEXIO. Additionally, new generation trickling filters with polypropylene cross flow media allow higher filter beds for increased performance per footprint. In Walvis Bay, one filter wall was raised to the maximum possible in accordance to the existing distributor capacity.

Conclusion

Filter One is loaded with 5500m³ per day. The incoming COD of 950mg/l is reduced to 240mmg/l, ammonia from 51mg/l to 4 mg/l. This equals a nitrification of more than 90%. The energy consumption to pump the water up to the distributor is 624kWh per day leading to 0,16kWh/kg-COD or 0,11kWh/m3 treated water (including nitrification, excluding pre and post treatment). This is a major cost advantage compared to activated sludge.

Both filters started operation in the end of 2012 and the costumer is highly satisfied with the treatment results.