Abstract
The Nordborg Sludge Reed Bed System was established and planted with reeds in September 2003. The Reed Bed System has a capacity of 350 TDS per year and consists of 10 basins, each having an area of approx. 705 m2 at the filter surface and a maximum area-loading rate of 50 kg DS/m2/year. Sludge production from the WWTP consists of activated sludge (SAS) directly from the activated sludge plant and digested sludge from a mesophil digester. The two sludge types are mixed before being added to the Reed Bed System. 90 – 120 m3 (approx. 0.5 % ds.) of SAS is mix with 3-6 m3 of digested sludge (approx. 2-3 % ds). Finally, the batch is diluted with effluent from the WWTP to a final volume of 140-160 m3. The system’s loading regime consists of applications of approximately 140-160 m3 of sludge (approx. 0.6-08 % ds.) once daily. From 2006, each basin was subjected to a loading quota of 600 m3 over a period of approximately 4 days. Loading was followed by a 36-64 rest period. Because of the increasing sludge production the area-specific loading rate has increased from approximately 17 kg DS/m2/year in 2004 to 44 kg DS/m2/year in 2006.
Keywords
Dewatering, Digested, Drying, Loading, Reed Beds, Surplus Activated Sludge, Treatment.
Wastewater in Nordborg is pumped into the Himmark Wastewater Treatment Plant (MBKND), which is dimensioned to process wastewater from 18,000 PE. The current load is approx. 13,000 PE, incl. an industrial load (Figure 1).
Himmark Wastewater Treatment Plant
The treatment plant mainly treats wastewater from residential areas. The plant is constructed with an aerated sand trap and grease trap (3), a primary tank (4), two active sludge plants in double ring canals (5), 3 clarifying tanks (6). Wastewater treatment uses Ferric Chloride as a precipitating agent for the removal of Phosphorus. The treatment process uses approx. 60,000 kg Ferric Chloride annually for phosphorus removal. The precipitant is added after the primary tank at a rate of c. 2,250 ml/min 6 times per hour.
In addition to wastewater, the Himmark treatment plant receives septic sludge. The wastewater is then led to the surplus activated tanks (5). Surplus activated sludge is pumped to the clarifying tanks (6) and becomes part of the biological process. The sludge has an age of approx. 20 – 22 days.
The sludge from the ring canals gravitates to a distributor and from there to the clarifying tanks. In the distributor, aerobic active sludge is taken from the ring canals for the sludge mineralisation plant. A portion of it is pumped to the stabilisation tank (15), where it is mixed with sludge from the digestion tank
.jpg)
