To achieve this, it is necessary to build a primary clarification stage. With its reduced space requirements and economic efficiency, the HUBER Drum Screen LIQUID represents the better alternative to a conventional primary clarifier.
The HUBER Drum Screen LIQUID is applied for fine screening the wastewater and designed for a partial flow treatment of 100 l/s. As the total flow to the sewage treatment plant is 256 l/s under stormwater conditions, 156 l/s are discharged in this case. Due to the very high COD removal rate of the HUBER Drum Screen LIQUID, the biological sewage treatment stage on site (see fig. 1) can soon be shut down. This will save considerable amounts of aeration energy. Moreover, the primary sludge generated from fine screening with the HUBER screen will be converted into energy-rich biogas in the digester and this biogas converted into electrical energy in a block heat and power plant.
The principle of the treatment process on STP Staßfurt
The HUBER Drum Screen LIQUID is installed downstream of the grit trap instead of a primary settling tank and integrated into the existing system. The maximum flow to the screen is controlled by a flow meter and control valve. Special focus has been placed on the fact that the HUBER screen is a gravity flow system. HUBER Drum Screen LIQUID screens are installed horizontally in the channel. The water flows through the screen from inside to outside. The maximum filter surface can be utilised due to the horizontal position of the screen drum and at the same time a very high maximum possible upstream level. As the water level upstream of the machine increases, a filter carpet is developing on the filter mesh. Due to the filter carpet leading to a deep bed filtration effect, all particles are retained that are much smaller than the nominal aperture size of the mesh. When the water level upstream of the drum screen reaches the maximum permissible water level, the screen basket is cleaned. The fine screenings (primary sludge) are removed from the screen surface and accumulate in the internal trough from where they are conveyed by gravity to the downstream continuous thickener. The statically thickened sludge from the continuous thickener is pumped into the digester or optionally further thickened in a HUBER Disc Thickener S-Disc unit. Also the surplus sludge generated is thickened in the HUBER Disc Thickener S-Disc prior to being pumped into the digester.
Situated on the river Prim at the foot of the Dreifaltigkeitsberg hills, Spaichingen is the third largest market town in the district of Tuttlingen. The river Prim is a tributary of the upper reaches of the river Neckar in Baden-Württemberg and flows along the steep escarpment of the Albtrauf hills. The mountains Dreifaltigkeitsberg and Heuberg belong to the Danube Hills Nature Park.
Designed or a capacity of 17,000 PE, the sewage treatment works Spaichingen clarifies the municipal and industrial wastewater of the municipalities Spaichingen and Balgheim. The sewage treatment plant is already operated as an anaerobic sludge stabilisation process with digestion. The maximum stormwater flow that can be handled by the plant is 175 l/s. After completion of this stage of extension it will have a capacity for 225 l/s. The sewage treatment plant is equipped with an Imhoff tank that is used as a primary clarifier. The Imhoff tank has reached its design capacity limit, this means that it fulfills its task under dry weather conditions and will do so in the future, but will be overloaded under stormwater conditions. Due to the planned plant extension by another 50 l/s a solution had to be found to improve the situation. Various options were discussed.
The first approach under discussion was to integrate a two-line primary clarifier and shut down the Imhoff tank. There would have been enough space on site for this solution but they actually did not want to give up the Imhoff tank that still worked well with dry weather conditions and were therefore looking for an alternative.