Water law acceptance and inauguration of the expansion of the wastewater treatment plant Hohenwestedt on 20th October 2015.

About 12 years the WWTP Hohenwestedt was rebuilt completely as a two-line activation plant in impoundage operation with a connection size of 8.800 population equivalents. After less than 10 years the treatment plant reached its capacity limits, due to strong growth of waste water production companies that have settled in Hohenwestedt.

In addition, the disposal problem of sewage sludge amount rose. Due to amendment of the sewage sludge and fertilizer regulation the plant can dispose the sludge quantities agriculturally yearly and cache it. This has led to significant costs because the existing sludge storage at the WWTP is not able to assure the required storage.

During the planning and tracking of options it was decided to supplement the WWTP by a mechanical sludge dewatering and caching the sludge in a roofed mud warehouse. For mechanical dewatering a technique should be chosen that matches the dimensions of the treatment plant, as well as bringing sustainable energy efficiency benefits. As suitable variant the principle of a screw press has prevailed since a simple handling of the machine without large personnel expenses and a low impulsion power is ensured with optimal dewatering. The sludge is dewatered to almost 25% and cached in the adjacent sludge storage building until it can be disposed by a contractor onto the neighboring agricultural land in autumn. The sludge in Hohenwestedt is constantly analyzed for its qualities and is currently well below the heavy metal limits therefore still can be used safely as fertilizer on agricultural land.

By the construction of a sludge treatment plant population equivalents at the WWTP have emerged, which have been used in the course of planning. One of the two existing sludge storage has been functionalized as a third activation stage, thereby building costs could be saved. The existing sludge storage has only been technically upgraded and the existing controller (PLC) system was adjusted to operate three-line. The existing activated sludge reactors were fitted with a new energy-efficient ventilation device, which has brought significant power savings. Aeration energy could be reduced to approx. 35%.

All in all, the reconstruction of the wastewater treatment plant only has brought benefits. Even savings were achieved within the total costs which ensures that waste water fees for the citizens will remain stable in long term.