RHV Steyr—a community environmental association serving the city of Steyr, Austria, and several neighboring villages—enlarged and modernized its sewage treatment facility to cope with the ever increasing requirements of more stringent legislation in the face of rising effluent levels and thus, increasing amounts of sludge. The city has benefitted from its experience in heavy industry and production of various commodities, always seeking the latest innovations and advanced technologies in order to streamline its business solutions. Based on its history, it was not surprising that RHV Steyr was looking for the best possible concept to implement its plans, given the following constraints:
- increase sludge treatment capacity to handle a volume of 140,000 population equivalent;
- controlled energy consumption; and
- controlled operating costs (maintenance, polymer and dumping over a period of eight years).
At the request of RHV Steyr, extensive independent testing was performed on both similar and different equipment, comparing multiple suppliers using the same technology.
Solution
Andritz Separation’s decanters, featuring the TurboJet weir plate solution and CentriTune centrifuge control system to minimize electricity consumption while ensuring the best possible performance in terms of polymer consumption and solids dryness, had convinced RHV Steyr and come out on top in the evaluation. Two parallel sludge processing lines are equipped with Andritz D4L decanters for a capacity of 600 kg dry solids/hr of sewage sludge.
Besides the TurboJet liquid discharge feature for lowest energy consumption, the decanter is equipped with the latest high-performance scroll, ensuring the lowest polymer consumption with high solids dryness at the discharge. The plant furthermore comprises a system to fill the dewatered sludge into truck containers. Operations and control are fully automated, including monitoring of the solids height in the container. If a container is full, the next container is activated automatically for filling.
Results
The D4L decanters were started up in June 2014 and, in the following evaluation period, the performance guarantees were met or surpassed. In fact, the polymer consumption was lower than guaranteed, and cake dryness was surpassed at the same time. The high dryness in the cake ensures the lowest possible annual dumping costs for the sludge. The outstanding performance with more 30% dryness in sewage sludge solids at the discharge is especially pleasing for the management of RHV Steyr.