Sludge is a bi-product from treatment of wastewater at any traditional wastewater treatment plant, and while treated water can be discharged to the receiving waters according to the requirements in the discharge permit, handling sludge treatment is more complicated. Generally, final disposal will be utilisation as fertiliser on farmland, deposition at waste disposal sites, or incineration onsite or at an external partner, often as part of energy generation.
Sludge pumping requires equipment that can keep viscous media moving – without becoming clogged. Primary sludge needs to be pumped from the primary clarifiers to the sludge treatment, and the sludge pumping station requires careful selection of the pumps, depending on the sludge content and flow.
Centrifugal pumps like the Grundfos ranges of SE/SL or S pumps with vortex impellers are often used and are designed for durable use in difficult environments. For sludge pumping, dry installed pumps are preferred as this allows frequent inspection and easy maintenance.
Control and monitoring systems increase the potential for improving both efficiency and reliability. Grundfos supplies external variable speed drives (Grundfos CUE), motor protection (MP204) to monitor motor conditions, ensuring optimal operation.
The main purpose of sludge thickening/dewatering is to minimise the volume of the sludge, thereby reducing the required size and capacity of subsequent treatment processes and equipment. Furthermore, a decrease in water content reduces energy consumption for heating the sludge in the digester. The efficiency of the dewatering depends on the type of equipment and sludge quality.
Grundfos can supply PLC-controlled, fully automatic systems to handle preparation and the reliable dosing of organic coagulants or poly-electrolytes. Grundfos has the specialist knowledge to do this and can tailor a dosing station utilising chemicals as concentrates, ready-to-use solutions or dry chemicals, according to your requirements.
Sludge can be dewatered directly from a concentration tank or sludge storage tank. Usually, sludge is thickened by gravitation in a sludge concentration tank or by mechanical dewatering in simple dewatering units, and quite simply involves removal of water from the sludge. Poly-electrolytes can be added to enhance formation of large sludge-flocs.
Removing the water is handled with the Grundfos ranges of SE/SL and S pumps, which are specifically designed for durable use and flow management, and can be installed dry or submerged.
The tanks can be equipped with a low-speed AMG mixer in order to secure a homogeneous sludge concentration. Grundfos mixers offer a robust design with corrosion resistant materials, easy service and maintenance, and trouble-free operation in difficult environments.
Sludge is often treated using a variety of digestion techniques, the purpose of which is to reduce the amount of organic matter and the number of disease-causing microorganisms present in the solids. Today, digesters are relatively easy to operate, and despite the relatively high temperatures required in the sludge digestion process, a retention time of 25 to 30 days is required. A low-speed AMG mixer can be used in this process.
Due to biological degradation of organic material, biogas will be produced in the system. The biogas can be utilised in a Combined Heat and Power (CHP) system, where it produces heat and electricity.
For large wastewater treatment plants, anaerobic digestion is the most widespread method for sludge treatment. Anaerobic digestion results in a further degradation of the sludge under anaerobic conditions, reducing the total organic content of the sludge by up to 40 to 60%.
After digestion, a final dewatering will take place. The dewatered sludge has to be disposed of in a secure way, for example by incineration for energy generation.
Grundfos can supply the specialist expertise to help meet your performance objectives, from the initial identification of needs, to the selection, installation, operation, and maintenance of the pumping solution. Grundfos commissioning agreements ensure correct installation and service agreements cover all eventualities, from routine maintenance to spare parts.