Volumetric flow regulator

hydraulic

Overview In secondary settling tanks, treated wastewater is clarified and sludge is thickened by separating activated sludge from clarified effluent. Secondary sludge has a specific gravity close to water, making sedimentation difficult. As the final unit in many wastewater treatment plants, secondary settling tanks must maintain high clarification efficiency to limit suspended solids, phosphorus and COD in the discharge.

Operational challenges Maintaining stable clarification is the main operational challenge. Symptoms include suspension washout and elevated phosphorus in the effluent. A common cause identified by CFD modelling and long-term hydraulic studies is a fixed inflow column that cannot adapt to changing process conditions, causing hydraulic disturbances and sludge resuspension.

Hydrograv – principle of operation A fixed inflow above the sludge blanket produces upward disturbances and sludge "clouds" by washing the upper sludge layer. Inflows well below the blanket can also entrain thickened sludge during high flows, creating a nozzle effect. Hydrograv Adapt addresses these issues with an adjustable inflow column that modifies inflow height and opening size to preserve the separation between clear effluent and the sludge layer under varying operating conditions.

Controller and control strategy Each installation receives a customised controller program based on CFD-informed simulation and historical plant operational data. Control uses online process signals (flow, sludge concentration, temperature, sludge volume index, recirculation rate) rather than relying solely on direct sludge-blanket measurement. This enables trend anticipation and proactive adjustment of both inflow height and opening to maintain effective separation.

Hydrograv - operational benefits

• Stabilises clarification performance in secondary settling tanks across variable hydraulic and process conditions
• Can substantially increase effective settler performance and reduce uncontrolled sediment discharge
• Limits suspended solids carryover, contributing to reductions in phosphorus and COD in the effluent
• Adapts inflow geometry automatically to changing flow and sludge conditions

Product variants / images shown Examples of mechanical designs include the "Bellows" (bellows-type) regulator and the "Cylinder" (cylinder-type) regulator as alternative variants of the Hydrograv family.

Documentation Detailed technical documentation, product sheets and a product card/booklet are provided (see product PDF files for installation details, hydraulic charts and control logic descriptions).

Technical characteristics / specifications

• Adjustable sewage inflow column: Hydrograv Adapt
• Custom controller program per installation based on CFD simulation and historical operational data
• Control inputs: current flow, sludge concentration, temperature, sludge volume index, recirculation rate (online signals)
• Controls both inflow height and inflow opening to maintain separation between clear effluent and sludge layer
• Designed to reduce suspended solids, phosphorus and COD in effluent and to limit sediment discharge
• Multiple mechanical designs available (e.g., bellows-type, cylinder-type)