Real time control of a combined UASB-activated sludge wastewater treatment configuration

Abstract

This paper presents a combined wastewater treatment configuration composed by an Upflow Anaerobic Sludge Blanket (UASB) reactor followed by an Activated Sludge (AS) system. A control strategy has been developed for this innovative (especially for domestic sewage) treatment configuration and tested in a real pilot-scale system called STEPAA-Wastewater Treatment System by Anaerobic and Aerobic Processes. The proposed UASB-AS control strategy, including fault detection and recovery, and its successful implementation in real time is presented. This novel control strategy was developed to keep the final effluent suspended solids concentration in the range specified by the State environmental agency, in spite of incoming load disturbances. The control strategy is based on two cascaded PI (Proportional + Integral) controllers, which manipulates the recycling rate into the AS-reactor to control the effluent suspended solids concentration. A 2-dimensional nonlinear mapping (an empirical look-up table), which gives the sludge waste rate as a function of the influent flowrate and AS-reactor biomass concentration, is used to keep the AS-reactor biomass concentration in a range that guarantees a good substrate removal without inconveniences to the AS-settler operation (and consequently to the solids removal). Experimental results are provided to demonstrate the system performance.

Activated Sludge and Other Aerobic Suspended Culture Processes

“…A cascaded, proportional integral strategy was developed to control an upflow anaerobic sludge blanket (UASB) reactor followed by a conventional activated sludge unit (Polito-Braga et al, 2002). The control strategy allowed the flowrate and mixed liquor concentrations to be controlled in a range that ensured acceptable effluent quality.…”

Start-Up Evaluation of a Full-Scale Wastewater Treatment Plant Consisting of a UASB Reactor Followed by Activated Sludge

“…The authors of [14] evaluated the operation of a pilot UASB-AS system, recommending a global hydraulic retention time of 7.9 h distributed as follows: 4.0 h UASB; 2.8 h aerobic reactor; and 1.1 h final clarifier. The authors of [26] presented an operational strategy for a combined pilot-scale UASB-AS system treating an influent with the typical sewage composition from the city of Belo Horizonte (Brazil). The selected control variables were the solid concentration in the effluent and the sludge wastage rate.…”