L. Larrea

Selection of operational strategies in activated sludge processes based on optimization algorithms

This paper presents a new optimization algorithm for the selection of design and operation parameters in complex Activated Sludge (AS) processes. The algorithm estimates automatically the dimensions and operating point of the plant that minimize a global penalty function combining effluent requirements and costs. The mathematical optimization is based on a direct search algorithm integrated in a previously developed simulation package. Some illustrative examples concerning the design and operation of the Alpha process have been included to show the potential of this kind of mathematical tool when the complexity of plant configuration increases. The results obtained by the optimization procedure generate useful guidelines for the design and operation and suggest a great potential in the application for solving more complex problems when additional objectives and costs are included.

Non-filamentous activated sludge bulking in a laboratory scale system

Abstract The paper describes the appearance of non-filamentous bulking in a lab-scale activated sludge plant with nitrification-denitrification and reaeration of return sludge. The inlet part of the denitrification zone was operated as an anoxic selector. Although filamentous microorganisms regularly occurred, the sludge settled properly. Deterioration of SVIs was observed after increasing the oleic acid concentration in synthetic wastewater. The bulking period was related to the abundant growth of viscous zoogloeal colonies. The intensive foam production resulted from the excessive appearance of exocellular polymers. A structure of short intertwined fingered projections formed the zoogloeal flocs. After decreasing the oleic acid proportion in the synthetic wastewater to the original level the zoogloeal flocs gradually changed to the well-settling sludge in 3 weeks.

Standard signal processing using enriched sensor information for WWTP monitoring and control.

Important indicators for monitoring and control of wastewater treatment plants (WWTP) often have to be obtained from the processing of on-line signal trajectories. Therefore, the quality of sensor instantaneous measurements can be improved significantly if they are complemented with valuable information about the geometric features of their trajectories. The present paper describes the design and implementation of a Standard Signal Processing Architecture (SSPA) from which enriched sensor information is generated automatically. The SSPA has been made up of three complementary modules: the pre-processing module, the storage module and the post-processing module. Moreover, the SSPA has been parameterised so as to allow its adaptation to the specifications of every signal. By performing basic calculations on pre-processed signal trajectories, the storage module produces enriched vectors which collect information of the first and second time derivatives, average and variance values, peak values, linear regression parameters, curvature, etc. Then, the enriched information vectors can be exploited to implement customised monitoring and control tools. In this respect, the effectiveness of the SSPA has been demonstrated in three different practical cases: (1) OUR and KLa identification algorithms; (2) processing of measurements for real-time controllers; and, (3) detection of bend-points in on-line signals of SBR processes.

KRAFT LIGNIN BEHAVIOUR IN DIFFUSED AERATION OF KRAFT EFFLUENTS

ABSTRACT Diffused aeration experiments carried out using a Kraft black liquor in batch reactors at 211°C were performed in order to characterize the relative importance of the mechanisms of chemical oxidation and condensation of lignin structures upon COD, lignin and colour removal and also to evaluate the influence of agitation intensity on these mechanisms. It was found that total COD decreased with time. This behaviour was independent of the aeration intensity and the reduction reached a value of about 18% of the initial COD after approximately 15 days. This reduction was attributed to chemical oxidation of some functional groups of the Kraft lignin contained in the substrate. However, filterable lignin (as absorbance at 272 nm) and colour (as absorbance at 465 nm) were not affected by chemical oxidation. It was also observed that agitation produced the formation of suspended solids by condensation of lignin structures. This took place during the first 2 days and provoked a reduction of filterable COD, lignin and colour which was dependent on the aeration intensity.