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Center for Environmental and Sustainability Research

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When hillclimbers beat genetic algorithms in multimodal optimization
Publication . Lobo, F.J.; Bazargani, Mosab
This paper investigates the performance of multistart next ascent hillclimbing and well-known evolutionary algorithms incorporating diversity preservation techniques on instances of the multimodal problem generator. This generator induces a class of problems in the bitstringdomain which is interesting to study from a theoretical perspective in the context of multimodal optimization, as it is a generalization of the classical OneMax and TwoMax functions for an arbitrary number of peaks. An average-case runtime analysis for multistart next ascent hill-climbing is presented for uniformly distributed equal-height instances of this class of problems. It is shown empirically that conventional niching and mating restriction techniques incorporated in an evolutionary algorithm are not sufficient to make them competitive with the hillclimbing strategy. We conjecture the reason for this behaviour is the lack of structure in the space of local optima on instances of this problem class, which makes an optimization algorithm unable to exploit information from one optimum to infer where another optimum might be. When no such structure exist, it seems that the best strategy for discovering all optima is a brute-force one. Overall, our study gives insights with respect to the adequacy of hillclimbers and evolutionary algorithms for multimodal optimization, depending on properties of the fitness landscape.
Nanofibrillated cationic cellulose derivatives as flocculants for domestic wastewater treatment
Publication . Ribau Teixeira, Margarida; Ismail, Abdullah; Medronho, Bruno; Alves, Luís; Pedrosa, Jorge F.S.; Ferreira, Paulo J.T.; Serrão Sousa, Vânia; Rosa Da Costa, Ana
Natural-based coagulants have emerged as a reliable option to implement more sustainable operations and management of wastewater treatment plants. This work aims at evaluating the use of cationic nanofibrillated celluloses (cNFC) as novel bio-based flocculants to treat domestic wastewaters by the most widely employed treatment process – coagulation/flocculation. Two cNFC samples were prepared with different charge densities and tested as coagulant/flocculants using different water characteristics. The effect of cNFCs was studied by measuring the residual turbidity and dissolved organic carbon. The aggregation mechanism and kinetics of flocculation were also evaluated. Results show that cNFC can be used as an efficient flocculant to treat medium and high DOC waters since they considerably reduce turbidity (turbidity removals varied between 66.0 % and 85.7 % for the waters and cNFCs tested) without increasing dissolved organic carbon. Instead, cNFC removed dissolved organic carbon from domestic wastewaters (between 22.1 % and 65.5 % of DOC removals for the waters and cNFCs tested), which is a novel remarkable finding and a step forward in this knowledge area. High density charged cNFC revealed superior removal capacity at lower doses than the commercial coagulant FeCl3.

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Funding agency

Fundação para a Ciência e a Tecnologia

Funding programme

6817 - DCRRNI ID

Funding Award Number

UIDB/04085/2020

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