Evaluation of flocculation and dissolved air flotation as an advanced wastewater treatment.
A bench scale study was carried out in order to evaluate the applicability of dissolved air flotation (DAF) as an advanced treatment for effluents from three different domestic wastewater treatment processes, namely: (i) a tertiary activated sludge plant; (ii) an upflow sludge blanket anaerobic reactor (UASB); and (iii) a high-rate stabilization pond.
INFLUÊNCIA DA FLOCULAÇÃO NA FLOTAÇÃO DE EFLUENTES DE REATORES ANAERÓBIOS (UASB)
Estudos recentes demonstram que a flotacao por ar dissolvido (FAD) constitui alternativa eficaz para o pos-tratamento de efluentes de reatores anaerobios, apresentando elevada eficiencia de remocao de solidos suspensos e de fosfato total, assim como reducao significativa de carga orgânica residual. Para maximizar o desempenho desse tipo de sistema e importante a adequacao das condicoes de coagulacao quimica e da floculacao antecedentes a flotacao. No presente trabalho sao apresentados os resultados de investigacao realizada com vistas a avaliacao da influencia do gradiente medio de velocidade (Gf) e do tempo de floculacao (Tf) na eficiencia de uma unidade de flotacao em escala de laboratorio alimentada com o efluente de reator anaerobio de manta de lodo (UASB) tratando esgoto sanitario. Apos a adequacao da dosagem de coagulante (65 mg/L de FeCl3), verificou-se que o emprego de valores de Gf em torno de 80 s -1 e de Tf entre 15 e 25 min, forneceram excelentes resultados no sistema de FAD, com remocao de ate 91% de DQO, 96 % de fosfato total 98% de turbidez e 98% de solidos suspensos.
Mechanical behaviour and durability of high volume fly ash cementitious composites
The purpose of this research is to separate different morphological particles of ASTM class F fly ash, and study their effect on mechanical behaviour and durability of high volume cementitious mixtures. In this research wet separation of raw fly ash is carried out, which resulted in three layers of different morphological particles. The first layer of particles float, comprise of about 1-5% of fly ash, is identified as cenospheres or hollow spheres. The second layer of particles is measured to be 55-60% of raw fly ash and consisting of porous spherical and rounded particles rich in Si and Al. The third layer particles is measured to be about 35-40% of raw fly ash. High volume fly ash cementitious composites containing second or third layer particles are tested under compression and bending, highlighting a higher strength and ductility in comparison to cementitious ones containing raw fly ash particles. KEYWORDS. Cementitious matrix; Raw fly ash; Second layer particles; Third layer particles.