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Abstract
The aim of this study is to investigate the flocculation capacity of activated sludge flocculant in chromium ion and nitrobenzene solutions. Besides comparing with activated carbon, we changed some potential factors which may influence the flocculation, such as solution pH value, reaction time, flocculant dosage, and solution initial concentration, and tested the flocculation capacity of this bioflocculant for both chromium and nitrobenzene. In addition, the flocculation of activated sludge after acidic or alkali modification for double solutions was also estimated. Compared with activated carbon, the activated sludge flocculant showed a good flocculation capacity for nitrobenzene, but poor flocculation for chromium following the initial concentration increase. The flocculation for nitrobenzene or chromium increased at initial stage and decreased gradually following the primary dosage of flocculant increase. The flocculation for nitrobenzene increased at the primary stage and decreased after peak, while the flocculation for chromium increased following the pH increase of both solutions. Although the flocculation for nitrobenzene decreased, the flocculation for chromium increased obviously, when we prolonged the reaction time. The flocculant showed a gradual increasing trend in double kinds of solution when they were heating. The flocculation for both nitrobenzene and chromium decreased after acid modification of activated sludge flocculant, while the flocculation increased after basic modification. The present research provided further theoretical basis of the biosorption of heavy metal waste water and nitrobenzene organic toxicants.
Highlights
With the rapid development of chemical industry, mining, and metallurgy, emissions of industrial wastewater usually contains an excess of heavy metals [1] and organic toxicants, such as nitrobenzene, which have threatened the environment and human health seriously [2]
In activated sludge wastewater treatment process, the degradation of pollutants is divided into two stages: the first stage is that sludge flocs adsorb organic pollutants from wastewater outside the cell wall of bacteria; the second stage is that bacteria transport pollutants to the substances and energy required for cell metabolism through active transportation
Many domestic scholars and abroad have discussed the influence of sludge EPS adsorption, but they mainly focus on the adsorption of heavy metals by activated sludge EPS [23]
Summary
With the rapid development of chemical industry, mining, and metallurgy, emissions of industrial wastewater usually contains an excess of heavy metals [1] and organic toxicants, such as nitrobenzene, which have threatened the environment and human health seriously [2]. The flocculation of some living or dead biomass has been explored in heavy metals and organic compounds [5] by many researchers, such as activated sludge, bacteria, fungi, or algae [6]. Activated sludge is for green environmental protection, and for circular economy in wastewater treatment field. It can decompose organic substances in industrial wastewater by the biochemical metabolic reactions of aerobic microbial substances, which is related to the flocculation, coagulation, and precipitation of activated sludge [7]. Activated sludge can effectively remove colloidal and dissolved substances in waste water and purify the wastewater [3, 8, 9]
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