Abstract
The aim of this study was the investigation of alternative pre-polymerized coagulants for the treatment of high-strength industrial wastewaters, such as those created by tanneries, or by yeast production industries. The novel inorganic composite coagulant examined in this study (as well as variations of it) was denoted as PSiFAC1.5-10-15. The contribution of a typical polyelectrolyte to improve the effectiveness of the coagulation/flocculation (C/F) process was additionally studied, either by adding it separately (i.e., as a flocculant aid) or by co-polymerizing it within the structure of inorganic coagulant (denoted as PAPEFAC1.5-10-15). It was found that the PSiFAC1.5:10:15 coagulant, either with or without the addition of polyelectrolyte, can provide better efficiency for the C/F process than the conventional coagulants. For example, the addition of 80 mg Al/L in yeast production wastewater samples resulted in a 56% reduction of COD, 40% of turbidity, and 43% of phosphates, regarding the pre-treated anaerobically wastewater samples and reduced by an extra 22%, 14%, and 38% for the pre-treated anaerobically plus aerobically wastewater samples, respectively. The residual aluminum concentration in the treated wastewaters was found to be below the legislation limit of 200 μg Al/L. The characterization of coagulants showed the relatively higher Al13 content of 51% and 43% for the cases of PSiFAC1.5-10-15 and PAPEFAC1.5-10-15, respectively, accompanied by the high zeta-potential measurements (50.5 and 39.5 mV).
Highlights
Domestic and industrial wastewaters can contain large concentrations of recalcitrant compounds, whereas their treatment by the application of biological processes in several cases was not found to be adequately effective, resulting in a treated effluent of rather low quality, e.g., causing severe eutrophication problems after disposal due to the remaining quite high nutrient concentrations
It can be observed that the addition of poly-silicic acid in the Al–Fe solution, when performed to induce the formation of composite coagulants, resulted in the increase of turbidity in comparison with the addition of anionic polyelectrolyte (APE) in the same FpA solution, i.e., the
When Al was firstly added to poly-silicic acid solution (pSi), i.e., to prepare the PSiFAC1.5-10-15 product, the turbidity value was quite high (211 NTU), most likely due to the interaction between the chemical forms of Al and Si, as Duan and Gregory (1998) [38] suggested, arguing that in aqueous solutions, silicic acid can interact with the chemical forms of Al to form hydroxy-alumino-silicate complexes (HAS)
Summary
Domestic and industrial wastewaters can contain large concentrations of recalcitrant compounds, whereas their treatment by the application of biological processes in several cases was not found to be adequately effective, resulting in a treated effluent of rather low quality, e.g., causing severe eutrophication problems after disposal due to the remaining quite high nutrient concentrations (among others) For this case, important is the presence of phosphorous (usually in the form of orthophosphates), which has to be efficiently removed (or recovered), especially from certain industrial wastewaters [1,2,3], noting that phosphorus can be removed from waters/wastewaters either biologically or (more effectively) by the addition of appropriate chemical agents [4]. Besides the satisfactory results, membrane fouling and the need for membrane cleaning could result in higher operational and maintenance costs when compared to conventionally applied treatment technologies
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