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Refereed/Peer-reviewed The textile industry uses a variety of synthetic dyes for dyeing and discharges a large amount of colored wastewater. It is difficult to achieve good decolorization effect for textile wastewater by conventional biological treatment methods, because it contains various synthetic dyes with complex structures. At present, coagulation is an economical and effective treatment method. However, in dye removal by coagulation research, the adaptability and mechanisms of coagulation removal of many dyes are still unknown due to the wide variety of dyes in use. In this study, ferric chloride (FeCl₃), aluminum chloride (AlCl₃) and magnesium chloride (MgCl₂) were selected as coagulants, and direct orange 26 (DO), direct yellow 11 (DY) and direct black 19 (DB) were used as the dye samples to conduct a series of coagulation experiments; in order to understand the coagulation adaptability and mechanism for high removal efficiency of direct dyes. In this system without particles, the direct dyes were dissolved directly in pure water and maintained in molecular state. The results showed that 1) AlCl₃, FeCl₃ and MgCl₂ exhibited superior coagulation efficiency on the three dyes. Direct dyes which contain more amino functional groups are more easily removed by coagulation. 2) The influence of hydraulic conditions on the residual turbidity was more significant compared with the color removal. 3) Zeta potential increased with the increase of the coagulant dosage, but the colloidal particles did not re-stabilize. This proved that charge neutralization is not the dominant mechanism of coagulation. The FT-IR and XRD patterns indicated that the direct dyes were removed by the chemical combination of the -SO₃H on the dye molecule and the hydrolysate of the coagulant.

Construction waste and waste fabric are two major types of solid waste that lead to landfill issue and environmental pollution. Considering the need for more efficient handling method by simultaneously handling both solid waste materials, this study reports an innovative solution to transform waste concrete and waste polyester fabric into environmentally friendly product, recycled foamed concrete (RFC). The dry density, compressive strength, water absorption, frost resistance and chemical erosion resistance of plain RFC (PRFC), PET fiber reinforced RFC (PETRFC) and recycled PET fiber reinforced RFC (RPETRFC) were evaluated. The results indicated that the added recycled powder (RP) can improve the compressive strength of foam concrete. Moreover, the addition of PET fiber (0.1 wt.% content and 6 mm length - optimum) improved the compressive strength (especially the early strength) and durability but had no significant effect on dry density and water absorption. Recycled PET fiber presented a better enhancement effect than PET fiber. The dry density and 28-day compressive strength of RPETRFC were 5.2% and 5.1% higher than those of PETRFC, respectively, and water absorption was 10.7% lower than that of PETRFC. Scanning electron microscopy (SEM) and X-ray diffraction (XRD) analysis indicated that recycled PET fiber had a multifilament structure, which can effectively improve the pore structure of RFC without changing the hydration mechanism. This study demonstrates a new direction for recycling waste concrete and polyester fabric with excellent economic and environmental benefits, and the findings provide reference for the development of lightweight RFC with improved physical properties and durability. Refereed/Peer-reviewed

Protein, the main component of extracellular polymeric substances, plays a vital role in sediment dewatering. Tannic acid (TA) can bind with protein, so was used as a new conditioner for sediment dewatering. The benefit of using TA as a conditioner for sediment dewatering and its mechanism were explored in this study. A series of laboratory-based experiments were conducted and the water content (Wc) of sediment cakes, specific resistance to filtration (SRF) and the filterable dehydration rate were used to evaluate the sediment dewaterability. The results showed that at the optimal dosage of 0.20 mmol/gTS (total solid), TA reduced Wc of sediment cakes by 12.3% and SRF by 70.6%, and increased the filterable dehydration rate by 9%. These results indicated TA effectively improved the dewatering performance of sediment. The conditioning mechanism study of TA supported that the protein content was reduced by combining with TA, and the bound water was gradually converted into free water. When TA was added in sufficient amount, the particle size gradually increased, large and dense aggregates were formed which enhanced the dewatering performance of the sediment. These results confirm the feasibility of using TA as an effective option for rapid dewatering of sediment and provide a reference for selecting the appropriate conditioner for sediment dewatering. Refereed/Peer-reviewed

The color removal efficiencies by coagulation of two groups of laboratory-prepared dye solutions were compared; one group comprised dyes with the same chromophores and auxochromes, and the other group consisted of dyes with different chromophores and the same or different auxochromes. Several coagulants, polyaluminum chloride (PAC), cationic polyacrylamide (CPAM), anionic polyacrylamide (APAM), aluminum sulfate (alum as Al2(SO4)3), ferric chloride (FeCl3), aluminum chloride (AlCl3), and magnesium chloride (MgCl2), were selected to cover a large range of experimental variations in order to obtain sufficient data to predict and model the color removal efficiency. The effect of coagulant dosage on the color removal efficiency was determined, and the dye removal mechanism by coagulation was further investigated using the best performing coagulants for each dye group (disperse, acid, reactive, and basic). It was shown that the best dye–coagulant combinations that achieved superior color removal efficiency for each dye group with the same structures and functional groups were disperse dye–MgCl2 at a pH of 12, acid dye–MgCl2 at a pH of 12, reactive dye–PAC at a pH of 7.5, and basic dye–APAM at a pH of 8.3, in descending order. When treated with the same coagulant, dyes with the same auxochromes and charge exhibited very similar color removal efficiency. The state of the dye molecules in water was shown to have a significant influence on the coagulation effect. The experimental results indicated that the dye color removal efficiency by coagulation is a function of the dye structures. Refereed/Peer-reviewed

The application of a new combined fractionation technique (CFT) using high performance size exclusion chromatography (HPSEC) and rapid resin fractionation (RRF) for characterization of natural organic matter (NOM) in raw and post-coagulated water samples was assessed. Two natural water samples from Myponga and Hope Valley reservoirs, South Australia, respectively, were selected for this NOM removal by coagulation study. With the use of HPSEC and RRF individually, removal in the low molecular weight (LMW) organic region was observed by comparison of the HPSEC profiles of raw and treated waters and the removal of the hydrophobic organics was observed by comparing the RRF results. A new organic fractionation and characterization technique involving the sequential application of the two techniques, called RRF-HPSEC, was developed to provide additional analytical information particularly to determine the key control factor for the removal of LMW organics. The RRF-HPSEC results showed that good removal of LMW organics could be linked to the presence of high ratio of hydrophobic LMW organics compared with hydrophilic LMW organics. It was revealed, therefore, that the removal of LMW organics was achieved mainly through the reduction of hydrophobic fractions compared with hydrophilic fractions with the corresponding molecular weight. Refereed/Peer-reviewed