As a substitute for extracellular polymeric substance from waste activated sludge, alginic acid (AA) has been proven to exert a significant inhibitory effect on struvite crystallization for phosphorus recovery from the sludge. The inhibitory effect is highly dependent on ionic strength in the sludge supernatant, especially in terms of seawater and brine as the magnesium source. However, the role of ionic strength in the inhibitory effect has remained elusive. The purpose of the study was, therefore, to comprehensively quantify and elucidate the role of ionic strength in the effect of AA on struvite crystallization. With ionic strength increasing from 0.001 to 0.2 mol/L NaCl, the induction time with 100 mg/L AA significantly increases from (626 ± 29) to (3602 ± 37) s. Meanwhile, the struvite growth rate at 100 mg/L AA decreases from 2.3 × 10–5 to 4.8 × 10–6 mol/min. It was revealed that the increase in ionic strength strengthened the inhibitory effect. Moreover, trimodal particle size distribution was proposed to well identify the impact effect of AA and ionic strength on the nucleation, growth, and aggregation of struvite crystals. Furthermore, the ionic strength-dependent effect is mainly dominated by the AA adsorption on struvite crystals, likely associated with struvite growth rate, electronic repulsive force, and chemical bonds. Interestingly, the chemical bonds were revealed to mainly involve hydrogen bonding as well as the surface complex between struvite and AA. The findings herein shed light on the role of ionic strength in the inhibitory effect of AA on struvite crystallization and the underlying mechanism thereof, which makes it applicable to the cases related to the synergetic effect of organic matter and ionic strength on mineral crystallization.
Although it is well known that phosphate retention in soils and sediments is strongly influenced by binding to secondary iron oxides, there have been relatively few studies examining its adsorption/desorption behavior on multicomponent particles of realistic natural complexity. Here, natural Mn-rich limonite (LM) was used to prepare naturally complex Fe- and Mn-oxide composite materials to examine phosphate adsorption/desorption. To isolate the role of the Mn-oxides, results for the LM sample were compared to those for an acid-treated version (LAT). The saturated adsorption capacity on LAT was almost double that on LM, suggesting phosphate adsorption to the iron oxides is strongly occluded by Mn-oxide fraction. This conclusion is reinforced by comparing the pH dependence and fitting adsorption isotherms, which indicate the apparent driving force decreases with increasing pH on LM but not on LAT. Hence, although the collective results confirm that phosphate uptake and strong binding are selectively controlled by the Fe-oxide fraction, our study reveals that the Mn-oxide fraction strongly interferes with this process. An important conclusion is that phosphate uptake behavior on metal oxides cannot be predicated solely on the basis of the Fe-oxide fraction present, but instead must take into account the deleterious impacts of other phases present.
Micro column rapid breakthrough (MCRB) method for conducting dynamic carbon adsorption test was presented. The results of comparative breakthrough experiments showed that MCRB could be employed to simulate the breakthrough state of large activated carbon adsorbers, to estimate the cost of carbon treatment, and to select the best activated carbon. MCRB required 5% of time and sample volume that would be necessary using conventional test methods while avoiding most of the common operating difficulties/problems. The carbon particle size and the empty bed contact time (EBCT) affected MCRB performance. Using 120~180 mesh activated carbon, the pressure of MCRB test was less than 3.03×105Pa. MCRB results for treatment of 2,4-DCP and MTBE simulated wastewater were reasonable.
The acid–base surface properties of vivianite crystals highly affect the adsorption capacity of vivianite for heavy metals and organic matters in aqueous solution. Therefore, the aim of the study was to innovatively explore and quantify the acid–base surface characterization of vivianite crystals in aqueous solution. It was found that the two surface active adsorption sites (≡POH and ≡FeOH) and five surface species thereof (i.e., ≡PO, ≡POH, ≡FeOH, ≡FeO − , and ≡FeOH 2 + ) underwent surface reaction on vivianite crystals. Moreover, the active surface site and point of zero charge of vivianite crystals were 18 sites/nm 2 and pH 5.9. Importantly, constant capacitance model was successfully employed to model the titration data, from which the distribution of surface species as function of pH and surface reaction constants were also accurately derived. The finding herein can be applied for plausible modeling molecular‐scale adsorption of the impurities on vivianite surface.
Pore structure characterization and fractal analysis have great significance for understanding and evaluating tight limestone reservoirs. In this work, the pore structure of tight limestone is characterized combined with low-temperature nitrogen adsorption (LTNA) and low-field nuclear magnetic resonance (NMR), and the fractal dimension of tight limestone pore structure is discussed based on LTNA and NMR data. The results indicate that the pores of tight limestone have H3 and H4 types, the pore size distribution (PSD) of H3 type is a wave distribution ranging from 2 to 10 nm, and the PSD of H4 type is a unimodal distribution ranging from 2 to 10 nm. The transverse relaxation time (T2) spectrum of tight limestone shows single peak (DF), double peak (SF) and three peak (TF), and the T2 spectrums for micropores, mesopores and macropores range from 0.1 to 10 ms, from 10 to 100 ms, and greater than 100 ms, respectively. The LTNA fractal dimension of tight limestone (DL) ranges between 2.4446 and 2.7688, with an average of 2.5729, and the NMR fractal dimensions of micropores (DNMR1), mesopores (DNMR2) and macropores (DNMR3) are distributed between 0.3744 to 1.1293, 2.4263 to 2.9395 and 2.6582 to 2.9989, respectively. Moreover, there is no correlation between fractal dimension and permeability and porosity, a negative correlation between DL and average pore radius, a positive correlation between DL and specific surface area, and a positive correlation between DNMR2 and DNMR3 and micropore content, while DNMR2 and DNMR3 are negatively correlated with the content of mesopores and macropores.
The import of so much suspended sediment, water pollution and saline water invasion had greatly imperilled the water environmental sustainable development of Pearl River Estuary. Supported by the information revolution, the water environmental sustainable development of Pearl River Estuary could be carried through. First, based on the environmental actuality of Pearl River Estuary, the uptodate advanced techniques and management, the Pearl River Estuary Integrated Observing System should be built and consummated. Second, the checkup in advance of environmental management should be enhanced. Finally, the effective environmental management system should be set up. To build the feasible development strategies and to realize the sustainable development, the market, government and individuals should be coalesced into one.
The seasonal variation and spatial distribution of pharmaceuticals in typical drinking water sources in the middle reaches of the Yangtze River were analyzed using the solid-phase extraction and high-performance liquid chromatography-tandem mass spectrometry methods. Combined with the risk entropy method, the corresponding ecological risks for aquatic organisms were evaluated. The results showed that 80% of the target pharmaceuticals were detected in the drinking water sources, with average concentrations of 0.07-13.00 ng·L-1. The concentrations of the target pharmaceuticals were lower than or comparable with those in other drinking water sources reported in China. The spatiotemporal distribution of different pharmaceuticals varied. Generally, the detection level in winter was higher than that in summer, and there was no significant difference between that upstream and that downstream. This might be mainly attributed to seasonal/regional use and emissions of the pharmaceuticals, the impact of flow rate on dilution, and the impact of temperature on biodegradation. Compared with those before the COVID-19 epidemic, the detection concentrations of the target pharmaceuticals were relatively low. The reason for this might be that the prevention and control of the epidemic reduced the use and emission of the pharmaceuticals to a certain extent, and the high rainfall and runoff strengthened the dilution of water flow. The target pharmaceuticals, especially antibiotics, posed medium or low risks to aquatic organisms (especially algae). Considering the ecological risks and genotoxicity of pharmaceuticals and the potential risks of antibiotic-resistant genes, it is suggested to strengthen the investigation, evaluation, treatment, and control of pharmaceuticals in the water environment.
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