Vector effect of polystyrene film microplastic in enriching Sudan III from natural particles and its burst release into simulated digestive fluid containing fatty acid.

Microplastics (MPs) have aroused tremendous attentions because of their ability in accumulating contaminants from adjacent environment. However, their capability of concentrating hydrophobic organic contaminants might be influenced by huge amounts of coexisting natural particles (NaPs). Yet, our knowledge about the relative concentrating capability of MPs versus NaPs is still rare. Herein, the distribution behavior of several hydrophobic pollutants was studied in simplified MPs/NaPs/pollutant/water quaternary systems. We found that 1-(4-(phenylzao)phenyl)azo-2-naphthol (Sudan III) had similar distribution behavior with many hydrophobic pollutants and thus was used as a model pollutant. Polyethylene (PE) film debris derived from disposable plastic wrap was the most efficient microplastic which concentrated tens of times Sudan III than coexisting NaPs including bentonite, kaolin, sawdust, and diatomite. An enrichment coefficient of over 1000 times was observed in the case of PE film debris versus quartz sand. The concentrating capability of PE film MPs was found approximately equal to biochar particles. MPs seem to have limited contribution on the long distance transportation of hydrophobic organic pollutants. However, notably, over 70% of the adsorbed Sudan III could be released back into water within 0.5 h in the presence of 0.5% sodium oleate, which is a common amphipathic matter forming micelles in digestive fluid. Microplastics might play an important vector-like role in increasing the biological accumulation of hydrophobic pollutants via intestine digestive absorption. Due to much bigger quantity of NaPs, the relative concentrating effect of MPs to hydrophobic organic pollutants over NaPs is possibly a more reasonable reference when considering their potential ecological risk.

Efficient fertilizer production from low phosphate water using in situ-formed vaterite/calcite calcium carbonate composite microspheres.

Phosphate, as an important non-renewable agricultural resource, needs to be recovered from wastewater at mg/L scale. Calcite carbonate fine powder was used in P-recovery but could only work in recovering high concentration phosphate. Herein, a new strategy is explored using in situ-formed CaCO3 microspheres (CaCO3-in situ) to realize efficient and fast P-recovery by adding CaCl2 and Na2CO3 solution into low phosphate water (10 mg-P/L). We find that freshly in situ-formed CaCO3 nanoparticles can capture phosphate ions very efficiently and self-assemble into composite CaCO3 microspheres consisting of vaterite and calcite phases. Phosphate ions are possibly immobilized between CaCO3 nanoparticles which stimulate the formation of metastable vaterite CaCO3. Under optimized conditions (Ca/P molar ratio, 6/1), 98% of phosphate can be recovered with a rather low residual phosphate level of ~0.2 mg-P/L within only 30 min which is much time-saving than existing methods. Importantly, superior class P-fertilizer can be obtained with P2O5 content of 20.8 wt% using this novel CaCO3-in situ recovery strategy, which is 4 times as high as that using prepared calcite CaCO3 nanoparticles. The yield of pakchoi, a fast-growing vegetable, was increased by 58.9% (fresh weight) when using the prepared CaCO3-in situ-P fertilizer. This strategy provides a new way of recycling low concentration phosphate while producing high quality fertilizer.

Surfactant stealth effect of microplastics in traditional coagulation process observed via 3-D fluorescence imaging.

Microplastics (MPs) have aroused rising social concerns. Although amounts of surfactants exist in wastewater and are expected to alter the surface properties of MPs significantly as they are designed to be adsorbed by hydrophobic particles. However, rare works have been done on the influence of surfactants on the coagulation removal process of MPs which was thought to be an effective way to remove MPs together with other natural particles, such as clay. We used 3-D fluorescence imaging to track the coagulation removal process of polystyrene MPs. Our results indicate that nonionic surfactant, tween 20 in ppm scale, could inhibit the coagulation removal of polystyrene MPs significantly. Residue MPs in the effluent is proportional with the surfactant concentration and increases up to tens of times, which will lead to a dramatic increase in their potential environmental risks. Apparent size effect exists in the coagulation in which smaller MPs can escape from the coagulation removal more easily. Mechanism study suggests that the steric resistance of the hydrophilic flexible polyethylene glycol (PEG) layer formed by tween 20 adsorbed on MP surface inhibits clay deposition and thus hinders subsequent agglomeration and precipitation. A surfactant stealth effect, which is used in the design of nanomedicine to avoid the human immune recognition and clearance of nano-drugs from blood circulation, also exists in the coagulation removal process of MPs. Our finding not only proves the strong influence of surfactants on MPs but also will stimulate related studies on other latent surfactant effects of MPs.

Phosphorus hyperaccumulation in nano-MgO using a circular recovery process based on multiple phase transitions from periclase to brucite.

Phosphorus recovery from water is not only necessary for the protection of aquatic environments but also to meet the needs of sustainable development. We find that the adsorption capacity of nano-MgO is far from being fully utilized because of its simultaneous hydration into brucite. Annealing is a useful method of recovering its adsorption capacity without the need for desorption. Phosphate can be accumulated to a much higher level, even surpassing its theoretical equilibrium adsorption limit, so that high-quality fertilizer can be obtained (115.9 mg-P/g-MgO). Phosphate ions exist as HPO42- and PO43- in the sorbent during its phase transition from periclase to brucite, which is the main reason for its extremely high and reactivatable phosphorus recovery properties. This finding not only provides a new efficient phosphorous recovery strategy but will also lead to new understandings of traditional reactive nano-sorbents.