Huanlin Chen

Enhanced lipid production of Chlorella vulgaris by adjustment of cultivation conditions.

To increase the lipid productivity and thus to reduce the production cost of microalgal biodiesel, effects of cultivation conditions including KNO(3)-level, CO(2) concentration and irradiance on the cell growth, chlorophyll a content and lipid accumulation of Chlorella vulgaris were systematically investigated in a membrane sparged photobioreactor. The biochemical compositions including carbohydrates, proteins and lipids were analyzed simultaneously by the FT-IR spectroscopy. The results showed that the largest biomass productivity and the highest lipid content were obtained at different cultivation conditions. The algae should be harvested at a point that optimized the biomass productivity and lipid content. When the cultivation conditions were controlled at 1.0mM KNO(3), 1.0% CO(2) and 60 micromol photons m(-2)s(-1) at 25 degrees C, the highest lipid productivity obtained was 40 mg L(-1)d(-1), which was about 2.5-fold that had been reported by Illman et al. (2000). The influences of cultivation conditions on the cell growth, lipid accumulation, and other biochemical compositions of cells were further discussed and illustrated by a schematic which was also useful for other microalgal species.

Role of NaA zeolites in the interfacial polymerization process towards a polyamide nanocomposite reverse osmosis membrane

This paper explores the behaviour and role of NaA nanozeolites during an interfacial polymerization process towards a polyamide thin film nanocomposite (TFN) reverse osmosis membrane by incorporating nanozeolites into two different reactive phases. In the two cases, the different interactions occurring between the zeolites and polyamide were investigated by FT-IR spectra, XPS analysis, and examining the membrane morphology and the desalination performance. The polyamide TFN membrane with an increased degree of cross-linking was obtained with nanozeolites in the organic phase, as the NaA zeolite reacted with the acyl chloride monomer in the organic phase. Additionally, the membrane with nanozeolites added to the organic phase had a superior reverse osmosis performance, since the porous zeolite appeared in the top layer as a water channel.

Acid and multivalent ion resistance of thin film nanocomposite RO membranes loaded with silicalite-1 nanozeolites

The incorporation of NaA nanozeolites into thin film composite (TFC) reverse osmosis (RO) membranes has been found to elevate water permeability, but the unfavorable acid and multivalent ion sensitivity of NaA limits the application of the thin film nanocomposite (TFN) membranes for seawater desalination. To overcome these drawbacks, the chemically stable silicalite-1 nanozeolite was incorporated into the skin layer of the RO composite membrane via interfacial polymerization. In this paper, the resulting membrane was characterized with outstanding chemical stability (acid and multivalent cation tolerance) compared with the NaA mixed membrane. Additionally, silicalite-1 showed better capacity to enhance membrane permeability than NaA, which can be explained by larger channel pores and a higher water diffusion rate in silicalite-1. This investigation indicates that the silicalite-1 mixed membrane has great potential in large-scale seawater desalination because of its excellent permeability and chemical stability.

Evaluation of FT-IR and Nile Red methods for microalgal lipid characterization and biomass composition determination.

To characterize lipid content of microalgal cells rapidly and accurately, the gravimetric determination, FT-IR and Nile Red (NR) staining were investigated on six typical eukaryotic and prokaryotic algae species. FT-IR and Nile Red were relative quantification methods and a standard curve was required in contrast to the gravimetric method. The FT-IR method determined the lipid, carbohydrate and protein contents simultaneously assuming that the algal cells only consisted of those three components. The Nile Red method was a relatively rapid method for neutral lipid content characterization by spectrofluorometry and could locate lipid body of the algal cell by fluorescence microscopy. According to sample sources and processing purposes, the gravimetric determination was preferable for large-scale cultivation with low-frequency monitoring, while FT-IR and Nile Red were suitable for general laboratory cultivation with medium-frequency monitoring, in particularly Nile Red was appropriate for small samples when high-frequency screening was required.

4-Dimethylaminopyridine promoted interfacial polymerization between hyperbranched polyesteramide and trimesoyl chloride for preparing ultralow-pressure reverse osmosis composite membrane.

We have presented a concept of ultralow-pressure reverse osmosis membrane based on hyperbranched polyesteramide through interfacial reaction promoted by pyridine derivate. In this strategy, a key catalyst of 4-dimethylaminopyridine, which can both eliminate the steric hindrance of acyl transfer reaction and facilitate the phase transfer in interfacial polymerization, is adopted to drive the formation of a thin film composite membrane from the hyperbranched polyesteramide and trimesoyl chloride. The results of the characterization demonstrate that a dense, rough, and hydrophilic active layer with a thickness of about 100 nm is formed when the 4-dimethylaminopyridine catalyst is used. The salt rejections for Na2SO4, NaCl, and MgSO4 of the as-prepared composite membrane are higher than 92%, especially for Na2SO4 with 98% rejection. The water fluxes reach about 30-40 L·m(-2)·h(-1) even at an operation pressure of 0.6 MPa. The membrane exhibits good chlorine-resistance ability but poor resistance abilities to acidic and alkaline solutions in the physical-chemical stability experiment. It is also found that the resultant membrane possesses excellent separation performance for PEG-200, showing a promising way to separate small organic molecules from water.

Sol–gel fabrication of a non-laminated graphene oxide membrane for oil/water separation

A non-laminated graphene oxide membrane crosslinked by polyethyleneimine was prepared via a one-step sol–gel process. In the as-prepared membrane, the GO nanosheets remain disordered as in the sol state to form a randomly arranged GO self-assembled structure, which results in a much higher flux compared with the general laminated GO membrane prepared via vacuum filtration or spin coating because of the lower flow resistance. Furthermore, this random self-assembly of GO nanosheets gives rise to a hierarchical micro/nanoscale rough structure on the membrane surface. Along with the crosslinking reaction, PEI was grafted onto the GO nanosheets to make them hydrophilic. Combining the hydrophilic surface chemistry with the micro/nanoscale hierarchical surface structure, the non-laminated GO membrane exhibited the desired superhydrophilic and underwater superoleophobic properties. We have tested the membrane to separate a series of surfactant-free and surfactant-stabilized oil-in-water emulsions. A high separation efficiency (>99%) and flux were achieved using only gravity without any extra power, much larger than commercial filtration membranes with similar permeation properties. Moreover, the membrane shows an outstanding antifouling performance for oil droplets and can be recycled easily for long-term use.

Morphology and Formation Mechanism of Poly(Vinylidene Fluoride) Membranes Prepared with Immerse Precipitation: Effect of Dissolving Temperature

Poly(vinylidene fluoride) (PVDF) membranes were prepared by the immersion precipitation method. The effects of polymer dissolving temperature for the dopes on the morphology, crystallization and performance of prepared membranes were examined. Polymer dissolving temperature was varied from 50 to 120°C. N,N-dimethylacetamide (DMAc) and de-ionized water were used as solvent and non-solvent, respectively. Based on the membrane morphology and the schematic phase diagram of the ternary system, the membrane formation mechanism was analyzed theoretically. The binodal liquid-liquid demixing took place first for the nucleation and growth of droplets in the polymer poor phase; then consequently the spinodal liquid-liquid demixing occurred in the polymer rich phase. The demixings together resulted in the prepared membranes having a cross-section composed of interconnected globule-like particulates with bi-continuous structured surfaces. The dissolving temperature of the dopes had a remarkable effect on the morphology of the cross-section, even when the solution underwent a long time cooling before the demixing. The increase of the diameter of the particulates with the dissolving temperature was theoretically analyzed according to the conditions of the polymeric solution.

Effect of carbon source on biomass growth and nutrients removal of Scenedesmus obliquus for wastewater advanced treatment and lipid production.

The combination of tertiary wastewater treatment and microalgal lipid production is considered to be a promising approach to water eutrophication as well as energy crisis. To intensify wastewater treatment and microalgal biofuel production, the effect of organic and inorganic carbon on algal growth and nutrient removal of Scenedesmus obliquus were examined by varying TOC (total organic carbon) concentrations of 20-120mgL(-1) in wastewater and feeding CO2 concentrations in the range of 0.03-15%, respectively. The results showed that the maximal biomass and average lipid productivity were 577.6 and 16.7mgL(-1)d(-1) with 5% CO2 aeration. The total nitrogen, total phosphorus and TOC removal efficiencies were 97.8%, 95.6% and 59.1% respectively within 6days when cultured with real secondary municipal wastewater. This work further showed that S. obliquus could be utilized for simultaneous organic pollutants reduction, N, P removal and lipid accumulation.

Saline wastewater treatment by Chlorella vulgaris with simultaneous algal lipid accumulation triggered by nitrate deficiency.

Chlorella vulgaris, a marine microalgae strain adaptable to 0-50 g L(-1) of salinity, was selected for studying the coupling system of saline wastewater treatment and lipid accumulation. The effect of total nitrogen (T N) concentration was investigated on algal growth, nutrients removal as well as lipid accumulation. The removal efficiencies of TN and total phosphorus (TP) were found to be 92.2-96.6% and over 99%, respectively, after a batch cultivation of 20 days. To illustrate the response of lipid accumulation to nutrients removal, C. vulgaris was further cultivated in the recycling experiment of tidal saline water within the photobioreactor. The lipid accumulation was triggered upon the almost depletion of nitrate (<5 mg L(-1)), till the final highest lipid content of 40%. The nitrogen conversion in the sequence of nitrate, nitrite, and then to ammonium in the effluents was finally integrated with previous discussions on metabolic pathways of algal cell under nitrogen deficiency.

A cross-linking graphene oxide–polyethyleneimine hybrid film containing ciprofloxacin: one-step preparation, controlled drug release and antibacterial performance

A novel drug delivery system based on a graphene oxide film cross-linked by polyethyleneimine was prepared via a one-step preparation technique. Due to cross-linking, the stability of the film was significantly improved compared with the bare graphene oxide film and an extra drug-loading site was endowed to the film by PEI. The release behavior of ciprofloxacin, as a model drug, was investigated under various pH values in vitro, and the results exhibited slow drug release without an initial burst effect. Release kinetic models were employed to represent the drug release processes, and the release behavior of ciprofloxacin of the resulting cross-linking film was consistent with near zero-order kinetics. In comparison to a graphene oxide-polyethyleneimine hybrid film, the ciprofloxacin loaded hybrid film exhibited a significant antibacterial effect due to the ciprofloxacin release and diffusion from the film. This study provides insight into the design of suitable cross-linking GO hybrid films for biomedical field and many other applications.