Influences of iron and calcium carbonate on wastewater treatment performances of algae based reactors

Responses of microbial communities and metabolic activities in the rhizosphere during phytoremediation of Cd-contaminated soil

Phytoremediation is an effective way to repair heavy metal contaminated soil and rhizosphere microorganisms play an important role in plant regulation. Nevertheless, little information is known about the variation of microbial metabolic activities and community structure in rhizosphere during phytoremediation. In this study, the rhizosphere soil microbial metabolic activities and community structure of Trifolium repensL. during Cd-contaminated soil phytoremediation, were analyzed by Biolog EcoPlate™ and high-throughput sequencing. The uptake in the roots of Trifolium repensL. grown in 5.68 and 24.23 mg/kg Cd contaminated soil was 33.51 and 84.69 mg/kg respectively, causing the acid-soluble Cd fractions decreased 7.3% and 5.4%. Phytoremediation significantly influenced microbial community and Trifolium repensL. planting significantly increased the rhizosphere microbial population, diversity, the relative abundance of plant growth promoting bacteria (Kaistobacter and Flavisolibacter), and the utilization of difficultly metabolized compounds. The correlation analysis among substrate utilization and microbial communities revealed that the relative abundance increased microorganisms possessed stronger carbon utilization capacity, which was beneficial to regulate the stability of plant-microbial system. Collectively, the results of this study provide fundamental insights into the microbial metabolic activities and community structure during heavy metal contaminated soil phytoremediation, which may aid in the bioregulation of phytoremediation.

Calcinated MIL-100(Fe) as a CO2 adsorbent to promote biomass productivity of Arthrospira platensis cells

In order to solve the problems of short residence time and low diffusion of CO₂ gas in microalgal solution, calcinated metal-organic framework MIL-100(Fe) were first used as CO₂ adsorbents to promote the growth of Arthrospira platensis cells by increasing carbon fixation. The adsorbent (MIL-100(Fe)-4 h) containing unsaturated metal sites, improved the conversion of CO₂ to dissolved inorganic carbon by 52.3% and concentration of HCO₃^- by 20.0% in culture medium, as compared to the medium without CO₂ adsorbent added. The increased HCO₃^- concentration facilitated carboxysome accumulation (increased to 21.7 times) to activate the photosynthetic Calvin cycle in Arthrospira cells. The increased cell growth rate promoted cell volume by 132% and knot length by 102%, while the fractal dimension of the cell surface decreased by 13.5%. The biomass productivity of Arthrospira cells cultivated with the CO₂ adsorbent MIL-100(Fe)-4 h remarkably increased by 81.9%.

Enhancing the pollutant removal performance and biological mechanisms by adding ferrous ions into aquaculture wastewater in constructed wetland

Aquaculture wastewater seriously threatens the human health. In this study, non-poisonous iron was added into constructed wetlands to purify aquaculture wastewater and the wastewater treatment performances of CWs were explored under the treatment conditions of different plant species and different dosages of ferrous ions. The optimal treatment conditions were experimentally determined as follows: 20 mg/L ferrous ions in CWs planted with Canna indica after 7-day operation, the removal efficiencies of TN, TP and COD were respectively 95 ± 1.9%, 77 ± 1.2% and 62 ± 2%. The improvements in the pollutant removal performance depended on biological mechanisms of plants and microorganisms. The optimal dosage of iron ions could adjust enzyme activities and functional amino acids. Specific functional bacteria (Paracoccus detected based on nirK genetic information and Hydrogenophaga detected based on pufM genetic information) were cultured and domesticated by iron ions. The functional bacteria promoted nitrogen and phosphorus removals.

Investigations on pyrolysis of microalgae Diplosphaera sp. MM1 by TG-FTIR and Py-GC/MS: Products and kinetics

In this work, pyrolysis characteristics and kinetics of microalgae Diplosphaera sp. MM1 cultivated in different mediums were investigated by TG-FTIR and Py-GC/MS. Harvested MM1s biomass varied with the changing in proximate and ultimate analyses presented different weight loss behaviors. The weight loss of MM1s cultivated in dairy and winery wastewater in main pyrolysis region was ~48.4 wt% and ~52.9 wt%, respectively, and both showed secondary weight loss after 570 °C. However, MM1 harvested from BG-11 medium exhibited maximum weight loss of ~63.5 wt% and no secondary weight loss. Further, the activation energies of MM1s harvested from dairy and winery wastewater (176.3 kJ/mol and 130.4 kJ/mol, respectively) were lower than that of BG-11medium (189.4 kJ/mol). The best mechanism function for MM1s pyrolysis was third-order f(α) = (1-α)³. Py-GC/MS results of MM1 cultivated in winery wastewater showed highest contents of C4-C10 and C11-C21 that characterized the carbon level of gasoline and diesel, respectively, which are the major components of bio-oils.

Influences of Iron Compounds on Microbial Diversity and Improvements in Organic C, N, and P Removal Performances in Constructed Wetlands

The effects of various combinations of iron compounds on the contaminant removal performance in constructed wetlands (CWs) were explored under various initial iron concentrations, contaminant concentrations, different hydraulic retention time (HRT), and different temperatures. The Combo 6 (nanoscale zero-valent iron combined with Fe³⁺) in CW treatments showed the highest pollutant removal performance under the conditions of C2 initial iron dosage concentration (total iron 0.2 mM) and I2 initial contaminant concentration (COD:TN:TP = 60 mg/L:60 mg/L:1 mg/L) in influent after 72-h HRT. These results were directly verified by two different microbial tests (Biolog test and high-throughput pyrosequencing) and microbial community analysis (principal component analysis of community-level physiological profile, biodiversity index, cluster tree, relative abundance at order of taxonomy level). Specific bacteria related to significant improvements in contaminant removal were domesticated by various combinations of iron compounds. Iron dosage was advised as a green, new, and effective option for wastewater treatment. Graphical Abstract .

Can algae-based technologies be an affordable green process for biofuel production and wastewater remediation?

Algae is a well-known organism that its characteristic is prominent for biofuel production and wastewater remediation. This critical review aims to present the applicability of algae with in-depth discussion regarding three key aspects: (i) characterization of algae for its applications; (ii) the technical approaches and their strengths and drawbacks; and (iii) future perspectives of algae-based technologies. The process optimization and combinations with other chemical and biological processes have generated efficiency, in which bio-oil yield is up to 41.1%. Through life cycle assessment, algae bio-energy achieves high energy return than fossil fuel. Thus, the algae-based technologies can reasonably be considered as green approaches. Although selling price of algae bio-oil is still high (about $2 L^-1) compared to fossil fuel's price of $1 L^-1, it is expected that the algae bio-oil's price will become acceptable in the next coming decades and potentially dominate 75% of the market.

Phosphate adsorption from aqueous solution by lanthanum-iron hydroxide loaded with expanded graphite

In this study, a novel adsorbent of expanded graphite loaded with lanthanum (III)-iron (III) hydroxide (EG-LaFe) was prepared for phosphate removal. The single factor of oscillating time, La/Fe molar ratio and total concentration of EG-LaFe were studied for optimization of preparation conditions. Effects of contact time, initial phosphate concentration, adsorption temperature and coexisting ions on the phosphate removal performance of EG-LaFe were investigated in detail. Adsorption kinetics and isothermal adsorption studies showed that the pseudo-second-order and the Langmuir model fitted the experimental data quite well. Thermodynamic analysis showed that the phosphate adsorption of EG-LaFe was spontaneous and endothermic. In addition, EG-LaFe exhibit high sorption selectivity toward phosphate over other coexisting ions. The phosphate adsorption mechanism was investigated by means of pH study, scanning electron microscopy and Fourier transform infrared spectroscopy. The results demonstrated that the probable mechanisms of phosphate adsorption on EG-LaFe were the replacement of surface hydroxyl groups (M-OH), electrostatic interaction and Lewis acid-base interaction.

Effects of iron and calcium carbonate on contaminant removal efficiencies and microbial communities in integrated wastewater treatment systems

In the paper, we explored the influences of different dosages of iron and calcium carbonate on contaminant removal efficiencies and microbial communities in algal ponds combined with constructed wetlands. After 1-year operation of treatment systems, based on the high-throughput pyrosequencing analysis of microbial communities, the optimal operating conditions were obtained as follows: the ACW10 system with Fe³⁺ (5.6 mg L^-1), iron powder (2.8 mg L^-1), and CaCO₃ powder (0.2 mg L^-1) in influent as the adjusting agents, initial phosphorus source (PO₄^3-) in influent, the ratio of nitrogen to phosphorus (N/P) of 30 in influent, and hydraulic retention time (HRT) of 1 day. Total nitrogen (TN) removal efficiency and total phosphorus (TP) removal efficiency were improved significantly. The hydrolysis of CaCO₃ promoted the physicochemical precipitation in contaminant removal. Meanwhile, Fe³⁺ and iron powder produced Fe²⁺, which improved contaminant removal. Iron ion improved the diversity, distribution, and metabolic functions of microbial communities in integrated treatment systems. In the treatment ACW10, the dominant phylum in the microbial community was PLANCTOMYCETES, which positively promoted nitrogen removal. After 5 consecutive treatments in ACW10, contaminant removal efficiencies for TN and TP respectively reached 80.6% and 57.3% and total iron concentration in effluent was 0.042 mg L^-1.

Effects of iron and calcium carbonate on the variation and cycling of carbon source in integrated wastewater treatments

Iron and calcium carbonate were added in wastewater treatments as the adjusting agents to improve the contaminant removal performance and regulate the variation of carbon source in integrated treatments. At different temperatures, the addition of the adjusting agents obviously improved the nitrogen and phosphorous removals. TN and TP removals were respectively increased by 29.41% and 23.83% in AC-100 treatment under 1-day HRT. Carbon source from dead algae was supplied as green microbial carbon source and Fe²⁺ was supplied as carbon source surrogate. COD concentration was increased to 30mg/L and above, so the problem of the shortage of carbon source was solved. Dead algae and Fe²⁺ as carbon source supplement or surrogate played significant role, which was proved by microbial community analysis. According to the denitrification performance in the treatments, dead algae as green microbial carbon source combined with iron and calcium carbonate was the optimal supplement carbon source in wastewater treatment.

Antiscaling efficacy of CaCO3and CaSO4on polyethylene glycol (PEG)-modified reverse osmosis membranes in the presence of humic acid: interplay of membrane surface properties and water chemistry

A specific polyethylene glycol (PEG)–humic acid–SO₄²⁻interaction results in promoted CaSO₄colloidal formation on PEG reverse osmosis membrane surfaces.

CO2 capture using limestone for cultivation of the freshwater microalga Chlorella sorokiniana PAZ and the cyanobacterium Arthrospira sp. VSJ

The present study reports a process wherein CO₂ is captured in the form of bicarbonates using calcium oxide and photosynthetically fixed into biomass. Microalgal cultures viz. Chlorella sorokiniana PAZ and Arthrospira sp. VSJ were grown in the medium containing bicarbonates. The rate of bicarbonate utilization by C. sorokiniana PAZ was higher when CO₂ trapped in the presence of 2.67mM calcium oxide than in the presence of 10mM sodium hydroxide and with direct addition of 10mM sodium bicarbonate. For Arthrospira sp. VSJ the bicarbonate utilization was 92.37%, 88.34% and 59.23% for the medium containing CaO, NaOH and NaHCO₃, respectively. Illumination of photosynthetically active radiation (PAR)+ultraviolet A radiation (UVA) enhanced the yield of C. sorokiniana PAZ and Arthrospira sp. VSJ by 1.3 and 1.8 folds, respectively. FTIR analysis revealed elevation in the biosynthesis of specific metabolites in response to the UVA exposure.

Microalgal cultivation with biogas slurry for biofuel production

Microalgal growth requires a substantial amount of chemical fertilizers. An alternative to the utilization of fertilizer is to apply biogas slurry produced through anaerobic digestion to cultivate microalgae for the production of biofuels. Plenty of studies have suggested that anaerobic digestate containing high nutrient contents is a potentially feasible nutrient source to culture microalgae. However, current literature indicates a lack of review available regarding microalgal cultivation with biogas slurry for the production of biofuels. To help fill this gap, this review highlights the integration of digestate nutrient management with microalgal production. It first unveils the current status of microalgal production, providing basic background to the topic. Subsequently, microalgal cultivation technologies using biogas slurry are discussed in detail. A scale-up scheme for simultaneous biogas upgrade and digestate application through microalgal cultivation is then proposed. Afterwards, several uncertainties that might affect this practice are explored. Finally, concluding remarks are put forward.