Modified mussel shell powder for microalgae immobilization to remove N and P from eutrophic wastewater

Promoting microalgal biofilm formation by crushed oyster shell-hydroxyapatite layer on micropatterned aluminum coating for heavy metal ions removal

Microalgal biomass has shown inspiring potential for the heavy metal removal from wastewater, and forming microalgal biofilm is one of the sustainable methods for the microalgal biomass production. Here we report the formation of microalgal biofilm by accelerated colonization of typical algae Chlorella on thermal sprayed aluminum (Al) coatings with biologically modified surfaces. Micro-patterning surface treatment of the Al coatings promotes the attachment of Chlorella from 6.31 % to 17.51 %. Further enhanced algae attachment is achieved through liquid flame spraying a bioactive crushed oyster shell-hydroxyapatite (CaCO3-HA) composite top layer on the micropatterned coating, reaching 46.03-49.62 % of Chlorella attachment ratio after soaking in Chlorella suspension for 5 days. The rapidly formed microalgal biofilm shows an adsorption ratio of 95.43 % and 85.23 % for low concentration Zn2+ and Cu2+ in artificial seawater respectively within 3 days. Quick interaction has been realized between heavy metal ions and the negatively-charged extracellular polymeric substances (EPS) matrix existing in the biofilm. Fourier transform infrared spectroscopy (FTIR) results indicate that both carboxyl and phosphoryl groups of biofilms are crucial in the adsorption of Cu2+ and the adsorption of Zn2+ is due to the hydroxyl and phosphate groups. Meanwhile, the biofilm could act as a barrier to protect Chlorella against the attack of the heavy metal ions with relatively low concentrations in aqueous solution. The route of quick cultivating microalgal biofilm on marine structures through constructing biological layer on their surfaces would give insight into developing new techniques for removing low concentration heavy metal ions from water for environmental bioremediation.

Bidirectional Enhancement of Nitrogen Removal by Indigenous Synergetic Microalgal-Bacterial Consortia in Harsh Low-C/N Wastewater

Conventional microalgal-bacterial consortia have limited capacity to treat low-C/N wastewater due to carbon limitation and single nitrogen (N) removal mode. In this work, indigenous synergetic microalgal-bacterial consortia with high N removal performance and bidirectional interaction were successful in treating rare earth tailing wastewaters with low-C/N. Ammonia removal reached 0.89 mg N L-1 h-1, 1.84-fold more efficient than a common microalgal-bacterial system. Metagenomics-based metabolic reconstruction revealed bidirectional microalgal-bacterial interactions. The presence of microalgae increased the abundance of bacterial N-related genes by 1.5- to 57-fold. Similarly, the presence of bacteria increased the abundance of microalgal N assimilation by 2.5- to 15.8-fold. Furthermore, nine bacterial species were isolated, and the bidirectional promotion of N removal by the microalgal-bacterial system was verified. The mechanism of microalgal N assimilation enhanced by indole-3-acetic acid was revealed. In addition, the bidirectional mode of the system ensured the scavenging of toxic byproducts from nitrate metabolism to maintain the stability of the system. Collectively, the bidirectional enhancement system of synergetic microalgae-bacteria was established as an effective N removal strategy to broaden the stable application of this system for the effective treatment of low C/N ratio wastewater.

Quorum Sensing as a Trigger That Improves Characteristics of Microbial Biocatalysts

Quorum sensing (QS) of various microorganisms (bacteria, fungi, microalgae) today attracts the attention of researchers mainly from the point of view of clarifying the biochemical basics of this general biological phenomenon, establishing chemical compounds that regulate it, and studying the mechanisms of its realization. Such information is primarily aimed at its use in solving environmental problems and the development of effective antimicrobial agents. This review is oriented on other aspects of the application of such knowledge; in particular, it discusses the role of QS in the elaboration of various prospective biocatalytic systems for different biotechnological processes carried out under aerobic and anaerobic conditions (synthesis of enzymes, polysaccharides, organic acids, etc.). Particular attention is paid to the biotechnological aspects of QS application and the use of biocatalysts, which have a heterogeneous microbial composition. The priorities of how to trigger a quorum response in immobilized cells to maintain their long-term productive and stable metabolic functioning are also discussed. There are several approaches that can be realized: increase in cell concentration, introduction of inductors for synthesis of QS-molecules, addition of QS-molecules, and provoking competition between the participants of heterogeneous biocatalysts, etc.).

Immobilized microalgal system: An achievable idea for upgrading current microalgal wastewater treatment

Efficient wastewater treatment accompanied by sustainable "nutrients/pollutants waste-wastewater-resources/energy nexus" management is acting as a prominent and urgent global issue since severe pollution has occurred increasingly. Diverting wastes from wastewater into the value-added microalgal-biomass stream is a promising goal using biological wastewater treatment technologies. This review proposed an idea of upgrading the current microalgal wastewater treatment by using immobilized microalgal system. Firstly, a systematic analysis of microalgal immobilization technology is displayed through an in-depth discussion on why using immobilized microalgae for wastewater treatment. Subsequently, the main technical approaches employed for microalgal immobilization and pollutant removal mechanisms by immobilized microalgae are summarized. Furthermore, from high-tech technologies to promote large-scale production and application potentials in diverse wastewater and bioreactors to downstream applications lead upgradation closer, the feasibility of upgrading existing microalgal wastewater treatment into immobilized microalgal systems is thoroughly discussed. Eventually, several research directions are proposed toward the future immobilized microalgal system for microalgal wastewater treatment upgrading. Together, it appears that using immobilization for further upgrading the microalgae-based wastewater treatment can be recognized as an achievable alternative to make microalgal wastewater treatment more realistic. The information and perspectives provided in this review also offer a feasible reference for upgrading conventional microalgae-based wastewater treatment.

Adsorption of Pyrethroids in Water by Calcined Shell Powder: Preparation, Characterization, and Mechanistic Analysis

Pyrethroids are common contaminants in water bodies. In this study, an efficient mussel shell-based adsorbent was prepared, the effects of factors (calcination temperature, calcination time, and sieved particle size) on the pyrethroid adsorption capacity from calcined shell powder were investigated via Box-Behnken design, and the prediction results of the model were verified. By characterizing (scanning electron microscopy, X-ray diffraction, Fourier infrared spectroscopy, and Brunauer-Emmett-Teller measurements) the adsorbent before and after the optimized preparation process, the results showed that calcined shell powder had a loose and porous structure, and the main component of the shell powder under optimized condition was calcium oxide. The adsorption mechanism was also investigated, and the analysis of adsorption data showed that the Langmuir, pseudo second-order, and intra-particle diffusion models were more suitable for describing the adsorption process. The adsorbent had good adsorption potential for pyrethroids, the adsorption capacity of the two pesticides was 1.05 and 1.79 mg/g, and the removal efficiency was over 40 and 70% at the maximum initial concentration, respectively.

Utilization of cockle shell powder as an adsorbent to remove phosphorus-containing wastewater

The paper demonstrates the capability of using cockle shells as an adsorbent for phosphorus removal from simulated petrochemical wastewater, focusing on the actual condition of the petrochemical facultative pond. In this study, the physicochemical properties of shell powder were determined, such as the functional groups, surface morphology, crystalline structure, and surface area using FTIR, SEM, EDX, XRD, and BET. It was observed that the optimum conditions for effective phosphorus removal are under the presence of rotational speed (125 rpm), higher dosage (7 g/L), and larger surface area (smaller particle size) of the shell powder. Fine powder achieved up to 52.27% of phosphorus removal after 40 min compared to coarse powder which could only give 16.67% removal. Additionally, calcined shell powder demonstrated a higher phosphorus removal rate, i.e., up to 62.37%, compared to raw shell powders. The adsorption isotherm was studied using Langmuir and Freundlich models, but the isothermal data fit better for the Freundlich model (R² = 0.9836). Overall, this study has successfully generated a greener and low-cost adsorbent.

Corncob biocarriers with available carbon release for Chlamydopodium sp. microalgae towards enhanced nitrogen removal from low C/N rare earth element tailings (REEs) wastewater

Low nitrogen (N) removal efficiency limits the potential of microalgae technology for the treatment of high nitrogen and low carbon rare earth tailings (REEs) wastewater. In this study, waste corncob was utilized as a biocarrier immobilizing Chlamydopodium sp. microalgae to realize high-efficient treatment of the REEs wastewater. In only 2.5 d, corncob-immobilized microalgae allowed the residual concentrations of N lower than the emission standards, and ammonia nitrogen (NH4+-N) removal rate is 83.3 mg L-1·d-1, total inorganic nitrogen (TIN) removal rate is 86.7 mg L-1·d-1, which was 18.5 times that of the previously-reported microalgae (4.68 mg L-1·d-1). Compared with other microalgae immobilization carriers, corncob possesses the ability to release available carbon sources for microalgae. Composition analysis and sugar verification experiments showed that the main content of TOC released by corncob was monosaccharide, and in a certain range, the removal rate of N was positively correlated with the TOC concentration. The utilization of biomass wastes with dual functions as biological carriers has great potential to improve the performance of microalgae, and is conducive to the development of engineering applications.

Hierarchical porous mussel shells as soil amendment for oil spill remediation

In this work, a new type of micromesoporous substance was prepared with fatty alcohol-polyoxyethylene ether (AEO) surfactant freezing penetration and pyrolysis using shells as raw materials. The obtained material exhibited good adsorbability and could be added to oil-contaminated soil to adsorb the pollutant, which resulted in the regeneration of the initially polluted soil. It was determined that the main component of the developed substance was CaCO₃. Importantly, the conducted experiments revealed that the obtained mussel micromesoporous material displayed certain adsorption effects toward petroleum hydrocarbons in a diesel solution. Moreover, it was found that chemical adsorption was more optimal than physical adsorption. The soil remediation effect was the best when the content of the mussel micromesoporous material in the soil was 400 g/kg. Under these conditions, the removal rate of petroleum hydrocarbon was established at 49.38%. This study indicated that micromesoporous material has great potential in the application of oil contaminated soil remediation.

Enhanced chlortetracycline removal by iron oxide modified spent coffee grounds biochar and persulfate system

Chlortetracycline (CTC) is a tetracycline derivative antibiotic that has been widely used in the livestock industry for prophylactic and therapeutic purposes. Effective measures should be taken to decrease the environmental risks associated with CTC-rich waste. Biochar produced by biomass waste showed great potential for organic contaminants removal by adsorption and catalytic degradation. This study prepared iron oxide-modified coffee grounds biochar (CGF) at different temperatures for enhanced CTC removal by adsorption and degradation. The main mechanism for CTC removal was found to be electrostatic interaction. In addition, pore diffusion, hydrogen bonds, and π-π bonds also contributed to CTC adsorption. Maximum CTC adsorption capacity was 223.63 mg/g for CGF800 (CGF prepared at 800 °C pyrolysis). The free radical content of CGF600 (CFG prepared at 600 °C pyrolysis) was higher than CGF800, and there were no significant advantages in using biochar prepared at a higher temperature for persulfate activation. The ion mass-to-charge ratio (M/z) is used to describe the ratio of mass to charge of an ion or peak, which can infer compound structure. The structure of CTC degradation products was analyzed by UPLC-MS, and the M/z values were determined as 444, 273, and 154. Thus, pyrolysis of coffee grounds at higher temperatures increased CTC adsorption capacity, and CGF can indirectly assist in CTC degradation by persulfate activation.

Effect of filamentous algae in a microalgal-bacterial granular sludge system treating saline wastewater: Assessing stability, lipid production and nutrients removal

In this study modified microalgal-bacterial granular sludge (MBGS) was constructed and employed to compare the performance for treating 1%-5% saline wastewater with aerobic granular sludge (AGS). Filamentous algae were found to flourish at 1% salinity when nutrients were temporarily restricted to low level (COD 0, N 10 mg/L, P 0.5 mg/L). A significant improvement of granule stability was detected as the integrity coefficients of MBGS was only 0.12-0.24 rather than 0.19-0.48 of AGS under 1%-5% salinities, which reduced the risk of particle disintegration. Filamentous algae including Leptolyngbya and Geitlerinema occupied 91.2% of identified algae, and were beneficial for enhancing the biomass content and lipid production to about 1.27-1.37, 3.1-5.0 times than AGS. The MBGS had best nitrogen and phosphorus removal efficiencies of 93.4% and 64.6% at 1% salinity, and showed higher resistance to 3%-5% salinities. This study could provide meaningful information for using this modified MBGS technology in practice.

Rice vinasse treatment by immobilized Synechococcus pevalekii and its effect on Dunaliella salina cultivation

The development of new strategies in microalgal studies represents an outstanding opportunity to mitigate environmental problems coupled with biomass production at a reduced cost. Here we present a combined bioprocess for the treatment of rice vinasse using immobilized cyanobacteria Synechococcus pevalekii in alginate beads followed by the use of the treated vinasse as a culture medium for Dunaliella salina biomass production. Cyanobacterial-alginate beads showed a chlorophyll a production of 0.68 × 10^-3 mg bead^-1 and a total carotenoid production of 0.64 × 10^-3 mg bead^-1. The first step showed a decrease in nitrate (91%), total solids (29%), and ions. Addition of treated vinasse into D. salina cultivation resulted in a significant increase in cell replication of about 175% (optimized cultivation). The use of natural seawater drastically reduced the medium cost to US$4.75 per m³ and the addition of treated vinasse has the potential to reduce it even more (up to 69%). This study not only provides an insight on the use of cyanobacteria for rice vinasse treatment but also demonstrates a promising lower-cost medium for marine microalgal biomass production with biotechnological purposes.

New developments in biological phosphorus accessibility and recovery approaches from soil and waste streams

Phosphorus (P) is a non-renewable resource and is on the European Union's list of critical raw materials. It is predicted that the P consumption peak will occur in the next 10 to 20 years. Therefore, there is an urgent need to find accessible sources in the immediate environment, such as soil, and to use alternative resources of P such as waste streams. While enormous progress has been made in chemical P recovery technologies, most biological technologies for P recovery are still in the developmental stage and are not reaching industrial application. Nevertheless, biological P recovery could offer good solutions as these technologies can return P to the human P cycle in an environmentally friendly way. This mini-review provides an overview of the latest approaches to make P available in soil and to recover P from plant residues, animal and human waste streams by exploiting the universal trait of P accumulation and P turnover in microorganisms and plants.

Enhanced adsorption of tetracycline by an iron and manganese oxides loaded biochar: Kinetics, mechanism and column adsorption

A Fe/Mn oxides loaded biochar (FeMn-BC) was prepared to enhance the adsorption of tetracycline (TC). γ-Fe₂O₃ and MnO₂ were assigned to the Fe and Mn oxides, respectively. The enhanced adsorption of TC was dominated by the loaded γ-Fe₂O₃ and MnO₂. According to Akaike-Information-Criteria evaluation, Elovich kinetic and Langmuir isotherm models could best describe the adsorption with a maximum capacity of 14.24 mg/g. During adsorption process, the γ-Fe₂O₃ and MnO₂ hydrolyzed into hydroxides (FeOOH and MnOOH) which acted as bases to complex with TC^2- ion under alkaline condition (pH = 11). After the adsorption, the concentrations of leached Fe and Mn could meet the requirements PRC standards GB13456-2012 and GB8978-1996, respectively. The FeMn-BC had ~24% on TC removal (initial concentration of 20 mg/L) after four-cycles regeneration. The FeMn-BC was also available for TC adsorptions in column tests and actual wastewater.

An insight into the structure, composition and hardness of a biological material: the shell of freshwater mussels

The shell of the freshwater mussel (Mollusca: Bivalvia) is a composite biological material linked with multifunctional roles in sustaining ecosystem services. Apart from providing mechanical strength and support, the shell is an important site for adherence and growth of multiple types of algae and periphyton. Variations in the shell architecture are observed in the mussels both within a species and among different species. Considering the prospective utility of the shell of the freshwater mussels as a biological material, an assessment of the shell characteristics was accomplished using Corbicula bensoni and Lamellidens marginalis as model species. The calcium carbonate (CaCO3) content of the shells, physical features and mechanical strength were assessed along with the morphometric analysis. The CaCO3 content of the shell (upto 95% to 96% of the shell weight) of both the mussels was positively correlated with the shell length, suggesting increased deposition of CaCO3 in shells with the growth of the species. The cross sectioned views of FE-SEM images of the shells exhibited distinct layered structure with external periostracum and inner nacreous layer varying distinctly. In the growing region, the growth line was prominent in the mussel shells revealed through the FESEM images. In addition XRD, FTIR and EDS studies on the mussel shells confirmed the existence of both aragonite and calcite forms of the calcium carbonate crystals with the incidence of various functional groups. The mechanical strength of the mussel shells was explored through nanoindentation experiments, revealed significant strength at the nanoparticle level of the shells. It was apparent from the results that the shell of the freshwater mussel L. marginalis and C. bensoni qualify as a biological material with prospective multiple applications for human well-being and sustaining environmental quality.

Nitrogen and phosphorus removals by the agar-immobilized Chlorella sacchrarophila with long-term preservation at room temperature

Immobilized microalgae have great potential on the nutrient removal during wastewater treatment. However, their applications are challenged by how to cost-effectively maintain and preserve large number of viable and active microalgal cells. In this study, the cells of Chlorella sacchrarophila were immobilized in the agar containing with algal nutrient, encapsulated in a transparent package and preserved at room temperature. After the preservation for 200 days, microalgal cells with viability of 47-52% were maintained and could be quickly revived after the cultivation in fresh algal medium. Based on the agar-immobilized microalgae, the NH₄⁺-N and PO₄^3--P were efficiently removed from batch and continuous cultures, with the highest removal efficiencies ranging from 96% to 99% were observed. Even being recycled for eight times, the agar-immobilized microalgae were still able to remove 94% of NH₄⁺-N and 66% of PO₄^3--P. Moreover, more than 60% of the nutrient removal efficiency was determined even the agar-immobilized microalgae being preserved for 120 days at room temperature. This work provides a simple, cost-effective and practicable method for the long-term preservation of microalgae at room temperature, which makes the application of microalgal species on the nutrient removal during wastewater treatment more convenient and useful.

Optimization of alginate bead size immobilized with Chlorella vulgaris and Chlamydomonas reinhardtii for nutrient removal

Photo-bioreactor experiments using three different size beads (2.0, 3.5, and 5.0 mm) immobilized with two different types of microalgae namely Chlorella vulgaris and Chlamydomonas reinhardtii were conducted to evaluate the nutrient removal efficiency. The highest nutrient removal was obtained at gel bead pore size of 3.5 mm for both species of C. vulgaris and Ch. reinhardtii. 95% removal of T-N and complete reduction of T-P were achieved within 3 stages of treatment in photo-bioreactors containing 20% algal bead volume fraction. Moreover, the results observed by confocal laser scanning microscopy (CLSM) using SYTOX red dye and SYTOX green dye in alginate beads indicated that the effective depth of C. vulgaris and Ch. reinhardtii was about 3.6 mm and 3.0 mm, respectively. This optimized cell immobilization technology would accelerate the nutrient uptake rate of microalgae for improving efficiency of wastewater treatment systems.

Immobilizing Microcystis aeruginosa and powdered activated carbon for the anaerobic digestate effluent treatment

The environment pollution caused by livestock anaerobic digestate effluent (ADE) is becoming increasingly severe recently. In this study, immobilized technology, embedding Microcystis aeruginosa (MA) and powdered activated carbon (PAC) with sodium alginate (SA), was employed to investigate the removal performance of nitrogen (N), phosphorus (P) and dissolved organic matter (DOM) in the treatment of ADE solution. Initially, orthogonal experiment was carried out to achieve the optimal conditions of the beads fabrication with the concentration of imbedding agents (PAC-SA) of 5% (w/w) and the ratio of microalgae and imbedding agents was 1:1 (v/v). The results indicated that the total nitrogen (TN), total phosphorus (TP) and total organic carbon (TOC) can be efficiently removed under the optimal operation conditions, with average removals of 91.88 ± 2.91% in TN, 98.24 ± 0.12 in TP and 78.31 ± 1.57% in TOC, respectively. Moreover, the fluorescence excitation-mission matrix (EEM) results illustrated that IMA-PAC beads joined system can efficiently diminish the concentrations of protein-like compounds and humic substances. Therefore, the organic contaminants and nutrients (i.e. N and P) can be efficiently removed in IMA-PAC beads joined system, which would contribute to developing new strategies for the treatment of ADE solution and nutrient recycle.

Removal of methylene blue dye from aqueous solutions by adsorption on levulinic acid-modified natural shells

This study has developed an innovative and environmentally friendly approach for the removal of methylene blue (MB) dye by natural shells (NShs) chemically modified with levulinic acid (LA). Almond shell (ASh), walnut shell (WSh), and apricot kernel shell (AKSh) were used as waste fillers. The adsorption behavior of MB onto the biosorbents was investigated with respect to parameters such as sorbent dosage (0.4-6 g/L), pH (3-10), initial dye concentration (10-500 mg/L), and temperature (25-65 °C). The biosorbents were analyzed by scanning electron microscopy (SEM), X-ray diffraction (XRD), and Fourier transform infrared (FTIR) analysis. The isotherm and kinetic adsorption data can be said to fit the Freundlich isotherm model and the pseudosecond-order model, respectively. The maximum adsorption capacity (q_max) of LA-modified walnut shell (LA-WSh), almond shell (LA-ASh), and apricot kernel shell (LA-AKSh) calculated by the Langmuir equation at 25 °C was 294.1, 270.2, and 180.0 mg/g, respectively. The results of thermodynamic analysis showed that adsorption was feasible, endothermic, and spontaneous.