Immobilization on cotton cloth pieces is ideal for storage and conservation of microalgae

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.

2,4,6-trinitrotoluene (TNT) degradation by Indiicoccus explosivorum (S5-TSA-19)

2,4,6-trinitrotoluene (TNT), a nitro-aromatic explosive commonly used for defense and several non-violent applications is contributing to serious environmental pollution problems including human health. The current study investigated the remediation potential of a native soil isolate, i.e., Indiicoccus explosivorum (strain S5-TSA-19) isolated from collected samples of an explosive manufacturing site, against TNT. The survivability of I. explosivorum against explosives is indirectly justified through its isolation; thus, it is being chosen for further study. At a TNT concentration of 120 mg/L within an optimized environment (i.e., at 30 °C and 120 rpm), the isolate was continually incubated for 30 days in a minimal salt medium (MSM). The proliferation of the isolate and the concentration of TNT, nitrate, nitrite, and ammonium ion were evaluated at a particular time during the experiment. Within 168 h (i.e., 7 days) of incubation, I. explosivorum co-metabolically degraded 100% TNT. The biodegradation procedure succeeded the first-order kinetics mechanism. Formations of additional metabolites like 2,4-dinitrotoluene (DNT), 2,4-diamino-6-nitrotoluene (2-DANT), and 2-amino-4,6-dinitrotoluene (2-ADNT), were also witnessed. TNT seems to be non-toxic for the isolate, as it reproduced admirably in TNT presence. To date, it is the first report of Indiicoccus explosivorum, efficiently bio-remediating TNT, i.e., a nitro-aromatic compound via different degradation pathways, leading to the production of simpler as well as less harmful end products. Further, at the field-scale application, Indiicoccus explosivorum may be explored for the bioremediation of TNT (i.e., a nitro-aromatic compound)-contaminated effluents.

Role of Microalgae in Global CO2 Sequestration: Physiological Mechanism, Recent Development, Challenges, and Future Prospective

The rising concentration of global atmospheric carbon dioxide (CO2) has severely affected our planet’s homeostasis. Efforts are being made worldwide to curb carbon dioxide emissions, but there is still no strategy or technology available to date that is widely accepted. Two basic strategies are employed for reducing CO2 emissions, viz. (i) a decrease in fossil fuel use, and increased use of renewable energy sources; and (ii) carbon sequestration by various biological, chemical, or physical methods. This review has explored microalgae’s role in carbon sequestration, the physiological apparatus, with special emphasis on the carbon concentration mechanism (CCM). A CCM is a specialized mechanism of microalgae. In this process, a sub-cellular organelle known as pyrenoid, containing a high concentration of Ribulose-1,5-bisphosphate carboxylase-oxygenase (Rubisco), helps in the fixation of CO2. One type of carbon concentration mechanism in Chlamydomonas reinhardtii and the association of pyrenoid tubules with thylakoids membrane is represented through a typical graphical model. Various environmental factors influencing carbon sequestration in microalgae and associated techno-economic challenges are analyzed critically.

Study on aerobic degradation of 2,4,6-trinitrotoluene (TNT) using Pseudarthrobacter chlorophenolicus collected from the contaminated site

2,4,6-trinitrotoluene or TNT, a commonly used explosive, can pollute soil and groundwater. Conventional remediation practices for the TNT-contaminated sites are neither eco-friendly nor cost-effective. However, exploring bacteria to biodegrade TNT into environment-friendly compound(s) is an interesting area to explore. In this study, an indigenous bacterium, Pseudarthrobacter chlorophenolicus, strain S5-TSA-26, isolated from explosive contaminated soil, was investigated for potential aerobic degradation of TNT for the first time. The isolated strain of P. chlorophenolicus was incubated in a minimal salt medium (MSM) containing 120 mg/L TNT for 25 days at specified conditions. TNT degradation pattern by the bacterium was monitored at regular interval using UV-Vis spectrophotometry, high-performance liquid chromatography, and liquid chromatography mass spectrophotometric, by estimating nitrate, nitrite, and ammonium ion concentration and other metabolites such as 2,4-dinitrotoluene (DNT), 2-amino-4,6-dinitrotoluene (2-ADNT), and 2,4-diamino-6-nitrotoluene (2-DANT). It was observed that, in the presence of TNT, there was no reduction in growth of the bacterium although it multiplied well in the presence of TNT along with no considerable morphological changes. Furthermore, it was found that TNT degraded completely within 15 days of incubation. Thus, from this study, it may be concluded that the bacterium has the potential for degrading TNT completely with the production of non-toxic by-products and might be an important bacterium for treating TNT (i.e., a nitro-aromatic compound)-contaminated sites.

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.

A novel porous nickel-foam filled CO2 absorptive photobioreactor system to promote CO2 conversion by microalgal biomass

In order to solve problems associated with a short residence time and low conversion efficiency when CO₂ gas is aerated directly into raceway ponds, a novel porous nickel-foam filled CO₂ absorptive photobioreactor system was developed to promote CO₂ conversion to NaHCO₃ in a short time to improve photosynthesis of microalgal cells. Numerical simulation showed that the porous nickel-foam promoted the Na₂CO₃ solution radial velocity and CO₂ volume fraction in the CO₂ absorption reactor, which enhanced the reaction rate of CO₂ gas and soluble Na₂CO₃. The conversion efficiency of CO₂ gas to soluble NaHCO₃ gradually increased with an increasing nickel-foam pore diameter and a decreasing CO₂ gas outflow rate, while it first increased and then decreased with an increasing relative nickel-foam height in the CO₂ absorption reactor. The conversion efficiency from soluble NaHCO₃ to microalgal biomass first increased and then decreased with an increasing nickel-foam pore diameter (peaking at 2 mm) and relative height (peaking at 0.24); and CO₂ gas outflow rate (peaking at 2 L/min). The chlorophyll fluorescence measurements showed that a sufficient HCO₃^- supply promoted the quantum ratio used for electron transfer (from 0.19 to 0.23) and the maximum photochemical efficiency (from 0.48 to 0.52), resulting in an increased biomass growth rate (by 1.1 times) when the nickel-foam pore diameter increased from 0.1 to 2 mm.

Aerobic biodegradation of HMX by Planomicrobium flavidum

In this report, aerobic biodegradation of octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine or high melting explosive (HMX), a highly explosive chemical by Planomicrobium flavidum strain S5-TSA-19, an isolate from an explosive-contaminated soil, was investigated. The isolate S5-TSA-19 degraded 70% of HMX in 20 days during which time nitrite ion was produced with the subsequent formation of metabolites, viz. methylenedintramine and N-methyl-N,N'-dinitromethanediamine with molecular weights 136 Da and 149 Da, respectively. The degradation mechanism was found to follow first-order kinetics with a half-life of 11.55 days and formation of above intermediates indicate single nitrite elimination pathway. The proliferation of isolate S5-TSA-19 in the absence of nitramines indicates the cometabolic degradation of HMX. Isolate S5-TSA-19 can thus be used as futuristic microbe for degradation of HMX at explosive-contaminated site.