In-situ Disinfection and Algal Lipid Extraction using Ozonation in Novel Microbubble Bioreactor for Biofuel Production

The scaling up and downstream processing costs of biodiesel from microalgae are major concerns. This study focuses on developing a new method by integrating ozone-rich microbubbles in both the production of microalgae and in downstream processes such as biomass harvesting and lipid extraction. A bacterial contaminant of a green algal (Dunaliella salina) culture was successfully screened, isolated and identified using 16S rRNA gene sequencing as a member of the Halomonas genus (gram-negative). Ozonation of mixed cultures of D. salina and Halomonas for 10 minutes at 8 mg/L reduced the bacterial contaminant without harming the microalgal cells. The sterilisation efficiency reached 66% after 5 minutes and increased to 93% after 10 minutes of ozonation. The algal cell growth performance (biomass concentration) was decreased by over 50% at 10% (v/v) contaminant concentration. Ozonation for 10 minutes at the beginning of the experiment resulted in a biomass reduction of 28.6%, which suggests that ozonation at the beginning of experiment can control the contamination. The optimum values for three parameters (culture media volume, ozone concentration and ozonation time) suggested by the statistical software were 30.63 mL, 8.20 mg/L and 37.7 min, respectively. Harvesting of D. salina cells through microflotation resulted in a 93.4% recovery efficiency. Ozonation of the harvested microalgae for 40 minutes produced three main saturated compounds [2-pentadecanone 6, 10, 14-trimethyl; n-hexadecanoic acid (palmitic acid); and octadecanoic acid (stearic acid)] that consist of 16 to 18 carbons. The main products increased significantly around 156%, 88.9% and 150% for 2-pentadecanone, 6, 10, 14-trimethyl; palmitic acid and stearic acid, respectively when the temperature was increased (60 ˚C), and smaller bubbles (generated by a fluidic oscillator) were introduced during the extraction process. By integrating microbubbles and ozonation into an airlift-loop bioreactor-processing system, this thesis describes a microbubble photobioreactor that delivers in-situ disinfection with microflotation harvesting and lipid extraction in an easily scalable and energy-efficient process

Revealing the potential of xylanase from a new halophilic microbulbifer sp. CL37 with paper de-inking ability

Paper de-inking is one of the critical processes in pulp and paper industry as it is ecofriendly and energy saving. This process requires microbial enzymes such as xylanases with ability to withstand harsh bioprocess conditions. Microbulbifer is a halophilic genus with ability to produce hydrolytic enzymes that could be applied in the biotechnological industry. So far, none of the xylanases from this genus have been studied, particularly in paper de-inking process. Therefore, in this study, the xylanase of a new halophilic bacterium, Microbulbifer sp. strain CL37, was characterized. Strain CL37 produced maximum amount of xylanase at 14th hour of incubation at 30 °C. The xylanase demonstrated optimal activity at 70 °C and pH 7. The xylanase was stable at wide range of NaCl (0–14%, w/v), in the presence of Al3+, Ca2+, Co2+, Cu+, Cu2+, Fe2+, Fe3+, Mn2+, Zn2+, acetone, chloroform, ethanol, sodium deoxycholate, Triton X-100, Tween 20, 40, 60, and 80, indicating that it is a halotolerant enzyme with high stability in various additives. The xylanase also demonstrated its ability to de-ink paper with considerably high efficiency (159%) as compared to other strains. The valuable characteristics possessed by xylanase of strain CL37 could potentially benefit to de-inking process in paper industry

Cross-kingdom regulation by plant microRNAs provides novel insight into gene regulation

microRNAs (miRNAs) are well known as major players in mammalian and plant genetic systems that act by regulating gene expression at the post-transcriptional level. These tiny molecules can regulate target genes (mRNAs) through either cleavage or translational inhibition. Recently, the discovery of plant-derived miRNAs showing cross-kingdom abilities to regulate mammalian gene expression has prompted exciting discussions among researchers. After being acquired orally through the diet, plant miRNAs can survive in the digestive tract, enter the circulatory system, and regulate endogenous mRNAs. Here, we review current knowledge regarding the cross-kingdom mechanisms of plant miRNAs, related controversies, and potential applications of these miRNAs in dietary therapy, which will provide new insights for plant miRNA investigations related to health issues in humans

Cultivation of marine microalgae, Nannochloropsis sp. in macro-bubbles photobioreactor system

Oil production from microalgae may be more effective, leaving a smaller environmental footprint and avoiding competition for arable land or biodiversity ecosystems. Present outdoor and open algae cultivation systems and lipid induction methods, on the other hand, need to be significantly improved and are vulnerable to being contaminated by other algae or algal grazers. The cultivation system for the current indoor bioreactor, however, is expensive due to its materials. Closed-culture systems (photobioreactor type) have high production but not cost-effective for maintenance, where else, opened-culture systems have contamination issues resulting in lower productivity. This study focuses on cultivating microalgae using a contemporary design of a closed system using an airlift loop photobioreactor with a draft tube placed in the middle of the reactor and using a cheaper material (autoclavable polycarbonate material). The cultivation optimisation of Nannochloropsis sp. was carried out at a different condition of photobioreactor system with a range of aeration rate, light intensity, and inoculum concentration. The best growth performance was in a macro-bubble column system with 0.211 g/mL and a 0.9 L/min aeration rate that produced a maximum cell dry weight of 0.288 g/mL of algal biomass. For the light intensity parameter, the best growth performance was at 3000 lux, with a dry cell weight of 0.211 g/mL followed by inoculum concentration at 15% v/v that produced the highest maximum dry cell weight of 0.213 g/mL of algal biomass. In this study, a low-cost indoor photobioreactor system using cheap autoclavable material has been tested and shown a promising result, thus has the potential to be commercialised in the future

In-situ sterilization of microalgae photobioreactor via ozone-rich macrobubbles

Aseptic technique plays a critical role in determining high volumes of microalgae biomass during the cultivation stage as the presence of a contaminant is one of the limiting factors. This study focuses on developing an energy-efficient method in sterilizing the 2 L microalgae photobioreactor. Initially, the seawater bacterial contaminant was successfully screened, isolated and identified as Kurthia gibsonii. The photobioreactor sterilization using ozonolysis was optimized using one factor at a time (OFAT), with 3 parameters studied: ozone aeration rate (0.5 L/min, 1.0 L/min and 1.5 L/min), bacterial culture volume (1.0 L, 1.5 L, and 2.0 L) and ozonation time (maximum of 180 minutes with 30-minute intervals). The ozonation technique at optimum condition reduced the contaminants up to 7 log reductions. The initial cells concentration in 1 L culture containing 6.73×107 cells/ml was reduced to 7 cells/ml after being ozonated for 180 min. The morphology study of the bacteria before and after ozonation (at 1000X magnification) confirmed that ozonation shattered the cells into small pieces. This study reveals the possibility of replacing energy-intensive sterilization techniques such as the autoclave method with ozonolysis. Ozonation method is more energy efficient, with a total 1.26 kW energy used during the sterilization process as compared to autoclaved method with 3.565 kWh. The study proves that the ozonation method is energy efficient, cheaper and easily applied to a larger industrial scale as well

Harvesting of freshwater microalgae, Arthrospira sp. using flocculation method

Arthrospira platensis is a well-known microalgae species that is widely used as the protein and vitamin supplements to aquatic organisms, as well as a complementary dietary ingredient for human. Efficient biomass recovery or harvesting of different algal species is nevertheless a vital bottleneck for a large-scale biorefinery process. Due to its high-efficiency, cost-effectiveness and scalability, chemical flocculation was performed to harvest the biomass production of Arthrospira platensis. In the present study, the flocculation was conducted using three chemical flocculants: chitosan, aluminium sulphate, and copper (I) chloride in hydrochloric acid. The harvesting was performed and optimised using one factor at a time (OFAT) and it was found that chitosan was the most effective flocculant, with 99.96% flocculation efficiency using 90 mg/L dosages while the settling time was above 80% efficiency at the first 5th minute and remained constant until the 60th minute of the experiment. Furthermore, chitosan was studied as a biodegradable polymer and non-toxic coagulant, which may be less harmful than other chemicals

Effects of BG11, SKM and MKM culture media on optical density of Spirulina platentis cultivation

Spirulina platensis is blue-green microalgae and well known due to its unique nutritional quality that has attracted a great deal of popularity in health products. In this research study, the culture medium uses BG11, SKM and MKM. All these alternative medium recipes are widely used and reported online. However, the suitability of the medium depending on the environment and the strain used. This study will analyse their effect on S. platensis by using growth parameters and determining the best culture medium for extensive cultivation. The optical density (OD) is one of the most critical parameters in Spirulina cultivation and recorded to measure the growth performance of S. platensis. In this study, the cultivation was conducted in 1 L conical flasks. The growth rate of S. platensis in the culture mediums observed for ten days of cultivation. Besides that, the initial pH also was recorded and monitored. The growth estimation by optical density was measured by using a spectrophotometer at 620 nm wavelength. The finding shows that MKM is the most suitable culture medium for cultivating S. platensis due to the best element compositions. The results showed the alternative low-cost culture medium, which was MKM, had been successfully formulated to cultivate S. platensis

A review of bacterial antibiotic resistance genes and their removal strategies from wastewater

Purpose of review: This review is intended to address the issues of unsafe disposal of antibiotics from various sources to the environment, its incomplete degradation, the resulting antibiotic resistance properties on microorganisms exposed to these antibiotics as well as some currently available techniques to remove both the antibiotic-resistant bacteria (ARBs) and antibiotic-resistant genes (ARGs) from water and wastewater systems. Recent findings: There is a linear correlation between the concentration of antibiotics in wastewater and the emergence of ARBs and the presence of ARGs. Wastewater treatment plant (WWTP) remains as one of the primary sources for ARB and ARG, even though the occurrence of ARBs and ARGs has also been reported in environment with no anthropogenic impact. Conventional removal techniques are available together with newer approaches that promises higher ARBs and ARGs removal efficiencies. Use of bioinformatic tools such as plasmidome is important to ensure sufficient information on ARGs, which may be directly mobilized and transferred to pathogens, can be obtained and analyzed. Summary: This review highlights the effects of continuous exposure to ARBs and ARGs present in the environment, notably wastewater, to human health. Various sources of antibiotics, classes of ARBs, and types of ARGs are adequately covered including highlights on recent reports from different countries. Conventional and newer approaches to remove ARBs and ARGs from wastewater were also elaborated to further assist reader’s understanding on the subject matter discussed