Search

Microalgae have gained attention as feedstock for value-added chemicals production. The extraction potential of four different organic solvents such as methanol, chloroform, dimethyl sulphoxide (DMSO) and acetone was assessed for obtaining chlorophyll (Chl a and Chl b), and total carotenoids over 48 h at every 4 h intervals utilizing mixed microalgal consortium. Maximum of 4.62 μg/ml of Chl a, 4.78 μg/ml of Chl b and 1.76 μg/ml of total carotenoids were obtained with DMSO, methanol and 80% acetone after 16 h, 40 h and 36 h respectively. Maximum astaxanthin yield of 0.82 μg/ml was obtained with DMSO after 20 min, which was found to decline on further increase in extraction time. Supplementing the solvent extraction process with microwave and ultrasound increased the pigment yield. The study would facilitate utilization of natural microalgal pigments as an eco-friendly and economical alternative for synthetic colorants used in the feed and agricultural industries.

Algal biofuels have received wide attention in recent years for its potential to reduce the dependence on conventional fossil fuels. Despite the portrayed advantages of high growth rate, carbon sequestration and waste remediation; large scale application of microalgal biofuels is still lacking because of the lower percentage of extractable lipids obtained from the harvested biomass. Thus, there is a substantial impetus to analyse the strategies for enhancing the lipid profile and yield to improve the microalgal biofuel quality as well as to reduce the costs incurred at field scale. Several biochemical and molecular strategies to increase the algal lipid accumulation has gained huge scientific interest in recent years and have opened up new avenues for algal biorefinery. However, the time and cost involved as well as the ecological risks associated with real-time applications often restricts their utilization. The present review gathers a compendium of the key milestones associated with the recent approaches of biochemical, genetic and metabolic engineering for lipid quantity and quality enhancement. Biochemical and engineering aspects of coercing the cells to environmental stress and altering the mode of nutrition has been elucidated. The advancements in genetic and metabolic engineering, the associated risk factors and the future perspectives have been highlighted. Strategic integration of the bioprocess and biomolecular techniques to explore its synergistic impact to rationally engineer microalgae with improved triacylglycerols has been emphasized. Assessment of the long term risks associated herewith can be used to avert the challenges, making algal biofuels a commercial reality in future.

Although urine constitutes less than 1% volume of the total wastewater, it adds up 50–80% of the nutrient load [Phosphates (PO43−) and Nitrates (NO3−), Ammonium (NH4+)] in wastewater treatment plants (WWTPs). Recovery of Phosphorous (P) and Nitrogen (N) from urine diminishes the eutrophication impact as well it could act as a sustainable source of P by lessening dependence on finite phosphorite reservoirs. Due to its environmental (carbon-negative process) and economic (produced from waste) value, biochar is gaining the researcher’s attention in recent years. Many studies are ongoing to introduce novel structures and modifications in the surface properties of biochar for efficient adsorption of P and N. Direct application of urine as fertilizer has been discouraged due to various hygienic pitfalls further forced to explore the alternative nutrient recovery methods. This review article explores the nutrient recovery paradigms from source-separated human urine for abridging the nutrient gap between wastewater treatment and agricultural productivity using pristine/engineered biochar. The influencing factors for P and N’s adsorption process by biochar and its detailed mechanisms have been outlined. Further, it deliberates the possible strategies of engineering the biochar to enhance the recovery of P and N from human urine. Applications of nutrient-loaded biochar in an agricultural field could act as a slow-release fertilizer to releases P and N in addition to soil conditioning. This review emphasized the challenges of storage, transportation, contamination of urine, and possible difficulties in the adsorption process by pristine/engineered biochar.

Since human urine alone contributes to 90% of phosphorous (P) and 50–70% of nitrogen (N) load to municipal wastewater, retrieval of nutrients in the form of struvite (magnesium ammonium phosphate) from urine has gained much attention as it can act as an excellent slow-release fertilizer for plant growth. The present study aimed to comprehend the effect of urine storage on its physicochemical characteristics for the recovery of ammonium and phosphate in the form of struvite by adding magnesium chloride as an external source of magnesium (Mg). Various influencing factors such as pH, conductivity, salinity, total dissolved solids, and ion concentrations of phosphate, ammonium, calcium, nitrate, sodium and potassium were monitored over a period of 25 days to delineate its role on struvite recovery. The highest yield of 619.3 ± 54.41 mg L−1 of struvite was obtained on day 24. It was found that phosphate and ammonium recovery reached up to 90% with the storage of 25 days. Excessive addition of Mg increased both struvite yield and phosphate recovery (by 20%) but affects struvite purity undesirably due to the formation of struvite analogs. Statistical analysis with Spearman's coefficients revealed that total dissolved solids exhibited a strong positive correlation for struvite yield.

The present work describes the inhibition studies of free as well as immobilized urease by different heavy metals. Porous silicon (PS) films prepared by electrochemical etching were used for urease immobilization by physical adsorption. The enzyme was subjected to varying concentrations of Cr(6+), Cr(3+), Cu(2+), Fe(2+), Cd(2+) and Ni(2+) and analyzed for the variation in the activity. To study the effect of other heavy metals on the interaction of urease and Cr(6+), free as well as immobilized urease was subjected to the combination of each metal ion with Cr(6+). Results proved the sensitivity of free as well as immobilized urease towards heavy metals by observed reduction in activity. Immobilized urease showed less degree of inhibition compared to free urease when tested for inhibition by individual metal ions and in combination with Cr(6+). IC(50) values were found higher for inhibition by the combination of metal ions with Cr(6+). Interaction of heavy metal ions with functional groups in active site of urease and limitations of mass transfer are the two factors responsible for the variation in activity of urease. Relation between the variation of urease activity and amount of heavy metals can be applied in biosensor development for determining the concentration of Cr(6+) present in the water samples.

Vibrio cholerae, the causative agent of the disease cholera still threatens a large proportion of world’s population and is considered as a top priority enteric pathogen. Role of biofilm in V. cholerae pathogenesis is well established as it provides the bacterium with enhanced transmission ability during epidemics and also enhanced tolerance to antimicrobial agents. The clinical efficacy of many existing antibiotics is being threatened by the emergence of multi-drug resistant V. cholerae. The rapidly increasing number of cholera outbreaks in several developing countries and emergence of multidrug resistant V. cholerae necessitates the development of an alternative strategy rather than the existing antibiotic therapy to control the pathogen. In the present chapter, we discuss the different quorum sensing pathways in V. cholerae, the common quorum quenching molecules that targets these pathways and a novel strategy of biofilm inhibition in V. cholerae using antibiofilm compounds in combination with antibiotics to control the disease. Co-dosing strategy reduce the dosage of antibiotics and such a combination therapy can in turn be used to control the spread of antibiotic resistance.

Microalgae have received a great deal of attention among researchers in recent decades in the production of sustainable bioenergy due to the limitations of second-generation biofuels. However, scalability and economics are the two key challenges that need to be overcome for sustainable biofuel production at field level, and mathematical modelling can be utilized as an effective tool to evaluate the influencing factors. This article focuses on the mathematical modelling of microalgal growth and carbon dioxide sequestration potential of a fixed photobioreactor (PBR) at 25° inclination facing south and a two-axis trackable PBR in Odisha, India. The total geographic area of Odisha has been represented in 1195 spatial sites, each site representing around 130 sq. km of the real scale dimensions approximately. The model incorporates site-specific data of solar radiation, climatic conditions and PBR configurations to derive the bioenergy content of microalgal biomass by photon energy balance. The effect of photoinhibition was also studied, and the outputs from the mathematical modelling, such as daily microalgal lipid production and carbon dioxide sequestration potential were plotted for the whole of Odisha using QGIS software. The net microalgal biomass production rate drastically reduced to around 30% and 40% due to the effect of photoinhibition in the case of fixed and trackable PBR systems respectively. The outcome of the present study could influence the policy-makers for selecting suitable sites for the implementation of microalgal-based biofuel production facility.