Amritanshu Shriwastav

Lipid extracted algae as a source for protein and reduced sugar: a step closer to the biorefinery

The objective of this study was to investigate the feasibility of using lipid extracted algae (LEA) as a source for protein and reduced sugar, and the effects of various procedural treatments on their yields. LEA provided comparable yields of protein and reduced sugars to those from total algae. Oven drying provided highest yields of all products followed by freeze drying, while sun drying significantly lowered their yields. Effective cell disruption by microwave and autoclave increased the lipid yields from algae, but resulted in increased loss of other compounds with lipid extracting solvents lowering their yields during sequential extraction. Relatively inefficient cell disruption by ultrasonication and osmotic shock lowered the amount of cell protein lost to the lipid extracting solvents. These results highlight the complexity of concurrent extraction of all value added products from algae, and the need for proper selection of the processes to achieve the objectives of integrated biorefinery.

Adaptability of growth and nutrient uptake potential of Chlorella sorokiniana with variable nutrient loading

Chlorella sorokiniana can sustain growth in conditions hostile to other species, and possesses good nutrient removal and lipid accumulation potentials. However, the effects of variable nutrient levels (N and P) in wastewaters on growth, productivity, and nutrient uptake by C. sorokiniana have not been studied in detail. This study demonstrates the ability of this alga to sustain uniform growth and productivity, while regulating the relative nutrient uptake in accordance to their availability in the bulk medium. These results highlight the potential of C. sorokiniana as a suitable candidate for fulfilling the coupled objectives of nutrient removal and biomass production for bio-fuel with wastewaters having great variability in nutrient levels.

Microalgae Applications in Wastewater Treatment

Algal wastewater treatment is effective in the removal of nutrients (C, N and P), coliform bacteria, heavy metals and the reduction of chemical and biological oxygen demand, removal and/or degradation of xenobiotic compounds and other contaminants. Microalgae wastewater treatment technologies have long been in existence; however, uptake of the technology to date has been limited mainly due to considerations of land requirements and volumes of wastewater to be treated. This chapter gives an overview of algal applications in wastewater treatment with specific reference to nutrient removal, phycoremediation of heavy metals, high-rate algal ponds, symbiosis of algae with bacteria for wastewater treatment, and utilisation of wastewater-grown microalgae.

Nutrient removal using algal-bacterial mixed culture.

Simultaneous nitrate (N), phosphate (P), and COD removal was investigated in photobioreactors containing both algae and bacteria. The reactors were operated in the semi-batch mode with a hydraulic retention time of 2xa0days. Reactors were operated in two phases, (1) with 33xa0% biomass recycle and (2) with no biomass recycle. In both phases, more than 90xa0% of N and P and 80xa0% of COD present in synthetic wastewaters with initial N and P concentrations of up to 110 and 25xa0mg/L, respectively, and initial COD of 45xa0mg/L could be removed. Biomass growth in reactors did not increase with the increase in initial N and P concentration in either phase. However, biomass growth was slightly more in reactors operated with no biomass recycle. In both phases, N and P uptake was greater in reactors with greater initial N and P concentrations. Also in all cases, N and P uptake in the reactors was far in excess of the stoichiometric requirements for the observed biomass growth. This “luxury uptake” of nitrogen and phosphorus by biomass was responsible for excellent nitrogen and phosphorus removal as observed. However, based on the results of this study, no advantage of biomass recycling could be demonstrated.

Modification of Winkler's method for determination of dissolved oxygen concentration in small sample volumes

Winklers method is the most popular procedure for determination of dissolved oxygen (DO) concentration in water samples. However, this method requires a relatively large sample volume of 200 mL for accurate DO determination. Many alternative methods have been proposed for measuring DO concentrations in small sample volumes, but most such methods have problems of either, low accuracy, high cost, complicated instrumentation or lengthy analysis times. In this paper, a simple modification to the Winklers method is proposed for measurement of DO concentrations in samples of 1 mL volume. The proposed method is accurate, low cost, simple and quick. DO concentrations were measured in 33 samples by both the conventional Winklers method (WM) and the proposed method (PM). For 23 of the 33 samples analyzed, the hypothesis that the population means of the measurements are equal (μ1 = μ2) could not be rejected at 95 percent confidence level and for 19 samples, the hypothesis that the population variances of the measurements are equal (σ21 = σ22)could not be rejected at 95 percent confidence interval. It was thus concluded that in most cases, DO measurements by WM and PM give comparable results both in terms of accuracy and precision.

A comprehensive mechanistic model for simulating algal growth dynamics in photobioreactors

A comprehensive mechanistic model for describing algal growth dynamics in a photobioreactor was developed in this work with state of the art understanding and realistic assumptions for major associated processes. The model included 27 state variables related to various algal processes. This model was validated with extensive experimental data obtained from independent growth experiments in batch reactors, and was able to simulate system performance reasonably well. The comprehensive nature of the formulation also highlights the complex inter-relationship between all processes, and provides a tool for gaining more systematic insights into algal behavior in photobioreactors and other such systems.

Phycoremediation of Emerging Contaminants

A special group of contaminants which poses serious threat to the human health as well as the environment, but has not been fully discovered and understood, are termed as emerging contaminants (ECs). Most of such contaminants possess diverse chemical properties and are of anthropogenic origin. The ubiquitous occurrence of ECs in the environment poses serious threat to the human health as well as deleterious effects to the flora and fauna even at minute concentrations, as most of the conventional wastewater treatment plants are not designed for the effective treatment and removal of such contaminants. Therefore, other than accidental release, ECs are majorly attributed to the environment through inadequately treated wastewater, sewage, and industrial effluents. Previous studies have shown that bioremediation could be an effective tool for the treatment; however, phycoremediation of emerging contaminants have been least studied. In this chapter we have explored the possibilities of phycoremediation of ECs and have reviewed and summarized findings of most of the recent studies. This chapter exclusively covers the phycoremediation potential of various algal species for the removal of pharmaceuticals, personal care products, pesticides, endocrine disruptors, and various other organics which are considered as potential contaminants of emerging concern.

Deconvoluting algal and bacterial biomass concentrations in algal-bacterial suspensions

Algae and algal-bacterial consortia have many applications including biofuel production, as source of many beneficial products, and in wastewater treatment. With increasing interest in such systems, a suitable method to estimate the individual biomass concentrations of algae and bacteria in a mixed suspension is still not available. The objective of this study was to develop a method for estimating the algal and bacterial concentrations in suspensions containing both algae and bacteria. The method involved (1) determination of algal number concentration in the algal-bacterial suspension through manual algal cell counting, (2) conversion of the algal number concentration to algal mass concentration by applying a consolidated conversion factor, and (3) determination of bacterial mass concentration in the suspension by subtracting the algal mass concentration from the gravimetrically determined total biomass concentration in the suspension. Using the protocols developed in this study, algal biomass concentrations estimated in purely algal or artificially constituted algal-bacterial suspensions were comparable, both in terms of mean values and precision, to the corresponding algal biomass concentrations determined through direct gravimetric measurements. Estimations of algal and bacterial biomass concentration in suspensions with unknown algae and bacteria concentrations are also reported.