Sheena Kumari

Bioprospecting for hyper-lipid producing microalgal strains for sustainable biofuel production

Global petroleum reserves are shrinking at a fast pace, increasing the demand for alternate fuels. Microalgae have the ability to grow rapidly, and synthesize and accumulate large amounts (approximately 20-50% of dry weight) of neutral lipid stored in cytosolic lipid bodies. A successful and economically viable algae based biofuel industry mainly depends on the selection of appropriate algal strains. The main focus of bioprospecting for microalgae is to identify unique high lipid producing microalgae from different habitats. Indigenous species of microalgae with high lipid yields are especially valuable in the biofuel industry. Isolation, purification and identification of natural microalgal assemblages using conventional techniques is generally time consuming. However, the recent use of micromanipulation as a rapid isolating tool allows for a higher screening throughput. The appropriate media and growth conditions are also important for successful microalgal proliferation. Environmental parameters recorded at the sampling site are necessary to optimize in vitro growth. Identification of species generally requires a combination of morphological and genetic characterization. The selected microalgal strains are grown in upscale systems such as raceway ponds or photobireactors for biomass and lipid production. This paper reviews the recent methodologies adopted for site selection, sampling, strain selection and identification, optimization of cultural conditions for superior lipid yield for biofuel production. Energy generation routes of microalgal lipids and biomass are discussed in detail.

Trends in biohydrogen production: major challenges and state-of-the-art developments

Hydrogen has shown enormous potential to be an alternative fuel of the future. Hydrogen production technology has gained much attention in the last few decades due to advantages such as its high conversion efficiency, recyclability and non-polluting nature. Over the last few decades, biological hydrogen production has shown great promise for generating large scale sustainable energy to meet ever increasing global energy demands. Various microorganisms, namely bacteria, cyanobacteria, and algae which are capable of producing hydrogen from water, solar energy, and a variety of organic substrates, are explored and studied in detail. Current biohydrogen production technologies, however, face two major challenges such as low-yield and high production cost. Advances have been made in recent years in biohydrogen research to improve the hydrogen yield through process modifications, physiological manipulations, through metabolic and genetic engineering. Recently, cell immobilization such as microbes trapping with nanoparticles within the bioreactor has shown an increase in hydrogen production. This review critically evaluated various biological hydrogen production technologies, key challenges, and recent advancements in biohydrogen research and development.

Application of quantitative RT-PCR to determine the distribution of Microthrix parvicella in full-scale activated sludge treatment systems.

Three wastewater treatment plants in South Africa were investigated to understand the phylogeny and distribution of Microthrix parvicella using real-time polymerase chain reaction (RT-PCR). The phylogenetic analysis of the 16S rRNA of M. parvicella revealed 98% to 100% homology of South African clones to M. parvicella reported in Genbank. The standard curves for RT-PCR showed R2 values greater than 0.99, accurate for quantification. The relative occurrence of M. parvicella 16S rRNA gene copies in the three wastewater treatment plants was in the range 0% to 3.97%. M. parvicella copies increased when the environmental temperature (≤20°C) and food/microorganism (F/M) ratio was low. The M. parvicella 16S rRNA copies could be positively correlated to the sludge volume index at low temperature. At higher temperature, there was a rapid reduction in M. parvicella population irrespective of other favorable factors, indicating the strong influence of temperature on filamentous proliferation. RT-PCR has potential applications in wastewater treatment plants to monitor sudden shift in the microbial population and assessing the plants efficacy.

Effect of thermal pre-treatment on inoculum sludge to enhance bio-hydrogen production from alkali hydrolysed rice straw in a mesophilic anaerobic baffled reactor.

The effect of thermal pre-treatment on inoculum sludge for continuous H2 production from alkali hydrolysed rice straw using anaerobic baffled reactor (ABR) was investigated. Two reactors, ABR1 and ABR2, were inoculated with untreated and thermally pre-treated sludge, respectively. Both reactors were operated in parallel at a constant hydraulic retention time of 20 h and organic loading rate ranged from 0.5 to 2.16 g COD/L d. The results obtained indicated that ABR2 achieved a better hydrogen conversion rate and hydrogen yield as compared with ABR1. The hydrogen conversion rates were 30% and 24%, while the hydrogen yields were 1.19 and 0.97 mol H2/mol glucose for ABR2 and ABR1, respectively. Similar trend was observed for chemical oxygen demand (COD) and carbohydrate removal, where ABR2 provided a removal efficiency of 53±2.3% for COD and 46±2% for carbohydrate. The microbial community analysis using 16S rRNA phylogeny revealed the presence of different species of bacteria, namely Clostridium, Prevotella, Paludibacter, Ensifer, and Petrimonas within the reactors. Volatile fatty acids generated from ABR1 and ABR2 were mainly in the form of acetate and butyrate and a relatively low fraction of propionate was detected in ABR1. Based on these results, thermal pre-treatment of inoculum sludge is preferable for hydrogen production from hydrolysed rice straw.

Use of mixed culture bacteria for photofermentive hydrogen of dark fermentation effluent

Hydrogen production (HP) from dark fermentation effluent of starch wastewater via vertical tubular photo-bioreactor was investigated. The reactor was inoculated with mixed culture of bacteria and operated at light intensity of 190 W/m(2). Hydraulic retention time (HRT) and organic loading rate (OLR) was varied between 0.9 to 4.0 h and 3.2 to 16 g COD/l.d., respectively. Increasing the HRT from 0.9 to 2.5 h, significantly (P<0.05) increased HP from 1±0.04 to 3.05±0.19 l/d, respectively. However, minimal increase in HP occurred when increasing the HRT up to 4.0 h. The HP remained unaffected when increasing the OLR from 3.2 to 6.4 g COD/l.d. Further increase in the OLR up to 8.2 and 16 g COD/l.d., resulted in a drop in HP i.e. 0.96 and 0.19 l/d, respectively. Microbial community analysis of the reactor samples showed the presence and dominance of hydrogen producing purple non-sulfur phototrophic (PNS) bacterium, Rhodopseudomonas palustris in the reactor.

Prospects, recent advancements and challenges of different wastewater streams for microalgal cultivation

Microalgae are recognized as one of the most powerful biotechnology platforms for many value added products including biofuels, bioactive compounds, animal and aquaculture feed etc. However, large scale production of microalgal biomass poses challenges due to the requirements of large amounts of water and nutrients for cultivation. Using wastewater for microalgal cultivation has emerged as a potential cost effective strategy for large scale microalgal biomass production. This approach also offers an efficient means to remove nutrients and metals from wastewater making wastewater treatment sustainable and energy efficient. Therefore, much research has been conducted in the recent years on utilizing various wastewater streams for microalgae cultivation. This review identifies and discusses the opportunities and challenges of different wastewater streams for microalgal cultivation. Many alternative routes for microalgal cultivation have been proposed to tackle some of the challenges that occur during microalgal cultivation in wastewater such as nutrient deficiency, substrate inhibition, toxicity etc. Scope and challenges of microalgal biomass grown on wastewater for various applications are also discussed along with the biorefinery approach.

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.

Physiological responses of carbon-sequestering microalgae to elevated carbon regimes

In order to identify a high carbon-sequestering microalgal strain, the physiological effect of different concentrations of carbon sources on microalgae growth was investigated. Five indigenous strains (I-1, I-2, I-3, I-4 and I-5) and a reference strain (I-0: Coccolithus pelagicus 913/3) were subjected to CO2 concentrations of 0.03–15% and NaHCO3 of 0.05–2 g CO2 l–1. The logistic model was applied for data fitting, as well as for estimation of the maximum growth rate (μmax) and the biomass carrying capacity (Bmax). Amongst the five indigenous strains, I-3 was similar to the reference strain with regards to biomass production values. The Bmax of I-3 significantly increased from 214 to 828 mg l–1 when CO2 concentration was increased from 0.03 to 15% (r = 0.955, P = 0.012). Additionally, the Bmax of I-3 increased with increasing NaHCO3 (r = 0.885, P = 0.046) and was recorded at 153 mg l–1 (at 0.05 g CO2 l–1) and 774 mg l–1 at (2 g CO2 l–1). Relative electron transport rate (rETR) and maximum quantum yield (Fv/Fm) were also applied to assess the impact of elevated carbon sources on the microalgal cells at the physiological level. Isolate I-3 displayed the highest rETR confirming its tolerance to higher quantities of carbon. Additionally, the decline in Fv/Fm with increasing carbon was similar for strains I-3 and the reference strain. Based on partial 28s ribosomal RNA gene sequencing, strain I-3 was homologous to the ribosomal genes of Chlorella sp.

Comparison of droplet digital PCR and quantitative PCR for the detection of Salmonella and its application for river sediments

Despite advances in microbial detection that quantitative polymerase chain reaction (qPCR) has led to, complex environmental samples, such as sediments, remain a challenge due to presence of PCR inhibitors. Aquatic sediments accumulate particle-bound microbial contaminants and thereby reflect a cumulative microbial load over time. The relatively new droplet digital PCR (ddPCR) has emerged as a direct quantitative method, highly tolerant to PCR inhibitors and relinquishing the necessity for calibration/standard curves. Information is virtually absent where ddPCR has been applied to detect pathogenic organisms in aquatic sediments. This study compared the efficacy of ddPCR with qPCR, for quantification of Salmonella in sediments from the Palmiet River near an informal settlement in Durban, South Africa. ddPCR significantly improved both analytical sensitivity and detection of low concentrations of Salmonella as compared to qPCR. The expected copy numbers measured from both qPCR and ddPCR showed good R2 values (0.999 and 0.994, respectively). The site mostly affected by the informal settlements exhibited Salmonella in the range of 255 ± 37 and 818 ± 30 Salmonella/g (p ≤ 0.0001) in qPCR and ddPCR, respectively. The improved detection of Salmonella in sediments with ddPCR makes it a promising technical method for the quantification of Salmonella in multifarious environmental samples.

Evaluation of phytotoxicity effect on selected crops using treated and untreated wastewater from different configurative domestic wastewater plants

ABSTRACT This study investigated the phytotoxicity effect of untreated and treated wastewater collected from two different configurations of domestic wastewater treatment plants in South Africa. The phytotoxicity effect on vegetable seed growth was studied in terms of germination index (GI), relative seed germination (RSG) and relative root elongation (RRE) using four commercial crop varieties, viz., tomato (Lycopersicon esculentum), radish (Raphanus sativus), carrot (Daucus carota) and onion (Allium cepa). According to phyototoxicity limits, 80% germination and above is regarded as non-toxic and less than 50% GI is regarded as highly toxic and not suitable for agricultural purposes. In our study, seeds were irrigated with concentrations of 25%, 50%, 75%, 100% of treated effluent (TE) and untreated effluent (UTE). The TE results were best with the highest GI (%) recorded as tomato, 177; carrot, 158.5; onion, 132; and lettuce, 124. The results of this study indicate that TE showed no phytotoxicty effects and recorded above 80% GI. The UTE irrigated crops reached a GI of only 50% and above which is clear evidence of the beneficial effect of waste water treatment. The overall results confirmed that treated wastewater has a beneficial effect on agricultural crops and can be used as a liquid fertilizer.