As the demand for freshwater continues to rise, the depletion of available water sources has become a pressing global issue. In this context, understanding the role of algae in water purification is crucial. Does algae clean water? This question drives research into the potential of these microscopic organisms to improve water quality. Algae and cyanobacteria, often found in both saltwater and freshwater, play significant roles in aquatic ecosystems. This article explores the benefits of algae, their cultivation for biodiesel production, and their potential in wastewater treatment.

The Role of Algae in Aquatic Ecosystems

Benefits of Algae

Algae are vital contributors to aquatic ecosystems. They produce oxygen through photosynthesis, enriching the water and supporting diverse marine life. Green algae, in particular, serve as a primary food source for zooplankton and small fish, which in turn support larger fish and wildlife. These organisms thrive in the epipelagic zone of oceans, where sunlight and nutrients are plentiful.

Algae also act as indicators of water quality. The presence of green algae and diatoms typically indicates oligotrophic (clean) conditions, while blooms of blue-green algae often signal eutrophic (polluted) waters, primarily associated with cyanobacteria. Understanding these dynamics is essential for effective water quality monitoring and management.

Cyanobacteria: The Blue-Green Algae

Cyanobacteria, classified as eubacteria, differ from algae in that they lack a membrane-bound nucleus. Despite being referred to as blue-green algae, they can appear in various colors, including olive and purplish hues. Under favorable conditions, cyanobacteria can proliferate rapidly, leading to blooms that can negatively impact water quality. Monitoring these organisms is critical for managing water resources effectively.

Cultivation for Biodiesel Production

Pseudochlorella pringsheimii

The microalga Pseudochlorella pringsheimii, formerly known as Chlorella ellipsoidea, has emerged as a promising candidate for biodiesel production due to its high lipid content. Enhancing lipid accumulation is essential for making microalgae a commercially viable biofuel source, offering a renewable alternative to fossil fuels.

Evaluation of Cultivation Conditions

Initial studies focused on laboratory-scale experiments using a 2 L setup to evaluate various nutrient conditions in Bold’s Basal Medium (BBM).

Researchers tested different concentrations of nitrogen (N), phosphorus (P), and iron (Fe) to determine their effects on lipid production. The optimal conditions for maximizing lipid content were identified as nitrogen deficiency (1.25 g/L N), limited phosphorus (0.1 mg/L P), and high iron concentration (10 mg/L Fe), supplemented with 6% CO2.

These findings were subsequently scaled up to a 2000 L photobioreactor (PBR), resulting in lipid accumulation of 25% w/w and a productivity rate of 74.07 mg/L/day.

Biodiesel Conversion Efficiency

The biodiesel conversion efficiency through transesterification was found to be 91.54 ± 1.43%. The fatty acid methyl esters (FAMEs) profile revealed significant constituents such as C16:0, C18:1, C18:2, and C18:3. Importantly, the biodiesel produced met ASTM and EU standards, indicating its high quality and suitability for commercial applications.

Cultivation Methods

Reagents and Chemicals

All chemicals used in the experiments were sourced from reputable suppliers, including Sigma Aldrich and E. Merck, ensuring high purity and reliability for the cultivation processes.

Microalgae Strain and Pre-Culture Conditions

The Pseudochlorella pringsheimii strain was preserved in BBM at pH 6.6, sourced from Egyptian culture collections. Pre-culture conditions involved testing various concentrations of bicarbonate (2, 4, and 8 g/L) and CO2 (4, 8, and 16%) in 2 L Erlenmeyer flasks to optimize lipid accumulation. The cultures were grown photo-autotrophically under fluorescent lights at an intensity of 2500 lx. The best results for biomass productivity were achieved with 8% CO2.

Large-Scale Cultivation in Photobioreactors

In the 2000 L PBR, Pseudochlorella pringsheimii was cultivated under optimal nutrient levels, including limited nitrogen (0.125 g/L) and phosphorus (0.13 g/L), along with 10 mg/L Fe and CO2 enrichment. The PBR was aerated continuously, and growth was maintained under a 24-hour photoperiod using fluorescent lights.

Harvesting and Growth Measurement

At the end of each batch cycle (repeated three times), the cultures were harvested, filtered, and centrifuged at 3000 x g for 15 minutes. The biomass was washed and frozen for further analysis. Growth was monitored every two days over 16 days, using dry cell weight and optical density (OD680 nm) measurements to assess biomass density.

Microalgae Growth Parameters

During the cultivation of microalgae, several key growth parameters were assessed to understand their potential for biodiesel production:

Biomass Productivity (PB):

Measured as the dry biomass produced (g L⁻¹ day⁻¹) during the stationary growth phase, biomass productivity involved centrifuging the algal suspension, washing the pellets, drying them, and weighing to determine dry biomass.

Specific Growth Rate (SGR):

Calculated by measuring the biomass concentration at the beginning and end of a selected time interval, reflecting the growth rate of the algae.

Total Chlorophyll a (Chl a):

Total chlorophyll a content was determined by harvesting a culture sample, centrifuging it, washing the algal pellet, re-suspending it in methanol, and measuring the chlorophyll spectrophotometrically.

Total Lipid Content:

The total lipid content in dried microalgae was assessed by extracting biomass with a hexane-methanol mixture. The organic layer was separated, and the lipid yield was calculated gravimetrically.

Lipid Productivity (LP):

Lipid productivity was determined by calculating the amount of lipids produced per unit of biomass over time.

This comprehensive assessment of growth parameters provides valuable insights into the cultivation of microalgae for biodiesel production, highlighting their potential as a sustainable energy source.

Algae in Wastewater Treatment

The Promise of Algal Bioremediation

As the demand for freshwater rises, finding effective methods for wastewater treatment is crucial. Current methods often rely on chemicals or ultraviolet radiation, which can be harmful and energy-intensive. Algae offer a sustainable and eco-friendly alternative for purifying wastewater.
Does algae clean water? Yes, algae can significantly enhance water quality by removing pollutants and harmful microorganisms. They utilize nitrogen, carbon, phosphorus, and heavy metals as nutrients, leading to a reduction in bacterial populations and improvement in overall water quality.

Dr. Pankaj Kumar Chauhan and his team

A team of scientists, led by Dr. Pankaj Kumar Chauhan from Shoolini University in India, has developed a wastewater treatment technology utilizing algal bioremediation. Their research highlights the effectiveness of using algae for wastewater purification.
The team focused on the microalga Pseudochlorella pringsheimii, known for its ability to tolerate high pollutant loads and grow across a wide temperature range. Under stress conditions, this algal strain accumulates high lipid levels, making it suitable for biofuel synthesis.

Experimental Findings

Researchers cultivated Pseudochlorella pringsheimii in artificial tanks filled with raw urban wastewater containing heavy metals and antibiotic-resistant bacteria. After 14 days, they assessed water quality, algal growth, and biochemical composition, as well as the potential for using treated water in fish farming.
The pilot-scale study yielded promising results, showing that P. pringsheimii cultivation significantly improved water quality. Indicators of water pollution, such as chemical oxygen demand (COD), alkalinity, and hardness, decreased by 83.2%, 66.7%, and 69.6%, respectively. The algal growth nearly eliminated total bacteria and coliforms, demonstrating the effectiveness of this bioremediation approach.

Benefits for Aquaculture

Notably, while no sucker fish survived in raw wastewater, 84% thrived in treated wastewater, with their body weight increasing by 47% over ten days. This indicates that treated water can be safely used for low-cost fish farming, further enhancing the economic viability of this approach.

Conclusion

The cultivation of microalgae like Pseudochlorella pringsheimii presents a sustainable solution for both biodiesel production and wastewater treatment. By utilizing their natural abilities to purify water, algae can significantly improve water quality and support aquaculture.

Does algae clean water? Yes, they do, offering a promising pathway toward a greener and more sustainable future. As research continues to advance, the potential of algae in environmental management and renewable energy sectors will likely expand, contributing to global efforts in sustainability.

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