inoculation and growth of arthrospira maxima in a high-rate algal pond (hrap) to purify biogas from swine waste

Microalgal Cultivation for Biomethane Obtention from Swine Waste Biogas

In recent years, several technologies have emerged to purify biogas to biomethane, promoting its use as non-fossil fuel, therefore mitigating undesairable methane emissions1. Air pollution is a problem that affects most of the world&#39;s population, particularly in urbanized areas; ultimately, around 92% of the world&#39;s population breathe polluted air2. In Latin America, the air pollution rates are mostly created by the use of fuels, whereby in 2014, 48% of the air pollution was brought on by the electricity and heat production sector3.
In the last decade, more and more studies on the relationship between pollutants in the air and the increase in mortality rates have been proposed, arguing that there is a strong correlation between both datasets, particularly in children populations.
As a way to avoid the continuation of air pollution, several strategies have been proposed; one of these is the use of renewable energy sources, including wind turbines and photovoltaic cells, which diminish the CO2 release into the atmosphere4,5. Another renewable energy source comes from biogas, a byproduct of the anaerobic digestion of organic matter, produced along with a liquid organic digestate6. This gas is composed of a mixture of gasses, and their proportions depend on the source of organic matter used for anaerobic digestion (sewage sludge, cattle manure, or agro-industrial biowaste). Generally, these proportions are CH4 (53%-70%vol), CO2 (30%-47%vol), N2 (0%-3%vol), H2O (5%-10%vol), O2 (0%-1%vol), H2S (0-10,000 ppmv), NH3 (0-100 ppmv), hydrocarbons (0-200 mg/m3) and siloxanes (0-41 mg/m3)7,8,9, where the scientific community is interested in the methane gas since this is the renewable energetic component of the mixture.
However, biogas cannot be simply burned as obtained because the byproducts of the reaction can be harmful and contaminant; this raises the need to treat and purify the mixture to increase the percentage of methane and decrease the rest, essentially converting it into biomethane10. This process is also known as upgrading. Even though, currently, there are commercial technologies for this treatment, these technologies have several economic and environmental drawbacks11,12,13. For example, systems with activated carbon and water washing (ACF-WS), pressure water washing (PWS), gas permeation (GPHR), and pressure swing adsorption (PSA) present some economic or other drawbacks of environmental impact. A viable alternative (Figure 1) is the use of biological systems such as those that combine microalgae and bacteria grown in photobioreactors; some advantages include the simplicity of design and operation, the low operating costs, and its environmentally friendly operations and byproducts10,13,14. When biogas is purified to biomethane, the latter can be used as a substitute for natural gas, and the digestate can be implemented as a source of nutrients to support microalgae growth in the system10.
A method widely used in this upgrading procedure is the growth of microalgae in open raceway photoreactors coupled with an absorption column due to the lower operation costs and the minimal investment capital needed6. The most used type of raceway reactor for this application is the high-rate algal pond (HRAP), which is a shallow raceway pond where the circulation of the algal broth occurs via a low-power paddle wheel14. These reactors need large areas for their installation and are very susceptible to contamination if used in outdoor conditions; in biogas purification processes, it is advised to use alkaline conditions (pH &#62; 9.5) and the use of algal species that thrive in higher pH levels to enhance the removal of CO2 and H2S while avoiding contamination15,16.
This research aimed to determine the biogas treatment efficiencies and final production of biomethane using HRAP photobioreactors coupled with an absorption-desorption column system and a microalgae consortium.

Author Spotlight: Scaling Microalgal Biotechnology for Enhanced Biomethane Production 

Biogas Purification through the use of a Microalgae-Bacterial System in Semi-Industrial High Rate Algal Ponds

Our research focuses on developing sustainable and viable microalgal biotechnology for biomethane We show that it was possible to scale the biogas filter up to some industrial scale under other conditions. The process of scaling is aimed at treating larger flows of biogas in smaller facilities with the aim of making it more economically viable. Additionally, the process seeks to promote operating conditions that can lead to greater production of value by products extracted from microalgal biomass.Through a full scale process exposed to outdoor conditions, we have discovered various species of microalgae that enable us to operate the microalgal filter efficiently. We have also identified the optimal operating conditions that lead to a higher volumetric concentration of biomethane. We were able to successfully scale up the microalgal filter to full scale operations, and identify the optimal operating conditions for photo bioreactors and microalgae filter to achieve methane concentrations of up to 85%volume.The use of other species of microalgae under the same operating conditions could improve the performance efficiency of the microalgae filter. In spring summer, the increase in temperature will help the efficiency of the system.

Watch this Scientific Journal Video about Inoculation and Growth of Arthrospira maxima  in a High-Rate Algal Pond HRAP to Purify Biogas from Swine Waste at JoVE.com

Inoculation and Growth of Arthrospira maxima  in a High-Rate Algal Pond (HRAP) to Purify Biogas from Swine Waste  

Inoculation and Growth of Arthrospira maxima in a High-Rate Algal Pond (HRAP) to Purify Biogas from Swine Waste

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