Impact of CO2 concentration and ambient conditions on microalgal growth and nutrient removal from wastewater by a photobioreactor

Abstract

The increase in atmospheric CO 2 concentration and the release of nutrients from wastewater treatment plants (WWTPs) are environmental issues linked to several impacts on ecosystems. Numerous technologies have been employed to resolves these issues, nonetheless, the cost and sustainability are still a concern. Recently, the use of microalgae appears as a cost-effective and sustainable solution because they can effectively uptake CO 2 and nutrients resulting in biomass production that can be processed into valuable products. In this study single (Spirulina platensis (SP.PL) and mixed indigenous microalgae (MIMA) strains were employed, over a 20-month period, for simultaneous removal of CO 2 from flue gases and nutrient from wastewater under ambient conditions of solar irradiation and temperature. The study was performed at a pilot scale photo-bioreactor and the effect of feed CO 2 gas concentration in the range (2.5-20%) on microalgae growth and biomass production, carbon dioxide bio-fixation rate, and the removal of nutrients and organic matters from wastewater was assessed. The MIMA culture performed significantly better than the monoculture, especially with respect to growth and CO 2 bio-fixation, during the mild season; against this, the performance was comparable during the hot season. Optimum performance was observed at 10% CO 2 feed gas concentration, though MIMA was more temperature and CO 2 concentration sensitive. MIMA also provided greater removal of COD and nutrients (~83% and >99%) than SP.PL under all conditions studied. The high biomass productivities and carbon bio-fixation rates (0.796-0.950 g dw .L −1 .d −1 and 0.542-1.075 g C .L −1 .d −1 contribute to the economic sustainability of microalgae as CO 2 removal process. Consideration of operational energy revealed that there is a significant energy benefit from cooling to sustain the highest productivities on the basis of operating energy alone, particularly if the indigenous culture is used.

Large-Scale Cultivation of Spirulina for Biological CO2 Mitigation in Open Raceway Ponds Using Purified CO2 From a Coal Chemical Flue Gas

“…The concentration of DIC in the culture medium can be increased by continuous or intermittent CO 2 aeration, as has been demonstrated in many studies (Matsudo et al, 2012;Chen et al, 2016;Duarte et al, 2017;Qiu et al, 2017;Almomani et al, 2019). Bao et al (2012) indicated that CO 2 absorptivity has a positive correlation with pH value and a negative correlation with total carbon concentration.…”

“…To improve the CO 2 fixation rate, excellent algal strains need to be selected. Almomani et al (2019) reported that mixed indigenous microalgae (MIMA, collected from a secondary basin of Doha South wastewater treatment plant) performed significantly better than a single Spirulina platensis (SP.PL) culture, especially with respect to growth and CO 2 biofixation (Almomani et al, 2019). Badger and Price (1994) indicated that high CO 2 levels could improve carbon fixation activity of the enzyme rubisco in microalgal cells, and rubisco facilitates the utilization of CO 2 , thus, increasing the biological fixation efficiency of CO 2 .…”

A technoeconomic assessment of microalgal culture technology implementation for combined wastewater treatment and CO2 mitigation in the Arabian Gulf

“…Carbon dioxide (CO2) fixation methods are well known, and include its conversion to chemical feedstock and fuels, biological conversion (photosynthesis) (Al Momani et al, 2004), and mineralisation for the production of metal carbonate/bicarbonates (Almomani et al, 2019a;Almomani et al, 2019b;Laumb et al, 2013). Whereas these methods mainly focus on CO2 utilisation following capture, biological conversion directly mitigates CO2 and uses it as a feedstock to create useful products.…”

“…Microalgae are acknowledged as providing an efficient means of mitigating carbon while generating products such as biofuels (Almomani et al, 2019a;Meher et al, 2006;Mutanda et al, 2011); interest in microalgae culture technology (MCT) has grown significantly since first it was pioneered in the late 1970s (Leduy and Therien, 1979). Algae can utilise both CO2 and organic carbon as the substrate, by autotrophic and mixotrophic growth respectively, such that the technology can potentially be employed for combined CO2 sequestration from flue gases and nutrient removal from wastewater (Almomani et al, 2017;AlMomani and Örmeci, 2016;Shurair et al, 2016;Almomani et al, 2014).…”

Techno‐economic analysis and a novel assessment technique of paper mill sludge conversion to bioethanol toward sustainable energy production

“…Several processes nowadays that can be used for the treatment of pulp and paper industry wastewater such as biological processes, adsorption, advanced oxidation, chemical coagulation, electrocoagulation, and membrane separation. [31][32][33][34] Cellulose content is the only consideration for the evaluation of a biomass source. This is because the extraction of sugars must practically take place under milder conditions than strong-acid hydrolysis at high temperature.…”