## 5 Potential for Concurrent Production of Biofuels
In addition, hydrogen production from _Chlamydomonas_ was significantly enhanced when it was placed in artificial symbiosis with a modified strain of hydrogenase _Escherichia coli_. In conclusion, microalgae can capture light energy and produce hydrogen, with the synergy of bacteria that remove oxygen produced during photosynthetic activity, without the use of exogenous organic substances or other nutrients [39]. Moreover, biochar is the solid, carbon-rich material produced by pyrolysis of any form of organic biomass (forestry, agricultural crop residues, paper sludge, and poultry farm waste). The pyrolytic process involves heating between 350 \({}^{\circ}\)C and 700 \({}^{\circ}\)C in the absence of oxygen. The creation of biochar from microalgae biomass is a carbon capture tool [40]. Biochar is considered a \"green\" product with the potential to be used in a sustainable strategy for the development of negative carbon emission technology. The conversion of biomass to biochar plays an important role in carbon capture and is an alternative approach to the energy utilization of biomass by capturing and storing CO\({}_{2}\), resulting in the production of biofuels with NET (negative emission technology) [41]. Biofuels remove carbon from the atmosphere as the raw materials for their production photosynthesize to grow, as well as through biochar production, as an amount of carbon returns to the soil when it is used as a soil improver. The ratio of 75:25 for biofuel production:biochar, is considered the most ideal, as by increasing the ratio to 90:10, the production of biofuels is maximized but the negative carbon footprint is reduced due to the reduction of biochar. Similarly, a 60:40 ratio would create the reverse effect. The strategic regulation of biofuel production in relation to biochar production is critical to our carbon footprint. Therefore, in optimizing the production of biofuels from microalgae, it would be environmentally important to add the production of biochar, as through the pyrolysis of microalgae biomass, energy production would be achieved while at the same time the biochar produced would capture a large percentage of carbon [40]. The characteristics of biochar, such as pH, porous structure, specific surface, bound carbon, ash, and ion exchange capacity, are affected by pyrolysis conditions, with the temperature and type of biomass being the most decisive. Biochar produced from microalgae is poorer in carbon, surface area, and ion exchange capacity, but with increased pH and minerals (P, Ca, K, and Mg) compared to biomass from lignite cellulosic materials [40]. Biochar can be used for heat and energy production, as a carbon sequestration agent, as an adsorbent in various industrial applications, and as a fertilizer. As a fertilizer, biochar has the potential to gradually release key nutrients (N and P), which enhance plant nutrition efficiency and consequently increase crop yields. In addition, biochar can improve the physicochemical characteristics of the soil, such as increasing residual nitrogen and carbon in the soil, improving the soil's pH and electrical conductivity. In biochar production, evaluation of its characteristics is important to determine its potential applications. Biochar must comply with certain specifications to be used as fertilizer, such as a C content of more than 50% on a dry basis, with a range of N and P from 1% to 45% (the usual values are 15% for P and 1% for N), pH up to 10, and a specific surface area greater than 150 m\({}^{2}\)/g. [42]. In the study of [PERSON] et al. [41], pyrolysis was applied in a stainless steel cylindrical reactor, using biomass produced by _Chlorella vulgaris_ FSP-E cultivated on modified basal medium substrate, in a photobioreactor with a continuous flow of 2.5% CO\({}_{2}\) and a temperature of 26 \(\pm\) 1 \({}^{\circ}\)C. Pyrolysis was carried out in a stainless steel cylindrical fixed-bed reactor at a temperature of 500 \({}^{\circ}\)C with a heating speed of 10\({}^{\circ}\) C/min, with a continuous flow of nitrogen of 100 mL/min.