## 1 Introduction
Fermenter-type reactors are modifications of well-known bioreactors developed for heterotrophic organisms. Because the development started from the fermenter, in which the control of the processes is well designed, all growth parameters can be controlled with high accuracy. Nowadays, these types are mainly used in optimization processes, and in the case of scaling up, the limiting factor is the relatively poor area-to-volume ratio. Stirring is usually accomplished with a stirring paddle or magnetic stirrer. There are a wide variety of devices within this type, with the usual goal to improve the area-to-volume ratio [19]. Hybrid photobioreactors are devices that combine two or more photobioreactor configurations to take advantage of each selected ones and minimize or even eliminate the disadvantages of each arrangement [2,8]. Hybrid reactors are often a combination of a conventional tank-type reactor and a tubular part. The conventional part is for control over culture variables: it makes it possible to integrate probes to finely regulate culturing circumstances. On the other hand, this part also acts as a degassing system. The tubular part acts as a light-harvesting unit since it provides a high surface area to volume ratio [2,8]. The conventional part usually is an airlift or bubble column reactor [8], while the tubular part can be horizontal parallel sets of tubes [20] or a loop-like structure [21,22]. On a laboratory scale, hybrid reactors are also constructed from an airlift, bubble column or fermenter, and a (generally helical) tubular part; several configurations are available in the commercial market. Although both parts of these hybrid reactors have their limitations in scalability, they are applied on an industrial scale [8]. Developments of photobioreactors are mainly related to the industrial sector (companies); 43% of the patents are linked to this sector. The participation of single contributors is very significant; 22% of registered patents are the result of individual development. The participation of research institutes in technological development is about 15%. There is little overlap between sectors: 12% of research institute patents have been filed with firms, other joint applications are even rarer [23]. Collaborations, proper communication, and scientifically demanding analyses of the effectiveness of different reactor types would be essential to develop increasingly economical production systems. Species of the green algae family Selenestracaceae are now among the most promising groups of algae from a biotechnological point of view. Although various isolates of other species, such as the genera _Spirulina_ or _Chlorella_, preceded the industrial use of Selenestracaea species for decades, more promising results are being obtained about them today [24]. _Monoraphidium braunii_, recently referred to as _Chlorolbion braunii_[25], has been one of the \"most popular\" since the 1990s. Research focuses on transport systems that are responsible for CO\({}_{2}\) and, in this context, nitrate uptake, as they play one of the most significant roles in biotechnology applications [26; 27; 28; 29]. In addition, enzymes with different functions also reveal a lot of information about the function and physiology of microorganisms of similar structures [30; 31; 32; 33; 34]. An important area related to the use of _Monoraphidium_ species is their sensitivity to metals, their possible role in bioindication, and/or bioremediation [35; 36; 37; 38]. In addition, their resistance to other substances also makes the _Monoraphidium_ species promising in phytoremediation [39]. In addition to their potential contaminant removing ability, their metabolic products also attract interest to _Monoraphidium_ species [24; 40]. In the present study, the goal was to compare the effects of the bioreactor type on biomass and lipid production of a _Monoraphidium pusillum_ (Printz) Komarkova-Legnorova strain.