# Halophyte Plants and Their Residues as Feedstock for Biogas Production--Chances and Challenges
## 6 Conversion of Halophytes into Biogas
### Inhibiting Effects of Halophytes on the AD Process
#### 6.3.1 Optimization of AD Microorganism Composition  
As previously mentioned, the AD process encompasses a sequence of phases, in particular, hydrolysis, acidogenesis, acetogenesis and methanogenesis. Notably, these different phases within this codependent conversion pathway are executed by the presence and activity of an intricate consortia of microbial bacteria facilitating to an efficient degradation of organic material. The bacterial activity that led the first three phases converts organic material into VFAs and further digested into acetate, H\({}_{2}\) and CO\({}_{2}\). The fourth phase is performed by the archaeal community, which utilizes the products from the acidogenic stage to produce CH\({}_{4}\)[97]. The overall conversion of organic material into methane demands a synergistic activity amongst the microbial community. Acid- and methane-forming bacteria vary considerably with respect to their nutritional requirements, rate of growth kinetics, physiology and responsiveness to environmental plasticity. Thus, the inability to sustain a degree of equilibrium between both bacterial communities is the main source of anaerobic reactor instability [89]. More specifically, according to the findings of [PERSON] et al. [96], the methanogenic microorganisms are significantly influenced by the variations in environmental conditions in comparison to the acidogenesis and hydrolysis phases of AD. For this reason, it is crucial to completely fathom the behavioral characteristics of the microorganisms to primarily improve the efficiency of the processes involved in anaerobic degradation. Halophytic biomass contains high amounts of minerals due to the physiological adaptation mechanisms by accumulating salt within their cells and tissues to optimally develop under high saline conditions. At high concentrations, these minerals can affect the behavioral activity of the microbial bacteria in the AD process; nevertheless, low mineral salt content is necessary for microbial growth and reproduction. It is essential, in the case of AD technologies, to create a process that can effectively operate at high salt concentration. Halophilic and/or halotolerant anaerobic microorganisms are basic to achieve this. On that account, it is integral to explore the behavior of the bacteria and archaea associated with the biogas/biomethane production from halophytic biomass at different concentrations of salinity. Several approaches were established to enhance the performance of AD at high salt conditions, for instance, the use of osmoprotectants [98], halotolerant bacteria [99] and an extended time for halophobic inocula to adjust to saline condition [100]. According to the findings of [PERSON] [95] and [PERSON] et al. [101], when treating raw materials with a high salt content, inoculum acclimization is more effective over a relatively long period of time. [PERSON] et al. [97] suggested that increasing the concentration of NaCl from 0 to 20 g L\({}^{-1}\) did not adversely affect the hydrolytic and acidogenic activity of bacteria, but rather promoted it, while on the other hand, the methanogenic activity of the archaeal community, in methanogenesis, was strongly inhibited. Additionally, it was stated that a significant shift in bacterial community was observed between 20 g L\({}^{-1}\) and 0 g L\({}^{-1}\) NaCl, in that a variety of halotolerant bacteria was able to acclimatze to the saline conditions. The experiments of [PERSON] et al. [102] showed similar methane production efficiencies between inoculum from a WTP (non-saline conditions) and halophilic inoculum from saline sediments tested to 35 g L\({}^{-1}\) salinity. However, at higher salinity methanogenesis was significantly reduced. The findings reported by [PERSON] et al. [103] indicate that testing to develop inoculum influenced the methanogens into an acclimatization period, where, as a result, they became more tolerant to saline environments and perhaps favor increased saline conditions. These findings were in alignment with those of [PERSON] et al. [104], [PERSON] et al.