A novel self-buffering membrane distillation-based thermophilic anaerobic bioreactor

• Published in: Environmental technology & innovation 2020-11, Vol.20, p.101077, Article 101077
• Main Authors: Duong, Chinh Cong, Chen, Shiao-Shing, Le, Huy Quang, Chang, Hau-Ming, Nguyen, Nguyen Cong, Cao, Dan Thanh Ngoc
• Format: Article
• Language: English
• Subjects: Alkalinity; Membrane distillation; Self-buffering; Thermophilic anaerobic bioreactor
• ISSN: 2352-1864; 2352-1864
• DOI: 10.1016/j.eti.2020.101077

The stability of an anaerobic bioreactor is a function of alkalinity that provides buffer capacity to maintain a suitable pH for anaerobic microorganisms. The greatest advantage of membrane distillation (MD) is the high rejection of most solutes, including alkaline salt, and it has a high potential to retain alkalinity for the anaerobic system. For the first time, a thermophilic anaerobic granular bioreactor integrated with an MD membrane to maintain the buffered pH was studied in an anaerobic bioreactor without alkalinity supplement. This study presented a comparison between a conventional thermophilic anaerobic bioreactor (TAn1) and a thermophilic anaerobic bioreactor integrated with a MD (TAn2-MD). The two TAns (TAn1 and TAn2) were operated in the same conditions except there was no alkalinity feeding for the TAn2-MD. The results showed that the pH in the TAn2-MD unit was always higher than 6.8 with the organic loading rates from 6 to 18 kg COD/m3/day. However, to maintain the pH of the TAn1 unit at the same level as the TAn2-MD unit, the minimum alkalinity requirements for TAn1 were 1.5, 1.56, 1.62, and 1.8 g/L as CaCO3 at an organic loading rate of 6, 10, 14, and 18 kg COD/m3/day, respectively. Although there was no alkalinity supplement for the TAn2-MD system, two stability indexes, FOS/TAC (volatile organic acids to buffer capacity) and IA/PA (intermediate alkalinity to partial alkalinity), indicated the system was operated at a stable condition. In summary, the designed TAn2-MD can accomplish high-efficiency organic carbon removal (higher than 99.4%) without alkalinity supplement, achieve zero-liquid-discharge, and reclaim high-quality wastewater in one step. [Display omitted] •Alkalinity supplement was not required in the novel self-buffered anaerobic bioreactor.•Stable pH was maintained for long-term operation by the self-maintained alkalinity.•The MD process can use waste heat from the thermophilic anaerobic granular bioreactor.•Water reclamation was accomplished in one step.