English abstract
Microbial desalination cell (MDC) is considered as an eco-friendly technology for water
purification in which organic contaminants in wastewater are used as energy source to
drive the desalination process. Microbial desalination and chemicals production cell
(MDCC) is a novel device, modified version of MDC that desalinate saline water, produce
electricity, and concurrently produce acid and base. However, several factors have limited
the MDCCs performance and their development, such as, pH imbalance and ions
accumulation. In addition, adding chemicals production compartment and bipolar
membrane (BPM) may increase the internal resistance (Rint). This research demonstrated
the proof-of-concept for a three-chamber circular MDCC (TC-MDCC) with a new
arrangement of the anion, cation exchange and bipolar membranes. The novel design
aimed to investigate – (i) the cell performance in terms of acid-base production, salt
removal and current generation with/without external power supply utilizing two salt
concentrations (35 g/L NaCl and 10 g/L NaCl), (ii) the effect of bipolar membrane and
initial NaCl concentrations on the cell internal resistance, and (iii) compering the cell
performances with/without external power source.
Results showed that the current production was increased in the TC-MDCC from 1.94 mA
and to 3.3 mA, when the initial NaCl concentration was increased from 10 to 35 g/L,
because of the high conductivity of electrolyte. Thus, the internal resistance decreased from
300 to 270 Ω, which were much higher than Rint of MDC (85 Ω for 10 g/L salt, 75 Ω for
35 g/L salt). The pH of the electrolyte chamber of MDCC always remained constant, which
greatly enhanced the activity of the microorganism in the anode chamber. Desalinating 10
g/L salt without any external applied energy, the pH of the HCl production chamber
decreased to 3.029 and the pH of the alkali-production chamber increased to 8.96. The pH
changes were enhanced by using more concentrated salt (2.79 (acid) and 9.41 (base))
achieving a maximum desalination rate of 51%. With applied voltages of 0.3-1.0 V, 27-
57% desalination rate were achieved within 24 hrs using 35 g/L salt with simultaneous
production of HCl and NaOH with an optimum production rates of 1.96 mg/h of acid and
65.4 mg/h for the base applying external 1.0 V. These results demonstrated proof of
concept for producing acid and base using renewable source of energy, which could be
enhanced by integrating it with the MFC as a sustainable source of energy.
