Comparative studies of the electricity generation, desalination and wastewater treatment performance of the Three-Chamber and newly developed Five Chamber Microbial Desalination Cells
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Date
2021-07-09
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Abstract
Poor wastewater treatment and limited potable water supply in the country are
problems that require sustainable solutions. Available technologies to solve these
problems are expensive especially to a developing country like Ghana. A recently
developed technology, Microbial Desalination Cell (MDC) is considered a less
expensive alternative to conventional wastewater treatment and desalination
technologies. In MDCs, wastewater treatment occurs in the anode chamber and
desalination in the desalination chamber. A third chamber, the cathode chamber is
present to create a potential difference across the anode chamber and itself for
electricity production. One setback of MDC systems however is that, most operate
with chemical oxidants and buffers which can make this technology expensive. Thus,
this research work sought to build MDCs which operate on alternative non-chemical
oxidants sources and also, MDCs which are able to buffer electrolytes without the use
of chemical buffers. Another objective of this study was to investigate the effects of
rhamnolipid on MDCs electricity generation, desalination and wastewater treatment
performances. The interactive effect of rhamnolipid and stirring on a five-chambered
MDC was also investigated and ion exchange membranes of selected MDCs
examined for the occurrence of fouled layers. A comparison between the electricity
generation, desalination and wastewater treatment performances of three-chamber
MDCs operating on different electron acceptor sources showed that, the threechamber chemical catholyte (3 C C) MDC performed better than the three-chamber
water catholyte (3 W C) MDC and three-chamber plant-supported (3 P C) MDC. The
3 C C MDC produced the highest peak voltage of 282.91± 0.09 mV, coulombic
efficiency of 78.61% and could desalinate 46.66% of saltwater. Its power (0.35 ± 0.10
W/m3
) and current (1.24 ± 0.35 A/m3
) densities were also the highest amongst the
three-chambered MDCs. It produced a 42.81% COD reduction, 1.14% nitrate
reduction and a 10.71% phosphorus reduction. On the other hand, the 3 P C MDC
produced the least performance. The highest voltage recorded from it was 193.99 ±
0.80 mV. The 3 P C MDC could desalinate 23.34% of saltwater, produce 0.25 ± 0.06
W/m3
of power, 1.09 ± 0.11 A/m3
of current density with coulombic efficiency (CE)
of 10.03%. It achieved a percentage COD reduction of 41.79%, highest percentage
nitrate removal of 1.05% and phosphorus reduction of 9.97%. Apparently, the pH
stabilization ability of neutralization chambers was lower than that of potassium
phosphate buffer they were compared to. For instance, with the neutralization
chamber, pH-change in the anolyte of the five-chamber chemical catholyte (5 C C)
MDC was 1.66 ± 0.11 whiles pH change in the 3 C C MDC was 1.52 ± 0.15.
Nonetheless, the 5 C C MDC produced a comparatively higher voltage of 343.57 ±
0.25 mV, percentage desalination of 50.01%, but a lower CE of 25.20%. Its power
and current densities were 0.62 2 ± 0.13 W/m3
and 1.61 ± 0.21 A/m3
respectively. It
was able to reduce COD concentration by 63.42%, nitrate concentration by 2.12% and
phosphorus by 3.85%. The supply of rhamnolipids to anolytes of the five-chamber
MDCs increased their performances. Voltage production of the 5 C C MDC increased
from 343.57 ± 0.25 mV to 630.60 ± 1.44 mV, percentage desalination from 50.01% to
67.63% and COD, from 63.42% to 72.78%. In the case of the five-chamber water
catholyte (5 W C) MDC, its voltage increased from 164.5 ± 0.11 to 623.7 ± 1.32 mV,
percentage desalination from 43.74% to 63.21% and percentage COD reduction from
48.74% to 65.31%. Stirring (60 rpm) of water catholyte alone, could increase the
percentage desalination of 5 W C MDC from 48.74% to 65.29% and voltage
production from 164.5 ± 0.11 to 567.27 ± 18.06 mV. However, the interaction effect
of rhamnolipid and stirring on the performance of the 5 W C MDC was insignificant.
Analysis of membranes of the 5 W C MDC showed that, the membranes were fouled
on both sides. And a comparison between the degree of fouling on cation exchange
membranes (CEMs) of the 5 C C MDC and 5 W C MDCs revealed that, the CEM of
the 5 C C MDC was more fouled though used for a lesser period of time. Having
assessed the core performances and material requirements of MDCs investigated in
this study, the 5 W C MDC was found to be the ideal MDC for possible future use in
Ghana. Thus, the 5 W C MDC when integrated with conventional wastewater
treatment and desalination technologies can aid these technologies achieve higher
treatment qualities aside the additional benefit of ‗free‘ electricity the 5 W C MDC
can provide.
Description
A thesis submitted to the Department of Civil Engineering College of Engineering in partial fulfilment of the requirement for the award of Doctor of Philosophy in Environmental Sanitation and Waste Management.
Keywords
Comparative Studies, Electricity Generation, Desalination Wastewater Treatment Performance, Three-Chamber,, Five Chamber Microbial Desalination Cells (MDC)