Operating and scale‐up factors for the electrolytic removal of algae from eutrophied lakewater

Abstract

Electrolytic removal of algae was conducted in batch and continuous reactors to investigate operating factors affecting removal ef®ciency and to explore engineering relationships which could be useful for operation and scale-up. The system integrated both electro-¯occulation and electrootation mechanisms by using polyvalent metal anodes and inert metal cathodes. Batch reactor studies con®rmed that high electrical input power or higher electrical current achieved higher and faster removal ef®ciencies. Natural liquid circulation was observed during electrolytic operation and increased with higher electrical power. However, a small degree of external mixing may be useful at lower electrical power input. Electro-¯otation alone could not achieve complete algae removal (maximum ef®ciency 40±50%), and showed the importance of algal¯oc formation for the complete removal of algae. In continuous electrolysis experiments, the ratio of the volumetric current intensity (amperes dm À3) and the chlorophyll a loading (mg dm À3 h À1) was found to be a useful operating and scale-up factor to balance high algal removal ef®ciency with minimum release of excess aluminum. This ratio was eventually found to be just the charge dose or the amount of coulombs required to remove a unit mass of chlorophyll a. The optimum charge dose was determined and used to relate the operating current and electrolysis time of a continuous process.

Electro-coagulation–flotation process for algae removal

“…Poelman et al found that excellent separation of cyanobacteria (>90%) could be achieved by electrolytic flocculation, with relatively low energy consumption (0.3 kWh/m 3 ) [24]. Alfafara et al demonstrated that the electroflotation alone also exhibited a maximum algae removal of 40-50% [25]. While complete removal of algae was obtained by Ghernaout et al when treating Keddara raw water by the electrocoagulation using aluminum electrodes [26].…”

Harvesting green algae from eutrophic reservoir by electroflocculation and post-use for biodiesel production

“…In the case of 10 V, after 60 min the efficiency was reversed to better results, which is according with the results showed in this research, Xu et al (2010), who obtained greater efficiency in the first minutes of the sedimentation process. The applied current is also an important variable in the EF process (Vandamme et al, 2011), as a result, higher electrical power produced more flocculants to enhance algal flocculation (Alfafara et al, 2002). All these results, as well as those obtained during the sedimentation time are summarized in Table 1.…”

“…Although the algae studied were different, it can be considered that the results were similar to those obtained in this investigation. Research conducted by Alfafara et al (2002) who studied the Microcystis sp., concluded that electro-flotation alone is not efficient but the combination of electro-flocculation and electro-flotation causes >90% removal of it. Many researchers have developed techniques for growing and harvesting algae for further use as biodiesel, many of them are summarized in the review conducted by Chen et al (2011) where an analysis of the latest research is made up to 2011.…”

“…Lee et al (2013) concluded in their study that electroflocculation is potentially a low cost Tetraselmis sp. microalgal harvesting technique; and Alfafara et al (2002) who combined the electroflocculation with electrocoagulation. Highlight the researched carried out by Liang et al (2008) who tried to eliminated the microcystin-LR during the cyanobacterial inactivation by electooxidation, obtaining more than 98% removal for total.…”

Harvesting and Downstream Processing—and Their Economics

“…This process has been run in both batch and continuous mode and found that higher power positively correlated with increased algal cell separation in eutrophic lake water (Alafara et al 2002). The advantage of this method is there is no need for the addition of chemicals to induce separation.…”