A Laboratory-Scale Study of the Applicability of a Halophilic Sediment Bioelectrochemical System for in situ Reclamation of Water and Sediment in Brackish Aquaculture Ponds: Establishment, Bacterial Community and Performance Evaluation

Abstract

In this study, we investigated the potential of using sediment bioelectrochemical systems (SBESs) for in situ treatment of the water and sediment in brackish aquaculture ponds polluted with uneaten feed. An SBES integrated into a laboratory-scale tank simulating a brackish aquaculture pond was established. This test tank and the control (not containing the SBES) were fed with shrimp feed in a scheme that mimics a situation where 50% of feed is uneaten. After the SBES was inoculated with microbial sources from actual shrimp pond sediments, electricity generation was well observed from the first experimental week, indicating successful enrichment of electrochemically active bacteria in the test tank sediment. The electricity generation became steady after 3 weeks of operation, with an average current density of 2.3 mA/m 2 anode surface and an average power density of 0.05 mW/m 2 anode surface. The SBES removed 20-30% more COD of the tank water, compared to the control. After 1 year, the SBES also reduced the amount of sediment in the tank by 40% and thus could remove approximately 40% more COD and approximately 52% more nitrogen from the sediment, compared to the control. Insignificant amounts of nitrite and nitrate were detected, suggesting complete removal of nitrogen by the system. PCR-DGGE-based analyses revealed the dominant presence of Methylophilus rhizosphaerae, Desulfatitalea tepidiphila and Thiothrix eikelboomii, which have not been found in bioelectrochemical systems before, in the bacterial community in the sediment of the SBES-containing tank. The results of this research demonstrate the potential application of SBESs in helping to reduce water pollution threats, fish and shrimp disease risks, and thus farmers' losses.

A Laboratory-Scale Study of the Applicability of a Halophilic Sediment Bioelectrochemical System for in situ Reclamation of Water and Sediment in Brackish Aquaculture Ponds: Effects of Operational Conditions on Performance

“…Indeed, our previous study pointed out that unique bacteria, including Methylophilus rhizosphaerae, Desulfatitalea tepidiphila and Thiothrix eikelboomii, might play key roles in the SBES, rather than the popular electroactive ones such as Geobacter spp., Shewanella oneidensis or Pseudomonas spp. [3]. However, the system also performed relatively well, like the one reported by Sajana and colleagues, in terms of removing COD and nitrogen contents of the pond water and sediment.…”

“…Two rectangular parallelepiped glass tanks (each having the dimensions of 30 cm × 20 cm × 25 cm) that were previously constructed [3] (Fig. S1) were used as pond models in this study.…”

“…One tank having a sediment bioelectrochemical system (SBES) installed was used as the test tank, while the other tank not having it served as the control. The SBES installed in the test tank consisted of a sediment anode and a cathode floating on the water surface (see detailed description in our previous study [3]). The sediment anode included a 2-cm-thick layer of graphite granules (3-5 mm in diameter) (Xilong Chemical Co., China) and an underlying graphite felt having the dimensions of 15 cm × 7 cm × 0.9 cm (Osaka Gas Chemicals Co., Japan).…”

“…A number of technologies for the reduction of water pollution in aquaculture ponds have been reported, including the use of artificial aeration systems and/or separate systems to treat and recycle the water, etc. [3]. Those technologies, although having high treatment efficiencies, were not cost-competitive because of their constructional and operational costs and energy expenses [1].…”

“…Bioelectrochemical oxidation of organic substances and ammonium (nitrification) are believed to enhance such bioremediation, in addition to natural degradation. Their studies inspired us to investigate the possibility of installing an SBES in brackish aquaculture models and evaluate its bioremediation performance (our previous study [3]). Such a study is necessary because there are numerous aquaculture farms with brackish water all over the world and processes (including bioelectrochemical processes) under high salinity conditions might be absolutely different.…”