Electrochemical technology enables nutrient recovery and ammonia toxicity control in anaerobic digestion

The aim of this study was to investigate the impact of an electrochemical system (ES) on the performance of an anaerobic digester during both low and high ammonium (NH4+) loading rates. For this, a Test (with ES) and Control (without ES) setup was used. Ammonia (NH3), in equilibrium with NH4+, is a toxic compound to the methanogenic community, limits the substrate loading rate and endangers process stability. We hypothesized that, through coupling of an ES to a digester, NH3 toxicity can be controlled with simultaneous recovery of this nutrient. The ES always had a temporary negative effect when switched on. However, during periods of high ammonium loading rates the CH4 production of the Test reactor was at maximum a factor 4.5 higher compared to the Control reactor, which could be explained through a combination of NH4+ extraction and electrochemical pH control. A nitrogen flux of 47 g N m-2 membrane d-1 could be obtained in the Test reactor, resulting in a current and removal efficiency of 38±5% and 28±2%, respectively. For this, an electrochemical power input 17±2 kWh kg-1 N was necessary. In addition, anodic oxidation of sulphide resulted in a significantly lower H2S emission

Operational and technical considerations for microbial electrosynthesis

Extracellular electron transfer has, in one decade, emerged from an environmental phenomenon to an industrial process driver. On the one hand, electron transfer towards anodes leads to production of power or chemicals such as hydrogen, caustic soda and hydrogen peroxide. On the other hand, electron transfer from cathodes enables bioremediation and bioproduction. Although the microbiology of extracellular electron transfer is increasingly being understood, bringing the processes to application requires a number of considerations that are both operational and technical. In the present paper, we investigate the key applied aspects related to electricity-driven bioproduction, including biofilm development, reactor and electrode design, substrate fluxes, surface chemistry, hydrodynamics and electrochemistry, and finally end-product removal/toxicity. Each of these aspects will be critical for the full exploitation of the intriguing physiological feat that extracellular electron transfer is today

Sanitation of blackwater via sequential wetland and electrochemical treatment

The discharge of untreated septage is a major health hazard in countries that lack sewer systems and centralized sewage treatment. Small-scale, point-source treatment units are needed for water treatment and disinfection due to the distributed nature of this discharge, i.e., from single households or community toilets. In this study, a high-rate-wetland coupled with an electrochemical system was developed and demonstrated to treat septage at full scale. The full-scale wetland on average removed 79 +/- 2% chemical oxygen demand (COD), 30 +/- 5% total Kjeldahl nitrogen (TKN), 58 +/- 4% total ammoniacal nitrogen (TAN), and 78 +/- 4% orthophosphate. Pathogens such as coliforms were not fully removed after passage through the wetland. Therefore, the wetland effluent was subsequently treated with an electrochemical cell with a cation exchange membrane where the effluent first passed through the anodic chamber. This lead to in situ chlorine or other oxidant production under acidifying conditions. Upon a residence time of at least 6 h of this anodic effluent in a buffer tank, the fluid was sent through the cathodic chamber where pH neutralization occurred. Overall, the combined system removed 89 +/- 1% COD, 36 +/- 5% TKN, 70 +/- 2% TAN, and 87 +/- 2% ortho-phosphate. An average 5-log unit reduction in coliform was observed. The energy input for the integrated system was on average 16 +/- 3 kWh/m(3), and 11 kWh/m(3) under optimal conditions. Further research is required to optimize the system in terms of stability and energy consumption

Microbial technology with major potentials for the urgent environmental needs of the next decades

Several needs in the context of the water-energy-food nexus will become more prominent in the next decades. It is crucial to delineate these challenges and to find opportunities for innovative microbial technologies in the framework of sustainability and climate change. Here, we focus on four key issues, that is the imbalance in the nitrogen cycle, the diffuse emission of methane, the necessity for carbon capture and the deterioration of freshwater reserves. We suggest a set of microbial technologies to deal with each of these issues, such as (i) the production of microbial protein as food and feed, (ii) the control of methanogenic archaea and better use of methanotrophic consortia, (iii) the avoidance of nitrification and (iv) the upgrading of CO2 to microbial bioproducts. The central message is that instead of using crude methods to exploit microorganisms for degradations, the potentials of the microbiomes should be used to create processes and products that fit the demands of the cyclic market economy

A Bioelectrochemical Approach to Characterize Extracellular Electron Transfer by Synechocystis sp. PCC6803

Biophotovoltaic devices employ photosynthetic organisms at the anode of a microbial fuel cell to generate electrical power. Although a range of cyanobacteria and algae have been shown to generate photocurrent in devices of a multitude of architectures, mechanistic understanding of extracellular electron transfer by phototrophs remains minimal. Here we describe a mediatorless bioelectrochemical device to measure the electrogenic output of a planktonically grown cyanobacterium, Synechocystis sp. PCC6803. Light dependent production of current is measured, and its magnitude is shown to scale with microbial cell concentration and light intensity. Bioelectrochemical characterization of a Synechocystis mutant lacking Photosystem II demonstrates conclusively that production of the majority of photocurrent requires a functional water splitting aparatus and electrons are likely ultimately derived from water. This shows the potential of the device to rapidly and quantitatively characterize photocurrent production by genetically modified strains, an approach that can be used in future studies to delineate the mechanisms of cyanobacterial extracellular electron transport