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

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

Pathway of nitrous oxide consumption in isolated Pseudomonas stutzeri strains under anoxic and oxic conditions

The microbial consumption of nitrous oxide (N2O) hasgained great interest since it was revealed that thisprocess could mitigate the greenhouse effect of N2O.The consumption of N2O results from its reduction todinitrogen gas (N2) as part of the denitrificationprocess. However, there is ongoing debate regardingan alternative pathway, namely reduction of N2OtoNH4+, or assimilatory N2O consumption. To date, thispathway is poorly investigated and lacks unambigu-ous evidence. Enrichment of denitrifying activatedsludge using a mineral nitrogen-free medium ren-dered a mixed culture capable of anoxic and oxicN2O consumption. Dilution plating, isolation anddeoxyribonucleic acid fingerprinting identified a col-lection ofPseudomonas stutzeristrains as dominantN2O consumers in both anaerobic and aerobic enrich-ments. A detailed isotope tracing experiment with aPseudomonas stutzeriisolate showed that consump-tion of N2O via assimilatory reduction to NH4+wasabsent. Conversely, respiratory N2O reduction wasdirectly coupled to N2fixation

Electrochemical nutrient recovery enables ammonia toxicity control and biogas desulfurization in anaerobic digestion

Organic waste streams can be valorized and reduced in volume with anaerobic digestion (AD). An often-encountered key issue however is the high ammonium (NH4+) content of certain waste streams. Ammonia (NH3), in equilibrium with NH4+, is a toxic compound to the methanogenic community, which limits the organic loading rate and endangers process stability. An electrochemical system (ES) linked to a digester could, besides recovering this nutrient, decrease NH3 toxicity through electrochemical extraction. Therefore, two digesters with and without ES attached in the recirculation loop were operated to test whether the ES could control NH3 toxicity. During periods of high ammonium loading rates, the methane (CH4) production of the ES-coupled reactor was up to 4.5 times higher compared to the control, which could be explained through simultaneous NH4+ extraction and electrochemical pH control. A nitrogen flux of 47 g N m(-2) membrane d1 could be obtained in the ES-coupled reactor, resulting in a current and removal efficiency of 38 +/- 5% and 28 +/- 2%, respectively, at an electrochemical power input of 17 +/- 2 kWh kg(-1) N. The anode also oxidized sulfide, resulting in a significantly lower H2S emission via the biogas. Lastly, limited methanogenic community dynamics pointed to a nonselective influence of the different operational conditions

Electrolytic Membrane Extraction Enables Production of Fine Chemicals from Biorefinery Sidestreams

Short-chain carboxylates such as acetate are easily produced through mixed culture fermentation of many biological waste streams, although routinely digested to biogas and combusted rather than harvested. We developed a pipeline to extract and upgrade short-chain carboxylates to esters via membrane electrolysis and biphasic esterification. Carboxylate-rich broths are electrolyzed in a cathodic chamber from which anions flux across an anion exchange membrane into an anodic chamber, resulting in a clean acid concentrate with neither solids nor biomass. Next, the aqueous carboxylic acid concentrate reacts with added alcohol in a water-excluding phase to generate volatile esters. In a batch extraction, 96 ± 1.6% of the total acetate was extracted in 48 h from biorefinery thin stillage (5 g L^–1 acetate) at 379 g m^–2 d^–1 (36% Coulombic efficiency). With continuously regenerated thin stillage, the anolyte was concentrated to 14 g/L acetic acid, and converted at 2.64 g (acetate) L^–1 h^–1 in the first hour to ethyl acetate by the addition of excess ethanol and heating to 70 °C, with a final total conversion of 58 ± 3%. This processing pipeline enables direct production of fine chemicals following undefined mixed culture fermentation, embedding carbon in industrial chemicals rather than returning them to the atmosphere as carbon dioxide