Pecologix Political Ecology Blotter » microbial cells

Ammonium recovery and energy production from urine by a microbial fuel cell

A. Cherson — Sun, 01 Apr 2012 17:42:33 +0000

Nitrogen recovery through NH3 stripping is energy intensive and requires large amounts of chemicals. Therefore, a microbial fuel cell was developed to simultaneously produce energy and recover ammonium. The applied microbial fuel cell used a gas diffusion cathode. The ammonium transport to the cathode occurred due to migration of ammonium and diffusion of ammonia. In the cathode chamber ionic ammonium was converted to volatile ammonia due to the high pH. Ammonia was recovered from the liquid–gas boundary via volatilization and subsequent absorption into an acid solution. An ammonium recovery rate of 3.29 gN d−1 m−2 (vs. membrane surface area) was achieved at a current density of 0.50 A m−2 (vs. membrane surface area). The energy balance showed a surplus of energy 3.46 kJ gN−1, which means more energy was produced than needed for the ammonium recovery. Hence, ammonium recovery and simultaneous energy production from urine was proven possible by this novel approach.

http://dx.doi.org/10.1016/j.watres.2012.02.025

Phosphate recovery as struvite within a single chamber microbial electrolysis cell

A. Cherson — Thu, 09 Feb 2012 03:26:16 +0000

An energy efficient method of concurrent hydrogen gas and struvite (MgNH₄PO₄·6H₂O) production was investigated based on bioelectrochemically driven struvite crystallization at the cathode of a single chamber microbial electrolysis struvite-precipitation cell (MESC). The MESC cathodes were either stainless steel 304 mesh or flat plates. Phosphate removal ranged from 20% to 40%, with higher removals obtained using mesh cathodes than with flat plates. Cathode accumulated crystals were verified as struvite using a scanning electron microscope capable of energy dispersive spectroscopy (SEM–EDS). Crystal accumulation did not affect the rate of hydrogen production in struvite reactors. The rate of struvite crystallization (g/m²-h) and hydrogen production (m³/m³-d) were shown to be dependent on applied voltage and cathode material. Overall energy efficiencies (substrate and electricity) were high (73 ± 4%) and not dependent on applied voltage. These results show that MESCs may be useful both as a method for hydrogen gas and struvite production.

DOI: http://dx.doi.org/10.1016/j.biortech.2011.12.038

Microbial carbon capture cell using cyanobacteria for simultaneous power generation, carbon dioxide sequestration and wastewater treatment

A. Cherson — Thu, 09 Feb 2012 03:21:36 +0000

Microbial carbon capture cells (MCCs) were constructed with cyanobacteria growing in a photo biocathode in dual-chambered flat plate mediator-less MFCs separated by an anion exchange membrane from the anode compartment containing Shewanella putrefaciens. The performance of the MCC with Anabaena sparged with CO₂–air mixture was compared with that of a conventional cathode sparged with air only. The power densities achieved were 57.8 mW/m² for Anabaena sparged with a CO₂–air mixture, 39.2 mW/m² for CO₂–air mixture sparging only, 29.7 mW/m² for Anabaena sparged with air, and 19.6 mW/m² for air sparging only. The pH of the cathode containing Anabaena gradually increased from 7 to 9.12 and power generation decreased from 34.7 to 23.8 mW/m² 17 due to pH imbalance associated voltage losses without CO₂–air mixture sparging. Sparging with a 5% CO₂–air mixture produced maximum power of 100.1 mW/m². In addition, the power density of MCC increased by 31% when nitrate was added into the catholyte.

DOI: http://dx.doi.org/10.1016/j.biortech.2011.12.067

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Enhanced hydrogen production from waste activated sludge by cascade utilization of organic matter in microbial electrolysis cells

A. Cherson — Mon, 23 Jan 2012 16:44:16 +0000

Fermentative hydrogen production from waste activated sludge (WAS) has low H₂ yield because WAS contains limited amounts of carbohydrate suitable for use by hydrogen-producing bacteria. Here, augmentation of hydrogen production from WAS by microbial electrolysis cells (MECs) was implemented. H₂ yields of 3.89 ± 0.39 mg-H₂/g-DS (5.67 ± 0.61 mg-H₂/g-VSS) from raw WAS and 6.78 ± 0.94 mg-H₂/g-DS (15.08 ± 1.41 mg-H₂/g-VSS) from alkaline-pretreated WAS were obtained in the two-chamber MECs (TMECs). This was several times higher than yields obtained previously by fermentation. Single-chamber MECs (SMECs) with low internal resistance showed a H₂ production rate that 13 times that of TMECs with similar H₂ yield when alkaline-pretreated WAS was used. However, methanogenesis was detected after several batch cycles. A yield balance calculation revealed that carbohydrates were not the only substrates for electrohydrogenesis. Protein and its acidification products, such as volatile fatty acids are also responsible for a portion of H₂ generation in MEC. Characterization of WAS in TMECs by three-dimensional excitation-emission matrix (EEM) fluorescence spectroscopy with parallel factor analysis indicated that electrohydrogenesis reacted on the extracellular polymeric substances and intracellular substances of WAS. Cascade utilization of organic matter in MECs increased hydrogen production from WAS. MECs showed high hydrogen yield from WAS, fewer H₂ sinks, and insensitivity to temperature. Optimizing MEC configurations and operation conditions and improving the pretreatment processes of WAS are necessary before practical application can take place on a large scale.

DOI: http://dx.doi.org/10.1016/j.watres.2011.11.073

Evaluation of potato-processing wastewater treatment in a microbial fuel cell

A. Cherson — Fri, 06 Jan 2012 03:45:46 +0000

Wastewaters from potato-processing industries have been traditionally treated by a sequence of steps that include the production of methane as the anaerobic one. This work explores the feasibility of replacing or supplementing methanogenesis with the emerging technology of microbial fuel cells (MFCs). Electricity producing biofilms have been enriched from a real anaerobic sludge, and the conversion of potato-processing wastewater into electricity has been studied. When tested as a single treatment step, MFCs were able to process the wastewater with high COD removal but with low energetic conversion efficiency. On the other hand, as a complimentary step for methanogenesis, they improved conversion efficiency and significantly reduced the organic matter load of the final effluent. These results point at the combination of the energetic yield of methanogenesis and the improved COD removal of the electricity producing treatment as the implementation choice.

doi:10.1016/j.biortech.2011.11.095

Simultaneous organic carbon, nutrients removal and energy production in a photomicrobial fuel cell (PFC)

A. Cherson — Tue, 04 Oct 2011 00:28:37 +0000

A sediment-type photomicrobial fuel cell (PFC), based on the synergistic interaction between microalgae (Chlorella vulgaris) and electrochemically active bacteria, was developed to remove carbon and nutrients from wastewater, and produce electricity and algal biomass simultaneously. Under illumination, a stable power density of 68 ± 5 mW m−2 and a biomass of 0.56 ± 0.02 g L−1 were generated at an initial algae concentration of 3.5 g L−1. Accordingly, the removal efficiency of organic carbon, nitrogen and phosphorus was 99.6%, 87.6% and 69.8%, respectively. Mass balance analysis suggested the main removal mechanism of nitrogen and phosphorus was the algae biomass uptake (75% and 93%, respectively), while the nitrification and denitrification process contributed to a part of nitrogen removal (22%). In addition, the effect of illumination period on the performance of PFC was investigated. Except notable fluctuation of power generation, carbon and nutrients removal was not significantly affected after changing the light/dark photoperiod from 24 h/0 h to 10 h/14 h. This work represents the first successful attempt to develop an effective bacteria–algae coupled system, capable for extracting energy and removing carbon, nitrogen and phosphorus from wastewater in one-step.

DOI: http://dx.doi.org/10.1039/C1EE02089G