Phosphorus, chemical base and other renewables from wastewater with three 168-L microbial electrolysis cells and other unit operations

Phosphate rock is a depleting resource and wastewater a sustainable long-term alternative for phosphorous mining. In modern wastewater treatment phosphate is concentrated 7500 times from wastewater into sludge as iron phosphate (FeP). Recently developed bioelectrochemical reactors enabled phosphate recovery from sewage sludge containing FeP. The integrated bioelectric process was found of much broader utility than initially elaborated. It refines all principle components of wastewater. The implementation is confronted to a number of challenges. Three pilot microbial electrolysis cells (MECs) of 168 L each were constructed and installed in different municipal wastewater treatment plants (WWTPs). The scale-up MECs generated renewable chemical base and co-extracted abundant species such as Na+, K+, Ca2+, Mg2+ and NH4+ from wastewater. The chemical base remobilized phosphate quantitatively from iron phosphates contained in digested sewage sludge. Phosphate extracts contained ammonia and upon magnesium (Mg2+) addition struvite crystalized. Inductively Coupled Plasma Mass Spectrometry (ICP-MS) on heavy metals, Direct Mercury Analysis (DMA), Liquid Chromatography Mass Spectroscopy (LC-MS/MS) on organic micropollutants, metagenomics sequencing, Scanning Electron Microscopy (SEM-EDS), and X-Ray Diffraction (XRD) indicated that a highly pure struvite-fertilizer was produced. Microbial electricity co-generation was verified by electrochemical characterisation and microbiome analysis using 16S rRNA V4-V5 methodology. Geobacter, Dechloromonas, Desulfobulbus and cyanobacteria were the principal electrogens found. All in all, renewable chemical base as well as phosphate were obtained in high quantities and other renewables became accessible such as the critical material magnesium and other compounds of importance like ammonia, potassium, calcium, solid P-free sludge useful as biofuel and purified water. In general, the process recycles important compounds from waste, in a close to traceless manner while purifying wastewater

Simulation and resolution of voltage reversal in microbial fuel cell stack

To understand the biotic and non-biotic contributions of voltage reversals in microbial fuel cell stacks (MFC) they were simulated with an electronic MFC-Stack mimic. The simulation was then compared with results from a real 3 L triple MFC-Stack with shared anolyte. It showed that voltage reversals originate from the variability of biofilms, but also the external load plays a role. When similar biofilm properties were created on all anodes the likelihood of voltage reversals was largely reduced. Homogenous biofilms on all anodes were created by electrical circuit alternation and electrostimulation. Conversely, anolyte recirculation, or increased nutriment supply, postponed reversals and unfavourable voltage asymmetries on anodes persisted. In conclusion, voltage reversals are often a negative event but occur also in close to best MFC-Stack performance. They were manageable and this with a simplified MFC architecture in which multiple anodes share the same anolyte

Stretched 1000-L microbial fuel cell

The construction of large microbial fuel cells (MFCs) and their long-term reliability are current challenges. MFCs generate power while purifying wastewater, save electricity, avoid pollutant stripping into the air and are a source of CO2. To understand larger MFCs, a 1000-L MFC was designed. It was built from transparent polyester and electrodes were from reticulated vitreous carbon. Four power management devices were connected to an ensemble of 64 MFC units and assembled as a 12 m long MFC. Two Raspberry and a personal computer with Python programmed software automatized power management. The MFC was run for one year under maximum power point tracking (MPPT). Temperatures between 11.5 °C and 21 °C corresponded to WWTP conditions. The reactor shared electrolytes within 12 m long half-cells and 80–95% COD was removed generating 0.015 to 0.060 kWh/m3 with an energy efficiency of 5.8–12.1%. Voltage reversal were seen as potential imbalances among MFC units and all self-healing. Ammonium removal reached 48%, phosphorous was reduced to 0.59 mg/L, and micropollutants degraded by 67%. Biofilm mapping by 16S rRNA metagenomics indicated bi-sectorial metabolic properties. 10 Major genera were essential in the elongated scale up MFC generating electricity, reduced energy needed, and purified wastewater

Cathode deposits favor methane generation in microbial electrolysis cell

Cathodes in microbial electrolysis cells are exposed to poisoning in particular when using activated sludge as substrate. In this work, it was examined how well hydrogen generation is possible and what kind of membrane protection is sufficient to produce hydrogen from activated sludge. Also model microbial electrolysis was performed to simulate hydrogen evolution in a mimic biological environment at pH = 7. With activated sludge, it was found that electrodeposition of calcium, iron and phosphor and other impurities inhibited the hydrogen evolution reaction. Applying 2.0 V, the biogas productivity increased notably as if it induced rather chemical hydrolysis than hydrogenation and favored methanisation. This MEC generated methane in up to highest purity, 67–97%. In addition, this room-temperature methanisation consumed far less energy than with comparable mesophile conditions

Two stage bioethanol refining with multi litre stacked microbial fuel cell and microbial electrolysis cell

Ethanol, electricity, hydrogen and methane were produced in a two stage bioethanol refinery setup based on a 10 L microbial fuel cell (MFC) and a 33 L microbial electrolysis cell (MEC). The MFC was a triple stack for ethanol and electricity co-generation. The stack configuration produced more ethanol with faster glucose consumption the higher the stack potential. Under electrolytic conditions ethanol productivity outperformed standard conditions and reached 96.3% of the theoretically best case. At lower external loads currents and working potentials oscillated in a self-synchronized manner over all three MFC units in the stack. In the second refining stage, fermentation waste was converted into methane, using the scale up MEC stack. The bioelectric methanisation reached 91% efficiency at room temperature with an applied voltage of 1.5 V using nickel cathodes. The two stage bioethanol refining process employing bioelectrochemical reactors produces more energy vectors than is possible with today’s ethanol distilleries

Scale-up of phosphate remobilization from sewage sludge in a microbial fuel cell

Phosphate remobilization from digested sewage sludge containing iron phosphate was scaled-up in a microbial fuel cell (MFC). A 3 litre triple chambered MFC was constructed. This reactor was operated as a microbial fuel cell and later as a microbial electrolysis cell to accelerate cathodic phosphate remobilization. Applying an additional voltage and exceeding native MFC power accelerated chemical base formation and the related phosphate remobilization rate. The electrolysis approach was extended using a platinum-RVC cathode. The pH rose to 12.6 and phosphate was recovered by 67% in 26 h. This was significantly faster than using microbial fuel cell conditions. Shrinking core modelling particle fluid kinetics showed that the reaction resistance has to move inside the sewage sludge particle for considerable rate enhancement. Remobilized phosphate was subsequently precipitated as struvite and inductively coupled plasma mass spectrometry indicated low levels of cadmium, lead, and other metals as required by law for recycling fertilizers

Scale-up of phosphate remobilization from sewage sludge in a microbial fuel cell

Phosphate remobilization from digested sewage sludge containing iron phosphate was scaled-up in a microbial fuel cell (MFC). A 3 litre triple chambered MFC was constructed. This reactor was operated as a microbial fuel cell and later as a microbial electrolysis cell to accelerate cathodic phosphate remobilization. Applying an additional voltage and exceeding native MFC power accelerated chemical base formation and the related phosphate remobilization rate. The electrolysis approach was extended using a platinum-RVC cathode. The pH rose to 12.6 and phosphate was recovered by 67% in 26 h. This was significantly faster than using microbial fuel cell conditions. Shrinking core modelling particle fluid kinetics showed that the reaction resistance has to move inside the sewage sludge particle for considerable rate enhancement. Remobilized phosphate was subsequently precipitated as struvite and inductively coupled plasma mass spectrometry indicated low levels of cadmium, lead, and other metals as required by law for recycling fertilizers. (C) 2015 Elsevier Ltd. All rights reserved