Enhanced MFC power production and struvite recovery by the addition of sea salts to urine

© 2016 The Authors Urine is an excellent fuel for electricity generation in Microbial Fuel Cells (MFCs), especially with practical implementations in mind. Moreover, urine has a high content in nutrients which can be easily recovered. Struvite (MgNH4PO4·6H2O) crystals naturally precipitate in urine, but this reaction can be enhanced by the introduction of additional magnesium. In this work, the effect of magnesium additives on the power output of the MFCs and on the catholyte generation is evaluated. Several magnesium sources including MgCl2, artificial sea water and a commercially available sea salts mixture for seawater preparation (SeaMix) were mixed with real fresh human urine in order to enhance struvite precipitation. The supernatant of each mixture was tested as a feedstock for the MFCs and it was evaluated in terms of power output and catholyte generation. The commercial SeaMix showed the best performance in terms of struvite precipitation, increasing the amount of struvite in the solid collected from 21% to 94%. Moreover, the SeaMix increased the maximum power performance of the MFCs by over 10% and it also changed the properties of the catholyte collected by increasing the pH, conductivity and the concentration of chloride ions. These results demonstrate that the addition of sea-salts to real urine is beneficial for both struvite recovery and electricity generation in MFCs

Influence of different ways of chloride contamination on the efficiency of cathodic protection applied on structural reinforced concrete elements

Cathodic protection is a method to protect reinforced concrete structures located in saline environments against corrosion effect produced by Cl− penetration. But there are significant differences among these aggressive environments. The aim of this article is to show how different ways of saline contamination can affect the efficiency of cathodic protection. For this research, a series of laboratory specimens representing structural elements were subjected to two versions of cathodic protection (cathodic protection strictly speaking, and cathodic prevention), while two different ways of saline contamination were applied (permanent immersion in a NaCl solution and periodic pouring of discrete amounts of a NaCl solution in atmospheric exposure). Depending on the saline environment, differences in the efficiency of cathodic protection were detected. Results can be useful to determine the specific features of the cathodic protection to be applied in each case, taking into account both the initial Cl− content of the structural element and the particular saline environment where it is located.This research was funded by the Spanish Ministerio de Economía y Competitividad (and formerly by the Spanish Ministerio de Ciencia e Innovación) and European Regional Development Fund (ERDF) through projects BIA2010-20548 and MAT2009-10866, respectively, and also through the project PROMETEO/2013/035 of Generalitat Valenciana (Spain)

Phosphorus availability of sewage sludge-based fertilizers determined by the diffusive gradients in thin films (DGT) technique

The plant-availability of phosphorus (P) in fertilizers and soil can strongly influence the yield of agricultural crops. However, there are no methods to efficiently and satisfactorily analyze the plant-availability of P in sewage sludge-based P fertilizers except by undertaking time-consuming and complex pot or field experiments. We employed the diffusive gradients in thin films (DGT) technique to quantify the plant P availability of various types of P fertilizers with a novel focus on sewage sludge-based P fertilizers. Mixtures of fertilizer and soil were incubated for 3 weeks at 60% water holding capacity. DGT devices were deployed at the beginning of the incubation and again after 1, 2, and 3 weeks. Two weeks of incubation were sufficient for the formation of plant-available P in the fertilizer/soil mixtures. In a pot experiment, the DGT technique predicted maize (Zea mays L.) biomass yield and P uptake significantly more accurately than standard chemical extraction tests for P fertilizers (e.g. water, citric acid, and neutral ammonium citrate). Therefore, the DGT technique can be recommended as a reliable and robust method to screen the performance of different types of sewage sludge-based P fertilizers for maize cultivation minimizing the need for time-consuming and costly pot or field experiments

Effect of Calcium Additive on the Crystallization of Struvite

Crystallization of struvite [MgNH4PO4.6H2O] may lead to the deposition of scale which may create significant problems in the process pipes, pumps and other industrial equipment. However, struvite precipitation can be benefited for phosphate recovery for use of fertilizer. The aim at the present work was to investigate calcium additive on struvite precipitation. The experiment was carried out in a batch mode using a 1-liter Pyrex glass vessel mechanically agitated for 200 rpm. The scale-forming solution was prepared for mixing solutions to MgCl2 and NH4H2PO4 with Mg+2 , NH4+ and PO4-3 in a molar ratio of 1: 1:1. The crystallization temperature of 30 and 40 °C was selected. Ca was added into the crystallizing solution to chloride dihydrate 0.4M (CaCl2•2H2O). Then each solution was pH adjusted to 9 by addition of KOH. The crystals obtained were characterized using SEM for morphology, EDS for elemental analysis as well as XRPD Rietveld analysis for crystaline phases. The induction periods varied from 10 to 90 min, which means that the struvite crystals began forming 10 to 90 min after mixing of the solution. It was observed that the Ca additive may inhibit the struvite crystallization. SEM analysis revealed that the struvite crystals obtained were predominantly of irregular prismatic morphology. Furthermore, the EDS pattern revealed that the elemental composition of the crystals consisted of Ca, Cl, S Mg, N, and P, providing that many crystalline phase found in the crystals such as Gypsum, CaCl2, struvite, struvite-(K) and sylvite. It was observed that the Ca additive appeared to inhibit the struvite crystallization