Influences of electrode distance and electrolysis time on phosphorus precipitation and composition during electrolysis of anaerobic digestion effluent.

Global demand for phosphorus (P) is increasing, which has led to concerns over future drought and has driven efforts to recover P from wastewater streams for reuse. In this study, platinum-coated titanium electrodes were applied to the electrochemical precipitation of P from anaerobic digestion effluent that was collected from a domestic wastewater treatment plant. The influence of the electrode distance on P removal and precipitation was investigated. In addition, the influence of the electrolysis time on the chemical structure and composition of the P precipitate was evaluated from the viewpoint of utilising the P precipitate as fertiliser. Regardless of the electrode distance (10, 5 and 1 mm), PO43-, Ca2+ and Mg2+ were removed. The bulk solution pH increased during electrolysis because of the consumption of generated H+ as HCO3- transitioned to H2CO3 near the anode. A greater increase in the bulk solution pH was observed when the electrode distance was narrowed because of the enhanced H+ consumption. Narrowing the electrode distance reduced the energy consumption for P precipitation. The increase in the bulk solution pH with the narrowing electrode distance changed the dominant P precipitation pathway from onto the cathode to in the bulk solution. X-ray diffraction spectra of the precipitates showed that increasing the electrolysis time transformed amorphous P to hydroxyapatite and struvite. Most P existed in a citric acid-soluble form, which is recommended for use as a slow P release fertiliser. There were no significant changes in the citric acid-soluble P content of the precipitates with increasing electrolysis time. Therefore, increasing the electrolysis time has little influence on the suitability of the precipitate as a slow P release fertiliser.

Phytohormone-dependent plant defense signaling orchestrated by oral bacteria of the herbivore Spodoptera litura.

A vast array of herbivorous arthropods live with symbiotic microorganisms. However, little is known about the nature and functional mechanism of bacterial effects on plant defense responses towards herbivores. We explored the role of microbes present in extracts of oral secretion (OS) isolated from larvae of Spodoptera litura, a generalist herbivore, in phytohormone signaling-dependent defense responses in Arabidopsis thaliana (Arabidopsis). In response to mechanical damage (MD) with application of bacteria-free OS (OS- ) prepared by sterilization or filtration of OS, Arabidopsis leaves exhibited enhanced de novo synthesis of oxylipins, and induction of transcript abundance of the responsible genes, in comparison to those in leaves with MD + nonsterilized OS (OS+ ), indicating that OS bacteria serve as suppressors of these genes. By contrast, de novo synthesis/signaling of salicylic acid and signaling of abscisic acid were enhanced by OS bacteria. These signaling networks were cross-regulated by each other. Meta-analysis of OS bacteria identified 70 bacterial strains. Among them was Staphylococcus epidermidis, an anaerobic staphylococcus that was shown to contribute to the suppression/manipulation of phytohormone-dependent plant defense signaling. The presence of OS bacteria was consequently beneficial for S. litura larvae hosted by Brassicaceae.

Utilisation of polarity inversion for phosphorus recovery in electrochemical precipitation with anaerobic digestion effluent.

Phosphorus is a non-replaceable and limited resource, whose future drought is a matter of concern. Its recovery from wastewater has gained attention as a method of making the recovered phosphorus available for beneficial use. This study applied electrolysis with a platinum-coated titanium electrode to an actual anaerobic digestion effluent and investigated the phosphorus removal and precipitation characteristics with various current values. The separation of the phosphorus precipitate from the sludge residue and the usefulness of the polarity inversion to recover the phosphorus precipitate were evaluated. The availability of the recovered precipitate as a fertiliser was also demonstrated. The anaerobic digestion effluent after the centrifugal dehydration process with a coagulant was collected from a wastewater treatment plant. Phosphorus was precipitated as a form of calcium phosphate, including hydroxyapatite, which was confirmed by X-ray diffraction. The generated gases from the electrodes during the electrolysis floated and condensed the sludge residue, leading to successful separation of the phosphorus precipitate from the sludge residue. The polarity inversion successfully detached the phosphorus precipitate from the electrode, and at least 3 min polarity inversion was enough to detach the whole phosphorus precipitate. The submerging phosphorus precipitate contained abundant phosphorus (12.6%), in which citric-acid-soluble phosphorus accounted for 94.4%, and the utilisation of the precipitate as a slow-release phosphorus fertiliser was suggested.