Organic wastes, such as cow manure, are often composted with earthworms (vermicomposting) while excess water is drained and collected. This wormbed leachate is nutrient-rich and it has been extensively used to fertilize plants. However, it is derived partially from a not yet finished compost process and could exhibit phytotoxicity or contain potentially hazardous microorganisms. The bacterial community in wormbed leachate derived from vermicomposting of cow manure was studied by pyrosequencing the 16S rRNA gene. The fresh wormbed leachate was rich in Mollicutes, particularly the genus Acholeplasma which contain phytopathogen species. The abundance of the Mollicutes decreased when the leachate was stored, while that of the Rhizobiales and the genus Pseudomonas increased. The bacterial communities changed rapidly in the leachate during storage. The changes in ammonium, nitrate and inorganic carbon content of the wormbed leachate when stored were correlated to changes in the bacterial community structure. It was found that storage of the wormbed leachate might be required before it can be applied to crops as large proportions of potentially plant pathogens were found in the fresh leachate.

Purpose The objective of the work is to determine the best operating conditions for variants of an ecological engineering tool (permeable reactive surface biobarrier -PRSB-) potentially useful for the protection of water resources, preventing the arrival of sediments and pesticides transported by runoffs and tile drainage from agricultural lands, to water bodies. Methods Four PRB-prototypes were constructed as fixed-bed horizontal channels packed with a porous material supporting an enriched microbial biofilm. Their dynamic and stoichiometric performance was evaluated in the presence or absence of granular activated carbon, with limiting or sufficient O 2 supply. The removal of the pesticides and their leading catabolic derivatives were determined by HPLC. The most abundant cultivable microorganisms were isolated and identified by the sequencing of 16sDNA amplicons. ResultsThe pollutant removal efficiencies obtained in the aerobic biobarriers or microaerophilia were similar. In addition, slight differences were observed in the presence of GAC as an adsorbent, meaning that the most economical and straightforward type of biobarrier was adequate to remove the pollutants studied. In addition, among the most abundant microorganisms isolated in the microbial biofilms colonizing the aerobic biobarriers, the microalgae Micractinium sp. showed the capacity to accumulate the insecticides permethrin and cypermethrin. Conclusions The main observed role of Micractinium sp. in the aerobic barriers was the bioaccumulation of pyrethroids, meaning that biosorption is also a valuable removal mechanism operating in the aerobic PRBs. In this aspect, they behave analogously to subsurface constructed wetlands but, instead of superficial plant life, aerobic PRSBs host microalgae.

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