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Objectives. To characterize the total content of heavy metals (Cd, Cr, Cu, Hg, Mo, Ni, Pb, and Zn) and trace elements (As and Se) of interest, their bioavailability and solubility during the composting of cow manure and tree litter in piles inoculated with beneficial microorganism (IBM), or not inoculated (NBM), on the university campus of the Universidad Nacional Agraria La Molina (UNALM). Methods. The investigation evaluated composting in six piles, three IBM piles and three NBM piles, for 120 days. Every 30 days, a composite sample was taken from each pile. The raw materials used were cattle manure and tree litter. The variables analyzed were the total concentrations (content) of metals and trace elements of interest, extracted with diethylenetriaminepentaacetic acid/pentatetic acid (DTPA) (for the bioavailability study) and extracted with deionized water (for the solubility study). Results. The average values (n = 3) of the total content (mg·kg−1) on day 120 in IBM were in the following order: Zn (404.33) > Cu (86.33) > Pb (71.2) > Cr (34.33) > As (28.0) > Ni (13.83) > Mo (2.86) > Se (1.38) > Cd (1.32) > Hg (0.39) and in NBM: Zn (466.0) > Cu (112.23) > Pb (73.23) > Cr (35.33) > As (29.67) > Ni (14.37) > Mo (3.23) > Se (1.55) > Cd (1.38) > Hg (0.38). The values complied with the Austrian Compost Standard for Landscaping and Land Rehabilitation and the Peruvian Standard for Nonorganic Agriculture. Significant differences were observed in some elements ( p  < 0.05) between 0 and 120 days in both types of pile (IBM and NBM). Conclusions. For nonorganic agriculture in Peru, urban compost is recommended, whereby raw organic materials are inoculated with beneficial microorganisms during the composting process to reduce the bioavailability of Cu and Zn, as these elements showed less bioavailability than noninoculated piles. The composting process for both piles (IBM and NBM) reduced the solubility in Cu, Pb, and Zn.

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Objectives: The Pb non-biodegradability results in bioaccumulation in living organisms causing serious health disorders. The present study aimed to investigate the capacity of Pb (II) adsorption in aqueous solutions using the Brassica nigra species as biosorbent. Methods: The present study was conducted using a synthetic solution with three Pb (II) concentrations (5, 15, and 30 ppm). The B. nigra was suitably treated until it became dry particles. After sifting it, three ranges of grain sizes were obtained. Samples of dry particles were analyzed before and after the biosorption to analyze their topography (SEM), as well as the elements on their surface (EDS). The influence of different operating variables on the biosorption of Pb (II) were analyzed. Kinetics of Pb (II) biosorption was analyzed with pseudo first and second order models. The biosorption in the equilibrium was studied with the Langmuir isotherm and Freundlich isotherm models. Results: The biosorbent B. nigra showed to be efficient for the adsorption of Pb (II). The most influential variables in the adsorption were pH, particle size, and biosorbent/solution ratio. The optimum pH for the adsorption of lead was 5 and removed 82.10% of lead from solution at 5 ppm, 82.24% at 15 ppm and 57.95% at 30 ppm. The results for the particle size between 177 and 297 μm were 82.65% for 5 ppm, 73.71% for 15 ppm, and 53.54% for 30 ppm. The biosorbent/solution ratio of 0.6 mg/mL or the 30 mg dose of biosorbent removed 80.26% for 5 ppm, 79.32% for 15 ppm, and 59.87% for 30 ppm. Biosorption isothermal data could be well interpreted by the Langmuir model with a maximum adsorption capacity of 53.476 mg/g of lead ion on B. nigra stem and roots biomass. The kinetic experimental data was properly correlated with the second-order kinetic model (R2 = 0.9997). Thus, the best desorbing agent was HNO3 (0.1N) for Pb (II) desorption. Conclusion: Our study showed that the herb B. nigra, without any chemical treatment, can be used to remove heavy metals such as Pb (II) from water and aqueous solution.

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