1410 annelid specimen used was Eisenia foetida. The environ- mental conditions ideal to the reproduction and control of these specimens were set up: temperature at 20 C, moisture around 60–85%, aeration conditions and darkness. The stabilization time was around 1 month and the humus obtained was dried in a room at a temperature between 30 and 40 C. Then, the humus was sieved to size 0.5 mm approximately. Next, the sample was calcinated to elimi- nate the organic matter. Three temperature levels were used: 500, 600 and 700 C for each agro-industrial waste by 19 h. Calcinations were carried out in a mufﬂe Lindberg/ Eurotherm model 847 with energy consumption of 0.17 kcal/h cm3, considering that the average density of the nanoparticles is around 0.1380 g/cm3, the consumed energy in the calcinations is approximately 1.2318 kcal/h by each gram of recuperated SiO2 particles. This energy could be considered low in comparison with other con- ventional process where fumed silica is manufactured with a consumed energy of until 15.48 kcal/h by each gram of SiO2 particles [40]. Thus, the samples were tried with nitric and hydrochloric acids (volume ratio 3:1). For each gram of calcinated sample, 4 ml of acid mix was added in order to eliminate impurities (calcium, potassium, magnesium, manganese, iron, boron and phosphorous). Acid treatment was achieved at 40 C by 4 h with constant stirring. Then, samples were ﬁltrated and washed with distilled water to neutralize them. Solids obtained were dried at room tem- perature. All reagents employed were provided by Sigma– Aldrich. Also, as a reference, SiO2 was obtained from the agro- industrial wastes without employing vermicompost bio- process. The extraction process to recuperate SiO2 is the same as described previously using calcination and acid treatment. In addition, commercial synthetic SiO2 Aerosil 130 provided by Degussa AG was employed to compare size and structure with SiO2 nanoparticles produced in this research. Aerosil 130 particles are amorphous SiO2 nanoparticles produced by high-temperature hydrolysis of silicon tetrachloride in an oxygen gas ﬂame [41]. Also, this research compares the particle features based on biotrans- formation process with those synthesized using chemical process. SiO2 powders were characterized by employing a Fou- rier transform infrared spectrophotometer (FTIR) Bruker Vector 33 using KBr powders. Transmission electron microscopy (TEM) was realized using a JEOL TEM-1010 transmission electron microscope, and high-resolution transmission electron microscopy (HRTEM) was realized in a Tecnai G2 T20 Microscope. Average particle size was determined for dynamic light scattering (DLS) using a Brookhaven model BI200SM with laser He–Ne of 35 mW model 9167 EB-1 Melles-Griot. Elemental analysis was carried out using energy dispersion spectroscopy (EDS) 123 Nanoscale Res Lett (2010) 5:1408–1417 mean software Oxford Inca X–Sight. EDS is adapted in equipment JEOL JSM-6060 LV Scanning Electron Microscope. X-ray diffraction (XRD) was realized in a diffractometer Rigaku, model MiniFlex, with a wavelength from 1.54 A˚ corresponding ka cupper radiations. Crystal- line structures present in the samples were analyzed with Materials Data Jade software of MDI Materials Data. Results and Discussion Figure 1 shows the FTIR spectroscopy analysis to the samples obtained from the agro-industrial wastes: rice husk, coffee husk and sugarcane bagasse after vermicom- post bioprocess, calcinations and extraction process. The spectra present three important bands that allow identifying the SiO2. At 1,080 cm-1, a band corresponds to stretch- ing antisymmetric mode of Si–O–Si group. Around 800–810 cm-1, bending vibration mode is detected. This peak corresponds to Si–O group. Also, the peak observed at 500 cm-1 corresponds to rocking mode of the Si–O group. At 3,500 and 1,640 cm-1 are observed stretching vibration mode of O–H and twisting vibration mode of H–O–H, respectively. The peaks formed at different temperatures of calcination (500, 600 and 700 C) do not show important differences in the infrared analysis. The FTIR results sug- gest that carbon from the organic matter is removed. Thus, silica is released, and then the suboxides found after cal- cinations are separated correctly. In addition, the SiO2 typical bands represent strong evidence of the efﬁciency in the synthesis process based on biotransformation with annelids. Also, the bands corresponding to O–H vibration mode and H–O–H twisting vibration mode indicate that particles synthesized remain hydrated. As can be observed in Fig. 1, commercial sample Aerosil 130 shows the same three bands corresponding to SiO2. However, the peaks at 3,500 and 1,640 cm-1 are weaker than the peaks belonging to the samples synthesized using vermicompost. The latter allows to assume that nanoparticles obtained by vermi- compost are further hydrated than Aerosil 130 particles. This could be important for developing hybrid materials, inasmuch as these types of materials use silanol groups to attach organic moieties to inorganic Si [42–45]. Figures 2 a–f show TEM images for the SiO2 particles obtained using the synthesis by vermicompost. The mor- phology and structure of these particles is not completely spherical. In addition, several particle clusters are observed in these images. This agglomerates show different shapes of nanometric size. Figure 2 g–h shows SiO2 particles obtained from the agro-industrial wastes without biotrans- formation. In these pictures are observed elliptical particles with different diameter and a relatively bigger size than particles analyzed in the Fig. 2 a–f. This reveals that