Rafael Marín Galvín
Abstract
Bio-solids are the final fate of pollution present in urban wastewater, reaching the production of these ones in Spanish WWTPs 701,751 T/year (dates of 2018). Considering that 85% of Spanish bio-solids are used in agronomy, it is important to know characteristics of biosolids there produced, and in this way, we have investigated bio-solids generated in La Golondrina´s WWTP (Córdoba, Spain) along 2000-2019. This WWTP is a conventional facility operated by activated sludges (26.55x106 m3/year treated) which has produced 1.43 kg of bio-solids per m3 of treated wastewater (38.000 T/year). Our results indicated that bio-solids had a dryness over initial mass of 22.3%, and 74.9% of organic matter over dried matter (o.d.m.). At the same time, major components detected in bio-solids were N, P and Ca which levels were 5.0%, 3.5% and 3.7%, respectively. On the other hand, concentration of total metals in bio-solids ranged 13,024 mg/kg o.d.m., being the main metal Fe (11.749 mg/kg o.d.m.) followed by Zn, Cu and Mn, with levels as mg/kg o.d.m. of 463.1, 392.8 and 265.7, respectively. Evolution per year of all the investigated parameters are shown in the paper. Taking into account the use of bio-solids in agronomy, we have evaluated levels of metals limited by the Spanish normative to this respect: thus, the seven metals restricted (Cd, Cu, Ni, Pb, Zn, Hg and Cr) exhibited concentration in bio-solids very lower than parametric values established. Moreover, we have estimated the ratios of accumulation of organics and metals from wastewater to bio-solids: thus, organic matter, N and P, were accumulated in bio-solids respectively, 342, 356 and 643 times, and total metals, 2,632 times. Finally, levels of Escherichia coli slightly varied from wastewater to bio-solids: 1.5x108 colony-forming units/L in the first one, and 0.9x108/g (o.d.m.) in the second ones.
Keywords
urban wastewater, Wastewater Treatment Plant (WWTP), biosolids, organic matter, chemical wastewater treatment, louds metals, nitrogen, phosphorous, potassium.
