Abstract
Objective: This research aimed to assay the dehydration and stabilization of surplus biosolids from a wastewater activated sludge treatment plant, with sludge-treatment wetlands, at the Iguazú National Park (Misiones, Argentina). Materials and Methods: A 12-cell sludge-treatment reed beds (STRB) system was built and operated for four years. Afterwards, the accumulated sediments were analyzed for total solids (TS) concentration, volatile solids (VS) reduction, specific oxygen-uptake rate (SOUR), and heavy metals and pathogens concentrations. Results and Discussion: TS concentration increased from 0.55 % to 14.3 %, VS were reduced by 33.3 %, and SOUR lowered to 1.09 mg O2gTS-1 h-1. These figures and the final concentrations of heavy metals and pathogenic microorganisms (102 MPN E.coli.gTS-1) indicated a degree of stabilization and sanitation that allowed classifying these biosolids as Class A, according to the Argentine guidelines, National Resolution 410/18, and enabled their reuse for soil amendment in landscapes and other agronomic purposes. Conclusion: The technology tested showed good results applied under a tropical climate, with annual temperatures between 17 and 27 °C, rainfall of 1870 mm y-1, and planted with autochthonous vegetation. Furthermore, it allowed the reuse of 221 t (144 m3) of a harmless product in an environmentally sustainable way.
Highlights
Biological wastewater treatment systems, especially those using a suspended biomass like activated sludge, generate a surplus of microbial biomass that must be systematically discarded in order to ensure the stability of the treatment process and the quality of the final effluent
The experimental project carried out at the Iguazú National Park, Misiones, Argentina, demonstrated that the sludge treatment reed beds technology was successful in: (i) Reaching a dewatering of waste sludges from 0.4 to 14 % total solids (TS) (ii) Generating a well stabilized sludge, (iii) Generating a sanitary, safe sludge —at < 103 E. coli NMP g TS-1, (iv) Generating a sludge enriched in N and P —at 21.9 g total nitrogen and 8.4 g total phosphorus per kg of TS, (v) Generating a Class-A-biosolids residue that, according to National Resolution
410/18 and to the Code of Federal Regulations, is reusable for agronomic and landscape purposes. These results were obtained in a tropical climate of average annual temperature of 17 to 27 °C and a rainfall of 1870 mm y-1 and with the locally available vegetation cover Hymenachne donacifolia (Raddi) Chase and H. pernambucense (Spreng.) Zuloaga, quite different from most of the systems referenced in the literature, with those being carried out in temperate or cold climates
Summary
Biological wastewater treatment systems, especially those using a suspended biomass like activated sludge, generate a surplus of microbial biomass (sludge, biosolids) that must be systematically discarded in order to ensure the stability of the treatment process and the quality of the final effluent. A technology designed for the treatment of waste biosolids in constructed wetlands referred to as the sludge treatment in reed beds, STRB by Nielsen and Bruun [1], the planted drying beds, PDB by Kengne and Tilley [2], and the sludge-treatment wetlands, STW by Uggetti et al [3] —has proven to be a suitable alternative to the dehydration and stabilization of surplus sludge both environmentally and economically These systems are made up of 8 to 12 cells with a filtering floor that is planted with helophytes. If the treated residue meets certain quality standards, that material can be used as fertilizer or for soil amendments or other defined agronomic purposes
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