Composting used as a low cost method for pathogen Elimination in sewage sludge

Spreading sewage sludge from municipal wastewater (MWW) treatment on land is still a common practice indeveloping countries. However, it is well known that sewage sludge without special treatment contains various pollutants, which are (re)introduced into the environment by sludge landspreading and which might in turn have harmful effects to the environment and human health.

Further Authors:
E. De los Ríos Ibarra - Independent Researcher
J. P. Mena - Salas, University Autonomous of Yucatan
D.Y. Escalante - Réndiz, University Autonomous of Yucatan

This is more dangerous in places like Merida, Mexico, where soil is calcareous with fractures along the ground and thin layers of humus (Duch 1988). Consequently, any liquid andsemisolid wastes has the potential of percolating to the subsurface and contaminate the aquifer (Magaña 2002).Management of residual sludge has become an important problem and, in some cases, with expensive solutions. One ofthe solutions implies the reduction of pathogen microorganisms before applying it to soils as a conditioner agent. Mexican legislation suggests addition of calcium hydroxide to a septic sludge to obtain a safe product. After that, disposal is carried out by putting all waste in ditches previously constructed (Comisión Nacional del Agua, 1997). In Merida, most householders use a septic tank as a sewage system. Once the septic tank is full, its content is collected anddischarged into an artificial oxidation pound system where sludge and water are separated by decantation. Separated sludge is put away on the ground where it is sun dried. Endemic birds and insects like flies and worms have continuouscontact with this waste. For flies, it becomes an ideal place for laying its eggs due to considerable amount of nutrients. As a consequence, they become a way of transporting viruses and bacteria with potential of spreading human diseases. The most common pollutants contained in sewage sludge from MWW are human pathogens like fecal coliforms, salmonella and helminth eggs. The main aim of this work was using composting as a low cost process to eliminate pathogens contained in sewage sludge from MWW treatment in order to use the final product for land spreading in a safe way for both environment and human health. Two piles for composting process at real scale were settled using a mixture of sewage sludge from municipal wastewater and green waste. Composting was carried out by windrow process and it was monitored during four weeks. Concentration of helminth eggs, salmonella and faecal coliforms were measured twice a week to observe its behaviour and, as a control process, Temperature, Moisture Content (MC), and pH were also measured. After 30 days of composting sludge from municipal waste water system, salmonella was eliminated by 99%, faecalcoliforms by 96% and helminth eggs by 81%. The results showed that a composting process is an economical and efficient method for pathogens elimination in sewage sludge from municipal waste water.

Copyright: © European Compost Network ECN e.V.
Quelle: Orbit 2012 (Juni 2012)
Seiten: 6
Preis inkl. MwSt.: € 6,00
Autor: Dr. D.Diana Cabañas-Vargas

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