Composting-vermicomposting of pigeon dropping waste. A contribution to the reduction of urban contamination

Purpose: Without a proper treatment, pigeon dropping waste (PDW) in the urban environment is a sanitary risk for the population because of nasty and irritating odors, a very high content of ammonium, and the presence of pathogens. This study deals with the recycling of PDW from a dovecote, situated in a public city plaza, to achieve its stabilization and eliminate sanitary risks. Method: Composting of PDW with other locally available lignocellulosic residues (sawdust and chipped tree pruning) and vermicomposting employing Eisenia fetida earthworms was applied. Two designs were selected for the vermicomposting stage: (1) Sectorized, with a zone with earthworms and another zone of composted PDW with gradual incorporation to the first one and, (2) Integrated, consisting of the composted PDW, with E. fetida in the entire solid. Results: The composting allowed a partial stabilization of the original mix of PDW, given its highly elevated initial content of ammonium (8693 mg kg-1). The combined processes almost eliminated the ammonium present (> 99% reduction) and the action of earthworms shortened the maturation time. Organic matter and electrical conductivity of the solids had important reductions. The treatment affected the resulting characteristics of the solids obtained but the germination index was above 80% in both cases. Conclusions: Both designs allowed the obtention of two mature, non-phytotoxic vermicomposts. The sectorized vermicompost had better properties and had the advantage of being obtained with fewer initial number of earthworms. Research Highlights • Pigeon dropping waste was recycled by combined composting-vermicomposting process. • Two vermicomposts were obtained by different sectorized and integrated designs. • High ammonium content was reduced and nasty odors and pathogens were neutralized. • Sectorized design produced a better vermicompost with fewer number of earthworms. • Undiluted extracts of the vermicomposts rendered germination indexes over 80%.