Microbial, chemical and physical aspects of citrus waste composting

Citrus waste supplemented with calcium hydroxide and with a CIN ratio of 24 :1, pH of 6.3 and moisture content of 60% was composted by piling under she lter. With regular turning over of the pile and replenishment of moisture, the thermic phase lasted for 65-70 days and composting was completed after 3 months. Compost thus prepared had an air-filled porosity of 14%, water-ho lding capacity of 590 ml l(-1), bulk density of 1.05 g cm(-3) and conductiv ity of 480 mS m(-1). Phosphorus content (in mg l(-1)) was 15, potassium 117 0, calcium 362, magnesium 121, sodium 32, chloride 143, boron 0.31, and wat er-soluble nitrogen and organic matter 126 and 4788, respectively. Total ca rbon amounted to 8.85% and total nitrogen to 1.26% of the dry weight, givin g a CIN ratio of 7. Mature compost showed some, but acceptable, levels of p hytotoxicity. Raw citrus waste was predominantly colonised by mesophilic ye asts. Thermophilous microorganisms present during the thermic phase mainly comprised the bacterial species Bacillus licheniformis, A macerans and B. s tearothermophilus and, to a lesser extent, fungi such as Absidia corymbifer a, Aspergillus fumigatus, Emericella nidulans, Penicillium diversum, Paecil omyces variotii, Rhizomucor pusillus, Talaromyces thermophilus and Thermomy ces lanuginosus. Bacteria prevalent in the final product included B. lichen iformis, B. macerans, Proteus vulgaris, Pseudomonas aeruginosa, P. fluoresc ens, P. luteola and Serratia marcescens, whereas fungi isolated most freque ntly comprised Aspergillus puniceus, A. ustus, E nidulans, Paecilomyces lil acinus, T lanuginosus, yeasts and a basidiomycetous species, probably Copri nus lagopus. (C) 2001 Elsevier Science Ltd. All rights reserved.