Vermicomposting of the leaf litter of acacia (Acacia auriculiformis): Possible roles of reactor geometry, polyphenols, and lignin P. Sankar Ganesh, S. Gajalakshmi, S.A. Abbasi * Centre for Pollution Control and Energy Technology, Pondicherry University, Kalapet, Puducherry 605 014, India article info Article history: Received 17 September 2007 Received in revised form 18 September 2008 Accepted 22 September 2008 Available online 20 November 2008 Keywords: Acacia Vermicomposting Vermireactor geometry Polyphenols Lignin abstract Vermicomposting of the pre-composted leaf litter of acacia (Acacia auriculiformis) was studied in reactors of identical volume but with surface area: height ratios varying from 4 to 250. In separate sets of exper- iments with these reactors, epigeic earthworm species Eudrilus eugeniae and anecic earthworm species Lampito mauritii were employed at densities of 75 and 150 adult animals per litre of reactor volume. The results reveal that greater the surface area: volume ratio of the reactor, higher is the vermicast out- put in terms of vermicast output per animal; the more densely populated reactors were comparatively under-productive. Even as the vermicast production remained consistently high in all the reactors, there was significant earthworm mortality throughout the course of the experiments and the worms who survived, steadily lost weight with time. A detailed investigation of the possible causes revealed that, whereas the C:N ratio of acacia compost was comparable with that of other substrates; the polyphenols and lignin content were much higher. Studies by other authors on leaf litter consumption by earthworms in natural or man-made forests have indicated that leaf litter rich in polyphenols and lignin are not preferred by most species of earthworm. This may perhaps be the reason for the high rate of mortality and weight loss in earthworms forced to feed upon acacia in the experiments conducted by the authors. Ó 2008 Elsevier Ltd. All rights reserved. 1. Introduction The vermicast produced by earthworms when the worms are made to feed upon a given substrate is called the vermicompost of that substrate. Traditionally vermicompost has been generated with animal manure (especially of the rumens) as the substrate and has been recognized as a good soil conditioner and fertilizer (Ismail, 1997). In recent years, other substrates have also been ver- micomposted and the products have been found to be as good as the manure-based vermicompost (Gajalakshmi and Abbasi, 2003a,b Gajalakshmi et al., 2002, 2005a,b). These findings have opened up the possibility of turning biowastes such as the organic fraction of the municipal solid waste, crop wastes, weeds, leaf litter etc., into gainful vermicompost. Acacia (Acacia auriculiformis) is one of the tree species used extensively in social forestry across the tropics and sub-tropics – eucalyptus, casuarina, and leuceiana being the others. The high survival rate of acacia saplings, their fast growth rate, and the fairly dense canopy acquired by the trees within a few years of planting have contributed to acacia’s popularity. Acacia is also able to grow on poor soils much better than most other trees can. As a result, acacia is planted in large numbers throughout the tropics and sub-tropics. It also yields substantial quantities of leaf litter which is either broomed into the existing piles of municipal solid waste (MSW), thereby adding to the MSW burden, or is made into heaps and set on fire, thereby causing air pollution. The present study was taken up to examine the feasibility of generating vermicompost from the acacia leaf litter, thus finding a means for gainfully employing the litter. Two species of earth- worm which are known to be voracious feeders and have other attributes suitable for vermicomposting – high fecundity, high rate of growth, preference for the temperatures (30 ± 2 °C) at which the present experiments were carried out, hardiness etc. – were em- ployed. These included an epigeic (phytophagous) earthworm spe- cies Eudrilus eugeniae and an anecic (geophytophagous) earthworm species Lampito mauritii. Vermicomposting of the pre-composted leaf litter of acacia (A. auriculiformis) was studied in reactors of identical volume but with surface area:height ratios varying from 4 to 250. In separate set of experiments with these reactors, Eudri- lus eugeniae or Lampito mauritii were employed at densities of 75 and 150 adult animals per litre of reactor volume. A novel feature of the present study is that it is one of the first ones to explore the effect of vermireactor geometry, particularly the aspect ratio, on the efficiency of vermicast production. No re- 0960-8524/$ - see front matter Ó 2008 Elsevier Ltd. All rights reserved. doi:10.1016/j.biortech.2008.09.051 * Corresponding author. Tel.: +91 94423 65262. E-mail address: Prof.S.A.Abbasi@gmail.com (S.A. Abbasi). Bioresource Technology 100 (2009) 1819–1827 Contents lists available at ScienceDirect Bioresource Technology journal homepage: www.elsevier.com/locate/biortech