Vermistabilization of primary sewage sludge Subrata Hait, Vinod Tare ⇑ Environmental Engineering and Management Programme, Department of Civil Engineering, Indian Institute of Technology Kanpur, Kanpur 208 016, India article info Article history: Received 15 July 2010 Received in revised form 4 October 2010 Accepted 6 October 2010 Available online 12 October 2010 Keywords: Activated composting Vermicomposting Primary sewage sludge Eisenia fetida Compost recycling abstract An integrated composting–vermicomposting process has been developed for utilization of primary sewage sludge (PSS). Matured vermicompost was used as bulking material and a source of active micro- bial culture during aerobic activated composting (AAC). AAC resulted in sufficient enrichment of bulking material with organic matter after 20 cycles of recycling and mixing with PSS and produced materials acceptable for vermicomposting. Vermicomposting caused significant reduction in pH, volatile solids (VS), specific oxygen uptake rate (SOUR), total organic carbon (TOC), C/N ratio and pathogens and substantial increase in electrical conductivity (EC), total nitrogen (TN) and total phosphorous (TP) as compared to compost. Environmental conditions and stocking density have profound effects on vermicomposting. Temperature of 20 °C with high humidity is favorable environmental condition for vermicomposting employing Eisenia fetida. Favorable stocking density range for vermiculture is 0.5–2.0 kg m À2 (optimum: 0.5 kg m À2 ) and for vermicomposting is 2.0–4.0 kg m À2 (optimum: 3.0 kg m À2 ), respectively. Ó 2010 Elsevier Ltd. All rights reserved. 1. Introduction In India, primary sewage sludge (PSS) is generated in huge quantities and poses challenges in safe disposal due to the pres- ence of certain soil contaminants, such as organic compounds, hea- vy metals, and human pathogens. Most of the conventional means of sewage sludge disposal like open dumping, sanitary land-filling, aerobic and anaerobic digestion and incineration have created more serious problems like soil and plant toxicity, surface and ground waters contamination and air pollution. Furthermore, the ever increasing cost and unavailability of land near urban areas, more stringent waste disposal regulations and public awareness have made open dumping and land-filling increasingly expensive and impractical (Ndegwa and Thompson, 2001). This frightening situation of sludge disposal and management is of no exception in other developing countries and probably prevails in other parts of the world too (Abbasi and Ramasamy, 2001). More recently, alkaline extraction for production of surface active value-added agents (García Becerra et al., 2010) and production of hydrogen as alternative energy (Massanet-Nicolau et al., 2010) have been employed to utilize sewage sludge, although these techniques are economically expensive. Hence, there is an utmost need for ecolog- ically as well as economically sustainable technologies which encourage possible recovery and recycling of nutrients and capable of sanitizing the human pathogens present in sewage sludge. Sludge treatment wetlands, also known as sludge drying reed beds, have been used in many regions of the world as a new sustainable technology based on constructed wetlands for sludge treatment (Peruzzi et al., 2009; Uggetti et al., 2009, 2010; Melidis et al., 2010). The major limitations of sludge treatment wetlands involving dewatering processes (draining and evapotranspiration) are requirements of large land area, favorable climatic conditions and further treatment to improve sludge hygienisation (Zwara and Obarska-Pempkowiak, 2000). Composting, another such ecologically and economically sustainable technology has been widely used over the years for stabilizing and sanitizing the sew- age sludge with bulking agents like green wastes, spent activated clay (bentonite), etc. (Tandy et al., 2009; Ho et al., 2010). The major drawbacks associated with traditional thermophilic composting are the long duration of the process, the requirement of frequent turning of the material, the necessity of reduced size of materials to provide required surface area, loss of nutrients during the prolonged composting process, and heterogeneous nature of the product (Ndegwa and Thompson, 2001). Vermicomposting is emerging as a most appropriate alternative to conventional aerobic composting. Vermicomposting is not only rapid, easily controllable, cost effective, energy saving, and zero discharge process, but also accomplishes most efficient recycling of organics and nutrients (Eastman et al., 2001). In contrast to tra- ditional composting, vermicomposting results in homogeneous product (vermicompost) with better quality in terms of desirable aesthetics, reduced levels of contaminants and more soluble and available plant nutrients (Ndegwa and Thompson, 2001). The use of earthworms in sludge processing and management has been 0960-8524/$ - see front matter Ó 2010 Elsevier Ltd. All rights reserved. doi:10.1016/j.biortech.2010.10.031 ⇑ Corresponding author. Tel.: +91 512 259 7792; fax: +91 512 259 7797. E-mail address: vinod@iitk.ac.in (V. Tare). Bioresource Technology 102 (2011) 2812–2820 Contents lists available at ScienceDirect Bioresource Technology journal homepage: www.elsevier.com/locate/biortech