N. Gamze Turan 1 Osman Nuri Ergun 2 1 Department of Environmental Engineering, Ondokuz Mayis University, Samsun, Turkey. Research Article Improving the Quality of Municipal Solid Waste Compost by Using Expanded Perlite and Natural Zeolite The scope of this study was to investigate the effects of natural zeolite and expanded perlite on the quality of municipal solid waste compost. Various ratios of the materi- als were added as supplements to the organic fraction of municipal solid waste. These applications were periodically compared with an untreated control process. The results obtained from experimental studies clearly showed that municipal solid waste collected from the metropolitan city center of Samsun, Turkey could not be com- posted without any additions due to the very high moisture content, which reached up to 75 – 80%. In the untreated control process, thermophilic temperatures were not supported during the composting. In this system, ammonia and other odors became a problem because of the high pH levels, and the electrical conductivity was too high for aged compost. However, the addition of natural zeolite and expanded perlite had a positive affect on the quality of the final compost. Natural zeolite trapped ammo- nium and reduced nitrogen losses from the compost. Expanded perlite held excess moisture and supported improved aeration. The results also indicated that the use of natural zeolite together with expanded perlite in municipal solid waste composting processes produced mature and stable compost. Keywords: Municipal Solid Waste; Composting; Zeolite; Perlite; Received: September 17, 2007; revised: December 5, 2007; accepted: December 12, 2007 DOI: 10.1002/clen.200700135 1 Introduction The composting of organic waste has a fairly long history in the treatment of municipal solid wastes. The composting process has been accepted as the simplest form of recycling organic wastes back to soil for many years [1, 2]. The most important factor affecting the successful application of compost for agricultural purposes is its final quality. Compost qual- ity is closely related to its degree of stability and maturity [3]. The application of unstable or immature compost may inhibit seed ger- mination, reduce plant growth and damage crops by competing for oxygen or causing phytotoxicity to plants due to insufficient biode- gradation of organic matter [4 – 7]. A number of criteria and parameters are proposed for testing compost stability and maturity, all of which express these character- istics as a function of composting time, independently of the com- posting process or feedstock composition. These include the C:N ratio, carbon dioxide evolution, NH4 + – N/NO3 – -N ratios, cation exchange capacity, water soluble C and production of humic sub- stances in the final compost [3, 8, 9]. The microporous crystalline structure of zeolites is able to adsorb species with diameters that fit through surface entry channels, while larger species are excluded, giving rise to molecular sieving properties that are exploited in a wide range of commercial applica- tions [10 – 12]. Currently, natural zeolites are used in soil benefica- tion, in air enrichment and in water and wastewater treatment [13, 14]. Zeolite minerals have also been used to take up heavy metals and ammonia from compost [15, 16]. Expandable forms of perlite have been very important natural materials for the last decade. Due to its favorable physical and chem- ical characteristics, expanded perlite finds diverse utilization in var- ious applications, e. g., as a lightweight aggregate in the construc- tion industry, as a rooting medium and soil conditioner in horticul- ture, as a bleaching agent in the textile industry, as an adsorbent in the chemical industry, as a filtration aid and as a filler in miscella- neous processes [17]. The aim of this study is to investigate the effects of the addition of expanded perlite and natural zeolite to the organic fraction of municipal solid waste for composting processes. Various ratios of the natural zeolite and expanded perlite are added to the organic wastes originating from Samsun in an effort to improve the com- post quality. A number of parameters are analyzed during the com- posting. 2 Materials and Methods A municipal solid waste sample was collected from the metropoli- tan city center of Samsun which is situated in the Black Sea coastal area of Turkey. The samples were brought into the laboratory and Correspondence: N. G. Turan, Dept. of Environmental Engineering, On- dokuz Mayis University, 55139, Samsun, Turkey. E-mail: gturan@omu.edu.tr i 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim www.clean-journal.com 330 Clean 2008, 36 (3), 330 – 334