quantitative and qualitative comparison of external materials in khomein and tehran compost plants, 1387

background: the quality of the compost produced is one of the most important and effective parameters in its marketing and external materials presence in the compost have specific consideration. this study was conducted to investigate the quantity and quality of foreign materials in the compost produced by khomein and tehran plants. methods: this study was conducted on the compost produced by khomein and tehran plants in 9 months; 10 composite samples were gathered and the external constituents such as glass, plastic, metal, miscellaneous and sand were analyzed, then to compare the data t-test analysis was used. findings: the average percentage of glass, plastic, metal, miscellaneous and sand in tehran and khomein compost were 0.62, 0.22, 0.84, 2.24 and 1.17, 0.17, 0.02, 1.36, 3.61, respectively; which were in accordance to the considered standards. moreover, the statistical analysis showed that except the plastic, there was a significant difference (p < 0.0001) between the other parameters average in tehran and khomein’s composts. conclusion: in general, the compost produced by tehran and khomein plants did not have any significant problem in terms of external materials. however, as the presence of external materials causes the farmers hesitation to buy the compost, the source separation of inorganic materials and prohibition of mixed compost production could improve the compost quality and its markets.