Composting and vermicomposting of spent mushroom substrate to produce organic fertilizer

Abstract

Description or the subject: Spent mushroom substrate (SMS) is a by-product of the mushroom cultivation industry. Mexico produces more than 350 thousand tons of SMS annually. Attempts have been made to use SMS as a soil amendment, among other applications, with some success. However, leaching from the SMS can discard into groundwater and potentially lead to eutrophication in discharge areas. These problems can be overcome by bioconversion of the waste. Objectives: Thus, the present study aimed to apply composting and vermicomposting methods on a pilot scale, to convert SMS into a highly enriched substrate suitable for soil amendment and horticulture. Method: For this purpose, 800 kg (fresh weight) of SMS was processed by each of the above-mentioned bioconversion methods for 120 days. The physicochemical properties of the initial material (SMS) and the compost and vermicompost obtained at the end of the two processes were analyzed by measuring pH, electrical conductivity, organic matter, total carbon, nitrogen content, cation exchange capacity (CEC), C/N, and micro- and macronutrient contents. Results: Both processes reduced the volume of SMS substantially (by around 60%), partly as a result of organic matter mineralization. The main characteristic of the vermicompost was its higher NO₃¯ content (292%) compared to the compost. The concentrations of most salts were significantly reduced, and the CEC increased, confirming the stability of the SMS at the end of both processes. Conclusions: In summary, the findings highlight the potential value of scaling up the composting/vermicomposting processes for industrial application in environmental waste management, particularly for SMS.