Quality Assessment of a Battery of Organic Wastes and Composts Using Maturity, Stability and Enzymatic Parameters

Chemical and biological parameters (NH4+-N/NO3--N ratio, humification indices, and the activities of hydrolytic exoenzymes), commonly used to assess compost maturity and/or stability, were considered for the quality evaluation of a battery of organic materials, intended to be land applied. Acid and alkaline phosphatases, beta-glucosidase, proteases and beta-glucosaminidase activities proved to be reliable tests to distinguish the organic materials that were in an active stage of microbial activity, highly correlated to the chemical parameters NH4+-N content and NH4+-N/NO3--N ratio. In fact, these chemical parameters evidenced as important in the quality assessment of an organic material, strongly correlated with the biological parameters. The same was not true for the majority of the humification indices, which proved inadequate to compare the quality of such diverse organic materials. This was demonstrated by a multivariate statistical treatment of data, performed with these results in combination with results from the Dewar self-heating test, respiration activity and germination index, obtained in previous studies. Concluding, in a similar scenario, where the organic materials in evaluation are varied, both in the raw material an in the stability of the organic matter, the quality should be assessed by the integrated use of both chemical and biological parameters.