Nitrogen losses during the composting of sewage sludge, and the effectiveness of clay soil, zeolite, and compost in adsorbing the volatilized ammonia: Fid-Bau Portal

Nitrogen losses during the composting of sewage sludge, and the effectiveness of clay soil, zeolite, and compost in adsorbing the volatilized ammonia

Witter, E. / Lopez-Real, J.

Abstract

AbstractNitrogen losses during the composting of sewage sludge-straw mixtures were measured in pilot-scale composting trials and using a laboratory composting-simulator. Both studies showed that virtually all losses resulted from ammonia volatilization in the initial stages of composting. In this period losses amounted to 16–29% of the nitrogen initially present in a polymer conditioned sludge, and more than 60% when composting a lime conditioned sludge with a higher initial nitrogen content. The total nitrogen losses during a following maturation phase increased to 50% over one year. The ratio of carbon dioxide-C to ammonia-N losses during peak rates of microbial activity indicated that mainly proteinaceous materials were decomposed in the initial stages of composting. There was, however, no change in the nitrogen distribution between the 6N HCl hydrolysable and non-hydrolysable fractions.A cover of zeolite (clinoptilolite) and of a clay soil placed on top of the compost pile proved very effective in adsorbing the volatilized ammonia, whereas a layer of matured sewage sludge-straw compost proved to be ineffective. Ammonia adsorption increased the Kjeldahl nitrogen content of the zeolite up to 2·5%, and doubled the Kjeldahl nitrogen content of the clay soil.