THE STUDY OF THE AEROBIC BACTERIAL MICROBIOTA AND THE BIOTOXICITY IN VARIOUS SAMPLES OF OLIVE MILL WASTEWATERS (ALPECHIN) DURING THEIR COMPOSTING PROCESS

Five different piles were prepared by mixing olive mill wastewater (al pechin) and alpechin sludge with two bulking agents (cotton waste and maize straw) and two organic wastes with high content of nitrogen (sew age sludge and poultry manure), which were composted by the Rutgers st atic pile composting system in a pilot plant. The aim of this work was to study the evolution of total nitrogen and different forms of organ ic matter and evaluate the variation in the aerobic bacterial microbio ta present and biotoxicity during the composting process. In piles pre pared with alpechin, the use of the maize straw as a bulking agent red uced the nitrogen losses whereas the use of sewage sludge, instead of poultry manure, with cotton waste originated the highest degradation o f organic matter. In piles prepared with alpechin sludge a similar evo lution of the composting process was observed. There were not great va riations during composting in the aerobic bacterial microbiota present in the mixtures. However, the pile prepared with alpechin sludge and maize straw was only one to present bacteria capable of growing in alp echin, and the toxicity study showed that this was only present in the starting mixtures. (C) 1997 Published by Elsevier Science Limited.