ASSESSMENT OF COMPOSTS QUALITY PRODUCED FROM PHOSPHATE WASHING SLUDGE AND LEACHATES, BASED ON RADIOACTIVITY, PHYTOTOXICITY AND DIFFERENT PHOSPHORUS FORMS

The capital key that encourages the farmers to use the compost to amend their soils is its quality. For this reason, we have aimed to confirm the final quality of the composts produced from phosphate washing sludge, leachate from landfill and green waste, from the point of view of radioactivity, phytotoxicity and different forms of phosphorus. The results of the concentrations of 238U, 232Th, 222Rn and 220Rn in the produced composts the equivalent doses to the farmer skin’s coming from the application of the compost were in conformity with the norms recommended by the International Commission of Radiological Protection. Concerning phytotoxicity, the results showed that composts based on 50 % phosphate washing sludge could be the best treatment to valorize the leachate and obtain mature compost. The monitoring of the different forms of phosphorus during the composting process, showed that the biological valorization of phosphate washing sludge increased significantly the phosphorus fractions immediately assimilable by plants and the labile phosphorus reserve protected from fixation in soils; the consequence is an important source of phosphorus released in the long term for crops and soils after the application of these composts. Using phosphate washing sludge, the proposed method to valorize the leachate and green waste will be a rewarding and simple strategy to enrich the Moroccan soils in organic matter and phosphorus without any danger for the environment and human health.