Recycle and reuse of natural zeolites from composting process: a 7-year project

A 25% w/w of natural zeolite (clinoptilolite) has been used in the composting process of sewage sludge for several times in order to define the recycle index (RI) and which mathematical model has the ability to describe this phenomenon. The final results indicated that under the circumstances, the same amount of natural zeolites can be used more than 22 times (RI = 22) which makes the whole process more sustainable and feasible. The uptake of heavy metals from sewage sludge using natural zeolite and the reuse times seems to assess the change of heavy metals in compost. The heavy metal content of zeolite directly reflects on the reuse times according to the final results. The results from the mathematical (theoretical) equations show similar results with the real experimental data.