The objective of this study was to identify the effect of mixture of additives to improve the enzymatic activities, organic matter humification and diminished the bioavailability of heavy metals (HMs) during biosolids co-composting. In this study, zeolite (Z) (10%, 15% and 30%) with 1% lime (L) (dry weight basis of biosolids) was blended into the mixture of biosolids and wheat straw, respectively. The without any amendment and 1% lime applied treatments were run for comparison (Control). The Z + L addition resulted rapid organic matter degradation and humification with maximum enzymatic activities. In addition, higher dosage of Z+ 1% L amendment reduced the bioavailability of HMs (Cu and Zn) and improved the end product quality as compared to control and 1% L applied treatments. However, the 30% Z+ 1% L applied treatment showed maximum humification and low bioavailability of HMs but considering the economic feasibility and compost quality results, the treatment with 10% Z + 1% L is recommended for biosolids co-composting.