FULL-SCALE CO-COMPOSTING OF SEWAGE SLUDGE AND WASTE MATERIALS AT VARIOUS MIXING PROPORTIONS AND AERATION CONDITIONS TO PRODUCE STABILIZED COMPOST

Two different sewage sludge (SS) waste materials were commercially co-composted with wood chips (WCh) and grass to determine their conversion potential and elucidate the manner that it is affected by the various process operational parameters. A blend of three different SS streams composted more efficiently in terms of temperature attained during the process than a single SS stream when the materials were co-treated with WCh acting as the bulking agent. WCh facilitated the accomplishment of a temperature over the sanitation limit and concurrently the establishment of a high decomposition rate over a long period. Further increasing the fraction of WCh in the composting mixture had an insignificant effect on the decomposition rate of organics in SS. The presence of grass in a mixture had a negative influence on the composting temperature that retained below the sanitization limits during the entire process. Aeration led to an increment in temperature but in all cases the enhancement remained at levels lower than 20 °C throughout the trials. Concentration of heavy metals in all mixtures was sufficiently reduced with composting regardless of the SS type, mixing ratio, the use of a secondary organic substrate and aeration.