Development of Heat-dried Biosolids Product for Application in the Wetlands

This work assessed the ability of iron-based salts (ferrate and ferric chloride) and the heat drying process on stabilizing municipal sludge. The specific objectives were:Evaluate the differences on stability between ferrate treatment and ferric chloride treatment.Optimize dosage of iron salts in regard to sludge characteristics by assessing VSS reduction, pathogen reduction/regrowth control and biological activity reduction, etc.Ferrate and ferric chloride were added to New Orleans municipal sludge in the dewatering step before heat drying. The study noted that ferrate was instable in the sludge cake, which has been substantiated the disinfection of New Orleans wastewater effluent going to the wetlands. For this study, the optimum dosage for ferric chloride was observed to be 2.3% as iron per total solids dry weight.When iron-based salts were added into biosolids and heat dried, the putrefaction was inhibited for over 5 to 6 days under the worst-case scenario conditions (moisture content within the range of 98% to 99% and seed). The heat-dried biosolids inactivated vegetative microbes through the stimulation of pasteurization. Therefore the biosolids would be able to resist the putrefication process for over 2 to 3 weeks. For two decades, ferrous and ferric salts have been used for controlling odors in collection systems. The rationale for this inhibition is that the iron ion provided an ORP buffer that can be expressed as an electron pke similar to pH buffer definition in an acid/base reaction. Ferric hydroxide was also reported to react with sulfide and thiocompounds and reduce odor. Meanwhile ferrate and ferric salts exhibited high affinities for sulfur in compounds and functional groups. Therefore, iron salts addition and heat-drying process were able to short-termly stabilize municipal sludge.