Enhancement of Municipal Wastewater Biosolids Drying through Interfacial Energy Modifying Amendments to Promote Uniform Agglomeration - Bench Scale Testing

Stine, Sarah G

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Enhancement of Municipal Wastewater Biosolids Drying through Interfacial Energy Modifying Amendments to Promote Uniform Agglomeration - Bench Scale Testing

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Biosolids Drying is the process of producing a fertilizer product for beneficial reuse from solids produced during municipal wastewater treatment. The drying of biosolids involves the evaporation of water to stabilize the material and produce a product for beneficial use. Thermal energy needs to be transferred to the biosolids to evaporate the water and heat the solids. Energy can be provided by combustion of fuels, re-use of waste heat or solar radiation (WEF, 2014). The most common technology for biosolids drying in the United States utilizes rotary drum dryers. In these systems, fines and crushed oversized pellets produced during the drying system are mixed with dewatered biosolids upstream of the dryer to create a 55% - 65% dry biosolid in the form of pellets. Reducing the percentage of fines generated during the drying process can potentially reduce the amount of energy required for drying. In earlier research completed by Zhang (2018) it was shown that energy modifying amendments, specifically cationic polyelectrolytes, can reduce the zeta potential of biosolids in solution and possibly promote aggregation of the fines. One of the tested amendments, polydiallyldimethylammonium chloride (PDADMAC), was also shown to increase the particle size of the biosolids in solution. In this work, a bench scale drying system was designed and developed to apply the polyelectrolyte amendments to biosolids during the mixing phase, and to gauge the impact on the pellet size distribution and the percentage of fines generated after drying. It was shown that PDADMAC, which is a high charge density cationic polyelectrolyte, had a measurable, though inconsistent, impact on pellet size when applied during the mixing phase. This work also highlights the varying characteristics of biosolids and the recycled biosolids produced during the drying process. Both PDADMAC, and polyallyamine, another cationic polyelectrolyte, when applied to biosolids during the mixing phase limited the increase in fines production as the mixing time was increased prior to drying.

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