Toward the conceptual and quantitative understanding of biosolids conditioning: the gel approach

Proper chemical conditioning of wastewater solids is crucial for both operational and economic reasons, but the process has defied satisfactory description to date, in either conceptual or quantitative terms. In this research, a new conceptual model of biosolids structure—likening it to a colloidal gel—was assessed as a means of interpreting conditioning mechanisms. The basis of the gel approach lies in the colligative properties that are altered by lowering of the solvent chemical potential by introducing a solute. Results indicate that inorganic conditioners form precipitates and complexes thus collapsing the gel network and forming particulates, whereas organic polymers lead to heterogeneous collapse with limited diffusion inside the gel. A gel model, based on the osmotic pressure, was found reasonably successful in defining the conditioning efficacy of biosolids. Beyond the model's fundamental value, these results validate a new way of understanding how conditioning and dewatering operate, which should help to improve the selection and optimization of these processes.