This study concerns the utility of the coagulation process in removing humic substances and its dependence on the properties of these substances and their concentrations. The coagulation process was performed on model solutions of natural humic acids. Polyaluminum chloride (PAX XL3) and aluminum sulfate were used for this study, which allowed for a comparison of the effectiveness of pre-hydrolyzed and hydrolyzing coagulants. The coagulant dosages were determined as gram aluminum per gram carbon, thanks to which it was possible to compare the process effectiveness for different initial organic carbon concentrations, whose values were in the range of 5.51-21.23 gC/m 3. The obtained values of reductions in organic carbon concentrations point to a significant process effectiveness (37.2-59.4% and 20.0-41.5% for pre-hydrolyzed and hydrolyzing coagulants, respectively), which increased with increasing molecular mass of the humic substances present in water. These results are analogous to those found for coagulation of surface waters and point to a greater effectiveness of pre-hydrolyzed coagulant in removing humic substances (at the same coagulant dosage). The effectiveness in removing organic substances increased with coagulant dosage and the initial total organic carbon concentration. The coagulation process most effectively removed aromatic substances absorbing UV light. The content of substances absorbing UV light in raw and post-coagulation water was proportional to the dissolved organic carbon content.
More stringent effluent limits, especially with regard to total nitrogen, force wastewater treatment plants to consider sidestream nitrogen removal from digested sludge dewatering liquor which can contain up to 20% of incoming nitrogen load. Deammonification, the most promising biological technology for sidestream nitrogen removal, is based on partial short-cut nitrification and the Anammox process. Both steps of this process are conducted by slowly growing autotrophic bacteria, namely nitrifies and Anammox, which however may form different types of sludge: flocculent and granular, respectively. Nevertheless, ensuring effective sludge separation from treated effluent is crucial for the ability to retain both kinds of slowly growing biomass in the system. This paper presents the principles of sludge settling modelling, the results of a series of column tests conducted on sludge from pilot-scale two-stage deammonification treatment facility, as well as an attempt to estimate settling parameters in order to fit a sedimentation model.
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