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  • Publication
    Characteristics and mechanisms of phosphate adsorption on dewatered alum sludge
    The adsorption characteristics of phosphate adsorption on the dewatered alum sludge were identified as a function of pH and ion strengths in solution. In addition, adsorption mechanisms were investigated by conducting batch tests on both the hydrolysis and P-adsorption process of the alum sludge, and making a comparative analysis to gain newer insights into understanding the adsorption process. Results show that the adsorption capacity decreased from 3.5 to 0.7 mg-P/g-sludge when the solution pH was increased from 4.3 to 9.0, indicating that adsorption capacity is largely dependent upon the pH of the system. The results of the competitive adsorption between phosphate and typical anions found in wastewater, such as SO42- and Cl-, onto alum sludge reveal that alum sludge can selectively adsorb phosphate ions. The insignificant effect of SO42- and Cl- on P-adsorption capacity indicates that phosphate adsorption is through a kind of inner-sphere complex reaction. During the adsorption process, the decrease of phosphate concentration in solution accompanied with an increase in pH values and concentrations of SO42-, Cl- and TOC (total organic carbon) suggests that phosphate replaced the functional groups from the surface of alum sludge which infers that ligand exchange is the dominating mechanism for phosphate removal. At the same time, the simultaneous decreases in PO43- and total aluminium concentration in solution indicate that chemical reaction and precipitation are other mechanisms of phosphate removal.
    Scopus© Citations 363  6227
  • Publication
    A promising approach of reject water treatment using a tidal flow constructed wetland system employing alum sludge as main substrate
    This study examined a novel reuse of the alum sludge, an inescapable by-product of the production of drinking water when aluminium salt is added as a coagulant, as the main medium in a laboratory-scale multi-stage constructed wetland (CW) system for reject water treatment. Such reject water is a main concern in municipal wastewater treatment plant (MWWTP) for increasing the organic and nutrient loading. A “tidal flow” strategy was employed to enhance the wetland aeration to stimulate organic pollutants and N oxidation while the “step feed” operation was adopted to supply the necessary amount of carbon source for denitrification. The results reveal that alum sludge acted as P adsorbent can secure the P removal. Meanwhile, high removals of ammoniacal-nitrogen and organic matters can also be obtained due to the active bacteria attached growth on the alum sludge surface. The results show that average removal efficiencies of 65.4 ± 12.3% for COD, 67.8 ± 9.2% for BOD5, 33.6 ± 17.0% for N and 99.5 ± 0.49% for P can be achieved over a period of 190 days. This indicates that novel reuse of alum sludge as medium in CW system can provide a promising approach for reject water treatment. Therefore, it will significantly reduce the amount of pollutants feedback through reject water recycling in a MWWTP.
      1896Scopus© Citations 30