At present, chemical processes are widely used to remove phosphorus and organic matter from wastewater either as the only advanced treatment method or as a pretreatment stage to biological treatment, and aluminium salts have been traditionally used as coagulants. The purpose of the present study was to study the interaction between orthophosphate or dissolved organic matter and two aluminium sources: alum [Al-2(SO4)(3) center dot 18H(2)O] and aluminium hydroxide [Al(OH)(3)(s)] in the wastewater treatment process. Amorphous aluminium hydroxide was chosen because it is the hydrolyzed (olated) product of alum and an important adsorbent of inorganic and organic substances in soils since bayerite, gibbsite and boehmite contain a large portion of aluminium hydroxides. Laboratory jar test studies were carried out using either an orthophosphate solution or a tannic acid solution as simulated wastewater and the effect of parameters such as coagulant dose, pH, temperature and different ions was studied. The values of these parameters were based upon measurements on municipal wastewaters from the input of a primary treatment of a wastewater plant in Athens. Orthophosphates at a concentration of 10 mg P/I have been chosen as a P surrogate as they are the major portion of the total P found in wastewater and tannic acid solution at a concentration of 50 mg C/I was used as a surrogate for soluble organic matter. It was proven that alum is much more efficient in phosphorus and tannic acid removal than aluminium hydroxide. Maximum orthophosphate and organic removal is achieved in pH values 5-6 in both cases, alum and aluminium hydroxide, although alum is efficient in a wider pH range (4-7) and a mechanism was proposed to interpret these results. Freundlich isotherm was proven to fit satisfactorily the experimental data for aluminium hydroxide and orthophosphate at 25 degrees C suggesting heterogeneous sorption. The findings of this work may not only contribute to a befter understanding of the chemistry of chemical wastewater treatment and therefore to an improvement of the process but also on phosphorus and organics fixation in soils that contain a large portion of aluminium hydroxides.
