Remoção de ortofosfatos de água e de esgoto com adsorvente produzido a partir de exoesqueleto de coral-sol: equilíbrio, cinética, termodinâmica e otimização de processo

Abstract

The excessive discharge of phosphorus (P) through untreated urban and industrial wastewater is related to eutrophication of recipient water bodies. It is crucial to promote efficient removal of P and, if possible, to promote the return of P to land by using it as fertilizer. The most used method to remove P from effluent is chemical precipitation. However, this technique is relatively expensive and requires disposal of the chemical sludge generated in the process. Therefore, searching for new low-cost strategies with high efficiency in removal of P is completely justified. In Brazil, two exotic species known as sun-coral (Coccinea Tubastraea e Tubastraea tagusensis) are already spread along 2000 Km of the Brazilian coast. These species are considered ecosystems engineers , since they create, modify and sustain habitats, which once established, can change totally the local ecosystem. Therefore, these species represent a serious threat; since they promote damage do the Brazilian marine biodiversity, which may include economic losses with reduction of economically important marine species. These species have exoskeleton with high concentration of calcium carbonate, which can be potentially used to treat wastewater, particularly for P removal. This investigation focused on the capacity of P removal from synthetic and real wastewaters using powder produced from c coral-sun exoskeleton as adsorbent in three different forms: raw (RCS); physically modified (CSA); chemically modified (CSC) comparing the results to those obtained with commercial activated carbon powder (CAC), which is the most used adsorbent in the world. In order to study the efficiency of the P removal, a factorial design with central composite design (CCD) was applied. In order to optimize the P removal, the influence of three independent variables were investigated: ration adsorbent/adsorbate, pH; temperature, associated to studies of kinetics, thermodynamics and equilibrium in the best configurations obtained with the DCCR for each material. The P removal capacities for RCS, CSA. CSC and CAC using synthetic effluent were 3685.0 mg P kg-1; 3712.5 mg P kg-1; 4567.5 mg P kg-1; and 1797.5 mg P kg-1 respectively. In all cases, the adsorption process followed the model proposed by Langmuir, being the process thermodynamically appropriate. For the real wastewater, the adsorbents produced with coral-sol removed about 100% of the P found in the samples. Based on these results, the exoskeleton powder showed to be a very good option potentially sustainable being useful in several applications, such as urban and industrial wastewater treatment, at the same time promoting the control of the sun-coral population, through its commercial exploitation.