Treatment of slaughterhouse wastewater by coagulation- flocculation.: Influence of pH and coagulant aids

A physicochemical treatment consisting of coagulation-flocculation was applied to the wastewater from a slaughterhouse. Fe-2(SO4)(3) and Al-2(SO4)(3). 18H(2)O were used as coagulants along with the following products: activated silica, powdered activated carbon and precipitated calcium carbonate. A series of experiments were made to find the optimal duration and speed of stirring during the flocculation step (slow stirring), settling time, pH and coagulant and coagulant aid doses, using initially the coagulation speed and time (rapid stirring) established in the bibliography for this type of wastewater. GOD, BOD5 and TSS were recorded at the beginning and end of each experiment in order to follow the progress of the process. It has been studied the influence of settling time on the interface height. In the coagulation process the pH must be strongly controlled. Comparisons between coagulants show that coagulation may be significantly influenced by pH, because coagulation occurs within a limited pH range specific for each coagulant. The addition of coagulant aids led to considerably shorter settling times.