Removal of colouration from Textile wastewaters

Abstract

This study investigated the effectiveness of three physical-chemical methods namely; pH adjustment, precipitation with alum and the use of polyelectrolytes. In the treatment of diary wastewater from Brookeside milk processing plant. It also investigated the drainability of the sludge produced by each of the three methods. Laboratory tests were carried out in three different batches, one for each of the three methods. In the alum method enough alum was added to the wastewater samples to cause precipitation by sweep floc. In the pH adjustment method, the pH of samples were lowered to the iso-electric point of the casein proteins of approximately pH 4.5 leading to their precipitation as a result of solubility changes. The polyelectrolytes method involved the use of two polyelectrolytes, Sudfloc 3820 and Sudfloc 3860 each of which was used to coagulate the dirty wastewater. For each of the three methods, the samples were taken in one-litre beakers and subjected to Jar tests to determine the optimum dosages. After one hour of settling the supernatants were decanted and subjected to standard Chemical Oxygen Demand (COD) tests, turbidity and pH measurements. The settled sludge was subjected to drainability studies. Results showed the treatment of dairy wastewater by the three physical-chemical methods to be effective. There were COD removals of between 60% and 90% and turbidity reduction of over 90%. The use of the sudfloc polyelectrolytes was found to be the least demanding in terms of effluent quality control as no pH adjustments of either the wastewater or the effluent was required. The use of polyelectolytes produced the least volumes of sludge and also the better drainability and solids concentration. Sudfloc 3820 was found to achieve better results than Sudfloc 3860 in terms of COD reduction and the drainability of sludge produced although both achieved the same drainability studies. This study showed that each of the three physical-chemical methods can be used effectively to remove the white colour of dairy wastewater as well as the bulk of the proteins and fats, hence, enabling the discharge of the effluents into natural waters to be of good assimilative capacity.