Use of alum sludge in a constructed wetland for greywater treatment (Tanzania)

This study assessed the potential use of alum sludge as a substrate in a constructed wetland for laundry greywater treatment. The experimental set-up to evaluate the performance of alum sludge consisted of lab-scale horizontal- constructed wetland units with two beds, one with gravel and another with alum sludge. The characterization results indicated that greywater had high organic contents and nutrients exceeding the effluent discharge standards. After 30days, the alum sludge was highly effective in removing TP (93%) and TN (62%) in comparison with the gravel which had TP and TN removal efficiencies of 91% and 59%, respectively. However, alum sludge had relatively lower organic contents removal of 67% BOD5 and 57% COD compared to 74% BOD5 and 78% removal in gravel filter media. The percentage removal of the faecal coliforms was 97% and 94% for the gravel-based filter and alum sludge filter, respectively. The alum sludge as the post-filter was effective in removing BOD5 (37%), COD (19%), TN (21%), TP (66%) and faecal coliforms (45%). The study recommends that the use of alum sludge as a filter or post-filter media could be an inexpensive method as the alum sludge is widely available as waste products from coagulation treatment plants.