Treatment of eutrophic lake water and phosphorus recovery by reusing alum sludge and/or wood

Treatment of eutrophic lake water was investigated, when alum sludge and/or wood were used as the media for lab-scale filtration. Process 1 consisted of Column 1 with wood and Column 2 with alum sludge in series, and Process 2 of Column 3 with alum sludge. The filtration velocity was 0.45 and 0.91 m/d for 49 days each. Both processes removed SS and T-P well with about 98% and 92% removal efficiency, respectively. Total nitrogen removal efficiency was higher in Process 1 (64–72%) than Process 2 (18–19%), because of biological denitrification using organics supplied from wood. The dissolution of organics and aluminium from wood and alum sludge, respectively, was not significant in the effluent. An alkaline extraction method was able to extract two-thirds of phosphorus in the alum sludge. Thus, alum sludge was excellent at removing and recovering phosphorus and the filtration combining wood and alum sludge enabled the concomitant removal of nitrogen and phosphorus.