The objective of this research was to study the comparison of soybean milk wastewater primary treatment efficiency between DAF and coagulation. In this experiment, parameters being studied were pH adjustment; concentration of ferric chloride or alum as coagulant adjustment ; concentration of cationic polymer or anionic polymer as coagulant aid adjustment. From the experimental results found that the best conditions for treated wastewater by DAF were optimum pH as 4.5, optimum recycle as 150% or A/S ratio 0.0027 mg.air/mg.solid, optimum dosage of ferric chloride as 150 mg/l and anionic polymer as 2 mg/l. The detention time and average floating velocity were equal to 30 min and 0.67 cm/sec respectively. The removal efficiency of COD TKN and TSS were 90.2% 91.6% and 90.8% respectively. The cost of chemical was equal to 12.11 Baht/CU.M. Result from sludge analysis found that protein conten and organic matter of slude were 45.3% and 94.8% respectively, while sludge production was 4.69 kg/CU.M and the sale price was 10.41 Baht/CU.M. The best conditions for treated wastwwater by coagulation were optimum pH as 4.5, optimum dosage of ferric chloride as 200 mg/l and anionic polymer as 2 mg/l. The detention time and average settling velocity were equal to 40 min and 0.425 cm/sec respectively. The removal efficiency of COD TKN and TSS were 92.6% 93.4% and 92.6% respectively. The cost of chemical was equal to 14.29 Baht/CU.M. Result from sludg analysis found that protein content and organic matter of sludge were 39.4% and 94.7% respectively, while sludge production was 4.84 kg/CU.M and the sale price was 10.65 Baht/CU.M. The cost of chemical from coagulation test was higher than DAF test at the same removal efficiency and sludge recovery from coagulation and DAF had nearly chemical characteristic In consideration of chemical cost and removal efficiency, DAF with 150% recycle was more suitable than coagulation for operation period.
