Screening and evaluation of alum and polymer combinations as coagulation/flocculation aids to treat effluents from intensive aquaculture systems.

摘要

As the application of intensive aquaculture systems continues to grow worldwide, so does the need for environmentally sound waste management and waste disposal techniques. The use of coagulants and flocculants to assist in removing suspended solids has long been a standard in waste treatment. Recently, The Conservation Funds Freshwater Institute in West Virginia, USA, has continued its research into coagulation/flocculation aids by examining the performance of alum coupled with various commercially available polymers. Alum is efficient in sequestering phosphorus through chemical precipitation and coagulation of fine solids through charge neutralization. Synthetic polymers are efficient in flocculating small particles together but do not efficiently remove dissolved phosphorus. The specific intention of this work was to use the qualities that distinguish both the alum and the polymer individually and combine the two to optimize waste water treatment for the removal of both suspended solids and phosphorus. The alum/polymer combinations were first screened to determine which polymers worked best with our waste and with the alum. Once the screening was completed, the six best performing combinations were further evaluated with triplicate tests in a jar test apparatus to determine a standard optimal dosage based on phosphorus and suspended solids removal. Using a combination of alum/polymer, the effluent total suspended solids (TSS) removal rate was close to 99%, with final TSS values ranging from 4 to 20 mg/litre. Reactive phosphorus was reduced by 92 to 99% to as low as 0.16 mg/litre P. Finally, total phosphorus was also significantly reduced (98%), with treated effluent concentrations from 0.9 to 3.0 mg/litre P. Although not intended for nitrogen removal, total ammonia nitrogen (TAN), nitrite nitrogen, nitrate nitrogen, and total nitrogen in the effluent were reduced on average by 64, 50, 68, and 87%, respectively. Removal rates for both 5 d carbonaceous biochemical oxygen demand (CBOD5) and chemical oxygen demand (COD) were also significant, with an average value of 97.3 and 96.4%..