EFFECTIVENESS OF GRASS STRIPS TO FILTER CATFISH (ICTALURUS-PUNCTATUS)POND EFFLUENT

Twelve 3 m x 24 m grass strips having two different slopes (3 and 1.5% ), two different grasses (Bermuda (Cynodon dactylon (L.) Pers. var: Da ctylon) and Bahia (Paspalum notatum Fluegge)) and three replications p er treatment were used to filter pond effluent from an intensive catfi sh (Ictalurus punctatus) production system. The effluent was applied a s overland flow at the upper ends of the plots and collected at the bo ttom as it flowed downslope through the grasses. From two years' data, it was found that the grass strips removed suspended solids in the ra nge of 18-82% from the pond water effluent depending upon the initial amounts of solids. When the initial concentrations of suspended solids in the effluent were above 200 mg L-1, there was a reduction of 62 an d 82% of solids owing to grass filtration in 1993 and 1994, respective ly. The reduction was about 18% when the initial concentrations of sol ids were less than 30 mg L-1, The concentrations of chemical oxygen de mand (COD) and total Kjeldahl nitrogen (TKN) were significantly lower in the filtered samples (11.8 and 60.8 mg L-1 respectively) than in th e applied effluent (17.9 and 77.9 mg L-1 respectively). There was no s ignificant difference between the concentrations of total phosphorus a nd total ammonia nitrogen in the filtered samples and the applied effl uent. This filtering technique may have practical application in reduc ing nutrient and sediment discharge to receiving waters. It can also b ecome a component of a pond water recirculating system. (C) 1997 Elsev ier Science B.V.