Surfacing of domestic wastewater applied to soil through drip tubing and reduction in numbers of Escherichia coli.
Drip tubing is a technology that is increasing in use. The effectiveness of such systems in distributing the wastewater uniformly through the soil matrix, providing adequate removal of bacteria from wastewater, and keeping wastewater from reaching the soil surface has not been adequately evaluated. Experiments were conducted at two sites that had used drip tubing for approximately 3 years. This 3-year-old drip tubing and newly installed tubing were used in this investigation. A solution containing Brilliant Blue FCF dye and Escherichia coli, at an approximate concentration of 1 x 10(6) cells ml(-1), was applied to the sites through drip emitters. Reduction i n Escherichia coli populations reaching the soil surface was generally less than 10%. The route of travel for the solution reaching the soil surface was consistently along preferential flow paths and not uniformly through the soil matrix. Instances of water reaching the soil surface for drip tubing installed at 15 cm was nearly 50%. Increasing burial of the drip tubing from 15 to 30 cm nearly eliminated water surfacing. A 31 per emitter dose of water, immediately following drip line installation later increased instances of water reaching the soil surface for drip tubing buried at 30 cm. The volume of water applied per dose had little effect on the number of times water reached the soil surface. Inherent soil structural characteristics limited the drip tubing's ability to uniformly distribute water and adsorb bacteria. Drip tubing installation to 30 cm may be an important practice to reduce public health hazards from the likelihood of wastewater surfacing.
D000327:Adsorption; D004926:Escherichia coli / Q000302:isolation & purification*; D005374:Filtration; D012987:Soil; D014865:Waste Disposal, Fluid / Q000379:methods*; D018508:Water Purification / Q000379:methods*
D012987:Soil