Problem: Industrial and municipal wastewaters may be suitable for irrigation in many arid and semi-arid areas, but often cause soil crusting problems that reduce infiltration rates. This is because these wastewaters often contain high levels of sodium and salinity. Soil conditioners including polyacrylamides (PAM) have the potential to prevent these problems.
Objective: To evaluate the performance of PAM soil conditioners to reduce soil crusting associated with wastewater irrigation, and to assess the economics and environmental impact of using these products.
Methods: Field research was conducted at the City of Kingsville wastewater treatment plant. Some of the average municipal wastewater concentrations were: sodium (410 parts per million or ppm); calcium (79 ppm); carbonates (220 ppm); chloride (480 ppm), and sulfates (350 ppm), and total dissolved solids (1,420 ppm). Treatments included applying gypsum, injecting high and low levels of PAM into wastewater, irrigation without the use of a soil amendment, and a control that included neither irrigation or the use of a soil amendment. Sprigs of Common Bermuda grass were planted in August 1993. The grass was irrigated once a week until November 1993. In February 1994, field-saturated hydraulic conductivity was measured using a constant head pressure, single-ring, infiltrometer. Conductivity was measured at the top and bottom of furrows. Soil samples were collected to determine mass soil moisture. Grass yields were not measured.
Results: Effects of PAM were immediately visually apparent in the field. Less erosion and greater structural stability were obvious. Use of PAM significantly improved infiltration and in some cases increased soil wetness. The persistence of PAM after irrigation had ceased shows that lower doses may also be effective. This research suggests that the use of PAM may allow for the more widespread irrigation of wastewaters without causing soil crusting or erosion.
Reference: Gardiner, D., and B. Mendez, "Effects of Polyacrylamide on Infiltration of Wastewater," Presented at 1995 Water for Texas Conference, TWRI, Texas A&M U., College Station, TX.
NOTE: This research project was funded by TWRI.