Writer: Kathleen Davis Phillips, (979) 845-2872, firstname.lastname@example.org
Contact: Naomi Assadian, (915) 859-9111
EL PASO — El Paso city leaders are taking a fresh look at a smelly old problem: What to do with the sludge that accumulates from sewage treatment plants.
It’s no longer waste to be buried in a dump; it’s called biosolids, a resource to be recycled on agricultural lands. Early experimental results are encouraging, and plans are being formulated to make beneficial use of a large percentage of El Paso’s daily 150 tons of treated biosolids.
“I see agriculture recycling nutrients from urban by-products such as biosolids or the material scraps from (nearby) garment factories,” said Naomi Assadian, cotton research associate at the Texas A&M University Agricultural Research Center here.
Assadian is proving the point on the area’s major crop — cotton. Her experiments with a portion of El Paso’s biosolids, commonly called sludge, could save landfill space and produce an economical benefit for farming.
“It’s a good sell to farmers. It’s relatively low-cost and readily available locally,” she said. The first year of test applications on experimental farms yielded an extra 57 pounds of cotton per acre for each ton of biosolids applied. Each ton of biosolids has about 28 pounds of nitrogen, some phosphorous and potassium and several micronutrients including zinc and calcium. Assadian said the biosolids could become a substitute for chemical fertilizers.
Assadian’s studies were supported in part by the El Paso Water Utilities, which handles about 50 dry tons of treated biosolids a day, according to John Balliew, environmental compliance manager.
Until 1989, El Paso had composted about 30 percent of its biosolids and dumped the remaining 70 percent in with other garbage, he said. When the quality of the composted biosolids decreased due to overload on the utility’s treatment plants, the company began “monofilling” or putting the biosolids in a specially dedicated landfill.
“We are currently working on a plan which will result in El Paso getting back into the beneficial use of biosolids,” Balliew said. “We are looking at various uses such as getting back into composting and applying it to farmland and rangeland.”
El Paso joins a host of other Texas cities either researching methods or currently making use of biosolids. As much as 40 percent of all biosolids generated in the state already are being applied to the land either as compost or are biosolids spread on fields, according to Louis Herrin, senior technology specialist with the Texas Natural Resources Conservation Commission watershed management division.
Herrin noted several suburbs of Houston and the cities of Fort Worth and Austin as being most active. Monte Akers of the Texas Municipal League said Tyler, Sulphur Springs, Azle, Amarillo, Lubbock, Galveston, Crockett and Sugar Land also are at least partially using biosolids in beneficial ways.
Balliew said finding beneficial uses for the biosolids may not be the most economical plan for a utility company.
“Putting it into the ground is probably the cheapest thing to do with it,” he said of the El Paso operation. “But for a small investment, we could put it to beneficial use. If it can be beneficial, then that is for the overall good of the community and that’s how it should be used.”
In addition to tracking cotton yield on fields treated with biosolids, Assadian hopes to determine rates of application and project long-term impact on the soil. In a companion study, she is applying the biosolids with water plant residuals that contain calcium and magnesium.
“Sometimes the biosolids contain a high sodium load, and that can degrade the soil, especially if the irrigation water contains salt like much of it here does,” she said. “Calcium and magnesium can be added to change the soil’s balance so that you can have good, permeable soil.”
Assadian is conducting a series of soil column studies on a small, experimental acreage where the treatments have been applied.
“We are looking at a long-term commitment, not a quick fix,” she said. “The farmer will want to know what will happen if the biosolids are put on the land repeatedly over a period of time. We don’t want to hurt the land just to put sludge on it.”
Depending on the outcome of her studies, Assadian hopes to apply biosolids on commercial farms next.
Balliew said the utility company could have enough biosolids available for area commercial farms by the 1995 growing season. “The utility company is evaluating several options for El Paso,” he said. “The final decision on biosolids management, including any fees realized from the sale of the biosolids, will be made by the Public Service Board.”