Reclamation of wastewater and wastewater products for beneficial land use in the upper Rio Grande floodplain

Reuse of wastewater and wastewater products (biosolids) will be a necessity to meet growing water demands in the upper Rio Grande floodplain. We investigated safe application of waste to prevent chemical or biological contamination of air, soil, and water resources. For the first study, the persistence and contamination of water-borne bacteriophage was evaluated in irrigated soil and spinach plants. Untreated municipal wastewater was blended with treated effluent, spiked with bacteriophage and applied to soil columns planted to spinach using subsurface drip irrigation. Wastewater disinfection prior to irrigation successfully reduced fecal coliforms to meet Texas water reuse guidelines. No virus contamination was found on spinach leaf surfaces. Phage persisted in soil for 28 days after the last irrigation. Movement was limited to areas around or above the subsurface emitter. Frequent subsurface irrigation may have contributed virus contamination near the surface of a silty clay loam soil. For the second study, surface or incorporated applications of selected salts plus pecan mulch were evaluated on the inhibition of early ammonia (NH 3) volatilization from lime stabilized biosolids. Ammonia gas was captured in boric acid traps, and biosolids nitrogen (N) determined after a 72 h volatilization period. Early NH3 loss was instantaneous with lime incorporation into aerobically-digested biosolids. Treatments regardless of application method did not completely prevent N losses from lime stabilized biosolids. A pecan shell mulch and a surface application of an iron salt significantly reduced NH3 losses by at least 40% relative to untreated aerobically-digested biosolids and lime-stabilized biosolids controls, respectively. Organic mulches and/or surface applied metal salts may create an NH3 barrier. However, application rates need further investigation. In the third study, the impacts of excess calcium (Ca) in biosolids amended soil on soil pH, salinity, and heavy metal mobility were evaluated. Biosolids-amended soils were packed into soil columns and then irrigated with water containing increasing Ca concentrations. Soil incorporated biosolids and Ca enrichment did not increase the alkalinity or sodicity of a moderately alkaline soil. Calcium enrichment increased soluble and exchangeable Ca soil fractions, salinity and copper mobility. Incorporation of lime stabilized biosolids appeared beneficial to moderately alkaline soils.