Pretreatment for potable reuse: Enhancing the biological removal of 1,4-dioxane from landfill leachate through cometabolism with tetrahydrofuran.

1,4-Dioxane is a probable human carcinogen and a persistent aquatic contaminant. Cometabolic biodegradation of 1,4-dioxane is a promising low-cost and effective treatment technology; however, further demonstration is needed for treating landfill leachate. This technology was tested in two full-scale moving bed biofilm reactors (MBBRs) treating raw landfill leachate with tetrahydrofuran selected as the cometabolite. The raw leachate contained on average 82 µg/L of 1,4-dioxane and before testing the MBBRs removed an average of 38% and 42% of 1,4-dioxane, respectively. First, tetrahydrofuran was added to MBBR 1, and 1,4-dioxane removal was improved to an average of 73%, with the control MBBR removing an average of 37% of 1,4-dioxane. During this period, an optimal dose of 2 mg/L of tetrahydrofuran was identified. Tetrahydrofuran was then fed to both MBBRs, where the 1,4-dioxane removal was on average 73% and 80%. Cometabolic treatment at the landfill significantly reduced the concentration of 1,4-dioxane received from the landfill at a downstream wastewater treatment and indirect potable reuse facility, reducing the load of 1,4-dioxane from 44% to 24% after the study. PRACTITIONER POINTS: Cometabolic degradation of leachate 1,4-dioxane with THF in MBBRs is a feasible treatment technology and a low-cost technique when retrofitting existing biological treatment facilities. The MBBRs can be operated at a range of temperatures, require no operational changes beyond THF addition, and operate best at a mass ratio of THF to 1,4-dioxane of 24. Source control of 1,4-dioxane significantly reduces the concentration of 1,4-dioxane in downstream wastewater treatment plants and potable reuse facilities.

Effect of temperature on toxicity and biodegradability of dissolved organic nitrogen formed during hydrothermal liquefaction of biomass.

This study investigated the nutrient content and reuse potential of wastewater generated during hydrothermal liquefaction of microalgal biomass. The hydrothermal liquefaction reaction was tested at 270, 300, 330, and 345 °C to determine the effect of temperature on the formation of non-biodegradable dissolved organic nitrogen (nbDON). Total nitrogen, ammonium, color, and toxicity were selected as key characteristics for the reuse of hydrothermal liquefaction wastewater. Results indicated that a higher concentration of nbDON5 (nbDON defined with a 5 day growth assay) and more diverse heterocyclic N-containing organic compounds were associated with greater toxicity as measured by a growth rate assay. For the tested temperature ranges, the total nitrogen content of the hydrothermal liquefaction wastewater slightly decreased from 5020 ±â€¯690 mg L-1 to 4160 ±â€¯120 mg L-1, but the % nbDON5 fraction increased from 57 ±â€¯3 %DON to 96 ±â€¯5 %DON. The temperature of hydrothermal liquefaction reactions can be optimized to maximize carbon conversion and nitrogen recovery.