Competitive adsorption of Cu2+, Pb2+, Cd2+, and Zn2+ onto water treatment residuals: implications for mobility in stormwater bioretention systems.

The lack of knowledge regarding competitive adsorption of heavy metal ions onto water treatment residuals has been hindering their reuse as a medium in stormwater bioretention systems. Competitive adsorption of copper(II), lead(II), cadmium(II), and zinc(II) onto polyaluminium chloride and anionic polyacrylamide water treatment residuals (PAC-APAM WTRs) was evaluated with different pH, temperature, initial concentration, and time. The competitive adsorption removal increased with the increase of pH and temperature. The analysis of the ratios of maximum adsorption capacity of a heavy metal ionic species in a multi-component system to that in a mono-component system (Qmix/Qmono) demonstrated that the coexisting ion had a negative effect on the adsorption of a metal ionic species. The Langmuir model provided a better fit, indicating that the adsorption could be a monolayer adsorption process. The modified Langmuir isotherm studies showed that the affinity order in the multi-component systems was Cu2+>Pb2+>Cd2+>Zn2+. The pseudo-second-order model better described the adsorption kinetics implying that the competitive adsorption behavior could be interpreted by diffusion-based mechanisms. This study contributed to a better understanding the mobility of those frequently occurring heavy metal ions in stormwater runoff in the PAC-APAM WTRs media layer of stormwater bioretention systems.

Adsorption of pyridine from aqueous solutions onto polyaluminium chloride and anionic polyacrylamide water treatment residuals.

The adsorption performance of pyridine onto polyaluminium chloride (PAC) and anionic polyacrylamide (APAM) water treatment residuals (WTRs) was investigated by batch experiments. This study confirmed the assumption that PAC-APAM WTRs had the ability to remove pyridine. The non-linear Dubinin-Radushkevich model and non-linear Freundlich model better described the isotherms, indicating that the adsorption was a chemically controlled multilayer process. The pyridine adsorption rate was simultaneously controlled by external film diffusion and intraparticle diffusion. The adsorption of pyridine was an endothermic reaction with randomness increase. The pyridine adsorption decreased with pH increase. Pyridine removal was observed to be a linear increase from 6.16% to 96.18%, with the increase of dosage from 2.5 g/L to 15 g/L. The Langmuir maximum adsorption capacity was 3.605 mg/g while the theoretical isotherm saturation capacity was 9.823 mg/g. Therefore, PAC-APAM WTRs recycled into contaminated soils for remediation is expected to be an innovative alternative disposal method. More research is recommended in the future to identify detailed adsorption mechanisms and the most appropriate mixing ratio of PAC-APAM WTRs to contaminated soils under various climatic conditions.

Nitrogen leaching losses from a wastewater land application system.

Potential contamination of groundwater because of nitrogen leaching has been an important concern in municipal wastewater land application systems; however, few efforts have made to measure nitrogen leaching (total N, NO(3-)-N, and NH(4+)-N) under field conditions. This research successfully developed a conceptual nitrogen mass balance model and quantified its components at a wastewater land application system located at the City of Littlefield, Texas, from October 2005 to September 2007. The concentrations of total nitrogen and nitrate-nitrogen in the leachate were significantly less than 10 mg/L, therefore, there was no potential nitrogen contamination to groundwater found at this site during the research period. Linear regression models were analyzed and resulted in R2 values of 0.918, 0.966, and 0.833 between cumulative applied total nitrogen mass and cumulative leached total nitrogen mass, cumulative applied nitrate-nitrogen mass and cumulative leached nitrate-nitrogen mass, and cumulative applied ammonia-nitrogen mass and cumulative leached ammonia-nitrogen mass, respectively. The nitrogen mass balance design approach for this site resulted in significant nitrogen removal. Organic nitrogen may leach with other forms of nitrogen, and denitrification plays an important role in nitrogen removal during the winter and spring seasons when the grass is dry.

Effects of sludge filtrate on the survival and reproduction of Ceriodaphnia dubia.

The objective of this study was to determine if the runoff from croplands fertilized with municipal sludge was toxic to aquatic biota and, therefore, a potential threat to either public health or the environment. Seven-day bioassays with Ceriodaphnia dubia showed that the No-Observed-Effect-Concentration (NOEC) was 24 g/L and the Lowest-Observed-Effect-Concentration (LOEC) for survival was 30 g/L for soil samples treated with 35.2 metric tonnes (MT)/ha of municipal sludge. For soil samples treated with 0 and 17.6 MT/ha of sludge, the survival rates of C. dubia were not significantly affected at concentrations of 6-30 g/L of soil. Reproduction was suppressed by 25% when daphnids were exposed to 3.3 g/L concentration of soil treated with sludge at 35.2 MT/ha. A 50% suppression of reproduction occurred when daphnids were exposed to 15 g/L concentration of soil treated with sludge at 17.6 MT/ha. A sludge application rate of 17.6 MT/ha suppressed reproduction at a treatment concentration of 18 g/L. These data indicate that the runoff from agricultural lands treated with municipal sludge has the potential to affect reproduction in daphnids and, therefore, the environment through the aquatic food chain.