Journal of Environmental Engineering

Community management is a common approach to securing access to clean water for rural residents. Its failure to sustain water services over acceptable lifetimes has been well-documented, adversely impacting human health when users return to unimproved sources during system downtimes. The objective of this study is to identify effective strategies for improving the performance of community-managed systems. The quantitative system dynamics models were developed using monitoring data for Bolivia and Colombia to simulate typical performance as infrastructure ages and to test strategies to improve performance. The two models captured the performance behavior revealed from monitoring data and were driven by the same structure: two reinforcing loops and two balancing loops. Although a strategy to professionalize the service provider enabled them to meet or exceed the target performance threshold, external financial support alone was ineffective. The paradigm shift from fix-on-failure corrective maintenance to preventive maintenance enables systems to sustain high performance levels over time. The models are useful for understanding the underlying system structure driving performance of community-managed systems and designing high-impact interventions using model simulations.

Mine water from upwellings in Commerce, Oklahoma is treated by the Mayer Ranch Passive Treatment System (MRPTS) to remove contaminants. Nickel [Ni(II)] and zinc [Zn(II)], which are toxic to both plants and animals when present in elevated concentrations, are still detectable at the effluent of the system out of the polishing pond (also known as Cell 6). Research has shown that living algae are capable of both adsorption and absorption of metals, whereas dead algae biomass can only adsorb metals due to the absence of metabolic processes. Previous exposure to metal contaminants influences the metal uptake efficiency of algae, as well as future growth rates when contaminants are present. Researchers have hypothesized that sorbed metals will be released from algae detritus as the algae decomposes. This research examined Ni(II) and Zn(II) sorption and release by a community of mixed algae species collected from MRPTS. Effluent water from MRPTS containing detectable levels of both Ni(II) ($>0.015\mathrm{mg}/\mathrm{L}$) and Zn(II) ($>0.25\mathrm{mg}/\mathrm{L}$) was used to create elevated concentration solutions (0.5, 2.0, 5.0, 10.0, and $20.0\mathrm{mg}/\mathrm{L}$) of both Ni(II) and Zn(II). A solution of MRPTS final cell effluent water with no addition of Ni(II) or Zn(II) also was included, along with a no-algae control solution with Ni(II) and Zn(II), for comparison of results. All analyses were performed in triplicate. Samples were incubated in the laboratory to mimic changing seasonal environmental conditions to which the native algae community in a passive treatment system (PTS) would be exposed, thus causing growth, death, and decomposition of that algae. Algae and associated solutions for each sample at the end of each phase (growth, chilled, and decomposition) were processed using microwave-assisted acid digestion to extract the metals present in the samples. The data obtained from these experiments showed sorption of both Ni(II) and Zn(II) by the algae community during the growth phase. The algae released a portion of the previously sorbed metals during the chilled phase. Samples showed continued sorption during the decomposition phase. Greater-concentration solutions had greater levels of sorption by the algae. The data followed the Langmuir isotherm model ($R^2>0.90$), indicating that the principal metal removal mechanism was adsorption. These data indicate that algae, and ensuing decomposing algal biomass, both are capable of removing and retaining Ni(II) and Zn(II) from contaminated waters. Hence, natural algae populations within PTS can provide additional water treatment.

Estrogens posing huge eco-environmental risks are universally found in water ecosystems. Laccase, as a multicopper oxidoreductase, can evoke humification and polymerization of estrogens to reduce their biotoxicity and removability, but little information exists in investigating the influence of humic acids (HAs) on E2 conversion kinetics, humification degree, and oligomer distribution at varying pH values. Herein, Trametes versicolor laccase (Tvlac) was able to efficiently convert $17\beta \text{-}\mathrm{estradiol}$ (E2) in the presence of two different HAs, and the process fitted a pseudo-first-order kinetic model ($R^2=0.8474–0.9952$). The kinetic constants were 0.048, 0.022, and $0.020{\min }^{-1}$ for HA-free, peat-derived HA, and commercial HA at pH 5.0, respectively. The changing pH not only affected E2 conversion kinetics, but altered the aromaticity and humification degrees of HAs. A total of five humified products including estrone (E1) and E2 self-oligomers (i.e., dimer, trimer, and tetramer), as well as E1-E2 copolymeric species, were tentatively identified, in which the dominant intermediates were E2 self-oligomers resulting from radical-based C─ C and/or C─ O bonds. Productions of E2 dimer, trimer, and tetramer with increased molecular sizes were the highest at pH 5.0 in the given pH conditions, and they were easily handled by centrifugation and filtration. In particular, E2 was capable of being covalently bound into HAs to form new humified supramolecular polymers, thus promoting E2 copolymerization and detoxification. Our results disclose that HAs exhibit a vitally important influence on the conversion kinetics and product distribution of E2 in Tvlac-started humification. Consequently, there is need to reunderstand the fate and geochemical behavior of estrogens with HAs present in the aquatic eco-environments at different pH conditions.

Biofouling triggers a chain of events that are deleterious to engineered systems providing safe water to the population and industry. The frequent use of dissolved biocides to combat biofilm growth has its own drawbacks, including the formation of noxious substances (e.g., organochlorinated compounds) and the discharge of significant amounts of nonspent biocides in the aquatic environment. This paper proposes affordable and robust approaches for water pretreatment to reduce organic (bio) and inorganic fouling to be implemented in developing rural areas. The pretreatment follows a sequential step strategy that includes particulate matter removal through optimized coagulation, phosphorus removal by iron oxide sorption using recovered inexpensive waste materials and, finally, an innovative biocidal treatment with functionalized particles. The following main experimental results were obtained: (1) coagulation treatment with aluminum sulfate at ${0.03\mathrm{mg}\mathrm{L}}^{-1}$ led to the elimination of particulate matter fouling, as confirmed by the improved performance of a downstream membrane separation system; (2) in the sorption step, iron-covered waste sand taken from filter backwash water allowed a reduction of microbial available phosphorous to levels where biofilm growth is highly limited; and (3) the novel bactericidal process, using inexpensive commercial alumina particles functionalized with benzalkonium chloride, was able to reduce to zero the microbial load of a contaminated water stream within 1 h of residence time, without leaching the biocide to the water. Implementation of this concept represents an affordable and environmentally sustainable treatment system because the basic materials used have low cost and are easily available.

The knowledge of adsorption characteristics of bentonite (B) is mandatory for heavy metals removal from the wastewater and contaminant retention in landfill liner. Adsorption characterization of geomaterials requires the use of a buffer for pH adjustment. Previous studies have not investigated the impact of using a buffer on the adsorption characteristics of swelling soils such as B. This study quantified the influence of sodium acetate (Na-Ac) buffer on the adsorption capacity of B and percentage removal of lead (${\mathrm{Pb}}^{2+}$) using a batch adsorption study (BAS). The solution was adjusted using either nitric acid or Na-Ac buffer to maintain $\mathrm{pH}=5$. The sediment volume of bentonite suspension in water at pH 5 adjusted with Na-Ac buffer was less than that using nitric acid. The lesser sediment volume was due mainly to the agglomeration of bentonite particles in the presence of Na-Ac buffer. The experimental findings corroborate that the use of Na-Ac buffer results in a notable reduction of adsorption capacity and percentage removal of ${\mathrm{Pb}}^{2+}$ by B. The highest percentage removal of ${\mathrm{Pb}}^{2+}$ ions was observed at a liquid-to-solid ratio ($L/S$) of 20 when pH was adjusted with nitric acid. The lowest percentage removal was noted at $L/S=100$ when pH was maintained using Na-Ac buffer. The influence of Na-Ac buffer also was evaluated by conducting a BAS for ${\mathrm{Pb}}^{2+}$ removal under a competitive environment of ${\mathrm{Na}}^{+}$ using sodium chloride (NaCl) and Na-Ac buffer. The interaction of ${\mathrm{Pb}}^{2+}$ with B in two different environments was confirmed by mineralogical, morphological, and spectral analysis postadsorption. According to this study, nitric acid can be a better alternative to Na-Ac buffer for the adsorption study of B in a controlled pH environment. If a buffer is used for the adjustment of pH in a BAS, its effect on the adsorption capacity and percentage removal should be taken into account when characterizing B for its practical application in water decontamination, waste containment system, and chemical reactive barrier projects.

Operations and maintenance (O&M) practices are becoming increasingly scrutinized as storm events become more frequent and intense, surpassing the design storms that dictated the original capacity. In order to get the best performance from infrastructure investments, communities are looking to establish effective operations and maintenance programs. In this study, an approach to assessing system vulnerability was developed using real-time sensors. By leveraging an adapted risk-based assessment model (RBAM), an alert rating system was developed to prioritize maintenance of ponded stormwater facilities. The degradation in performance of stormwater systems was progressively monitored using indicators for probability and consequence of failure. Failure in this context is a stormwater facility’s vulnerability to meet the design performance due to decreased capacity. Probability of failure was rated using a hydrologic model calibration statistic to assess the difference between the observed data set and a drawdown model. Consequence of failure was rated by evaluating the duration of drawdown periods based on regional regulatory criteria and operator schedules. The predictive maintenance alert methodology enables management of distributed assets more effectively through maintenance alerting and builds resilience into stormwater networks because issues are identified early and program resources are optimized.

In water treatment processes, the use of biochars has risen due to their relative abundance, sustainability, and low cost compared with conventional technologies. The objective of this work was to investigate the physical and chemical properties of six chars that promote phosphate removal. The chars were further engineered with magnesium chloride (engineering biochars) prior to heat treatment to increase removal of phosphate. The impregnated magnesium was converted to magnesium oxide (MgO) under inert conditions at temperatures greater than 450°C. The solutions were analyzed using an ultraviolet visible spectrophotometer at 810 nm for phosphate concentration. To simulate real-world municipal water reuse applications, reclaimed wastewater was used as the source water for the experiments. Thermally treated sugar beet pellets were converted to biochar with inherent magnesium content, and demonstrated removal of more than 85% when pyrolyzed at greater than or equal to 550°C for 15 min. Dosing of MgO increased the solution pH, thus having phosphate species as ${\mathrm{HPO}}_4^{2-}$ and ${\mathrm{H}}_2{\mathrm{PO}}_4^{-}$, and bound the hydrated $\mathrm{Mg}(\mathrm{OH}{)}_2$ as ${\mathrm{MgHPO}}_4$ and ${\mathrm{Mg}}_2({\mathrm{H}}_2{\mathrm{PO}}_4)$. The porosity of biochar is not solely responsible for phosphate removal but is required after impregnation of magnesium for increasing accessibility. Contact pH is a good indicator of biochar performance. MgO was shown to be an excellent sorbent for phosphate removal in reclaimed water when impregnated as ${\mathrm{MgCl}}_2$ and dosed separately with biochar.

Water above 374°C and 22.1 MPa becomes supercritical, a special state where organic solubility increases and oxidation processes are accelerated. Supercritical water oxidation (SCWO) has been previously shown to destroy hazardous substances such as halogenated compounds. Three separate providers of SCWO technology were contracted to test the efficacy of SCWO systems to reduce per- and poly-fluoroalkyl substances (PFAS) concentrations from solutions of dilute aqueous film-forming foam (AFFF). The findings of all three demonstration studies showed a greater than 99% reduction of the total PFAS identified in a targeted compound analysis, including perfluorooctanesulfonic acid (PFOS) and perfluorooctanoic acid (PFOA). PFOS was reduced from $26.2\mathrm{mg}/\mathrm{L}$ to $240\mathrm{\mu g}/\mathrm{L}$, $30.4\mathrm{mg}/\mathrm{L}$ to $0.310\mathrm{\mu g}/\mathrm{L}$, and $190\mathrm{mg}/\mathrm{L}$ to $8.57\mathrm{\mu g}/\mathrm{L}$, from the Aquarden, Battelle, and 374Water demonstrations, respectively. Similarly, PFOA was reduced from 930 to $0.14\mathrm{\mu g}/\mathrm{L}$, 883 to $0.102\mathrm{\mu g}/\mathrm{L}$, and $\mathrm{3,100}\mathrm{\mu g}/\mathrm{L}$ to nondetect in the three evaluations. Additionally, the chemical oxygen demand of the dilute AFFF was shown to reduce from 4,750 to $5.17\mathrm{mg}/\mathrm{L}$ after treatment, indicating significant organic compound destruction. In one demonstration, a mass balance of the influent and effluent found that the targeted compounds accounted for only 27% of the generated fluoride, suggesting that more PFAS were destroyed than measured and emphasizing the limitations of targeted analysis alone. As a destructive technology, SCWO may be an alternative to incineration and could be a permanent solution for PFAS-laden wastewaters rather than disposal by injection into a deep well or landfilling. Additional investigation of reaction byproducts remains to be conducted for a complete assessment of SCWO’s potential as a safe and effective PFAS treatment technology.

Historical use of aqueous film-forming foam (AFFF) has led to widespread contamination of water and soil, due to the high per- and polyfluoroalkyl substance (PFAS) content in AFFF. Due to the high toxicity and environmental persistence of PFAS, legacy AFFF is being phased out, and end-of-life disposal options are needed. While incineration has historically been the preferred disposal option for AFFF, the practice is being phased out due to mounting concerns around the emission of harmful byproducts. Hydrothermal alkaline treatment (HALT) is an effective PFAS destruction process, which has been previously shown to generate no toxic PFAS degradation byproducts. In this case study, HALT is evaluated as an end-of-life destruction option for AFFF stockpiles. A legacy AFFF sample containing $\sim 3.2\mathrm{wt\%}$ total PFAS is treated at 350°C, $>20.7\mathrm{MPa}$, 5 M-NaOH loading, and residence times of 2 to 6 h in a batch reactor setup. In two cases, a proprietary catalytic surface is introduced, which is demonstrated to increase the rate and extent of PFAS destruction. Forty PFAS analytes are measured before and after HALT treatment to quantify destruction efficacy and to demonstrate that all PFAS are degraded during processing. Ion chromatography is used to quantify fluoride yield at one condition, where 120.5% theoretical defluorination efficiency is measured. This indicates that HALT is effective at degrading detected and undetected PFAS, through cleavage of the strong carbon-fluorine bonds. Overall, HALT appears to be a technically viable option for safe disposal of legacy AFFF stockpiles.

Kinetic models for inactivation of microorganisms by chemical disinfectants have described the instantaneous rate of kill as a function of the instantaneous residual. Laboratory batch experiments were conducted exposing cysts of Giardia muris to low doses of dissolved ozone in water from Lake Audubon, ND, and Vancouver, BC. Viability was assessed by excystation. Substantial inactivation was found to continue following disappearance of ozone residual, indicating that the fundamental postulate of modeling chemical disinfection may not be universally applicable. The mechanism for this effect, the extent of applicability, and the alternative modeling frameworks needs further study. However, this finding, if generalizable, has significance particularly in treatment of wastewater for reuse, and may provide a pathway for achieving greater log removals while keeping disinfectant byproducts low.