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The biodegradation rates of carbon nanotube (CNT)/ polymer nanocomposites (PNCs) containing poly-ε-caprolactone (PCL) were investigated using Pseudomonas aeruginosa, a microorganism commonly found in the environment. CNT/PCL nanocomposite mass loss profiles revealed that the rate of PCL matrix biodegradation decreased systematically as the CNT loading increased from 0.1 to 10% w/w. Addition of even a low CNT loading (<1% w/w) caused the CNT/PCL biodegradation rate constant to decrease by more than 50%. Similar trends in biodegradation rate were observed for both pristine and oxidized multiwall CNTs embedded in PCL. During PCL matrix biodegradation, CNT accumulation was observed at the surface of CNT/PCL nanocomposites and single particle inductively coupled-mass spectrometry experiments revealed no measurable CNT release to the culture fluid. Experimental data indicated that biodegradation proceeded as a result of biofilm formation on the CNT/PCL nanocomposites and decreased as a function of CNT loading due to the cytotoxicity of CNTs toward P. aeruginosaand the physical barrier presented by the surface-accumulated CNTs to the underlying PCL substrate. As the CNT loading in the CNT/PCL nanocomposites increased, the microbial proliferation of planktonic cells in the surrounding media also decreased as did the biodegradation rate of PCL samples present in the same reactors. Results from this study demonstrate that the inclusion of CNTs into polymer matrices could increase the environmental persistence of polymers in lakes, landfills, and surface waters.

The use of nontherapeutic broad-spectrum antimicrobial agents triclosan (TCS) and benzalkonium chloride (BC) can contribute to bacterial resistance to clinically relevant antibiotics. Antimicrobial-resistant bacteria within wastewater may reflect the resistance burden within the human microbiome, as antibiotics and pathogens in wastewater can track with clinically relevant parameters during perturbations to the community. In this study, we monitored culturable and resistant wastewater bacteria and cross-resistance to clinically relevant antibiotics to gauge the impact of each antimicrobial and identify factors influencing cross-resistance profiles. Bacteria resistant to TCS and BC were isolated from wastewater influent over 21 months, and cross-resistance, taxonomy, and monthly changes were characterized under both antimicrobial selection regimes. Cross-resistance profiles from each antimicrobial differed within and between taxa. BC-isolated bacteria had a significantly higher prevalence of resistance to “last-resort antibiotic” colistin, while isolates resistant to TCS exhibited higher rates of multidrug resistance. Prevalence of culturable TCS-resistant bacteria decreased over time following Food and Drug Administration (FDA) TCS bans. Cross-resistance patterns varied according to sampling date, including among the most clinically important antibiotics. Correlations between strain-specific resistance profiles were largely influenced by taxonomy, with some variations associated with sampling date. The results reveal that time, taxonomy, and selection by TCS and BC impact features of cross-resistance patterns among diverse wastewater microorganisms, which could reflect the variety of factors influencing resistance patterns relevant to a community microbiome.

Low permeability regions in which solute movement is governed by diffusion reduce the availability of pollutants for remediation and can function as long‐term sources of groundwater contamination. The inherent difficulty in understanding mass transfer from these regions of sequestered contamination is further complicated by unknown solute distributions within the low‐permeability regions (sequestering regions). When models are calibrated to reproduce temporal histories of solute release from a sequestering region (desorption), the fitted parameter values are used to infer the physical or chemical characteristics of the media; however, the calibrated parameters also reflect the case‐specific initial conditions (i.e., the solute distribution within the sequestering region domain at the onset of desorption). This phenomenon is demonstrated using model simulations of solute diffusion from hypothetical solids with characteristics similar to those of the well studied Borden, Ontario aquifer system. Solute release from the solids is simulated using a batch diffusion model under different initial solute distributions within the solids. The results of these model simulations are used to calibrate parameters of a multiple first‐order rate desorption model (MRM) to illustrate how the fitted MRM parameters increase or decrease depending on the initial “aging” of the solids. Further numerical simulations are conducted for a one‐dimensional flow system under steady‐state and variable‐rate hydraulic flushing. These simulations show that although aging reduces desorptive mass flux during early stages of flushing, aged sites have greater desorptive mass flux (greater solute availability) than “freshly” contaminated media during the later stages of remediation. Overall, the results demonstrate why the physicochemical meaning of observed desorption rates cannot be accurately deduced without first understanding the initial solute distribution within the media.

Reduction of disinfection by‐product (DBP) precursors upon riverbank filtration (RBF) at three drinking water utilities in the midwestern United States was compared with reductions obtained using a bench‐scale conventional treatment train on the corresponding river waters. The river waters were subjected to a treatment train consisting of coagulation, flocculation, sedimentation, filtration, and ozonation. RBF performed as well as or better than the bench‐scale conventional treatment with respect to DBP precursor removal. Total and dissolved organic carbon concentrations were reduced by 20 to 50% after bench‐scale treatment, compared with reductions between 30 and 70% after subsurface travel to the closer wells at the three sites. Reductions in precursor material for a variety of DBPs (trihalomethanes, haloacetic acids, haloacetonitriles, haloketones, chloral hydrate, and chloropicrin) after bench‐scale treatment were generally in the range of 40 to 80%, whereas reductions after RBF ranged from 50 to 100%. After RBF and bench‐scale treatment, a shift was observed from the chlorinated to the more‐brominated DBP species, with the shift more pronounced for the bank‐filtered waters. This shift was likely attributable to the increase in the ratio of bromide to dissolved organic carbon.

At three drinking water utilities in the midwestern United States, significant reductions were observed in total organic carbon (TOC), dissolved organic carbon (DOC), and disinfection byproduct precursors after riverbank filtration (RBF). TOC and DOC reductions at the closer wells at the three sites ranged from 35 to 67%. Trihalomethane formation potential and haloacetic acid formation potential concentrations were reduced by 50 to 80% at the three sites. Reductions in precursors for haloacetonitriles, haloketones, chloral hydrate, and chloropicrin ranged from 30 to 100% following RBF. Reductions in the concentrations of Clostridiumwere observed in excess of 3 logs. Log reductions in the rivers and wells ranged from >2.6 to >3.3 for E. coliC bacteriophage and from >1.9 to >2.3 for E. coliF‐amp bacteriophage. Limited occurrence of Giardiaand Cryptosporidiumin the river and well waters prevented the establishment of firm conclusions for the removal of these organisms.

A strip‐pit pond formed as a result of past coal mining activities in northeastern Ohio is contaminated with alkylbenzenes and chlorobenzene from tanktruck washing operations. Batch aerobic studies are performed on samples from a strip‐pit pond containing about 100 μg/L each of chlorobenzene, toluene, ethylbenzene, xylenes, styrene, and aniline in order to determine the potential for their biotransformation under field conditions. Microorganisms capable of biotransforming the aromatic compounds are present in the strip‐pit pond water. However, under natural conditions, the biotransformation rate is slow as incomplete removal is observed over a 43‐day incubation period. Volatilization rates exceed the natural rates of biotransformation. Addition of acetate, nitrogen, and phosphorus markedly increase the rate of biotransformation of the aromatic compounds. Enhanced biotransformation rates are more than an order of magnitude faster than volatilization rates. Chlorobenzene is mineralized to carbon dioxide. The presence of 0.61 g/L sediment does not significantly affect biotransformation of the aromatic compounds at a 95&percent; level of confidence. The prospect for successfully stimulating and exploiting biotransformation of the contaminants in a bioreclamation scheme appears very good.

A relatively recent development in drinking-water technology is the use of biological treatment to produce a biologically stable water. Biological stability is achieved by removing biodegradable substances — mainly naturally occurring organic polymers, specific organic micropollutants, and ammonium-through the action of selected bacteria. The technology involves immobilization and accumulation of the desired bacteria through natural attachment to solid particles as biofilms. The critical review describes the constituents making up biological instability and how their presence adversely affects drinking-water treatment and the quality of the water supplied to the consumer. Particularly important is a critical analysis of methods to measure the low concentrations of biodegradable organic matter (i.e., less than 1 mg/1). The fundamentals and practice of biological drinking-water treatment are thoroughly explored. Finally, the future of biological processes in drinking-water treatment is examined in light of new trends in process technology and regulation of drinking-water quality.

Biomass accumulation in laboratory‐scale filters is not impaired by backwash with water alone. Experiments tracked the deposition of two model bacteria—Pseudomonas aeruginosaand Klebsiella pneumoniae—onto clean filter media (i.e., glass beads and filter sand) and the subsequent removal of the bacteria by backwashing. The ability of bacteria to accumulate and be retained in a frequently backwashed filter is critical for effective removal of biodegradable organic matter in a process termed biofiltration. Column filtration experiments showed that the bacteria, especially P. aeruginosa, readily attached to the filter media during filtration, despite unfavorable chemical conditions. Water backwash was not effective at removing bacteria from the filter media, with only 20–40 percent removal during 10‐min backwash cycles at hydraulic loading rates ranging from 23 to 53 m/h (9.3 to 22 gpm/sq ft) and bed expansions ranging from 15 to 50 percent. Incomplete removal of biomass during backwashing was beneficial for removal of biodegradable total organic carbon, typically allowing a backwashed biofilter to maintain treatment at levels similar to the period immediately preceding the backwash.

Batch experiments proved to be effective for obtaining a preliminary estimate of the biodegradation potential of NOM. Batch degradation experiments were conducted to evaluate the extent of biodegradation of natural organic matter (NOM) as a function of ozone dosage. Four NOM sources that might be encountered in drinking water treatment were characterized and tested. The biodegradability of all sources was enhanced as the ozone dose was increased from 0 to 7.3 mg ozone/mg total organic carbon (TOC). Increased ozonation resulted in cnsistently improved TOC removals for NOM souces having a large fraction of high‐molecular‐weight organics. Greater biodegradation was observed for the unozonated sources with lower UV‐absorpotion ‐to‐TOC rations and larger fraction of low‐molecular‐weight organics.

Optimizing the coagulant dosage offers the most effective means of maximizing TOC removal; biofiltration may be used to augment removals. Laboratory‐scale biologically active sand filters were used to evaluate the effect of natural organic matter (NOM) source and empty bed contact time (EBCT) on the removal of total organic carbon (TOC) from coagulated and ozonated NOM solutions. Ozonation at dosages in the range of 2.0 to 4.0 mg ozone/mg TOC were used to enhance biodegradation of the organic matter. TOC removal in the biofilters ranged from 16 to 33 percent of the biofilter influent concentration. TOC removal was significantly affected by the source of the organic carbon but was independent of EBCT in the range of 4 to 20 min. In the context of an entire water treatment plan, including coagulation and biofiltration, the contribution of biofiltration to TOC removal was relatively small compared with total removals across the entire treatment train. In one biofiltration experiment, however, removal of the biodegradable fraction of TOC was 100 percent, suggesting that biofilters may be effective in reducing subsequent regrowth in distribution systems.

Biological processes have the potential to remove pollutants that may be ineffectively removed by conventional treatment, such as biodegradable organics, synthetic organic compounds, ammonia, nitrate, iron, and manganese. Biooxidation of organic matter and ammonia decreases available substrates for microbial regrowth in distribution systems, reduces tastes and odors, and decreases the amount of precursor available to form disinfection by‐products. Biological removal of certain contaminants could extend the service time or capacity of subsequent physicochemical processes. In US water treatment, the practice is often to impair or preclude development of biological activity by prechlorination, rigorous scouring of filter media, and frequent backwashing of granular activated carbon. Practical experience in Europe with media containing microbial activity has been favorable.