Journal of Environmental Engineering

A comprehensive study using a novel aluminum oxide microfiltration (MF) membrane and a thorough analysis of the effects of various operating conditions on the treatment of produced water were carried out. To set up the experiments and optimize the process parameters, an L9 orthogonal array of the Taguchi method and the larger-the-better target group analysis method was used. The impacts on filtrate flux and fouling control of operating conditions such as pH, temperature, crossflow velocity (CFV), and transmembrane pressure (TMP) were examined. Optimum operating conditions were determined to be 50°C, 1.8 bar, $1.8\mathrm{m}/\mathrm{s}$, and a pH of 5 and allowing for a maximum flux of $975\mathrm{L}/\mathrm{h}·{\mathrm{m}}^2$. The microfiltration (MF) membrane showed an oil-rejection rate of 98.25%, and the CFV was considered to be the most significant operating variable contributing to the regulation of the flux. Furthermore, 97% recovery was achieved with a mixture of cleaning solutions combining NaOH and ${\mathrm{HNO}}_3$. Two flux decline models were used to interpret the data including the Hermia and an artificial neural network (ANN). Hermia’s cake-forming process had the average highest correlation with permeate flux decline data for the nine experiments ($\mathrm{R}2=0.83$). Using ANN simulation, the best results were obtained with two hidden layers and 25 neurons in each layer. Its performance in terms of the mean squared error as a percentage of the maximum flux was 0.4%.

Conventional activated sludge processes, as the main biological treatment approach for municipal wastewater treatment in centralized wastewater treatment plants (WWTP), generate a large amount of waste-activated sludge (WAS) that needs to be managed before disposal. However, the degradation of WAS is usually limited by the slow hydrolysis rate and low biodegradable rate. Here, an effective pretreatment strategy using calcium hypochlorite treating waste-activated sludge before aerobic digestion was explored. Performance results showed that after the pretreatment with $0.1\mathrm{g}{\mathrm{Ca}(\mathrm{ClO})}_2$ per gram of total solids (TS), volatile solids (VS) in WAS were reduced by $65.05\%\pm 2.68\%$ after 20 days of aerobic digestion, nearly twice the reduction of VS in un-pretreated WAS. The best treatment conditions under tested experiment conditions were 12 h of WAS pretreatment process with $0.1\mathrm{g}{\mathrm{Ca}(\mathrm{ClO})}_2\mathrm{per}1\mathrm{g}$ TS and 12 days hydraulic retention time (HRT) of aerobic digestion. Kinetic model analysis revealed that the VS reduction of WAS during aerobic digestion was enhanced by the ${\mathrm{Ca}(\mathrm{ClO})}_2$ pretreatment, likely through cell lysis and extracellular polymeric substances (EPS) decomposition. Moreover, microbial community analysis revealed that the relative abundance of certain bacteria (e.g., Xanthomonadaceae, Saprospirales, and Cytophagaceae) increased, which can be attributed to the change of the chemical and biological environment in the aerobic digesters after pretreatment. This study demonstrated the feasibility of applying calcium hypochlorite pretreatment in WAS aerobic digestion to improve sludge digestibility and volume reduction.

Aerobic digestion of waste activated sludge is a common practice at water reclamation facilities. Dewatering of digester effluent produces a liquid stream, commonly referred to as a sidestream, that is rich in nitrogen and phosphorus. Removal of nitrogen from the sidestream improves mainstream treatment, but usually requires input of energy and/or chemicals. The purpose of this study was to evaluate the microbial fuel cell (MFC) as a candidate technology to remove nitrogen from the sidestream of aerobic digestion while simultaneously producing electricity, without requiring input of energy or chemicals. Toward this goal, a bench-scale MFC was constructed and operated for a period of 125 days to remove nitrogen (nitrate) from an aerobic digester sidestream from a treatment facility in Hillsborough County, Florida. The average removal rate of nitrogen was $14\mathrm{mg}/(\mathrm{L}·\mathrm{day})$, the average power production was ${0.38\mathrm{mW}/\mathrm{m}}^2$ of electrode surface area, and the apparent efficiency of electron transfer from anode to cathode was 41%. The nitrogen removal rate and apparent electron transfer efficiency are similar to those observed in previous MFC studies treating other nitrate-containing streams via cathodic denitrification. The low power generation may be due partly to the two-chamber configuration of the MFC employed, which was appropriate for the goals of this study but is not the most advanced MFC configuration. Therefore, we conclude that the MFC remains a promising candidate for nitrate removal from aerobic digester sidestreams, but that MFC configurations more advanced than the one employed here will be required for the technology to be viable at a larger scale.

The bacterial, archaeal, and fungal taxonomies of a semi-batch-fed, lab-scale cellulolytic enrichment reactor inoculated by the organic fraction of municipal solid waste were explored using 16SrRNA and internal transcribed spacer (ITS) sequencing. Biomass samples were partitioned into total, planktonic, and sessile (biofilm) fractions using a centrifugation separation technique developed to quantify sessile biomass growth on cellulose particles during anaerobic digestion. The relative abundances of bacteria and archaea taxa were determined over a 1-day period. The sessile and planktonic biomass fractions showed significantly different relative abundances for 13 taxa, with the sessile biomass having 10 times lower relative abundance of Unclassified Firmicutes, nearly 20 times higher relative abundance of Methanothrix spp., double the relative abundance of Hydrogenispora spp., and 44.3% higher relative abundance of an uncultured Leptospira sp. than the planktonic biomass. This study shows how a relatively simple physical separation method can be employed to add another dimension to taxonomic studies. Better understanding the microbial communities in these systems is a key first step toward achieving performance improvements such as enhanced cellulose solubilization rates and other microbial biotransformations through process, genetic, and/or other manipulations.

The influence of soil organic matter and pore water velocity on the transport of naphthalene in flow-through columns was investigated. Pulse injection experiments were conducted using three different soils (with 0%, 1.9%, and 3.9% organic content by weight) and flow rates (0.05, 0.1, and $0.2\mathrm{mL}/\min$) and solvent extractions were performed to measure the nondesorbable naphthalene fraction. To describe interactions between contaminants in the aqueous and solid phases, observed breakthrough data were described using two-site models, four different formulations of a three-site model, and two fully kinetic models. While the two-site models did not adequately describe the breakthrough data for all cases, simulations based on the three-site models matched the observations well with the exception of high organic content soils and high flow rates. For soils with high organic content, the fully kinetic models described the observed data better compared to the three-site models. Results indicate that as long as the equilibrium, rate-limited, and irreversible sorption domains are included in the models, different conceptualizations about how contaminants interact in the aqueous and solid phases do not produce significantly different results.

Water stress is increasingly affecting hundreds of millions of people around the world. In East Africa, severe and persistent drought periods negatively impact health and livelihoods. Drought increases reliance on mechanized boreholes to extract groundwater. However, without adequate resource allocations, effective monitoring of borehole functionality, and reliable maintenance service, breakdown rates increase and downtimes last many months. Our study applies system dynamics modeling to investigate the effects of allocating resources to borehole maintenance and repair in the Afar Region in Ethiopia and Turkana County in Kenya. We inform model calibration with runtime and functionality estimates derived from sensors installed on 245 boreholes and apply sensitivity analyses varying budget allocations to optimize for functionality. We conclude that increasing the borehole repair and maintenance budgets in Turkana from the current 30% to 85% of available budgets could result in an additional 83 working boreholes and 95% functionality in 2030. In Afar, increasing maintenance budgets from 38% to 79% could result in functionality levels of 75% by 2030, well above currently projected levels of 54%.

There are mixed opinions on whether municipal wastewater treatment plants (MWTP) act as a significant hub for the selective growth and proliferation of antibiotic-resistant bacteria. In this study, investigations were carried out on the occurrence and fate of fluoroquinolone (FQ) antibiotics and antibiotic-resistant bacteria at different units within an activated sludge-based MWTP in India. The results indicated that the raw wastewater at the inlet of the MWTP had concentrations of ciprofloxacin, norfloxacin, and ofloxacin in the range of $6–17\mu \mathrm{g}/\mathrm{L}$, which was significantly higher than the concentrations of these antibiotics reported in wastewater treatment plants in developed countries. The biological treatment unit of the MWTP removed 60%–90% of influent antibiotics. The fractional concentration of FQ-resistant bacteria in the total bacterial population rose from an average value of 0.22 at the inlet to a value of 17 within the unit—an increase of two orders of magnitude. In addition, studies involving 16 other commonly used antibiotics revealed that the average multi-antibiotic resistance (MAR) index value increased in the wastewater treatment plant. The MAR index distribution data also indicated that the treatment plant might contribute to bacteria gaining resistance to more antibiotics classes. Further, 16S rRNA gene sequencing revealed that the antibiotic-resistant bacteria within the MWTP belonged to the family Enterobacteriaceae, of which Escherichia, Salmonella, and Shigella were dominant species. The antibiotic-resistant bacteria even evaded a disinfection step that used chlorination, and showed up in the final discharge from the MWTP into the River Ganges.

Some microorganisms with the nitrification function can carry out nitrogen conversion under oxygen-limited conditions. In this study, a continuous-flow biofilm reactor was operated to investigate the removal of ammonium nitrogen (${\mathrm{NH}}_4\text{-}\mathrm{N}$) under microaerobic or anoxic conditions. After more than 100 days of long-term operation, the ${\mathrm{NH}}_4\text{-}\mathrm{N}$ removal rate and removal percentage reached 2.92 $\mathrm{mg}/(\mathrm{L}·\mathrm{h})$ and 72.3%, respectively. In the batch experiments, ${\mathrm{NH}}_4\text{-}\mathrm{N}$ removal was achieved regardless of the presence or absence of nitrite. The main microorganisms relating to nitrogen metabolism in the system were Nitrospira, Nitrosomonas, Candidatus Kuenenia, and denitrifying bacteria. The metagenomics analysis indicated that these functional microorganisms constituted the main nitrogen metabolic network in the system, and microorganisms such as Rhodanobacter, Nitrosomonas, Defluvii, and Cyanobacteria had the possible capacity for oxygen production. Without organic carbon in the synthetic wastewater, heterotrophs including denitrifying bacteria might utilize organic carbon such as extracellular polymeric substances produced by autotrophs. The removal of ${\mathrm{NH}}_4\text{-}\mathrm{N}$ under oxygen-limited conditions might be achieved through interactions among nitrifying bacteria, anammox bacteria, and heterotrophs, which deserves further investigation.

In recent years, biochar-amended soil cover has shown promise for enhancing microbial methane (${\mathrm{CH}}_4$) oxidation and mitigate fugitive ${\mathrm{CH}}_4$ emissions at municipal solid waste landfills. However, addition of biochar in landfill cover soil has an initial lag phase due to microbial acclimation and colonization, resulting in lower ${\mathrm{CH}}_4$ oxidation rates relative to ${\mathrm{CH}}_4\text{-}\mathrm{exposed}$ landfill cover soil. Therefore, this study explored amendment of landfill cover soil with biochar infused with methane-oxidizing bacterial (MOB) consortium (termed activated biochar) to reduce acclimation time and enhance the ${\mathrm{CH}}_4$ oxidation activity. Experimental long-term incubation tests were performed on soil columns containing one of four different biocovers: soil control (CS), soil with 10% by weight of biochar (B10), soil with 5% MOB-activated biochar (AB5), and soil with 10% MOB-activated biochar (AB10), exposed to continuous flow of simulated landfill gas (LFG). The AB10 soil column had a reduced lag phase with notable ${\mathrm{CH}}_4$ oxidation efficiency (ranging from 13% to 50%) during the initial exposure phase compared with all other biocover columns (0.4%–36%). In addition, the activated biochar–amended soil biocovers had higher ${\mathrm{CH}}_4$ oxidation rates ($69–74.3\mathrm{\mu g}{\mathrm{CH}}_4{\mathrm{g}}^{-1}{\mathrm{day}}^{-1}$) than the nonactivated biochar–amended soil ($42\mathrm{\mu g}{\mathrm{CH}}_4{\mathrm{g}}^{-1}{\mathrm{day}}^{-1}$) and soil control ($36\mathrm{\mu g}{\mathrm{CH}}_4{\mathrm{g}}^{-1}{\mathrm{day}}^{-1}$). The activated biochar–amended columns had higher relative abundances of Type II methanotrophs, mainly Methylocystis and Methylosinus (relative abundance $\sim 10\%$) than did nonactivated biochar–amended soil and control columns (relative abundance 3.0%–3.6%). A positive correlation was observed between ${\mathrm{CH}}_4$ oxidation rate and the ratio of Type II/Type I abundance ($R^2=0.84$, $p<0.01$), further suggesting an important role for the biochar activation in the biological ${\mathrm{CH}}_4$ mitigation process. Overall, biochar activation appears to be a promising mechanism to reduce microbial lag phase and enhance ${\mathrm{CH}}_4$ oxidation rates in biochar-amended landfill cover soils.

Cu–Al layered double hydroxides (Cu–Al LDHs) were prepared by coprecipitation and used as a catalyst in heterogeneous a catalytic ozonation of ciprofloxacin. The structure of the synthesized Cu–Al LDHs was investigated by X-ray diffraction (XRD) patterns and Fourier-transform infrared spectra. Experimental results showed that the ${\mathrm{Cu}}_3–\mathrm{Al}$ LDHs had the best crystallization structure and the highest catalytic efficiency for ozonation. Response surface methodology (RSM) was used to optimize the operation conditions of ozone dose, ozone dosage, and initial pH. Under the optimal conditions ($\mathrm{pH}=9$, LDH dosage $0.79\mathrm{g}/\mathrm{L}$, ozone dosage $61.2\mathrm{mg}/\min$), the total organic carbon (TOC) removal of ciprofloxacin by catalytic ozonation method can be as high as 72%. In addition, the TOC removal of ozone alone was about 30%, and the adsorption process contributed about 10%. Hydroxyl radicals, superoxide radicals, and singlet oxygen were proved to be involved in this process through electron paramagnetic resonance tests. Several degradation products were determined with LC-MS, suggesting that the pathway for ciprofloxacin degradation might include a substitution reaction, decarboxylation reaction, ring-opening reaction, and oxidation reaction.

Natural resource agencies need effective strategies to control the spread of aquatic invasive species (AIS) such as invasive fish, which can expand their range using rivers as hydrological pathways to access new areas. Lock and dam structures within major rivers are prospective locations to deploy techniques, such as carbon dioxide (${\mathrm{CO}}_2$) infusion into lock water, that could impede upstream AIS migration without disrupting vessel passage and lock operation. The current pesticide label for ${\mathrm{CO}}_2$ in the United States allows injections of $100–150\mathrm{mg}/\mathrm{L}{\mathrm{CO}}_2$ as a behavioral deterrent treatment for invasive carps. This research describes the first operationalizing and testing of a ${\mathrm{CO}}_2$ injection and manifold distribution system at a 1,548,000-L navigation lock chamber on the Fox River near Kaukauna, Wisconsin, USA. Two chemical distribution manifolds located on the floor and wall of the chamber were independently tested to quantify mixing time, mixing homogeneity, injection efficiency, and operational power requirements under a range of operating parameters. Both manifold configurations were able to meet most performance benchmarks established during previous fish behavior studies. Certain limitations were exhibited and quantified for both manifold configurations in terms of mixing homogeneity and operational power. This research details the design and performance of ${\mathrm{CO}}_2\text{-}\mathrm{to}\text{-}\text{water}$ infusion systems that could be used to deter the spread of AIS at navigation pinch-points. These results may inform future ${\mathrm{CO}}_2$ system designs and operating conditions to support natural resource management plans to limit the spread of AIS.

Since the 1980s, the occurrence of harmful algae blooms (HABs) in the Persian/Arabian Gulf has increased concurrently with the rapid expansion of Gulf seawater desalination. Moreover, Gulf HABs have been observed simultaneously with established HABs in the adjacent outer ocean basin. The freshwater sink generated by seawater desalination is balanced by a stronger near-surface influx of the Gulf exchange flow, which carries salt into the Gulf and may also carry HABs that travel passively. Here, the hypothesis that seawater desalination has strengthened Gulf exchange influx, probably leading to accelerated horizontal advection of established HABs in the outer ocean basin into the Gulf and enhanced HAB dispersal within the Gulf, is examined. Two scenarios with differing magnitudes of freshwater loss from seawater desalination and one scenario devoid of freshwater loss are simulated in a coupled Gulf-Atmosphere Model and compared. The results show that, because of this freshwater loss, mean March–June exchange influx (outflux) strengthened by 3.93% (5.38%) and mean July–February exchange influx (outflux) weakened by $-10.16\%$ ($-9.08\%$); flushing time decreased by $\approx 21\mathrm{days}$, and peak exchange influx occurred sooner by $\approx 1\mathrm{month}$. These results support the above-stated hypothesis and suggest a linkage between Gulf seawater desalination and the recent shift in the seasonal regime of Gulf HABs. This causal mechanism for the increase in Gulf HABs highlights the need for a basin-scale management strategy to monitor and forecast the Gulf’s state under the stresses of seawater desalination and provide early warning signs of environmental problems. Such a strategy is already in place in several marginal seas with anthropogenic activities. The findings here provide design elements for developing this strategy in the Gulf.