Journal of Environmental Engineering

Forum papers are thought-provoking opinion pieces or essays founded in fact, sometimes containing speculation, on a civil engineering topic of general interest and relevance to the readership of the journal. The views expressed in this Forum article do not necessarily reflect the views of ASCE or the Editorial Board of the journal.

As biofuels and blended biofuels are being globally used and expected to increase in the near future, their fate and transport in the soil-water system is an area of major concern. The biological origin and differences in physical-chemical characteristics of biodiesels from petro-diesels may alter its fate and transport behaviors in the subsurface. Introduction of biodiesel liquids into a partially saturated zone can modify the air-water system as a multiphase (i.e., biodiesel-air-water) system which controls its distribution in the subsurface. Competitive adsorption and high volatilization of lighter compounds from blended biodiesels can also alter the movement of the free phase. Similarly, the rapid-dissolving nature of biodiesels in pore water provides sufficient carbon sources to subsurface microbial communities which significantly enhance microbial cometabolisms and therefore biodegradation rate under an aerobic condition. This manuscript presents the review updates and current understanding of fate, transport, and bioremediation of biodiesel and blended biodiesel in the subsurface. The insights discussed in this manuscript may help groundwater scientists, environmentalists, and geochemists in predicting the behavior of biodiesel and blended biodiesel contaminants in a different landscape and in assessing risks of contaminations.

To confirm the higher-availability and lower-resistance superiority of a proposed seawater/seawater cascade-scrubbing solution meeting the emission control area (ECA) requirements under harsh high-sulfur and low-alkalinity conditions, desulfurization experiments for the exhaust gas of a 162-kW marine diesel engine were compared between the cascade-scrubbing model and currently used once-through, open-loop solution. With the once-through seawater to scrub ${\mathrm{SO}}_2$ levels of $\mathrm{1,000}–\mathrm{2,860}\mathrm{mg}/{\mathrm{Nm}}^3$ (equal to about 1.8%–5% fuel-sulfur content), the desulfurization efficiency of the once-through system increased with the liquid-gas ratio and seawater alkalinity and decreased with ${\mathrm{SO}}_2$ concentration. At the harsh ${\mathrm{SO}}_2$ concentration of $\mathrm{2,860}\mathrm{mg}/{\mathrm{Nm}}^3$ where the once-through scrubbing thoroughly failed to meet the ECA’s requirements, an additional liquid-gas ratio increase above $8\mathrm{L}/{\mathrm{Nm}}^3$ was confirmed to be infeasible because of the potential for liquid flooding. In contrast, with a total liquid-gas ratio $\ge 9\mathrm{L}/{\mathrm{Nm}}^3$ (typically liquid-gas ratios of 7 and $2\mathrm{L}/{\mathrm{Nm}}^3$ in the main and auxiliary scrubbing sections, respectively), the cascade-scrubbing model easily met the ECA’s desulfurization requirements under harsh high-sulfur and low-alkalinity conditions, along with its lower packing pressure-drop levels allowing for a further liquid-gas ratio increase. Aside from the above superiority compared with the once-through open-loop solution, the achievement of high-efficiency seawater desulfurization in this work suggests that the proposed seawater/seawater cascade-scrubbing solution should be more economical in comparison to the current closed-loop solution and hybrid system, which both necessitate costly NaOH usage.

Phycoremediation encompasses microalgae as a sustainable treatment system by integrating the wastewater treatment with bioenergy recovery. However, transforming this technology to real time from lab scale is limited due to temperature and cell volume (inoculum size). Thus, the present study aims to investigate the influence of inoculum size (10%–30% v/v) and temperature condition (25°C–35°C) for the growth of five microalgal species in paddy-soaked wastewater (PSWW), using response surface methodology (RSM). The optimal conditions for better biomass production and wastewater treatment were found to be at 25°C and 30% inoculum size. Among five selected microalgae, Chlorella pyrenoidosa exhibited maximum dry biomass content ($831\mathrm{mg}/\mathrm{L}$) with greater ($>90\%$) removal on ammonical nitrogen (${\mathrm{NH}}_3\text{-}\mathrm{N}$) and phosphates (${\mathrm{PO}}_4\text{-}\mathrm{P}$) at a rate of 0.025 and $0.006\mathrm{mg}\mathrm{P}/\mathrm{mg}$ of dry biomass, respectively, with significant $p$ value ($p<0.05$). Similar results were obtained for Chlorella vulgaris and Scenedesmus obliquus (an indigenous sp.) with more than 80% removal efficiency. However, at higher temperatures, Chlorella pyrenoidosa exhibited better results when other strains failed to maintain biomass production and removal on ${\mathrm{NH}}_3\text{-}\mathrm{N}$ and ${\mathrm{PO}}_4\text{-}\mathrm{P}$. This study demonstrated that phycoremediation is a viable option upon selecting appropriate strains and conditions imminent for scale-up applications.

Economic development and the related increase in global energy demands have created pressure on the supply of energy resources. To promote sustainable development, a safe and renewable energy is required. For this, wastewater contributes significantly in creating a safe environment and renewable energy. Currently, in developing countries, with the scarcities of energy, an attractive wastewater treatment technology like membrane bioreactors (MBR), which produces high-quality recyclable treated water and energy, has been proposed. However, fouling of the membrane is the main drawback of the MBR process, as it leads to a decline in the permeate flux or increase in the transmembrane pressure (TMP) with processing time, resulting in higher operating costs for membrane cleaning and eventually decreases the lifespan of membranes. This situation invites researchers to develop integrated MBR technology intended for wastewater treatment alternatives under several scenarios. A related review shows that integration of a microfuel cell (MFC) with MBR as post-treatment in wastewater treatment technologies makes it possible to accomplish good quality and extract abundant energy obtained in wastewater and future trends like MFC-MBR. An MFC-MBR (microbial fuel cell–membrane bioreactor) integrated system makes it possible to achieve better effluent and harvest the energy contained in wastewater simultaneously with different factors like reactor integration, electricity generation, and membrane fouling, and it also highlights the probable challenge and future development of MFC-MBR integrated systems in the large scale.

To treat heavy-loaded wastewater from small-scale livestock farms, a combined constructed wetland system was designed, which includes series of hybrid constructed wetlands made up of surface flow (SF) and subsurface flow (SSF) compartments, as well as two anaerobic units, also in series, as its pretreatment. The combination of multitype and multistage treatment units and the division of the wetland area into compartments in a horizontal baffled layout prolongs the hydraulic retention time (HRT), reduces clogging and short-circulating, and keeps specific operation conditions for each unit, including loading input, bacteria, padding material, and vegetation. The system demonstrates various benefits, such as efficiency, simplicity, flexibility, low cost, and easy management, which were demonstrated by a pilot system for the treatment of wastewater from a small-scale pig farm. The first running result showed excellent removal efficiency and removal rate for organic materials in terms of chemical oxygen demand (${\mathrm{COD}}_{cr}$) and biological oxygen demand (${\mathrm{BOD}}_5$), nutrients in terms of total nitrogen (TN), ammonia nitrogen (${\mathrm{NH}}_3\text{-}\mathrm{N}$), and total phosphorus (TP), and heavy metals in terms of Cu and Zn. The effluent met relative standards for all aforementioned indicators except for TP. Heavy input load and limited plant uptake could be the main reasons for the failing to meet the standard for TP. Solutions to this issue include adding one or more SF compartments before and after the SSF units, using special padding material economical in cost and with strong sorption capacity, and replacing the padding material regularly.

The aim of this study was to ascertain the biocidal efficacy, based on the so-called C·t values, and the usage expenses of seven disinfection products in recreational waters using Escherichia coli and Pseudomonas aeruginosa as microorganism models of fecal and environmental contamination, respectively. A 250-L indoor fully equipped pool basin was harnessed as a proof-of-concept setup for the evaluation of chlorine-based [viz., trichloroisocyanuric acid (trichloro), sodium hypochlorite, sodium hypochlorite + isocyanuric acid, and saline electrolysis] and unconventional (viz., 1-bromo-3-chloro-5,5-dimethylilhidantoine, chlorine dioxide and hydrogen peroxide) biocides at 30°C and different pH values. The economic losses resulting from human action, mimicked by urea addition, were also considered. Experimental results showed that trichloro, chlorine dioxide, and sodium hypochlorite were the most effective disinfection agents with a log 3 removal of both organisms in 60 s regardless of the water pH. On the other hand, sodium hypochlorite and trichloro afforded unparalleled cost-effectiveness. Chlorine dioxide exhibits the greatest biocide efficacy, yet its elevated usage costs make it merely applicable in shock treatments to offset high organic loads.

The objective of this study was to evaluate the use of natural minerals to enhance the precipitation of phosphorus and cyanobacteria during alum coagulation, and to reduce phosphate release during sediment capping in eutrophic lakes. Laboratory coagulation experiments were conducted on lake water spiked with Anabaena sp. using alum and four natural minerals (zeolite, calcite, limestone, and sand) to determine the effect of natural minerals on chlorophyll a, phosphate, and turbidity removal. Long-term column sediment-capping experiments were also conducted using different minerals after alum coagulation to evaluate their effectiveness in reducing phosphate release. The results showed that alum coagulation effectively removed phosphate and chlorophyll a from lake water samples. The added natural particles did not substantially affect coagulation performance during combined alum and particle treatment. However, natural particles increased the floc settling kinetics during coagulation. The combined treatment with alum and particles also increased the resistance of the sediment to disturbance by mixing. The long-term sediment-capping experiments showed that capping with natural minerals reduced the levels of phosphate released from the sediment.

Increasing global warming concerns are compelling humanity to find alternative fuels to fossil fuels. Ammonia, with its carbon-free structure, can be combusted to produce only water and nitrogen. This study includes exergy analysis–based thermoecologic analysis and life cycle assessment–based environmental pollution cost analysis of a Turbec T100 microturbine. A Turbec T100 microturbine is normally operated with natural gas combustion and is modeled using commercially available software for (1) natural gas; (2) 10% ammonia and 90% natural gas; and (3) 20% ammonia and 80% natural gas mass fractions. The ecologic objective function and ecological coefficient of performance parameters for natural gas combustion are $-174.441$ and 0.37336, respectively. The 20% ammonia combustion has the best ecologic objective function and ecological coefficient of performance results, which are $-156.818$ and 0.3986, respectively. The 20% ammonia combustion also decreases the environmental and life cycle–based environmental payback period. However, 20% ammonia combustion slightly increases the payback period of the system. The 20% ammonia has the lowest ${\mathrm{CO}}_2$-equivalent emission rate due to producing the lowest ${\mathrm{CO}}_2$-equivalent emissions during combustion. Finally, 20% ammonia combustion decreases total and specific environmental pollution costs.

In drinking water treatment, it is difficult to predict the remaining service life of a partially spent granular activated carbon bed when contaminants are intermittent, such as taste and odor-causing compounds. A laboratory-scale minicolumn test using a grab granular activated carbon (GAC) sample from a full-scale bed was assessed using pore and surface diffusion model (PSDM) simulations. The impact of bed depth and flow velocity on the performance of preloaded GAC was negligible provided that the minicolumn test matched the same empty bed contact time as at full scale. The impact of minicolumn diameter was insignificant when the minicolumn to GAC particle diameter ratio was larger than 13. Minicolumns using a single representative grain size fraction were predicted to simulate full-scale beds with reasonable accuracy. The impact of temperature may be significant. A potential limitation of the test is that the media may be harvested at different GAC bed depths: accuracy requires that the adsorption capacity and kinetics of the adsorbate be relatively constant across those depths.

To recover a preferred carbon source from waste activated sludge (WAS), this study systematically investigated the effects of a low-temperature thermal hydrolysis process (THP) on WAS solubilization and dewaterability at 25°C–120°C for 60 min. Experimental results indicated that organics [soluble chemical oxygen demand (SCOD), proteins, carbohydrates, and lipids] and nutrients (N and P) were efficiently released into the sludge supernatant after THP. Deoxyribonucleic acid (DNA) tests identified 60°C as the threshold of sludge cell disintegration, which increased DNA from nearly $0–166.64\mathrm{mg}/\mathrm{L}$. Sludge dewaterability deteriorated after THP, as evidenced by longer filtration times and higher water contents of sludge cake, particularly at 120°C, which was due to the release of abundant soluble extracellular polymeric substances. The optimal heating temperature for carbon source recovery was 80°C, which achieved the highest biodegradability (5-day biochemical oxygen demand/SCOD 0.62), satisfied SCOD/total nitrogen (18.6), and had acceptable dewaterability.

Fluoride is commonly found at elevated concentrations in groundwaters worldwide and is difficult to remove even with activated alumina (AA) adsorption, the best available technology. Consequently, alternative treatment technologies for fluoride removal continue to be researched, including the use of bone char (BC) adsorption. However, BC studies are limited mostly to batch or equilibrium studies, which can be difficult to extend to full-scale applications. Therefore, the goal of this study was to compare a BC to a commercial AA for treating groundwater with a naturally occurring fluoride concentration of $8.5\mathrm{mg}/\mathrm{L}$ using pilot- and bench-scale fixed-bed adsorption tests. At the pilot scale using an empty bed contact time (EBCT) of 10 min, fluoride breakthrough reached $1.5\mathrm{mg}/\mathrm{L}$ within 450 bed volumes (3.1 days) and 650 bed volumes (4.5 days) for BC and AA, respectively. Two designs of the rapid small-scale column test (RSSCT) were applied to simulate the pilot columns, where the proportional diffusivity RSSCT (PD-RSSCT) design provided a more adequate prediction of fluoride breakthrough to $1.5\mathrm{mg}/\mathrm{L}$. The PD-RSSCT was also used to evaluate BC and AA EBCTs of 10 and 20 min, with the longer EBCT providing no significant increase in adsorbent use efficiency. Complete BC regeneration using countercurrent flow to the PD-RSSCT was limited by exposure to the sodium hydroxide regenerant solution and, potentially, the presence of arsenic.

In this study, cobalt oxides were loaded on a ${\mathrm{CeO}}_2$ nanorod and synthesized using a hydrothermal method and wet impregnation to reduce nitrogen monoxide (NO) by carbon monoxide (CO). A series of catalysts were characterized by nitrogen physisorption, high-resolution transmission electron microscopy (HRTEM), X-ray diffraction (XRD), X-ray spectroscopy (XPS), and in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) to determine the reacting path in the reduction zones. Co species were highly dispersed on the ${\mathrm{CeO}}_2$ nanorod when the precursor solution content was less than 20% by weight. ${\mathrm{Co}}^{3+}$ species were the most active components in the $\mathrm{NO}+\mathrm{CO}$ reaction, and the ${\mathrm{Co}}^{3+}$ fraction reached a maximum when the precursor concentration was 10% by weight. A possible mechanism for the $\mathrm{CO}+\mathrm{NO}$ reaction was suggested in which NO adsorbs onto the surface of ${\mathrm{CoO}}_{\mathrm{x}}{-\mathrm{CeO}}_2$ and transforms to some nitrite/nitrate species under the reacting condition. At lower temperature ($<300°\mathrm{C}$), adsorbed CO species react with a nitro complex to generate ${\mathrm{N}}_2\mathrm{O}$ and ${\mathrm{CO}}_2$, whereas as the temperature increases, these nitro complexes transform to coordinate nitrates reacting with CO species to generate nontoxic ${\mathrm{N}}_2$ and ${\mathrm{CO}}_2$.

Computational fluid dynamics (CFD) is a tool to simulate the coupled hydrodynamics and particulate matter (PM) fate in unit operations (UOs) subject to transient rainfall-runoff events. Most frequently, CFD is applied for the relatively rapid analysis of steady flows $(\mathrm{CFD}{)}_{\mathrm{s}}$. More recently, an event-based stepwise steady flow CFD model $(\mathrm{CFD}{)}_{\mathrm{ss}}$ was developed to predict particulate matter (PM) separation with reduced computational overhead compared with unsteady CFD modeling $(\mathrm{CFD}{)}_{\mathrm{us}}$. This study developed an event-based $(\mathrm{CFD}{)}_{\mathrm{ss}}$ model to evaluate longer-term UO performance. The $(\mathrm{CFD}{)}_{\mathrm{ss}}$ models simulated PM fate (separation and washout) in a rectangular clarifier (RC) and a screened hydrodynamic separator (SHS) for a representative year of runoff (2007) in North Florida. Washout and separation for all unsteady events were integrated into a time domain continuous simulation model. The $(\mathrm{CFD}{)}_{\mathrm{ss}}$ model was validated with measured PM separation and washout data from full-scale physical models. The annual PM separation for the RC was 40% with no washout and 38% with washout. Annual PM separation for the SHS was 37% with no washout and 27% with washout. The annual SHS washout profile indicated maintenance cleanout at the start and end of the wet season. Coupling $(\mathrm{CFD}{)}_{\mathrm{ss}}$ with continuous simulation represents a tool extending UO evaluations from an unsteady event-basis to an annual basis. Simulating all runoff events in 2007 required 14 h of computational time for the RC and SHS. Implications from these results indicate that longer-term prediction of UO separation/washout is viable with $(\mathrm{CFD}{)}_{\mathrm{ss}}$ coupled with a continuous simulation model such as the Storm Water Management Model (SWMM), and can serve as a tool for UO testing/certification.

Numerous testing of data reported in the relevant scientific literature widely available to the public has led to the discovery of several physical mathematical models in nature applicable to the subject of oxygenation in water from submerged bubble aeration. The mass transfer coefficient commonly symbolized as ${\mathrm{K}}_{\mathrm{L}}\mathrm{a}$ is the product of the overall liquid film coefficient ${\mathrm{K}}_{\mathrm{L}}$ and the overall gas-liquid interfacial area that the gas flux passes through, expressed by the letter $\mathrm{a}$. The rate of mass transfer (the rate at which the solute gas dissolves into a given liquid) is a function of the mass transfer coefficient ${\mathrm{K}}_{\mathrm{L}}\mathrm{a}$ and the driving force exerted against the fluid being aerated. In a nonsteady state test where the oxygen content of the water is usually lowered to approximately zero prior to initiating the test, the driving force gradually diminishes as the dissolved oxygen increases until it reaches saturation. Given that ${\mathrm{K}}_{\mathrm{L}}\mathrm{a}$ is a function of many variables, in order to have a unified test result, it is necessary to create a baseline mass transfer coefficient ${\mathrm{K}}_{\mathrm{L}}{\mathrm{a}}_0$, so that all tests will have the same measured baseline. ${\mathrm{K}}_{\mathrm{L}}\mathrm{a}$ is an exponential function of this new coefficient and dependent on the height of the liquid column ${\mathrm{Z}}_{\mathrm{d}}$ through which the gas flow stream passes. The mass transfer coefficient ${\mathrm{K}}_{\mathrm{L}}\mathrm{a}$ is dependent on the gas average flow rate (${\mathrm{Q}}_{\mathrm{a}}$) passing through the liquid column. ${\mathrm{Q}}_{\mathrm{a}}$ is expressed in terms of volume of gas per unit time and is calculated by the universal gas law, or Boyle’s Law, if the liquid temperature is uniform throughout the liquid column, taking the arithmetic mean of the flow rates over the tank column. ${\mathrm{K}}_{\mathrm{L}}\mathrm{a}$ is directly proportional to this averaged gas flow rate to power $q$, where $q$ is usually less than unity for water in a fixed column height and a fixed gas supply rate at standard conditions. This paper provides case studies that verify this concept of a standardized specific baseline mass transfer coefficient $({\mathrm{K}}_{\mathrm{L}}{\mathrm{a}}_0{)/\mathrm{Q}}_{\mathrm{a}}^{\mathrm{q}}$ that is applicable to submerged bubble aeration tests.

The water quality of Dianchi Lake has deteriorated in the last 50 years due to excessive human activities. The Niulan River to Dianchi Lake Water Diversion Project (NRDLWDP) was implemented in 2013 to improve the water environment by enhancing the water exchange and transport in the lake. Since the start of its operation, the water quality of the lake has been improved except in flood seasons, when the turbidity of the water pumped from the water source of the project, the Deze Reservoir, exceeded the regulatory standards. The characteristics of flow and sediment transport near the intake and its upper reaches along the Niulan River and its tributary were first analyzed based on field observations in the Deze Reservoir. The effectiveness of the check dams and multi-water-level intake on reducing the sediment concentration of the intake was evaluated by using a three-dimensional model SCHISM (semi-implicit cross-scale hydroscience integrated system model). The results revealed that the original design of placing the intake near the riverbed in order to be able to take in water at low water levels overlooked the possibility that the very fine incoming sediments and the frequently occurring density currents tended to occur near the bottom where the intake is located. The construction of check dams can encourage the deposition processes upstream and thus decrease the sediment concentration or water turbidity at the intake. However, the reduced turbidity is still too high to meet the standard of 17.1 NTU. Therefore, a multi-water-level intake should be adopted to solve the sediment problems of the NRDLWDP because it can be fully adapted to the stratified characteristics of the sediment concentration at the intake of the Deze Reservoir. With the multi-water-level intake, the turbidity of the pumped water can be substantially reduced when compared with the current approach of a single-water-level intake and the construction of check dams.