Journal of Environmental Engineering

Multiple biomass-for-energy feedstock resources have been proposed and many or all of these may ultimately be needed. This paper focuses on perennial lignocellulosic feedstocks. In the United States, Perlack and colleagues estimated that by 2050 1.3 billion Mg of biomass could be sustainably harvested annually. However, over half of the herbaceous biomass in their estimate was derived from crop residues, a source that presents numerous concerns. Availability of land resources and the economic prospects for diverting land from food to energy production is further clouded by unknown variables such as the impact of increased human populations and higher living standards. Much effort is currently being given to corn and other starch or grain crops that can be readily converted to ethanol. Although these crops have served to jumpstart the fuel ethanol industry, they have much less potential to meet the growing demand, much greater potential for negative environmental impacts, and their use feeds the “food versus fuel” debate. The 2007 Energy Bill mandated annual production of 136 billion L of fuel (ethanol, etc.) from renewable feedstocks by 2022, a goal that will greatly impact U.S. agriculture. From 2009, all increases in renewable fuel production are to come from nonstarch sources, yet production of “cellulosic ethanol” is currently limited by the conversion technologies. In addition to conversion constraints, all bioenergy technologies will require equipment systems that can cost effectively collect, store, and deliver bulky distributed biomass to the bioenergy plant. These systems will emulate commercial systems that move herbaceous crops (e.g., cotton and sugarcane) to processing plants; however they must be fine tuned to address the requirements of the crop and the constraints of the land base. Important interactions occur between each component of the supply chain—agronomy, logistics, and processing—that are best not studied in isolation. Significant social issues also stand to influence landowner decisions regarding market entry and these will affect the function and profitability of a bioenergy plant. The business plan must provide a “win-win” for both the feedstock supplier and the plant owner. Other large questions about the development of bioenergy resources reside outside the system, e.g., bioenergy systems may be more cost competitive if the policy allows them to benefit from the potential ecosystem services they provide such as sequestering carbon.

Energy requirements and greenhouse gas (GHG) emissions for current landfilling of municipal solid waste (MSW) was compared to potential biodegradation of MSW in anaerobic digesters (AD) throughout the United States. A hybrid life-cycle analysis was completed to assess the potential for anaerobic biodegradation of MSW to methane, a valuable energy source. Conversion of MSW to methane in AD would generate a form of renewable energy, reduce GHG emissions, and save landfill space for nonbiodegradable materials. Based on laboratory- and pilot-scale studies conducted in the United States, full-scale data from facilities in Europe, and economic input-output life-cycle analysis, the annual 127 million t of MSW landfilled in the United States could be biologically converted to $5.9\text{billion}{\text{m}}^3$ of methane. Net methane production would have an estimated value of $1.5 billion/year when converted to an equivalent amount of electricity at an assumed value of $0.1/kWh. The 15 billion kWh/year of renewable energy released through the biodegradation process is estimated to satisfy the annual consumption of 1.3 million United States households. The analysis also suggests that diversion of MSW from landfills to AD systems would result in GHG emissions reductions of 146 million t ${\text{CO}}_2\text{e}$ per year, due to decreased landfill activity and use of biogenic methane instead of fossil fuel for electricity production. This represents a reduction in total emissions of 1.9% compared to U.S. GHG emissions in 2006. Nationwide AD systems are projected to reduce cumulative energy consumption by nearly 15 million TJ and reduce GHG emissions by 7.2 billion t ${\text{CO}}_2\text{e}$ , over a 50-year period. Logistics and capital costs of developing a nationwide reactor-based system for MSW management are considerable. Development of appropriate national policy and incentives would be needed to stimulate such a transition from the current landfill-based system that currently exists. It is estimated that a carbon emissions credit on the order of $30 to $60/t ${\text{CO}}_2\text{e}$ would facilitate break-even economics for nationwide implementation of AD systems. Alternatively, renewable energy credits would enhance the value of electricity produced from AD biogas. Carbon emissions taxes on landfills would further improve the economics of AD systems.

Wastewater from a corn wet-milling ethanol plant was treated with Rhizopus microsporus mold in a continuous biofilm reactor (attached growth system). Plastic composite support tubes, composed of 50% (w/w) polypropylene and 50% (w/w) agricultural products were used as support media. The effects of operating pH (3.5, 4.0, and 4.5) and hydraulic retention times (HRTs) (5.0, 3.75, 2.5, and 1.25 h) on fungal growth, chemical oxygen demand (COD) removal and unwanted bacterial growth were evaluated under nonaseptic conditions. COD removal and biomass production were highest at pH 4.0 with lowest bacterial competition. Maximum COD removal of up to 80% was achieved at a 5.0 h HRT with a biomass yield of 0.44 g volatile suspended solids per g COD removed. A higher biomass yield was achieved at a shorter HRT of 2.5 h due to increased substrate availability; however, the biofilm was more sensitive to changes in wastewater composition. A HRT of 3.5–4 h was considered optimal in achieving organic removal and fungal biomass production. Significant loss of fungal biomass due to washout occurred at a 1.5 h HRT. Undesirable bacterial populations as a fraction of total biomass decreased with reducing HRT, excluding the 1.25 h HRT. Reductions in COD removal and biomass production were observed with decreases in aeration rate (1.0–0.25 L/min or 0.8–0.2 vvm (air volume per reactor working volume per minute). The recovered fungal biomass was found to contain protein of up to 40% (dry mass basis), which could serve as a source of high-value animal feed.

Algae grown on wastewater media are a potential source of low-cost lipids for production of liquid biofuels. This study investigated lipid productivity and nutrient removal by green algae grown during treatment of dairy farm and municipal wastewaters supplemented with ${\text{CO}}_2$ . Dairy wastewater was treated outdoors in bench-scale batch cultures. The lipid content of the volatile solids peaked at Day 6, during exponential growth, and declined thereafter. Peak lipid content ranged from 14–29%, depending on wastewater concentration. Maximum lipid productivity also peaked at Day 6 of batch growth, with a volumetric productivity of 17 mg/day/L of reactor and an areal productivity of $2.8\text{g}/{\text{m}}^2/\text{day}$ , which would be equivalent to 11,000 L/ha/year (1,200 gal/acre/year) if sustained year round. After 12 days, ammonium and orthophosphate removals were 96 and $>99\%$ , respectively. Municipal wastewater was treated in semicontinuous indoor cultures with 2–4 day hydraulic residence times (HRTs). Maximum lipid productivity for the municipal wastewater was 24 mg/day/L, observed in the 3-day HRT cultures. Over 99% removal of ammonium and orthophosphate was achieved. The results from both types of wastewater suggest that ${\text{CO}}_2$ -supplemented algae cultures can simultaneously remove dissolved nitrogen and phosphorus to low levels while generating a feedstock potentially useful for liquid biofuels production.

The overall goal of this project was to quantify the long-term water quality impacts of land management changes associated with increased demands for corn as a transportation biofuel feedstock in the United States. A modeling approach that considers a nonpoint source model, Groundwater Loading Effects of Agricultural Management Systems and National Agricultural Pesticide Risk Analysis, was used to simulate annual losses in runoff, percolation, erosion, nitrate-nitrogen, total phosphorus, atrazine (1-chloro-3-ethylamino-5-isopropylamino-2,4,6-triazine), and pyraclostrobin (Methyl {2-[1-(4-chlorophenyl)-1H-pyrazol-3-yloxymethyl] phenyl} methoxycarbamate) to the edge-of-field and bottom-of-root zones associated with multiple cropping scenarios. Model results for representative soils, throughout Indiana, were analyzed to determine 10% (worst case) and 50% (average case) probability of exceedence in the aforementioned water quality indicators. Modeling results indicated significant differences $\left(p<0.05\right)$ in water quality indicators between continuous corn and corn-soybean rotations. The results showed that agricultural management decisions would have greater impacts on nutrient, runoff, erosion, and pesticides losses from agricultural fields compared to water quality indicators associated with the projected changes in crop rotation systems. The model results point to the need for additional research to fully understand the water impacts of land management decisions associated with corn grain as a feedstock for biofuel production.

Microalgal biomass production offers a number of advantages over conventional biomass production, including higher productivities, use of otherwise nonproductive land, reuse and recovery of waste nutrients, use of saline or brackish waters, and reuse of ${\text{CO}}_2$ from power-plant flue gas or similar sources. Microalgal biomass production and utilization offers potential for greenhouse gas (GHG) avoidance by providing biofuel replacement of fossil fuels and carbon-neutral animal feeds. This paper presents an initial analysis of the potential for GHG avoidance using a proposed algal biomass production system coupled to recovery of flue-gas ${\text{CO}}_2$ combined with waste sludge and/or animal manure utilization. A model is constructed around a 50-MW natural gas-fired electrical generation plant operating at 50% capacity as a semibase-load facility. This facility is projected to produce 216 million k⋅Wh/240-day season while releasing 30.3 million kg-C/season of GHG- ${\text{CO}}_2$ . An algal system designed to capture 70% of flue-gas ${\text{CO}}_2$ would produce 42,400 t (dry wt) of algal biomass/season and requires 880 ha of high-rate algal ponds operating at a productivity of $20\text{g-dry-wt}/{\text{m}}^2\text{-day}$ . This algal biomass is assumed to be fractionated into 20% extractable algal oil, useful for biodiesel, with the 50% protein content providing animal feed replacement and 30% residual algal biomass digested to produce methane gas, providing gross GHG avoidances of 20, 8.5, and 7.8%, respectively. The total gross GHG avoidance potential of 36.3% results in a net GHG avoidance of 26.3% after accounting for 10% parasitic energy costs. Parasitic energy is required to deliver ${\text{CO}}_2$ to the algal culture and to harvest and process algal biomass and algal products. At ${\text{CO}}_2$ utilization efficiencies predicted to range from 60–80%, net GHG avoidances are estimated to range from 22–30%. To provide nutrients for algal growth and to ensure optimal algae digestion, importation of 53 t/day of waste paper, municipal sludge, or animal manure would be required. This analysis does not address the economics of the processes considered. Rather, the focus is directed at determination of the technical feasibility of applying integrated algal processes for fossil-fuel replacement and power-plant GHG avoidance. The technology discussed remains in early stages of development, with many important technical issues yet to be addressed. Although theoretically promising, successful integration of waste treatment processes with algal recovery of flue-gas ${\text{CO}}_2$ will require pilot-scale trials and field demonstrations to more precisely define the many detailed design requirements.

The U.S. Environmental Protection Agency’s (USEPA) Urban Watershed Management Branch monitored a best management practice (BMP) wetland in the Richmond Creek (RC) watershed. This BMP, designated Richmond Creek #5 (RC-5), is owned and operated by the New York City Department of Environmental Protection’s as part of the Bluebelt program. During monitoring performed in 2003 and 2004, RC-5 was monitored for several water quality parameters including suspended solids (SS), chemical oxygen demand (COD), and phosphorous. Calculated SS loads demonstrated a 61% removal which is in line with the anticipated removals of 55%–57%, however, COD was not being removed from RC-5. Due to visible accumulation of sediment in the forebay and leaves throughout the BMP, maintenance activity was performed in the spring of 2005, to remove the sediment and organic matter (leaves) by vactor truck and physical labor. About four truck loads of sediment and leaf litter, estimated at $35{\text{m}}^3$ (46 cubic yards), was removed from the site. Monitoring during the fall of 2005 measured the effects of this maintenance activity. The effluent concentrations of COD were significantly less and less variable after maintenance, and calculated influent and effluent COD loading indicated removals. The reduction in COD effluent coincided with drops in effluent phosphorous levels. Effluent SS concentrations were not significantly altered, implying RC-5 still had capacity to remove sediments before maintenance occurred. Indications are that the maintenance activity significantly reduced the COD effluent and may help communities manage phosphorous loadings.

The elaboration, management, and design of the sedimentation devices require an improved knowledge not only on the suspended solids (SS) settling velocity but also on the distributions of these particulate pollutants by category of SS settling velocity. Nevertheless, there is currently a lack of available data regarding the settling velocity grading of particle bound pollutants. As a consequence, this study investigating the settling velocity grading of particle bound polycyclic aromatic hydrocarbons (PAHs) in wet weather flows within combined sewers was launched. The pursed objectives were to compare the SS and PAH settling velocity grading curves and hence to assess whether or not PAHs were associated with a specific settling velocity category. Investigations were carried out for three storms at two sampling sites within the Parisian combined sewer. Results indicate that most of PAHs seem to be preferentially associated with particles with a settling velocity $>0.3\text{mm}{\text{s}}^{-1}$ .

The quantitative effects of hydrodynamic conditions on sediment oxygen demand (SOD) under smooth surface conditions were investigated using the following three practical and compact experimental systems: (1) a continuous flow system containing sediment core samples; (2) a rectangular flume system; and (3) a system combining the first two. Experimental results demonstrated that SOD showed a monotonically increasing tendency as the flow velocity increased with reduction of the thickness of the diffusive boundary layer. The experimental results were compared with numerical models theoretically relating SOD and flow velocity under smooth surface conditions. The features of each experimental system are discussed. The continuous flow system is advantageous because it simultaneously produces a steady state and different dissolved oxygen (DO) conditions. The rectangular flume system is suitable for fundamental studies of hydrodynamic effects on SOD because it makes controlling hydrodynamic conditions easy, while the combined system is appropriate for studying the effect of microscopic phenomena on exchange rates, as it can reproduce natural microscopic physicochemical processes.

Pump and treat (P&T) system is widely used to remove contaminants in groundwater and maintain hydraulic capture of contaminants. A P&T system usually becomes costly in removing contaminant mass after operation for a period of time because the cost of pumping stays high while concentration of contaminants in extracted groundwater decreases significantly over time. However, the P&T system may have to continue operation before contaminants in groundwater reach the cleanup goals. In such cases, the optimization of the existing remedial system and an exit strategy will be necessary and beneficial to all stakeholders. This study examined a P&T system at a remediation site near a coastal wetland. We developed a three-tier approach to optimize the existing remedial system. The remedial process optimization (RPO) was achieved by reducing pump wells and monitoring frequency and developing an exit strategy. In the first tier, we used descriptive trend plot, trend factor analysis, and autocorrelation analysis to capture the temporal trend in the monitoring data and determine optimum sampling frequency; in the second tier, we used multivariate analysis include principal component analysis (PCA) and partial least square regression (PLSR) to identify the spatial and temporal pattern in the monitoring data, and to construct a statistical model to predict future contaminant levels; in the third tier, we used MODFLOW, a USGS developed finite-difference flow module for aquifer simulation, and interpretation of the hydraulic capture of extraction wells and contaminant migration. Based on the tiered analysis, we designed an improved groundwater monitoring program and pumping strategy. The RPO is expected to save 68% groundwater monitoring cost, and 30% P&T operation and maintenance (O&M) cost.

Ceramic filtration has recently been identified as a promising technology for drinking water treatment in households and small communities. This paper summarizes the results of a pilot-scale study conducted at the U.S. Environmental Protection Agency’s (EPA) Test & Evaluation (T&E) Facility in Cincinnati on two ceramic filtration cartridges with pore sizes of 0.05 and $0.01\mu \text{m}$ to evaluate their ability to remove turbidity and microbiological contaminants such as bacteria [Bacillus subtilis $\left(\approx 1.0\mu \text{m}\right)$ and Escherichia coli $\left(\approx 1.4\mu \text{m}\right)$ ], Cryptosporidium oocysts $\left(4–6\mu \text{m}\right)$ , polystyrene latex (PSL) beads $\left(2.85\mu \text{m}\right)$ (a surrogate for Cryptosporidium), and MS2 bacteriophage $\left(\approx 0.02\mu \text{m}\right)$ (a surrogate for enteric viruses). The results demonstrated that the relatively tighter $0.01\text{-}\mu \text{m}$ cartridge performed better than the $0.05\text{-}\mu \text{m}$ cartridge in removing all the biological contaminants and surrogates. For turbidity removal, the $0.01\text{-}\mu \text{m}$ cartridge performed slightly better than the $0.05\text{-}\mu \text{m}$ cartridge; however, the permeate rate in the $0.01\text{-}\mu \text{m}$ cartridge reduced rapidly at higher feed water turbidity levels indicating that a tighter membrane should only be used with adequate pretreatment or at a low feed water turbidity to prolong membrane life. Microbiological monitoring was identified as a more sensitive indirect integrity monitoring method than turbidity and particle count monitoring to ensure effective treatment of water by ceramic filtration. Both PSL beads and B. subtilis showed potential as effective surrogates for Cryptosporidium, with B. subtilis showing higher degree of conservatism. Any opinions expressed in this article are those of the writer(s) and do not necessarily reflect the official positions and policies of the EPA. Any mention of products or trade names does not constitute recommendation for use by EPA. This document has been reviewed in accordance with EPA’s peer and administrative review policies and approved for publication.

Synthetic musk fragrances are common personal care product additives and wastewater contaminants that are routinely detected in the environment. This study examines the presence of eight synthetic musk fragrances [7-acetyl-1,1,3,4,4,6-hexamethyl-1,2,3,4-tetrahydronaphthalene (AHTN), 1,3,4,6,7,8-hexahydro-4,6,6,7,8-hexamethylcyclopenta- $\gamma$ -2-benzopyran (HHCB), 5-acetyl-1,1,2,6-tetramethyl-3-iso-propylindane (ATII), 4-acetyl-1,1-dimethyl-6-tert-butylindane (ADBI), 6-acetyl-1,1,2,3,3,5-hexamethylindane (AHMI), 6,7-dihydro-1,1,2,3,3,-pentamethyl-4-(5H)-indanone (DPMI), 1-tert-butyl-3,5-dimethyl-2,4,6-trinitrobenzene (musk xylene), and 4-tert-butyl-3,5-dinitro-2,6-dimethylacetophenone (musk ketone)] in source water and the removal of these compounds as they flow through a Midwestern conventional drinking water plant with lime softening. The compounds were measured in water, waste sludge, and air throughout the plant. HHCB and AHTN were detected in 100% of the samples and at the highest concentrations. A mass balance on HHCB and AHTN was performed under warm and cold weather conditions. The total removal efficiency for HHCB and AHTN, which averaged between 67–89%, is dominated by adsorption to water softener sludge and its consequent removal by sludge wasting and media filtration. Volatilization, chlorine disinfection, and the disposal of backwash water play a minor role in the removal of both compounds. As a result of inefficient overall removal, HHCB and AHTN are a constant presence at low levels in finished drinking water.

Powdered activated carbon (PAC) is an excellent adsorbent for drinking water treatment of many trace organic contaminants. To evaluate and design a PAC adsorption process for a particular application, it is necessary to know the minimum (lowest economical) carbon (adsorbent) usage (MCU) defined thermodynamically. In this work, an explicit relationship is developed for predicting the MCU required for a desirable level of treatment of a target trace organic compound (TC). The adsorption processes considered are PAC slurry contactors idealized either as batch reactors, plug flow reactors, or continuous-flow stirred tank reactors. Comparing with the ones previously available in the literature, this newly developed relationship, as a predictive tool for practical uses as well, is more accurate because it does not need to assume that the MCU required for target TC removal can always reduce the competing background natural organic matter (NOM) to a level much less than the NOM initial/influent concentration. Applications of the relationship developed herein to PAC adsorption of typical trace organic contaminants in natural water are demonstrated with isotherm data from multiple literature sources.

The different sludge floc distributions along the rectangular secondary settling tank were confirmed experimentally. Along the settling tank, three different regions can be formed: the fast settling zone near the inlet, the compaction zone in the middle, and the slowly settling zone near the outlet. Further investigation of morphological change of sludge flocs also showed corresponding floc characteristics: the bigger size of particles in the front, the relatively smaller particles with high density in the middle, and the small loose flocs in the rear. These were determined by the hydraulics and floc construction. The preceding results can be used as a guide to design systems to collect loose sludge solids.

Using the industrial wastewater from a dairy plant, the performance of enhanced biological phosphorus removal (EBPR) with complex organic substances was evaluated. A laboratory-scale sequencing batch reactor (SBR) was operated and the organic loading rate in total chemical oxygen demand (tCOD) increased gradually from 200– $600\text{g-tCOD}{\text{m}}^{-3}{\text{cycle}}^{-1}$ in three steps. As the organic loading increased, the food to microorganism ratio $\left(F/M\right)$ increased from 0.16–0.27 (g-tCOD/g-MLVSS d). When it increased over $600\text{g-tCOD}{\text{m}}^{-3}{\text{cycle}}^{-1}$ , the effluent phosphorus concentration fluctuated, showing an unstable EBPR activity. During the anaerobic condition, higher fraction of poly-3-hydroxyvalerate (PHV) was observed and the ratio of PHV to poly-3-hydroxybuyrate (PHB) production $\left(\Delta \text{PHV}/\Delta \text{PHB}\right)$ ranged $1.2\sim 3.4\text{mM-C/mM-C}$ . PHV was produced faster and used later than PHB. By applying fluorescent in situ hybridization (FISH) technique, the percentage of Rhodocyclus-related bacteria to the total cell counts was monitored as an indicator of phosphorus accumulating organisms (PAOs). The population accounted for $38.3\pm 16.2\%$ at low organic loading rate and stayed at the same level as the organic loading rate increased.

Electrical conductivity (EC) is used for monitoring different types of aqueous systems. The measured EC value at any temperature needs to be corrected for a standard temperature, for reporting or comparison, since EC is dependent on temperature. A temperature compensation factor has been derived for conductivity correction from anaerobic digester supernatant/centrate samples of five different wastewater treatment plants in western Canada. For a temperature compensation factor of $0.0198°{\text{C}}^{-1}$ , corresponding to the standard temperature at $25°\text{C}$ , the estimated ${\text{EC}}_{25}$ values were found to be reasonably accurate, with a maximum error of 2.01%. The estimated EC values, based on any standard temperature, were found to be statistically similar to each other. Considering the temperature dependence of EC, a relationship between EC and ionic strength was developed in this study for anaerobic digester supernatant/centrate samples. This relationship can be used to estimate the ionic strength of the solution in a system associated with struvite formation from anaerobic digester supernatant/centrate and effectively monitor the system performance.

Laboratory experiments are described that investigate the potential for using electrokinetic geosynthetics (EKGs) [materials that permit the combined exploitation of geosynthetics with electrokinetics (EKs)] to dewater slurry waste from a tunneling operation. The results demonstrate that the EK is reproducible for different slurries and that the process can significantly dewater tunneling slurry wastes. Higher electrode element surface area, increased potential gradient, and longer processing time increase water removal from a slurry waste. Higher potential gradients and current densities were found to consume more energy, with thicker samples (lower voltage gradients) and close element spacing using less power to achieve a particular dewatering efficiency than other configurations tested. The resultant pH of the treated slurry and the effluent water were found not to be sufficiently altered by the EK process to prevent their safe disposal or reuse. The potential of three different forms of EKG to treat tunneling slurry are discussed and a conceptual scheme for an EK enhanced belt press is proposed. While further investigation would be required to optimize their operating parameters, preliminary designs, and cost estimates can be based on the results presented herein.

We measure and model the steady transport of specific conductivity and dissolved oxygen through a groundwater plume from a highway infiltration basin in southeastern Massachusetts. Specific conductivity is treated as a conservative surrogate for runoff contamination, and the data calibrate a 0.27-m vertical dispersivity $\alpha$ of the aquifer and the bottom streamline elevation of the plume, which falls to an 8-m depth below the water table. The dissolved oxygen degrades as a first order reactant in the plume to levels below 1 mg/L, with a decay constant $\lambda$ of $0.12{\text{day}}^{-1}$ . The latter may be attributed in part to the historical use of an alternative de-icing agent calcium magnesium acetate on the highway, since acetate is a readily biodegradable substrate for microorganisms. The calibrated kinetics suggest that plume microbes and geochemistry degrade oxygen over two orders of magnitude faster than their ambient groundwater counterparts, which impose a linear decrease of dissolved oxygen concentration below the plume. Simulations suggest that the anoxic groundwater plume extends 1,600 m downgradient of the infiltration basin, a distance that will shorten by an order of magnitude if salt is used exclusively to de-ice the highway.

The correlation between settling velocity and associated pollutant concentrations is of major importance for best management practice in designing, redesigning, or evaluation of the efficiency of existing pond facilities for retaining unwanted pollutants. The prospect of this note is to state the relationship between the settling velocity of the runoff particles and the corresponding metal and polyaromatic hydrocarbon (PAH) concentration directly instead of dealing with two unknowns—the density and the shape of a single particle fraction in a settling velocity calculations. The measurements show that the highest cadmium, chromium, zinc, and nickel concentrations is associated with the most slowly falling particles and the lowest concentration associated within the faster falling fraction. This tendency is not clear for some of the sediments due to high content of organic matter and clearly not for lead and copper and there is no significant correlation between PAH concentration and settling velocity. The largest mass of metals and PAH within each pond can be found on the particle fraction with a settling velocity of 5.5–2.5 mm/s.