Journal of Environmental Engineering

Microbial fuel cell (MFC) is an eco-friendly energy source that generates electricity by degrading natural wastes through bacterial activity. The electrolyte that is sandwiched between the electrodes for the separation and transportation of protons is a critical component of the MFC system. Currently available membranes used as electrolytes to transport protons are expensive and exhibit high oxygen crossover with low mechanical and chemical stability, which make the commercialization of MFC difficult. Therefore, in this study, we synthesized a cost-effective ionically-crosslinked nanocomposite membrane made up of cationic aniline-treated polysulfone (APSf) doped with anionic sulfonated multiwalled carbon nanotube (SMWCNT) to lower the oxygen crossover and enhance the chemical, tensile, and thermal stabilities. The impact of the incorporation of SMWCNT on oxygen diffusivity of the synthesized membrane was evaluated by molecular dynamics (MD) simulation. Polysulfone is a material that conducts protons but has low ion exchange power and electrons are produced to a marginally lesser extent than in case other membranes. However, when aniline is used as a crosslinking agent in the polysulfone polymer solution to produce APSf membrane, the material becomes electron driven, which results in a functional bearing unit that can engage in hydrogen bonding interactions. The APSf/SMWCNT membrane containing 1% by weight of carbon nanotubes provided a maximum power density of $304.2\mathrm{mW}/{\mathrm{m}}^2$ with substantially high columbic efficiency (17%) and considerable removal of chemical oxygen demand (COD) (82%) as compared to Nafion 117 or APSf incorporated with 0.5% by weight nanotubes. The APSf/SMWCNT (1% by weight) membrane also exhibited high ion exchange capacity ($1.6\mathrm{meq.}{\mathrm{g}}^{-1}$) as well as proton conductivity ($0.19{\mathrm{Scm}}^{-1}$). The low oxygen diffusivity of APSf/SMWCNT membrane ($8.3\times {10}^{-8}{\mathrm{cm}}^2{\mathrm{s}}^{-1}$) obtained from MD simulation compared to plain APSf ($8.16\times {10}^{-7}{\mathrm{cm}}^2{\mathrm{s}}^{-1}$) and Nafion 117 ($6.5\times {10}^{-7}{\mathrm{cm}}^2{\mathrm{s}}^{-1}$) are good indications of its potential in MFC application. These results indicate that the membranes synthesized in this study play a crucial role in the performance of MFCs and could be inexpensive alternatives to existing commercial membranes for MFC-based treatment of domestic and industrial wastewater.

Effects of harvesting ages (45, 70, and 90 days), pretreatments (fresh and silage), and temperatures (35°C and 55°C) on biogas production from P. purpureum × P. typhoideum (giant juncao grass, GJG) were investigated. The biochemical methane potential test was used to determine specific methane yields, and results were simulated using the modified Gompertz model. GJGs at younger harvesting ages gave higher specific methane yields, partly due to their lower lignin content. Ensiled GJGs tended to offer superior degradation performance to fresh grass under mesophilic conditions. However, under thermophilic conditions, similar specific methane yields were obtained, suggesting that effects of high temperature digestion prevailed over ensiling process advantages. Higher specific methane yields were attained under thermophilic conditions for GJGs having the same harvesting age and pretreatment. Owing to its high mass yield, the fresh 90-day GJG was recommended as the feedstock for biogas production under thermophilic conditions. Methane yield up to $\mathrm{10,356}{\mathrm{m}}^3{\mathrm{CH}}_4{\mathrm{ha}}^{-1}{\mathrm{year}}^{-1}$ was provided from this grass, which was 1.6–90.1 times higher than that estimated from other biomass types investigated.

Bypass wastewaters in excess of plant capacity require in-plant wastewater treatment strategies capable of lessening the contamination magnitude prior to their discharge into water bodies. This study introduces a novel hybrid potassium ferrate(VI)–iron electrocoagulation system for the treatment of bypass wastewater. To understand the synergistic effect of the hybrid system, the response surface methodology and the Box Behnken design were utilized based on four preselected variables (current density, potassium ferrate(VI) dosage, interelectrode distance, and time). The current density and potassium ferrate(VI) dosage and their interaction were found significant in achieving a higher soluble chemical oxygen demand (sCOD) removal and faster ferrous (${\mathrm{Fe}}^{2+}$) oxidation. The addition of 0.10 mM potassium ferrate(VI) to the electrocoagulation cell operated for 45 min at a $22\mathrm{mA}/{\mathrm{cm}}^2$ current density and 15 mm interelectrode distance increased the sCOD removal efficiency from 39.71% to 63.57%. Moreover, the addition of 0.1 mM potassium ferrate(VI) to the previously stated electrocoagulation cell conditions decreased the percentage of ${\mathrm{Fe}}^{2+}$ to the electrochemically supplied total iron (${\mathrm{Fe}}_{\mathrm{t}}$) from 34.02% to 4.63%. The oxidation effect provided by the addition of potassium ferrate(VI) to the iron electrocoagulation cell increased the sCOD removal by about 10%. In addition, the pH increase that resulted from the dissociation of potassium ferrate(VI) promoted favorable conditions to quickly oxidize the ${\mathrm{Fe}}^{2+}$ ions generated at the iron anode to form the favorable $\mathrm{Fe}(\mathrm{OH}{)}_3$ precipitates. The experimental results clearly demonstrated the synergetic effect of the coupled processes for the removal of sCOD from bypass wastewater.

The adsorbent derived from the processing of green coconut husk (powder) was chemically treated with a primary amine to investigate its adsorption potential for metal ions, ${\mathrm{Cu}}^{2+}$ and ${\mathrm{Cd}}^{2+}$, present in an aqueous solution. The treatment of the adsorbent was carried out using monoethanolamine impregnation with a mass ratio of $1:1$. The adsorbent was characterized before and after treatment as well as after the monocomponent adsorption ions ${\mathrm{Cu}}^{2+}$ and ${\mathrm{Cd}}^{2+}$ by Fourier transform infrared (FTIR) spectroscopy, thermogravimetry/differential thermal analyzer (TGA/DTA), specific surface area, volume, and pore size. The kinetic models’ pseudo-first-order, pseudo-second-order, and intraparticle diffusion were tested. The adsorption rate did not change after treatment; however, a greater adsorption capacity was observed for the treated adsorbent, i.e., the amine compounds in coconut husk powder favored its adsorption capacity. The interaction mechanism between the functional groups of the adsorbent and ${\mathrm{Cu}}^{2+}$ and ${\mathrm{Cd}}^{2+}$ ions was investigated by adjusting the experimental data from the adsorption equilibrium studied to other theoretical models. Through the thermodynamic study, it was observed that the monocomponent adsorption of ${\mathrm{Cu}}^{2+}$ by the coconut husk powder treated with amine is endothermic and has a chemical mechanism, while the untreated material is exothermic and has a physical mechanism. ${\mathrm{Cd}}^{2+}$ adsorption, in turn, has a physical mechanism for both coconut shell powder samples (CP and CPA). The chemical treatment by impregnation of monoethanolamine improves adsorption capacity of coconut husk powder through the interaction between the functional groups present in the adsorbent and the metal ions ${\mathrm{Cu}}^{2+}$ and ${\mathrm{Cd}}^{2+}$.

To explore the bioaccumulation of the emerging contaminants in the freshwater bodies and food crops, and the possible implications, this study investigated the chromium-enriched industrial wastewater irrigation on Lablab purpureus with respect to the physical growth, photosynthetic pigments, proline content, and antioxidant defense responses. Chromium enrichment inhibited the elongation of roots and shoots by 68% and 76% respectively, as a function of chromium concentration. The total chlorophyll, chlorophyll-$a$, chlorophyll-$b$, and total carotenoids were severely retarded by 81%, 84%, 76%, and 63%, respectively, and excessive accumulation of proline was detected at 2.80 μmol/g fresh weight. The activities of ascorbate peroxidase, guaiacol peroxidase, and catalase were significantly altered, with a strong stimulation at the chromium concentration of 0.30 mM, predicting chromium-induced toxicity of the food crop. The findings provide insight into the interference of heavy metal–contaminated wastewater irrigation practice and its alarming implications for the sustainability of food safety, the dynamic equilibrium of ecosystems, and the water–food nexus.

The growing demand for organic products in the market promotes their use in various fields. One such products is biochar (BC). It was found that for climate change mitigation, biochar production from lignocellulosic biomass has more potential rather than biomass combustion for energy generation. Among the innovative environmental applications, biochar has potential as an adsorbent for retaining contaminants in environmental engineering and agrotechnical systems. Artificial modification of biochar can improve its adsorption capacity; however, indirect or natural change of biochar composition (e.g., contaminated biomass) based on syngenetic elements provides prospects for new applications of biochar as well as decreases the modification costs. The types of feedstock were lignin and wood of birch and pine trees growing in the area of aerogenic contamination and in the soil contaminated with potentially toxic elements. The temperatures of pyrolysis were 450°C and 700°C. The residence times of pyrolysis were 1, 2, and 4 h. The aim of this article is to evaluate the influence of the methods of modifying biochar syngenetically on its adsorptive properties. In the course of the study, it was found that the feedstock chemical composition mainly determined the composition of the biochar produced ($R=0.434–0.906$). It was found that the cation exchange capacity (CEC) of biochar had correlation with Pb, Cr, Ni, and Cd concentrations in biochar.

Micro and nano bubbles have increased water treatment efficiency in laboratory and field experiments due to the elevated pressure inside small bubbles and their large specific surface area, which enhance mass transfer into surrounding water. Existing theoretical studies are limited to size dynamics and stability of (mostly) single bubbles or transport of stable bubbles through porous media. We present a theoretical modeling approach combining bubble generation, stability, and treatment reaction mechanisms in batch reactors. We consider bubble dynamics as quasi-steady compared to other reaction time-scales involved. For a single treatment gas, we demonstrate two regimes (stable bubbles or not) in agreement with previous work. The critical transition point into the stable bubble regime is defined in terms of a minimum treatment substance concentration and minimum stable bubble radius. The results are discussed through hypothetical examples and further validated using existing ozone nanobubble batch experiment data for butylated hydroxytoluene (BHT) remediation.

A bench-scale biofiltration study was conducted to investigate the potential benefits of adjusting water pH and alkalinity as a simple water quality control on biofilter efficacy in terms of organic carbon removal, ammonia removal, and head loss development. Two biofilter columns were tested at pH values between 6.0 and 10.0 with low and high alkalinity levels of 25–50 and $180–220\mathrm{mg}{\mathrm{CaCO}}_3/\mathrm{L}$, respectively. Total organic carbon (TOC) removal was 67% at the lower pH range tested (6.0–7.5), and then decreased as the pH increased to an observed low of 31% removal at pH 10. Ammonia removal demonstrated the opposite trend, with a low of 13% removal at pH 6.0, 48% at pH 7.5, and greater than 90% at pH 9–10. An assessment of the available dissolved oxygen (DO) indicated it may have been a limiting factor in complete ammonia removal. Changes in alkalinity demonstrated a modest impact on biofilter activity, i.e., TOC, ammonia removals, and adenosine triphosphate (ATP) levels. Overall, pH 7.5 demonstrated an optimum condition for water quality and head loss control with 67% and 48% removal in terms of TOC and ammonia, respectively, and with the lowest head loss development.

This study is focused on a technologically viable and zero-energy green synthesis of zeolite Na-X by aging fly ash from lignite coal (CFA) in alkaline solutions at ambient conditions resembling a quasi-natural crystallization process. The smart utilization of CFA instead of its disposal will contribute to reducing landfill areas and to the recovery of polluted soils. The obtained coal ash zeolites were characterized by X-ray diffraction, scanning electron microscopy (SEM), and ${\mathrm{N}}_2$ physisorption regarding their phase composition morphology and surface properties, respectively. The highest yield of zeolite Na-X was achieved by incubating CFA in $1.5\mathrm{mol}/\mathrm{L}$ NaOH for 1 year. However, significant crystallization extent was established after 8 months of alkaline aging. Coal fly ash zeolites (CFAZs) obtained by atmospheric crystallization have specific surface values up to $280{\mathrm{m}}^2/\mathrm{g}$ CFAZ, which make them suitable amendments to uptake contaminants from polluted soils and ground waters. Examples on the retaining ability of CFAZ for methylene blue as a model dye and of ${\mathrm{Cd}}^{2+}$ ions were provided.

Fixed-bed column adsorption is an important operation for separation of gas mixtures and recovery of volatile organic compounds (VOCs). In industrial processes, the exothermal characteristic of adsorption could cause increasing of bed temperature, lead to bed combustion incidents and reduce adsorption capacity. In this work, the widely applied hypercrosslinked polymeric adsorbents (HPA) were chosen as adsorbent. The parameters [VOCs concentrations, flow rate, ratio of column height and diameter ($\mathit{H}\mathrm{/}\mathit{D}$), and temperature] that affect adsorption performance were analyzed and investigated in the dynamic adsorption of trichloroethylene (TCE). Under isothermal conditions, breakthrough adsorption capacities decreased with increasing of temperature and inlet flow rate. Ratio of $\mathit{H}\mathrm{/}\mathit{D}$ should be set above $2:1$. Dynamic adsorption rate increases with increase of TCE concentration and temperature, and decreases with the increase of flow rate and $\mathit{H}\mathrm{/}\mathit{D}$. Under near-adiabatic conditions, temperature in the column naturally increased, resulting in lower adsorption capacity and higher adsorption rate; in addition, the maximum temperature, which increased with TCE concentration, was approximate for different height measurements at central axial, but decreased for higher detected height at peripheral axial. Because of the thermal conductivity, the temperature was lower at peripheral axial than central axial. Finally, water vapor, used to regenerate the saturated bed, could help reduce the bed temperature and then slow the adsorption rate. However, water vapor was only advantageous for TCE adsorption at relative humidity lower than 50%. At higher relative humidity (80%), water molecules could occupy adsorption volume of TCE and reduce the adsorption capacity of TCE.

Wastewater treatment plants (WWTPs) have a significant role in urban system serviceability. Flooding can impact the performance of WWTPs by causing malfunction in its unit operations, which results in releasing partially treated or even untreated effluent into natural water bodies, causing environmental predicaments of significant proportions. In particular, the biological parameters could go through changes that need to be assessed and monitored in order to implement effective adaptation strategies. In this study, the uncertainty analysis and estimation of biological parameters of WWTP modeling under flood conditions is investigated by using Bayesian inference. In the first step, the proper prior distribution is fitted to the important parameters recognized by sensitivity analysis. Next, the effluent parameters in times of wet weather [five-day biochemical oxygen demand (${\mathrm{BOD}}_5$), total suspended solids (TSS), and ammonia and total nitrogen (TN)] are used as new data to update and estimate the value of the parameters. By using the Bayesian inference concept, the posterior distributions of parameters are obtained. Two types of likelihood functions are used: formal, derived from the stochastic error series, and informal, which uses predefined performance criteria to characterize the relationship between the observation and model output. Finally, Markov chain Monte Carlo (MCMC) methods are used to sample from the posterior distribution. Parameter posteriors are summarized using the posterior mean for parameter estimation (in wet weather) and coefficient of variation (CV) for degree of uncertainty. The results show that there are a number of parameters for which the value of CV drops significantly at the time of flood conditions. This means their uncertainty decreases, whereas for some other parameters, it is negligible. Moreover, by using the formal likelihood function, the parameters are pinpointed more precisely, and the range of parameters is narrowed up to 98%. The methodology developed in this study could be used to plan for effective simulation and monitoring of WWTPs in different geographic settings.

This paper presents an analytical study of mass transfer from a single bubble rising in stagnant water and its size variation. A model for bubble–water mass transfer was established and validated using the experimental measurements from a rising carbon dioxide bubble. The effects of bubble horizontal velocity, bubble release depth, initial bubble size, background dissolved gas concentration in the water, and bubble swarms on the bubble–water mass transfer were examined. The bubble size changed along the rising path in response to both the mass transfer and the local hydrostatic pressure, whereas their relative importance varied under different conditions. Compared with previous models, the proposed model improved the prediction accuracy by including the influence of changing dissolved gas concentration in the water and mass transfer across the water surface. The model is applicable for different gases and can be used in a wide range of engineering applications.

Recently, eco-efficiency and cost-effectiveness biosorbents have been a hot topic in the research fields of environmental engineering and material science. In this work, the modification of the two common yard wastes (elm branches and turfgrass) included a process where the waste was oven-dried at 90°C for 12 h, milled and sieved through 0.25 mm, and soaked in $1\mathrm{mol}·{\mathrm{L}}^{-1}$ sodium citrate with a mass ratio of $1:3$ for 24 h to hydrolyze protein. The adsorption potential of prepared biosorbents toward acid fuchsin (AF) were tested and compared with commercial activated carbon (AC). The effects of doses, pH, and initial concentration of AF were investigated and the appropriated parameters for adsorption were obtained. The adsorption thermodynamics and kinetics showed that the rates of adsorption by modified branches (MB) and modified turfgrass (MG) are rapid and efficient, superior to AC. The best adsorption parameters found in the experimental tests are as follows: pH 4, temperature 35°C, initial concentration of AF solution of $40\mathrm{mg}·{\mathrm{L}}^{-1}$, and modified biosorbents of $400\mathrm{mg}·{\mathrm{L}}^{-1}$. In practical application, pH 5 and a temperature of 25°C could hold promise to adsorb the dye. The MG and MB showed more pore and mesoporous structures than raw materials according to scanning electron microscope (SEM). In the processes of adsorption, AF mainly reacted with benzene ring skeleton, C─ C, heterocyclic compounds, ─ OH, ─ CH, C─ O, P─ C─ O, and Si═O. Fourier transform infrared spectrometry (FTIR) analysis indicates the peak area changes of MG and MB are consisting with the $Q_m$ calculated by Langmuir model due to the higher binding capacities of carboxyl and phenolic groups. The maximum sorption capacities ($Q_m$) of the both prepared biosorbents are above $142.76\mathrm{mg}·{\mathrm{g}}^{-1}$, presenting comparative adsorption capacities to the reported various patterns of biosorpents. This work prepared potential low-cost biosorbents with comparative sorption capacities by easy physical and chemical modification and provide an eco-efficiency and cost-effectiveness way to promote the sustainable management and the reuse of these city raw lignocellulosic waste.

An innovative single-cathode three-anode microbial fuel cell (SCTA-MFC) was constructed, using sodium acetate as the anode organic substrate and nitrate as the cathode electron acceptor. It was found that in the case of a closed circuit with chemical oxygen demand (COD) in the cathode, higher maximum power density (${\mathrm{PD}}_{\mathrm{M}}$, $642.51\mathrm{mW}·{\mathrm{m}}^{-3}$), COD, and nitrate removal efficiency (85.70%, 64.35%) could be obtained. The influence of initial organic concentration of the anode was investigated. When the concentration was about $600\mathrm{mg}·{\mathrm{L}}^{-1}$, removal efficiency of COD was 87.20%, maximum coulombic efficiency (${\mathrm{CE}}_{\mathrm{M}}$) in the anode was 3.42%, ${\mathrm{PD}}_{\mathrm{M}}$ was $795.70\mathrm{mW}·{\mathrm{m}}^{-3}$, and the nitrate removal efficiency and the ${\mathrm{CE}}_{\mathrm{M}}$ in the cathode were 75.52% and 99.50%, respectively. The presence of cathode organics can couple autotrophic and heterotrophic denitrification of SCTA-MFCs, and further enhance denitrification rates. An anode organic concentration of $600\mathrm{mg}·{\mathrm{L}}^{-1}$ is beneficial to electricity generation of SCTA-MFCs.

Carbon dioxide sequestration in unminable coal bed seams has been proposed as an option to mitigate the excessive emissions of carbon dioxide (${\mathrm{CO}}_2$) from burning fossil fuels (coal, crude oil fractions, and natural gas) and increase natural gas production. Through laboratory experiments on ${\mathrm{CO}}_2$ adsorption using a volumetric technique, the effects of subcritical ${\mathrm{CO}}_2$ on coal structure were studied to investigate any alteration of coal textural properties induced after ${\mathrm{CO}}_2$ exposure at low pressure. Coal samples were obtained from the Mukah-Balingian and Merit-Pila coal mines of Sarawak, Malaysia. Adsorption and desorption behaviors of ${\mathrm{CO}}_2$ on dry coals were investigated utilizing a volumetric technique at 273–318 K and pressures up to 99 kPa. Brunauer–Emmett–Teller (BET) surface areas for the adsorption isotherms of ${\mathrm{N}}_2$ at the temperature of 77 K and $P/P_o=0.1-0.3$ (where $P$ is equilibrium pressure and $P_o$ is the saturation vapor pressure of the adsorbate) were determined for the micropores present in the coal matrix. The results of ${\mathrm{N}}_2$ adsorption and desorption isotherms are found to be represented by the Type III equilibrium adsorption, showing a formation of the unlimited multilayer. The ${\mathrm{CO}}_2$ adsorption and desorption isotherms of the four coal samples were not identical. Thus, positive hysteresis was observed between adsorption and desorption of ${\mathrm{CO}}_2$ on all coal samples. The results showed that the ${\mathrm{CO}}_2$ adsorption capacity increases with increases in micropore surface area of the samples and pressure, and it is reduced by an increase in the temperature. Interestingly, meso- and micropore characteristics of the coal samples were only slightly altered after ${\mathrm{CO}}_2$ subcritical exposure. The Langmuir isotherm model presented the best fit with the experimental data. This confirms that the ${\mathrm{CO}}_2$ molecules occupied the surface of the coal sample uniformly and created a monolayer.

Ecological studies indicate that impervious cover (IC) greater than approximately 5%–20% may have adverse effects on receiving-stream ecology. It is difficult to separate the effects of runoff quality from other effects of urbanization on receiving streams. This study presents the results of a numerical experiment to assess the effects of increasing IC on water quality using the Stochastic Empirical Loading and Dilution Model (SELDM). Hydrologic and physiographic variables representative of southern New England were used to simulate receiving water quality in a basin with IC ranging from 0.1% to 30%. Simulation results mirror the results of ecological studies; event mean concentrations (EMCs) of total phosphorus (TP) increase proportionally to the logarithms of imperviousness for a given risk percentile. Simulation results indicated that commonly used stormwater treatment methods may be insufficient for mitigating the effects of imperviousness. Therefore, disconnection, rather than treatment, may be needed to protect water quality, and efforts to preserve undeveloped stream basins may be more effective than efforts to remediate conditions in highly developed basins. Results also indicate that commonly used water-quality criteria may be too restrictive for stormwater because TP EMCs frequently exceed these criteria, even in minimally developed basins.

This study detetmined optimal microwave irradiation (MI) conditions for removal of ammonia nitrogen (${\mathrm{NH}}_3\text{-}\mathrm{N}$) from swine wastewater. The wastewater was treated using a laboratory-scale industrial microwave unit (2,450-MHz frequency). The removal of ${\mathrm{NH}}_3\text{-}\mathrm{N}$ increased with the increase of pH (9.5–12.5), final temperature (FT) ($50°\mathrm{C}\le FT\le 100°\mathrm{C}$), and MI time (MIT) ($0\le MIT\le 140\min$). Compared with conventional heating (CH), MI removed more ${\mathrm{NH}}_3\text{-}\mathrm{N}$. The calculated ${\mathrm{NH}}_3\text{-}\mathrm{N}$ half-lives decreased as FT and pH increased. FT (80°C–100°C) and MIT (2.5–5.5 min) significantly affected the ${\mathrm{NH}}_3\text{-}\mathrm{N}$ removal. Within the design boundaries, optimal conditions for ${\mathrm{NH}}_3\text{-}\mathrm{N}$ removal (94.9%) were $FT=100°\mathrm{C}$, $MIT=5.5\min$, and pH 10. This work shows the potential of MI as an effective method to reduce the ${\mathrm{NH}}_3\text{-}\mathrm{N}$ content in swine wastewater.

Graphene is an evolving class of carbon nanomaterials whose exceptional adsorption features toward organic compounds have not been well understood. In the current research, a modified Hummers’ technique was adopted to synthesize the graphene oxide nanosheets (GONS) from graphite to investigate its adsorption efficiency to remove methylene blue dye (MB) from aqueous solutions. Response surface methodology (RSM) was applied to optimize the removal parameters, namely, pH, contact time, and adsorbent dosage. The as-synthesized GONS displayed 98.8% removal efficiency, the kinetics data were described properly by the pseudosecond-order model, and the maximum adsorptive uptake suggested by the Langmuir model was $270{\mathrm{mg}\mathrm{g}}^1$. Unlike most previous works, which reported that the MB adsorption onto graphene oxide occurs in monolayers, in this study, the equilibrium data were best fitted to the Temkin model. It was proposed that the $\pi \text{-}\pi$ electron donor-acceptor mechanism and the electrostatic interactions play an important role in the adsorption process. The results suggest that the GONS is a good candidate to be synthesized on a large scale for potential application in dye-bearing wastewater treatment.

Volatile fatty acids (VFA) may serve as building blocks for the production of chemicals and polymers. A technology enabling high-rate VFA production from carbohydrate-rich wastewater is the anaerobic granular sludge process. In this study, the characteristics of an anaerobic granular sludge process fermenting glucose was evaluated at different solid retention times (SRT). A lab-scale anaerobic sequencing batch reactor fed with $6\mathrm{g}·{\mathrm{L}}^{-1}$ glucose was operated at a pH of 5.5 and at SRT values of 1–2, 10–20, and 40–50 days and operated in total for 215 days. A low sludge volume index (SVI) of $\mathrm{1,144}\mathrm{mL}·{\mathrm{gTSS}}^{-1}$ allowed for the high SRT and high volatile suspended solid (VSS) concentration that reached $59\mathrm{gVSS}·{\mathrm{L}}^{-1}$. This high VSS concentration enabled a glucose consumption rate of $\mathrm{1,100}\mathrm{gCOD}·{\mathrm{L}}^{-1}·{\mathrm{day}}^{-1}$ at an SRT of 40–50 days. Two product spectra were obtained: (1) a propionate:acetate mixture with a ratio of $2.05:1$ (${\mathrm{mol}}_{\mathrm{propionate}}:{\mathrm{mol}}_{\mathrm{acetate}}$) produced at an SRT of 40–50 days; and (2) an acetate dominated product spectrum was obtained at 1–2 days and 10–20 days SRT (0.71–0.75 ${\mathrm{mol}}_{\mathrm{acetate}}·{\mathrm{mol}}_{\mathrm{VFA}}^{-1}$). Overall, a high VFA yield between 0.77 and 0.79 was obtained throughout all enrichments. This work demonstrates that high-rate VFA production combining high yields and low solid concentrations in the effluent technologically can be achieved. This work contributes to the implementation of waste-based production of VFA using anaerobic granular sludge.

A parsimonious nutrient-periphyton model quantifying uptake and recycling below a steady nutrient point source was tested in a shallow, stony-bed river during summer low flow. Close to the source DIN and DRP concentrations decreased linearly with distance, the DIN:DRP uptake ratio was constant (although twice the Redfield ratio), and rates of photosynthesis and algal biomass were high—consistent with model predictions. Further downstream, DIN concentrations were near the detection limit (but DRP was measurable), and rates of photosynthesis and algal biomass were low—also consistent with model predictions. However, two model features were not supported by observations. First, concentrations of organic N and P remained constant, whereas the model predicts increasing concentrations. Second, observations showed that N and P recycling were decoupled, whereas the model assumes close coupling. Although the model was reliable close to the source, it over-simplified recycling in the test stream. The model could be improved by separating dissolved from particulate organics and including recycling from settled particulates and pH-mediated P release from sediment, although this would increase complexity and reduce parsimony.