Salt-Induced Recovery of Volatile Organic Acids Using Non-Ionic Surfactants

Non-ionic surfactants are one of the most useful surfactants as they are the second largest group, produced by volume at about 35%. Due to their low toxicity, the demand for them is escalating due to an extensive use of these amphiphilic materials for an efficient, non-energy-requiring recovery of volatile organic acids (VOAs) from aqueous mixtures. This separation process is mainly due to the cloud point property of surfactants, which is referred to as the temperature of the system at which two phases are formed. One of the phases is micellar-rich and the other is micellar-poor. In these micelles, the surfactant molecules are oriented in such a way that the hydrophilic heads shield the hydrophobic tails from the other water molecules in the system. This assembly partitions the organic compounds within the interior of the micelles, which act as the pseudo-organic phase. This work elucidates how salting-out affects the cloud point of ethoxylated non-ionic surfactants, resulting in VOA separation. Studies suggest the sensitivity of the cloud point to the presence of electrolytes and its dependence on the parameters’ hydrophile–lipophile balance (HLB) and on the number of ethylene oxide (EON) units in the surfactant molecule. Electrolyte addition, in the form of salt, causes the dehydration of micelles as salt is a water-structure maker. The salt changes the solvent structure through aggregation and formation of larger micelles. This translates into a lipophilic shift, which reduces the cloud point and the surfactant’s HLB. As the HLB decreases, the more hydrophobic the surfactant becomes, resulting in better separation. The type of salt influences the characteristics of the interphase that separates the phases formed. Typically, polyvalent cations such as Al3+ and Ca2+ are more effective in decreasing the HLB than the monovalent cations (e.g., Na+ and K+) because of their higher surface charge densities. Since the surfactant’s HLB is dictated by its ethylene oxide component (i.e., HLB decreases with EON), it follows that non-ionic surfactants with a lower EON could achieve better separation in the presence of salt. Although the actual separation of VOAs could possibly be affected by other parameters (e.g., amount of added surfactant and salts and mass transfer rates), the response of surfactant’s properties (i.e., cloud point, HLB, and EON) to salt addition could be utilized to establish an enhanced VOAs extraction from aqueous systems

Adsorption kinetic modeling using pseudo-first order and pseudo-second order rate laws: A review

Adsorption for water and wastewater treatment has been the subject of many research in the scientific community, focusing mainly on either equilibrium or kinetic studies. Adsorption kinetics are commonly modeled using pseudo-first and pseudo-second order rate laws. Analyses of published works in the past two decades indicated that the pseudo-second order is considered to be the superior model as it can represent many adsorption systems. However, critical assessment of modeling techniques and practices suggests that its superiority could be a consequence of currently acceptable modeling norms which tend to favor the pseudo-second order model. The partiality was due to several modeling pitfalls that are often neglected. In addition, commonly used model validation tools are often used haphazardly and redundantly. As such, they cannot sufficiently provide any kind of certainty on the validity of a model. To eliminate modeling biasness, a new validation method was proposed and was then employed to re-examine previously published adsorption kinetic data

Using Self-Organizing Map Algorithm to Reveal Stabilities of Parameter Sensitivity Rankings in Microbial Kinetic Models: A Case for Microalgae

Microalgae are multi-purpose microbial agents due to their capability to efficiently sequester carbon dioxide and produce valuable biomass such as protein and single-cell oils. Formulation and tuning of microalgae kinetics models can significantly contribute to the successful design and operation of microalgae reactors. This work aimed to demonstrate the capability of self-organizing map (SOM) algorithm to elucidate the patterns of parameter rankings in microalgae models subject to stochastic variations of input forcing functions–bioprocess influent component concentration levels. These stochastic variations were implemented on a modeled chemostat with a deterministic microalgae kinetic model consists of ten time-dependent variables and eighteen model parameters. The methodology consists of two major stages: (1) global sensitivity analysis (GSA) on the importance of model parameters with stochastic sampling of bioreactor influent component concentrations, and (2) training of self-organizing maps on the datasets of model parameter rankings derived from the GSA indices. Results reveal that functional principal components analysis can project at least 99% of the time-dependent dynamic patterns of the model variables on B-splines basis functions. The component planes for hexagonal lattice SOMs reveal that the sensitivity rankings some parameters in the algae model tested can be stable over a wide range of variations in the levels of influent component concentrations. Therefore, SOM can be used to reveal the trends in multi-dimensional data arrays arising from the implementation of GSA of kinetic models under stochastic perturbation of input forcing functions

Evaluation of the Methane Production Potential of Catfish Processing Wastewater Using Various Anaerobic Digestion Strategies

The U.S. catfish industry is a major industry that has been declining over the years due to imports competition and growing operational costs. Catfish processing wastewater management and high energy requirement put a large financial burden on catfish processing facilities. Recovered protein-based solids have provided some value-added co-products, however, more co-products are needed to offset processing costs. Anaerobic digestion is a proven waste treatment method that produces methane, which is an energetic co-product that can be used within the processing facilities. This study was conducted to evaluate the potential of anaerobic digestion as an alternative to the currently used aerobic biotreatment of catfish processing wastewater. Initial assessments indicated the recalcitrance of the full-strength wastewater to anaerobic digestion, yielding only ~4 m3 per ton (U.S.) of input chemical oxygen demand (CODinput). Thus, several strategies were evaluated to improve the methane yield from the wastewater. These strategies include nutrient (nitrogen and sulfur) amendment, along with ozone, HCl, and NaOH pretreatment. The results showed that nutrient amendment was the most suitable strategy for improving the digestibility of the catfish processing wastewater. A methane yield of 121–236 m3/ton (U.S.) CODinput was obtained, with a purity of 67–80 vol.%. These results are similar to yields and purities of biogas from other feedstock, such as food waste, wastewater solids, and fish canning wastewater. This indicates that anaerobic digestion could be a viable alternative for simultaneous treatment and energetic co-product generation from catfish processing wastewater

The Potential of Non-Ionic Surfactants for Extraction of Lactic Acid from Aqueous Solution

Lactic acid, an important commodity chemical for various applications, is mainly produced through fermentation. In this study, the potential of non-ionic surfactants (an alcohol ethoxylate (AE) and two alcohol alkoxylates (AAs)) as solvents for the extraction of lactic acid from aqueous solutions is reported for the first time. Ternary mixtures containing lactic acid, water, and surfactants were prepared for the assessment. The results indicated that for all the systems, the water–surfactant binary pair exhibits partial immiscibility. Furthermore, the results suggested that with respect to the size of the two-phase region and stability of phases developed, the AE is the suitable solvent for the targeted extraction process. Thus, tie-lines for the system lactic acid + water + AE were then determined to establish the phase diagram of the system at 308.15 K. From the tie-lines, distribution coefficients and separation factors were estimated, which indicated that a compromise between the size and number of extraction units is necessary if AE is to be used as a solvent for lactic acid extraction. The extraction efficiency was estimated to be only about 37–48%. Nevertheless, the biodegradability and non-toxicity of AE makes it a viable solvent for the development of the extractive lactic acid fermentation process

Analysis of Methanotroph Populations from Various Sources for Production of High-Value Products

Methanotrophs are bacteria that can consume methane as their sole carbon and energy source to produce a wide variety of high-value products such as lipids, biopolymers, ectoine, and single cell proteins (SCPs). Collected samples from various sources were subjected to DNA extraction followed by 16S rRNA analysis to determine the identity and relative abundance of their microbial population. Several taxa of methanotrophs were detected in the samples including Type I (Methylobacter), Type X (Methylocaldum), Type II (Methylocystis, Methylosinus, and Beijerinckia), and Type III (Verrucomicrobium). This paper expounds the effects of environmental/cultivation conditions on the growth and population of different types of methanotrophs. The results could be used to systematically identify source(s) of natural consortia that can be enriched and developed to produce specific target product(s) under a given cultivation conditions/limitations

Analysis of Methanotroph Populations from Various Sources for Production of High-Value Products

Methanotrophs are bacteria that can consume methane as their sole carbon and energy source to produce a wide variety of high-value products such as lipids, biopolymers, ectoine, and single cell proteins (SCPs). Collected samples from various sources were subjected to DNA extraction followed by 16S rRNA analysis to determine the identity and relative abundance of their microbial population. Several taxa of methanotrophs were detected in the samples including Type I (Methylobacter), Type X (Methylocaldum), Type II (Methylocystis, Methylosinus, and Beijerinckia), and Type III (Verrucomicrobium). This paper expounds the effects of environmental/cultivation conditions on the growth and population of different types of methanotrophs. The results could be used to systematically identify source(s) of natural consortia that can be enriched and developed to produce specific target product(s) under a given cultivation conditions/limitations