SBR Treatment of High COD Effluent from Bottling Plant

The feasibility of bench scale sequencing batch reactors (SBRs) in treating a bottling plant effluent is demonstrated at various influent chemical oxygen demands (CODs) ranging from 300 to over 4,000 mg∕L. The SBRs removed over 75% of the biodegradable fraction of the influent COD at a fixed react time of 5.5 h. An easy to use process model is presented to predict the temporal variations of substrate, biomass, and dissolved oxygen concentrations during the fill and react periods in SBRs. The model satisfactorily predicted effluent COD and final biomass concentrations, as well as temporal variations of COD, biomass, and dissolved oxygen throughout the fill and react cycles.     

Fermentative biohydrogen production II: Net energy gain from organic wastes

Several reports have demonstrated the feasibility of hydrogen production by dark fermentation (DF). However, most reports had resorted to mesophilic or thermophilic conditions to increase hydrogen yield, overlooking the energy input to the process and hence, loss of net energy gain. For net positive energy gain, energy input to the process should be minimized and additional energy should be harvested from the aqueous end products of DF. Our previous study presented an approach to assess the potential for net energy gain from the hydrogen produced by DF, and from the end products of DF via anaerobic digestion (AD) or microbial fuel cells (MFC). In this study, that approach is extended to identify the most promising process configuration and operating conditions to maximize net energy gain possible from liquid and particulate organic wastes. Based on this analysis, DF followed by MFC appears to result in higher net energy gains.     

Fermentative biohydrogen production: Evaluation of net energy gain

Most dark fermentation (DF) studies had resorted to above-ambient temperatures to maximize hydrogen yield, without due consideration of the net energy gain. In this study, literature data on fermentative hydrogen production from glucose, sucrose, and organic wastes were compiled to evaluate the benefit of higher fermentation temperatures in terms of net energy gain. This evaluation showed that the improvement in hydrogen yield at higher temperatures is not justified as the net energy gain not only declined with increase of temperature, but also was mostly negative when the fermentation temperature exceeded 25 °C. To maximize the net energy gain of DF, the following two options for recovering additional energy from the end products and to determine the optimal fermentation temperature were evaluated: methane production via anaerobic digestion (AD); and direct electricity production via microbial fuel cells (MFC). Based on net energy gain, it is concluded that DF has to be operated at near-ambient temperatures for the net energy gain to be positive; and DF + MFC can result in higher net energy gain at any temperature than DF or DF + AD.     

Modeling fermentative hydrogen production from sucrose supplemented with dairy manure

Our previous studies had shown that fermentative hydrogen production from sucrose could be improved with dairy manure as a supplement. In addition to contributing to nearly 10% more hydrogen yield at ambient temperature, dairy manure was shown to be capable of providing the required nutritional needs, buffering capacity, and hydrogen-producing organisms, improving the practical viability of fermentative hydrogen production. In this report, we present a kinetic model for fermentative hydrogen production from sucrose supplemented with dairy manure. This model includes hydrogen production from sucrose as well as from the soluble products hydrolyzed from particulate manure. The integrated model was calibrated using experimental data from one batch reactor and validated with dissolved COD, hydrogen, and volatile fatty acid data from four other reactors. Predictions by this model agreed well with the temporal trends in the experimental data, with r² averaging 0.85 for dissolved COD; 0.94 for total COD; 0.84 for hydrogen; 0.84 for acetic acid; and 0.89 for butyric acid; quality of fit in the case of propionic acid was lower with r² averaging 0.57.     

Dark and acidic conditions for fermentative hydrogen production

Bacterial consortium capable of producing hydrogen in low pH (LpH) range of 3.3–4.3 is reported in this study. This operational pH is two full units below that of previously reported hydrogen producing organisms. Low pH inocula were derived from a batch biohydrogen reactor inoculated with heat treated compost (∼120 °C, 2 h), which was allowed to accumulate biogas to reach three atmospheres of equivalent headspace pressure and system pH of 3.0. Acclimation effect had positive influence on H₂ production and LpH inocula were passed sequentially into more than 15 generations to achieve consistent conversion efficiency and hydrogen composition, further tested in 23 other culture cycles. With hydrogen composition in the headspace ranging from 50% to 60%, conversion efficiency of ∼43% achieved in LpH systems is comparable to that of other buffered systems. Feasibility of hydrogen production in LpH systems is demonstrated in unbuffered reactors under intermittent pressure release conditions and in absence of initial pH adjustment and stirring. Conversion efficiencies, however, decreased by ∼1-fold for each 3 °C drop below the optimum temperature of 22 °C.     

Feasibility of biohydrogen production at low temperatures in unbuffered reactors

Feasibility of biohydrogen production by dark fermentation at two temperatures (22 °C and 37 °C) in unbuffered batch reactors was evaluated using heat-treated compost as inocula and sucrose as substrate, without any initial pH adjustment or inorganic nutrient supplements. Gas production was quantified by two different pressure release methods – intermittent pressure release (IPR) and continuous pressure release (CPR). Hydrogen production (47.2 mL/g COD/L) and sucrose-to-hydrogen conversion efficiency (53%) were both found to be highest at the lower temperature and IPR conditions. Hydrogen production was higher at the lower temperature irrespective of the pressure release condition. The high yield of 4.3 mol of hydrogen/mole of sucrose obtained in this study under IPR conditions at 22 °C is equivalent to or better than the literature values reported for buffered reactors. Even though literature reports have implied potential inhibition of hydrogen production at high hydrogen partial pressures resulting from IPR conditions, our results did not show any negative effects at hydrogen partial pressures exceeding 5.0 × 10⁴ Pa. While our findings are contrary to literature reports, they make a strong case for cost-effective hydrogen production by dark fermentation.     

Modeling dark fermentation for biohydrogen production: ADM1-based model vs. Gompertz model

Biohydrogen production by dark fermentation in batch reactors was modeled using the Gompertz equation and a model based on Anaerobic Digestion Model (ADM1). The ADM1 framework, which has been well accepted for modeling methane production by anaerobic digestion, was modified in this study for modeling hydrogen production. Experimental hydrogen production data from eight reactor configurations varying in pressure conditions, temperature, type and concentration of substrate, inocula source, and stirring conditions were used to evaluate the predictive abilities of the two modeling approaches. Although the quality of fit between the measured and fitted hydrogen evolution by the Gompertz equation was high in all the eight reactor configurations with r² ∼0.98, each configuration required a different set of model parameters, negating its utility as a general approach to predict hydrogen evolution. On the other hand, the ADM1-based model (ADM1BM) with predefined parameters was able to predict COD, cumulative hydrogen production, as well as volatile fatty acids production, albeit at a slightly lower quality of fit. Agreement between the experimental temporal hydrogen evolution data and the ADM1BM predictions was statistically significant with r² > 0.91 and p-value <1E-04. Sensitivity analysis of the validated model revealed that hydrogen production was sensitive to only six parameters in the ADM1BM.     

Use of Computerized Dynamic Assessment to Improve Student Achievement: Case Study

Recent studies have reported on the benefits of dynamic assessment (DA) in improving student learning and achievement through diagnostic monitoring of student misunderstandings, providing context-specific feedback, and assessing the improvement thereafter. Following these reports, a computer-based DA system has been developed by us for use in an undergraduate hydraulic engineering course. This case study presents data collected before and after implementation of this DA system that shows improvement in student performance. In this study, student performance is quantified by the percent of questions correctly answered in the fundamentals of engineering (FE) exam relative to the national average. Since implementation of the DA system in 2004, this measure for our students has increased from below national level [mean = 0.942; SD = 0.068] in nine administrations of the FE exam, to above national level (mean = 1.068; SD = 0.028) in the last five administrations. Based on this measure, performance of these students in fluid mechanics has been higher than that in the other subjects where DA was not used (mean = 1.068; SD = 0.028 versus mean = 0.854; SD = 0.029). Performance of our students in fluid mechanics has also been higher than that of their peers in the Carnegie top tier programs (mean = 1.068; SD = 0.028 versus mean = 1.022; SD = 0.020).     

Anaerobic fermentation of cattle manure: modeling of hydrolysis and acidogenesis

A mathematical model for the hydrolysis and acidogenesis reactions in anaerobic digestion of cattle manure is presented. This model is based on the premise that particulate hydrolysable fraction of cattle manure is composed of cellulose and hemicellulose that are hydrolyzed at different rates according to a surface-limiting reaction; and, that the respective soluble products of hydrolysis are utilized by acidogens at different rates, according to a two-substrate, single-biomass model. Batch experimental results were used to identify the sensitive parameters and to calibrate and validate the model. Results predicted by the model agreed well with the experimentally measured data not used in the calibration process, with correlation coefficient exceeding 0.91. These results indicate that the most significant parameter in the hydrolysis-acidogenesis phase is the hydrolysis rate constant for the cellulose fraction.