Cady R. Engler

Effects of ammonia nitrogen on H2 and CH4 production during anaerobic digestion of dairy cattle manure

A number of researchers have verified the inhibitory effects of elevated H2 concentrations on various anaerobic fermentation processes. The objective of this work was to investigate the potential for using hydrogen gas production to predict upsets in anaerobic digesters operating on dairy cattle manure. In an ammonia nitrogen overload experiment, urea was added to the experimental digesters to obtain increased ammonia concentrations (600, 1,500, or 3,000 mg N/l). An increase in urea concentration resulted in an initial cessation of H2 production followed by an increase in H2 formation. Additions of 600, 1,500, or 3,000 mg N/l initially resulted in the reduction of biogas H2 concentrations. After 24 h, the H2 concentration increased in the 600 and 1,500 mg N/l digesters, but production remained inhibited in the 3,000 mg N/l digesters. Both methane and total biogas production decreased following urea addition. Volatile solids reduction also decreased during these periods. The digester effluent pH and alkalinity increased due to the increased NH4 formed with added urea. Based on these results, changes in H2 concentration could be a useful parameter for monitoring changes due to increased NH3 in dairy cattle manure anaerobic digesters.

Biodegradation of coumaphos, chlorferon, and diethylthiophosphate using bacteria immobilized in Ca-alginate gel beads.

Calcium-alginate immobilized cell systems were developed for the detoxification and biodegradation of coumaphos, an organophosphate insecticide, and its hydrolysis products, chlorferon and diethlythiophosphate (DETP). Optimum bead loadings for bioreactor operation were found to be 200 g-beads/L for chlorferon degradation and 300 g-beads/L for DETP degradation. Using waste cattle dip (UCD) solution as substrate, the degradation rate for an immobilized consortium of chlorferon-degrading bacteria was five times greater than that for freely suspended cells, and hydrolysis of coumaphos by immobilized OPH(+)Escherichia coli was 2.5 times greater. The enhanced degradation of immobilized cells was due primarily to protection of the cells from inhibitory substances present in the UCD solution. In addition, physiological changes of the cells caused by Ca-alginate immobilization may have contributed to increased reaction rates. Degradation rates for repeated operations increased for successive batches indicating that cells became better adapted to the reaction conditions over time.

Attached-film media performance in psychrophilic anaerobic treatment of dairy cattle wastewater

Retention of microorganisms in anaerobic digesters by providing an attachment medium can potentially increase their productivity at lower operating temperatures. The objective of this work was to investigate the effectiveness of attached-film bioreactors for psychrophilic anaerobic digestion of dairy manure. Eight digesters were maintained in an environmental chamber, with the temperature varied between 37 and 10°C. Two digesters were packed with limestone gravel, two with pieces cut from non-woven polyester matting, two with a combination of limestone gravel and polyester pieces, and two had no packing. Digester operation was initiated at a temperature of 37°C. After the digesters reached stable operation at the initial temperature, the temperature was lowered slowly to 10°C. The temperature was held at 10°C for 5 weeks after stabilizing. The polyester medium with its high porosity and surface to volume ratio had the best overall performance for methane productivity at both 37 and 10°C. The biogas production (ml/d) and methane production (ml/d) were significantly higher for the polyester medium when compared to the limestone and combination media reactors (p < 0.0001 and 0.0002, respectively). At 10°C, the polyester medium reactors performed significantly better than all others for biogas (ml/d) and methane (ml/d) production (p < 0.0001). The polyester medium also yielded the maximum reductions in volatile solids (VS) and chemical oxygen demand (COD) at 37°C.

Feedstock storage, handling and processing

Abstract This paper is a review of the technology and research covering components of a methane from biomass system between the field and the digester. It deals primarily with sorghum as a feedstock and focuses on research conducted by the Texas Agricultural Experiment Station. Subjects included in this paper are harvesting, hay storage, ensiling, materials handling, pumping and hydraulic characteristics, hydraulic conductivity, pressure/density relationship, and biological pretreatment. This paper is not a comprehensive design manual; however, design equations and coefficients for sorghum are presented, where available, along with references describing the development and application of design models.

Enhanced‐Rate Biodegradation of Organophosphate Neurotoxins by Immobilized Nongrowing Bacteria

Pesticide wastes generated from livestock dipping operations containing the organophosphate (OP) insecticide coumaphos (CP) are well suited for disposal by biodegradation since they are highly concentrated (∼1 g/L), generally contained, and lack additional toxic components. In this study, a significantly enhanced efficiency of degrading CP in cattle dip waste (CDW) is reported using a dense, nongrowing cell population that functions without the addition of nutrients required for growing cell cultures. A recombinant strain of Escherichia coli containing the opd gene for organophosphate hydrolase (OPH), which is capable of active hydrolysis of OP neurotoxins including CP, was cultivated in a rich medium containing all essential nutrients. Cells were harvested and utilized in lab scale experiments in the form of either freely suspended cells or cells immobilized within a macroporous gel matrix, poly(vinyl alcohol) (PVA) cryogel. Significantly higher degradation rates were achieved with either suspended or immobilized OPH+ cells compared to rates with the microbial consortium naturally present in CDW. Of the two nongrowing cell systems, the detoxification rate with immobilized cells was approximately twice that of freely suspended cells, and kinetic studies demonstrated that a higher maximum reaction rate was achieved with the immobilized cell system. A comparative study using both the CDW and pure CP substrates with free cells indicated that the CDW contained one or more factors that reduced the bioavailability of CP. The immobilized cells retained their activity over a 4‐month period of use and storage, demonstrating both sustained catalytic activity and long‐term mechanical stability.

Volatile fatty acid fermentation of AFEX-treated bagasse and newspaper by rumen microorganisms

Abstract The anaerobic digestion of bagasse and newspaper by rumen microorganisms was studied. A one-half replicate of a 25 factorial design was used to evaluate the effect of type of substrate (bagasse and newspaper), AFEX (Ammonia Fiber Explosion) pretreatment, liquid residence time (LRT), solid/liquid residence time ratio (SRT/LRT), and loading rate (LR) on volatile fatty acid (VFA) yield, productivity, and acid composition. A fermentor for the continuous culture of rumen microorganisms, which allows solids to be retained longer than liquid (SRT/LRT> 1), was used. Yields averaged 8.8 mmoles and 5.8 mmoles VFA per g volatile solids (VS) in bagasse and newspaper fermentations, respectively. The propionic acid molar percent was 52% higher in bagasse fermentation (19%) than in newspaper fermentation (12.5%). AFEX pretreatment increased VFA yield by 21% and decreased propionic acid molar percent by 9.1 %. The best reactor performance (i.e., high VFA yield and high VFA productivity) was achieved with AFEX-treated material at a LR of 14.1 g substrate per 1 day, LRT of 11 h, and SRT of 44 h. At these experimental conditions, productivity and yield were 163 mmoles VFA per 1 per day and 0.64 g VFA/g VS in bagasse fermentation, and 81 mmoles per 1 per day and 0.31 g VFA/g VS in newspaper fermentation. The rumen fermentation product yields are significantly higher than the sugar yields from extracellular cellulase/hemicellulase. A promising application of the rumen fermentation is to produce mixed VFA calcium salts which may be used to remove sulfur from coal-fired boilers. It is estimated that these salts may be produced from municipal solid waste for

A logistic model of subsurface fungal growth with application to bioremediation

119–137/tonne.

Process modelling considerations for the production of lactate from whey using membrane recycle bioreactors operated in continuous and cyclic batch modes

Abstract The goal of this research was to determine the potential of the fungal sterol ergosterol as an indicator of fungal biomass and to determine the growth response of the transformed strain of T. virens (GvT6) to added substrate and changes in temperature. Experiments in liquid culture and agar plates containing a rich medium of glucose, yeast extract, and casein (GYEC), or a soil extract medium supplemented with maltose (SE) showed that the ergosterol content of GvT6 was greatest when grown on GYEC agar plates (14.02 mg/g dry biomass). For both media, plate cultures produced higher specific ergosterol values than liquid cultures. Changes in specific ergosterol values over time were generally not significant. A value of 5.41 mg ergosterol / g dry biomass, determined for SE plate cultures, was used to convert ergosterol values to biomass values in growth experiments in soil bioreactors. Data from experiments in soil bioreactors treated with different levels of substrate (0.5–8 mg maltose / g dry soil) at three different temperatures (22, 27, 32°C) showed subsurface growth of GvT6 can be described by the logistic equation. Culture conditions of 32°C and 8 mg/g substrate produced the highest levels of biomass, but growth at 32°C and 4 mg/g substrate was somewhat faster than at the higher substrate level.

Low temperature anaerobic digestion response to organic loading rate and bioaugmentation

Abstract Using a membrane recycle bioreactor (MRB) to produce lactate from whey is potentially more cost effective than a traditional batch fermentation. Membrane recycle bioreactors can be operated in two modes: (1) cyclic batch; (2) continuous. Mathematical modelling of these two modes along with a batch fermentation is used to compare cost and reactor productivity and to examine the effects of selected process and kinetic parameters. Both modes have an optimum operating cell concentration, because there exists an economic trade-off between reactor vessel cost and membrane filtration cost with cell concentration as an optimization variable. The continuous mode is much more sensitive than the cyclic batch to the value of desired residual lactose concentration leaving the reactor, such that, for given kinetic parameters, there exists a value of residual lactose concentration below which the cyclic batch mode becomes more cost effective than the continuous mode. The big disadvantage of cyclic batch is that it is highly sensitive to any cell growth lag time between cycles.

Biodegradation of Hazardous Compounds Using Immobilized Microorganisms

Abstract Experiments were conducted to determine the influence of organic loading rate (OLR) and Yucca schidigera extract bioaugmentation on the performance of attached‐film anaerobic digesters under low temperature conditions (10°C). The digesters were packed with layered media (polyester above limestone). Digester performance was evaluated with respect to biogas production, methane production, and methane yield based on volatile solids added. Methane yield increased as OLR was reduced, apparently because of continued digestion of solids that had accumulated at the higher OLRs. After the OLR was reduced to its lowest value (0.01 kg VS/m3.d), yield began decreasing as stable operation was approached. Bioaugmentation appeared to improve methane production in a digester operated under stress (10°C and a very low OLR of 0.01 kg VS/m3.d).