Gene F. Parkin

Mineral requirements for methane fermentation

Mineral deficiency appears to pose a more critical problem in the anaerobic treatment process than in the aerobic treatment process. Furthermore, the methane fermentation step of anaerobic treatment appears to be the stage most sensitive to mineral deficiency. Commonly the mineral deficiency is a trace metal, and, since the fermentation step is the terminal stage in the treatment process, a build‐up of these reactants (mainly acetate, propionate, butyrate and hydrogen) can adversely affect the overall process. A review of the literature follows concerning the mineral requirements of methane fermentation in order to facilitate a proper understanding of the anaerobic process, especially in its application to treatment of industrial waste waters that are prone to be deficient in certain minerals. Types of limiting nutrients are considered with specific attention given to nitrogen, sulfur, phosphorus and the trace metals, and the physiological role and intracellular concentration of minerals is discussed. An ...

Characterization of soluble microbial products from anaerobic treatment by molecular weight distribution and nickel-chelating properties

Nine anaerobic chemostats fed glucose as the sole carbon and energy source were used to investigate the characteristics of soluble microbial products (SMP). These reactors were maintained at solids retention times (SRT) of 15, 25, and 40 days (3 reactors for each SRT) with organic loading rates of 0.25 or 0.50 g COD/1-d. Results showed that the concentration of SMP increased with increasing SRT (steady-state SMP for 15-, 25-, and 40-d systems were 54, 126, and 291 mg COD/1, respectively). Distribution of SMP among three molecular weight categories (MW 10,000) was bimodal. The fraction of SMP with MW > 10,000 was found to increase with increasing SRT (34 mg/l and 48% of total SMP for a 15-d SRT, 83 mg/l and 62% for a 25-d SRT, and 242 mg/l and 76% for a 40-d system). The stability constant (cK) between Ni and SMP was approximately 103.62, a value very similar to some naturally occurring organic acids. The total SMP-ligand concentration (CT,L) ranged from 0.07 to 1.33 mM as Ni and increased with increasing SRT. The complexation capacity ranged from 0.65 to 5.97 μmol of Ni/mg SMP, and was independent of SRT with an average of 2.49 μmol of Ni/mg SMP.

Nickel stimulation of anaerobic digestion

Abstract An acetate-enriched methanogenic culture was assayed for nutritional stimulation by nickel in combination with other inorganic and organic nutrients, i.e. iron, cobalt, yeast extract, riboflavin and vitamin B12. Acetate was automatically maintained at 2–3 g l−1 by a pH Stat system so that substrate was not limiting. In the absence of nickel, the specific acetate utilization rates were in the range of 2–4.6 g acetate g−1 VSS day−1. In the presence of nickel, this rate was as high as 10 and when both nickel and yeast extract were supplemented this rate temporarily increased to 12–15 g acetate g−1 VSS day−1 . The maximum acetate utilization rate was observed to be 51 g l−1 day−1 as compared to 3.3 g l−1 day−1 for conventional high-rate digestion. Daily phosphate additions were required to sustain these high acetate utilization rates. An acetate utilization rate of 20–30 g l−1 day−1 was maintained for over 25 days. Microscopic examination of the culture revealed a predominance of a sarcina whenever stimulation was noted.

A comparison of the characteristics of soluble organic nitrogen in untreated and activated sludge treated wastewaters

Soluble organic materials containing nitrogen (SON) are present in effluents from activated sludge treatment of domestic wastewater, but little is known about the sources and characteristics of these materials. The objective of this research was to evaluate the characteristics of SON in untreated wastewaters and activated sludge effluents. Characterization techniques used included low microbial seed biodegradability, molecular weight distribution using gel filtration chromatography, removal by activated carbon and ion exchange, and analysis for free and combined amino acids. Activated sludge effluent SON was more refractory (40–50%; first-order decay rates for the remainder were about 0.014 day−1 than SON in untreated wastewater (18–38%; decay rates for the remainder were 0.08–0.16 day−1). SON produced biologically during treatment had decay rates (about 0.028 day−1) similar to SON in municipal activated sludge effluents, and was from 20 to 100% refractory. Less than 10% of the SON in municipal activated sludge effluent consisted of free or combined amino acids. Approximately 15–30% appeared to nucleic acid degradation products. Fifty to 60% of the SON and SCOD had apparent molecular weights of less than 1800. Apparent molecular weight distributions of treated and untreated wastewaters were similar; however, the excess SON produced during activated sludge start-up contained considerably more SON with molecular weights greater than 1800. The 165–340 molecular weight fraction had a significantly higher SON to SCOD ratio than any other fraction for all wastewaters examined. Activated carbon adsorption efficiently removed SON (72 ± 9%) and SCOD (78 ± 6%) from treated and untreated wastewaters, and from biologically produced organics. Significantly more SON was removed by cationic exchange at pH 2.0 (33–56%) than by anionic exchange at pH 9.5 (10–24%) for all wastewaters tested. Cationic exchange at pH 2.0 selectively removed more biologically produced SON relative to SCOD.

Tailored Synthesis of Photoactive TiO2 Nanofibers and Au/TiO2 Nanofiber Composites: Structure and Reactivity Optimization for Water Treatment Applications

Titanium dioxide (TiO2) nanofibers with tailored structure and composition were synthesized by electrospinning to optimize photocatalytic treatment efficiency. Nanofibers of controlled diameter (30-210 nm), crystal structure (anatase, rutile, mixed phases), and grain size (20-50 nm) were developed along with composite nanofibers with either surface-deposited or bulk-integrated Au nanoparticle cocatalysts. Their reactivity was then examined in batch suspensions toward model (phenol) and emerging (pharmaceuticals, personal care products) pollutants across various water qualities. Optimized TiO2 nanofibers meet or exceed the performance of traditional nanoparticulate photocatalysts (e.g., Aeroxide P25) with the greatest reactivity enhancements arising from (i) decreasing diameter (i.e., increasing surface area), (ii) mixed phase composition [74/26 (±0.5) % anatase/rutile], and (iii) small amounts (1.5 wt %) of surface-deposited, more so than bulk-integrated, Au nanoparticles. Surface Au deposition consistently enhanced photoactivity by 5- to 10-fold across our micropollutant suite independent of their solution concentration, behavior that we attribute to higher photocatalytic efficiency from improved charge separation. However, the practical value of Au/TiO2 nanofibers was limited by their greater degree of inhibition by solution-phase radical scavengers and higher rate of reactivity loss from surface fouling in nonidealized matrixes (e.g., partially treated surface water). Ultimately, unmodified TiO2 nanofibers appear most promising for use as reactive filtration materials because their performance was less influenced by water quality, although future efforts must increase the strength of TiO2 nanofiber mats to realize such applications.

Isolation and characterization of autotrophic, hydrogen-utilizing, perchlorate-reducing bacteria

Recent studies have shown that perchlorate (ClO4−) can be degraded by some pure-culture and mixed-culture bacteria with the addition of hydrogen. This paper describes the isolation of two hydrogen-utilizing perchlorate-degrading bacteria capable of using inorganic carbon for growth. These autotrophic bacteria are within the genus Dechloromonas and are the first Dechloromonas species that are microaerophilic and incapable of growth at atmospheric oxygen concentrations. Dechloromonas sp. JDS5 and Dechloromonas sp. JDS6 are the first perchlorate-degrading autotrophs isolated from a perchlorate-contaminated site. Measured hydrogen thresholds were higher than for other environmentally significant, hydrogen-utilizing, anaerobic bacteria (e.g., halorespirers). The chlorite dismutase activity of these bacteria was greater for autotrophically grown cells than for cells grown heterotrophically on lactate. These bacteria used fumarate as an alternate electron acceptor, which is the first report of growth on an organic electron acceptor by perchlorate-reducing bacteria.

Inhibition of bacterial perchlorate reduction by zero-valent iron

Perchlorate was reduced by a mixed bacterial culture over a pH range of 7.0–8.9. Similar rates of perchlorate reduction were observed between pH 7.0 and 8.5, whereas significantly slower reduction occurred at pH 8.9. Addition of iron metal, Fe(0), to the mixed bacterial culture resulted in slower rates of perchlorate reduction. Negligible perchlorate reduction was observed under abiotic conditions with Fe(0) alone in a reduced anaerobic medium. The inhibition of perchlorate reduction observed in the presence of Fe(0) is in contrast to previous studies that have shown faster rates of contaminant reduction when bacteria and Fe(0) were combined compared to bacteria alone. The addition of Fe(0) resulted in a rise in pH, as well as precipitation of Fe minerals that appeared to encapsulate the bacterial cells. In experiments where pH was kept constant, the addition of Fe(0) still resulted in slower rates of perchlorate reduction suggesting that encapsulation of bacteria by Fe precipitates contributed to the inhibition of the bacterial activity independent of the effect of pH on bacteria. These results provide the first evidence linking accumulation of iron precipitates at the cell surface to inhibition of environmental contaminant degradation. Fe(0) was not a suitable amendment to stimulate perchlorate-degrading bacteria and the bacterial inhibition caused by precipitation of reduced Fe species may be important in other combined anaerobic bacterial–Fe(0) systems. Furthermore, the inhibition of bacterial activity by iron precipitation may have significant implications for the design of in situ bioremediation technologies for treatment of perchlorate plumes.

THE RESPONSE OF METHANE FERMENTATION TO CYANIDE AND CHLOROFORM

The anaerobic digestion process has excellent potential for the treatment of warm industrial wastewaters. However this process is generally considered to be especially sensitive to many toxicants which occur occasionally or chronically in industrial wastewaters. Cyanide and chloroform were selected as sample toxicants which show inhibition of methane production at concentrations less than 1 mg/1. This study was directed toward an evaluation of the inhibition pattern of these two toxicants. The effect of toxicant concentration on methane production recovery pattern was determined. Suspended growth systems were used to study toxicity acclimation characteristics and recovery patterns. These systems demonstrated that the methanogens can acclimate and recover from cyanide and chloroform concentrations which were heretofore considered lethal. Prolonged periods of no methane production were not indicative of ultimate process failure. Anaerobic filters metabolizing acetate were fed gradually increasing concentrations of cyanide and chloroform to establish the maximum concentration which could be tolerated without inhibiting methane production. With acclimation, the anaerobic filters could tolerate 20 to 40 mg/1 of cyanide and chloroform without inhibition of methane production. One day slug doses of 750 mg/1 cyanide and 200 mg/1 of chloroform were administered to acclimated anaerobic filters of one day hydraulic detention time. Severe inhibition of methane production would result the following day, but complete recovery of methane production would be observed four days later. In summary, even though cyanide and chloroform show extreme toxicity to unacclimated methanogens, with proper attention paid to solids retention time and acclimation rate, the toxicity tolerance could be increased 50 fold.

Influence of Chloride and Fe(II) Content on the Reduction of Hg(II) by Magnetite

Abiotic reduction of inorganic mercury by natural organic matter and native soils is well-known, and recently there is evidence that reduced iron (Fe) species, such as magnetite, green rust, and Fe sulfides, can also reduce Hg(II). Here, we evaluated the reduction of Hg(II) by magnetites with varying Fe(II) content in both the absence and presence of chloride. Specifically, we evaluated whether magnetite stoichiometry (x = Fe(II)/Fe(III)) influences the rate of Hg(II) reduction and formation of products. In the absence of chloride, reduction of Hg(II) to Hg(0) is observed over a range of magnetite stoichiometries (0.29 < x < 0.50) in purged headspace reactors and unpurged low headspace reactors, as evidenced by Hg recovery in a volatile product trap solution and Hg L(III)-edge X-ray absorption near edge spectroscopy (XANES). In the presence of chloride, however, XANES spectra indicate the formation of a metastable Hg(I) calomel species (Hg2Cl2) from the reduction of Hg(II). Interestingly, Hg(I) species are only observed for the more oxidized magnetite particles that contain lower Fe(II) content (x < 0.42). For the more reduced magnetite particles (x ≥ 0.42), Hg(II) is reduced to Hg(0) even in the presence of high chloride concentrations. As previously observed for nitroaromatic compounds and uranium, magnetite stoichiometry appears to influence the rate of Hg(II) reduction (both in the presence and absence of chloride) confirming that it is important to consider magnetite stoichiometry when assessing the fate of contaminants in Fe-rich subsurface environments.

Product distribution during transformation of multiple contaminants by a high-rate, tetrachlorethene-dechlorinating enrichment culture.

Radiolabeled tetrachloroethene (PCE) and carbon tetrachloride (CT) were added to batch systems containing a lactate-enrichment culture displaying apparent dehalorespiration abilities to analyze the influence of mixtures on product distribution. Both CT and PCE were readily dechlorinated, although significant carbon disulfide (CS2) formation was observed during CT transformation. Calculated 1,2-14C-PCE recoveries for biotic treatments were between 91 and 104%, but an inability to recover products such as CS2 led to lower recoveries of 14C-CT (55 to 62%). While the majority of activity in 14C-CT-spiked treatments was recovered in the volatile fraction, 14CO2 increased significantly over time. 1,2-14C-PCE was primarily recovered in volatile and non-strippable fractions, but a significant increase in 14CO2 relative to cell-free controls suggested that the presence of a non-specific dechlorination pathway complementing dehalorespiration. The addition of both CT and PCE inhibited the transformation of the individual compounds and reduced the percentages recovered as 14CO2. However, the magnitude of these reductions was not severe and appeared to be the result of slower overall transformation rather than a complete inhibition of mineralization pathways.