Batch Bioassays Research Articles

Impacts of crude glycerol on anaerobic ammonium oxidation (Anammox) process in wastewater treatment

This work investigated the impact of a waste-derived carbon source, crude glycerol (CG), on Anammox. Batch bioassays were conducted to identify inhibitory component(s) in CG, and the relationship between Anammox activity and the concentration of CG, pure glycerol, and methanol were assessed. The results showed that the half-maximal inhibitory concentration of CG and methanol are 434.5 ± 51.8 and 143.0 ± 19.6 mg chemical oxygen demand (COD) L-1, respectively, while pure glycerol at 0–2283 mg COD L-1 had no significant adverse effect on Anammox. The results suggested methanol is the major inhibitor in CG via a non-competitive inhibition mechanism. COD/total inorganic nitrogen ratio of > 1.3 was observed to cause a significant Anammox inhibition (>20 %), especially at low substrate level. These results are valuable for evaluating the feasibility of using CG for nitrogen removal in water resource recovery facilities, promoting sustainable development.

High-rate and -yield continuous fluidized-bed bioconversion of glucose-to-gluconic acid for enhanced metal leaching

Continuous low-cost bulk biolixiviant production remains as one of the main challenges of heterotrophic bioleaching towards large scale application. This study aimed at developing non-aseptic Gluconobacter oxydans-amended fluidized-bed reactor (FBR) process for continuous production of gluconic acid for efficient leaching of rare earth elements (REEs) and base metals from spent nickel-metal-hydride (NiMH) batteries. In preliminary experiments, the FBR became contaminated and massively overgrown by air-borne fungus, Leptobacillium leptobactrum. In a series of batch bioassays, operational conditions were investigated to discourage the fungal activity i.e., an ecologically engineered niche for gluconic acid production. High gluconate concentration (≥100 g/l) and/or low pH (≤2.5) gave a selective preference for G. oxydans growth over L. leptobactrum and controlled the activity of possible contaminants during FBR continuous operation. The highest gluconic acid production rate of 390 g/l∙d with corresponding glucose-to-gluconic acid conversion yield of 94% was obtained at hydraulic retention time (HRT) of 6.3 h and 380 g/l∙d glucose loading rate. Using the FBR effluents as leaching agents, respectively, total base metals and REEs leaching yields of up to 82% and 55% were achieved within 7 days at 1% (w/v) spent battery pulp density. The obtained glucose-to-gluconic acid conversion rates and yields were one of the highest reported for any glucose biotransformation process. The REE leaching yields were higher than those reported for similar high metal-grade REE secondary sources. The high-rate glucose-to-gluconic acid bioconversion in the non-aseptic system utilizing microbial ecology based FBR operation strategy rather than aseptic chemostats indicates industrial feasibility of gluconic acid production and thus, the applicability of heterotrophic bioleaching.

High tolerance of chemolithoautotrophic sulphur oxidizing bacteria towards pulp and paper mill wastewaters and their organic constituents supporting sulphur recovery in alkaline conditions

This study reports the tolerance of chemolithoautotrophic biotransformation of sulphurous compounds towards pulp and paper (P&P) mill wastewaters (primary filtrate of bleaching (PFB) and composite wastewater (WW)) and their constituents under haloalkaline conditions. The effects of organic compounds (methanol, acetate, D(+)-xylose, phenol and benzene) that may be present in P&P wastewaters, and yeast extract, a complex organic compound on thiosulphate biotransformation by Thioalkalivibrio versutus were investigated. All experiments were carried out in batch bioassays at pH 10 and 13–23 g Na+/L. Phenol and benzene reduced thiosulphate biotransformation by 88 and 94% at 0.25 and 1 g/L, respectively in 10 days. 20 g/L methanol, 20 g/L yeast extract and 10 g/L xylose reduced the biotransformation by 90, 88 and 56%, respectively. No inhibition of biotransformation occurred with acetate at concentrations up to 20 g/L. The growth was also enhanced by 1 to 10 g/L yeast extract likely serving as additional nutrients. At pH (∼10), the studied organic acids remain mostly unprotonated and, thus control their access through the cell membrane. Therefore, the inaccessibility of these compounds to the cytosol is a likely mechanism for having non-inhibitory effects. The 87% (v/v) WW did not affect thiosulphate biotransformation efficiency while 87% (v/v) PFB reduced it by 36% by day 10. The resistance of T. versutus to common organics present in P&P wastewaters indicates its potential use for sulphur recovery from P&P mill wastewaters at haloalkaline conditions and thus, supports the circular economy approach.

Effects of metal extraction liquors from electric vehicle battery materials production on iron and sulfur oxidation by heap bioleaching microorganisms

• Effects of metal extraction liquors on biological Fe 2+ and S 0 oxidation. • ≤1% ( v/v ) metal extraction liquors stimulated biological Fe 2+ oxidation. • >2% ( v/v ) metal extraction liquors reduced the rate of Fe 2+ oxidation. • ≤8% ( v/v ) metal extraction liquor 1 stimulated biological S 0 oxidation. • ≥6.3 mg/L neodecanoic acid and > 20 g/L (NH 4 ) 2 SO 4 reduced the rate of Fe 2+ oxidation. This study reports the effects of metal extraction liquors that are used for production of electric vehicle batteries on biological iron and sulfur oxidation. These liquors include ammonium sulfate and organic solvent constituents, and thus are potentially stimulatory or inhibitory for heap bioleaching microorganisms. The effects of the liquors and their constituents were studied in batch bioassays at pH 2 and 27 ± 2 °C. Both metal extraction liquors had a negative effect on biological iron oxidation at >2% ( v/v ), whereas biological sulfur oxidation was enhanced with ≤8% ( v/v ) metal extraction liquor 1. Biological iron oxidation was negatively affected by ammonium sulfate at above 20 g/L. From the studied low-solubility organic solvents (neodecanoic acid, Nessol D100, Cyanex 272, and Baysolvex D2EHPA), neodecanoic acid was the only one negatively affecting biological iron oxidation, and this effect occurred at ≥ 6.3 mg/L (2.5% of its aqueous solubility). Since these extraction liquors and some of their potential constituents inhibited biological iron oxidation, they may also inhibit heap bioleaching and have adverse impacts in recipient waters, if released to the environment. With ammonium limited culture, iron oxidation was stimulated with ≤ 1% ( v/v ) of metal extraction liquor 1 and 2, and therefore, would also likely enhance heap bioleaching.

Enrichment of Autotrophic Denitrifiers From Anaerobic Sludge Using Sulfurous Electron Donors.

This study compared the rates and microbial community development in batch bioassays on autotrophic denitrification using elemental sulfur (S0), pyrite (FeS2), thiosulfate (S2O32–), and sulfide (S2–) as electron donor. The performance of two inocula was compared: digested sludge (DS) from a wastewater treatment plant of a dairy industry and anaerobic granular sludge (GS) from a UASB reactor treating dairy wastewater. All electron donors supported the development of a microbial community with predominance of autotrophic denitrifiers during the enrichments, except for sulfide. For the first time, pyrite revealed to be a suitable substrate for the growth of autotrophic denitrifiers developing a microbial community with predominance of the genera Thiobacillus, Thioprofundum, and Ignavibacterium. Thiosulfate gave the highest denitrification rates removing 10.94 mM NO3– day–1 and 8.98 mM NO3– day–1 by DS and GS, respectively. This was 1.5 and 6 times faster than elemental sulfur and pyrite, respectively. Despite the highest denitrification rates observed in thiosulfate-fed enrichments, an evaluation of the most relevant parameters for a technological application revealed elemental sulfur as the best electron donor for autotrophic denitrification with a total cost of 0.38 € per m3 of wastewater treated.

Effect of carbon source and metal toxicity for potential acid mine drainage (AMD) treatment with an anaerobic sludge using sulfate-reduction.

This study compares sulfate-reduction performance in an anaerobic sludge with different carbon sources (ethanol, acetate, and glucose). Also, the toxic effect of copper was evaluated to assess its feasibility for possible acid mine drainage (AMD) treatment. Serological bottles with 1.5 g VSS/L and 150 mL of basal medium (0.67 g COD/g SO42- at a 7-8 pH) were used to determine the percentage of electron equivalents, maximum specific methanogenic (SMA), and sulfide generation activities (SGA). The copper effect was evaluated in a previously activated sludge in batch bioassays containing different concentrations of copper (0-50 mg/L), 3 gVSS/L, and 150 mL of basal medium (0.67 g COD/g SO42-). Carbon source bioassays with glucose obtained the best results in terms of the SGA (1.73 ± 0.34 mg S2-/g VSS•d) and SMA (10.41 mg COD-CH4/g VSS•d). The electron flow in the presence of glucose also indicated that 21.29 ± 5.2% of the metabolic activity of the sludge was directed towards sulfidogenesis. Copper toxicity bioassays indicated that a considerable decline in metabolic activity occurs above 10 mg/L. The 20%IC, 50%IC, and 80%IC were 4.5, 14.94, and 35.31 mg Cu/L. Compared to the other carbon sources tested, glucose proved to be a suitable electron donor since it favors sulfidogenesis. Finally, copper concentrations above 15 mg/L inhibited metabolic activity in the toxicity bioassays.

Ammonia and chromate interaction explains unresolved Hyalella azteca mortality in Flanders’ sediment bioassays

Agricultural, industrial and household chemicals are emitted in large rivers along populated areas, transported by water and deposited in sediments, posing (eco)toxicological risks. Sediments have received less attention than surface waters, likely because of the intrinsic complexity of interactions between sediment constituents complicating correct framing of exposures. Sadly, thorough assessment of the in situ behavior of sediment constituents in bioassays is often not practical.Alternatively, we related physicochemical properties of sediments from field testing to results from bioassays. The case study covers Flemish sediment (incl. Scheldt and Meuse) and mortality of Hyalella azteca, a sensitive bio-indicator. Though variable across Flanders’ main water bodies, heavy metals and ammoniacal nitrogen dominate the observed toxicity according to toxic unit (TU) assessments. Depending on the water body we explain between 50 and 90% of the variance in the observed H. azteca mortality, substantially more than previous ecotoxicity studies. We attribute the remaining variance to potential incoherently documented biophysicochemical sediment properties and concentrations of non-target biocides, testing conditions/set-ups and/or species variabilities.We discuss the relative influence of heavy metals/metaloxides, nitrogen (e.g. fertilizer), polycyclic aromatics and organochlorides. We highlight both direct and indirect mortality mechanisms. We note potential synergetic mixture effects between ammoniacal nitrogen and chromium. Such synergy may be phenomenological of ‘standard’ aerobic bioassays, and prove a complementary method alongside the ‘acid-volatile sulfide test’ to more effectively link concentration to toxicity. Future study ought to include variation in biophysicochemical properties between sampling locations and batch bioassays. Our approach enables water managers to interpret their monitoring data by converting sediment concentrations to H. azteca mortality and prioritize substances that contribute most.

Influence of different waste compositions from tilapia fish on methane production

Aquaculture represents a promising agribusiness branch in the world by having the biggest growth rate. As it surpasses cattle, swine and poultry farming, it emerges as a livestock model. The fish filleting process generates up to 65% of organic waste based on the fresh fish weight, with high variations in terms of moisture and chemical composition. This study aimed to evaluate the biochemical methane potential of different residues from the processing of tilapia (Oreochromis niloticusOreochromis niloticus): head, carcass, viscera, fin, skin, scale and a mixed fraction composed by all other residues. The methane potential was determined through batch bioassays conducted under mesophilic temperature with an inoculum to substrate ratio of 3. Two different kinetic models (first-order model and modified Gompertz model) were evaluated for methane predictions. Significant statistical difference (p < 0.05) was observed among the methane yields. The mixed fish waste resulted in a methane potential of 445 LN kg volatile solids−1. The highest methane yield was obtained by the head (571 LN kg volatile solids−1) while the scales had the lowest value (136 LN kg volatile solids−1). Due to the moisture variation of the residues, the methane yield was also expressed in a fresh matter basis. In this case the viscera showed the highest methane yield (206 LN kg fresh matter−1), while the mixed waste produced 125 LN kg fresh matter−1 and the scales only 35 LN kg fresh matter−1. Lipids showed to be the best parameter to explain the variation of the results (R = 0.98). The first-order was found to be the best model to predict the methane potential of fish waste, with R2 ≥ 0.997 and deviations under 4%.

Inhibition and removal of trichloroacetaldehyde by biological acidification with glucose co-metabolism

Biological acidification plays a crucial role in biological removal of organic compounds during petrochemical wastewater treatment. Trichloroacetaldehyde is a typical organic pollutant in petrochemical wastewater, however, no studies have been conducted on its effect on biological acidification. In this study, batch bioassays of volatile fatty acids were conducted to explore the inhibitory effect of trichloroacetaldehyde on biological acidification, the variations of key enzymes and extracellular polymeric substances under trichloroacetaldehyde shock, and the mechanism of trichloroacetaldehyde removal. The results of these bioassays indicated that trichloroacetaldehyde inhibited the acid yield at higher concentrations (EC50 112.20 mg/L), and butyric fermentation was predominant. Moreover, the contents of extracellular polymeric substances and several key acidifying enzymes greatly decreased when the trichloroacetaldehyde concentration exceeded 100 mg/L, which was due to the toxicity that trichloroacetaldehyde poses to the microbes involved in biological acidification. The trichloroacetaldehyde mechanism was as follows: first, trichloroacetaldehyde was adsorbed by extracellular polymeric substances and anaerobic granular sludge, and then transformed into trichloroethanol, trichloroethane, dichloroacetaldehyde, and dichloroethanol under the combined action of the aldehyde reductase and reductive dehalogenases secreted from the microbial consortium. The ability of biological acidification to remove trichloroacetaldehyde was limited; therefore, trichloroacetaldehyde should be pretreated before it enters biological treatment systems.

Simultaneous biological nitrification and desulfurization treatment of ammonium and sulfide-rich wastewater: Effectiveness of a sequential batch operation.

Sulfide inhibition to nitrifying bacteria has prevented the integration of digestate nitrification and biogas desulfurization to simplify anaerobic digestion systems. In this study, liquid digestate with NaHS solution was treated using nitrifying sludge in a sequential-batch reactor with a long fill period, with an ammonium loading rate of 293mg-N L-1d-1 and a stepwise increase in the sulfide loading rate from 0 to 32, 64, 128, and 256mg-S L-1d-1. Batch bioassays and microbial community analysis were also conducted with reactor sludge under each sulfide loading rate to quantify the microbial acclimatization to sulfide. In the reactor, sulfide was completely removed. Complete nitrification was maintained up to a sulfide load of 128mg-S L-1d-1, which is higher than that in previous reports and sufficient for biogas treatment. In the batch bioassays, the sulfide tolerance of NH4+ oxidizing activity (the 50% inhibitory sulfide concentration) increased fourfold over time with the compositional shift of nitrifying bacteria to Nitrosomonas nitrosa and Nitrobacter spp. However, the sulfur removal rate of the sludge slightly decreased, although the abundance of the sulfur-oxidizing bacteria Hyphomicrobium increased by 30%. Therefore, nitrifying sludge was probably acclimatized to sulfide not by the increasing sulfide removal rate but rather by the increasing nitrifying bacteria, which have high sulfide tolerance. Successful simultaneous nitrification and desulfurization were achieved using a sequential-batch reactor with a long fill period, which was effective in facilitating the present acclimatization.

Diazole and triazole inhibition of nitrification process in return activated sludge

Azoles are emerging contaminants that are resistant to biodegradation during wastewater treatment. Their presence has been widely reported in wastewater effluents and receiving waters. In this work, the potential inhibition of nitrification process by six different azole compounds in wastewater treatment plants was investigated in batch bioassays. The azoles studied included three diazoles: pyrazole (Pz); 1-methylpyrazole (MePz); 3,5-dimethylpyrazole (DMePz); and three triazoles: 1,2,4-triazole (Tz); benzotriazole (BTz); and 5-methyl benzotriazole (MeBTz). The concentration of azoles causing 50% inhibition (IC50) increased (azoles became less inhibitory) in the following order (mg L−1): BTz (1.99) < MeBTz (2.18) < Pz (2.69) < Tz (3.53) < DMePz (17.3) < MePz (49.6). No clear structure-inhibitory relationships were found using Log P and pKa as structural properties. The toxicity of any given azole may be related to the role of substituent groups on disabling/enabling binding to the active sites of metallo-enzymes in nitrifying microorganisms. This is exemplified by the low toxicity of MePz, which has a cyclic N blocked by a methyl group. The observed inhibition caused to nitrifying bacteria is more severe than their cytotoxicity to other target organisms (e.g., methanogens and heterotrophic bacteria), suggesting a specific inhibition to the copper-containing enzyme, ammonium monooxygenase, in ammonia oxidizing nitrifying microorganisms.

Dissolution and final fate of arsenic associated with gypsum, calcite, and ferrihydrite: Influence of microbial reduction of As(V), sulfate, and Fe(III)

Several studies have demonstrated that gypsum (CaSO4·2H2O) and calcite (CaCO3) can be important hosts of arsenic in contaminated hydrogeological systems. However, the extent to which microbial reducing processes contribute to the dissolution and transformation of carbonate and sulfate minerals and, thereby, to arsenic mobilization is poorly understood. These processes are likely to have a strong impact on arsenic mobility in iron-poor environments and in reducing aquifers where iron oxyhydroxides become unstable. Anoxic batch bioassays with arsenate (As(V)) coprecipitated with calcite, gypsum, or ferrihydrite (Fe(OH)3) were conducted in the presence of sulfate or molybdate to examine the impact of bioprocesses (i.e. As(V), sulfate, and Fe(III)-reduction) on arsenic dissolution, speciation, and eventual remineralization. Microbial reduction of As(V)-bearing calcite caused an important dissolution of arsenite, As(III), which remained in solution up to the end of the experiment (30 days). The reduction of As(V) from gypsum-As(V) also led to the release of As(III), which was subsequently remineralized, possibly as arsenic sulfides. The presence of sulfate triggered arsenic dissolution in the bioassays with ferrihydrite-As(V). This study showed that although gypsum and calcite have a lower capacity to bind arsenic, compared to iron oxides, they can play a critical role in the biogeochemical cycle of arsenic in natural calcareous and gypsiferous systems depleted of iron since they can be a source of electron acceptors for reducing bioprocesses.

Effect of feed glucose and acetic acid on continuous biohydrogen production by Thermotoga neapolitana

This study focused on the effect of feed glucose and acetic acid on biohydrogen production by Thermotoga neapolitana under continuous-flow conditions. Increasing the feed glucose concentration from 11.1 to 41.6 mM decreased the hydrogen yield from 3.6 (±0.1) to 1.4 (±0.1) mol H2/mol glucose. The hydrogen production rate concomitantly increased until 27.8 mM of feed glucose but remained unaffected when feed glucose was further raised to 41.6 mM. Increasing the acetic acid concentration from 0 to 240 mM hampered dark fermentation in batch bioassays, diminishing the cumulative hydrogen production by 45% and the hydrogen production rate by 57%, but induced no negative effect during continuous operation. Indeed, throughout the continuous flow operation the process performance improved considerably, as indicated by the 47% increase of hydrogen yield up to 3.1 (±0.1) mol H2/mol glucose on day 110 at 27.8 mM feed glucose.

Stable nitrification under sulfide supply in a sequencing batch reactor with a long fill period

Ammonia-containing wastewater often also contains sulfide, which severely inhibits biological nitrification. In this study, the applicability of a sequencing batch reactor (SBR) with a long fill period to achieve stable nitrification of sulfide-containing anaerobic digestion effluent was evaluated. During the start-up period, in which no sulfide was supplied to the reactor (Phase I, experimental days 0–18), ammonium was oxidized to nitrate stably after day 6. During the period in which sulfide was supplied at 32 mg-S L−1 d−1 (Phase II, experimental days 18–30), the nitrification efficiency temporarily decreased to 79%, but recovered rapidly to 100% within two days. The sulfide tolerance of the sludge in the SBR was evaluated by batch bioassays at the end of the start-up period. The results showed that the half-maximum inhibitory concentration (IC50) for the sludge was 0.73 mg-S L−1, which was a typical value. Therefore, pre-existing sulfide tolerance of the sludge was not the main factor enabling stable nitrification during the sulfide supply period. Throughout the experimental period, the reactor was operated using a long sludge retention time of 139 days. The effective sludge retention in the SBR with a long fill period probably promoted the acclimatization of the microbes to sulfide, allowing the nitrification performance to remain stable even under sulfide supply.

Effect of Cu, Ni and Zn on Fe(II)-driven autotrophic denitrification

Fe(II)-mediated autotrophic denitrification in the presence of copper (Cu), nickel (Ni) and zinc (Zn) with four different microbial cultures was investigated in batch bioassays. In the absence of metals, complete nitrate removal and Fe(II) oxidation were achieved with a Thiobacillus-dominated mixed culture and Pseudogulbenkiania sp. 2002 after 7 d. A nitrate removal of 96 and 91% was observed with a pure culture of T. denitrificans and an activated sludge enrichment, respectively, after 10 d of incubation. Cu, Ni and Zn were then supplemented at an initial concentration of 5, 10, 20 and 40 mg Me/L. A decrease of approximately 50% of the soluble metal concentrations occurred in the first 4 d of denitrification, due to metal precipitation, co-precipitation, sorption onto iron (hydr)oxides, and probably sorption onto biomass. A higher sensitivity to metal toxicity was observed for the microbial pure cultures. Pseudogulbenkiania sp. 2002 was the least tolerant among the biomasses tested, resulting in only 6, 8 and 6% nitrate removal for the highest Cu, Ni and Zn concentrations, respectively. In contrast, the highest nitrate removal efficiency and specific rates were achieved with the Thiobacillus-dominated mixed culture, which better tolerated the presence of metals. Averagely, Cu resulted in the highest inhibition of nitrate removal, followed by Zn and Ni.

Elemental sulfur-based autotrophic denitrification and denitritation: microbially catalyzed sulfur hydrolysis and nitrogen conversions

The hydrolysis of elemental sulfur (S0) coupled to S0-based denitrification and denitritation was investigated in batch bioassays by microbiological and modeling approaches. In the denitrification experiments, the highest obtained NO3−-N removal rate was 20.9 mg/l·d. In the experiments with the biomass enriched on NO2−, a NO2−-N removal rate of 10.7 mg/l·d was achieved even at a NO2−-N concentration as high as 240 mg/l. The Helicobacteraceae family was only observed in the biofilm attached onto the chemically-synthesized S0 particles with a relative abundance up to 37.1%, suggesting it was the hydrolytic biomass capable of S0 solubilization in the novel surface-based model. S0-driven denitrification was modeled as a two-step process in order to explicitly account for the sequential reduction of NO3− to NO2− and then to N2 by denitrifying bacteria.

Influence of pH, EDTA/Fe(II) ratio, and microbial culture on Fe(II)-mediated autotrophic denitrification.

Fe(II)-mediated autotrophic denitrification with four different microbial cultures under different pH and EDTA/Fe(II) conditions was investigated in batch bioassays. Initially, the highest nitrate removal (72%) was achieved with an activated sludge inoculum. The use of pure cultures of Pseudogulbenkiania strain 2002 and Thiobacillus denitrificans resulted in a 55 and 52% nitrate removal, respectively. No denitrification was observed for a mixed culture dominated by Thiobacillus thioparus and T. denitrificans. A longer enrichment on Fe(II) and the supplementation of thiosulfate as additional electron donor were needed to stimulate the denitrifying activity of the Thiobacillus-mixed culture. A second subculture on Fe(II) as sole electron donor resulted in higher denitrification efficiencies for all microbial cultures. In particular, nitrate removal reached up to 84% with a specific nitrate removal rate of 1.160mM·(g VSS·day)-1 in the bioassays seeded with the Thiobacillus-mixed culture. All cultures were favored by decreasing the EDTA/Fe(II) molar ratio from 2.0 to 0.5. The most significant denitrification enhancement was observed for the Pseudogulbenkiania species, indicating a lower tolerance to EDTA. The two pure cultures effectively maintained denitrification at pH7.0 and were more sensitive to a pH decrease. Conversely, the optimal pH was 6.0 for the Thiobacillus-mixed and activated sludge cultures.

Effects of different nickel species on autotrophic denitrification driven by thiosulfate in batch tests and a fluidized-bed reactor

Nickel is a common heavy metal and often occurs with nitrate (NO3−) in effluents from mining and metal-finishing industry. The present study investigates the effects of increasing concentrations (5–200mgNi/L) of NiEDTA2− and NiCl2 on autotrophic denitrification with thiosulfate (S2O32−) in batch tests and a fluidized-bed reactor (FBR). In batch bioassays, 50 and 100mgNi/L of NiEDTA2− only increased the transient accumulation of NO2−, whereas 25–100mgNi/L of NiCl2 inhibited denitrification by 9–19%. NO3− and NO2− were completely removed in the FBR at feed NiEDTA2− and NiCl2 concentrations as high as 100 and 200mgNi/L, respectively. PCR-DGGE revealed the dominance of Thiobacillus denitrificans and the presence of the sulfate-reducing bacterium Desulfovibrio putealis in the FBR microbial community at all feed nickel concentrations investigated. Nickel mass balance, thermodynamic modeling and solid phase characterization indicated that nickel sulfide, phosphate and oxide precipitated in the FBR during NiCl2 injection.

Sequential anaerobic-aerobic biodegradation of emerging insensitive munitions compound 3-nitro-1,2,4-triazol-5-one (NTO)

Insensitive munitions, such as 3-nitro-1,2,4-triazol-5-one (NTO), are being considered by the U.S. Army as replacements for conventional explosives. Environmental emissions of NTO are expected to increase as its use becomes widespread; but only a few studies have considered the remediation of NTO-contaminated sites. In this study, sequential anaerobic-aerobic biodegradation of NTO was investigated in bioreactors using soil as inoculum. Batch bioassays confirmed microbial reduction of NTO under anaerobic conditions to 3-amino-1,2,4-triazol-5-one (ATO) using pyruvate as electron-donating cosubstrate. However, ATO biodegradation was only observed after the redox condition was switched to aerobic. This study also demonstrated that the high-rate removal of NTO in contaminated water can be attained in a continuous-flow aerated bioreactor. The reactor was first fed ATO as sole energy and nitrogen source prior to NTO addition. After few days, ATO was removed in a sustained fashion by 100%. When NTO was introduced together with electron-donor (pyruvate), NTO degradation increased progressively, reaching a removal efficiency of 93.5%. Mineralization of NTO was evidenced by the partial release of inorganic nitrogen species in the effluent, and lack of ATO accumulation. A plausible hypothesis for these findings is that NTO reduction occurred in anaerobic zones of the biofilm whereas ATO was mineralized in the bulk aerobic zones of the reactor.

Anaerobic digestion for solids reduction and detoxification of refinery waste streams

Lab scale studies were conducted to test the anaerobic digestibility of two waste streams acquired from a petrochemical refinery. The waste streams comprised float from the dissolved air flotation (DAF) unit and waste activated sludge (WAS) from the biological treatment unit. Three semi continuous anaerobic digesters (AD) examined mono and co-digestion of the substrates. Mono-digestion of WAS yielded the highest reductions in organics whereas substrates with portions of DAF float showed inhibition. Prior to AD, batch bioassays were used as a preliminary tool to determine the toxicity profiles and the biodegradability of the samples. Pretreatment of the feeds by ozonation exhibited improvement in the digestion of DAF float with a higher digester hydraulic retention time (HRT), indicated by increased solids removal. Ozonation also resulted in enhanced removal of toxic organic compounds found in DAF float.