Microalgae-based processes for the biodegradation of pretreated piggery wastewaters

The potential and limitations of photosynthetic oxygenation on carbon and nitrogen removal from swine slurry were investigated in batch experiments using Chlorella sorokiniana and an acclimated activated sludge as model microorganisms. While algal-bacterial systems exhibited similar performance than aerated activated sludge in tests supplied with four and eight times diluted slurry, a severe inhibition of the biodegradation process was recorded in undiluted and two times diluted wastewater. Daily pH adjustment to 7 in enclosed algal-bacterial tests at several swine slurry dilutions allowed the treatment of up to two times diluted slurries (containing up to 1,180 mg N-NH(4) (+) l(-1)). The combination of high pH levels and high NH(4) (+) concentrations was thus identified as the main inhibitory factor governing the efficiency of photosynthetically oxygenated processes treating swine slurry. Measurements of soluble total organic carbon (TOC) and volatile fatty acids (VFA) present in the slurry suggested that VFA degradation (mainly acetic and propionic acid) accounted for most of the soluble TOC removal, especially during the initial stages of the biodegradation process. On the other hand, assimilation into biomass and nitrification to NO(2) (-) constituted the main NH(4) (+) removal processes in enclosed algal-bacterial systems.     

Microbial degradation of formaldehyde in white mineral dispersions preserved with formaldehyde-releasing biocides

Two different formaldehyde-degrading microorganisms, Pseudomonas putida and Methylobacterium extorquens, were isolated from calcium carbonate slurry containing the formaldehyde-releasing biocide (ethylenedioxy) dimethanol. Their relative formaldehyde biodegradation and formic acid production kinetics were studied in broth and in calcium carbonate slurry for each microorganism individually, as well as in mixed cultures. Furthermore, the minimal inhibition concentration (MIC) was determined. The results indicated that in slurry, M. extorquens is more tolerant of formaldehyde than P. putida. In slurry, microbial-induced oxidation of formaldehyde caused a temporary accumulation of formic acid, which is presumed to be responsible for pH drop and destabilisation of the calcium carbonate slurry suspension systems. In addition, the residual formaldehyde concentration was observed to drive dominance and recovery of individual formaldehyde-resistant microorganisms in the slurry. Overall, this investigation indicated that biodegradation of formaldehyde in calcium carbonate slurry is brought about by alternating dominance of bacterial genera of mixed formaldehyde-resistant microbial populations.     

Rheology of corn stover slurries at high solids concentrations--effects of saccharification and particle size

The rheological characteristics of untreated and dilute acid pretreated corn stover (CS) slurries at high solids concentrations were studied under continuous shear using plate-plate type measurements. Slurry rheological behavior was examined as a function of insoluble solids concentration (10-40%), extent of pretreatment (0-75% removal of xylan) and particle size (-20 and -80 mesh). Results show that CS slurries exhibit shear-thinning behavior describable using a Casson model. Further, results demonstrate that the apparent viscosity and yield stress increase with increasing solids concentration (which corresponds to a decrease in free water). Dilute acid pretreatment leads to lower viscosity and yield stresses at equivalent solids concentrations, as does smaller particle size. Taken together, these findings are consistent with the hypothesis that the availability of free water in the slurry plays a significant role in determining its rheological behavior. In particular, as the free water content of the slurry decreases, e.g., with increasing solids concentration, the greater interaction among particles likely increases the apparent viscosity and yield stress properties of the slurry. The results also suggest that the availability of free water, and thereby slurry rheological properties, depend on the chemical composition of the corn stover as well as its physical characteristics such as particle size and porosity. Hydrophilic polymers within the cell wall, such as xylan or pectin, or larger pores within bigger particles, facilitate sequestration of water in the solid phase resulting in decreased availability of free water. Thus, dilute acid pretreated slurries, which contain smaller size particles having significantly lower xylan content than slurries of untreated milled stover, exhibit much lower viscosities and yield stresses than untreated slurries containing large particles at similar solid concentrations.     

Persistence of Shiga toxin-producing Escherichia coli O26 in cow slurry

AIMS: The main objective of this study was to evaluate the growth and survival of Shiga toxin-producing Escherichia coli (STEC) O26 in cow slurry; this serogroup is regarded as an important cause of STEC-associated diseases. METHODS AND RESULTS: Four STEC were examined by polymerase chain reaction (PCR) to determine whether they harbour key virulence determinants and also by pulsed-field gel electrophoresis (PFGE) to obtain overview fingerprints of their genomes. They were transformed with the pGFPuv plasmid and were separately inoculated at a level of 10(6) CFU ml(-1) in 15 l of cow slurry. All STEC O26 strains could be detected for at least 3 months in cow slurry without any genetic changes. The moisture content of the slurry decreased over time to reach a final value of 75% while the pH increased from 8.5 to 9.5 units during the last 50 days. CONCLUSION: STEC O26 strains were able to survive in cow slurry for an extended period. SIGNIFICANCE AND IMPACT OF THE STUDY: Long-term storage of waste slurry should be required to reduce the pathogen load and to limit environmental contamination by STEC O26.     

Comparison of sulfuric and hydrochloric acids as catalysts in hydrolysis of Kappaphycus alvarezii (cottonii)

In this study, hydrolysis of marine algal biomass Kappaphhycus alvarezii using two different acid catalysts was examined with the goal of identifying optimal reaction conditions for the formation of sugars and by-products. K. alvarezii were hydrolyzed by autoclave using sulfuric acid or hydrochloric acid as catalyst with different acid concentrations (0.1-1.0 M), substrate concentrations (1.0-13.5%), hydrolysis time (10-90 min) and hydrolysis temperatures (100-130 (°)C). A difference in galactose, glucose, reducing sugar and total sugar content was observed under the different hydrolysis conditions. Different by-product compounds such as 5-hydroxymethylfurfural and levulinic acid were also observed under the different reaction conditions. The optimal conditions for hydrolysis were achieved at a sulfuric acid concentration, temperature and reaction time of 0.2 M, 130 °C and 15 min, respectively. These results may provide useful information for the development of more efficient systems for biofuel production from marine biomass.     

Potential availability of anaerobic treatment with digester slurry of animal waste for the reclamation of acid mine water containing sulfate and heavy metals

The use of an anaerobic digester slurry of cattle waste for the reclamation of acid mine water was examined. When the digester slurry was mixed with acid mine water, anaerobic digestion, including sulfate reduction and methanogenesis, was enhanced. In the mixture of acid mine water and the digester slurry, sulfate reduction proceeded without diminishing methanogenesis. The digester slurry and its supernatant (SDF-sup) showed a significant capacity to act as a strong alkaline reagent, and the pH of the acid mine water was markedly elevated by the addition of the digester slurry of SDF-sup even at the low ratio of 1% (v/v). Precipitation of heavy metals in the acid mine water occurred as the pH was elevated by the addition of SDF-sup. When the digester slurry was added at the ratio of 5% (v/v) to acid mine water which had been pretreated with SDF-sup, the rate of sulfate reduction increased with increasing the concentration of sulfate in the mixture up to about 1,400 mg·l⁻¹. In acid mine water pretreated with SDF-sup and supplemented with the digester slurry at the ratio of 5% (v/v), the maximum amount of sulfate reduced within 20 d of incubation was about 1,000 mg·l⁻¹, and the maximum rate of sulfate reduction was about 120 mg SO₄²⁻·l⁻¹·d⁻¹.     

Biodegradation of polychlorinated dibenzo-p-dioxins by recombinant yeast expressing rat CYP1A subfamily

Thiols represent preferential targets of peroxynitrite in biological systems. In this work, we investigated the mechanisms and kinetics of the reaction of peroxynitrite with the dithiol dihydrolipoic acid (DHLA) and its oxidized form, lipoic acid (LA). Peroxynitrite reacted with DHLA being oxidation yields higher at alkaline pH. The stoichiometry for the reaction was two thiols oxidized per peroxynitrite. LA formation accounted for approximately 50% DHLA consumption at pH 7.4, probably reflecting secondary reactions between LA and peroxynitrite. Indeed, peroxynitrous acid reacted with LA with an apparent second-order rate constant (k(2app)) of 1400 M(-1) s(-1) at pH 7.4 and 37 degrees C. Nitrite and LA-thiosufinate were formed as reaction products. Surprisingly, the k(2app) for peroxynitrite-dependent DHLA oxidation was only 250 M(-1) s(-1) per thiol, at pH 7.4 and 37 degrees C. Testing various low-molecular-weight thiols, we found that an increase in the thiol pK (pK(SH)) value correlated with a decrease of k(2app) for the reaction with peroxynitrite at pH 7.4. The pK(SH) for DHLA is 10.7, in agreement with its modest reactivity with peroxynitrite.     

Activation and inactivation of methanol: 2-mercaptoethanesulfonic acid methyltransferase from Methanosarcina barkeri.

Methanol is converted to methane by crude extracts of Methanosarcina barkeri. The first reaction involved in this process, is catalyzed by methanol:2-mercaptoethanesulfonic acid methyltransferase (EC 2.1.1.-). The methyltransferase has an optimum at pH 6.5 and is not inhibited by 2-bromoethanesulfonic acid. Pyridoxal-5'-phosphate acts as an inhibitor (Ki = 0.30 mM). The methyltransferase was tested in the presence of 2-bromoethanesulfonic acid, which inhibits the conversion of 2-(methylthio)ethanesulfonic acid to methane. The reaction is subject to activation and inactivation. Inactivation is brought about by the presence of oxygen, flavin mononucleotide, flavin adenine dinucleotide, and 2-(methylthio)ethanesulfonic acid, the product of the reaction. Activation of the system requires the presence of ATP and Mg2+ and of hydrogen. Hydrogen can be replaced by enzymatic systems, such as pyruvate dehydrogenase, which deliver free hydrogen.     

Evaluation of the sulfate-reducing bacterial population associated with stored swine slurry

Hydrogen sulfide, produced by sulfate-reducing bacteria (SRB), is one of the most potent malodors emitted from anaerobic swine waste storage systems. However, little is known about the prevalence and diversity of SRB in those systems. The goals of this study were to evaluate the SRB population in swine manure storage systems and to develop quantitative, real-time PCR (QRT-PCR) assays to target four of the SRB groups. Dissimilatory sulfite reductase (DSR) gene sequences were obtained from swine slurry stored in underground pits (43 clones) or in lagoons (34 clones). QRT-PCR assays were designed to target the dsrA gene of four novel groups of SRB. Sequences of dsrA clones from slurry samples grouped with those from three different cultured SRB: Desulfobulbus sp. (46 clones), Desulfovibrio sp. (24 clones and 5 isolates), and Desulfobacterium sp. (7 clones). However, DsrA sequences from swine slurry clones were generally less than 85% similar to those of cultured organisms. SRB from all four targeted SRB groups were detected in underground waste storage pits (6.6 x 10(3)-8.5 x 10(7) dsrA copies mL(-1) slurry), while only two groups of SRB were detected in lagoons (3.2 x 10(5)-2.5 x 10(6) dsrA copies mL(-1) slurry). To date, this is the only study to evaluate the phylogeny and concentration of SRB in any livestock waste storage system. The new QRT-PCR assays should facilitate sensitive, specific detection of the four novel groups of SRB in livestock waste storage systems.     

Formation of homovanillic acid dimer by enzymatic or Fenton system - catalyzed oxidation

Homovanillic acid is the most extensively employed reagent for the fluorometric detection of peroxidase. However, the assays based on the determination of the oxidation product of homovanillic acid do not allow a selective detection of the enzyme, because chemical or physical factors can interfere with the fluorometric determination. The aim of this work was to verify if other enzymatic or non-enzymatic systems might catalyze the homovanillic acid oxidation. The reaction was investigated by spectrophotometric and fluorometric assays; HPLC analysis was used to separate homovanillic acid from its oxidation product and to obtain information on the oxidation process. The results obtained showed that soybean lipoxygenase in the presence of hydrogen peroxide can oxidize homovanillic acid with the formation, by an o,o'-biphenyl linkage, of the corresponding dimer as the sole reaction product. The reaction followed Michaelis-Menten kinetics, for both homovanillic acid and hydrogen peroxide. Other systems, such as cytochrome c/H(2)O(2) and Fenton reagents, were also able to oxidize homovanillic acid to its dimer. It can be affirmed that possible interference by other oxidative systems - that could be present in the biological materials tested - should be considered in assays of peroxidase activity based on the detection of the dimer of homovanillic acid.     

A site-specific slurry application technique on grassland and on arable crops

There is evidence that unequal slurry application on agricultural land contributes to N losses to the environment. Heterogeneity within fields demands adequate response by means of variable rate application. A technique is presented which allows site-specific application of slurry on grassland and arable land based on pre-defined application maps. The system contains a valve controlling flow rate by an on-board PC. During operation, flow rate is measured and scaled against set point values given in the application map together with the geographic position of the site. The systems worked sufficiently precise at a flow rate between 0 and 25 l s(-1) and an offset of actual slurry flow from set point values between 0.33 and 0.67 l s(-1). Long-term experimentation is required to test if site-specific application de facto reduces N surplus within fields and so significantly contributes to the unloading of N in agricultural areas.     

Polyacrylamide gel electrophoresis: reaction of acrylamide at alkaline pH with buffer components and proteins

The chemical reaction of monomeric acrylamide with primary, secondary, and tertiary amines, used as buffer components in polyacrylamide gel electrophoresis systems, was investigated in the basic pH range. Adduct formation proceeded for several minutes up to weeks, depending on the reactivity of the amino groups. A pH shift in the reaction mixture due to an altered pK value of the reaction product was observed. However, a few primary amines (tris(hydroxymethyl)aminomethane, 2-amino-2-methyl-1,3-propanediol) and secondary amines 3-([2-hydroxy-1,1-bis(hydroxymethyl)ethyl]amino)-1-propanesulfonic acid, 3-(dimethyl(hydroxymethyl)methylamino)-2-hydroxypropanesulfonic acid) showed negligible shifts of pH. They are, therefore, useful as components in the polymerization mixture; whereas some tertiary amines showing complete pH stability as well (e.g., triethanolamine) are not suitable, as they acted as accelerators of gel polymerization. Acrylamide can also covalently bind to proteins by reacting with the epsilon-amino group of lysine residues, especially. Bovine serum albumin, having an acidic isoelectric point, and the basic protein cytochrome c were treated with different acrylamide concentrations at alkaline pH yielding modified protein molecules with altered electrophoretic mobilities in different polyacrylamide gel electrophoresis systems. This reaction gave rise to artifacts in alkaline polyacrylamide gels and isoelectric focusing systems when residual acrylamide monomers were still present in the gel matrix after the polymerization process ceased.     

Soluble and insoluble solids contributions to high-solids enzymatic hydrolysis of lignocellulose

The rates and extents of enzymatic cellulose hydrolysis of dilute acid pretreated corn stover (PCS) decline with increasing slurry concentration. However, mass transfer limitations are not apparent until insoluble solids concentrations approach 20% w/w, indicating that inhibition of enzyme hydrolysis at lower solids concentrations is primarily due to soluble components. Consequently, the inhibitory effects of pH-adjusted pretreatment liquor on the enzymatic hydrolysis of PCS were investigated. A response surface methodology (RSM) was applied to empirically model how hydrolysis performance varied as a function of enzyme loading (12-40mg protein/g cellulose) and insoluble solids concentration (5-13%) in full-slurry hydrolyzates. Factorial design and analysis of variance (ANOVA) were also used to assess the contribution of the major classes of soluble components (acetic acid, phenolics, furans, sugars) to total inhibition. High sugar concentrations (130g/L total initial background sugars) were shown to be the primary cause of performance inhibition, with acetic acid (15g/L) only slightly inhibiting enzymatic hydrolysis and phenolic compounds (9g/L total including vanillin, syringaldehyde, and 4-hydroxycinnamic acid) and furans (8g/L total of furfural and hydroxymethylfurfural, HMF) with only a minor effect on reaction kinetics. It was also demonstrated that this enzyme inhibition in high-solids PCS slurries can be approximated using a synthetic hydrolyzate composed of pure sugars supplemented with a mixture of acetic acid, furans, and phenolic compounds, which indicates that generally all of the reaction rate-determining soluble compounds for this system can be approximated synthetically.     

Evaluation of the interaction between biodegradation and sorption of phenanthrene in soil-slurry systems

This work develops and utilizes a non-steady-state model for evaluating the interactions between sorption and biodegradation of hydrophobic organic compounds in soil-slurry systems. The model includes sorption/desorption of a target compound, its utilization by microorganisms as a primary substrate existing in the dissolved phase, and/or the sorbed phase in biomass and soil, oxygen transfer, and oxygen utilization as an electron acceptor. Biodegradation tests with phenanthrene were conducted in liquid and soil-slurry systems. The soil-slurry tests were performed with very different mass transfer rates: fast mass transfer in a flask test at 150 rpm, and slow mass transfer in a roller-bottle test at 2 rpm. The results of liquid tests indicate that biodegradation of the soil-soluble organic fraction did not significantly enhance the biodegradation rate. In the slurry tests, phenanthrene was degraded more rapidly than in liquid tests, but at a similar rate in both slurry systems. Modeling analyses with several hypotheses indicate that a model without biodegradation of compound sorbed to the soil was not able to account for the rapid degradation of phenanthrene, particularly in the roller-bottle slurry test. The model with sorbed-phase biodegradation and the same biokinetic parameters, but unique mass transfer coefficients, simulated the experimental data in both slurry tests most successfully. Reduced mass transfer resistance to bacteria attached to the soil is the most likely phenomenon accounting for rapid sorbed-phase biodegradation.     

Candidasp．99-125脂肪酶催化猪油酸解合成1，3-二油酸-2-棕榈酸甘油三酯

人乳脂是一种在甘油骨架Sn-2位上富含棕榈酸（C16：0）的结构酯。经分析可知,猪油中棕榈酸主要分布在甘油酯的Sn-2位,可作为制备1,3-二油酸-2-棕榈酸甘油三酯（OPO）的原料。以Candidasp．99—125脂肪酶作催化剂,以猪油和油酸为原料,通过正交试验对无溶剂体系中酸解合成OPO的工艺条件进行研究,得到最适反应条件：猪油与油酸的质量比为1：2．0,酶用量为总底物质量的10％,反应温度40℃,反应时间4h。在该反应条件下,经酸解合成的产物三甘酯中,Sn-2C16：0的含量大于70％,占总脂肪酸中棕榈酸含量的93％以上,并合有43％以上的OPO。     

The adenosine triphosphate inhibition of the pyruvate kinase reaction and its dependence on the total magnesium ion concentration

1. The effects of ATP, PP(i) and EDTA on the skeletal-muscle pyruvate kinase reaction at various concentrations of magnesium (where ;magnesium' refers to total Mg(2+), both free and in the form of complexes) were investigated. The reaction rate was determined as the amount of pyruvate formed in a recorded time of incubation. 2. At 44mm-magnesium the K(m) values for ADP and phosphoenolpyruvate were unaltered by the presence of ATP up to 6.8mm in systems buffered with either tris-hydrochloric acid or glycylglycine-sodium hydroxide, but the K(m) values were different in these systems. The K(m) for one substrate was independent of the concentration of the second substrate. 3. At 10mm-magnesium in the tris-hydrochloric acid system ATP inhibited the reaction competitively with respect to ADP and phosphoenolpyruvate. In the glycylglycine-sodium hydroxide system the inhibition appeared to be non-competitive. At 10mm-magnesium the K(m) values were lower than at 44mm-magnesium and dependent on the system used. 4. In the tris-hydrochloric acid system the reaction rate rose with increasing magnesium concentration up to a maximum at a concentration 10-20 times that of ADP. Further increase inhibited the reaction and at 44mm-magnesium the rate was 25-50% of its maximum. This inhibition paralleled that produced by increasing trimethylammonium chloride concentrations and was not due to a specific effect of the Mg(2+) ion. 5. In the presence of 6.8mm-ATP no reaction occurred below 4-6mm-magnesium, and further increase apparently abolished the inhibition as the reaction rate increased and became equal to those obtained in the absence of ATP at 10-25mm-magnesium. Further increase in magnesium concentration gave reaction rates that were slightly higher in the presence of ATP than in its absence. The maximal rate in the presence of ATP was distinctly lower than in its absence. When 6.8mm-PP(i) or 6.8mm-EDTA was present the variations in reaction rate with rising magnesium concentration were similar to that obtained in the presence of ATP below 6-8mm-magnesium but further increase in the magnesium concentration resulted in an increase in the rate up to a maximum comparable with that of the control. The effect of pure chelation was thus a displacement of the reaction maximum to higher magnesium concentrations without changing the maximal rate. When correction had been made for this effect, ATP gave inhibition at 44mm-magnesium that was competitive with respect to ADP (K(i) 2.1x10(-2)m). This degree of inhibition is far less than was reported earlier and its importance for the mechanism of the pyruvate kinase reaction is discussed.     

Oxidative degradation of glucose adducts to protein. Formation of 3-(N epsilon-lysino)-lactic acid from model compounds and glycated proteins

The chemistry of Maillard or browning reactions of glycated proteins is being studied in model systems in vitro in order to characterize potential reaction pathways and products in biological systems. In previous work with the Amadori rearrangement product N alpha-formyl-N epsilon-fructoselysine (fFL), an analog of glycated lysine residues in proteins, we showed that fFL was oxidatively cleaved between C-2 and C-3 of the carbohydrate chain to yield N epsilon-carboxymethyllysine (CML) and D-erythronic acid. We then detected CML in proteins glycated in vitro, as well as in human lens proteins and collagen in vivo (Ahmed, M. U., Thorpe, S. R., and Baynes, J. W. (1986) J. Biol. Chem. 261, 4889-4894). This work provided an explanation for the origin of CML in human urine and evidence for non-browning pathways of the Maillard reaction in vivo. In this report we describe the identification of a second set of products resulting from oxidative cleavage of fFL between C-3 and C-4 of the sugar chain, i.e. 3-(N epsilon-lysino)-lactic acid (LL) and D-glyceric acid. The formation of LL from fFL was increased at slightly acid pH, representing about 30% of the yield of CML at pH 6.4, compared with 4% at pH 7.4 in phosphate buffer. By gas chromatography-mass spectroscopy, LL was detected in proteins glycated in vitro and then identified as a natural product in human lens proteins and urine. Our results indicate that oxidative degradation of Amadori adducts to proteins occurs in vivo, leading to formation and excretion of CML and LL. These non-browning pathways for reaction of Amadori compounds may be physiologically relevant mechanisms for averting potentially damaging consequences of the Maillard reaction.     

Kinetic modelling of Amadori N-(1-deoxy-D-fructos-1-yl)-glycine degradation pathways. Part I--reaction mechanism

The fate of the Amadori compound N-(1-deoxy-D-fructos-1-yl)-glycine (DFG) was studied in aqueous model systems as a function of pH and temperature. The samples were heated at 100 and 120 degrees C with initial reaction pH of 5.5 and 6.8. Special attention was paid to the formation of the free amino acid, glycine; parent sugars, glucose and mannose; organic acids, formic and acetic acid and alpha-dicarbonyls, 1- and 3-deoxyosone together with methylglyoxal. For the studied conditions decreasing the initial reaction pH with 1.3 units or increasing the temperature with 20 degrees C has the same effect on the DFG degradation as well as on glycine formation. An increase in pH seems to favour the formation of 1-deoxyosone. The lower amount found comparatively to 3-deoxyosone, in all studied systems, seems to be related with the higher reactivity of 1-deoxyosone. Independently of the taken pathway, enolization or retro-aldolization, DFG degradation is accompanied by amino acid release. Together with glycine, acetic acid was the main end product formed. Values of 83 and 55 mol% were obtained, respectively. The rate of parent sugars formation increased with pH, but the type of sugar formed also changed with pH. Mannose was preferably formed at pH 5.5 whereas at pH 6.8 the opposite was observed, that is, glucose was formed in higher amounts than mannose. Also, independently of the temperature, at higher pH fructose was also detected. pH, more than temperature, had an influence on the reaction products formed. The initial steps for a complete multiresponse kinetic analysis have been discussed. Based on the established reaction network a kinetic model will be proposed and evaluated by multiresponse kinetic modelling in a subsequent paper.     

猪场废水施用对直播稻磷素吸收利用与氮磷生态化学计量的影响

以直播稻为对象,在上海农场进行了猪场处理废水基肥和穗肥不同用量组合的田间试验,研究猪场废水对水稻磷养分吸收利用与氮磷生态化学计量的影响。结果表明:施用猪场处理废水对直播水稻干物质积累、植株磷含量有显著影响。水稻拔节期、齐穗期和成熟期干物质积累量以及产量随废水施用量增加而增加;拔节期、齐穗期和成熟期植株、秸秆及籽粒含磷量与废水用量皆呈显著正相关;不同施肥处理在整个生育期水稻植株N∶P为3.13~5.10,在拔节期、齐穗期、成熟期分别为3.13~4.83、3.42~4.35、3.98~5.10,总体上以齐穗期N∶P值较低;成熟期秸秆N∶P值变动较大(4.30~6.57),而籽粒变化较小(3.85~4.37);齐穗期植株、成熟期秸秆、籽粒和植株的N∶P值与废水施用总量皆呈显著正相关,表明废水施用对直播稻氮素吸收的促进作用大于磷素。     

Two-liquid-phase slurry bioreactors to enhance the degradation of high-molecular-weight polycyclic aromatic hydrocarbons in soil

High-molecular-weight (HMW) polycyclic aromatic hydrocarbons (PAHs) are pollutants that persist in the environment due to their low solubility in water and their sequestration by soil and sediments. The addition of a water-immiscible, nonbiodegradable, and biocompatible liquid, silicone oil, to a soil slurry was studied to promote the desorption of PAHs from soil and to increase their bioavailability. First, the transfer into silicone oil of phenanthrene, pyrene, chrysene, and benzo[a]pyrene added to a sterilized soil (sandy soil with 0.65% total volatile solids) was measured for 4 days in three two-liquid-phase (TLP) slurry systems each containing 30% (w/v) soil but different volumes of silicone oil (2.5%, 7.5%, and 15% [v/v]). Except for chrysene, a high percentage of these PAHs was transferred from soil to silicone oil in the TLP slurry system containing 15% silicone oil. Rapid PAH transfer occurred during the first 8 h, probably resulting from the extraction of nonsolubilized and of poorly sorbed PAHs. This was followed by a period in which a slower but constant transfer occurred, suggesting extraction of more tightly bound PAHs. Second, a HMW PAH-degrading consortium was enriched in a TLP slurry system with a microbial population isolated from a creosote-contaminated soil. This consortium was then added to three other TLP slurry systems each containing 30% (w/v) sterilized soil that had been artificially contaminated with pyrene, chrysene, and benzo[a]pyrene, but different volumes of silicone oil (10%, 20%, and 30% [v/v]). The resulting TLP slurry bioreactors were much more efficient than the control slurry bioreactor containing the same contaminated soil but no oil phase. In the TLP slurry bioreactor containing 30% silicone oil, the rate of pyrene degradation was 19 mg L(-)(1) day(-)(1) and no pyrene was detected after 4 days. The degradation rates of chrysene and benzo[a]pyrene in the 30% TLP slurry bioreactor were, respectively, 3.5 and 0.94 mg L(-)(1) day(-)(1). Low degradation of pyrene and no significant degradation of chrysene and benzo[a]pyrene occurred in the slurry bioreactor. This is the first report in which a TLP system was combined with a slurry system to improve the biodegradation of PAHs in soil.