Specific methanogenic activity of halophilic and mixed cultures in saline wastewater

Wastewater containing high concentrations of salt, are difficult to treat using biological treatment processes, especially anaerobic processes. Limited information is available on methanogenic activity in saline environments. The objective of this research was to investigate the activity of halophilic methanogens, digester sludge and a mixed culture of halophilic and methanogenic bacteria, at various levels of salinity, in terms of lag period and specific methanogenic activity (SMA) at two temperatures. For the halophilic bacteria at 35 °C, the initial SMA ranged from 0.46 to 0.90 g acetate/g VSSd, but decreased at higher salt concentrations. The maximum SMA varied from 1.2 to 2.08 g acetate/g VSSd. High sodium chloride concentrations had a significant adverse effect on digester sludge. At 25 °C, at salt concentrations of 30 g/l and above, the digester sludge could not acclimate even in 50 days. Little difference was observed in the maximum SMA of mixed culture and halophilic bacteria at high salt concentrations of40–50 g/l.     

Anaerobic digester sludge as nutrient source for culturing of microalgae for economic biodiesel production

After decades of ‘living dangerously’, the human kind has paused to think of Mother Nature. Alternate energy sources are being developed as a part of this realization. The use of indigenous sources of nutrients would considerably bring down the cost of production. A mixed consortium of Chlorella vulgaris, Arthrospira platensis, and tap water-originated Scenedesmus dimorphus was cultured using natural seawater, anaerobic digester sludge, and its growth was compared with synthetic commercial media like Zarrouk’s media, NaNO₃ media, and NH₄Cl media. A spectrophotometric method was standardized for regular biomass estimation. The dry biomass of a 15-day pure, batch culture of Arthrospira was found to yield around 600 mg/L in anaerobic digester sludge, whereas the pure batch culture of chlorella’s growth was hindered mainly due to the presence of bacteria and grazers. Regular microscopic observation and biomass monitoring revealed a drastic reduction in grazing activity, with the use of autoclaved AD sludge, resulting in a strong and stable microalgal mixed consortia. The consortia growth in AD sludge was found to be better than with the synthetic media with no cost of nutrient. The mixed consortia yielded a biomass up to 600 mg/L and lipid of 21.18%. The lipid generated from AD sludge had around 95% unsaturates and contained around 5% omega-3 fatty acids. The use of anaerobic digester sludge in a non-sterile condition reduces the total cost of the biodiesel production process as a whole and introduces a decentralized system for waste water treatment as well.     

地下水中三氯乙烯-苯酚的好氧共代谢的实验研究

以苯酚作为三氯乙烯（TCE）降解的共代谢基质,用瓦勃氏微量呼吸测压仪（简称瓦呼仪）作为测试手段,分析了经苯酚驯化后的混合微生物对苯酚、TCE的降解特性;并讨论了以苯酚作为共代谢基质时TCE降解的可能性。实验结果表明：未驯化的活性污泥不能降解TCE; 经苯酚驯化后的活性污泥,当TCE的质量浓度为50 μg/L时其降解效果较好,TCE的氧化率达3369%;TCE的质量浓度为100 μg/L时其降解效果较差,其氧化率仅为3.2%;苯酚和TCE共代谢降解时,苯酚的存在促进了TCE的降解,当苯酚质量浓度为40 mg/L、TCE质量浓度为50 μg/L时共代谢降解效果最好,TCE的氧化率为79.11%。     

Study of syntrophic anaerobic digestion of volatile fatty acids using enriched cultures at mesophilic conditions

Volatile fatty acids are the most important intermediates in anaerobic digestion, and their degradations are extremely complicated thermodynamically. In this research, syntrophic anaerobic digestion of volatile fatty acids using enriched acetogenic and methanogenic cultures in a batch reactor at mesophilic conditions was investigated. Interactive effects of key microbiological and operating variables (propionic, butyric and acetic acids, retention time and methanogen to acetogen populations ratio) on the anaerobic degradation of volatile fatty acids were analyzed. Acetogenic and methanogenic anaerobes in the granular sludge from an up-flow anaerobic sludge blanket reactor were enriched at mesophilic conditions within a period of four weeks, separately. Enriched cultures were mixed with known proportions and then used in the bioreactor. Experiments were carried out based on central composite design and analyzed using response surface methodology. Four parameters (final concentrations of propionic, butyric and acetic acids and biogas production) were directly measured as response. Also, the optimum conditions for volatile fatty acid degradation were found to be 937.5 mg/L, 3275.5 mg/L, 2319.5 mg/L, 45 h and 2.2 proportions for propionic acid, butyric acid, acetic acid, retention time and methanogen to acetogen populations ratio, respectively (corresponding to maximum volatile fatty acid removal efficiencies and biogas production). The results of the verification experiment and the predicted values from the fitted correlations at the optimum conditions were in close agreement at a 95% confidence interval. The present study provides valuable information about the interrelations of quality and process parameters at different values of microbiological and operating variables.     

The dominant acetate degradation pathway/methanogenic composition in full-scale anaerobic digesters operating under different ammonia levels

Ammonia is a major environmental factor influencing biomethanation in full-scale anaerobic digesters. In this study, the effect of different ammonia levels on methanogenic pathways and methanogenic community composition of full-scale biogas plants was investigated. Eight full-scale digesters operating under different ammonia levels were sampled, and the residual biogas production was followed in fed-batch reactors. Acetate, labelled in the methyl group, was used to determine the methanogenic pathway by following the ¹⁴CH₄ and ¹⁴CO₂ production. Fluorescence in situ hybridisation was used to determine the methanogenic communities’ composition. Results obtained clearly demonstrated that syntrophic acetate oxidation coupled with hydrogenotrophic methanogenesis was the dominant pathway in all digesters with high ammonia levels (2.8–4.57 g NH₄ ⁺-N L^?1), while acetoclastic methanogenic pathway dominated at low ammonia (<1.21 g NH₄ ⁺-N L^?1). Thermophilic Methanomicrobiales spp. and mesophilic Methanobacteriales spp. were the most abundant methanogens at free ammonia concentrations above 0.44 g NH₃-N L^?1 and total ammonia concentrations above 2.8 g NH₄ ⁺-N L^?1, respectively. Meanwhile, in anaerobic digesters with low ammonia (<1.21 g NH₄ ⁺-N L^?1) and free ammonia (<0.07 g NH₃-N L^?1) levels, mesophilic and thermophilic Methanosaetaceae spp. were the most abundant methanogens.     

Diphytanyl glycerol ether distributions in sediments of the Orca Basin

Archaebacterially produced diphytanyl glycerol ether (DPGE) was examined in core sediments from the Orca Basin, an anoxic hypersaline basin in the northwestern Gulf of Mexico, to observe its spatial variability and potential origin. A differential extraction protocol was employed to quantify the isopranyl glycerol ethers associated with unbound, intermediate-bound, and kerogen-bound lipid fractions. Archaebacterial lipids were evident at all depths for the unbound and intermediate-bound fractions. Concentrations of DPGE ranged from 0.51 to 2.91 micrograms/g dry sediment at the surface and showed secondary maxima deeper in basin sediments. Intermediate-bound DPGE concentrations exhibited an inverse relationship to unbound DPGE concentrations. Kerogen-bound DPGE concentrations were normally below detection limits. Earlier studies describing the general homogeneity of lipid components within the overlying brine and at the brine/seawater interface suggest that the large-scale sedimentary DPGE variations observed in this study result from spatial and temporal variations in in situ production by methanogenic or extremely halophilic archaebacteria.     

Treatability of landfill leachate by combined upflow anaerobic sludge blanket reactor and aerated lagoon

Continuous upflow anaerobic sludge blanket reactor performs more favorably at the higher organic loading rate than other anaerobic treatment. The treatment of municipal landfill leachate of Shiraz??s city investigated using continuous flow anaerobic reactor and subsequently aerated lagoon. Landfill leachate has chemical oxygen demand of 45,000?C90,000?mg/L and ammonia nitrogen at 1,000?C2,500 and heavy metals that can impact biological treatments. Capacity of anaerobic and aerobic reactors is 10 and 20?L that operated at detention time of 2 and 4?days, respectively. Organic loading rate of upflow anaerobic sludge blanket is between 0.5?C20?g chemical oxygen demand/L/day. Chemical oxygen demand removal efficiencies are between 57?C87, 35?C70 and 66?C94% in the anaerobic, aerobic and whole system, respectively. As the entry, leachate organic loading rate increased from 1 to 20?g/L/day, the chemical oxygen demand removal efficiency reached a maximum of 71% and 84% in the anaerobic reactor and whole system, respectively, at high organic loading rate. Ammonium removal efficiency was about 54% after the aerobic stage.     

Preservation of thermophilic mixed culture for anaerobic palm oil mill effluent treatment by convective drying methods

The generation of huge amount of liquid waste known as palm oil mill effluent is a major problem in oil palm industry. Meanwhile, anaerobic biodegradation of such organic effluent at thermophilic condition is a promising treatment technology due to its high efficiency. However, storage and transportation of thermophilic mixed culture sludge are challenging due to constant biogas generation and heating requirement. Hence, drying of thermophilic sludge was conducted to obtain dormant thermophiles and thus enables easier handling. In this study, thermophilic sludge was dried using heat pump at 22 and 32 °C as well as hot air oven at 40, 50, 60, and 70 °C. Subsequently, quality of dried sludge was examined based on most probable number enumeration, chemical oxygen demand, and methane yield. Average drying rate was found to increase from 3.21 to 17.84 g H₂O/m² min as drying temperatures increases while average moisture diffusivity values ranges from 5.07 × 10^?9 to 4.34 × 10^?8 m²/s. Oven drying of thermophilic mixed culture resulted in highest chemical oxygen demand removal and lowest log reduction of anaerobes at 53.41% and 2.16, respectively, while heat pump drying resulted in the highest methane yield and lowest log reduction of methanogens at 53.4 ml CH₄/g COD and 2.09, respectively. To conclude, heat pump at 22 °C was most suitable drying technique for thermophilic mixed culture as the original methane-producing capability was largely retained after drying, at a slightly lower yet still comparable chemical oxygen demand removal when palm oil mill effluent was treated with the rehydrated culture.     

Aqueous heavy metals removal by adsorption on β-diketone-functionalized styrene–divinylbenzene copolymeric resin

An investigation was undertaken regarding the adsorption of different heavy metal ions from aqueous solutions using ??-diketone-functionalized styrene divinylbenzene resin under different experimental conditions such as initial concentration of metal ions, contact time, pH, and chelating capacity. The functionalization of resin was carried out by the condensation reaction of sodium salt of ??-diketones (pentane-1,3-dione) and chloromethylated styrene?Cdivinylbenzene resin in dichloromethane. Functionalized resin beads were characterized by Fourier transform infrared spectroscopy. The batch method was employed using different metal ions solution from 5 to 15?mg/L at different contact times. The adsorption kinetics was tested for the pseudo-first order, pseudo-second order reaction at different experimental conditions. The rate constant of adsorption kinetic models were also calculated and good correlation coefficient (R ²?>?0.9941) was obtained for pseudo-second order kinetic model. The maximum adsorption value obtain for lead (0.725728?mg/g), chromium (0.9199?mg/g), nickel (0.4974?mg/g), cobalt (0.6196?mg/g) and cadmium (0.6519?mg/g) at equilibrium condition, which shows that ??-diketone-functionalized styrene divinylbenzene resin is an effective adsorbent for toxic metal ions.     

Model for the distribution of sulfate reduction and methanogenesis in freshwater sediments

A model, based on the in situ physiological characteristics of methanogens and sulfate reducers, was developed to describe the distribution of methanogenesis and sulfate reduction in freshwater sediments. The model predicted the relative importance of methane production and sulfate reduction in lakes of various trophic status and generated profiles of sulfate, acetate, methanogenesis, and sulfate reduction comparable to the profiles that are expected based on field studies. The model indicated that at sulfate concentrations greater than 30μM a sulfate-reducing zone develops because sulfate reducers maintain acetate concentrations too low for methanogens to grow. At lower sulfate concentrations a methanogenic zone develops because the dual limitations of low sulfate concentrations and acetate consumption by methanogens prevents sulfate reducers from growing. The model and a compilation of previously published field data indicate that, within the reported range of sulfate concentrations, the relative importance of methanogenesis and sulfate reduction in freshwater sediments is primarily dependent upon the rates of organic matter decomposition.     

Start-up of halophilic nitrogen removal via nitrite from hypersaline wastewater by estuarine sediments in sequencing batch reactor

Nitrogen removal from hypersaline wastewater was successfully started up by inoculating estuarine sediments for 140 days. Efficient ammonia and total nitrogen removal was sustained under specific ammonia loading of 0.016–0.139 kg N/[kg VSS day] in a sequencing batch reactor. Stable nitrite accumulation was observed during nitrification. The specific ammonia consumption rate was higher than the value of freshwater activated sludge and salt-acclimated freshwater activated sludge. With methanol as carbon source, specific nitrite reduction rate of halophilic denitrifiers was much less than the freshwater counterpart. Halophilic activated sludge was characterized as good settling and flocculation prosperity with small floc size and net-like sludge structure. The abundance of ammonia-oxidizing bacteria outnumbered ammonia-oxidizing archaeas in both estuarine sediments and the activated sludge. Nitrifier population was dominated by the halophilic members of genus Nitrosomonas. This study demonstrated the application of mixed halophilic consortia for efficient nitrogen removal, overcoming the limits and difficulties of applying freshwater bacteria for saline wastewater treatment.     

Effect of soil amendments on phytoextraction potential of Brassica juncea growing on sewage sludge

A pot experiment was conducted to investigate the influence of elemental sulfur, gypsum and chelating agent (Ethylenediaminetetraacetic acid) on copper, zinc, nickel, cadmium, chromium and lead uptake by Brassica juncea from sewage sludge. Addition of sulphur acidified the sludge, which caused the pH decrease to 5.4 with an initial pH 6.7. The shoot and root biomass were increased with sulfur addition, while decreased with Ethylenediaminetetraacetic acid addition. Applications of Ethylenediaminetetraacetic acid and sulfur resulted in a considerable increase in copper and lead concentrations in the plant. The highest root concentration of copper obtained to be 110?mg/kg?dw at Ethylenediaminetetraacetic acid treatment. For sulfur treatment, lead concentrations in shoots indicated almost high concentrations 77?mg/kg, about twofold increases relative to roots (34?mg/kg). The Transportation Index of all studied metals were quite low (TI?<?0.5), whereas the Bioaccumulation Factor values were much higher, varied from 0.01 to 9.67. Furthermore, the plant showed better Bioaccumulation Factor for copper and lead metals in both shoot and root. The efficiency to remove copper and lead from sludge is high in this plant. As a result, elemental sulfur will be effective amendment for phytoextraction of heavy metals from sewage sludge.     

Improvement in nitrification through the use of natural zeolite: influence of the biomass concentration and inoculum source

A batch nitrification process was studied using synthetic wastewater as substrate and Chilean natural zeolite as biomass carrier at ambient temperatures (20 °C). Three groups of experiments were carried out: a first experimental set (I) with and without added zeolite using initial biomass concentrations of 1,000 and 2,000 mg VSS/L; a second set of experiments (II) with added zeolite and at the same initial biomass concentrations. In these two experimental sets, biomass from an activated sludge process located in an urban wastewater treatment plant at La Farfana, Santiago de Chile, was used as inoculum (1). Finally, a third set of experiments (III) was carried out with zeolite at an initial biomass concentration of 1,000 mg VSS/L using an inoculum derived from an activated sludge process treating wastewater from a paper mill (inoculum 2). Nitrifying biomass concentration values in the range of 13,000–18,800 mg VSS/L were achieved when initial biomass concentrations varied between 1,000 and 2,000 mg VSS/L. Inoculum (1) generated higher biomass concentrations than inoculum (2). Ammonium N removals higher than 70 % were obtained in experimental sets II and III when zeolite was used. For both initial biomass concentrations tested, an exponential biomass growth was observed up to the second day of operation, and a slight decrease was evident afterwards, achieving stationary values after 10–12 days of operation. The third experimental set (III) revealed that the highest N consumption took place between days 11 and 16 of digestion.     

Changes in physical and chemical properties of three soil types in India as a result of amendment with fly ash and sewage sludge

The use of coal fly ash and domestic sewage sludge in agriculture is being considered as one of the methods for recycling of these wastes in an environmental beneficial manner. Mixtures with soil were prepared at different proportions of fly ash and sludge, either alone or in combination at a maximum application rate of 52 t ha^-1. The changes in the selected properties and heavy metal contents of three soil types in India were studied after incubating the respective mixtures for 90 days at near field capacity moisture level. Sewage sludge, due to its acidic and saline nature, high organic matter and heavy metals content, had more impact on soil properties than the fly ash. Sludge application produced several changes including an increase in available nitrogen, organic carbon, salinity and water-holding capacity of the soils. The concentrations of major cations and heavy metals also increased because of the sludge application and the pH was decreased. However, the levels of individual metal concentrations in all the mixture types were below the allowable limits prescribed by several environmental agencies. Using fly ash either alone or in equal quantity with sewage sludge had little influence on soil properties and heavy metal content. The relative availability (RA) of heavy metals in three soils amended with 52 t ha^-1 of sewage sludge was observed to be highest in oxisol, followed by alfisol and vertisol.     

Adsorption of reactive dyes from aqueous solutions by tannery sludge developed activated carbon: Kinetic and equilibrium studies

Adsorption kinetic and equilibrium studies of two reactive dyes, namely, Reactive Red 31 and Reactive Red 2 were conducted. The equilibrium studies were conducted for various operational parameters such as initial dye concentration, pH, agitation speed, adsorbent dosage and temperature. The initial dye concentration was varied from 10 - 60 mg/L, pH from 2–11, agitation speed from 100–140 rpm, adsorbent dosage from 0.5 g to 2.5 g and temperature from 30 °C -50 °C respectively. The activated carbon of particle size 600 μm was developed from preliminary tannery sludge. The dye removal capacity of the two reactive red dyes decreased with increasing pH. The zero point charge for the sludge carbon was 9.0 and 7.0 for the two dyes, respectively. Batch kinetic data investigations on the removal of reactive dyes using tannery sludge activated carbon have been well described by the lagergren plots. It was suggested that the Pseudo second order adsorption mechanism was predominant for the sorption of the reactive dyes onto the tannery sludge based carbon. Thus, the adsorption phenomenon was suggested as a chemical process. The adsorption data fitted well with Langmuir model than the Freundlich model. The maximum adsorption capacity(q⁰) from Langmuir isotherm were found to have increased in the range of 23.15–39.37 mg/g and 47.62–55.87 mg/g for reactive dyes reactive red 31 and reactive red 2, respectively.     

Heavy metals removal from synthetic wastewater by a novel nano-size composite adsorbent

The effects of varying operating conditions on metals removal from aqueous solution using a novel nano-size composite adsorbent are reported in this paper. Characterization of the composite adsorbent material showed successful production of carbon nanotubes on granular activated carbon using 1 % nickel as catalyst. In the laboratory adsorption experiment, initial mixed metals concentration of 2.0 mg/L Cu²⁺, 1.5 mg/L Pb²⁺ and 0.8 mg/L Ni²⁺ were synthesized based on metals concentration from samples collected from a semiconductor industry effluent. The effects of operation conditions on metals removal using composite adsorbent were investigated. Experimental conditions resulting in optimal metals adsorption were observed at pH 5, 1 g/L dosage and 60 min contact time. It was noted that the percentage of metals removal at the equilibrium condition varied for each metal, with lead recording 99 %, copper 61 % and nickel 20 %, giving metal affinity trend of Pb²⁺ > Cu²⁺ > Ni²⁺ on the adsorbent. Langmuir’s adsorption isotherm model gave a higher R² value of 0.93, 0.89 and 0.986 for copper, nickel and lead, respectively, over that of Freundlich model during the adsorption process of the three metals in matrix solution.     

Removal of uranium(VI) from aqueous solutions using Eucalyptus citriodora distillation sludge

Adsorption and desorption of uranium(VI) from dilute aqueous solutions by Eucalyptus citriodora distillation sludge was studied in a batch mode. The potential of Eucalyptus citriodora distillation sludge to remove uranium(VI) from aqueous solutions has been investigated at different conditions of solution pH, metal ion concentrations, biosorbent dosage, biosorbent particle size, contact time and temperature. The results indicated that biosorption capacity of Eucalyptus citriodora distillation sludge was strongly affected by the medium pH, the biosorbent dose, metal ion concentrations and medium temperature. Reduction in particle size increased the biosorption capacity. Langmuir and Freundlich isotherm models were applied to biosorption data to determine the biosorption characteristics. An optimum biosorption capacity (57.75 mg/g) was achieved with pH 4.0, particle size 0.255 mm, biosorbent dose 0.5 g/100 mL and initial uranium(VI) concentration of 100 mg/L. Uranium(VI) removal by Eucalyptus citriodora distillation sludge was rapid, the equilibrium was established within 60 min and pseudo-second-order model was found to fit with the experimental data. The biosorption process decreased with an increase in the temperature indicating its exothermic nature. Pretreatments of biomass with different reagents affected its biosorption capacity. A significant increase (34 %) in biosorption capacity (83.25 mg/g) was observed with benzene treatment. Fourier-transform infra-red studies showed the involvement of carbonyl, carboxyl and amide groups in the biosorption process. The results indicated that sulfuric acid had the best effects as an eluent showing 93.24 % desorption capacity.     

Uptake of Zn,Cu, Pb,and Cd by water hyacinth in the initial stage of water system remediation

The removal efficiency of water hyacinth for Zn, Cu, Pb and Cd after their entry into an undisturbed fresh water body was studied using minicosms placed within a reservoir. Variable parameters were water pH (6 or 8), single or multi-metal additions, and the plant biomass. The initial concentrations of Zn, Cu, Pb and Cd in water (500, 250, 250 and 50 μg/L, respectively) quickly decreased in the order Pb ≈ Cu ? Cd ≈ Zn in the first days. Metal removal was more efficient at pH 8 than at pH 6, and it was only slightly higher for single metals compared to multi-metal additions. After 8 days the remaining amounts of metals relative to their initial concentrations for multi-metal pollution treatments were 8% and 24% (Cu), 11% and 26% (Pb), 24% and 50% (Cd), and 18% and 57% (Zn) at pH 8 and pH 6, respectively. Increasing plant biomass promoted faster metal removal. The bioconcentration factor (the ratio of the metal concentration in whole plants to the initial metal concentration in water) exceeds 2000 for all metals (with the exception of Zn and Cd at pH 6). It was concluded that the water hyacinth can be successfully used for fast removal of metals in the initial stage of water body remediation.     

以秸秆为微生物碳源的尾矿原位修复:动态实验的初步分析

对铜陵相思谷尾矿砂中的重金属在生物和非生物条件下的淋滤行为进行了研究。设置两个动态反应柱进行实验(实验柱填充尾矿砂+污泥+秸秆,对照柱仅填充尾矿砂,进水SO42-1000 mg/L,pH 7.5)。结果表明,实验初期(0~20 d)实验柱出水重金属浓度明显高于对照柱,归因于柱内微生物加速了矿物分解和重金属的淋滤;此后实验柱出水SO42-浓度逐渐降低,同时Cu2+、Cd2+、Zn2+、总Fe浓度分别降至0.1 mg/L、0.1 mg/L0、.4 mg/L和1 mg/L以下。据此推测,实验柱中出现了微生物作用下的硫酸盐还原作用,生成了可以吸持重金属的硫化物沉淀。研究结果表明,以稻草为碳源、污泥为微生物接种源构建尾矿砂-微生物体系,能够有效还原硫酸盐并去除重金属,该方法可以用于矿山尾矿的原位修复。     

Immobilization of Cd,Zn and Pb in sewage sludge using red mud

Sewage sludge is an inevitable end by-product of sewage treatment. Land application provides a cost-effective alternative for sewage sludge disposal. However, sewage sludge contains heavy metals that may limit its application. In this work, red mud was employed for the immobilization of heavy metals in sewage sludge. The effect of red mud amendment on heavy metal immobilization was evaluated using Toxicity Characteristic Leaching Procedure (TCLP) method. The TCLP results showed that the immobilization efficiency of Cd, Zn and Pb was 100, 92, and 82%, respectively, when sewage sludge was mixed with 10% red mud. Tests carried out in leaching columns demonstrated that heavy metal concentrations in the leachate of 10% red mud amended sludge were lower than those of the unamended sludge. Moreover, red mud decreased plant available heavy metal (Cd, Zn and Pb) content from 18.1, 17.2 and 14.6% to 6.9, 11.4 and 7.6%, respectively. Sequential chemical extraction experiments showed that after sludge was amended with 10% red mud, exchangeable fraction was reduced and iron and manganese oxides fraction was increased. Red mud amendment can effectively immobilize Cd, Zn and Pb in sewage sludge before land application.