Biosynthesis of Poly(3-hydroxybutyrate) from Cheese Whey by <Emphasis Type="Italic">Bacillus megaterium</Emphasis> NCIM 5472

Microbial polyhydroxyalkonate such as homopolyester of poly(3-hydroxybutyrate) (PHB) was produced from cheese whey by Bacillus megaterium NCIM 5472. Due to their numerous potential industrial applications, the focus was given to competently enhance the amount of PHB produced. The amount of PHB produced from whole cheese whey, and ultrafiltered cheese whey was first compared, and after observing a rise in PHB production by using ultrafiltered cheese whey, cheese whey permeate was chosen for further analysis. The presence of PHB was then confirmed by GCMS. Since the main aim of the study was to increase the amount of PHB produced through batch fermentation, various process parameters like time, pH, C/N ratio, etc. were optimized. After optimization, it was found that B. megaterium NCIM 5472 was capable of accumulating 75.5% of PHB of its dry weight and a PHB yield of 8.29 g/L. The chemical structure of the polymer was further analyzed by using FTIR and NMR spectroscopy methods. Also, the physical and thermal properties were studied by using Differential scanning calorimetry and Thermogravimetric analysis. It was found that the polymer produced had excellent thermal stability, thus allowing the possibility to exploit its properties for industrial purposes such as adhesives, packaging materials, etc.     

1,3-Propanediol Production Potential by a Locally Isolated Strain of Klebsiella Pneumoniae in Comparison to Clostridium Beijerinckii NRRL B593 from Waste Glycerol

The fermentative production of 1,3-propanediol (1,3-PDO) by Klebsiella pneumoniae under different initial substrate concentrations (between 5 and 110 g/L) was investigated. It was found that glycerol was almost 100% utilized and 1,3-PDO production increased up to 20 g/L of influent substrate concentration, but there was a significant decrease in both glycerol consumption and 1,3-PDO production at substrate concentrations exceeding 20 g/L. Furthermore, pH control was essential, and a lack of pH control negatively effects of 1,3-PDO production. In the second part of the study, two microorganisms, namely Clostridium beijerinckii NRRL B593 and K. pneumoniae were comparatively studied in terms of their 1,3-PDO productivity under pH controlled conditions. Higher 1,3-PDO production was achieved under pH controlled fermentation conditions (pH = 7) for both microorganisms. Even though the two microorganisms had almost the same 1,3-PDO yield (0.60 mol/mol for C. beijerinckii, 0.61 mol/mol for K. pneumoniae) at the end of fermentation period, K. pneumoniae completed the 1,3-PDO production in one-third of the time (t = 8 h with a productivity of 1.34 g/L/h) than C. beijerinckii (t = 24 h). The results of this study clearly indicated that a substrate inhibition is a challenge that needs to be studied further for higher productivities.     

Polyhydroxybutyrate Accumulation in Bacillus megaterium and Optimization of Process Parameters Using Response Surface Methodology

The accumulation of polyhydroxybutyrate of Bacillus megaterium is growth associated and significantly dependent on carbon sources. In the present investigation B. megaterium strain isolated from soil was studied for PHB production in fructose minimal media. The PHB production was found to be growth associated. The polymer production by the strain was found to vary from 24 to 48 % content (w/w) of the dry cell weight. Box Bohn design was used to study the interactive effect of four variables on cell growth and PHB production. The optimized medium conditions with the constrain to maximize cell growth and PHB content were glucose 4.32 g/L, Mannitol 4.52 g/L and Na succinate 3.45 g/L and PHB yield 1.38 g/L amounting to 49 % of dry cell weight which is more than 1.8 folds the basal medium. The polymer production by the strain was found to vary from 12.18 to 57.2 % content (w/w) of the dry cell weight.     

Kinetic Study of Biopolymer (PHB) Synthesis in <Emphasis Type="Italic">Alcaligenes</Emphasis> sp. in Submerged Fermentation Process Using TEM

Poly-β-hydroxybuyrate (PHB) is a carbon—energy storage material which is accumulated as intracellular granule in variety of microorganism under nutrient starved conditions. Solid PHB is a biodegradable thermoplastic polymer and is utilizable in various ways similar to many conventional plastics. Ralstonia eutropha (Alcaligenes sp.), a gram negative bacteria accumulates PHB as insoluble granules inside the cells when nutrients other than carbon are limited. In this report effort has been made to analyze PHB granule synthesis inside Alcaligenes sp. NCIM 5085 by transmission electron microscopy and qualitative estimation of PHB was carried out by fourier transform infrared spectroscopy which provide better precision compared to other conventional techniques previously applied for PHB determination. Maximum PHB concentration of 2.20 ± 0.40 g/L and cell biomass of 3.42 ± 0.20 g/L was obtained after 48.0 h of fermentation. Leudking-Piret equation deduced mixed growth associated product formation which varies from earlier reports.     

Desiccation of contaminant barrier materials amended with aqueous carboxymethyl cellulose solution

The stabilization potential of negatively charged sodium carboxymethyl cellulose (CMC) solution was assessed through investigation of its retention on clays under environmental conditions that promote soil desiccation. Sodium montmorillonite and kaolinite, commonly used in clayey soils, were mixed with aqueous CMC solutions in concentrations ranging from 0 to 10 g/L. These samples were dried in a specially-designed desiccation chamber which was operated at a temperature of 25°C and relative humidity of 30%. The results show an inverse proportionality between liquid loss and CMC concentration. Liquid loss from clayey soil follows the first-order reaction with a rate constant in the range of 4.6–6.7 mg/h. CMC half-lives on sodium montmorillonite during desiccation ranged from 103 to 181 h for an aqueous concentration range of 0.5–10 g/L compared to 108 h for distilled water. For kaolinite, more liquid was retained at 10 g/L CMC concentration than at other concentrations, but liquid retention was generally insignificant. These conclusions are valid for a desiccation duration of 890 h, a time that is reasonably simulative of the duration of exposures of bare ground surfaces to weather elements. The experimental results are explained in terms of the role of CMC molecular interactions with clay minerals in controlling fluid flow to desiccating clay surfaces.     

Preformed Amide-containing biopolymer for Improving the Environmental Performance of Synthesized Urea–formaldehyde in Agro-fiber Composites

Investigations have continued for production high performance agro-based composites using environmentally acceptable approaches. This study examines the role of adding amide-containing biopolymers during synthesis of urea–formaldehyde (UF) on properties of adhesive produced, especially its adhesion potential. The environmental performance of UF-resin synthesized in the presence of modified amide-containing biopolymer was evaluated by evaluating the free-HCHO of both adhesive (during processing) and of the eventual engineered composite product. Also, the benefits of this synthesis-modified adhesive in enhancing the bondability of sugar-cane fibers used in engineered composite panels was evaluated and compared to using UF-resin. The results obtained show that, static bending of the produced composites varied from 27.7 to 33.13 N/mm² of modulus of rupture (MOR) and from 2860 to 3374 N/mm² of Modulus of Elasticity (MOE); while for internal bond (IB) it’s varied from 0.64 to 0.866 N/mm². Based on the ANSI and EN Standards modified UF-based agro composites produced meet the performance requirements for high grade particleboards with respect to static bending strength. These agro-based composite also tested out as having free-HCHO values of ~13 mg/100 g board.     

Influence of zinc chloride addition on the chemical structure of bio-oil obtained during co-pyrolysis of wood/synthetic polymer blends

The chemical structure of liquid products of the pinewood sawdust (W) co-pyrolysis with polystyrene (PS) and polypropylene (PP) with and without the zinc chloride as an additive was investigated. The pyrolysis process was carried out at 450 °C with the heating rate of 5 °C/min. The yield of liquid products of pyrolysis was in the range of 37–91 wt% and their form was liquid or semi-solid depending on the composition of the wood/polymer blend. The zinc chloride addition to wood/polymer blends has influenced the range of samples decomposition as well as the chemical structure of resulted bio-oils. All bio-oils from wood/polypropylene blends were two-phase (liquid and solid). Contrarily, all bio-oils obtained from biopolymer/polypropylene blends with zinc chloride added were yellow liquids. All analyses proved that the structure and the quality of bio-oil strongly depend on both the composition of the blend and the presence of ZnCl₂ as an additive. The FT-IR analyses of oils showed that oxygen-containing groups and hydrocarbons content highly depend on the composition of biomass/synthetic polymer mixture. The fractionation of bio-oils by column chromatography with four different solvents was followed by GC–MS analysis. Results confirmed the significant removal and/or transformation of oxygen-containing organic compounds due to the zinc chloride presence during pyrolysis process.     

Investigation of the effect of culture type on biological hydrogen production from sugar industry wastes

The bio-hydrogen generation potential of sugar industry wastes was investigated. In the first part of the study, acidogenic anaerobic culture was enriched from the mixed anaerobic culture (MAC) through acidification of glucose. In the second part of the study, glucose acclimated acidogenic seed was used, along with the indigenous microorganisms, MAC, 2-bromoethanesulfonate treated MAC and heat treated MAC. Two different COD levels (4.5 and 30 g/L COD) were investigated for each culture type. Reactors with initial COD concentration of 4.5 g/L had higher H₂ yields (20.3–87.7 mL H₂/g COD) than the reactors with initial COD concentration of 30 g/L (0.9–16.6 mL H₂/g COD). The 2-bromoethanesulfonate and heat treatment of MAC inhibited the methanogenic activity, but did not increase the H₂ production yield. The maximum H₂ production (87.7 mL H₂/g COD) and minimum methanogenic activity were observed in the unseeded reactor with 4.5 g/L of initial COD.     

Treatment of municipal landfill leachate using a combined anaerobic digester and activated sludge system

The main objective of this study was to assess the feasibility of treating sanitary landfill leachate using a combined anaerobic and activated sludge system. A high-strength leachate from Shiraz municipal landfill site was treated using this system. A two-stage laboratory-scale anaerobic digester under mesophilic conditions and an activated sludge unit were used. Landfill leachate composition and characteristics varied considerably during 8 months experiment (COD concentrations of 48,552–62,150 mg/L). It was found that the system could reduce the COD of the leachate by 94% at a loading rate of 2.25 g COD/L/d and 93% at loading rate of 3.37 g COD/L/d. The anaerobic digester treatment was quite effective in removing Fe, Cu, Mn, and Ni. However, in the case of Zn, removal efficiency was about 50%. For the rest of the HMs the removal efficiencies were in the range 88.8–99.9%. Ammonia reduction did not occur in anaerobic digesters. Anaerobic reactors increased alkalinity about 3.2–4.8% in the 1st digester and 1.8–7.9% in the 2nd digester. In activated sludge unit, alkalinity and ammonia removal efficiency were 49–60% and 48.6–64.7%, respectively. Methane production rate was in the range of 0.02–0.04, 0.04–0.07, and 0.02–0.04 L/g COD_rem for the 1st digester, the 2nd digester, and combination of both digesters, respectively; the methane content of the biogas varied between 60% and 63%.     

Heterotrophic Biological Denitrification Using Microbial Cellulose as Carbon Source

The objective of this study was to investigate the feasibility of using a microbial biopolymer produced by Acetobacter xylinum as a carbon source for heterotrophic biological denitrification. The denitrification rate, COD availability and nitrite concentration were response parameters. Under the experimental conditions, a denitrification rate of about 0.74 kg NO₃ ⁻N/m³d at 6 h retention time was achieved with microbial cellulose (MC). The reactor effluent contained significantly COD concentrations (20–86 mg/L) so it was not carbon limited, and was receiving enough carbon to facilitate the denitrification process. The maximum nitrite concentration in the effluent was found to be 0.4 mg/L. However, decreasing the retention time to 3 h significantly reduced the efficiency. It can be concluded that the MC is a suitable carbon source for nitrate removal in a heterotrophic biological denitrification process.     

Composition and production rate of medical waste from a small producer in Greece

The objective of this work was to determine the composition and production rate of medical waste from the health care facility of social insurance institute, a small waste producer in Xanthi, Greece. Specifically, produced medical waste from the clinical pathology (medical microbiology) laboratory, the X-ray laboratory and the surgery and injection therapy departments of the health facility was monitored for six working weeks. A total of 240 kg medical solid waste was manually separated and weighed and 330 L of liquid medical waste was measured and classified. The hazardous waste fraction (%w/w) of the medical solid waste was 91.6% for the clinical pathology laboratory, 12.9% for the X-ray laboratory, 24.2% for the surgery departments and 17.6% for the injection therapy department. The infectious waste fraction (%w/w) of the hazardous medical solid waste was 75.6% for the clinical pathology laboratory, 0% for the X-ray laboratory, 100% for the surgery departments and 75.6% for the injection therapy department. The total hazardous medical solid waste production rate was 64 ± 15 g/patient/d for the clinical pathology laboratory, 7.2 ± 1.6 g/patient/d for the X-ray laboratory, 8.3 ± 5.1 g/patient/d for the surgery departments and 24 ± 9 g/patient/d for the injection therapy department. Liquid waste was produced by the clinical pathology laboratory (infectious-and-toxic) and the X-ray laboratory (toxic). The production rate for the clinical pathology laboratory was 0.03 ± 0.003 L/patient/d and for the X-ray laboratory was 0.06 ± 0.006 L/patient/d. Due to the small amount produced, it was suggested that the most suitable management scheme would be to transport the hazardous medical waste, after source-separation, to the Prefectural Hospital of Xanthi to be treated with the hospital waste. Assuming this data is representative of other small medical facilities, medical waste production can be estimated for such facilities distributed around Greece.     

PLA Based Biopolymer Reinforced with Natural Fibre: A Review

In recent years renewed interest on the development of biopolymers, based on constituents obtained from natural resources is gaining much attention. Natural fibres such as kenaf, hemp, flax, jute, bamboo, elephant grass and sisal based polymer with thermoplastic and thermoset matrices offer reductions in weight, cost and carbon dioxide emission, less reliance on foreign oil resources and recyclability. Reinforced biopolymer with natural fibres is the future of “green composites” addressing many sustainability issues. Among the available biopolymer, PLA (polylactide) is the only natural resource polymer produced at a large scale of over 140,000 tonnes per year. Natural fibre reinforced PLA based biocomposites are widely investigated by the polymer scientists in the last decade to compete with non renewable petroleum based products. The type of fibre used plays an important role in fibre/matrix adhesion and thereby affects the mechanical performance of the biocomposites. The aim of this review is to investigate the effects of processing methods, fibre length, fibre orientation, fibre-volume fraction, and fibre-surface treatment on the fibre/matrix adhesion and mechanical properties of natural-fibre-reinforced PLA composites. Although much work has been performed to engineer the design of such superior biocomposites, the information is scattered in nature. A comprehensive review on the major technical considerations undertaken to prepare such biocomposites over the last decade is investigated to address the feasibility of wide scale industrial acceptance to such biocomposites. A brief review on the available natural fibres and biopolymer is also given for a comparative study.     

Statistical Optimization of Polyhydroxybutyrate Production by <Emphasis Type="Italic">Bacillus Pumilus</Emphasis> H9 Using Cow Dung as a Cheap Carbon Source by Response Surface Methodology

A gram positive bacterium (designated strain H9) found to be a potential polyhydroxybutyrate (biodegradable polymer) producer was isolated from the soil samples of a stress prone environment (municipal waste areas). This bacterium was identified as Bacillus pumilus H9 from its morphological, physiological and 16S rRNA gene sequence analysis. A four-factor central composite rotary design was employed to optimize the medium and to find out the interactive effects of four variables, viz. concentrations of cow dung, sucrose, peptone and pH on PHB production. Using response surface methodology, a second-order polynomial equation was obtained by multiple regression analysis and a yield of 2.47 g/L of PHB dry weight was achieved from the optimized medium at pH 7. Here, we report cow dung as a cheap carbon source for the production of PHB. Further, phbA, phbB and phbC genes were amplified by polymerase chain reaction which confirms the bacterium to be able to produce polyhydroxybutyrate.     

Investigation of Biosurfactant Activity and Asphaltene Biodegradation by <Emphasis Type="Italic">Bacillus cereus</Emphasis>

In this research, a biosurfactant-producing bacterium with capability of asphaltene degradation was isolated from oil-contaminated soil samples, and identified as Bacillus cereus. This strain produced an effective biosurfactant in the presence of molasses and the surface tension was reduced to the level of 36.4 mN/m after 48 h under optimum conditions. The optimum values of carbon-to-nitrogen ratio (C:N), pH, and temperature for biosurfactant production were determined as 30:1, 7.3 and 29 °C, respectively, using response surface methodology. The maximum emulsification activity in the culture broth was 53 % after 48 h using kerosene at 25 °C. The goodness of fit of four growth kinetic models including Tessier, Contois, Logistic and Westerhoff was compared for the bacterial growth and molasses utilization of B. cereus in 5-L batch bioreactor during 120 h. Conducted kinetic study showed that biosurfactant production had a good fit with the Contois growth kinetic model (R² = 0.962) and the maximum specific growth rate (µ _max ), saturation constant (K _s ) and the yield of biomass per substrate (Y _x/s ) were determined to be 0.145 h^?1, 1.83 g/L and 0.428 g/g, respectively. The asphaltene biodegradation in flask was evaluated by FTIR analysis and quantified by a spectrophotometer. This bacterium was able to degrade up to 40 % of asphaltene as a sole carbon and energy source after 60 days at 28 °C. The resulting surface tension of 30.2 mN/m with the critical micelle concentration of 23.4 mg/L indicated good efficiency of the biosurfactant.     

Purification and biochemical characterization of recombinant alcohol dehydrogenase from the psychrophilic bacterium <Emphasis Type="Italic">Pseudomonas</Emphasis><Emphasis Type="Italic">frederiksbergensis</Emphasis>

A gram-negative psychrophilic bacterium, with potential for biodegradation of long-chain n-alkanes was isolated from ice samples collected in Spitzbergen, Denmark. On the basis of results of biochemical and morphological tests and sequence analysis of 16S rRNA, the strain was identified as Pseudomonas frederiksbergensis. In this work, a short-chain NAD⁺-dependent alcohol dehydrogenase (alcDH) (Accession number: AAR13804) from the P. frederiksbergensis was cloned and transformed in E. coli BL21 (3DE) competent cells. The alcDH activity was highest in the crude extract of cells induced with 1.0 mM IPTG. The recombinant alcDH enzyme was purified to 93.4% homogeneity using three consecutive purification steps including ammonium sulphate, Q-Sepharose Fast Flow column and gel filtration chromatography employing Superdex 200 10/30 HR column. Enzyme enrichment and yield levels of 31.4 folds and 25.5%, respectively, were achieved. While the subunit molecular mass of the enzyme was determined on SDS-PAGE to be ~38 kDa, the aggregated native form of the enzyme had a molecular mass of ~238 kDa by gel filtration analysis. Reaction conditions optima for the recombinant alcDH were determined with propan-1-ol as the substrate. While the optimum pH was 9, the optimum temperature was 35 °C. The alcDH enzyme exhibited moderate thermal stability with half-lives of 150 min at 55 °C, 27 min at 65 °C and 8 min at 75 °C. Results for kinetic parameters indicated that the apparent K _m value for alcDH with propan-1-ol as the substrate was found to be 1.42 mM and the V _max value was 0.63 mmol mg⁻¹ min⁻¹. Experimental evidence revealed that the recombinant alcDH exhibited a wide range of substrate specificity, with higher levels of specific activity for aliphatic alcohols as compared to secondary alcohols. Taken together, the present study highlights the potential of alcDH as a member of cold-adapted enzymes in several key biotechnological applications including environmental bioremediation and biotransformations. It is envisaged that, with the ongoing screening of microorganisms and metagenomes, directed evolution approaches and the subsequent overexpression of recombinant proteins, more enzymes will be found that are suitable for bioremediation purposes.     

Chemical oxidation using stabilized hydrogen peroxide in high temperature,saline groundwater impacted with hydrocarbons and MTBE

In situ chemical oxidation (ISCO) of petroleum hydrocarbons (PHCs) within groundwater is considered a proven approach to addressing PHC‐impacted groundwater in nonsaline environments. One of the most common oxidants used for oxidation of PHCs in groundwater is hydrogen peroxide (H₂O₂). Due to its highly reactive nature, H₂O₂ is often stabilized to aid in increasing its reactivity lifespan. Limited research and application of ISCO has been completed in warm, saline groundwater environments. Furthermore, even fewer studies have been completed in these environments for ISCO using stabilized H₂O₂. In this research, stabilized H₂O₂ was examined to determine its effectiveness in the treatment of PHCs and the additive methyl tert‐butyl ether (MTBE). Three stabilizers (citrate, phytate, silica [SiO₂]) were tested to determine if the stabilizers could enhance and extend the treatment life of H₂O₂ within saline groundwater. To determine the effect of salinity on the three stabilizers, groundwater and aquifer samples were collected from two saline locations that had different salinity (total dissolved solids of about 7,000 mg/L and 18,000 mg/L). Specific target chemicals for treatment were water soluble, mobile components of gasoline including benzene, toluene, ethylbenzene, xylenes, (BTEX) and MTBE. Previous studies using unactivated persulfate indicated that the PHCs within the groundwater could be oxidized, however, only limited oxidation of the MTBE could be affected. The results of the laboratory tests indicated that greater than 95 percent of the target hydrocarbons were removed within 7 days of treatment. Microcosms with citrate‐stabilized H₂O₂ demonstrated a significantly faster and greater decline with most hydrocarbon concentrations reaching < 5 μg/L. The exceptions were ethylbenzene and m‐xylene, which were slightly decreased to about 30 and 20 μg/L, respectively. Initial mean concentrations of the BTEX compounds within the citrate‐stabilized microcosms were 10,554 μg/L, 9,318 μg/L, 6,859 μg/L, and 14,435 μg/L, respectively. The silicate‐stabilized H₂O₂ microcosms showed no significant benefit over the unstabilized control microcosms. The better performance of citrate‐stabilized microcosms was confirmed by increasing δ13C values of remaining hydrocarbons. MTBE declined from > 400 mg/L to < 100 mg/L in all microcosms, again with the best removal (> 90 percent) being measured in the citrate‐stabilized microcosms. Unfortunately, H₂O₂ oxidation in the microcosms also resulted in production of up to 40 mg/L TBA or approximately 10 percent of the MTBE oxidized.     

<Emphasis Type="Italic">Mesua ferrea</Emphasis> L. Seed Oil Based Highly Branched Environment Friendly Polyester Resin/Clay Nanocomposites

To develop a high performance environment friendly material, highly branched polyester/clay nanocomposites have been prepared from Mesua ferrea Linn seed oil-based polyester resin and hydrophilic bentonite nanoclay. The prepared nanocomposites were characterized by Fourier transform infra-red spectroscopy, X-ray diffractometer, scanning electron microscope, transmission electron microscope and rheological studies. Partial exfoliation of clay layers by the polymer chains with good interfacial interactions was observed in the nanocomposites. The formation of delaminated nanocomposites was manifested through the enhancement of tensile strength, scratch hardness, chemical resistance, impact resistance, thermostability, etc. The results show enhancement of three times in tensile strength and 18 °C in thermostability by inclusion of 5 wt% nanoclay as compared to the pristine polymer. By the influence of 5 wt% nanoclay four times enhancement in elongation at break as compared to the pristine polymer was noticed. Thus these nanocomposites have the potential to be used in many advanced applications.     

Optimization and validation of enhanced biological reduction of 1,2,3‐trichloropropane in groundwater

Laboratory and field demonstration studies were conducted to assess the efficacy of enhanced biological reduction of 1,2,3‐trichloropropane (TCP) in groundwater. Laboratory studies evaluated the effects of pH and initial TCP concentrations on TCP reduction and the activity of a microbial inoculum containing Dehalogenimonas (Dhg). Laboratory results showed successful reduction at a pH of 5 to 9 with optimal reduction at 7 to 9 and at initial TCP concentrations ranging from 10 to over 10,000 micrograms per liter (μg/L). Based on findings from the laboratory study, the effects of TCP concentration, geochemical conditions, and amendment concentration on bioremediation efficacy were investigated during a field demonstration at a site with relatively low initial concentrations of TCP (< 2 μg/L). The field demonstration included injection of emulsified vegetable oil (EVO) and lactate as a carbon substrate for biostimulation, followed by bioaugmentation using the microbial inoculum containing Dhg. Post‐injection performance monitoring demonstrated reduction of TCP to below laboratory detection limits (< 0.005 μg/L) after an initial lag period of approximately six months following injections. TCP reduction was accompanied by generation of the degradation byproduct propene. A marginal increase in TCP concentrations, potentially due to an influx of upgradient aerobic groundwater containing TCP, was observed eight months after injections thereby demonstrating the sensitivity of this bioaugmentation application to changes in geochemical parameters. Despite this marginal increase, performance monitoring results indicate continued TCP biodegradation 15 months after implementation of the injection program. This demonstration suggests that enhanced biodegradation of TCP by combining biostimulation and bioaugmentation may be a promising solution to the challenges associated with remediation of TCP, even when present at low part per billion concentrations in groundwater.     

Tannic acid as a novel and green leaching reagent for cobalt and lithium recycling from spent lithium-ion batteries

Tannic acid–acetic acid is proposed as novel and green chemicals for cobalt and lithium recycling from spent lithium-ion batteries through a leaching process. The synergism of both acids was documented through batch and continuous studies. Tannic acid promotes cobalt dissolution by reducing insoluble Co³⁺ into soluble Co²⁺, while acetic acid is critical to improve the dissolution and stabilize the metals in the pregnant leach solution. Based on batch studies, the optimum conditions for metal recovery at room temperature are acetic acid 1 M, tannic acid 20 g/L, pulp density 20 g/L, and stirring speed 250 rpm (94% cobalt and 99% lithium recovery). The kinetic study shows that increasing temperature to 80 °C improves cobalt and lithium recovery from 65 to 90% (cobalt) and from 80 to 99% (lithium) within 4 h at sub-optimum condition (tannic acid 10 g/L). Kinetic modeling suggests the leaching process was endothermic, and high activation energy indicates a surface chemical process. For other metals, the pattern of manganese and nickel recovery trend follows the cobalt recovery trend. Copper recovery was negatively affected by tannic acid. Iron recovery was limited due to the weak acidic condition of pregnant leach solution, which is beneficial to improve leaching selectivity.

     

Improved biogas production from rice straw by co-digestion with kitchen waste and pig manure

In order to investigate the effect of feedstock ratios in biogas production, anaerobic co-digestions of rice straw with kitchen waste and pig manure were carried out. A series of single-stage batch mesophilic (37 ± 1 °C) anaerobic digestions were performed at a substrate concentration of 54 g/L based on volatile solids (VS). The results showed that the optimal ratio of kitchen waste, pig manure, and rice straw was 0.4:1.6:1, for which the C/N ratio was 21.7. The methane content was 45.9–70.0% and rate of VS reduction was 55.8%. The biogas yield of 674.4 L/kg VS was higher than that of the digestion of rice straw or pig manure alone by 71.67% and 10.41%, respectively. Inhibition of biogas production by volatile fatty acids (VFA) occurred when the addition of kitchen waste was greater than 26%. The VFA analysis showed that, in the reactors that successfully produced biogas, the dominant intermediate metabolites were propionate and acetate, while they were lactic acid, acetate, and propionate in the others.