Paper Mill Sludge Research Articles

Hydrogen production and pollutants emission characteristics by co-gasified of paper-mill sludge and automobile shredder residues in a commercial scale fluidized bed gasifier

This research investigated the hydrogen production and energy conversion from automobile shredder residues (ASRs) and paper mill sludge (PMS) co-gasified in a full-scale fluidized bed gasification plant. The results obtained from full-scale tests provided important information on the feasible assessment of ASRs-to-energy and the selection of alternative technologies for ASRs. Based on the analysis results of produced gas composition, H2, CO, and CH4 composition produced from paper-mill sludge gasified were 4.17%–6.01%, 3.08%–4.32%, 1.71%–2.4%, respectively. Another C2 gas composition ranged from 2.9% to 3.59%. The heating value of produced gas ranged between 1.64 MJ/Nm3 and 2.18 MJ/Nm3. In the case of 10% ASR addition, the heating value of produced gas was slightly increased to 1.84 MJ/Nm3-2.34 MJ/Nm3. The dioxin emission concentration of flue gas was approximately 0.064 ng I-TEQ/Nm3. It can comply with Taiwan regulation thresholds. The dioxin leaching concentrations of residues derived from gasification were also in compliance with regulation limits by the TCLP test. Meanwhile, in the case of 10% ASRs addition, the dioxin equivalence concentration of gasified residue was nearly 0.002 ng I-TEQ/Nm3. It was far below the current regulation standard limit. In summary, the results of this research have proved the performance of ASRs-to-energy by co-gasified with paper mill sludge using a full-scale gasification plant. The results obtained from this research also provided the information for selecting ASRs alternative technologies and operating full-scale gasifiers in the future.

Sustainable utilization of incinerated paper mill sludge ash for the manufacture of building bricks

Sustainable utilization of incinerated paper mill sludge ash for the manufacture of building bricks

Treatment of laundry wastewater using extracellular polymeric substances (EPS)

The problem of management and treatment of wastewater from commercial laundries is a matter of concern. The present study provides an effective and eco-friendly solution to the treatment of wastewater from commercial laundries in Quebec (Canada) by using the extracellular polymeric substance (EPS) as a bio-flocculant. EPS was produced from the valorization of crude glycerol and paper mill sludge by a bacterial strain (BS-04). Two different types of EPS: Slime EPS (S-EPS) and Broth EPS (B-EPS) were used for the treatment of commercial laundry wastewater (CLWW). This is the first study for the treatment of CLWW using bio-flocculant EPS. A comparison between the conventional treatment of laundry wastewater (LWW) by chemical coagulants (FeSO4, CaCl2, Alum) and enhanced treatment by bio-flocculant EPS has been drawn in the study. Moreover, LWW treatment by a combination of EPS and chemical coagulants was also investigated. It was observed that S-EPS (0.6 g/L) gave better flocculation activity (FA) than B-EPS. S-EPS alone can remove 83.20% of turbidity, 77.69% of suspended solids (SS), and 76.37% of chemical oxygen demand (COD). The best results were obtained by combining S-EPS (0.6 g/L) with alum (300 mg/L) at pH 7 for a treatment time of 30 min. This combination was able to remove 98% of turbidity, 95.42% of SS, and 83.08% of COD from LWW. When treatment time has been increased to 4 h at pH 7, it resulted in more than 88% COD removal from CLWW.Graphical

Fabrication of novel biocomposite made of chemically treated sludge fibers and various molecular weight polypropylene

The effect of the chemical treatment of paper mill sludge fibers and polypropylene molecular weight were studied relative to the physical, mechanical, and morphological properties of a novel cellulosic biocomposite. Paper mill sludge fibers were treated with acetic anhydride, and succinic anhydride was mixed with maleic anhydride polypropylene (MAPP) and coupling agent (0 and 3%). The ratio of fibers and polymer materials was considered 30 to 70, which was manufactured by the hot-pressing method at 180 °C. Water absorption, volume swelling, and contact angle were examined on each specimen according to ASTM standards, while Fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM) explored the efficiency of chemical modification of fibers and the morphology of biocomposites, respectively. The results showed that chemical treatment of fibers reduced the water absorption and volumetric swelling. Both tensile and flexural strength were increased with chemical treatment using the coupling agent. Comparison of fibers treated with succinic acid and acetic acid showed that the succinic acid enhanced the mechanical properties better than the acetic acid treatment. Finally, FTIR analysis showed that the hydroxyl groups decreased, and SEM images indicated the interface between fibers and polypropylene improved via chemical treatment of sludge fibers.

Enhanced Internal Coating Structure and Light Reflectance of Coated Papers: A Sludge Valorization Process

Paper mill sludge (PMS) is a high-volume waste of the pulp-papermaking industry, containing cellulose fibers. This paper introduces cellulose nanofibers extracted from PMS (CNFsPMS) and their application in paper coatings using a wire-wound coating method to enhance internal and optical properties of paper. Three factors were investigated: (i) CNFsPMS amount, (ii) number of layers, and (iii) surface treatment via a 4 × 2 × 2 factorial design. The experimental responses were tracked by fundamentally important internal properties including porosity, air permeability, thickness, roughness, and optical properties of brightness, gloss, and CIE L*a*b* color coordination. The results showed that CNFPMS enhances porosity to 91 mL/min, permeability to 0.5 × 10–3 μm2, and gloss to 29.5 at 1 wt % CNFsPMS applied in two layers with 500 pli calendering. Roughness improves to 2 μm at all levels of CNFsPMS applied to two layers with 500 calendering. CNFsPMS prevents a decrease in brightness and improves lightness, suggesting more colors can be produced in printing applications. The utilization of PMS for papermaking applications can add value to these underutilized residues and open a new revenue stream by reusing it as a high-value material.

Walnut-shaped calcium oxide-cancrinite spheres for transesterification of waste frying oil

Producing biodiesel via transesterification of waste oils or fats with short-chain alcohol is one of the possible ways to alleviate global energy and environmental issues, and further reducing the cost of transesterification catalyst is the essential strategy to enhance the competitiveness of biodiesel, such as applying industrial solid wastes as the source of catalyst active species. Thus in this work, via one-step pyrolysis of the calcium-rich residue, a byproduct from the hydrothermal treating (140–180 °C for 2–4 h) of paper mill sludge (PMS), a novel walnut-shaped calcium oxide-cancrinite based catalyst was prepared and applied to the transesterification of waste frying oil. The hydrothermal condition (changed from 140 oC-2 h to 180 oC-4 h) of PMS slightly influenced the yield of fatty acid methyl ester (YFAME), which ranged from 98.87% to 96.95% due to the slight decrease of the total basicity of strong basic sites (TSBβ+γ) from 149.6 to 102.9 μmol g−1. On the contrary, the pyrolysis temperature had a much greater effect on the transesterification performance of obtained catalysts. The optimum pyrolysis temperature was 750 °C and when it was increased to 850 °C, the increased bonding tendency of Si with Ca passivated the activity of calcium species and reduced the basic intensity and basicity of PSC-850, thus lowering its transesterification activity. Besides, the key process parameters were optimized and at the conditions of 70 °C, 3 h, 6.0 wt% of catalyst dosage, 10:1 of molar ratio of methanol to oil, over 95% of YFAME can be reached. The work herein not only provided a feasible way to recycle the inorganic solid residue of PMS but further lowered the cost of preparing biodiesel.

Paper mill sludge rich enzymes and microbial community promotes the hydrogenesis of black liquor containing furfural

Black liquor (BL) bioconversion into valuable by-products is essential to develop a bioeconomy strategy; however, its furfural content hinders microbial fermentation activities. Hence, this study utilizes paper mill sludge (PMS) to provide extracellular enzymes, furfural-degrading microbial consortia, and electron donor required for promoting the BL hydrogenesis potential. Three up-flow anaerobic sequential batch reactors (UASBRs) are fed with PMS (UASBR1), BL (UASBR2), and PMS + BL (UASBR3) and operated in parallel at 15 min fill, 72 h reaction, and 4 h settling. The UASBR3 achieves the maximum volumetric H2 of 1.483 ± 0.088 L/L/d and H2 yield of 2.06 ± 0.12 mol/mol glucose, which drops by 88% in UASBR2 and 24% in UASBR1. The insufficient H2 productivity values in UASBR2 could be due to a lack of nutrients availability (C:N = 440:1 and C:P = 19:1), higher furfural concentration (2116 ± 422 mg/L), and involvement of the butyrate fermentation pathway. The synergetic effect between PMS and BL overcomes these limitations and enriches the fermentation medium with Proteobacteria phyla (22.8%) and Acinetobacter sp. degrading furfural (6.1%). The microbial community at the phylum level (e.g., Proteobacteria, Firmicutes, and Actinobacteria) in UASBR3 maximizes the migration of electrons (e−eq = 9.34 ± 0.54%) towards efficient H2 formation.

Ex-situ magnetic activated carbon for the adsorption of three pharmaceuticals with distinct physicochemical properties from real wastewater.

Pharmaceuticals are able to evade conventional wastewater treatments and therefore, are recurrently found in the environment with proven potential to cause harm to human and wildlife. Adsorption onto activated carbon (AC) is a promising complement. However, AC production from non-renewable resources and its difficult after-use recuperation are prohibitive. Hence, a waste-based magnetic activated carbon (MAC) was produced from paper mill sludge, via an ex-situ synthesis, for the adsorptive removal of carbamazepine (CBZ), sulfamethoxazole (SMX) and ibuprofen (IBU) from ultrapure water and wastewater. The MAC was obtained through the promotion of electrostatic interactions between magnetic and activated carbon particles in a water suspension at controlled pH between the points of zero charge of both surfaces. The optimized condition (MACX3) presented remarkable properties regarding specific surface area (SBET=795m2 g-1) and saturation magnetization (MS=19emug-1). Kinetic and equilibrium adsorption studies were performed under batch conditions. Adsorption equilibrium was reached in up to 30min for all pharmaceuticals in both matrices, proving the low dependence on the adsorbate and the broad applicability of MACX3 in pharmaceutical adsorption. Regarding equilibrium experiments, high Langmuir maximum adsorption capacities (qm) were achieved in ultrapure water (up to 711 ± 40 µmol g-1). Equilibrium studies in wastewater revealed a decay in qm when compared to ultrapure water: 28% for CBZ (468 ± 20 µmol g-1 (111 ± 5 mg g-1)), 78% for SMX (145±10 µmol g-1 (37 ± 3 mg g-1)) and 62% for IBU (273 ± 8 µmol g-1 (56 ± 2 mg g-1)), attributed to the wastewater pH, which dictates the speciation of the pharmaceuticals and controls electrostatic interactions between pharmaceuticals and MAC, and to competition effects by organic matter. It was demonstrated the promising applicability of a waste-based ex-situ MAC, rapidly retrievable from water, as an alternative tertiary wastewater treatment for pharmaceuticals removal.

Activated Biocarbon from Paper Mill Sludge as Electrode Material for Supercapacitors: Comparative Performance Evaluation in Two Aqueous Electrolytes.

The valorization of a South African paper mill waste sludge into an activated biocarbon electrode material for energy storage application is reported. The valorization method is a two-step synthesis that comprises hydrothermal carbonization and NaOH activation of paper mill waste at 700 °C to produce activated biocarbon. The development of high porosity carbon material with a surface area of 1139 m2/g was observed. The synthesized biocarbon electrode exhibited good specific capacitance (C sp) values of 206 and 157 Fg-1, from a three-electrode cell in neutral (1 M Na2SO4) and alkali (3 M KOH) electrolytes, respectively. The electrolyte concentration purportedly has a considerable effect on specific capacitance. In both electrolytes, symmetric triangular curves in galvanostatic charge-discharge point to a quick charge-discharge process. Synthesized material testing with a two-electrode cell in 3 M KOH and 1 M Na2SO4 electrolytes, respectively, delivered specific capacitances of 125 and 152 Fg-1, with the corresponding energy densities of 17.4 and 21.1 Wh kg-1. The material had capacity retention efficiencies of 83 and 92% after 5000 cycles in 3 M KOH and 1 M Na2SO4 electrolytes, respectively. The electrode material performance of the activated biocarbon from paper sludge clearly shows its potential for electrochemical energy storage. The reported results present an exciting potential contribution of the pulp and paper industry toward the transition to green energy.

Solid phase extraction using biomass-based sorbents for the quantification of pharmaceuticals in aquatic environments

The contamination of aquatic ecosystems with pharmaceuticals, such as carbamazepine (CBZ) and sulfamethoxazole (SMX), poses a risk to both humans and environmental biodiversity. In this regard, research aimed at the detection of pharmaceuticals in the environment remains a priority. The low levels at which these contaminants occur together with the complexity of the samples usually imply the need of sample clean-up and preconcentration strategies prior to quantification. Solid phase extraction (SPE) is frequently used due to the possibility of automatization and the vast diversity of sorbents available. However, its use in large environmental screenings significantly increases the cost of the analytical process, generally associated to the sorbents. In this work, two biomass-based sorbents, derived from waste materials (spent brewery grains and primary paper mill sludge), were used in SPE cartridges for the preconcentration of CBZ and SMX, which were then quantified using high-performance liquid chromatography (HPLC) with UV or fluorescence detection. The SPE procedure was optimized considering the type and mass of sorbent for each pharmaceutical, as well as the type and volume of eluent used, contact time during elution and sample volume. After the optimization procedure, limits of detection reached 0.69 μg/L for CBZ, compared with 164 μg/L without the extraction procedure, and 0.015 μg/L for SMX, compared with the 3 μg/L without the extraction procedure. Recovery results demonstrated that the developed method was accurate, reproductible, and suitable to be used for the determination of SMX and CBZ in surface waters, however it should be improved for their determination in effluent water.

Environmental Acceptability of Geotechnical Composites from Recycled Materials: Comparative Study of Laboratory and Field Investigations.

The environmental properties of three geotechnical composites made by recycling wastes were investigated on a laboratory scale and in the field with the use of lysimeters designated for the revitalization of degraded mining sites. Composites were prepared by combining the mine waste with paper-mill sludge and foundry sand (Composite 1), with digestate from municipal waste and paper ash (Composite 2), and with coal ash, foundry slag and waste incineration bottom ash (Composite 3). The results of laboratory leaching tests proved that Composites 1 and 3 are environmentally acceptable, according to the legislative limits, as the potentially hazardous substances were immobilized, while in Composite 2, the legislative limits were exceeded. In the field lysimeters, the lowest rate of leaching was determined for optimally compacted Composites 1 and 3, while for Composite 2 the leaching of Cu was high. This study proved that optimally installed Composites 1 and 3 are environmentally acceptable for use in construction as an alternative to virgin materials, for the revitalization of degraded mining sites or, along with Composite 2, for closure operations with landfills. In this way, locally available waste streams are valorised and channelized into a beneficial and sustainable recycling practice.

Amelioration of Biogas Production from Waste-Activated Sludge through Surfactant-Coupled Mechanical Disintegration

The current study intended to improve the disintegration potential of paper mill sludge through alkyl polyglycoside-coupled disperser disintegration. The sludge biomass was fed to the disperser disintegration and a maximum solubilization of 6% was attained at the specific energy input of 4729.24 kJ/kg TS. Solubilization was further enhanced by coupling the optimum disperser condition with varying dosage of alkyl polyglycoside. The maximum solubilization of 11% and suspended solid (SS) reduction of 8.42% were achieved at the disperser rpm, time, and surfactant dosage of 12,000, 30 min, and 12 μL. The alkyl polyglycoside-coupled disperser disintegration showed a higher biogas production of 125.1 mL/gCOD, compared to the disperser-alone disintegration (70.1 mL/gCOD) and control (36.1 mL/gCOD).

Vermicomposting Process of Organic Waste and Paper Mill Sludge

Vermicomposting Process of Organic Waste and Paper Mill Sludge

MECHANICAL PROPERTIES AND MICROSCOPIC MECHANISM OF PAPER MILL SLUDGE-MAGNESIUM OXYCHLORIDE CEMENT COMPOSITES

To make use of industrial solid waste from paper mills, namely paper mill sludge (PMS), and to develop green construction materials, the samples were tested by using these methods that include unconfined compressive strength tests, dry density tests, water absorption tests, scanning electron microscopes (SEM), and X-ray diffractometers (XRD). The effects of different dosages, different particle sizes, and different initial water contents of PMS on the strength and microscopic properties of magnesium oxychloride cement were studied. Results show that the compressive strength of the samples decrease with the increasing of particle size and initial water content, and it first increases before decreasing when PMS content increases. PMS can lessen water absorption while having little impact on the dry density. The compressive strength, which can reach 58.47 MPa, is at its highest when the mixing percentage of PMS is 60%. At this point, the composite material's Phase 5 crystal is longer and the water absorption rate is only 6.8%. The obtained conclusions can provide a reference for the engineering application of paper mill sludge-magnesium oxychloride cement composites. Keywords: Magnesium oxychloride cement, Paper mill sludge, Composite materials, Mechanical properties, Microscopic mechanism, Cemento de oxicloruro de magnesio, Lodos de papelera, Materiales compuestos, Propiedades mecánicas, Mecanismo microscópico.

Field Testing of Geomorphic Landform Design Features in Central Appalachia

Reclamation Highlights: We assessed construction methods for the application of geomorphic landforming and the use of paper mill sludge as a soil amendment for coarse coal refuse. The cap and cover system included a growth layer and low-permeability layer over coarse refuse. Coarse coal refuse and paper mill sludge blend can sustain vegetation.

Can TEMPO-Oxidized Cellulose Nanofibers Be Used as Additives in Bio-Based Building Materials? A Preliminary Study on Earth Plasters

Interest towards cellulose nanofibers obtained from virgin and waste sources has seen a significant growth, mainly thanks to the increasing sensitivity towards the concept of circular economy and the high levels of paper recycling achieved in recent years. Inspired by the guidelines of the green building industry, this study proposes the production and characterization of TEMPO-oxidized and homogenized cellulose nanofibers (TOHO CNF) from different sources and their use as additives for earth plasters on two different raw earth samples, characterized by geotechnical laboratory tests and mineralogical analysis: a high-plasticity clay (T2) and a medium-compressibility silt (ABS). Original sources, including those derived from waste (recycled cardboard and paper mill sludge), were characterized by determining chemical content (cellulose versus ashes and lignin) and fiber morphology. TOHO CNF derived from the different sources were compared in terms of nanofibers medium diameter, crystallinity degree, thermal decomposition and oxidation degree, that is the content of carboxylic groups per gram of sample. Then, a preliminary analysis of the influence of CNF on earth plasters is examined. Adhesion and capillary absorption tests highlighted the effect of such nanofibers on blends in function of two factors, namely the cellulose original source and the oxidation degree of the fibers. In particular, for both earth samples, T2 and ABS, a significant increase in adhesion strength was observed in the presence of some TOHO CNF additives. As far as capillary sorption tests, while an undesired increase in water adsorption was detected for T2 compared to the control, in the case of ABS, a significant reduction in water content was measured by adding TOHO CNF derived from recycled sources. These results pave the way for further in-depth investigation on the role of TOHO CNF as additives for earth plasters.

Challenges in developing strategies for the valorization of lignin-a major pollutant of the paper mill industry.

Apart from protecting the environment from undesired waste impacts, wastewater treatment is a crucial platform for recovery. The exploitation of suitable technology to transform the wastes from pulp and paper industries (PPI) to value-added products is vital from an environmental and socio-economic point of view that will impact everyday life. As the volume and complexity of wastewater increase in a rapidly urbanizing world, the challenge of maintaining efficient wastewater treatment in a cost-effective and environmentally friendly manner must be met. In addition to producing treated water, the wastewater treatment plant (WWTP) has a large amount of paper mill sludge (PMS) daily. Sludge management and disposal are significant problems associated with wastewater treatment plants. Applying the biorefinery concept is necessary for PPI from an environmental point of view and because of the piles of valuables contained therein in the form of waste. This will provide a renewable source for producing valuables and bio-energy and aid in making the overall process more economical and environmentally sustainable. Therefore, it is compulsory to continue inquiry on different applications of wastes, with proper justification of the environmental and economic factors. This review discusses current trends and challenges in wastewater management and the bio-valorization of paper mills. Lignin has been highlighted as a critical component for generating valuables, and its recovery prospects from solid and liquid PPI waste have been suggested.

Boosting persulfate activation via paper mill sludge-based biochar for efficient degradation of bisphenol A: Inherent multiple active sites

Paper mill sludge generated from the pulp and papermaking industries has inherent iron and carbon contents. Herein, the biochar derived from paper mill sludge (PSBC) was synthesized via simple pyrolysis processes and applied as an efficient persulfate (PDS) activator for the removal of Bisphenol A (BPA) in water. The unique properties of PSBC endowed it with multiple active sites including Fe(II) species, oxygen vacancy, CO, and graphite sp2-C with defects, owing to which, the PSBC/PDS process presented satisfactory performance with BPA removal efficiency up to 98 % within 60 min. Both of the radical and non-radical pathways were revealed to be involved in the BPA degradation. Based on the results of theoretical calculation, the existences of some special structures in PSBC effectively facilitated the electron transfer process of PDS activation. The process also exhibited a high anti-interference capability to coexisting substances and the universality toward various organic contaminants degradation. And the used PSBC can be recovered by simple thermal treatment. This work provided a promising heterogeneous PDS activator with plentiful active sites and satisfactory efficiency, which can be beneficial to the cost reduction of wastewater treatment and promotes the application of paper mill sludge in the area of environmental remediation.

Experimental study on the combustion behavior and NOx emission during the co-combustion of combustible industrial solid wastes

The combustible industrial solid wastes (CISW) include waste of textiles, paper, woody products, sludge and so on, generated from light industrial production. Excessive CISW can cause serious environmental pollution if not treated effectively. Incineration has become an efficient method for the disposal of CISWs due to its merits in rapid reduction and energy recovery. However, the incineration plants have often suffered from unstable combustion and serious air pollutant emissions due to the mismatch in the properties between the practical CISW blend and the designed target fuel. To achieve compatible CISW blends for the plant, the fundamental understanding of the combustion behavior and pollutant emission characteristics of individual CISWs and their designated blends during combustion is highly necessary. In this work, the combustion behavior of five CISWs has been studied on a thermogravimetric analyzer and the corresponding comprehensive combustion indexes (CCI) have been analyzed. Meanwhile, NOx emission during the combustion of individual or blended CISWs has been studied. It has been revealed that adding fungi or waste tires to paper mill sludge can effectively increase the CCI of blended fuels and reduce NOx emission. A linear correlation has been established between the conversion ratio of fuel-N to NOx and fuel components. The synergetic effect generated from the proper blending among different CISWs has been observed and quantitatively analyzed. Such an effect played a significant role in inhibiting NOx generation during the co-combustion of different CISWs caused by the reduction of porous char with high activity and several inorganic minerals. This study provides a theoretical basis for seeking a way of the suitable fuel blends.

Sustainable value methodology to compare the performance of conversion technologies for the production of electricity and heat, energy vectors and biofuels from waste biomass

The Sustainable Value methodology was used to compare and rank eight combinations of waste biomass types and conversion technologies on a common assessment basis to produce energy, energy vectors and advanced biofuels. The studied combinations included agricultural and agro-industrial residues, slurries and effluents, pulp and paper mill sludge, piggery effluents and organic fractions of municipal solid waste, to produce biodiesel by (trans)esterification, biogas by anaerobic digestion, ethanol by fermentation, hydrogen by dark fermentation, electricity and heat by combustion, biogas and synthesis gas by gasification, and bio-oils by pyrolysis or hydrothermal liquefaction. The numerator “Functional Performance” of the Sustainable Value indicator was estimated according to 14 criteria of process technology, material and energy inputs and outputs, and acceptance by the stakeholders. The performance of the technologies was classified based on the values of relative importance (φ) and level of satisfaction ( S ) attributed to each criterion. The gasification of residues from the olive-oil industry reached the highest “Functional Performance”, followed by anaerobic digestion of chestnut processing residues and pig-rearing effluents. The Sustainable Value denominator “Costs” depended mainly on the degree of maturity of the technologies, which penalised pyrolysis, hydrothermal liquefaction and dark fermentation. The final ranking of the Sustainable Value indicator was gasification > combustion > anaerobic digestion > (trans)esterification > pyrolysis and fermentation to ethanol > hydrothermal liquefaction > dark fermentation, respectively for the most adequate waste biomass types under study. Thermochemical conversions were mainly impacted by process and input criteria, while output and social acceptance criteria were more decisive for the biochemical conversions. • Sustainable Value (SV) analysis applies to waste biomass-to-energy (WBtoE) conversion • SV indicator enables the ranking of bio- and thermochemical WBtoE technologies • Costs uncertainty of low-maturity WBtoE technologies negatively impacts the SV score • Gasification of olive-oil industrial residues delivers the highest SV score of 4.09 • Biogas production by codigestion can further increase the SV score to 6.76