Paper Mill Sludge Research Articles

Simultaneous production of polyhydroxybutyrate and biogas from paper mill sludge through sodium citrate-mediated disperser-induced phase separated pretreatment

Paper mill waste activated sludge is an excess sludge produced from the paper industry wastewater treatment plant. Because of the bulk nature, its disposal concerns both economic and environmental perspectives. However, it widely consists of organic components and is considered a major attraction for its valorization to produce bioenergy and valued products. During the bioenergy and valued product retrieval, the enzymatic hydrolysis got hampered due to the presence of exopolymeric substances and thus require proper pretreatment prior to the product recovery. The application of two different phases of pretreatment by removing the flocs in the first step and then followed by the cell disintegration by mechanical means helps in enhancing the organics efficiently in soluble phase. In this study, the upshot of sodium citrate mediated disperser disintegration on sludge from a paper mill was explored enhance enzymatic hydrolysis. Firstly, the floc deaggregation results at 0.05 g sodium citrate per g suspended solid with the maximum floc deaggregation degree of 89 %. Further, the consequence of disperser disintegration on the floc deaggregated sludge sample shows solid reduction and solubilization of 12.5 % and 17.5 %, respectively, higher than the disperser alone disintegration (9.57 % and 13.4 %). The anaerobic biodegradability assay shows the maximum biogas production of 174.3 mL/g of chemical oxygen demand while utilizing pretreated settled sludge as substrate. There was no accumulation of polyhydroxybutyrate using pretreated sludge supernatant. Thus, the phase-separated pretreatment by sodium citrate-induced disperser pretreatment is a suitable approach for enhancing hydrolysis during bioenergy recovery.

Addition of fibers derived from paper mill sludge in paper coatings: impact on microstructure, surface and optical properties

Traditionally, cellulose nanofiber (CNF) production has primarily relied on virgin cellulose sources. Yet, the shift to using paper mill sludge (PMS) as a source for CNF underscores the significance of reusing and recycling industrial byproducts. PMS contains significant amounts of cellulose that can be extracted as a raw material. The purpose of present study is to provide a sustainable approach to PMS utilization as a paper coating additive in the cellulose nanofibrils (CNFPMS) form via simply scalable wire-wound rod coating method. The effect of CNFPMS additive amounts at two coating layers on microstructure and surface properties of coatings such as porosity, air permeability surface roughness and optical properties such as brightness, gloss and CIE L*a*b* is studied, which they can also provide insight for the eventual print performance. Results indicated that the obtained CNFPMS in paper coating shows 52% decrease in porosity, presenting significant improvement in the coating microstructure. The marginal increase in permeability coefficient and surface roughness, 54% and 10%, respectively, suggests improving color reproduction and preventing color density losses. Optical analysis showed slight decrease in brightness and gloss, as was expected. Notably, the lightness was improved, which also indicates increasing color gamut volume in printing applications. As a result, the current work offers a sustainable approach to manage PMS for use in paper coatings as a high-value-added material.

Physical Properties of Retisol under Secondary Pulp and Paper Sludge Application

A positive effect of pulp and paper mill sludges as a rich source of organic substrates on soil properties was previously found for some types of sludge and soil. In this study, the effect of secondary pulp and paper sludge on water characteristics and thermal properties of Retisol, as well as the growth parameters of lettuce (Lactuca sativa L.), was tested on the basis of a pot experiment when watering plants with a 20 or 40% sludge solution. The sludge application enhanced plant growth with an increase in biomass accumulation of 21 and 53%, respectively, for 20 and 40% sludge treatments. When the sludge dose was increased from 0 to 40%, the number of leaves increased by 25%, and the leaf mass per area value increased by 42%. Due to the accumulation of more biomass in the shoots than in the roots, sludge causes a change in the allocation of plant biomass. A significant effect of the sludge application on soil particle and microaggregate sized compositions, as well as on the saturated soil hydraulic conductivity, was not found in this study. However, fitted soil water retention curves showed an increased soil water content in sludge-treated soil at all water content values exceeding field capacity. Secondary sludge application led to an increase in the saturated water content from 0.50 to 0.56 cm3 cm−3. The 40% sludge solution increased soil thermal conductivity from 0.92 to 0.98 W m−1 K−1 under saturated water content and from 0.83 to 0.92 W m−1 K−1 under field capacity. The thermal conductivity was higher in the sludge-treated than untreated soil due to a more pronounced positive effect of increased saturated water content than the negative effect of the increased organic matter content on heat transfer. The positive impact of secondary sludge application on both plant growth parameters and physical properties of Retisol, such as increased soil water-holding capacity and thermal conductivity coefficient confirms the possibility of using it to improve soil characteristics and plant productivity.

Experimental and theoretical study to control the heavy metals in solid waste and sludge during pyrolysis using modified expanded vermiculite

Na+/K+/Mg2+/Ca2+ expansion–modified vermiculite and calcination expansion (700 °C, 800 °C and 900 °C)–modified vermiculite (700-Mg-V, 800-Mg-V and 900-Mg-V) were prepared as additives to control the emission of five heavy metals (Zn, Cr, Cu, Pb, and Cd) during the pyrolysis of municipal sewage sludge, paper mill sludge, municipal domestic waste, and aged refuse. Mg2+-Modified vermiculite obtained via thermally activated calcination at 800 °C retained 65% of heavy metals from all raw materials at 450 °C. Zn, Cr, and Cu retained nearly 90%. Although modified vermiculite could reduce the ecological risk, Cd had an ecological risk level higher than Zn, Cr, Cu, and Pb. The fine textural properties, laminated morphology, and expansion capacity of modified vermiculite were positively correlated with its retention of heavy metals. Heavy metals interacted with the (002) surface of vermiculite, and the reactions were mainly concentrated near the 17-O and surrounding atoms. The heavy-metal monomers were less capable of binding to the (002) surface of vermiculite than the oxides and chlorides of heavy metals. The effect of heavy-metal oxides and chlorides binding to the (002) surface of vermiculite was related to heavy metals.

High biosorption of cationic dye onto a novel material based on paper mill sludge

The valorization of paper mill sludge (PMS) is the main goal of this study. The emissions of PMS continue to increase at global scale, especially from packaging paper and board sectors. The raw sludge was used to prepare an adsorbent to remove toxic pollutants from wastewater, the methylene blue (MB), an organic dye. Firstly, the physico-chemical characterization of PMS was done determining the crystalline phases of PMS fibers, the content of main elements, and the pH zero point charge, which was determined at around pH 7. The adsorption of MB on PMS powder was studied at 18 °C with an agitation of 200 rpm, being the best operating conditions 30 min of contact time, 250 mg L−1 of initial MB concentration and 0.05 g in 25 mL of adsorbent dose. Experimental data of MB adsorption was fitted to Langmuir and Freundlich isotherm equations. The Langmuir model was more accurate for the equilibrium data of MB adsorption at pH 5.1. The PFOM and PSOM were adjusted to experimental adsorption kinetics data, being PSOM, which describes better the MB adsorption by PMS powder. This was confirmed by calculating the maximum adsorption capacity with PSOM, which was 42.7 mg g−1, being nearly similar of the experimental value of 43.5 mg g−1. The analysis of adsorption thermodynamics showed that the MB was adsorbed exothermically with a ΔH0 = − 20.78 kJ mol−1, and spontaneously with ΔG0 from − 0.99 to − 6.38 kJ mol−1 in the range of temperature from 291 to 363 K, respectively. These results confirm that the sludge from paper industry can be used as biosorbent with remarkable adsorption capacity and low cost for the treatment of wastewater. PMS can be applied in the future for the depollution of the effluents from the textile industry, which are highly charged with dyes.

EFFECTS OF MODIFIERS ON MAGNESIUM OXYCHLORIDE CEMENT DOPED WITH PAPER MILL SLUDGE

To apply the composite material of magnesium oxychloride cement (MOC) doped with paper mill sludge (PMS) to engineering, the four modifiers such as phenylacrylic emulsion (PE), sodium methyl silicate (SMS), sodium phosphate monobasic (SPM), and citric acid (CA) were used to explore their effects on the composite material. The effects of these modifiers on the setting time, flowability, mechanical strength, softening coefficient, and strength loss coefficient of the composites were analyzed by physical properties, mechanical strength, water resistance, and resistance to sulfate attack, as well as by XRD. Results show that all four different modifiers can delay the setting time of the slurry and increase the fluidity of the mortar. With the increase of modifier dosage, the strength of mortar modified by different modifiers is lower than that of the control group, and the softening coefficient and sulfate erosion resistance coefficient of the modified mortar are significantly improved. At 2% and 1.5%, respectively, SPM and CA have the best modification effects, but PE integration decreases the softening coefficient of the mortar and only increases it by 47.30% at 0.5%. The obtained conclusions can provide a reference for the engineering application of PMS-MOC. Keywords: Magnesium oxychloride cement, Paper mill sludge, Composite materials, Modification, Softening coefficient.

Calcium peroxide induced mechanical disintegration in acidic environment for efficient biogas and biopolymer generation from paper mill sludge

The proposed research envisioned to improve the accessibility of organics and hydrolysis of paper mill waste activated sludge for polyhydroxybutyrate production and anaerobic digestion. In order to fill this research gap an exploration has been made by adding lower dosage of calcium peroxide at acidic pH for the removal of exopolymeric substances thereby improving the disintegration efficacy. The results indicate that the calcium peroxide dosage of 0.06 g/g SS at pH 5 was optimum for floc fragmentation. The influence of floc fragmented sludge on disintegration by disperser shows the solubilization and solid decrement of 18.8% and 12.4% at the specific energy input of 4729.24 kJ/kg total solid. The impact of pretreated supernatant on polyhydroxybutyrate accumulation shows the maximum polyhydroxybutyrate content of 85.03 % while utilizing 60% (v/v) of pretreated sludge supernatant as a carbon source at 42 h. Subsequently, the settled sludge was directed towards an anaerobic biodegradability assay and found about 167 mL/g of chemical oxygen demand of biogas generation, which is higher than the crude sample (52 mL/g of chemical oxygen demand). The higher solubilization in pretreated sample reveals the easier accessibility of substrate by the microorganisms, thereby enhances bioenergy and valued product generation.

Sustainable use of wastes as reactive material in permeable reactive barrier for remediation of acid mine drainage: Batch and continuous studies

The aim of this work was to evaluate the feasibility of the use of different industrial and agricultural wastes as reactive materials in Permeable Reactive Barriers (PRB) for Acid Mine Drainage (AMD) remediation. Sugar foam (SF), paper mill sludge (PMS), drinking water sludge (DWS) and olive mill waste (OMW) were evaluated in terms of pH neutralization and metal removal from AMD. Laboratory batch tests and continuous pilot scale up-flow columns containing 82% of Volcanic Slag (VS), as porous fill material, and 18% w/w of one of the industrial and agricultural wastes previously indicated, were tested.From the batch tests it was observed that the reactive material presenting the best results were the SF and the PMS. The results obtained in all the PRB were accurately described by a pseudo-first order model, presenting coefficient of determination higher than 0.96 in all the cases.During the continuous operation of the PRB, the porosity and hydraulic retention time (HRT) of most of the up-flow columns strongly decreased due to chemical precipitation and biofilm growth. The SF presented a significant number of fine particles that were washed out by the liquid flow, generating an effluent with very high total suspended solid concentration. Despite SF was the material with the highest alkalinity potential, the reduction of the HRT limited its neutralization and metal removal capacity. PMS and DWS presented the best pollutant removal yields in the continuous operation of the PRB, ranging from 55 to 99% and 55–95% (except in the case of the Mn), respectively. These results allowed the metal removal from the AMD. Additionally, these wastes presented very good biological sulphate reduction.Based on these results, the use of PMS and DWS as reactive material in PRB would allow to simultaneously valorise the industrial waste, which is very interesting within the circular economy framework, and to remove metals from the AMD by means of a low-cost and environmentally sustainable procedure.

Autogenous iron-based peroxidase-like nanozyme from paper mill sludge for ascorbic acid detection

The high-value conversion of waste resources to carbon materials offers an opportunity to alleviate the resource crisis. Owing to their low cost and easy preservation, iron-based nanoenzymes are receiving increasing attention in the fields of catalysis, detection and biomedicine. In this work, for the first time, paper mill sludge (PMS), which contains iron ions from a flocculant used in paper mill wastewater treatment, is used as a precursor to produce iron-doped carbon quantum dots (Fe-CQDs) by oil bath pyrolysis process. The synthesized Fe-CQDs with carboxyl groups and abundant carbon-deficient structure, exhibit higher peroxidase-like activity. Compared to horseradish peroxidase (HRP), Fe-CQDs have a better affinity for the substrate and better stability. Based on the good affinity of Fe-CQDs for H2O2, a rapid colourimetric assay for ascorbic acid (AA) detection was developed with a wide range of 1–120 μM and a detection limit of 0.435 μM (3σ/k). The peroxidase-like activity of Fe-CQDs has been proved to originate from their ability to catalyze H2O2 to produce·OH, and successfully applied to determine AA content in the roots and leaves of sweet potato. This work indicates the reliability of the method in practical application and provides a greening strategy for the value-added utilization of solid sludge.

Potential Use of Paper Mill Sludge in Improving Soil Quality for Plant Growth

This study evaluated the impact of soil modifiers on seed germination and soil quality. Mixtures of paper mill sludge (PMS) with camellia oilseed cake (CO) and peat moss (P), as well as with oilseed cake of toothache tree (TO) and peat moss (P), showed promising results as biostimulants for seed germination. The addition of PMS increased the germination index, indicating its beneficial effects on seed performance. The pH levels remained optimal, and the electrical conductivity values stayed within acceptable ranges, suggesting minimal hindrance to plant growth. The cation exchange capacity increased with PMS, enhancing nutrient availability. Composted mixtures exhibited increased phosphorus levels, contributing to soil fertility. While the organic matter content decreased after composting, the carbon-to-nitrogen ratio remained balanced. The bulk density increased after composting, potentially improving soil drainage. Overall, the TO-containing mixture demonstrated superior growth rates compared to the P. These findings support the use of PMS-based soil modifiers for enhancing seed germination and improving soil quality.

Improving coarse-textured mineral soils with pulp and paper mill sludges: Functional considerations at laboratory scale

Building up the organic matter content of coarse-textured soils with organic amendments seeks to ameliorate the productivity of these soils, which is limited by plant available water and nutrient supply. Wood fibre-based sludges from the pulp and paper industry have potential for soil conditioning. In this study, the effects of three different pulp and paper mill sludges at application rates of 10 and 20 vol-% on water retention, respiration, and nitrogen (N) dynamics were examined in a series of laboratory studies using coarse field soils. Water retention curves comprising 13 matric potentials revealed that the amendments increased total soil porosity and volumetric water content at matric potentials corresponding to macro- and mesopores size range with pore diameters of >30 μm and 30–0.2 μm, respectively. Volumetric water content at field capacity increased by c. 10–30%, depending on the type (fresh, lime-stabilised and fibre sludge) and application rate of the amendment, with no marked change in the water content at the permanent wilting point. This was reflected as a mean increase of 1.9–3.3 mm in the plant available water content relative to the non-amended soils (17 mm), which corresponds to 19–33 m3 per hectare. At most, an increase of 5.5 mm (55 m3 ha−1) in plant available water was achieved by the fibre sludge amendment at an application rate of 20 vol-%. During a 60-day laboratory incubation, c. 30–40% of the carbon (C) added to soil in the sludge materials was respired as carbon dioxide. Additional N accelerated decomposition without increasing total respired C. Decomposition of the amendments in the soil led to a net N immobilisation of roughly 5–10 mg min-N g−1 added C, which occurred mainly during the first two weeks after soil incorporation. Overall, pulp and paper mill sludge amendments may serve to alleviate water shortages during drought in coarse-textured soils, but may generate a transient plant-microbe competition in N uptake.

Effect of thermal-calcium peroxide mediated exopolymer release on disperser pre-treatment for efficient anaerobic digestion

The present study aimed to improve the hydrolysis potential of paper mill sludge through a two-phase disintegration process. In Particular, attention was focused on removal of extracellular polymeric substance (EPS) i.e. deflocculation of sludge in order to improve the efficiency of subsequent disperser disintegration. During deflocculation, carbohydrate, protein and deoxyribonucleic acids (DNA) were used as assessment parameters. During disintegration, soluble chemical oxygen demand (SCOD) and suspended solids (SS) reduction were used as assessment index to evaluate the efficiency of disintegration. A greater EPS removal was attained while deflocculating the sludge at calcium peroxide dosage of 0.05 g/g suspended solids (SS) and at a temperature of 70 °C. When comparing the disintegrated samples, a clear variation was noted in deflocculated and disintegrated sludge (19.2%) than the disintegrated sludge alone (13.5%). This clearly shows the need for deflocculation prior to disintegration. Likewise, a higher biomethane production of 0.214 L/g COD was achieved in deflocculated and disintegrated sludge than the pretreated sludge alone. Deflocculation reduces sludge management cost from 170 USD (Disperser alone (D alone disintegration)) to 51 USD (Thermal calcium peroxide mediated-Disperser (TCaO2-D disintegration), indicating the efficiency of the proposed disintegration.

Box–Behnken Design-Based Optimization of the Saccharification of Primary Paper-Mill Sludge as a Renewable Raw Material for Bioethanol Production

In this study, the primary paper-mill sludge characterized as containing 51% glucan was used to optimize the enzymatic saccharification process for the production of bioethanol using a Box–Behnken design (BBD). Polyethylene glycol 4000 (PEG-4000) surfactant-assisted enzymatic saccharification of dried primary sludge (DPS) showed a 12.8% improvement in saccharification efficiency. There was a statistically significant effect of solid enzyme loading and saccharification time on the enzymatic saccharification of DPS at a 95% confidence level (p < 0.05). The optimum levels of 10.4% w/w DPS solid loading, 2.03% enzyme loading (10 FPU g/DPS), and 1% (w/w DPS) PEG-4000 loading for a saccharification efficiency of 57.66% were validated experimentally and found to be non-significant with regard to the lack of fit with the predicted saccharification efficiency of 56.76%. Furthermore, Saccharomyces cerevisiae fermented the saccharified sugars into ethanol (9.35 g/L) with a sugar-to-ethanol conversion yield of 91.6% compared with the theoretical maximum. Therefore, DPS is a more suitable renewable biomass for determining the presence of fermentable sugar and for the production of ethanol.

Optimisation of β-Glucosidase Production in a Crude Aspergillus japonicus VIT-SB1 Cellulase Cocktail Using One Variable at a Time and Statistical Methods and its Application in Cellulose Hydrolysis.

Pulp and paper mill sludge (PPMS) is currently disposed of into landfills which are reaching their maximum capacity. Valorisation of PPMS by enzymatic hydrolysis using cellulases is an alternative strategy. Existing commercial cellulases are expensive and contain low titres of β-glucosidases. In this study, β-glucosidase production was optimised by Aspergillus japonicus VIT-SB1 to obtain higher β-glucosidase titres using the One Variable at a Time (OVAT), Plackett Burman (PBD), and Box Behnken design (BBD)of experiments and the efficiency of the optimised cellulase cocktail to hydrolyse cellulose was tested. β-Glucosidase production was enhanced from 0.4 to 10.13 U/mL, representing a 25.3-fold increase in production levels after optimisation. The optimal BBD production conditions were 6 days of fermentation at 20 °C, 125 rpm, 1.75% soy peptone, and 1.25% wheat bran in (pH 6.0) buffer. The optimal pH for β-glucosidase activity in the crude cellulase cocktail was (pH 5.0) at 50 °C. Optimal cellulose hydrolysis using the crude cellulase cocktail occurred at longer incubation times, and higher substrate loads and enzyme doses. Cellulose hydrolysis with the A. japonicus VIT-SB1 cellulase cocktail and commercial cellulase cocktails resulted in glucose yields of 15.12 and 12.33 µmol/mL glucose, respectively. Supplementation of the commercial cellulase cocktail with 0.25 U/mg of β-glucosidase resulted in a 19.8% increase in glucose yield.

Development of value-added sustainable products from paper mill sludge: An experimental approach

The disposal of paper mill sludge waste generated by the paper industry is a tough and challenging task. In this work, an attempt is made to develop various value-added products namely bricks, briquettes, ground chakra base, and eco-friendly composites from the secondary paper mill sludge (PMS). The secondary PMS was initially dewatered to remove the moisture content, ground to powder, and mixed with cement, MSand. quarry dust, and fly ash to produce bricks. The brick specimens were tested for compressive strength, water absorption, and efflorescence as per the standards and found to be 5.29 ± 0.11 N/mm2, 3.84 ± 0.13% respectively, and have NIL efflorescence. The PMS is mixed with paraffin wax and compressed in a squeeze moulding to form briquettes and observed that the percentage of ash content in the briquette is 66.6% which is less than that of the PMS. Further, a ground chakra base is produced using a slurry of starch and dried in a heater at 60° exhibiting better properties. An eco-friendly composite pottery product was developed by mixing PMS, clay, and starch and tested for breakage.

Total Mikroba pada Tanah yang Dicemari Sludge Limbah Pabrik Kertas dengan Perlakuan Pupuk Guano

There are 83 paper mills in Indonesia recorded by the Indonesian Pulp and Paper Association (APKI) spread throughout the archipelago. These paper companies produce products in the form of tissues, various types of paper, and other fiber-based products. Efforts to meet the needs of this raw material produce innovations in the form of using waste paper by separating the ink from the fibers contained in the paper, this separation process is known as the deinking process. Paper mill solid waste can be in the form of sludge, pith, and biosludge. Sludge is a factory solid waste originating from the settling of WWTP which consists of 90% solid and 10% liquid. Paper mill waste in the form of solid waste from sludge contains heavy metals such as Cd, Cr, Pb, Ni, Cu, and Zn. These metals can be overcome by bioremediation using guano fertilizer which is an organic material derived from bat droppings which is rich in phosphate. The purpose of this study was to determine the microbial population in soil contaminated with paper mill sludge waste treated with guano fertilizer. The parameters observed in this study were the total number of bacteria and fungi that survive in soil contaminated with paper mill waste as an indication that the land can still be planted with certain plants. This research was conducted at the Laboratory of Soil Biology, Laboratory of Soil and Land Fertility Agrotechnopark – Faculty of Agriculture – University of Jember. This study used a 3x3 two factorial experimental design with the basic pattern of Randomized Block Design (RAK), namely between the concentration of paper mill effluent and the dose of guano fertilizer, each treatment was repeated three times. The microbial population can be determined by analyzing total bacteria, total fungi. Soil that had been contaminated with paper mill waste was incubated with guano fertilizer, each combination was analyzed at 15 hst and 30 hst for total bacterial and total fungal populations. During the incubation period, irrigation was carried out using a sprayer to maintain moisture in the incubation media. The results showed that the total population of bacteria and fungi in the growing media contaminated with paper mill sludge waste by administering different doses of guano showed results that were not significantly different, but the total population tended to increase. with increasing incubation period. Pollution of sludge waste in the planting medium has a significant effect on increasing the total Fungi Population when compared to the control. The relationship between paper mill effluent pollution and guano fertilization is very low with a coefficient of determination of less than 0.5.

Integrated enzyme hydrolysis assisted cellulose nanofibril (CNF) fabrication: A sustainable approach to paper mill sludge (PMS) management

The landfilling of paper mill sludge (PMS) has been restricted or even banned in many countries due to the raised concern about greenhouse gas (GHG) emissions and contamination of the soil and water, calling for a sustainable PMS management approach. The potential valorization of PMS to nanomaterials combined with traditional biorefinery was examined in this work. Three types of PMS-derived cellulose nanofibrils (CNFs) were prepared and evaluated: enzymatically assisted CNF (AU: with in-house produced enzyme and CT: with commercial enzyme), mechanically pretreated CNF (BT), and chemically pretreated CNF by TEMPO oxidation (TEMPO). It was found that enzyme-assisted mechanical fibrillation-derived CNFs had a comparable average diameter (27.9 nm for AU and 22.7 nm for CT) with that produced from mechanical pretreatment (26.5 nm for BT) and TEMPO oxidation pretreatment (20.0 nm for TEMPO), and they showed the best drainage properties among the three types of CNF. The CNFs resulting from enzymatic pretreatment reduced 15% of energy consumption compared to the mechanical method and had better thermostability than TEMPO oxidation method. In addition, the on-site produced enzyme showed similar performance to the commercial enzymes towards the CNF properties. These findings provide new insights into a promising integrated strategy in engineering CNF from PMS with on-site enzyme production as a novel and sustainable approach for PMS management and valorization.

Thermogravimetric Analysis on Co-Gasification Characteristics of Sludge and Straw under CO2 Atmosphere

To maximize the potential energy utilization of agricultural and forestry wastes and sludge, experimental studies were conducted on the co-gasification characteristics of two types of sludge (municipal sludge, MS; paper-mill sludge, PS) and a typical biomass straw (ST) under CO2 atmosphere. In this paper, the main two stages of the gasification process, the pyrolysis in the low-temperature region and the CO2-gasification in the high-temperature region, were separately studied and analyzed. The experimental results showed that biomass could effectively promote the pyrolysis of the sludge in the low-temperature region and improve the gasification in the high-temperature region. Due to the complex interactions between components, the characteristic parameters presented obvious nonlinear rules during the co-pyrolysis and co-gasification processes. For the MS-ST mixtures, when increasing the ST content, (i) in the pyrolysis process, the initial reaction temperature gradually decreased, but the final reaction temperature, the peak reaction rate and the corresponding temperature, and the pyrolysis index gradually increased; (ii) in the gasification process, the initial reaction temperature, the reaction final temperature, and the temperature corresponding to the peak gradually increased. Combined with the reaction kinetics analysis of the co-pyrolysis and the co-gasification processes, 25% may be a reasonable mixing ratio for ST for the MS-ST mixtures, which had a relatively lower reaction temperature, relatively high pyrolysis index and low activation energy (26.58 kJ·mol−1 and 178.29 kJ·mol−1 for the co-pyrolysis and co-gasification processes, respectively). For the PS-ST mixtures, when increasing the ST content, (i) in the pyrolysis process, the initial reaction temperature, the peak reaction rate, the temperature corresponding to the peak and the pyrolysis index gradually decreased, but the final reaction temperature gradually increased; (ii) in the gasification process, the initial and final reaction temperatures and the temperature corresponding to the peak gradually decreased, but the peak reaction rate gradually increased. Combined with the reaction kinetics analysis of the pyrolysis and the gasification processes, 25% may be a reasonable mixing ratio for ST for the PS-ST mixtures, which had a relatively lower reaction temperature, relatively high pyrolysis index and low activation energy (64.29 kJ·mol−1 and 301.16 kJ·mol−1 for the co-pyrolysis and co-gasification processes, respectively). These findings can provide useful information for the co-gasification of sludge and straw under CO2 atmosphere.

Lignin-Degrading Bacteria in Paper Mill Sludge.

The effluents generated in the paper industry, such as black liquor, have a high content of lignin and other toxic components; however, they represent a source of lignin-degrading bacteria with biotechnological potential. Therefore, the present study aimed to isolate and identify lignin-degrading bacteria species in paper mill sludge. A primary isolation was carried out from samples of sludge present in environments around a paper company located in the province of Ascope (Peru). Bacteria selection was made by the degradation of Lignin Kraft as the only carbon source in a solid medium. Finally, the laccase activity (Um-L-1) of each selected bacteria was determined by oxidation of 2,2'-azinobis-(3-etilbencenotiazolina-6-sulfonate) (ABTS). Bacterial species with laccase activity were identified by molecular biology techniques. Seven species of bacteria with laccase activity and the ability to degrade lignin were identified. The bacteria Agrobacterium tumefasciens (2), Klebsiella grimontii (1), and Beijeinckia fluminensis (1) were reported for first time. K. grimowntii and B. fluminensis presented the highest laccase activity, with values of 0.319 ± 0.005 UmL-1 and 0.329 ± 0.004 UmL-1, respectively. In conclusion, paper mill sludge may represent a source of lignin-degrading bacteria with laccase activity, and they could have potential biotechnological applications.

Hierarchical pore carbon-calcium nanocages for highly effective removal of ammonium-nitrogen and phosphorus

Reconstructing industrial waste slags as adsorbents to purify ammonium‐nitrogen and phosphorus wastewater is a promising method. However, owing to the tight structure, most slags only have a few exposed strong metal adsorption sites for limited treatment. Thus in this paper, paper mill sludge rich in both CaCO3 and organic carbon was selected to construct a highly-active multi-porous carbon‑calcium nanocages adsorbent (Ca-pPSC750). Activation test reflected that KOH intervention not only made sludge organic matter into multistage-pore carbon, but also facilitated the uniform distribution of active CaCO3 nanoparticles. Adsorption results showed that the maximum removal capacity of Ca-pPSC750 for NH4+-N and PO43−-P was up to 248.9 and 104.1 mg g−1, more than 10 times that of the same kind of adsorbents. The whole adsorption process is not limited by the initial pH and coexisting ions of water. This work not only experimentally verifies the existence of a slightly-alkaline microenvironment on the surface of hierarchical pore carbon‑calcium nanocages adsorbents for the first time, but also eliminates the pH limitation of the adsorption reaction for pollutant remediation, thereby expanding the applicability of papermaking sludge adsorption technology. It provides a solution for the efficient purification of high concentration NH4+-N and PO43−P wastewater.