Pulp Mill Sludge Research Articles

Adsorption of acid-extractable organics from oil sands process-affected water onto biomass-based biochar: Metal content matters

The impact of biochar properties on acid-extractable organics (AEO) adsorption from oil sands process-affected water (OSPW) was studied. Biochar from wheat straw with the highest ash content (14%) had the highest adsorption capacity (0.59 mg/g) followed by biochar from pulp mill sludge, switchgrass, mountain pine, hemp shives, and aspen wood. The adsorption capacity had no obvious trend with surface area, total pore volume, bulk polarity and aromaticity. The large impact of metal content was consistent with the carboxylates (i.e., naphthenate species) in the OSPW binding to the metals (mainly Al and Fe) on the carbon substrate. Although the capacity of biochar is still approximately two orders of magnitude lower than that of a commercial activated carbon, confirming the property (i.e., metal content) that most influenced AEO adsorption, may allow biochar to become competitive with activated carbon after normalizing for cost, especially if this cost includes environmental impacts.

Enhanced Methane Yields in High-Solids Anaerobic Digestion Through Inoculation with Pulp and Paper Mill Sludge

High-solids anaerobic digestion (HS-AD) is used to recover energy and nutrients from the organic fraction of municipal solid waste. However, the low degradability of lignocellulosic wastes, such as yard wastes, limits the rate and extent of methane production from this process. This study investigated the potential to enhance methane yields from lignocellulosic waste during HS-AD through inoculation with granular anaerobic digester sludge from pulp and paper mill wastewater treatment systems (P&P sludge). P&P sludge contains microbial populations that are acclimated to a lignin-rich waste stream and has been shown to enhance methane production from agricultural residues. In this study, side-by-side bench-scale HS-AD experiments were carried out with yard waste inoculated with P&P sludge and domestic wastewater anaerobic digester (WW-AD) sludge. Average methane yield with the P&P inoculation strategy reached 100.2 ± 2.4 L CH4/kg volatile solids (VS), a 72.7% enhancement compared with WW-AD sludge (58.1 ± 1.2 L CH4/kg VS) over 106 days of batch digestion under mesophilic conditions. Trends in evolution of leachate volatile fatty acid and total ammonia nitrogen concentrations suggested that hydrolysis was accelerated in the P&P-inoculated digesters, causing methanogenesis to become rate limiting. Additional experiments were carried out to determine if the enhancement could be sustained through inoculation of fresh yard waste with digestate from the initial digesters, resulting in a 68.5% enhancement of methane yield. Although observed improvements are comparable to certain pretreatment methods, inoculation with sludge from the pulp and paper industry could be a low cost and less resource-intensive alternative to pretreatment and improve the overall sustainability of HS-AD processes.

Thermal Valorization of Pulp Mill Sludge by Co-processing with Coal

At the pulp and paper industries, large volumes of primary and secondary sludge are generated from wastewater treatment. Aiming to assess the co-processing of each type of sludge with coal, thermogravimetric (TG) analysis has been used in this work. First, combustion and pyrolysis TG curves of coal (C), primary (L1) and secondary (L2) pulp mill sludge were obtained under oxidizing and inert atmosphere, respectively. Then, under identical experimental conditions, TG analysis was carried out on the primary sludge–coal (CL1) and the secondary sludge–coal (CL2) blends. The corresponding differential thermogravimetric (DTG) curves showed evident differences between C, L1 and L2, which were mainly related to the relative large fixed carbon and low volatiles content of C. However these differences, the combustion of CL1 and CL2 mostly resembled that of C. Meanwhile, the pyrolysis of CL1 and CL2 showed lower devolatilization temperatures and char yields than that of C. Non-isothermal kinetic analysis of TG data showed slightly lower apparent activation energy (E) for the combustion of C than for the combustion of either CL1 or CL2. Contrarily, much lower E values were determined for the pyrolysis of CL1 and CL2 than for the pyrolysis of C. Yet, lower E values than the weighted calculated ones were determined for the combustion and, especially, for the pyrolysis of the blends.

Enhanced Separation of the Organic Fraction from Paper Mill Effluent for Energy Recovery

In this study pre-treatment of pulp and paper mill sludge was investigated to enhance the energy recovery by anaerobic digestion. Two approaches were followed using hydrolytic enzymes or microbiological treatment at 30 °C. In the first attempt, anaerobic digestion of the whole sludge, no significant improvement of the methane production potential was found. In the second test series only the liquid phase after pre-treatment and solids separation was anaerobically degraded. This option provided up to ten times increased methane production compared to the untreated sample. Sludge mass reduction between 6 and 13 % was achieved after pre-treatment. Moreover this concept can be easily integrated in the established wastewater treatment scheme utilizing an existing upflow anaerobic sludge blanket reactor.

Co-digestion of manure with grass silage and pulp and paper mill sludge using nutrient additions

ABSTRACTThere is an increasing worldwide demand for biogas. Anaerobic co-digestion involves the treatment of different substrates with the aim of improving the production of biogas and the stability of the process. This study evaluates how methane production is affected by the co-digestion of pig and dairy manure with grass silage and pulp and paper mill sludge and assesses whether methane production is affected by factors other than nutrient deficiency, low buffering capacity, inadequate dilution, and an insufficient activity and amount of microorganism culture. Anaerobic digestion was performed in batch reactors under mesophilic conditions for 20 days. The season of grass silage and manure collection proved to be an important factor affecting methane production. Spring grass silage produced a maximum of 250 mL/VSadded and spring manure 150 mL/VSadded, whereas autumn grass silage produced at most 140 ml/VSadded and autumn manure 45 mL/VSadded. The pulp mill sludge used is comprised of both primary and secondary sludge and produced at most 50 mL/VSadded regardless of season; this substrate benefitted most from co-digestion.

Conversion of Paper Mill Residuals to Fermentable Sugars

The state of Wisconsin has existing pulp mill infrastructure capable of converting wood into biofuel and value-added products such as lumber, pulp, and paper. Each day, pulp and paper mills produce a waste material that is commonly referred to as sludge. Sludge is typically sent to a landfill or concentrated for burning to produce steam. The primary material present in pulp and paper mill sludge is fiber, which is mostly cellulose. This study showed how to convert pulp mill waste to fermentable sugars using commercially available enzymes. Preliminary economic analysis has shown that sludge can be converted into a fermentable sugar with chemicals costing less than $0.10 per pound of sugar produced.

Recycling pulp mill sludge to volcanic soil: a column leaching study

A leaching experiment was conducted to determine the influence of four successive applications of pulp mill sludge on some parameters of an Andisol. Undisturbed soil columns were treated with pulp mill sludge (0 to 30 Mg ha-1) every three months during one year with a hydraulic regime of 1200 mm per year. Leachates of each treatment were analyzed periodically and, at the end of the period, columns were fractionated at three depths (0-20, 20-40 and 40-60 cm) and soil chemical parameters were analyzed. Sludge added successively to Andisol increased the nitrate concentration in leachates. After the fourth application of 30 Mg ha-1 sludge, nitrate leaching was about 1.7 times higher than in the control column, however, this level is still lower than the limit under Chilean regulations. Low ammonium concentrations were observed in leachates as a result of nitrification processes and retention by clay and organic matter in the Andisol. In fractionated soil columns, pH, organic matter, total nitrogen and phosphorus increased as the sludge rate increased,with the highest values found in the upper part of the columns. The concentration of nitrate and ammonium in soil columns followed an inverse pattern: while ammonium concentration was the highest at 0 to 20 cm, nitrate concentration was the lowest in that fraction; sludge addition caused a linear increase in ammonium and nitrate content at the three depths analyzed.

Removal of pharmaceuticals from municipal wastewater by adsorption onto pyrolyzed pulp mill sludge

A charcoal was produced from primary pulp mill sludge and then used for the adsorptive removal of diclofenac, salicylic acid, ibuprofen and acetaminophen. A main aim was to assess the utilization of this material for the tertiary treatment of sewage. For this purpose, the adsorption of the selected pharmaceuticals from the secondary effluent of a sewage treatment plant (STP) was compared with their adsorption from ultrapure water. Differences in the adsorption kinetics and equilibrium were evident between the four pharmaceuticals considered. However, differences between the adsorption from the two aqueous matrixes considered were negligible. It was hypothesized that synergetic microorganism removal compensated the competitive effects in wastewater.

Thermogravimetric analysis of the co-pyrolysis of a bituminous coal and pulp mill sludge

Thermal valorization of organic wastes by co-processing with coal may be a management option for such wastes. In this work, the separate pyrolysis of coal and primary and secondary pulp mill sludge was assessed by thermogravimetric (TG) analysis. Then, under the same experimental conditions, the pyrolysis TG curves of the coal blends with a 10 mass% of either primary or secondary pulp mill sludge were obtained. The corresponding differential thermogravimetry curves made evident that the devolatilization of coal starts at higher temperature and reaches higher char yields than that of primary or secondary paper mill sludge. Under blending, lower devolatilization temperatures and char yields, close to the weighted calculated ones, are observed. Non-isothermal kinetic analysis showed that the Arrhenius activation energy (E) corresponding to the pyrolysis of coal was lower than that corresponding to either L1 or L2. Moreover, lower E than the weighted calculated ones was determined for the co-pyrolysis of the blends.

Combustion of primary and secondary pulp mill sludge and their respective blends with coal: A thermogravimetric assessment

Properties of primary and secondary pulp mill sludge are unalike and are also very different from those of coal. Thermogravimetric analysis was used to assess the separate combustion of coal, primary and secondary pulp mill sludge. Then, the co-combustion of coal with primary and with secondary pulp mill sludge was studied under identical experimental conditions. Both Differential Thermogravimetry burning profiles (DTG) and Differential Scanning Calorimetric analysis (DSC) showed remarkable differences between the combustion of coal, primary and secondary paper mill sludge. However, compared with the combustion of coal, the effects of adding a 10 wt.% of either primary or secondary paper mill sludge were not relevant in terms of weight loss or heat release. This was further proved by non-isothermal kinetic analysis, which was used to evaluate the apparent activation energy corresponding to the single combustions and to the co-combustion of blends.

Simultaneous biodegradation of organic (chlorophenols) and inorganic compounds from secondary sludge of pulp and paper mill by Eisenia fetida

Present research communicates the role of Eisenia fetida in converting pulp and paper mill sludge into valuable products by removing the high concentration of different chlorophenols and metals present in the sludge. Pulp and paper mill sludge was toxic to Eisenia fetida and therefore, it was mixed with composted material in different ratio of experimental set up such as Set up: 1, (95:5), Set up: 2 (80:20) and Set up: 3 (50:50) on dry weight basis. We found very promising results by the application Eisenia fetida in the sludge. Eisenia fetida removed all the twelve different chlorophenols more than 95 % from the sludge which is declared as carcinogenic compounds by United States Environmental Protection Agency (US-EPA) in 90 days of incubation. Heavy metals concentration was decreased significantly during the incubation period whereas some metal concentration was also increased in the sludge due to mineralization. Carbon (C) and Nitrogen (N) were increased in the composted material, C:N ratio for Set 1 9:4 in Set 2 13:4 and Set 3 18:4 was observed which acts as soil conditioner. Whereas some other metals like (Ca, Mg, Na, K, Fe and Zn) was increased that are essential for the plant growth. There was great reduction in adsorbable organic halogen (AOX) 95 % and extractable organic halogen (EOX) 90 % as compare to control. Eisenia fetida also removed pentachlorophenol (PCP) from the sludge with artificially increased concentration about 100 mg/kg. By observing chlorophenols concentration, metals and carbon–nitrogen ratio, Eisenia fetida is acting as a potential candidate for the reclamation of industrial sludge. The result indicated that vermicomposting with Eisenia fetida is better option to manage the sludge or convert the sludge into nutrient-rich composted material in a short span of time.

Microwave-assisted pyrolysis and activation of pulp mill sludge

This work analyses the effects of microwaves on the production of char – the solid product of pyrolysis. Using pulp mill sludge and a 1200 W microwave oven, the pyrolysis of the sludge was analyzed and compared with that of conventional heating. Alkali metal hydroxide is an effective microwave absorber; adding a mass fraction of 5% of KOH to dried sludge enabled a complete pyrolysis in a few minutes, compared to hours in conventional pyrolysis. Microwave-assisted pyrolysis, however, retained 20% less carbon from the sludge, likely caused by the faster release of volatiles. The secondary sludge yielded more char than the primary sludge, which may be attributed to its greater protein content. Microwave-assisted combined pyrolysis and activation was feasible, due to the dual roles of alkali metal hydroxides as activating agent and microwave absorber. The combined one-step process generated an activated carbon with a specific surface area of 660 m2g−1 from the sludge in three minutes.

Production of lactic acid from the mixture of softwood pre-hydrolysate and paper mill sludge by simultaneous saccharification and fermentation.

Paper mill sludge is a solid waste material composed of pulp residues and ash generated from pulping and paper making process. The carbohydrate portion of the sludges from Kraft/Recycle paper mill has chemical and physical characteristics similar to those of commercial wood pulp. Because of its high carbohydrate content and well-dispersed structure, the sludge can be biologically converted to value-added products without pretreatment. In bioconversion of solid feedstock such as paper mill sludge, a certain amount of water must be present to attain fluidity. In this study, hemicellulose pre-hydrolysate, in place of water, was added to the sludge to increase the concentration of the final product. Pre-hydrolysate was obtained by hot-water treatment of pine wood in which the total sugar concentration reached 4 wt.%. The mixture was processed by simultaneous saccharification and fermentation (SSF) using enzymes (cellulase and pectinase) and Lactobacillus rhamnosus (ATCC-10863). Pectinase was added to hydrolyze mannose oligomers in the pre-hydrolysate to monomers. During the SSF of the mixture, calcium carbonate in the paper sludge acted as a buffer, yielding calcium lactate as the final product. External pH control was unnecessary due to the buffer action of calcium carbonate that maintained the pH near optimum for the SSF. The lactic acid yield in the range of 80-90 % of the theoretical maximum was obtained. Use of the mixed feed of pre-hydrolysate and pulp mill sludges in the SSF raised the product concentration to 60 g of lactate/L.

ISOTHERMAL PYROLYSIS OF KRAFT PULP MILL SLUDGE

Kraft pulp mill sludge cake composed of rejected wood fibers and activated sludge microorganisms. With a heating value about 14 MJ/kg (dried basis), this type of biomass had a potential as an alternative energy source. Unfortunately, it had an ash content of 27.6% and a moisture content of 80%. For reducing moisture content with minimum energy consumption, a combination of mechanical dewatering and thermal drying was studied previously. Meanwhile, experiments on isothermal pyrolysis had been carried out for further improvement on ultimate and proximate analysis of solid fuel. Final mass of char obtained from pyrolysis at 500 o C was not significantly different from that of 700 o C, so pyrolysis was considered to be optimum at 500 o C. A char obtained from pyrolysis at temperature of 500 o C had a pore surface area of 77.049 m 2 /g (highest among other temperatures). Kinetic of isothermal pyrolysis was well represented with a first order modified volumetric model with a frequency factor of 0.782 1/s and an activation of 34.050 kJ/mol.

Adsorption of Phenolic Compounds onto the Activated Carbon Synthesized from Pulp and Paper Mill Sludge: Equilibrium Isotherm, Kinetics, Thermodynamics and Mechanism Studies

A new activated carbon was produced from pulp and paper mill sludge as a low cost precursor via chemical activation by zinc chloride. The activated carbon was successfully used for the adsorption of phenol and two of its derivatives, i.e. 2-chlorophenol and 4-nitrophenol from aqueous solutions. The characterization of the prepared activated carbon demonstrated high textural properties for the synthesized activated carbon. The results revealed the superior adsorption performance of the prepared activated carbon in this study compared to the commercial one. The effect of main affecting parameters such as pH, contact time, concentration and temperature on adsorption of phenolic compounds was experimentally investigated in discontinuous system. The adsorption capacities followed the order of 4-nitrophenol > 2-chlorophenol >phenol which was attributed to the property of substituent groups in their chemical structure. Among isotherm models used to describe experimental equilibrium data, the best match was obtained by Sips isotherm which revealed the heterogeneous behavior of the adsorption sites on the adsorbent surface. Kinetic study demonstrated that the adsorption kinetics followed pseudo-second-order kinetic model. Based on thermodynamic analysis, the negative values obtained for free Gibbs energy, enthalpy and entropy indicated spontaneous, exothermic and randomness behavior of the adsorption process, respectively.

Mineralizable Nitrogen of Organic Wastes and Soil Chemical Changes under Laboratory Conditions

This study looks at the ability of organic wastes from different sources to efficiently promote chemical attributes and enhance nitrogen (N) concentrations in an Oxisol Ustox with a sandy texture. This experiment was performed in a randomized design using wastes from pulp mill sludge, petrochemical complex, sewage treatment plant, dairy factory sewage treatment plant, and pulp fruit industry, on 10 different days. Results showed that addition of the wastes to the soil amended their chemical attributes. The different characteristics of the organic wastes seem to have influenced the N mineralization rates during the 112 days. There was a close relationship between the N mineralization and organic waste C/N ratio: blank soil (SP) (Nma = 3.17) < Treated pulp mill sludge (PMS) (Nma = 30.49, C/N 63.6:1) < Organic compost from the fruit pulp industry (FPW) (Nma = 67.6, C/N 11.9:1) < Treated urban sewage sludge (USS) (Nma = 76.22, C/N 7.2:1) = Petrochemical complex sludge (PS) (Nma = 84.0, C/N 7.7:1) < Treated dairy industry sewage sludge (DSS) (Nma = 102.17, C/N 8.4:1).

Dynamic adsorption of phenolic compounds on activated carbon produced from pulp and paper mill sludge: experimental study and modeling by artificial neural network (ANN)

A new low-cost activated carbon (AC) was produced from pulp and paper mill sludge through chemical activation by zinc chloride. Different characterization analyses were carried out on developed AC; these demonstrated a carbon material with highly porous structure. Dynamic adsorption of phenolic compounds (i.e. phenol, 2-chlorophenol, and 4-nitrophenol) from simulated aqueous solution was investigated in a fixed-bed adsorption column using the prepared AC. Dynamic behavior of the adsorption column was assessed in terms of breakthrough curves obtained at different key operating conditions such as bed height, feed flow rate, inlet concentration, and temperature. Sharp breakthrough curves were observed at high-feed flow rate, high-inlet concentration, high temperature, and low-bed height which show the correct dynamic behavior of the adsorption column. The breakthrough times followed the order of 4-nitrophenol > 2-chlorophenol > phenol at all key operating conditions. This arrangement was attributed to their relative adsorption capacities. Data-oriented artificial neural network (ANN) technique along with two empirical physical models (Thomas and Yan model) was employed to characterize breakthrough curves for the adsorption of phenolic compounds through the fixed-bed column. Although, both Thomas and Yan models were able to fit well the breakthrough curves obtained at various operating conditions, a nearly perfect match between experimental breakthrough curves and the predicted ones was attained using ANN. The results of the present study demonstrated that the ANN technique can be employed as a powerful technique for modeling of adsorption process.

Anthroposol development from limestone quarry substrates

Cohen-Fernandez, A. C., Naeth, M. A. and Wilkinson, S. R. 2013. Anthroposol development from limestone quarry substrates. Can. J. Soil Sci. 93: 555–566. Limestone quarry reclamation worldwide requires development of substrates or anthroposolic soils. The suitability of three limestone substrates (gray, gray brown, crushed) for revegetation was assessed in two greenhouse experiments. In the first experiment amended substrates (pulp mill sludge, two manures, hay, straw, wood shavings, capping with two soils) alone and in combination with fertilizer and elemental sulfur were evaluated. Amendment rates were assessed in a second experiment. Plant density and above- and below-ground biomass were used to determine substrate suitability. The three limestone substrates supported germination, emergence and establishment of five native grasses when amended. Addition of fertilizer yielded three times more above-ground biomass and two times more below-ground biomass compared with the control, despite reducing plant de...

Transformation and removal of wood extractives from pulp mill sludge using wet oxidation and thermal hydrolysis

In order to remove wood extractive compounds from pulp mill sludge and thereby enhancing anaerobic digestibility, samples were subjected to either oxidative hydrothermal treatment (wet oxidation) or non-oxidative hydrothermal treatment (thermal hydrolysis). Treatments were carried out at 220 °C with initial pressure of 20 bar. More than 90% destruction of extractive compounds was observed after 20 min of wet oxidation. Wet oxidation eliminated 95.7% of phenolics, 98.6% fatty acids, 99.8% resin acids and 100% of phytosterols in 120 min. Acetic acid concentration increased by approximately 2 g/l after 120 min of wet oxidation. This has potential for rendering sludge more amenable to anaerobic digestion. In contrast thermal hydrolysis was found to be ineffective in degrading extractive compounds. Wet oxidation is considered to be an effective process for removal of recalcitrant and inhibitive compounds through hydrothermal pre-treatment of pulp mill sludge.

Supercapacitors based on carbons with tuned porosity derived from paper pulp mill sludge biowaste

Hydrothermal carbonization followed by chemical activation is utilized to convert paper pulp mill sludge biowaste into high surface area (up to 2980m2g−1) carbons. This synthesis process employs an otherwise unusable byproduct of paper manufacturing that is generated in thousands of tons per year. The textural properties of the carbons are tunable by the activation process, yielding controlled levels of micro and mesoporosity. The electrochemical results for the optimized carbon are very promising. An organic electrolyte yields a maximum capacitance of 166Fg−1, and a Ragone curve with 30Whkg−1 at 57Wkg−1 and 20Whkg−1 at 5450Wkg−1. Two ionic liquid electrolytes result in maximum capacitances of 180–190Fg−1 with up to 62% retention between 2 and 200mVs−1. The ionic liquids yielded energy density–power density combinations of 51Whkg−1 at 375Wkg−1 and 26–31Whkg−1 at 6760–7000Wkg−1. After 5000 plus charge–discharge cycles the capacitance retention is as high at 91%. The scan rate dependence of the surface area normalized capacitance highlights the rich interplay of the electrolyte ions with pores of various sizes.