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• The PBAT/PLA coated paper shows high methane yield under AD condition. • Plastic film residues remain after the digestion of PBAT/PLA coated paper. • The decrease of hydrophobicity for PBAT/PLA bags is due to the formation of PLA monomers. • The bacterial community shows difference between PBAT/PLA coated paper and bags. • Methanoculleus is enriched on the plastic surface under mesophilic AD. Poly (lactic acid) (PLA) and Poly(butylene adipate-co-terephthalate) (PBAT) are two of biodegradable plastics with the highest production capacities in 2021. Bioplastic waste management can be easily integrated with organic waste management, especially when bioplastics are used as food packaging material, since they are potentially biodegradable. The aim of this study was to assess the biodegradability of biodegradable polymer-coated paper (BPCP) and bioplastic bags made from PBAT/PLA blend during mesophilic and thermophilic anaerobic digestion (AD) and to reveal the changes in the physicochemical properties of the bioplastics. BPCP obtained 155 NmL-CH 4 /g VS and 307.3 NmL-CH 4 /g VS under mesophilic and thermophilic conditions, respectively, but left bioplastic film residues. The bioplastic bags did not exhibit significant biodegradation during the AD processes. 1H NMR results indicated that the ratio of PLA to PBAT decreased significantly after AD of the BPCP film and that PLA monomers were formed from the bioplastic bags, leading to a decrease in the hydrophobicity on the surfaces of the materials. Methanoculleus was found to be enriched on the bioplastic surface after mesophilic AD. From the perspective of coupling bioplastic waste management with the food waste management, the incorporation of BPCP into the AD reactor not only enhances system stability and methane production to a greater extent than biodegradable plastic bags but also raises concerns regarding the residual biofilm when utilizing the digestate for direct land applications. [ABSTRACT FROM AUTHOR]

Paper crumb (PC) is a type of paper sludge residue from the wastepaper recycling industry. It is a by-product from the various fiber purification stages that is particularly composed of short cellulose fibers, lignin, organic compounds and inorganic filler residues. Despite representing a reject material for the paper recycling sector, this feedstock can be turned into a bioresource to enable cross-sector industrial symbiosis in the form of a more sustainable concrete, hence an opportunity for novel Net Zero supply chains. This study sought to valorise the PC by the sequential anaerobic digestion to produce methane (CH 4) from the organic compounds, followed by utilization of the digestate as a water replacement in concrete. The 21-day digestion of PC yielded 163 ml CH 4 per gram volatile solids and the resulting digestate improved concrete compressive strength up to 50% water replacement grade, meeting the requirements for structural grade (C32/40) applications with substitution grades up to 50% and 25%, with and without the addition of plasticiser respectively. In a minor capacity, the digestate reduced workability of the concrete mix, however we demonstrate this issue can be resolved by the addition of plasticiser or increased water to cement ratios. The admixture addition is important to facilitate pumpability on site and ensure satisfactory compaction. This study highlights the potential of anaerobic digestate as a concrete supplement (additive), which would improve the sustainability of both the construction and the paper sector. [Display omitted] [ABSTRACT FROM AUTHOR]

Food waste and waste paper are the two largest components of municipal solid waste, and many previous studies found that their co-digestion improved methane yield. This study investigated the anaerobic co-digestion of 0–100% food waste with paper food packages on lab-scale with feedstock-to-inoculum (F/I) ratios from 0.5 to 6 (based on volatile solids, VS) and total solids contents from 8% to 28%. In addition to methane yield, volumetric productivity and process economics were also used to evaluate the operating parameters. Results showed that the highest cumulative methane yield of around 530 L/kg-VS feed was obtained from 100% food waste at F/I ratios of 0.5, 1, and 2; the highest volumetric methane productivity of 44.2 L/L work was achieved with 25% food waste at an F/I ratio of 6; and the highest annual net profit was obtained from 75% food waste at an F/I ratio of 2, which also achieved the highest internal rate of return (20.7%) and the shortest payback period (5 years). Addition of waste paper packages to food waste could enhance the digester stability, and it is beneficial to allow certain amount of paper packages and tissues to be collected together with food waste during the initial source separation. [Display omitted] [ABSTRACT FROM AUTHOR]

Paper wastes form the major biodegradable fraction of the municipal solid waste. One of the best ways to treat paper wastes is using them as a feedstock for biomethane production through anaerobic digestion (AD). However, the AD characteristics, kinetics, and energy potential of different types of paper wastes are not clear. In this study, four kinds of typical paper wastes including corrugated board (CB), office paper (OP), tissue paper (TP), and magazine paper (MP) were used as feedstocks to produce biomethane at different volatile solids (VS) organic loading (OL). TP had a high cellulose content and showed high biomethane potential, while the lowest was obtained by CB, possibly due to its high lignin content. Kinetic analysis showed that Cone and modified Gompertz model could fit the biomethane production process well. Energy potential analysis revealed that biomethane yield, electric generating efficiency, and electricity price were the principal factors accounting for the profitability of biomethane production project treating paper wastes. Overall, paper wastes could be a promising feedstock for biomethane production, because paper wastes not only had high biomethane yield and biodegradability that exceeded many kinds of organic wastes but also could be continuously supplied for AD plants without the influence of seasonal changes. • Anaerobic digestion characteristics of typical paper wastes were investigated. • High cellulose content in tissue paper might account for its high biomethane yield. • Corrugated board with high lignin content showed the lowest biomethane yield. • Energy potential of the anaerobic digestion of paper wastes was evaluated. [ABSTRACT FROM AUTHOR]

Biohydrogen and biomethane production via two stage sequencing system from paper mill effluent (PME) was evaluated to enhance its COD reduction. Heat-shock pretreatment of anaerobic sludge at 90 °C for 15 min was chosen to obtain a mixed microbial inoculum for dark fermentative hydrogen production. The effect of initial pH (5, 6 and 7) on the efficiency of hydrogen fermentation at different concentrations of substrate (3, 5 and 7 g-COD/L) was investigated, which the maximum hydrogen yield was obtained at initial pH 5. After that, the effects of substrate concentration (3, 5, 7, 10 and 15 g-COD/L) and fermentation temperature (37 and 55 °C) were investigated on the hydrogen production yield. The efficiency of dark hydrogen fermentation for all substrate concentrations was higher at 55 °C. The hydrogen production was enhanced as substrate concentration increased up to 5 g-COD/L, but then it was reduced, and the optimum hydrogen yield of 38.8 mL H 2 /g-COD initial was obtained at substrate concentration of 5 g-COD/L at 55 °C. The highest hydrogen (35.1 mL H 2 /g-COD initial) was obtained at 5 g-COD/L and 55 °C and the highest methane (553.8 mL CH 4 /g-COD initial) was obtained at 3 g-COD/L and 37 °C. Maximum COD reduction of 88.1% was obtained in two-stage sequencing dark fermentation/anaerobic digestion system at 3 g-COD/L and 37 °C. • BioH 2 and bioCH 4 were generated in expend of COD reduction from PME. • Effects of initial pH, COD loading and temperature were studied. • Primary step dark fermentation showed higher hydrogen yields at 55 °C. • Max COD reduction 88.1% was obtained in 2-stage sequencing system (3 g-COD/L, 37 °C). • 38.8 mL H 2 /g-COD initial at 55 °C and 553.8 mL CH 4 /g-COD initial at 37 °C were obtained. [ABSTRACT FROM AUTHOR]

Recycling helps reduce organic matter and sulfur content in effluents from the paper industry, as well as minimize large volumes usually generated, making the anaerobic process a feasible alternative to treat such waste. The objective of this paper is to evaluate simultaneous sulfate and organic matter removal in a bench-scale horizontal-flow anaerobic immobilized biomass (HAIB) reactor continuously fed with diluted wastewater from a full paper recycling plant. The reactor was filled with wood charcoal matrices containing immobilized anaerobic sludge. The tested wastewater contained Chemical Oxygen Demand (COD) of 1745 mg L −1 and concentrations of sulfate ranging from 220 (phase 1) to 585 mg L −1 (phase 2). The anaerobic process from paper recycling effluent was followed by partial oxidation of sulfide to elemental sulfur. Sulfate reduction, methanogenesis and effluent desulfurization occurred in the same reactor and were spatially segregated by the plug-flow regime. The investigated HAIB reactor anaerobically removed organic matter and sulfate at high removal efficiencies (>90%), converting about 30% of the inconvenient dissolved sulfide to elemental sulfur. Therefore, integrated sulfate reduction and elemental sulfur production, as presented herein, can be considered an attractive component for sustainable wastewater treatment. [ABSTRACT FROM AUTHOR]

[Display omitted] • Food delivery boxes are tested for aerobic disintegration and anaerobic degradation. • Boxes made of paper only or with coatings (including polylactic acid) are analysed. • Paper is highly suitable for biological treatments behaving similarly to food waste. • Aerobic disintegration of coated boxes is much slower than that of paper only boxes. • Undigested polylactic acid coating is found in anaerobic semi-continuous tests. This study evaluated the fate of food delivery boxes when subjected to biological treatments, reproducing at the lab-scale the conditions of full-scale plants. Four paper-based boxes were composted: two made of paper only, one coupled with polylactic acid (PLA), and one with a barrier coating. One paper only box and the box with PLA were also investigated for their anaerobic degradability with biochemical methane potential (BMP) and semi-continuous tests. During composting, the boxes were not recognisable inside the compost after four (paper only boxes), eight (box with PLA), and twelve (box with barrier coating) weeks. In BMP tests, the paper only box showed a degradability similar to that of food waste (92 %), while the box with PLA degraded only at 76 %. Furthermore, undigested pieces of PLA were found in semi-continuous tests. Accordingly, paper resulted suitable for biological treatments, while the presence of PLA or other barrier coatings can be critical. [ABSTRACT FROM AUTHOR]

Anaerobic treatment of sedimented fibers collected from bottom of a bay that had been receiving pulp and paper mill wastewater for about 70 years were studied for the first time in semi-continuously fed continuously stirred tank reactors (CSTR). Anaerobic treatment of the fiber sediment was shown to be feasible, without dilution and with nitrogen and buffer supplement, at organic loading rates (OLR) up to 2.5 kg VS/m 3 d and hydraulic retention times (HRT) of 60 d resulting in methane yields of 201 ± 18 L CH 4 /kg VS. Co-digestion of sedimented fiber with sewage sludge at an OLR of 1.5 kg VS/m 3 d and HRT of 20 d resulted in a methane production of 246 ± 10 L CH 4 /kg VS. The techno-economic feasibility of mono and co-digestion process together with several case dependent factors such as maximum operable OLR, digestate utilization needs to be evaluated before making further conclusions for larger scale remediation applications. [ABSTRACT FROM AUTHOR]

Thermophilic methane fermentation was a valid approach for handling the stillage eluted from ethanol fermentation of waste paper and kitchen waste. The wide organic loading rate (OLR) range (2–14 g VTS/(L d)) for stable performance and relatively high energy recovery efficiency (79.0%) were achieved, and OLR of 8 g VTS/(L d) was optimum for achievement of highest biogas evolution and VTS removal efficiency. Microbial community analysis revealed that hydrolysis of cellulose was the critical step for methane production from the stillage. [ABSTRACT FROM AUTHOR]

[Display omitted] • A total of 20 different paper sludges were investigated. • A wide range of biomethane potentials was determined. • Inhibiting substances for some paper sludge were identified. • Co-digestion resulted in methane yield increase of 5–10%. • The possibility of anaerobic co-digestion could be demonstrated. In this work, the feasibility of the anaerobic digestion of paper sludge as a co-substrate in anaerobic digestion mechanical–biological treatment (MBT) plants is investigated. In the first phase, the biochemical properties, biomethane potential (BMP), and pollutant contents of 20 different industrial paper sludges are determined. Following the general evaluation in the BMP tests, the second phase of the project involves the semi-continuous co-digestion of six paper sludges in continuous stirred reactors (CSTR). Paper sludges are categorized according to their origin within the pulp and paper mills: Deinking Sludge (DS), Primary Sludge (PS) and Biological Sludge (BS). The analysis of potentially inhibiting elements shows that the concentrations of chlororganic compounds, mineral oil and some heavy metals are highest in DS, while the mean heavy metal loads in all paper sludges are relatively low compared to other industrial sludges. Large differences in total solids (TS) and volatile solids (VS) contents are observed among the different paper sludges investigated, with DS having the highest TS due to the high inorganic contents. The BMP of the investigated sludges ranges from 90 to 355 NL CH 4 kg−1 VS. In subsequent semi-continuous co-digestion experiments simulating MBT conditions, three DS and two fiber sludges (a mixture of PS and BS) show good methane generation rates, while one fiber sludge causes inhibition and indicates an increase in viscosity. In general, co-digestion of paper sludge in anaerobic digestion MBT plants can be a viable option for energy production and also facilitates a safe disposal of the paper sludge digestates. [ABSTRACT FROM AUTHOR]

In the anaerobic digestion of lignocellulosic materials such as waste paper, the accessibility of microorganisms to the fermentable sugars is restricted by their complex structure. A mechanical pretreatment with a Hollander beater was assessed in order to reduce the biomass particle size and to increase the feedstock’ specific surface area available to the microorganisms, and therefore improve the biogas yield. Pretreatment of paper waste for 60 min improves the methane yield by 21%, from a value of 210 ml/gVS corresponding to untreated paper waste to 254 ml/gVS. 30 min pretreatment have no significant effect on the methane yield. A response surface methodology was used to evaluate the effect of the beating time and feedstock/inoculum ratio on the methane yield. An optimum methane yield of 253 ml/gVS was achieved at 55 min of beating pretreatment and a F/I ratio of 0.3. [ABSTRACT FROM AUTHOR]

Different heating processes were applied to pretreat the pulp and paper mill sludge to enhance the hydrolysis stage. Hot air oven, autoclave, microwave and water bath were used for comparison. Chemical analyses exposed that all the pretreatment methods have shown improvement in solubilisation of organic matter. Among the pretreatments studied, heat transfer through hot air (80 °C for 90 min) mode had the highest impact on sludge solubilisation. There was an increase in cellulose (P = 0.0096), acid soluble (P = 0.0053) and insoluble lignin (P = 0.0012), but decrease in hemicellulose (P = 0.0009) content after pretreatment. The XRD and FT-IR spectroscopic characterisation shows the development of aliphatic, unsaturated and carbonyl carbon functionalities in the pretreated samples at higher severities. FESEM picture also confirms the change in structure after pretreatment. Thus, pretreatments contribute to disruption of the lignocellulosic structure making the cellulose easily accessible to acidogenic microorganisms. [ABSTRACT FROM AUTHOR]

The application of anaerobic digestion is mounting worldwide because of its economic and environmental benefits. As a concern, the rate and extent of the anaerobic digestion of pulp and paper mill sludge was tested using the biochemical methane potential (BMP) with different food/microorganisms (F/M) ratio. The study was evaluated at five different F/M ratios (i.e. 0.5, 1.0, 1.5, 2.0, 2.5). In addition to that reaction kinetics and the influence of biodegradability were also evaluated for the biomethane potential of substrates. The highest cumulative methane yield was obtained in F/M ratio 2.0 with 3.4 L followed by F/M ratio 1.5 and 2.5 with 3.3 L and 2.9 L, respectively. The maximum methane production rate 3.66 L CH 4 was perceived as per kinetics. The biomass activity may be affected due to the high substrate concentration during BMP test of lower F/M ratios. On the other hand, F/M ratio greater than 2.0, methane yield was decreased due to increased volatile fatty acid production reduces the reactor pH and inhibits methanogens activity. [ABSTRACT FROM AUTHOR]

Paper mill effluents are complex mixtures containing different toxic compounds including endocrine-disrupting (EDCs) and genotoxic compounds. In the present study non-concentrated raw and biologically treated wastewaters from two paper mill plants with different paper production technologies i) Paper mill A uses virgin fibres, and ii) Paper mill B uses recycled fibres for paper production and the corresponding receiving surface waters, were assessed for their cytotoxic/genotoxic activity with SOS/ umuC , Ames MPF 98/100 Aqua, and comet assay with human hepatoma HepG2 cells. In addition the levels of seven selected EDCs were quantified in wastewater samples and receiving surface waters. All investigated EDCs were confirmed in raw and biologically treated effluents from both paper mills with concentrations being markedly higher in Paper mill B effluents. In the receiving surface waters three of the studied EDCs were determined downstream of both paper mills effluent discharge. The wastewater samples and the recipient surface water samples from Paper mill A were not mutagenic for bacteria and did not induce DNA damage in HepG2 cells. On the contrary, half of the raw wastewater samples from Paper mill B were mutagenic whereas biologically treated wastewater and the recipient surface water samples were negative. In HepG2 cells most of the raw and biologically treated wastewater samples from Paper mill B as well as surface water samples collected downstream of Paper mill B effluent discharge induced DNA damage. The results confirmed that genotoxic contaminants were present only in wastewaters from Paper mill B that uses recycled fibres for paper production, and that the combined aerobic and anaerobic wastewater treatment procedure efficiently reduced contaminants that are bacterial mutagens, but not those that induce DNA damage in HepG2 cells. This study highlights that in addition to chemical analyses bioassays are needed for a comprehensive toxicological evaluation of complex wastewater samples. [ABSTRACT FROM AUTHOR]

Various organic and inorganic hazardous substances are commonly originated during the processing of virgin or recovered fibers (RCFs), when the pulp and paper (P&P) are produced. Hence, pulp and paper industry (PPI) strongly need to employ advanced waste treatment processes as a powerful tool to comply with the stringent environmental regulations in one hand, and to increase their profitability in the current declining P&P markets, on the other hand. Among the treatment alternatives, anaerobic digestion (AD), is an interesting cost-effective alternative with a small environmental footprint and has been increasingly adopted by the PPI to reach this goal. However, the application of AD to deal with wastes generated in P&P mills has been restricted due to a number of limitations, regarding the anaerobic reactor design and the operating conditions. Hence, the optimization of the AD performance would be a crucial step in order to increase the economic benefits, and also to satisfy the strict environmental protection standards. To this end, this paper presents an overview on the current state of the developments associated with AD treatment of P&P mill wastes to assess the applicability of this treatment process for the management of this type of complex wastes. In this context, suggestions are provided to maximize both biogas production and removal efficiency, focusing on the relationship between waste composition and reactor design and operational conditions, which will enhance methane capture and contribute to prevent global warming. [ABSTRACT FROM AUTHOR]

Sewage fine sieved fraction (FSF) is a heterogeneous substrate consisting of mainly toilet paper fibers sequestered from municipal raw sewage by a fine screen. In earlier studies, a maximum biodegradation of 62% and 57% of the sewage FSF was found under thermophilic (55 °C) and mesophilic (35 °C) conditions, respectively. In order to research this limited biodegradability of sewage FSF, this study investigates the biodegradation of different types of cellulosic fibers-based hygiene papers including virgin fibers based toilet paper (VTP), recycled fiber based toilet paper (RTP), virgin pulp for paper production (VPPP) as a raw material, as well as microcrystalline cellulose (MCC) as a kind of fiberless reference material. The anaerobic biodegradation or digestibility tests were conducted under thermophilic and mesophilic conditions. Results of the experiments showed different biomethane potential (BMP) values for each tested cellulose fiber-based substrate, which might be associated with the physical characteristics of the fibers, type of pulping, presence of lignin encrusted fibers, and/or the presence of additive chemicals and refractory compounds. Higher hydrolysis rates (K h ), higher specific methane production rates (SMPR) and shorter required incubation times to achieve 90% of the BMP (t 90% CH 4 ), were achieved under thermophilic conditions for all examined substrates compared to the mesophilic ones. Furthermore, the biodegradability of all employed cellulose fiber-based substrates was in the same range, 38–45%, under both conditions and less than the observed FSF biodegradability, i.e. 57–62%. MCC achieved the highest BMP and biodegradability, 86–91%, among all cellulosic substrates. [ABSTRACT FROM AUTHOR]

The effects of five commercially available hydrolytic enzyme additives on methane yields from dehydrated paper pulp sludge (DPPS) were determined in 5L pilot-scale reactors operated in semi-continuous mode for 60 days. Methane production was 40% and 43% higher in reactors receiving Novozymes and Novalin additives, respectively, compared to controls. Effects of time of DPPS inclusion on bacterial and archaeal microbial communities were many times larger than effects of enzyme type as enzyme addition did not produce rearrangements larger than random fluctuations observed in reactors receiving only DPPS. The ratio between volatile organic acids and alkalinity signified progressive decrease in process stability until day 45 irrespective of enzyme supplementation. Complementation with clarified pig slurry (1.5% vol.) for subsequent 15 days effectively stabilized process parameters and was sufficient for microbial communities to maintain DPPS hydrolytic capacity and process additional carbon flow derived from hydrolytic activity of enzyme additives. Consequently, initially unadapted full-scale biogas plant inoculum was capable of significantly increased methane yields from DPPS. Based on annual DPPS availability in EU the potential for additional energy recovery was estimated to be in the range of nearly 1 TJ. [ABSTRACT FROM AUTHOR]

The effect of organic loading rates (OLRs) on membrane performance and mixed-liquor suspended solids (MLSS) properties were examined using a laboratory-scale thermophilic submerged anaerobic membrane bioreactor (ThSAnMBR) that treats primary sludge from a thermomechanical pulp mill. Membrane performance was evaluated by monitoring its flux and corresponding transmembrane pressure (TMP). Changes in membrane chemical and physical properties resulting from operating conditions were investigated using Fourier transform infrared (FTIR), scanning electron microscopy (SEM), contact angle, energy-dispersive X-ray analyzer (EDX), and pore size measurement. While MLSS properties are analyzed by X-ray photoelectron spectroscopy (XPS), zeta potential, and particle size distribution (PSD) analysis. Membrane performance and MLSS properties were studied at different OLRs ranging from 1.5 to 3.9 kg-TSS/m3d, and hydraulic retention times (HRTs) of 3–8 d. This study showed that the increased OLR reduced the membrane performance and degradation of the primary sludge, as well as the biogas yield. This result indicates that OLR of less than 1.5 kg TSS/m3d, HRT of 8d, and solids retention time (SRT) of 32d should be maintained to achieve stable membrane performance and better biogas production. Also, results showed that important changes occurred on the membrane morphology and MLSS characteristics under the tested operating conditions. High-resolution SEM images reveal distinct differences in the pore morphology between the virgin and used membranes indicating the effect induced by the operating conditions. Thermophilic temperature led to an expansion of membrane pores. Overall, the primary sludge from pulp and paper mills can be treated successfully by ThSAnMBR for methane production with stable membrane performance and high treatment efficiency. [Display omitted] • The effect of OLRs on membrane performance and MLSS properties was studied. • Important changes occurred in the membrane morphology due to induced environment. • Primary sludge from thermomechanical pulp mill can be successfully treated by AnMBR. • Thermophilic temperature led to an increase of the portion of large membrane pores. • A higher OLR or shorter HRT led to more irremovable membrane fouling. [ABSTRACT FROM AUTHOR]

[Display omitted] • Mixed sludge from pulp and paper mill wastewater treatment was treated with HTC. • HTC enhanced energy recovery in hydrochars having 37% increased heating value. • No significant sludge dewaterability improvement was observed after HTC. • HTC increased filtrate organics content and volumetric methane production potential. • Mixed sludge hydrochars are potential for carbon sequestration. The pulp and paper industry's mixed sludge represents waste streams with few other means of disposal than incineration. Hydrothermal carbonization (HTC) could be advantageous for the sludge refinement into value-added products, thus complementing the concept of pulp and paper mills as biorefineries. Laboratory HTC was performed on mixed sludge (at 32% and 15% total solids) at temperatures of 210–250 °C for 30 or 120 min, and the characteristics of the HTC products were evaluated for their potential for energy, carbon, and nutrient recovery. The energy content increased from 14.9 MJ/kg in the mixed sludge up to 20.5 MJ/kg in the hydrochars. The produced filtrates had 12–15-fold higher COD and 3–5-fold higher volumetric methane production than untreated sludge filtrates, even though the methane yield against g-COD was lower. The increased value of the hydrochars in terms of energy content and carbon sequestration potential promote HTC deployment in sludge treatment and upgrading. [ABSTRACT FROM AUTHOR]

Pulp and paper mills generate large amounts of waste organic matter that may be converted to renewable energy in form of methane. The anaerobic treatment of mill wastewater is widely accepted however, usually only applied to few selected streams. Chemical oxygen demand (COD) removal rates in full-scale reactors range between 30 and 90%, and methane yields are 0.30–0.40 m 3 kg −1 COD removed. Highest COD removal rates are achieved with condensate streams from chemical pulping (75–90%) and paper mill effluents (60–80%). Numerous laboratory and pilot-scale studies have shown that, contrary to common perception, most other mill effluents are also to some extent anaerobically treatable. Even for difficult-to-digest streams such as bleaching effluents COD removal rates range between 15 and 90%, depending on the extent of dilution prior to anaerobic treatment, and the applied experimental setting. Co-digestion of different streams containing diverse substrate can level out and diminish toxicity, and may lead to a more robust microbial community. Furthermore, the microbial population has the ability to become acclimated and adapted to adverse conditions. Stress situations such as toxic shock loads or temporary organic overloading may be tolerated by an adapted community, whereas they could lead to process disturbance with an un-adapted community. Therefore, anaerobic treatment of wastewater containing elevated levels of inhibitors or toxicants should be initiated by an acclimation/adaptation period that can last between a few weeks and several months. In order to gain more insight into the underlying processes of microbial acclimation/adaptation and co-digestion, future research should focus on the relationship between wastewater composition, reactor operation and microbial community dynamics. The potential for engineering and managing the microbial resource is still largely untapped. Unlike in wastewater treatment, anaerobic digestion of mill biosludge (waste activated sludge) and primary sludge is still in its infancy. Current research is mainly focused on developing efficient pretreatment methods that enable fast hydrolysis of complex organic matter, shorter sludge residence times and as a consequence, smaller sludge digesters. Previous experimental studies indicate that the anaerobic digestibility of non-pretreated biosludge from pulp and paper mills varies widely, with volatile solids (VS) removal rates of 21–55% and specific methane yields ranging between 40 and 200 mL g −1 VS fed. Pretreatment can increase the digestibility to some extent, however in almost all reported cases, the specific methane yield of pretreated biosludge did not exceed 200 mL g −1 VS fed. Increases in specific methane yield mostly range between 0 and 90% compared to non-pretreated biosludge, whereas larger improvements were usually achieved with more difficult-to-digest biosludge. Thermal treatment and microwave treatment are two of the more effective methods. The heat required for the elevated temperatures applied in both methods may be provided from surplus heat that is often available at pulp and paper mills. Given the large variability in specific methane yield of non-pretreated biosludge, future research should focus on the links between anaerobic digestibility and sludge properties. Research should also involve mill-derived primary sludge. Although biosludge has been the main target in previous studies, primary sludge often constitutes the bulk of mill-generated sludge, and co-digestion of a mixture between both types of sludge may become practical. The few laboratory studies that have included mill primary sludge indicate that, similar to biosludge, the digestibility can range widely. Long-term studies should be conducted to explore the potential of microbial adaptation to lignocellulosic material which can constitute more than half of the organic matter in pulp and paper mill sludge. [ABSTRACT FROM AUTHOR]

This study considered the possibility of reducing the environmental footprint of paper and pulp industry by producing bioenergy from paper sludge by using process wastewater instead of fresh water, and reclaiming water trapped in paper sludge. Experimental studies are conducted with streams from three different pulp and paper mills (virgin pulp mill (VP), corrugated recycling mill (CR), tissue printed recycling mill (TPR)) for sequential bioethanol and biogas production with simultaneous reclamation of water from paper sludge (PS). Total energy yields of 9215, 6387, 5278 MJ/tonne dry PS for VP, CR and TPR, respectively, were obtained for ethanol-biogas production. Virgin pulp paper sludge gave the highest yield for ethanol and biogas in stand-alone processes (275.4 kg and 67.7 kg per ton dry PS respectively) and also highest energy conversion efficiency (55%) in sequential process compared with CR and TPR. Energy and environmental case study conducted on virgin pulp mill has proven the possibility of using paper sludge bioenergy to reduce energy demand by 10%, while reclaiming 82% of the water from the PS, reducing greenhouse gas emissions (GHG) by 3 times and producing solids suitable for land spreading. Integration of a sequential bioprocessing technology into the pulp and paper industry treats wastewater, produces bioenergy and eliminates the need to landfill paper sludge. [Display omitted] • Process wastewater substituted clean water in fermentation and anaerobic digestion. • Sequential bioprocessing reclaimed 65%−85% of entrapped water from paper sludge. • 80% of GHG emissions from landfills is avoided in paper sludge bioprocessing. • Integration of paper sludge bioprocessing in pulp mills can reduce energy demand by 10%. [ABSTRACT FROM AUTHOR]

Abstract The effects of paper waste (PW) ratio on biogas production by two-stage thermophilic anaerobic co-digestion (coAD) of food waste (FW) and PW, two main components of organic fraction of municipal solid waste, were evaluated in lab-scale continuously stirred tank systems with semi-continuous feeding. Four PW ratios (0, 20, 40, and 50%) were studied in the test. The experimental results showed the two-stage thermophilic coAD could operate stably after an adjustment period at all PW ratios. Although the increase of PW ratio decreased methane content, production and yield, reaction rates of four AD steps, it could increase the methane production of substrate when the FW was fixed. The pH, total volatile fatty acids, total alkalinity, and total ammonium of the sludge in the second stage of AD, also decreased with the increase of PW ratio in the test. The change of the substrate's organic composition, increase of carbohydrate and decrease of protein and lipid, were the main reason for the decrease of methane content, production and yield and changes of the second stage sludge characteristics. An apposite PW ratio (PW-20%) could enhance the degradation of matters (TS, VS and TCOD). Highlights • Increase of PW ratio decrease the of biogas and methane yield of mixture. • Increase of PW ratio increase the methane production when FW was fixed. • Some characteristics of second stage sludge decreased with increase of PW ratio. • 20% of PW ratio could enhance the degradation of matters (TS, VS and TCOD). • Changes of organic composition were the main reason for experimental result. [ABSTRACT FROM AUTHOR]

This paper evaluates the environmental impacts of different alternatives for handling of sludge from paper and pulp mills in Sweden, using Life Cycle Assessment (LCA). The common practice of incineration of biosludge with energy recovery followed by landfilling of ash (System A) was compared with the alternative of digesting sludge anaerobically to produce biogas using different digestate residue management options. The digestate produced from anaerobic digestion (AD) was assumed to be incinerated for heat energy recovery in System B or pyrolyzed for biochar production in System C to be mixed with forest soils. The impact categories considered in this work are climate change, non-renewable energy use, mineral extraction, aquatic ecotoxicity, carcinogens and non-carcinogens. The LCA results demonstrate that the two proposed systems significantly reduce the environmental impacts of biosludge management relative to incineration. An 85% reduction in the aquatic ecotoxicity impact is achieved in System C, due to the reduced mobility of heavy metals in biochar relative to ash. System C, on the whole, outperformed the other two, leading the authors to the recommendation that the use of pulp and paper mill biosludge in biogas-biochar production systems is preferable to merely recovering energy from it. • Anaerobic digestion (AD)-pyrolysis and AD-incineration were modelled as biosludge treatment technologies. • Immobilization of the heavy metals in biochar significantly reduced aquatic ecotoxicity. • The lowest carcinogens and non-carcinogens impacts were offered by the AD-pyrolysis system. • From an environmental point of view, biogas-biochar is preferable to merely energy recovery. [ABSTRACT FROM AUTHOR]

A large amount of sheep dung (SD) produced on farms in China is a potential feedstock for production of clean energy in the form of biogas. Similarly, waste paper can be a notable energy source that is worth exploiting. In this study, we assessed the feasibility of co-digesting nitrogen-rich SD with the carbon-rich corrugated board (CB) or waste office paper (OP) in varying volatile solids (VS) ratios, to produce methane. Synergistic effect of co-digesting SD with CB and SD with OP on methane production was found in this study. The highest methane yields of 151.62 and 198.85 mL/g-VS were obtained during the co-digestions of SD with CB at 4:1 ratio (SDCB) and SD with OP at 2:3 ratio (SDOP), respectively. High-throughput 16 S rRNA gene sequencing demonstrated that the microbial diversity and richness in SDCB and SDOP co-digests were higher than in SD and OP mono-digests, respectively. Characteristic bacteria and archaea in the digests were strongly substrate-related and might contribute to methane production. The validated results indicated that methane production through anaerobic co-digestion of SD and waste paper can be an efficient way that could not only reduce environmental pollution but also contribute to methane production. [ABSTRACT FROM AUTHOR]

The aim of the study was to use black liquor produced during the soda pulping process in a pulp and paper mill to increase methane production during pulp and paper industry sludge treatment and decrease the treatment cost. The effects of black liquor on sludge solubilization and methane production were assessed and the economic feasibility of the process was evaluated. Black liquor and NaOH were found to be equivalent in the thermochemical pretreatment process to solubilize sludge and disintegrate flocs. However, adding black liquor increased the background chemical oxygen demand and volatile fatty acid concentration and increased the amount of methane produced by approximately 7–30%. A start-up delay was emphasized by first-order kinetics model due to black liquor addition while methane production remained stable. Economic assessments of five scenarios were performed. It was found to be economically feasible to use black liquor to replace NaOH for the thermal pretreatment process. The surplus methane generated suggested that co-digestion of sludge and black liquor allows surplus bioenergy to be produced during the thermochemical pretreatment anaerobic digestion process. [Display omitted] • Black liquor played the same role as NaOH during pretreatment. • Black liquor increased the organic co-substrate concentration. • Lignin-derived compounds probably depress enzyme activity. • Replacing NaOH with black liquor was found to be economically feasible. [ABSTRACT FROM AUTHOR]

Biohythane, the promising gaseous biofuel, can be produced by the recirculated two-phase anaerobic digestion (R-TPAD). The effect of hydraulic retention time (HRT) as 30, 20 and 10 days on biohythane production via R-TPAD (recirculation ratio = 0.4) was investigated with co-digestion of food waste and paper waste. The results showed that HRTs of 30 and 20 days maintained stable performance for R-TPAD but HRT of 10 days led to the final decrease in biogas production. The failure in the end was attributed to the wash-out of microbes. The removal efficiencies for COD and carbohydrates were decreased by short HRTs while for VS it remained relatively stable at about 75.7 ± 4.0%. All through the operation, acidogenic phase and methanogenic phase were separated stably and butyrate pathway was the dominant pathway for hydrogen fermentation in the first stage. The microbial community in the first stage reached the highest diversity when total HRT was 20 days, where the hydrogen production rate was the highest. The genera Lactobacillus and Caproiciproducens kept dominating the dark fermentation in the acidogenic phase, and Ruminococcus and Methanosarcina were decreasing in the methanogenic phase. The biohythane yields were 411 mL/g-VS fed , 332 mL/g-VS fed and 253 mL/g-VS fed , respectively, where the H 2 contents were 18.4%, 14.7% and 8.8%, respectively. [Display omitted] • The R-TPAD system (R = 0.4) was operated for biohythane production. • R-TPAD operated under HRTs of 30 and 20 maintained stable performance. • Organic removals and biohythane yields were lowered by short HRTs. • Different microbial communities were identified by co-occurrence network. • Biohythane yields affected by different parameters were discussed. [ABSTRACT FROM AUTHOR]

A two-stage thermophilic hydrogen fermentation and mesophilic methane production from paper sludge was successfully explored. The maximum hydrogen and methane potential were 0.165 L/g VS and 0.376 L/g COD effluent , respectively with Clostridium thermocellum augmentation. 63 L of hydrogen and 122 L of methane were recovered from 1 kg Paper sludge (PS, dry weight) with an energy yield of 4.5 MJ/kg PS, 50% higher compared to the single-stage anaerobic digestion (94 L CH 4 , 3.0 MJ/kg PS). The bacterial community of second-stage process was dominated by genus Propionispira , Mesotoga and Aminobecterium with stability, whereas the bacterial structure in single-stage process presented dynamic changes where genus Acetivibrio and Fibrobacter played an indispensable role. However, Genus Methanosaeta , Methanosarcina , Methanobacterium and Methanospirillum existed stably and predominantly in the archaeal community of single-stage and second-stage processes. The present study suggests the potential application of the established two-stage process in valorization of low-value waste biomass. Image 1 • C. thermocellum enhanced two-stage H 2 and CH 4 production from PS was established. • 50% more energy recovery was achieved from two-stage than single-stage. • Archaeal community structure of two BMP tests showed no difference. [ABSTRACT FROM AUTHOR]

While anaerobic digestion is commonly practiced in the municipal sector, it has not gained popularity in the pulp and paper industry mainly because of its long sludge residence time requirement of 20–30 days. The construction of large digesters to provide such extended residence times is capital-intensive and thus the implementation of anaerobic digestion has remained economically prohibitive. A review of the literature suggests that recent developments in sludge preconditioning technologies have substantially reduced the sludge residence time requirement to the order of 7 days. Also, the preconditioned sludges have been reported to hold potential for higher methane recovery with reduced excess sludge production requiring disposal. Such advantages, coupled with escalating fuel prices and the introduction of carbon credits under the Kyoto Accord, have significantly improved the economics of anaerobic digestion. As the cost of sludge management varies from one mill to another, mill-specific economic assessment of anaerobic digestion could identify cost-saving opportunities. [Copyright &y& Elsevier]

Abstract: Cellulose hydrolysis is the rate-limiting step in anaerobic digestion. In the present study, waste paper was used as a model of cellulosic biomass and was pretreated with rumen fluid prior to methane production. To achieve a high methane yield, the reaction time of the pretreatment was examined. Waste paper was soaked with rumen fluid for 6 and 24h at 37°C. Various volatile fatty acids, especially acetate, were produced by the pretreatment. Semicontinuous methane production was carried out over a 20-day period. The best daily methane yield was obtained by the 6-h pretreatment. The amount was 2.6 times higher than that of untreated paper, which resulted in 73.4% of the theoretical methane yield. During methane production, the cellulose, hemicellulose and lignin degradabilities were improved by the pretreatment. Pretreatment by rumen fluid is therefore a powerful method to accelerate the methane yield from a cellulosic biomass. [Copyright &y& Elsevier]

Abstract: The unbalanced nutrients of algal sludge (low C/N ratio) were regarded as an important limitation factor to anaerobic digestion process. Adding high carbon content of waste paper in algal sludge feedstock to have a balanced C/N ratio was undertaken in this study. The results showed adding 50% (based on volatile solid) of waste paper in algal sludge feedstock increased the methane production rate to 1170±75ml/lday, as compared to 573±28ml/lday of algal sludge digestion alone, both operated at 4g VS/lday, 35°C and 10 days HRT. The maximum methane production rate of 1607±17ml/lday was observed at a combined 5g VS/lday loading rate with 60% (VS based) of paper adding in algal sludge feedstock. Results suggested an optimum C/N ratio for co-digestion of algal sludge and waste paper was in the range of 20–25/1. [Copyright &y& Elsevier]

Pulp and paper mills (PPMs) generate large amount of wastewater with high chemical oxygen demand (COD) concentration. Recently, anaerobic digestion receives much attention for the treatment of PPM wastewater. Through anaerobic digestion treatment, biogas can be generated and converted to bioenergy via combined heat and power (CHP). However, there are limited studies on the systematic allocation of bioenergy from CHP to wastewater treatment (WWT) and PPM to form an integrated pulp and paper biorefinery (IPPB). Therefore, the current work explores the potential of energy integration in an IPPB through a two-stage optimization approach. In the first stage, an optimal cost effective WWT for the treatment of PPM wastewater is synthesized. Next, the generated biogas from WWT is converted into four different forms of bioenergy. The detail allocation of the generated bioenergy is then determined in the second stage optimization. A case study is solved to illustrate the proposed approach. [ABSTRACT FROM AUTHOR]

• Simulation model developed for an anaerobic digester in Aspen Plus. • Organic feeds like cow dung, banana stem, and waste paper pulps are used. • Parameters like PTT, HRT, and F/W ratios are optimized for BioHydrogen production. • Sequence of influencing parameter is: PTT > HRT > F/W. • Optimal BioHydrogen yield obtained is 24.59% (CD), 25.27% (BS), and 24.21% (WPP). A simulation model was developed for biohydrogen production from organic feeds such as cow dung (CD), banana stem (BS), and waste paper pulps (WPP). Data from the model was used to generate a design of experiment (DoE) that analysed the data and optimizes the input parameters for optimized biohydrogen yield. Three input parameters taken for optimization were pretreatment temperature (PTT), hydraulic retention time (HRT), and feed-to-water (F/W) ratio. Results showed the optimal sequence of influencing parameters is PTT > HRT > F/W ratio. The optimal value of PTT was 75 ℃ for all feeds. In contrast, the HRT and F/W ratios were 13.1 days and 0.5 ratio for CD, 16.6 days and 1.5 ratio for BS, and 11.7 days and 1.4 ratio for WPP. At the same time, the optimal biohydrogen yield was 24.59 % (CD), 25.27 % (BS), and 24.21 % (WPP). Therefore, the current simulation and optimization had convincing results in optimizing commercial plants' biohydrogen production. [ABSTRACT FROM AUTHOR]

The feasibility and performance of hydrogen production from paper sludge without inoculation was investigated under thermophilic conditions. The maximum hydrogen production reached 64.32 mM with 7.4% PS. The dynamic changes in bacterial community structures during hydrogen production were investigated by analyzing 16S rDNA gene sequences using high throughput sequencing technology. The results showed that microbial community was dominated by order Clostridiales and Thermoanaerobacterales . Genus Thermoanaerobacterium and Ruminiclostridium played a leading role in the fermentation process, which was responsible for the hydrolysis of PS and hydrogen production. Effect of inoculation with Clostridium thermocellum on hydrogen production from PS was also studied. The results showed that C. thermocellum supplement significantly increased hydrogen yield and holocellulose degradation rate by 96.80% and 32.95%, respectively. In addition, inoculation of C. thermocellum enhanced VFA generation and shortened the lag phase of hydrogen production. The present study lays the foundation on the valorization of waste lignocellulose. [ABSTRACT FROM AUTHOR]

Highlights: [•] Total reuse of Waste Activated Sludge from pulp and paper industry was studied. [•] The WAS hydrolysis solubilises over 90% of tCOD and hygienises the solid residue. [•] It is possible to use solid residue of WAS as a raw material in cardboard production. [•] Biogas can be produced from solubilised portion of WAS in an UASB reactor. [•] Presented “zero-sludge” concept produces renewable energy and raw materials. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • Successful co-production of bioH 2 and bioCH 4 was achieved by R-TPAD process. • The R-TPAD process was feasible to treat OFMSW (FW + PW) with PW content ≤50%. • Increasing PW favored H 2 yields by enriching H 2 -producing bacteria in the process. • The major cellulose-degrading bacteria grew only in the mesophilic phase (2nd stage). • The H 2 -producers were recirculated to the 1st phase after growing in the 2nd phase. Abstract To achieve the co-production of H 2 and CH 4 , co-digestion of food waste (FW) and paper waste (PW) was performed on the recirculated two-phase anaerobic digestion (R-TPAD). The PW content in the feedstock increased from 0% to 20%, 40% and 50% (in total solids) with FW as the rest. The results showed that bioH 2 and bioCH 4 were simultaneously and stably produced in the long-term operation. With the increasing PW content, the removal efficiency of volatile solids decreased slightly from 84.9% to 78.4%; the bioH 2 yields increased from 50 to 79 NL-H 2 /kg-VS fed while the bioCH 4 yields decreased from 426 to 329 NL-CH 4 /kg-VS fed. With the fixed amount of FW, adding PW could significantly increase the total bioenergy yields. The relative abundance showed that the key H 2 -producing bacteria, Caproiciproducens and Thermoanaerobacterium , increased after PW addition. The microbial distribution suggests that the H 2 -producers were recirculated to the first stage after proliferating in the second stage. [ABSTRACT FROM AUTHOR]

This paper describes a new option for integrated recovery and esterification of carboxylates produced by anaerobic digestion at a pH above the pK a . The carboxylates (acetate, propionate, butyrate, valerate and lactate) are recovered using a strong anion exchange resin in the bicarbonate form, and the resin is regenerated using a CO 2 -expanded alcohol technique, which allows for low chemicals consumption and direct esterification. Paper mill wastewater was used to study the effect of pH and the presence of other inorganic anions and cations on the adsorption and desorption with CO 2 -expanded methanol. Calcium, which is present in paper mill wastewater, can cause precipitation problems, especially at high pH. Esters yields ranged from 1.08 ± 0.04 mol methyl acetate/mol of acetate in to 0.57 ± 0.02 mol methyl valerate/mol of valerate in . [ABSTRACT FROM AUTHOR]

In order to optimize the biogas recovery from the co-digestion of food waste (FW) and paper waste (PW), the effect of PW content on two-phase anaerobic digestion (TPAD) was investigated. The mixtures of FW and PW, with the ratios of 10:0, 8:2, 6:4 and 5:5 (total solids), were fed into TPAD to recover biomethane. After the long-term expriment, it is elucidated that the methanogenesis in TPAD was stable for PW ≤ 40%. When PW = 50%, NH 4 HCO 3 was added to the methanogenic phase to provide nitrogen. As the indicators of the stability of the anaerobic process, the ammonia and alkalinity in the methanogenic phase were simulated for their decreasing trend. The simulation results quantified the nitrogen deficiency in the methanogenic phase for PW = 50%. Also, the comparison of alkalinity and ammonia revealed that ammonia was the major contributor to the alkalinity. Furthermore, via stoichiometric calculations, high C/N ratios were found to increase the microbial yield and exacerbated the nitrogen deficiency. In the energy estimation, adding PW showed significant increase only when PW ≥ 40%. It was concluded that 40% was the optimal PW content for bioenergy augmentation from co-digestion of FW and PW using TPAD. [ABSTRACT FROM AUTHOR]

Because paper sludge discharged from the waste paper recycling process contains high levels of lignin and ash, it is not hydrolyzed effectively during anaerobic digestion. In this study, we investigated the effects of pretreatment with rumen fluid on paper sludge and on the methane fermentation process. Paper sludge was pretreated with rumen fluid at 37 °C for 6 h. Following pretreatment, 4.5% of the total solids in paper sludge were degraded and converted, and the dissolved chemical oxygen demand and volatile fatty acid concentration increased. Batch methane fermentation was conducted at 37 °C for 20 days. During methane fermentation, the degradation and hydrolysis of paper sludge were enhanced by pretreatment with rumen fluid. The amounts of total methane production from pretreated paper sludge (excluding methane generated from rumen fluid), rumen fluid and untreated paper sludge were 650.4, 819.9 and 190.8 ml, respectively. The volume of methane gas produced from pretreated paper sludge was 3.4 times larger than that from untreated paper sludge. These results indicate that pretreatment with rumen fluid enhances methane production from paper sludge. [ABSTRACT FROM AUTHOR]

The objective of this study was to measure the anaerobic biodegradation of different types of paper products in laboratory-scale landfill reactors. The study included (a) measurement of the loss of cellulose, hemicellulose, organic carbon, and (b) measurement of the methane yields for each paper product. The test materials included two samples each of newsprint (NP), copy paper (CP), and magazine paper (MG), and one sample of diaper (DP). The methane yields, carbon storage factors and the extent of cellulose and hemicellulose decomposition all consistently show that papers made from mechanical pulps (e.g., NPs) are less degradable than those made from chemical pulps where essentially all lignin was chemically removed (e.g., CPs). The diaper, which is not only made from chemical pulp but also contains some gel and plastic, exhibited limited biodegradability. The extent of biogenic carbon conversion varied from 21 to 96% among papers, which contrasts with the uniform assumption of 50% by the Intergovernmental Panel on Climate Change (IPCC) for all degradable materials discarded in landfills. Biochemical methane potential tests also showed that the solids to liquid ratio used in the test can influence the results. [ABSTRACT FROM AUTHOR]

Abstract: With the final aim of reducing the energy consumption and increase the methane production at Swedish pulp and paper mills, the methane potential of 62 wastewater effluents from 10 processes at seven pulp and/or paper mills (A–G) was determined in anaerobic batch digestion assays. This mapping is a first step towards an energy efficient and more sustainable utilization of the effluents by anaerobic digestion, and will be followed up by tests in lab-scale and pilot-scale reactors. Five of the mills produce kraft pulp (KP), one thermo-mechanical pulp (TMP), two chemical thermo-mechanical pulp (CTMP) and two neutral sulfite semi-chemical (NSSC) pulp. Both elementary and total chlorine free (ECF and TCF, respectively) bleaching processes were included. The effluents included material from wood rooms, cooking and oxygen delignification, bleaching (often both acid- and alkali effluents), drying and paper/board machinery as well as total effluents before and after sedimentation. The results from the screening showed a large variation in methane yields (percent of theoretical methane potential assuming 940NmL CH4 per g TOC) among the effluents. For the KP-mills, methane yields above 50% were obtained for the cooking effluents from mills D and F, paper machine wastewater from mill D, condensate streams from mills B, E and F and the composite pre-sedimentation effluent from mill D. The acidic ECF-effluents were shown to be the most toxic to the AD-flora and also seemed to have a negative effect on the yields of composite effluents downstream while three of the alkaline ECF-bleaching effluents gave positive methane yields. ECF bleaching streams gave higher methane yields when hardwood was processed. All TCF-bleaching effluents at the KP mills gave similar degradation patterns with final yields of 10–15% of the theoretical methane potential for four of the five effluents. The composite effluents from the two NSSC-processes gave methane yields of 60% of the theoretical potential. The TMP mill (A) gave the best average yield with all six effluents ranging 40–65% of the theoretical potential. The three samples from the CTMP process at mill B showed potentials around 40% while three of the six effluents at mill G (CTMP) yielded 45–50%. [Copyright &y& Elsevier]

[Display omitted] • Field deployable platform to monitor inhibitory compounds in anaerobic digesters. • Paper sensors in a well-microplate prevent cross-contamination during gas pervaporation/diffusion. • Simultaneous ammonia and sulfide determination without sample treatment. • Fast and semi-automated processing of digital colorimetric images. • Good recoveries are obtained in anaerobic supernatants and wastewater. A simple and low-cost field-deployable method using paper sensors in combination with a 3D-printed portable platform to simultaneous determination of ammonia and sulfide has been developed. Ammonia and sulfide are harmful pollutants for the environment and important toxicants inhibiting anaerobic digestion, therefore, are key monitoring parameters during wastewater treatment. The sample preparation system consisted of a well microplate and sensor paper discs placed inside the microplate sealing system. Gas pervaporation and diffusion of ammonia and hydrogen sulfide across a Teflon membrane onto a paper discs, impregnated with bromothymol blue and methylene blue assay reagents, allowed the ammonia and sulfide determination, respectively. The detection system consisted in a 3D-printed photographic lightbox with LED plates and a smartphone. A code was developed in ImageJ for a fast colorimetric measurement of the digital images. Under optimal conditions, limits of detection of 1.3 and 1.7 mg L-1 and linear concentration ranges between 5 and 50 mg L-1 and 5–45 mg L-1, were obtained for ammonia and sulfide, respectively. The analysis of an anaerobic digester and wastewater samples revealed good precisions (RSDs < 10 %) and recoveries (91–105 %). This methodology shows advantages such as a high precision, a simple paper discs preparation and a reusable system. [ABSTRACT FROM AUTHOR]

Abstract: Anaerobic digestion of pulp and paper mill primary sludge and co-digestion of primary and secondary sludge were studied for the first time in semi-continuously fed continuously stirred tank reactors (CSTR) in thermophilic conditions. Additionally, in batch experiments, methane potentials of 210 and 230 m3CH4/t volatile solids (VS)added were obtained for primary, and 50 and 100 m3CH4/tVSadded for secondary sludge at 35 °C and 55 °C, respectively. Anaerobic digestion of primary sludge was shown to be feasible with organic loading rates (OLR) of 1–1.4 kgVS/m3d and hydraulic retention times (HRT) of 16–32 d resulting in methane yields of 190–240 m3CH4/tVSfed. Also the highest tested OLR of 2 kgVS/m3d and the shortest HRT of 14–16 d could be feasible, if pH stability is confirmed. Co-digestion of primary and secondary sludge with an OLR of 1 kgVS/m3d and HRTs of 25–31 d resulted in methane yields of 150–170 m3CH4/tVSfed. In the digestion processes, cellulose and hemicellulose degraded while lignin did not. pH adjustment and nitrogen deficiency needs to be considered when planning anaerobic digestion of pulp and paper mill wastewater sludges. [Copyright &y& Elsevier]

The aim of this research it is to show how the biogas anaerobic digestion from treatment of recycled pulp and paper wastewater industry (RPPW) can be a renewable energy. Furthermore, a kinetic study of hydrolyzed COD and productions of methane from UASB digester treating RPPW for the continuous test is established. This will allow to reduce the organic matter deposited in landfills and CO 2 emissions and to find viable solutions to minimize the environmental impact of RPPW. This study analyses the biogas products and energy recovery processes from a thermic and electric point of view from the theoretical equations. Thus, this study evaluated the performance of mesophilic methanogenic up-flow sludge blanket reactors (UASB) operating continuously in single-stage (UASB I). The maximum methane yields were 250.9 mLCH 4 /gCOD removed for UASB I, corresponding to 82.7% of the maximum theoretical energy 6.336 kJ/gCOD removed, Methanogenic potential were 4 137 928 m3CH 4 /year and electrical energy potential were 510 703 MWh/year. The kinetic study allowed us a hydrolysis rate kh = 0.04 indicates a correct simulation for the UASB digester treatment system for RPPW with an R = 99.668%. • Anaerobic treatment for RPPW by UASB digester under mesophilic conditions. • Energy generated was 6.336 kJ/gCOD removed and Electrical energy 510 703 MWh/year. • 84% COD and 48% TS were removed at an OLR of 7 g COD/L.d. • At optimal OLR was required to produce average 46 L/d CH 4. • Methane yields were 250.9 mLCH 4 /gCOD removed. [ABSTRACT FROM AUTHOR]

Abstract: A microbial consortium MC1 was used to pretreat filter paper, office paper, newspaper, and cardboard to enhance methane production. The results of pretreatment indicated that sCOD of hydrolysates of the four substrates increased significantly in the early stage, and peaked on day 7. During pretreatment, ethanol, acetic acid, propionic acid, butyric acid, and glycerol were the predominant volatile organic products in hydrolysates. MC1 had strong degradation ability on the four substrates, and the weight loss of filter paper, office paper, newspaper, and cardboard reached 78.3%, 80.5%, 39.7%, and 49.7%, respectively. The results of anaerobic digestion showed that methane production yields and rates of the four substrates significantly increased after pretreatment. This study is the first attempt to explore the microbial pretreatment method for anaerobic digestion of waste paper and cardboard. Microbial consortium pretreatment could be an effective method for enhancing methane production of waste paper and cardboard into bioenergy. [Copyright &y& Elsevier]

Pulp and paper industry is one of the most polluting, energy and water intensive industries in the world. Produced pulp and paper mill sludge (PPMS) faces a major problem for handling and its management. An anaerobic digestion has become an alternative source. This review provides a detailed summary of anaerobic digestion of PPMS – An overview of the developments and improvement opportunities. This paper explores the different pretreatment methods to enhance biogas production from the PPMS. First, the paper gives an overview of PPMS production, and then it reviews PPMS as a substrate for anaerobic digestion with or without pretreatment. Finally, it discuss the optimal condition and concentration of organic and inorganic compounds required for the anaerobic metabolic activity. Future research should focus on the combination of different pretreatment technologies, relationship between sludge composition, reactor design and its operation, and microbial community dynamics. [ABSTRACT FROM AUTHOR]

Different undiluted liquid digestates from mesophilic and thermophilic anaerobic digesters of pulp and paper industry biosludge with and without thermal pretreatment were characterized and utilized for cultivating Scenedesmus acuminatus . Higher S. acuminatus biomass yields were obtained in thermophilic digestates (without and with pretreatment prior to anaerobic digestion (AD): 10.2 ± 2.2 and 10.8 ± 1.2 g L −1 , respectively) than in pretreated mesophilic digestates (7.8 ± 0.3 g L −1 ), likely due to differences in concentration of sulfate, iron, and/or other minor nutrients. S. acuminatus removed over 97.4% of ammonium and 99.9% of phosphate and sulfate from the digestates. Color (74–80%) and soluble COD (29–39%) of the digestates were partially removed. Different AD processes resulted in different methane yields (18–126 L CH 4 kg −1 VS), digestate compositions, and microalgal yields. These findings emphasize the importance of optimizing each processing step in wood-based biorefineries and provide information for pulp and paper industry development for enhancing value generation. [ABSTRACT FROM AUTHOR]

Abstract: Sulfide can be removed from wastewater and recovered as elemental sulfur using an electrochemical process. Recently, we demonstrated this principle of product recovery on synthetic feeds. Here, we present a lab scale electrochemical reactor continuously removing sulfide from the effluent of an anaerobic treatment process operated on paper mill wastewater. The effluent contained 44 ± 7 mg of sulfide-S L−1. Sulfide was reduced to 8 ± 2 mg-S L−1, at a removal rate of 0.845 ± 0.133 kg-S m−3 of total anodic compartment (TAC) d−1. The removed sulfide was recovered (75 ± 4% recovery) as pure concentrated alkaline sulfide/polysulfide solution, from which solid elemental sulfur was obtained. The electrochemical sulfide removal was not affected by different soluble constituents or particulate materials present in the wastewater. However, over time sulfide removal decreased due to biological sulfur reduction using the organics present in the wastewater. Therefore, a periodic switching strategy between anode and cathode was developed. Biofilm formation was avoided as the pH of the cathode solution increased to inhibitory levels during cathodic operation, while still allowing full recovery of the sulfur as end product. [Copyright &y& Elsevier]

Abstract: Anaerobic digestion of pulp and paper sludge (PPS) and monosodium glutamate waste liquor (MGWL) was studied in completely stirred tank reactors (CSTR) at 37 ± 2 °C. This work focused on the effect of increased organic loading rate (OLR) on the methane production in long-term experiments. For OLR in the range of (1.5–5.0) kg m−3 d−1 based on VS fed, VFA and SCOD concentrations decreased for the first 10 days and then kept stable at about 2.3 kg m−3 and 4.0 kg m−3 respectively until to the critical OLR of 5.0 kg m−3 d−1; and the methane generation rate enhanced to 0.838 m3 m−3 d−1 during this period until to the reactor failure. Additionally, reaction rate constant k and sludge retention time (SRT) are described on the basis of a mass balance in a CSTR followed a first order kinetic equation. In the present study, values for ym and k were obtained as 0.733 m3 kg−1 of removed VS and 0.07 d−1, respectively. The simple model can apply for dimensioning a CSTR digesting of organic wastes from pulp and paper industries, food processing industries, sewage treatment plants or biogas crops. [Copyright &y& Elsevier]