Pulp Mill Wastewater: Characteristics and Treatment

The production of chemical pulp in recent times is 180 million tons per year; while the production of eucalyptus pulp has increased intensively, especially in the southern hemisphere. The pulp and paper industry has long been considered a large consumer of natural resources (wood and water) and one of the largest sources of pollution to the environment (air, water courses and soil). Important efforts are being made to reduce the pollutant levels and water consumption of the industry. The wastewater composition, and therefore, the efficiency of effluent treatments and characteristics of the discharges to water are strongly dependent on the applied technology and raw materials. Despite a large body of literature on softwood-based wastewater, few studies have examined the characteristics of kraft eucalyptus bleaching effluents and their behaviour in the different biological treatments. The largest secondary treatment systems today use the activated sludge process. Sixty to seventy-five per cent of all the biological effluent treatment plants within the pulp and paper industry use this kind of treatment system. This chapter reviews the current pulping technologies at mills and compares the chemical composition and biological treatment of wastewater between softwood and hardwood bleached pulps

Heterologous expression and application of lipolytic enzymes for mitigation of lipophilic compounds in eucalyptus species.

Doctor of Philosophy in Microbiology. University of KwaZulu-Natal, Durban, 2017.Abstract available in PDF file

Sustainable Development and Application of Renewable Chemicals from Biomass and Waste

Advancements in efficient energy sources have played a pivotal role in determining the present world energy structure. Renewable biomass energy has been incorporated in industrial regulations and policies in many European countries. Based on the statistics, more than one-seventh of the total world energy consumption is generated from biomass.The renewable energies movement was prompted by two important factors: a) growing world energy consumption and b) the abundance of generated biomass residues, especially in agriculture. In the case of the first, batteries containing different metals are considered, as is the production of items for human consumption (food, clothing, home comfort, etc.). In the second case, the biomass waste from plants and animals, as byproducts of cultivating and production processes, is the main source of generated waste

Remediation of Pulp and Paper Mill Biosolids using Vermiculture

Historical wastewater treatment systems at a New Zealand pulp and paper mill, resulted in a biosolid mass in the K-basin at Kinleith mill. Products extracted during the pulping process include resin acids, which are further transformed in the K-basin by microbial activity into recalcitrant end products retene and fichtelite. These products are toxic to fish due to bioaccumulation and subsequent endocrine disruption. Traditional methods for diverting these toxins from waterways were deposition into landfills and incineration, neither of which are considered environmentally sound. The aim of this study was to investigate the viability of vermicomposting as a method for bioremediation of recalcitrant resin acid derivatives from biosolids. Vermicomposting is a cost-effective option for not only reducing toxicity but also reducing biomass. It was hypothesised that earthworms can degrade organic extractives, principally resin acids and derivatives, through microbial, enzymatic, and oxidative mechanisms. A series of vermicomposting experiments were set up, to test the ability of Eisenia fetida (the tiger worm) to reduce both the amount of resin acids and overall biomass in a range of substrates. These included the original biosolid collected from K-basin, a simulated biosolid containing potting mix with and without additional extractive resins, as well as sterilised and unsterilised controls. Five samples were taken from each experimental composter over 28 days and extracted into dichloromethane after removal of excess water followed by mechanical blending. Samples were concentrated and the amount of each extractive group was determined using gas chromatography mass spectroscopy. The overall biomass in each composter as well as the depurated earthworm mass was measured at the start and cessation of the experiment. A slight reduction in biomass was observed in two out of the three substrates. This reduction was slightly enhanced by the presence of earthworms in the composter, however, it was not significant. The use of methyl bromide to sterilise the substrate was also not a significant factor in biomass reduction. The overall weight of the earthworms decreased in all cases indicating the unsuitability of any of the substrates as a desirable food source. The addition of supplements such as yeast or manure to the biosolid composter may increase its appeal. There was a significant reduction in extractive content in all substrates over the 28 day period however no significant difference attributable to the presence or absence of worms was observed. It was hypothesised that the rigorous sampling process encouraged oxidative breakdown of the extractives due to increased exposure to both air and light. This was evident when the extractive content of K-basin measured in 1993 was compared to the samples used in this study collected in 2006. Whilst vermicomposting does not appear to be an effective treatment for removing resin acids from biosolid mass, the sampling processes used in this study highlighted the effect that rigorous stirring and increased exposure to air and light can have on the natural breakdown of these products. An effective treatment for the removal of resin acids from K-basin may be as simple as regular ploughing

Investigating the effects of wood chemistry and cooking conditions on pulp properties at a dissolving wood pulp mill.

Masters Degree. University of KwaZulu-Natal, Durban.Pulp viscosity is the main criteria used to determine the endpoint of the pulping process in acid bisulphite pulping for production of dissolving pulp (DP). However, pulping performance is highly dependent on the relative abundance, structure, and reactivity of wood chemical components, mainly cellulose, hemicellulose and lignin. Thus, the chemistry of wood components has become an important factor when selecting wood species for use in the production of DP. It is believed that the chemical composition of wood components in tree species can be used to predict the pulp properties after pulping the wood. Although this correlation has been reported in Kraft pulping studies, there is very limited knowledge of such correlations in the acid sulphite pulping processes. This study entailed an investigation to ascertain if there are correlations between wood chemistry components and the resulting pulp properties from acid sulphite pulping process. The study was conducted on wood samples from Eucalyptus species, coded in this study as (E.001, E.002, E.003, E.004), Acacia mearnsii (Wattle) and additional clones and hybrids of eucalyptus species (W962-71, G438-105, A189-97, 100 GN). The samples were pulped using the magnesium acid sulphite cooking process, at wood specific base charge of 2.5 and 3.0. The wood chemistry of the trees and properties of their resultant brown pulp samples were determined. The results showed that there were variations in wood chemical composition among the Eucalyptus species that were evaluated. A lower base ratio of 2.5 produced pulps with lower viscosity and lower kappa than those produced at base ratio 3.0. These pulping conditions resulted in about 1 to 2% lower pulp yields than those reported for standard mill pulping conditions. Comparison of data on wood chemistry composition and pulp properties seemed to indicate good correlations on samples cooked at base ratio of 3.0 with a correlation coefficient (r) maximum of 0.71: the correlation was between alpha cellulose and total pulp yield. Correlation coefficients above 0.5 are considered significant. The results suggested that for some eucalyptus species pulped at base ratio of 3.0, a higher syringyl to guaiacyl S/G ratio in wood resulted in a higher delignification rate, resulting in lower residual lignin (K number) and higher pulp brightness. Eucalyptus wood samples with higher total lignin produced lower total pulp yields and brightness values whereas those with higher alpha cellulose content produced higher pulp yields with higher brightness values. Analysis of a combination of various wood components, namely, S/G ratio, hemicellulose content, and alpha cellulose content led to derivation of a formula that showed these parameters could be used to predict the viscosity of resultant pulps: the correlation coefficient was approximately 0.7 was obtained at base ratio 3.0, whereas 0.67 was obtained at base ratio 2.5

Alternative Raw Materials for Pulp and Paper Production in the Concept of a Lignocellulosic Biorefinery

The main source of cellulosic fibre used for pulp and paper production comes from wood, while non-wood fibres are used to a lesser extent. However, a renewed interest exists in the use of non-woody raw materials due to their abundance as source of low-cost fibres and because they are sometimes the only exploitable source of fibres in certain geographical areas, mainly in developing countries. Moreover, the great variety of characteristics, fibre dimensions and chemical composition of these alternative raw materials give them a great potential to produce different types of papers. On the other hand, the pulp and paper industry is an excellent starting point for the development of lignocellulosic biorefineries, possessing the necessary technology and infrastructure as well as extensive experience in lignocellulosic biomass transformation. Since its beginnings, the pulp and paper industry has been practicing certain aspects of the biorefinery concept, generating the energy necessary for the production of cellulosic pulp from the combustion of lignocellulosic waste and black liquors, recovering the chemical reagents used and generating high value-added products (e.g. tall oil) together with cellulosic pulp. However, the evolution of the pulp and paper industry to a lignocellulosic biorefinery requires technological innovations to make bioenergy and new bioproducts available alongside traditional products

Oxidative activation of wood fibers for the manufacture of medium-density fiberboard (MDF)

The aim of this thesis work was to study the possibilities of radical formation in wood fiber surfaces to enable direct fiber-to-fiber adhesion by radical-based reactions in the manufacture of fibreboard, particularly medium-density fiberboard (MDF). The fibers were produced by defibration at high temperatures. Radical formation was achieved by treatment with laccase, treatment with Fenton's reagent, or gamma-irradiation. High-temperature defibration was found to cause cleavage of interunit beta-aryl ether linkages of lignin, resulting in formation of mechanoradicals and phenolic hydroxyl groups. The proportion of water-extractable low-molecular weight lignin and hemicelluloses present in the fibers increased with an increase in defibration temperature. In the laccase treatment of fibers in water suspension, much more radicals were formed in hardwood than in softwood fibers for fibers produced at equal temperature. Radical formation increased with increasing defibration temperature. The treatment of fibers with Fenton's reagent in water suspension resulted in the formation of similar numbers of radicals in hardwood and softwood fibers. Radical formation increased with increasing defibration temperature but not so drastically as with laccase treatments. Also the gamma-irradiated fibers contained large numbers of radicals. Their content increased as a function of increasing defibration temperature and was higher for hardwood than for softwood fibers. The internal bond strength (IB) of fiberboards made from fibers treated with laccase or Fenton's reagent in the defibrator blowline improved with increasing defibration temperature. The IB of boards made from laccase-treated fibers correlated with the number of radicals formed in the fibers on laccase treatment in water suspension, indicating that adhesion in the boards was largely due to reactions of radicals on the fiber surfaces. The IB of boards made from fibers treated with Fenton's reagent also correlated with the radical content of the fibers, but this relationship was not as strong as with the laccase treatments. This suggests that bonding mechanisms other than radical coupling may have contributed significantly to adhesion. Gamma-irradiation of fibers before their fabrication into boards resulted in a marked increase in board IB, indicating that radicals play a significant role in the adhesion of boards made from gamma-irradiated fibers.reviewe

Development of novel building composites based on hemp and multi-functional silica matrix

This study focuses on the development of novel bio-composites using a silica matrix that provides dual functionality: as a hydrophobic surface treatment and as a binder for hemp-shiv. The hydrophilic nature of hemp shiv, a plant based aggregate, results in composites having poor interfacial adhesion, weak mechanical properties and long drying times. In this work, sol-gel process has been utilised to manufacture durable low density hemp based composites. Morphological characterisation by scanning electron microscopy (SEM) showed that hemp shiv was embedded well in the matrix. Detailed chemical analysis using x-ray photoelectron spectroscopy (XPS) and gas chromatography-mass spectrometry (GC-MS) indicate the presence of water soluble and ethanol soluble extractives leached from the hemp shiv which are incorporated into the silica matrix inducing the binding effect. The composites were water resistant and showed good mechanical performance having the potential to develop novel thermal insulation building materials

Sequenced anaerobic - aerobic treatment of hemp pulping wastewaters

Biological treatment is an indispensable instrument for water management of non-wood pulp mills, either as internal measure to enable progressive closure of water cycles, or as end of pipe treatment. In this thesis, the sequenced anaerobic-aerobic treatment of hemp ( Cannabis sativa L. ) pulping wastewaters is described, with a focus on the treatability of thermomechanical pulping (TMP) effluents and soda pulping black liquors. The research was performed within the framework of the Dutch Hemp Programme, which aimed to develop environmentally safe and economically feasible pulping processes as a measure to explore non-food markets for arable farming.Pulp and paper industry wastewaters are highly heterogeneous, depending on the feedstock and the pulping processes utilized. Hemp TMP wastewaters were found to be non-toxic to methanogens and highly suitable for sequenced anaerobic-aerobic treatment, which enabled 63-66% COD removal at loading rates up to 27 g COD/ lUASBd. Hemp black liquors on the other hand, were somewhat more problematic, due to the high methanogenic toxicity, causing 50% inhibition of acetoclastic methanogenic activity (50% IC) at concentrations ranging from 2-6 g COD/ l , which is 10 to 100 times lower than the black liquor concentrations in industry and comparable to the methanogenic inhibition of wood pulping wastewaters.Apolar hemp extractives (resinous compounds) were observed to be the main source of inhibitory substances in hemp black liquors. Lignin derivatives on the other hand, were less important for methanogenic inhibition, since the main share of lignin in hemp black liquors was non-toxic. Despite the high methanogenic toxicity of hemp black liquors, anaerobic treatment was feasible, provided that adequate dilution was applied. Anaerobic treatment of diluted hemp stem wood black liquor (HSWBL) facilitated recovery of methane and high treatment efficiencies at high organic loading rates. Subsequent aerobic post-treatment provided almost complete removal of BOD, however COD-removal was limited due to the presence of recalcitrant lignin. Additionally, substantial detoxification was obtained after anaerobic-aerobic treatment. The major removal of inhibitory compounds was accomplished in the aerobic step.The effective reduction of methanogenic toxicity during sequenced anaerobic-aerobic treatment of hemp black liquors was used as a detoxification strategy denominated upfront dilution, recirculating the aerobic effluent to dilute the incoming influent to sub-toxic concentrations. The feasibility of the upfront dilution method was demonstrated in an experiment, in which direct anaerobic treatment and sequenced anaerobic-aerobic treatment with upfront dilution were compared. Direct anaerobic treatment of 12 g COD/ l HSWBL led to almost complete inhibition of the methanogenic activity within 14 days. While recirculation of 75% of the aerobic post-treatment effluent for upfront dilution of the toxic HSWBL, enabled anaerobic treatment at loading rates up to 21.5 g COD/ lUASBd without noticeable inhibition of methanogenesis. Extensive detoxification was confirmed during anaerobic-aerobic treatment of 20 g COD/ l HSWBL recirculating 86% of the aerobic effluent. COD and BOD removal was 47% and 68%, respectively, after anaerobic treatment; and 74% and 97%, respectively, after anaerobic-aerobic treatment at an overall loading rate of 3.6 g COD/ l d, while 30-35% of the incoming COD was recovered as methane.Lignin removal during anaerobic-aerobic treatment of hemp pulping wastewaters was remarkably high and ranged up to 44%, of which globally half was obtained anaerobically. Studies on hemp TMP wastewater revealed that lignin removal during anaerobic treatment corresponded to the lowest molecular weight derivatives, indicating that biodegradation was the major removal mechanism. Subsequently, aerobic post-treatment of hemp pulping wastewaters caused extensive polymerization of lignin to molecular weights in excess of 34 kD, which was associated with strong increases in wastewater color. Autoxidative polymerization of polyphenols formed out of lignin by anaerobic bioconversion is proposed as a mechanism for the observed increase in lignin molecular weight and color. Apart from the highly stable high molecular weight lignin-derived humic COD, biologically treated pulping effluents are relatively clean, which offers benefits for lignin removal during tertiary treatment, such as reduced fouling of ultrafiltration membranes and improved precipitation with divalent salts.Comparison of anaerobic-aerobic treatment and aerobic treatment shows that treatment efficiencies and detoxification were similar. The anaerobic-aerobic treatment system however, provided 50% lower surplus sludge production, production of methane as an energy source (0.16 m 3/kg COD removed ), less nutrient dosage and substantial reductions in aeration costs.The results of this research demonstrate that sequenced anaerobic-aerobic treatment is a suitable technology for the treatment of hemp pulping wastewaters. Upfront dilution effectively reduced inhibition of methanogenesis by extractive compounds during anaerobic treatment, whereas the observed increase in lignin molecular weight after biological treatment offers benefits for lignin removal during optional tertiary treatment.</p