Teemu Kinnarinen

Effect of mixing on enzymatic hydrolysis of cardboard waste: Saccharification yield and subsequent separation of the solid residue using a pressure filter

Cellulosic wastes, from sources such as low-quality cardboard and paper, are regarded as potential feedstocks for bioethanol production. One pathway from these cellulosic materials to ethanol is saccharification (hydrolysis) followed by fermentation. Saccharification is commonly performed using enzymes that are able to cleave the cellulosic structure to smaller units, preferably to glucose monomers. During the hydrolysis, mixing conditions have a considerable impact on the performance of the enzymes. Thus mixing conditions in the hydrolysis tank can also influence the downstream operations and, consequently, the overall economy of the bioethanol process. In this experimental study, four types of impeller, at different hydrolysis conditions were used. The effect of mixing on the glucose yield and on the filtration characteristics of the hydrolysate was evaluated. It was shown that not only the sugar yield depended on the mixing conditions: the effect on the solid-liquid separation step was even more significant.

Enabling safe dry cake disposal of bauxite residue by deliquoring and washing with a membrane filter press.

Dry cake disposal is the preferred technique for the disposal of bauxite residue, when considering environmental issues together with possible future utilisation of the solids. In order to perform dry cake disposal in an economical way, the deliquoring of the residue must be carried out efficiently, and it is also important to wash the obtained solids well to minimise the amount of soluble soda within the solids. The study presented in this article aims at detecting the most important variables influencing the deliquoring and washing of bauxite residue, performed with a horizontal membrane filter press and by determining the optimal washing conditions. The results obtained from pilot-scale experiments are evaluated by considering the properties of the solids, for instance, the residual alkali and aluminium content, as well as the consumption of wash liquid. Two different cake washing techniques, namely classic washing and channel washing, are also used and their performances compared. The results show that cake washing can be performed successfully in a horizontal membrane filter press, and significant improvements in the recovery of alkali and aluminium can be achieved compared with pressure filtration carried out without washing, or especially compared with the more traditionally used vacuum filtration.

Influence of enzyme loading on enzymatic hydrolysis of cardboard waste and size distribution of the resulting fiber residue

Enzymatic hydrolysis of lignocellulosic biomass to sugars alters the properties of the cellulosic fibers. Several process variables, including enzyme loading, play an important role in these changes. Many physical properties of fibers are affected: their length and width, porosity, specific surface area, and degree of fibrillation, for instance, may undergo dramatic changes when subjected to enzymatic degradation. In this study, the influence of enzyme loading on the fiber size was investigated using milled cardboard waste as the raw material. The effect of cellulases and hemicellulases on the monosaccharide production and the resulting fiber size was studied using commercial enzyme products. It was shown that the cellulase loading largely determined the amount of sugars produced. The fiber length was reduced during the course of hydrolysis, although the size reduction was not especially dramatic. Based on the SEM images, no significant damage to the fiber surfaces occurred during the process.

Removal of chloride from fly ash produced in hazardous waste incineration by leaching and displacement washing in a vertical filter press

Fly ash is generated in large quantities by waste incineration processes. Chloride is commonly present in the fly ash produced by the incineration of hazardous materials, such as polyvinylchloride plastic. Major difficulties related to the disposal and handling of fly ash include the high concentration of easily leachable chlorides, heavy metals and toxic compounds. In order to avoid adverse environmental effects from the disposal of fly ash, the content of soluble chlorides must be reduced. One of the most effective options for chloride removal is leaching and displacement washing in a filter press. The primary aim of this study was to obtain efficient removal of chloride from fly ash by utilizing a leaching and displacement washing process, carried out in a filter press. The secondary objective was to obtain high filtration capacities and low filter cake moisture contents. The slurry was prepared by mixing fly ash with water at an ash:water ratio of 1:2 and filtered to separate the solids from the liquid. After solid–liquid separation, most of the dissolved residual chloride was removed from the filter cake by washing the cake with fresh water in the second stage of separation. It was possible to remove up to 98% of the total chloride and to obtain sufficient filtration capacities. The residual moisture content of the filter cakes varied from 22 to 35 wt%, which meant that the cakes could be disposed of in landfill, or possibly utilized as a construction material.

Steam Dewatering of Filter Cakes in a Vertical Filter Press

Steam dewatering of filter cakes is recognized as a competitive alternative to conventional air drying and thermally assisted mechanical dewatering (TAMD). The main benefit of cake dewatering with high-pressure steam is that mechanical and thermal dewatering can be efficiently performed in a single process step. The target of this study was to determine the potential of a steam-dewatering technique for two industrial mineral suspensions. The first mineral, kaolin, was very difficult to dewater using conventional mechanical dewatering techniques, whereas the second one, ground calcium carbonate (GCC), represented only moderate resistance to filtration. The secondary objective was to compare the filterability of the original kaolin slurry with the same slurry treated with a coagulant (aluminum sulphate, Al2(SO4)3 · 16H2O). Four different kinds of experiments were performed: tests without any kind of cake dewatering, tests with air drying, tests with steam drying, and tests with both coagulation and steam drying. The obtained results show that steam dewatering is an efficient technique for achieving lower cake-moisture contents. Also, the positive influence of coagulation on the filtration capacity was found to be considerable in the case of kaolin. An approximate energy balance was created for the steam-drying process and the determined energy efficiencies were compared with those obtainable with an ideal thermal drier. The main conclusion from these comparisons is that steam drying can be effectively used instead of traditional thermal drying if the large energy losses can be reduced by proper insulation and heat recovery systems.

Extraction of hazardous metals from green liquor dregs by ethylenediaminetetraacetic acid

Green liquor dregs are the major inorganic solid side stream of kraft pulp mills which contain environmentally hazardous metals. The presence of hazardous metals in this industrial residue brings statutory limits for its landfilling, although they are not easily mobilized from the solid phase. In this study, the chelating agent ethylenediaminetetraacetic acid (EDTA) is utilized to extract hazardous metals such as Cd, Pb and Zn from green liquor dregs. Furthermore, the influence of EDTA on the removal of Ca as the main mineral nutrient present in the green liquor dregs is studied. The effect of parameters such as EDTA dosage, L/S ratio and contact time on the removal rate of the elements is investigated. In addition, the experimental data are fitted to the Elovich model and the pseudo-first-order model to describe the desorption kinetics. The results show that 59 wt% of Cd, 13 wt% of Co, 62 wt% of Cu, 3 wt% of Mn, 12 wt% of Ni, 43 wt% of Pb, 16 wt% of Zn, and less than 1 wt% of Ca were extracted from green liquor dregs with EDTA dosage of 0.035 gEDTA salt/gdregs and the L/S ratio of 6.25 ml/g. The current study opens up new possibilities to use the green liquor dregs for improving the soil fertility instead of landfilling.

Experimental Study on the Influence of Selected Process Variables on the Separation of a Fine Particle Suspension with a Pilot Scale Decanter Centrifuge

Decanter centrifuges are used widely in the chemical and process industries for dewatering and classification of solid-liquid suspensions. The most important applications of this class of centrifuges are found in wastewater sludge treatment and in pigment production. The objective of this study was to investigate the operation of a pilot scale decanter centrifuge in a challenging dewatering application. Dewatering tests were performed using fine-particle slurries consisting of water and various concentrations of kaolin. In addition to the solid concentration of the feed, the feed rate of the suspension and the differential speed between the bowl and the conveyer screw were also chosen as variables. The experimental conditions were selected according to a factorial test design and the responses monitored included the production capacity (productivity) of the decanter, the solid contents of the cake and the centrate, as well as the time that was required for the stabilization of the test unit. The results obtained clearly showed that the studied variables have a significant influence on the performance of the dewatering process. The variables were also able to explain the dewatering results at a high level of statistical significance. The repeatability of the experiments was, in most cases, good: On average, the relative standard deviations for the productivity and the solid contents of the cake were 6.0% and 0.5%. It was also apparent that random variations in the feed conditions may have a remarkable and long-lasting impact on the operation of the centrifuge.

Empirical Modelling of Cake Washing in a Pressure Filter

The focus of this article is on empirical modelling of filter cake washing. The filtration experiments introduced in this paper were conducted by using a pilot-scale (0.1 m2) filter press according to the basic principles of factorial designs. Five different variables of the filtration, pressing, cake washing, and air drying stages were considered in the tests and the examined product characteristics were the overall capacity of the filter and the purity of the cake. The results obtained from the tests were used for creating different kinds of regression models for explaining the influence of the studied variables on the success of the cake washing process. The goal of the modelling strategy for the cake washing was to determine the simplest empirical models and compare these with theoretical equations complemented with linear terms. It was found that the empirical equation could model the results more accurately than the theory-based equations could.

Removal of hazardous trace elements from green liquor dregs by mechanical separation methods

Abstract Green liquor dregs represent the most important inorganic residue of chemical pulp mills. The dregs are usually settled in thickeners, washed and deliquored with lime mud precoat filters, and transported to the landfill. The utilization of dregs is challenging, due to the high concentration of hazardous trace elements (HTE) in their solid phase. There are basically two potential strategies for the reduction of the HTE content of dregs: mechanical classification according to differences in the size and density of particles, and removal of HTE by various chemical treatments. The objective of this study was to evaluate the applicability of straightforward mechanical separation methods for the purification of dregs from HTE. The evaluated separation methods included particle size–based classification by sieving, and classification on the basis of differences in the settling properties of particles in gravitational and centrifugal separation. It can be concluded that all the evaluated separation methods could be used to reduce the HTE content of dregs, although the separation efficiency was not very high in most cases. Centrifugation had clearly the best performance of the investigated techniques. The fractions consisting of large particles contained consistently lower concentrations of HTE, compared to fractions containing a lot of fines.

Effective removal of hazardous trace metals from recovery boiler fly ashes

The objective of this study is to introduce a treatment sequence enabling straightforward and effective recovery of hazardous trace elements from recovery boiler fly ash (RBFA) by a novel method, and to demonstrate the subsequent removal of Cl and K with the existing crystallization technology. The treatment sequence comprises two stages: dissolution of most other RBFA components than the hazardous trace elements in water in Step 1 of the treatment, and crystallization of the process chemicals in Step 2. Solid-liquid separation has an important role in the treatment, due to the need to separate first the small solid residue containing the trace elements, and to separate the valuable crystals, containing Na and S, from the liquid rich in Cl and K. According to the results, nearly complete recovery of cadmium, lead and zinc can be reached even without pH adjustment. Some other metals, such as Mg and Mn, are removed together with the hazardous metals. Regarding the removal of Cl and K from the process, in this non-optimized case the removal efficiency was satisfactory: 60-70% for K when 80% of sodium was recovered, and close to 70% for Cl when 80% of sulfate was recovered.