Hannu Nurmesniemi

Chemical and physical properties of cyclone fly ash from the grate-fired boiler incinerating forest residues at a small municipal district heating plant (6 MW)

In Finland, the new limit values for maximal allowable heavy metal concentrations for materials used as an earth construction agent came into force in July 2006. These limit values are applied if ash is utilized, e.g. in roads, cycling paths, pavements, car parks, sport fields, etc. In this study we have determined the most important chemical and physical properties of the cyclone fly ash originating from the grate-fired boiler incinerating forest residues (i.e. wood chips, sawdust and bark) at a small municipal district heating plant (6 MW), Northern Finland. This study clearly shows that elements are enriched in cyclone fly ash, since the total element concentrations in the cyclone fly ash were within 0.2-10 times higher than those in the bottom ash. The total concentrations of Cd (25 mg kg(-1); d.w.), Zn (3630 mg kg(-1); d.w.), Ba (4260 mg kg(-1); d.w.) and Hg (1.7 mg kg(-1); d.w.) exceeded the limit values, and therefore the cyclone fly ash cannot be used as an earth construction agent. According to the leached amounts of Cr (38 mg kg(-1); d.w.), Zn (51 mg kg(-1); d.w.) and sulphate (50,000 mg kg(-1); d.w.), the cyclone fly ash is classified as a hazardous waste, and it has to be deposited in a hazardous waste landfill.

Effect of biological wastewater treatment on the molecular weight distribution of soluble organic compounds and on the reduction of BOD, COD and P in pulp and paper mill effluent.

Pulp and paper mill wastewater was characterizated, before (influent) and after (effluent) biological wastewater treatment based on an activated sludge process, by microfiltration (8, 3, 0.45 and 0.22microm) and ultrafiltration (100, 50, 30 and 3kDa) of the wastewater samples into different size fractions. Various parameters were measured on each fraction: molecular weight distribution (MWD) using high performance size exclusion chromatography (HPSEC), total organic carbon (TOC), biochemical oxygen demand (BOD), chemical oxygen demand (COD), total phosphorus (Tot-P), phosphate phosphorus (PO(4)-P), electrical conductivity, pH, turbidity, charge quantity and zeta potential. The MWD, TOC and COD(Cr) results indicated that the majority of the material present in both the influent and effluent was in the medium molecular weight (MW) range (i.e. MW<10kDa) with three main MW sub-fractions. There were no significant differences in the range of the MWD between the influent and effluent samples. The magnitude of the MWD in the effluent was about one half that in the influent, the greatest reduction being in the 6kDa fraction. The 3kDa fractions of both the influent and effluent showed a considerable increase in BOD(7), probably due to the removal of compounds harmful to bacteria in 3kDa ultrafiltration. Influent turbidity decreased considerably in microfiltration (8-0.22microm). As the turbidity was removed by 0.22microm filtration, the anionic charge quantity started to decrease. Particles in the influent and effluent contained 19-29% and 14-20% of the total phosphorus, respectively. The major phosphorus fraction was in the form of soluble phosphate.

Size fractionation of wood extractives, lignin and trace elements in pulp and paper mill wastewater before and after biological treatment.

Integrated kraft pulp and paper mill wastewater was characterized before (influent) and after (effluent) the activated sludge process by microfiltration (8, 3, 0.45 and 0.22 microm) and ultrafiltration (100, 50, 30 and 3 kDa) into different size fractions. Wood extractives, lignin, suspended solids and certain trace elements were determined in each fraction. Forty four percent of the resin and fatty acids in the influent (12.8 mg/L) occurred in particles (>0.45 microm), 20% as colloids (0.45 microm-3 kDa) and 36% in the <3 kDa fraction. The corresponding values for sterols (1.5 mg/L) were 5, 46 and 49%. In the effluent, resin and fatty acids (1.45 mg/L) and sterols (0.26 mg/L) were mainly present in the <3 kDa fraction, as well as a small proportion in particles. beta-sitosterol was present in particles in the effluent (88+/-50 microg/L). Lignin in the influent was mainly in the colloidal and <3 kDa fractions, whereas in the effluent it was mainly in the <3 kDa fraction. Thus the decrease of lignin in the biological treatment was concentrated on the colloidal fraction. In the influent, Mn, Zn and Si were mainly present in the <3 kDa fraction, whereas a significant proportion of Fe and Al were found also in the particle and colloidal fractions. In the effluent, Fe and Al were mainly present in the colloidal fraction; in contrast, Mn, Zn and Si were mainly in the <3 kDa fraction. The results indicated that the release of certain compounds and elements into the environment could be significantly decreased or even prevented simply by employing microfiltration as a final treatment step or by enhancing particle removal in the secondary clarifier.

Chemical sequential extraction of heavy metals and sulphur in bottom ash and in fly ash from a pulp and paper mill complex.

A five-stage sequential extraction procedure was used to determine the distribution of 11 metals (Cd, Cr, Cu, Mo, Pb, Zn, As, Co, V, Ni, Ba), and sulphur (S) in bottom ash and in fly ash from a fluidized bed co-combustion (i.e. wood and peat) boiler of Stora Enso Oyj Oulu Mill at Oulu, Northern Finland, into the following fractions: (1) water-soluble fraction (H2O); (2) exchangeable fraction (CH3COOH); (3) easily reduced fraction (NH2OH—HCl); (4) oxidizable fraction (H2O2 + CH3COONH 4); and (5) residual fraction (HF + HNO3 + HCl). Although metals were extractable in all fractions, the highest concentrations of most of the metals occurred in the residual fraction. From the environmental point of view, this fraction is the non-mobile fraction and is potentially the least harmful. The Ca concentrations of 29.3 g kg—1 (dry weight) in bottom ash and of 68.5 g kg— 1 (dry weight) in fly ash were correspondingly approximately 18 and 43 times higher than the average value of 1.6 g kg— 1 (dry weight) in arable land in Central Finland. The ashes were strongly alkaline pH (∼ 12) and had a liming effects of 9.3% (bottom ash) and 13% (fly ash) expressed as Ca equivalents (dry weight). The elevated Ca concentrations indicate that the ashes are potential agents for soil remediation and for improving soil fertility. The pH and liming effect values indicate that the ashes also have a pH buffering capacity. From the environmental point of view, it is notable that the heavy metal concentrations in both types of ash were lower than the Finnish criteria for ash utilization.

Utilization of steel, pulp and paper industry solid residues in forest soil amendment: Relevant physicochemical properties and heavy metal availability

Industrial residue application to soil was investigated by integrating granulated blast furnace or converter steel slag with residues from the pulp and paper industry in various formulations. Specimen analysis included relevant physicochemical properties, total element concentrations (HCl+HNO3 digestion, USEPA 3051) and chemical speciation of chosen heavy metals (CH3COOH, NH2OH·HCl and H2O2+H2O2+CH3COONH4, the BCR method). Produced matrices showed liming effects comparable to commercial ground limestone and included significant quantities of soluble vital nutrients. The use of converter steel slag, however, led to significant increases in the total concentrations of Cr and V. Subsequently, total Cr was attested to occur as Cr(III) by Na2CO3+NaOH digestion followed by IC UV/VIS-PCR (USEPA 3060A). Additionally, 80.6% of the total concentration of Cr (370 mg kg(-1), d.w.) occurred in the residual fraction. However, 46.0% of the total concentration of V (2470 mg kg(-1), d.w.) occurred in the easily reduced fraction indicating potential bioavailability.

Leachability of metals in fly ash from a pulp and paper mill complex and environmental risk characterisation for eco-efficient utilization of the fly ash as a fertilizer

Abstract A five-stage, sequential leaching procedure was used to determine the distribution of metals (Cd, Cu, Pb, Cr, Zn, Ni, Co, As, V, Ba, Ti and K) in fly ash from a pulp and paper mill complex between the water-soluble fraction (H2O), exchangeable fraction (CH3COOH), easily reduced fraction (HONH3Cl), oxidizable fraction (H2O2.CH3COONH4), and the residual fraction (HF+HNO3+HCl). The possible environmental risk associated with the eco-efficient utilization of fly ash as a fertilizer, especially the Cd load, was estimated. In addition, the mobility (i.e. bioavailability) of Cd, Cu, Pb, Zn, Ni and Cr was evaluated. The fly ash was derived from an electrostatic precipitator of a fluidized bed boiler in the co-combustion (55% bark and wood residues,45% peat) process at pulp and paper mill in Northern Finland. The accuracy of the leaching procedure was tested using a certified reference material SRM 1633b (Coal Fly Ash). The metals were determined by graphite furnace atomic absorption spectrometry (GFAAS) or by inductively coupled plasma atomic emission spectrometry (ICP-AES). The mobility factors (i.e. bioavailability) of the metals followed the order: Cd, Cu, Zn, Ni, Pb and Cr. The fly ash from the pulp and paper mill was enriched in Ca, Mg, P and K, and could therefore be used as a soil amendment for liming purposes.

Chemical and leaching properties of paper mill sludge

Abstract Paper mills produce large amounts of paper mill sludge in the treatment of process water. According to overburden studies, the hydraulic conductivity of the paper mill sludge originating from a paper mill in Northern Finland at a pressure of 30kPa was 4.4×10∓10 ms∓1, and 1.7×10∓ 10 ms∓1at a pressure of 100kPa. These values well meet the generally required values of between 1.0×10∓7 ms∓1 and 1.0×10∓9 ms-1 for a geological barrier in landfill base and sides at landfills in the European Union. Paper mill sludge can also be used in the artificially constructed geological barrier layer of landfill cover structures. The angle of internal friction of the paper mill sludge was 34.8° and the cohesion of inter-particle adhesion 23 kPa, which are important measures for assessing the shear strength of paper mill sludge and thus the stability of the landfill layer in which it is used. During a 28-day period, the biodegradability of the paper mill sludge in soil was ca 0.4% and in ground water under 1%, whereas according to the OECD 301F standard concentrations (BOD28), it was ca 8%. For the determination of total element concentrations in the paper mill sludge, the dried sample was digested using USEPA method 3052. A five-stage sequential leaching procedure was also used to fractionate trace elements in the paper mill sludge between the water-soluble (H2O), exchangeable (CH3COOH), easily reduced (HONH3CD, oxidizable (H2O2 + CH3COONH4), and (5) the residual (HF + HNO3 + HCl) fractions. This paper covers also examples of case studies how paper mill sludge is utilized in Finland.

Particle size distribution and dissolution properties of metals in cyclone fly ash

The particles in the examined cyclone fly ash were all smaller than 0.25 mm. in diameter, and particles smaller than 0.075 mm. in diameter accounted for 88.4 % of the ash weight. This result indicates that cyclone fly ash consists of particles with a small diameter. The metals in the cyclone fly ash were enriched in small particles. The highest concentrations for zinc, copper, lead, cadmium and molybdenum in the cyclone fly ash were found in the smallest particle size fraction (< 0.075 mm.) and for Barium, chromium, nickel, Vanadium and Cobalt in the second to smallest particle size fraction (0.075-0.125 mm.). From an environmental and toxicological standpoint, the smallest particles are of the greatest concern when ash is handed at landfill disposal sites (transport and disposal especially in stormy weather conditions), and some studies have reported risks to workers from prolonged exposure to ash. The results of the comparison of various dissolution methods for metals showed that the digestion procedures with nitric acid alone (USEPA 3051) or with a mixture of nitric acid + hydrogen peroxide (USEPA 3050B) slightly underestimated the metal concentrations in the cyclone fly ash. Although the use of hydrofluoric acid is often necessary for the determination of a number of elements associated with siliceous minerals, its use can result in loss of trace elements during dissolution.

Heavy metals leaching in bottom ash and fly ash fractions from industrial-scale BFB-boiler for environmental risks assessment

Abstract The bottom ash and fly ash from the co-combustion of wood residues and peat at a bubbling fluidised bed boiler (296 MW) contained only quartz (SiO 2 ), microcline (KAlSi 3 O 8 ) and albite (NaAlSi 3 O 8 ). Thus, X-ray powder diffraction (XRD) was not useful for clarifying the difference in the release of associated heavy metals from ash matrices. In order to assess the release of heavy metals from ashes under changing environmental conditions, they were sequentially extracted and fractionated by the BCR-procedure into acid soluble/exchangeable (CH 3 COOH), reducible (NH 2 OH–HCl) and oxidizable (H 2 O 2 /CH 3 COONH 4 ) phases. The CH 3 COOH extractable fraction in conjunction with the total heavy metals concentrations were used to calculate the risk assessment code values for heavy metals leaching from the ash matrix. The leaching studies indicate that the heavy metals in the bottom ash and fly ash are bound to different fractions with different strengths. From the environmental and utilization perspectives, heavy metals in ashes posed different levels of environmental contamination risk. Only As in the bottom ash posed a very high risk. High risk metals were Cd in the bottom ash as well as As, Cd and Se in the fly ash.

Comparison Study of Manometric Respirometric Test and Common Chemical Methods in the Determination of BOD7 in a Pulp and Paper Mill's Wastewaters

The biological oxygen demand (BOD) test is widely used in many wastewater treatment plants. The conventional BOD tests are usually time-consuming and the results are often out of date for process control purposes. The aim of this research was to compare the manometric respirometric test with common chemical methods in the determination of BOD of wastewater from a pulp and paper mills as well as to evaluate the BOD 7 values of both wastewaters from the short-term respirometric measurements. The results showed that there were differences in the BOD7 values of paper mill samples measured by conventional and respirometric methods. The main cause was found to be the dilution solution used in the conventional BOD tests. Using the same mineral solution in the respirometric measurements diminished the difference remarkably. Evaluation of the BOD7 value after two or three days incubation was proved to work very well and the estimated results were close to measured values (deviations 1%–12%).