Total Cyanide Research Articles

Effectiveness of wetting method for control of konzo and reduction of cyanide poisoning by removal of cyanogens from cassava flour.

Konzo is an irreversible paralysis of the legs that occurs mainly among children and young women in remote villages in tropical Africa and is associated with a monotonous diet of bitter cassava. Konzo was discovered in 1938 by Dr. G. Trolli in the Democratic Republic of Congo (DRC). It also occurs in Mozambique, Tanzania, Cameroon, Central African Republic, and Angola. It was first controlled in Kay Kalenge village, DRC, in 2011 with the use of a wetting method to remove cyanogens from cassava flour. Fourteen months later, another visit was made to Kay Kalenge. To determine whether Kay Kalenge women were still using the wetting method, whether there were new cases of konzo, and whether the wetting method had spread to other villages. Meetings were held with chiefs, leaders, and heads of mothers' groups, women from 30 households were interviewed, and three nearby villages were visited. Total cyanide and thiocyanate were analyzed in cassava flour and urine samples, respectively. The women in Kay Kalenge village still used the wetting method. There were no new cases of konzo. The mean cyanide content of the flour samples was 9 ppm, and no child had a mean urinary thiocyanate content greater than 350 micromol/L. The use of the wetting method had spread naturally to three adjacent villages. The wetting method has been readily accepted by rural women as a simple and useful method to control konzo by removing cyanide from cassava flour, and its use has spread to nearby villages. The wetting method should be promoted by health authorities to control konzo and reduce cyanide poisoning from high-cyanide cassava flour.

Removal of total cyanide in coking wastewater during a coagulation process: Significance of organic polymers

Whether a cationic organic polymer can remove more total cyanide (TCN) than a non-ionic organic polymer during the same flocculation system has not been reported previously. In this study, the effects of organic polymers with different charge density on the removal mechanisms of TCN in coking wastewater are investigated by polyferric sulfate (PFS) with a cationic organic polymer (PFS-C) or a non-ionic polymer (PFS-N). The coagulation experiments results show that residual concentrations of TCN (Fe(CN)3−6) after PFS-C flocculation (TCN < 0.2 mg/L) are much lower than that after PFS-N precipitation. This can be attributed to the different TCN removal mechanisms of the individual organic polymers. To investigate the roles of organic polymers, physical and structural characteristics of the flocs are analyzed by FT-IR, XPS, TEM and XRD. Owing to the presence of N+ in PFS-C, Fe(CN)3−6 and negative flocs (Fe(CN)3−6 adsorbed on ferric hydroxides) can be removed via charge neutralization and electrostatic patch flocculation by the cationic organic polymer. However, non-ionic N in PFS-N barely reacts with cyanides through sweeping or bridging, which indicates that the non-ionic polymer has little influence on TCN removal.

Cyanide reduction pattern of cassava (mannihot Esculenta) as affected by variety and air velocity using fluidized bed dryer

Detoxification of two cassava varieties (TMS30572 and TMS98/0581) by varying drying temperature and air velocity to produce cassava chips was studied at the Department of Food Science and Technology, Federal University of Technology Akure, Ondo; State Nigeria. Quantitative determination of total cyanide (HCN) in cassava chips was carried out using alkaline titration method. Results show that varieties and air velocity interactions highly significantly reduced (P≤0.05) the total cyanide content in the dried chips. Drying at temperature of 40 oC, air velocity of 2.03 m/s, 2.25 m/s, 2.45 m/s and 2.75 m/s reduced the cyanide content from 8.19 mg/kg to range between 2.53 mg/kg-1.07 mg/kg; at temperature of 50 oC at same air velocity gave result of 4.05 mg/kg-1.63 mg/kg; at temp of 60 oC same set of air velocity gave 6.75 mg/kg-1.01 mg/kg and temperature of 70 oC at same air velocity of 7.08 mg/kg - 1.87 mg/kg for TMS30572. TMS98/0581 at temperature of 40 oC, 50 oC, 60 oC and 70 oC and air velocity of 2.03 m/s, 2.25 m/s, 2.45 m/s and 2.75 m/s gave result of 7.43 mg/kg-3.04 mg/kg; 0.45 mg/kg-0.67 mg/kg;0.68 mg/kg-0.59 mg/kg and 0.59 mg/kg respectively. It was noted that total HCN content in cassava chips can be substantially reduced by drying at temperature of 70 oC and air velocity of 2.75 m/s for TMS30572 and temperature of 60 oC and 70 oC at air velocity of 2.75 m/s. This study shows

Stability of Prussian Blue in Soils of a Former Manufactured Gas Plant Site

Soil contamination with iron-cyanide complexes is a common problem at former manufactured gas plant (MGP) sites. Dissolution of the cyanide, from Prussian Blue (ferric ferrocyanide), creates an environmental hazard, whereas the risk of groundwater contamination depends on the stability of dissolved iron–cyanide complexes. Lack of a standard leaching method to determine the water-soluble (plant-available) cyanide fraction generates potential limitations for implementing remediation strategies like phytoremediation. Applicability of neutral solution extraction to determine the water-soluble cyanide fraction and the stability of Prussian Blue in surface and near-surface soils of an MGP site in Cottbus, undersaturated and unsaturated water conditions, was studied in column leaching and batch extraction experiments. MGP soils used in the long-term tests varied according to the pH (5.0–7.7) and the total cyanide content (40–1718 mg kg−1). Column leaching, after four months of percolation, still yielded effluent concentrations exceeding the German drinking water limit (> 50 μg L−1) and the solubility of Prussian Blue reported in the literature (< 1 mg L−1) from both alkaline and acidic soils. Long-term (1344 h) extraction of MGP soils with distilled water was sufficient to dissolve 97% of the total cyanide from the slightly alkaline soils and up to 78% from the acidic soils. Both experiments revealed that dissolution of ferric ferrocyanide under circum-neutral pH and oxic water conditions is a function of time, where the released amount is dependent on the soil pH and total cyanide content. Unexpectedly high and continuous solubility of Prussian Blue, both in acidic and slightly alkaline MGP soils, implies the need to introduce an additional cyanide fraction (“readily soluble fraction”) to improve and specify cyanide leaching methods. Long-term extraction of cyanide-contaminated soil in neutral solution seems to be a promising approach to evaluate the potential hazard of groundwater pollution at the MGP sites.

Environmental Law, Public Health, and the Values Conundrum

In September 1996, when I was nearing the end of my sixth year as a Justice Department environmental crimes prosecutor, one of my colleagues sent me an email that there was a “good-sounding RCRA [Resource Conservation and Recovery Act] knowing endangerment case developing in Idaho.” A twenty-year-old man named Scott Dominguez had collapsed inside a storage tank at an Idaho fertilizer manufacturing facility called Evergreen Resources. Mr. Dominguez could not be rescued for nearly an hour, because firefighters who responded to the scene did not know what was in the tank and what safety precautions they needed to take before entering the tank. The owner, Allan Elias, insisted that there was nothing in the tank that could hurt anyone, but later investigation would reveal that Elias had used the tank to conduct a cyanide-leaching operation at another facility he owned. By the time Dominguez was rushed to an area hospital, he had suffered permanent brain damage from cyanide poisoning. There was enough cyanide remaining in the tank to kill tens of thousands of people, based on total cyanide levels.

Successful startup of a full-scale acrylonitrile wastewater biological treatment plant (ACN-WWTP) by eliminating the inhibitory effects of toxic compounds on nitrification

During the startup of a full-scale anoxic/aerobic (A/O) biological treatment plant for acrylonitrile wastewater, the removal efficiencies of NH(3)-N and total Kjeldahl nitrogen (TKN) were 1.29 and 0.83% on day 30, respectively. The nitrification process was almost totally inhibited, which was mainly caused by the inhibitory effects of toxic compounds. To eliminate the inhibition, cultivating the bacteria that degrade toxic compounds with patience was applied into the second startup of the biological treatment plant. After 75 days of startup, the inhibitory effects of the toxic compounds on nitrification were eliminated. The treatment plant has been operated stably for more than 3 years. During the last 100 days, the influent concentrations of chemical oxygen demand (COD), NH(3)-N, TKN and total cyanide (TCN) were 831-2,164, 188-516, 306-542 and 1.17-9.57 mg L(-1) respectively, and the effluent concentrations were 257 ± 30.9, 3.30 ± 1.10, 31.6 ± 4.49 and 0.40 ± 0.10 mg L(-1) (n = 100), respectively. Four strains of cyanide-degrading bacteria which were able to grow with cyanide as the sole carbon and nitrogen source were isolated from the full-scale biological treatment plant. They were short and rod-shaped under scanning electron microscopy (SEM) and were identified as Brevundimonas sp., Rhizobium sp., Dietzia natronolimnaea and Microbacterium sp., respectively.

Coagulation behaviors and in-situ flocs characteristics of composite coagulants in cyanide-containing wastewater: Role of cationic polyelectrolyte

In this paper, composite coagulants (PFS, PFSC05, PFSC1 and PFSC5), prepared by mixing polyferric sulfate (PFS) and cationic polyelectrolyte (CP) coagulants with different weight percent (W p) of CP (W p = 0%, 0.5%, 1% and 5%, respectively), were adopted to treat cyanide-containing wastewater. PFSC5 exhibited superior coagulation performances at optimal conditions: the removal of total cyanide (TCN) and chemical oxygen demand (COD) was 95%–97% and 50%–55%, respectively. The effects of CP on the properties and structure of flocs were investigated by laser diffraction instrument and small-angle laser light scattering (SALLS), respectively. The results show that the flocs of PFSC5 have higher growth rate, higher strength factor and lower recovery factor than other flocs. They are also much denser and more uniform owing to the higher fractal dimension (Df) and less microflocs (10–100 μm). Furthermore, the dense structure of the PFSC5 flocs can be restored after shear and is more resistant to hydraulic conditions. Particularly, detailed morphology evolution of the flocs was in-situ detected by on-line particle imaging. Due to strong ionic strength in wastewater, the CP in PFSC5 plays a significant role of adsorption, while the main mechanism of CP is electrostatic patch aggregation during the PFSC05 systems.

Treatment of tapioca starch wastewater by a novel combination of physical and biological processes

A pilot plant combining dissolved air flotation, anaerobic degradation in an expanded granular sludge bed (EGSB) reactor and aerobic post-treatment in a vertical flow constructed wetland has been used to treat tapioca starch wastewater for more than 2.25 years. It is demonstrated that organic matter (chemical oxygen demand by >98%), nitrogen (Kjeldahl-N by >90%) and cyanide (total cyanide by >99%) can be removed very efficiently under stable operating conditions. The removal efficiency for phosphorus is lower (total-P by 50%). The treatment concept, which includes several sustainable aspects, e.g. production of energy to be used on-site, low operation demands and minimal use of chemicals, could be interesting for small- and middle-sized tapioca processing plants.

Efficient treatment of an electroplating wastewater containing heavy metal ions, cyanide, and organics by H2O2 oxidation followed by the anodic Fenton process

A real electroplating wastewater, containing heavy metals, cyanide, and organic contaminants, was treated by electrocoagulation (EC), H2O2 oxidation, H2O2 pre-oxidation followed by EC, and the anodic Fenton process and the efficacy of the processes was compared. Concentration of cyanide, Cu, Ni, Zn, and Cr was largely decreased by EC within 5 min. When the reaction time was extended, removal of residual cyanide, Cu, and Ni was limited. In H2O2 oxidation, the concentration of cyanide decreased from initial 75 to 12 mg L(-1) in 30 min. The effluents from the H2O2 oxidation were further treated by EC or anodic Fenton. In EC, the concentration of total cyanide, Ni, and Cu decreased to below 0.3, 0.5, and 1.5 mg L(-1), respectively. Removal efficiency of chemical oxygen demand by EC was less than 20.0%. By contrast, there was 73.5% reduction by the anodic Fenton process with 5 mM H2O2 at 30 min; this can be attributed to the oxidation induced by hydroxyl radicals generated by the reaction of H2O2 with the electrogenerated Fe(2+). Meanwhile, residual cyanide, Cu, and Ni can also be efficiently removed. Transformation of organic components in various processes was analyzed using UV-visible and fluorescence excitation-emission spectra.

Coking wastewater treatment for industrial reuse purpose: Combining biological processes with ultrafiltration, nanofiltration and reverse osmosis

A full-scale plant using anaerobic, anoxic and oxic processes (A1/A2/O), along with a pilot-scale membrane bioreactor (MBR), nanofiltration (NF) and reverse osmosis (RO) integrated system developed by Shanghai Baosteel Chemical Co. Ltd., was investigated to treat coking wastewater for industrial reuse over a period of one year. The removals reached 82.5% (COD), 89.6% (BOD), 99.8% (ammonium nitrogen), 99.9% (phenol), 44.6% (total cyanide (T-CN)), 99.7% (thiocyanide (SCN−)) and 8.9% (fluoride), during the A1/A2/O biological treatment stage, and all parameters were further reduced by over 96.0%, except for fluoride (86.4%), in the final discharge effluent from the currently operating plant. The pilot-scale MBR process reduced the turbidity to less than 0.65 NTU, and most of the toxic organic compounds were degraded or intercepted by the A1/A2/O followed MBR processes. In addition, parameters including COD, T-CN, total nitrogen, fluoride, chloride ion, hardness and conductivity were significantly reduced by the NF-RO system to a level suitable for industrial reuse, with a total water production ratio of 70.7%. However, the concentrates from the NF and RO units were highly polluted and should be disposed of properly or further treated before being discharged.

Determination of Cyanogenic Compounds in Edible Plants by Ion Chromatography

Cyanogenic glycosides are HCN-producing phytotoxins; HCN is a powerful and a rapidly acting poison. It is not difficult to find plants containing these compounds in the food supply and/or in medicinal herb collections. The objective of this study was to investigate the distribution of total cyanide in nine genera (Dolichos, Ginkgo, Hordeum, Linum, Phaseolus, Prunus, Phyllostachys, Phytolacca, and Portulaca) of edible plants and the effect of the processing on cyanide concentration. Total cyanide content was measured by ion chromatography following acid hydrolysis and distillation. Kernels of Prunus genus are used medicinally, but they possess the highest level of total cyanide of up to 2259.81 CN−/g dry weight. Trace amounts of cyanogenic compounds were detected in foodstuffs such as mungbeans and bamboo shoots. Currently, except for the WHO guideline for cassava, there is no global standard for the allowed amount of cyanogenic compounds in foodstuffs. However, our data emphasize the need for the guidelines if plants containing cyanogenic glycosidesare to be developed as dietary supplements.

Improved processing methods to reduce the total cyanide content of cassava roots from Burundi.

The identification of highly effective procedures that reduce the cyanogens contained in cassava roots which require no sophisticated equipment, and can readily be adopted by subsistence farmers is of tremendous importance. This study, which used cassava root samples collected in Burundi, included fermentation tests using both selected and native cultures at different temperatures for variable times. Moreover, drying procedures with and without fermentation were carried out. A factorial analysis of variance (ANOVA) showed that the detoxification was mainly affected by fermentation length and by the initial cyanogens content of the roots. When fermentation lasted 48 h and the initial cyanide level was lower than 300 mg/kg dry weight (d.w.), the detoxification was also found to vary based on the microorganism inoculated; Saccharomyces cerevisiae demonstrated the greatest effectiveness. In terms of drying conditions, a temperature of 60°C, even for a shorter duration of time (8 h), lowered the initial cyanide level by more than 90%. Finally, when dehydration followed fermentation, the pressed pulp showed a substantial reduction in cyanide content. By means of this last procedure, safe cassava was produced according to FAO/WHO amendments (10 mg HCN equivalent per kilogram flour), if the initial cyanide level of roots did not exceed 200 mg/kg d.w. Actually, the initial maximum total cyanide content was confirmed to be fundamental in order to obtain safe products in relation to processing method adopted. Keywords : Cassava, cyanide, detoxification, drying, fermentation. African Journal of Biotechnology Vol. 12(19), pp. 2685-2691

Spatial and temporal trace metal distribution of a Peruvian basin: recognizing trace metal sources and assessing the potential risk

Recent efforts have been made to determine the environmental impact of mining over the past 11years in the Jequetepeque River basin, in northern Peru. We have now analyzed data from two studies to elucidate the spatial and temporal trace metal distributions and to assess the sources of contamination. These two studies were carried out from 2003 to 2008 by a Peruvian government administration and from 2008 to 2010 by us. We analyzed 249 samples by principal component analysis, measuring: pH, electrical conductivity, total dissolved solids, total suspended solids, chloride, weak-acid-dissociable cyanide, total cyanide, nitrite and nitrate, ammonium, sulfate, and trace metals and metalloids (Al, As, Ca, Cd, Cu, Cr, Fe, Mg, Mn, Ni, Pb, and Zn). Within the spatial distribution of the basin, the highest Al, As, Cu, Fe, Ni, and Pb concentrations were found at the closest point to the mine sites for both periods of time, with the higher peaks measured during the first years of the sampling data. Temporal trends showed higher concentrations of Cu and Fe in samples taken before 2005, at which point the two mines were closed. Risk assessment was quantified by the hazard quotient as related to water ingestion. The risk for human health posed by the concentrations of several trace metals and metalloids was found to be highly adverse (As and Cr), significant (Al, Cd, Cu, Fe, and Pb), or minimal (Ni and Zn).

Ultratrace determination of total and available cyanides in industrial wastewaters through a rapid headspace-based sample preparation and gas chromatography with nitrogen phosphorous detection analysis

A new analytical method for the determination of both available (free and weak acid dissociable, WAD) and total cyanides in industrial wastewaters has been developed. It is based on the static headspace (HS) sampling procedure followed by a GC separation and the selective nitrogen-phosphorous detection (NPD), in which different thermal treatment allows the speciation of total and available cyanides. Detection limits (0.5μg/L), recovery (84.7–114.6% for free and 76.8–121.5% for total cyanides) and precision (5% at 5μg/L), evaluated on both real and synthetic samples, were fit-for-purpose for the legal requirement (5μg/L) enforced in the Venice lagoon, without significant interfering species. In addition, analytical results of the HS-GC-NPD method have been compared with those obtained using the 4500 CN and EN ISO 14403 official methods for the determination of total and free cyanides, respectively. The new method has been successfully applied for the determination of cyanide concentrations in main influent and final effluent to the Venice lagoon to verify the efficiency of the industrial wastewater treatment plant of Porto Marghera (Venice, Italy). The capability of the proposed method to detect the WAD cyanides has been tested by studying the acid dissociation of K2[Ni(CN)4]. An unexpected speciation picture was obtained for this complex, which suggests that the present definition and analytical strategy of this cyanide class should be reconsidered.

Cassava interspecific hybrids with increased protein content and improved amino acid profiles

Cassava (Manihot esculenta) is a principal food for large populations of poor people in the tropics and subtropics. Its edible roots are poor in protein and lack several essential amino acids. Interspecific hybrids may acquire high protein characteristics from wild species. We analyzed 19 hybrids of M. esculenta with its wild relative, M. oligantha, for crude protein, amino acid profile, and total cyanide. Some hybrids produced roots with high protein content of up to 5.7%, while the common cultivar that we examined had just 2.3% crude protein. The essential amino acids alanine, phenylalanine, and valine were detected in the hybrids. The sulfur-containing amino acids cysteine and methionine were found at relatively high concentrations in the roots of 4 hybrids. The proportion of lysine in one hybrid was 20 times higher than in the common cultivar. The levels of total cyanide ranged from 19.73 to 172.56 mg/kg and most of the roots analyzed were classified as "non-toxic" and "low toxic". Furthermore, 2 progenies showed reasonable levels of cyanide, but higher protein content and amino acid profile more advantageous than the common cassava.

Long-Term Release of Iron-Cyanide Complexes from the Soils of a Manufactured Gas Plant Site

Iron-cyanide (Fe-CN) complexes have been detected at Manufactured Gas Plant sites (MGP) worldwide. The risk of groundwater contamination depends mainly on the dissolution of ferric ferrocyanide. In order to design effective remediation strategies, it is relevant to understand the contaminant’s fate and transport in soil, and to quantify and mathematically model a release rate. The release of iron-cyanide complexes from four contaminated soils, originating from the former MGP in Cottbus, has been studied by using a column experiment. Results indicated that long-term cyanide (CN) release is governed by two phases: one readily dissolved and one strongly fixed. Different isotherm and kinetic equations were used to investigate the driving mechanisms for the ferric ferrocyanide release. Applying the isotherm equations assumed an approach by which two phases were separate in time, whereas the multiple first order equation considered simultaneous occurrence of both cyanide pools. Results indicated varying CN release rates according to the phase and soil. According to isotherm and kinetic models, the long-term iron cyanide release from the MGP soils is a complex phenomenon driven by various mechanisms parallely involving desorption, diffusion and transport processes. Phase I (rapid release) is presumably mainly constrained by the transport process of readily dissolved iron-cyanide complexes combined with desorption of CN bound to reactive heterogeneous surfaces that are in direct contact with the aqueous phase (outer-sphere complexation). Phase II (limited rate) is presumably driven by the diffusion controlled processes involving dissolution of precipitated ferric ferrocyanide from the mineral or inner-sphere complexation of ferricyanides. CN release rates in phase I and II were mainly influenced by the pH, organic matter (OM) and the total CN content. The cyanide release rates increased with increasing pH, decreased with low initial CN concentration and were retarded by the increase in OM content.

Interlaboratory Study of Free Cyanide Methods Compared to Total Cyanide Measurements and the Effect of Preservation with Sodium Hydroxide for Secondary‐ and Tertiary‐Treated Waste Water Samples

Several methods exist for the measurement of cyanide levels in treated wastewater,typically requiring preservation of the sample with sodium hydroxide to minimize loss of hydrogen cyanide gas (HCN). Recent reports have shown that cyanide levels may increase with chlorination or preservation. In this study, three flow injection analysis methods involving colorimetric and amperometric detection were compared within one laboratory, as well as across separate laboratories and equipment. Split wastewater samples from eight facilities and three different sampling periods were tested. An interlaboratory confidence interval of 3.5 ppb was calculated compared with the intralaboratory reporting limit of 2 ppb. The results show that free cyanide measurements are not statistically different than total cyanide levels. An artificial increase in cyanide level is observed with all methods for preserved samples relative to nonpreserved samples, with an average increase of 2.3 ppb. The possible loss of cyanide without preservation is shown to be statistically insignificant if properly stored up to 48 hours. The cyanide increase with preservation is further substantiated with the method of standard additions and is not a matrix interference. The increase appears to be correlated with the amount of cyanide observed without preservation, which appears to be greater in those facilities that disinfect their wastewater with chlorine, followed by dechlorination with sodium bisulfite.

Hydrogen Cyanide Accumulation and Transformations in Non-polluted Salt Marsh Sediments

While cyanide is known to be produced by many organisms, including plants, bacteria, algae, fungi and some animals, it is generally thought that high levels of cyanide in aquatic systems require anthropogenic sources. Here, we report accumulation of relatively high levels of cyanide in non-polluted salt marsh sediments (up to 230 μmol kg−1). Concentrations of free cyanide up to 1.92 μmol L−1, which are toxic to aquatic life, were detected in the pore-waters. Concentration of total (free and complexed) cyanide in the pore-waters was up to 6.94 μmol L−1. Free cyanide, which is released to the marsh sediments, is attributed to processes associated with decomposition of cord grass, Spartina alterniflora, roots and possibly from other sources. This cyanide is rapidly complexed with iron and adsorbed on sedimentary organic matter. The ultimate cyanide sink is, however, associated with formation of thiocyanate by reaction with products of sulfide oxidation by Fe(III) minerals, especially polysulfides. The formation of thiocyanate by this pathway detoxifies two poisonous compounds, polysulfides and hydrogen cyanide, preventing release of free hydrogen cyanide from salt marsh sediments into overlying water or air.

Spatial determinants of hazardous chemicals in surface water of Qiantang River, China

Spatial regression, incorporating spatial error or lag dependency, was performed to interpret determinants of hazardous chemicals at full sub-basin scale and at 500m riparian buffer scale in Qiantang River, eastern coastal China. Monitoring data from 41 monitoring stations were collected between 1996 and 2003 and pretreated for 7 variables—petroleum, hexavalent chromium, total cadmium, total lead, total mercury, total cyanide, and volatile phenol. Results showed that primary predictors and the predictive ability of spatial regression differed with variables and scales. Topology, distance to river source, land use/land cover (LULC), population density, and gross domestic product (GDP) can be primary predictors for the pattern of certain hazardous chemical variables in 1996 and 2003. LULC types were good predictors for changes of cyanide and heavy metals, while GDP and population density contributed to petroleum dynamics between 1996 and 2003. This study demonstrated that spatial regression is a promising tool for generating indicators to tackle with hazardous chemical pollution. We also advocate applying multi-scale approaches to uncover the dynamics of hazardous chemicals.

Pilot test operation of biological nitrogen removal of gold mill effluents

Effluents from gold mills are a potential environmental hazard, unless toxic substances such as nitrogen compounds (sodium cyanide, thiocyanate and ammonia) and heavy metals are removed. In northern Sweden, there are gold mines that are either already in operation, or to be opened, among them is the proposed Lappland Goldminers AB gold mill facility. The environmental permit for this new activity requires stringent removal levels of nitrogen. It was decided to operate a pilot plant to study the biological nitrogen removal performance. It has been based on a continuous activated sludge plant suited for biological nutrient removal. The plant has been operated at a neighbouring gold mill plant with an identical gold extraction process. The pilot study focused primarily on nitrification; however, also the denitrification performance and cyanide removal were monitored. The test results have been encouraging, showing up to a 100% nitrification capacity. The specific nitrification rate has been in the range (0.5) of 1.1–2.6g Nox/kg VSS/h, at temperatures ranging from 7.6 to 20°C. Different unintended process disturbances have been allowed for conclusions on the process stability and recovery potential. Low levels of total cyanide were recorded in the inlet, but virtually no traces were found in the treated water.