Remediation of arsenic-contaminated soils and washing effluents

Laboratory experiments were conducted to determine the distribution of various arsenic species in tailings and soils. Other specific goal of the tests were to evaluate the extraction efficiency of arsenic using alkaline or acid washing, to determine optimum operational parameters of alkaline washing, and to evaluate the arsenic precipitation of washing effluents by pH adjustment or ferric chloride addition. Alkaline washing using sodium hydroxide was found to be favorable in removing arsenic from tailings or soils having a higher portion of arsenic in the operationally defined crystalline mineral fraction of crystalline oxide and amorphous aluminosilicates. This is due to the ligand displacement reaction of hydroxyl ions with arsenic species and high pH conditions that can prevent readsorption of arsenic because predominant negatively charged crystalline oxides do not attract the negatively charged oxyanions. For tailings, sodium hydroxide had 10-20 times higher extraction efficiencies than hydrochloric- or citric acid. The optimum concentration of sodium hydroxide for soil washing was determined to be 200 mM for all samples, while the optimum ratios were 10:1 and 5:1 for tailings and field/river sedimentary soils, respectively. The washing effluent of river soil was effectively treated by adjusting pH to 5-6 with hydrochloric acid, resulting in arsenic concentrations of <50 microgl(-1). In the case of field soil effluent, an addition of ferric chloride with a minimum mass ratio of 11 (Fe/As) was needed to reduce the arsenic below 50 microgl(-1).     

Ecotoxicological and chemical evaluation of phenolic compounds in industrial effluents

The aim of this paper was to evaluate the ecotoxicological response of industrial effluents containing phenolic compounds. All complex effluents collected from a chemical plant and then after both a chemical–physical and biological treatment were characterised with chemical analysis, biodegradability tests and four ecotoxicological tests (Daphnia magna, Artemia salina, Brachionus plicatilis and Vibrio fisheri with Microtox^®). The evaluation of the chemical and ecotoxicological data was useful for predicting the effect of the raw effluent on the treatment plant and the impact of the final treated effluent on the receiving water. Besides the toxicity of the effluent from the chemical plants, the acute toxicity of its main components was also determined. The results of the tests and toxicity data from literature were transformed in Toxic Units (TUs). Effluent toxicity was under- or over-estimated by calculating the sum of the TUs of the individual components, depending on which toxicity data and test organisms were used.     

Phytotoxicity tests of solid wastes and contaminated soils in the Czech Republic

Background, aim, and scope  

The purpose of this study was to compare the suitability of different phytotoxicity testing procedures for the evaluation of toxicity associated with both soil contamination and solid wastes, both of which can be of environmental risk to plants. Ten different representative types of contaminated soils and solid waste samples were chosen from the Czech Republic.     

Observations and assessment relating to incineration of chlorinated chemical wastes

Tests have been carried out on the chemical waste incinerator operated by Re-Chem International at Bonnybridge, Scotland, to determine whether any emissions of polychlorodibenzo-p-dioxins (PCDD) or polychlorodibenzofurans (PODF) occurred during incineration under typical conditions of certain organo-chlorine feedstocks. No detectable emissions of PCDDs or PCDFs were found during the incineration of 2,4,5-I esters, pentachlorophenol residues or PCB in liquid form. A just measurable amount of 2,3,7,8 TCDF was detected during the incineration of large intact capacitors and prior shredding, or puncturing, is preferred. The measured levels of PCDDs and PCDFs in soils collected in the vicinity of the Bonnybridge plant were found to be comparable to or less than those reported in urban or rural environments elsewhere. The reported detection of these compounds in a soil sample collected in 1877 suggests that they may be ubiquitous. It is demonstrated that cows grazing close to the Bonnybridge incinerator are unlikely to have suffered ill-effects from these emissions.     

Identification of chemical substances in industrial wastes and their pyrolytic decomposition products

In order to quantify the sources of chemical pollutants in the leachate from reclaimed wastes, chemical substances in 11 different types of industrial wastes were identified. Their elution behaviors were also investigated. Alkanes (5.3-890 ng g(-1)), benzenes (8.1-110 ng g(-1)), polyaromatic hydrocarbons (PAHs) (3.2-560 ng g(-1)), alcohols, steroids, phenol (7.1 ng g(-1)), ketones, furans (190-210 ng g(-1)), phthalates (8.9-560 ng g(-1)), benzoquinones, dibenzothiophene (190 ng g(-1)), benthiocarb (4.2 ng g(-1)), sulfur, nitrile compounds, amino compounds, amido compounds, pyridines, quinolines (1.8-15 ng g(-1)), isoquinolines, carbazoles, acridines, chlordenes (1.5-1.6 ng g(-1)) and nonachlors (1.1-1.6 ng g(-1)) were detected in 9 types of industrial wastes. The chemical substances detected in waste at the highest concentrations were alkanes, PAHs and phthalates. Water supply sludge, dust and brick garbage contained many kinds of chemical substances. The elution behaviors of specific chemical substances, COD and nutrients varied by characteristic and production process of each waste. Over 100 different compounds were detected in pyrolysis products including carbohydrate, carotynoid, amino acids, proteins, humic acids, lignin and combustion products.     

Degradation of isoxaben in soils and an aqueous system.

The degradation of isoxaben [N-[3-(1-ethyl-1-methylpropyl)-5-isoxazolyl]-2,6-dimethoxybenzamide] was studied in soil and in an aqueous system. Soil studies were conducted in Erlenmeyer flasks (treated with 1 microg/g isoxaben) and mineralization studies in Biometer flasks (treated with 1 microg/g unlabeled and 14C-isoxaben) incubated at 23 C. Degradation in the aqueous system was performed in Erlenmeyer flasks under aerobic and anaerobic conditions incubated at 23 degrees C. Incubation mixtures were extracted at selected times and analyzed for isoxaben and degradation products by HPLC with product identification confirmed by GC-MS. After 8 weeks, 78% and 23% of the total isoxaben disappeared in nonsterile and sterile soils, respectively. After 12 weeks, approximately 1% of the labeled isoxaben was recovered as CO2 in the Biometer flask experiments; no volatile products were detected, and 5% and 33% of the total radioactivity was recovered from the nonsterile and sterile soils, respectively. In the aquatic system after 8 weeks, isoxaben had decreased from 1microg/g to 0.1 and 0.004 microg/g under aerobic and anaerobic conditions, respectively. Degradation products detected from the soil studies were 3-nitrophthalic acid and 4-methoxyphenol, and 3-nitrophthalic acid in the aqueous system studies. Microbial activity was considered to be a major factor in the degradation of isoxaben in this study.     

Combined chemical treatment of pharmaceutical effluents from medical ointment production

Three wastewater samples from a pharmaceutical plant formulating medical ointments were subjected to lab-scale treatment by a Fenton-like system in combination with lime coagulation. All samples were plant pre-treated by adsorption/flocculation/filtration processes with utilization of bentonite, but the quality of effluents did not comply with the regulations for wastewater discharged to local sewerage. The optimization of Fenton-like oxidation demonstrated the highest process efficacy at H(2)O(2)/COD weight ratio of 2:1, H(2)O(2)/Fe(2+) molar ratio of 10:1 and 2h of treatment time. The fast pH decrease to acidic values approximately 3 during first min of oxidation for all effluents suggested that pH adjustment was unnecessary. Combination of Fe(III) precipitation and lime coagulation proved feasible to improve considerably COD and residual iron concentration reduction in pharmaceutical effluents. Additionally, considerable BOD(7) reduction and BOD(7)/COD ratio improvement of pharmaceutical wastewater samples was achieved by combined treatment. The application of Fenton-like oxidation with subsequent iron (III)/lime coagulation did not only enhance the quality of pharmaceutical effluents with different chemical characteristics and help to meet the requirements for wastewater discharged to sewage, but also improve the biodegradability of pharmaceutical effluents.     

Studies on water hyacinth as a biological filtre for treating contaminants from agricultural wastes and industrial effluents

The aquatic weed--water hyacinth [Eichhornia crassipes (Mart) Solms] showed a remarkable capacity to withstand the effects of pH changes ranging from 5 to 8 in the aquatic environment. Growth continued to be normal except when placed for longer periods in medium containing iron ions at pH 3.3. The ability of this plant to neutralize some very acid solutions of heavy metals such as salts of copper, cadmium and zinc individually and in combinations, is being reported. Plants placed in pure acid and alkali solutions were also able to neutralize the medium. Calcium appears to play an important role in the mechanism involved in the adaptability of these plants to such environments.     

Examining farmland applications of composted biosolid wastes depending on nutrient balance in soils

This study emphasizes nutrient balance of soils in the farmland application of composted biosolid wastes. The loading rates of plant nutrients following the compost application to farmland in Japan were estimated and compared with the nutrient uptake of agricultural plants. Results show that the current compost application in Japan can meet the requirements of agricultural plants for plant nutrient Ca, except for K, Mg, P, Fe, Mn, Cu, and Zn. The compost application could realize the safe disposal of biosolid wastes and the effective recycling of plant nutrients in composts to soils without causing heavy metal accumulation. The application manner of composts affects the heavy metal accumulation in farmlands. Field examination indicates that the excessive compost application has led to the heavy metal accumulation in compost-amended farmlands. Measuring the nutrient balance in compost-amended farmlands is well suitable for explaining the accumulation of heavy metals, such as Cu and Zn.     

Biological and chemical assessments of zinc ageing in field soils

As zinc (Zn) is both an essential trace element and potential toxicant, the effects of Zn fixation in soil are of practical significance. Soil samples from four field sites amended with ZnSO₄ were used to investigate ageing of soluble Zn under field conditions over a 2-year period. Lability of Zn measured using ⁶⁵Zn radioisotope dilution showed a significant decrease over time and hence evidence of Zn fixation in three of the four soils. However, 0.01 M CaCl₂ extractions and toxicity measurements using a genetically modified lux-marked bacterial biosensor did not indicate a decrease in soluble/bioavailable Zn over time. This was attributed to the strong regulatory effect of abiotic properties such as pH on these latter measurements. These results also showed that Zn ageing occurred immediately after Zn spiking, emphasising the need to incubate freshly spiked soils before ecotoxicity assessments.     

Solanum nigrum L. weed plants as a remediation tool for metalaxyl-polluted effluents and soils

In this work, the phytoremediation potential of metalaxyl, a commonly used persistent, mobile and leachy fungicide, by Solanum nigrum L. plants was studied. The study revealed that this plant species can be used as an excellent metalaxyl phytoremediation tool, thus providing a cost effective and environmentally friendly clean technology for the decontamination of sites and effluents. As it can be sowed directly in the remediation site, is able to complete its life cycle without suffering major stress. Because it accumulates high amounts of the fungicide in the aboveground tissues, enables its concentration and proper disposal by cutting off the corresponding plant part. The study also suggests that the tolerance to metalaxyl is due to a suitable antioxidant response comprising proline accumulation and guaiacol peroxidase and glutathione-S-transferase enhanced activities, that reduce oxidative damage to the plant organs.     

基于PEG/DEX双水相体系的餐厨垃圾乳酸发酵

利用聚乙二醇(PEG)/葡聚糖(DEX)双水相体系分离餐厨垃圾发酵产物乳酸,分析了聚合物浓度和分子量的影响,以及餐厨垃圾多批次连续发酵时乳酸产率。实验结果表明,PEG/DEX双水相体系对乳酸菌生长影响不大,PEG和DEX浓度变化对乳酸产率、相体积比无显著影响;当DEX分子量由20 000升至40 000,乳酸生成速率由0.631 g/(L.h)降至0.518 g/(L.h),乳酸浓度由33 g/L降至22 g/L。多批次餐厨垃圾连续发酵可极大缩短发酵时间,在不投加缓冲剂的情况下,单批次乳酸产率仍大于0.30 g/g,累积产率大于0.45 g/g。     

Treatment of organic aqueous wastes: Wet air oxidation and Wet Peroxide Oxidation

There is growing concern about the problems of waste elimination. We should consider our environment as being borrowed from future generations and refrain from leaving a legacy of problems we are not able to solve. Various oxidation techniques are suited for the elimination of organic aqueous wastes, but because of the environmental drawbacks of incineration, enclosed processes, like liquid phase oxidation should be preferred. Wet air oxidation (WAO) under high temperature (200-325 degrees C) and pressure (50-150 bar) is suited to such liquid wastes and various catalysts, including hydrogen peroxide, can be used in order to increase the efficiency without increasing temperature and pressure. Wet Peroxide Oxidation (WPO) is a similar process. A comparable oxidation efficiency is obtained when using hydrogen peroxide as the oxidising agent instead of oxygen, at a temperature of only 100-120 degrees C. As opposed to WAO, which is capital intensive, WPO needs limited capital but generates higher running costs. The paper reviews the major results obtained for both processes and assesses the field of possible application of each of them. TOC removal efficiencies typically obtained range from 65 to 90% or more for most of the pollutants.     

Release of trace metals, sulfate and complexed cyanide from soils contaminated with gas-purifier wastes: a microcosm study

Deposited gas-purifier wastes are commonly contaminated with trace metals, sulfate and cyanide (CN) compounds. We investigated their release from three soils contaminated with gas-purifier wastes into solution in microcosm experiments under varying redox conditions (E(H) 170-620 mV). The soils differed in pH (2.2; 4.9; 7.4) and featured low amounts of trace metals, but large amounts of total S and total CN. The pH governed trace metal release in the case of the acidic soil and CN release in the case of the slightly alkaline soil. The redox potential controlled trace metal and CN release in the case of the moderately acidic soil. Sources of dissolved SO(4)(2-) were dissolution of gypsum, desorption from Fe oxides and probably oxidation of elemental S. The geochemical behaviors of trace metals (soluble under acidic and reducing conditions) and CN (soluble under alkaline and oxidizing conditions) were diametrically opposed.     

Response of kidney bean to concentration and chemical form of cadmium, zinc, and lead in polluted soils

Seven soils which had been polluted with heavy metals from a zinc smelter were sequentially extracted so that Cd, Zn, and Pb could be partitioned into five operationally defined geochemical fractions: exchangeable, carbonate, Fe-Mn oxide, organic, and residual fractions. Kidney beans were planted in the soils to examine the effect of concentration and chemical form of the metals in soil on the growth and metal uptake of the plants. The growth of kidney bean was restricted in heavy metal polluted soils compared with controls. Metal concentration and metal uptake by plants were correlated. The highest relationship was found between amount of metal uptake and the metal concentration in exchangeable + carbonate forms. The uptake of metals was according to their solubility sequence, i.e. Cd > Zn > Pb. The uptake rate of exchangeable + carbonate forms was the same for the three elements.     

Solid wastes from the enzyme production as a potential biosorbent to treat colored effluents containing crystal violet dye

Environmental Science and Pollution Research - Sugarcane bagasse, a largely available waste worldwide, was submitted to solid-state fermentation (SSF) using the fungus Metarhizium anisopliae,...