Phosphate removal from wastewater using red mud

Red mud, a waste residue of alumina refinery, has been used to develop effective adsorbents to remove phosphate from aqueous solution. Acid and acid-thermal treatments were employed to treat the raw red mud. The effects of different treatment methods, pH of solution and operating temperature on adsorption have been examined in batch experiments. It was found that all activated red mud samples show higher surface area and total pore volume as well as higher adsorption capacity for phosphate removal. The red mud with HCl treatment shows the highest adsorption capacity among all the red mud samples, giving adsorption capacity of 0.58 mg P/g at pH 5.5 and 40 degrees C. The adsorption capacity of the red mud adsorbents decreases with increase of pH. At pH 2, the red mud with HCl treatment exhibits adsorption of 0.8 mg P/g while the adsorption can be lowered to 0.05 mg P/g at pH 10. However, the adsorption is improved at higher temperature by increasing 25% from 30 to 40 degrees C. The kinetic studies of phosphate adsorption onto red mud indicate that the adsorption mainly follows the parallel first-order kinetics due to the presence of two acidic phosphorus species, H(2)PO(4)(-) and HPO(4)(2-). An analysis of the adsorption data indicates that the Freundlich isotherm provides a better fitting than the Langmuir model.     

Phosphate removal from water using lithium intercalated gibbsite

In this study, lithium intercalated gibbsite (LIG) was investigated for its effectiveness at removing phosphate from water and the mechanisms involved. LIG was prepared through intercalating LiCl into gibbsite giving a structure of [LiAl2(OH)6]+ layers with interlayer Cl- and water. The results of batch adsorption experiments showed that the adsorption isotherms at various pHs exhibited an L-shape and could be fitted well using the Langmuir model. The Langmuir adsorption maximum was determined to be 3.0 mmol g(-1) at pH 4.5 and decreased with increasing pH. The adsorption of phosphate was mainly through the displacement of the interlayer Cl- ions in LIG. In conjunction with the anion exchange reaction, the formation of surface complexes or precipitates could also readily occur at lower pH. The adsorption decreased with increasing pH due to decreased H(2)PO(4)(-)/HPO4(2-) molar ratio in solution and positive charges on the edge faces of LIG. Anion exchange is a fast reaction and can be completed within minutes; on the contrary, surface complexation is a slow process and requires days to reach equilibrium. At lower pH, the amount of adsorbed phosphate decreased significantly as the ionic strength was increased from 0.01 to 0.1M. The adsorption at higher pH showed high selectivity toward divalent HPO4(2-) ions with an increase in ionic strength having no considerable effect on the phosphate adsorption. These results suggest that LIG may be an effective scavenger for removal of phosphate from water.     

Phosphate removal from solution using steel slag through magnetic separation

Steel slag with magnetic separation was used to remove phosphate from aqueous solutions. The influence of adsorbent dose, pH, and temperature on phosphate removal was investigated in a series of batch experiments. Phosphate removal increased with the increasing temperature, adsorbent dose and decreased with increasing initial phosphate concentrations, while it was at its peak at pH of 5.5. The phosphate removal predominantly occurred through ion exchange. The specific surface area of the steel slag was 2.09m2/g. The adsorption of phosphate followed both Langmuir and Freundlich isotherms. The maximum adsorption capacity of the steel slag was 5.3mgP/g. The removal rates of total phosphorus (TP) and dissolved phosphorus (DP) from secondary effluents were 62-79% and 71-82%, respectively. Due to their low cost and high capability, it was concluded that the steel slag may be an efficient adsorbent to remove phosphate both from solution and wastewater.     

Electrodialytic removal of cadmium from wastewater sludge

This paper presents for the first time laboratory results demonstrating electrodialytic removal of Cd from wastewater sludge, which is a method originally developed for soil remediation. During the remediation a stirred suspension of wastewater sludge was exposed to an electric dc field. The liquid/solid (ml/g fresh sludge) ratio was between 1.4 and 2. Three experiments were performed where the sludge was suspended in distilled water, citric acid or HNO3. The experimental conditions were otherwise identical. The Cd removal in the three experiments was 69, 70 and 67%, respectively, thus the removal was approximately the same. Chemical extraction experiments with acidic solutions showed that 5-10 times more Cd could be extracted from decomposed sludge than from fresh sludge. It is likely that the mobilization of Cd during decomposition of the sludge contributes to the efficient removal of Cd by the electrodialytic method. Extraction experiments and electrodialytic remediation using distilled water as enhancement agent showed that 0.3% Cd could be extracted from decomposed sludge during 1 week in closed flasks, whereas 69% was removed during 2 weeks of electrodialytic remediation in a stirred solution in contact with atmospheric air. A combination of aerobic decomposition and electrodialytic treatment could be a promising method for Cd removal from wastewater sludge, and thus Cd could be removed without the addition of chemicals to the sludge.     

Phosphate removal from aqueous solutions using raw and activated red mud and fly ash

The effect of acidification and heat treatment of raw red mud (RM) and fly ash (FA) on the sorption of phosphate was studied in parallel experiments. The result shows that a higher efficiency of phosphate removal was acquired by the activated samples than by the raw ones. The sample prepared by using the RM stirred with 0.25 M HCl for 2h (RM0.25), as well as another sample prepared by heating the RM at 700 degrees C for 2h (RM700), registered the maximum removal of phosphate (99% removal of phosphate). This occurred when they were used in the phosphate sorption studies conducted at pH 7.0 and 25 degrees C with the initial PO(4)(3-) concentration of 155 mg P/l. The FA samples treated in the same way described above can achieve 7.0 and 8.2 mg P/l phosphate removal for FA0.25 and FA700 respectively, corresponding to 45.2% and 52.9% removal. The activated materials performed higher phosphate removal over broader pH range compared with the raw ones. The influences of various factors, such as initial pH and initial phosphate concentration on the sorption capacity were also studied in batch equilibration technique. Solution pH significantly influenced the sorption. Each sample achieved the maximal removal of phosphate at pH 7.0. The amount of phosphate removal increased with the solute concentration. The Freundlich and Langmuir models were used to simulate the sorption equilibrium. The results indicate that the Langmuir model has a better correlation with the experimental data than the Freundlich model.     

转炉污泥吸附性能研究

Converter sludge, a byproduct produced on large amounts in the steel making process, is an important resource that can be utilized effectively. This paper describes an experiment in which converter sludge was tested as an adsorbent for the removal of phosphorus from waste water. It was found that the phosphorus removal depended on the amount of converter sludge added, the pH value and the contact time. Under laboratory conditions when the added sludge was 2. 0mg/100ml, the contact time 4h and the pH value of equalized 4, over 88% of phosphorus was removed; the experimental data on converter sludge adsorption of phosphorus in the water fitted the Freundlich isotherm model. Converter sludge was found to be very effective in adsorbing the phosphorus.     

Evaluation of electrokinetic removal of heavy metals from sewage sludge

The presence of heavy metals is one of the main obstacles for agricultural use of million tonnes of dewatered sewage sludge produced in wastewater treatment plants. Electrokinetic (EK) treatment can be applied to remove heavy metals from sludge. The aim of this study was to increase the efficiency of electrokinetic removal of heavy metals from dewatered sewage sludge. EK experiments were carried out with and without pH adjustment in cathode chamber of acidified sewage sludge. The selective sequential extraction (SSE) was used to determine the fractionation of heavy metals in sewage sludge. The mobility of heavy metals in sludge significantly increased after its acidification at pH 2.7 and followed the order: Ni, Zn, Cu, As, Cr, Pb. Removal efficiencies of heavy metals in the experiment with acidified sewage sludge and pH adjustment at cathode chamber at 2.0 were: 95% for Zn, 96% for Cu, 90% for Ni, 68% for Cr, 31% for As and 19% for Pb. The concentrations of Zn, Cu, Ni, Cr and Pb after EK treatment were below the United States Environmental Protection Agency limits for biosolids applied to agricultural land, forest, public contact sites or reclamation sites.     

Techno-economic evaluation of PHB production from activated sludge

Activated sludge biomass enriched under suitable conditions is a promising source for poly-3-hydroxybutyrate (PHB) production, a biodegradable polymer. The techno-economic evaluation of PHB production using activated sludge biomass has been carried out. The PHB yield and plant capacity was found to significantly affect the PHB production cost. The PHB production cost for a plant processing (fermentation) capacity of 100 m³/day and 44% PHB yield is about US$ 11.8/kg, which reduces to US$ 5.38/kg for 1,000 m³/day plant capacity and 70% PHB yield. The cost of the carbon substrate was found to significantly affect the overall economics of PHB production.     

Phosphate removal from water by fly ash: factorial experimental design

The influence of three variables (phophate concentration, initial pH of solution (pH(0)) and the fly ash dosage) on the removal efficiency of phosphate (% E) and equilibrium pH of solution (pH(eq)) by using fly ash was studied by means of 2(3) full factorial experimental designs. The parameters coded as x(1), x(2) and x(3), consecutively(,) were used. The parameters were investigated at two levels (-1 and 1). The effects of these factors on dependent variables, namely, % E and pH(eq) were investigated. To determine the significance of effects, the analysis of variance with 95% confidence limits was used. It was shown that % E and pH(eq) obtained in this study were found to be 99.6% and 11.16, corresponding to the operating condition of 25 mg l(-1), 2 g l(-1) and 5.5 for the phosphate concentration, fly ash dosage and pH(0), respectively.     

污水厂脱水污泥制吸附剂及脱除H2S效能研究

采用热解炭化法制备了一系列污泥吸附剂,优化制备工艺,利用扫描电镜(SEM)、比表面积和孔径分析等技术对污泥吸附剂的结构进行了表征,并研究了脱除H2S效能。结果表明,活化温度、活化时间和固液比等因素均对污泥吸附剂的碘吸附值产生影响。当活化温度为550℃、活化时间为2.0h、固液比为1∶2时所制备材料(SA)的碘吸附值最高,为493.12mg/g;制备的SA具有较好的脱除H2S效能,能满足精脱硫的要求,当空速为4600h-1时,SA的除臭时间可达48min;此外SA中含有的多种金属元素,平均孔径为3.4nm,这些性质均有利于H2S的吸附脱除。     

Models for organics removal from vinasse from ethanol production

Global ethanol production generates almost 100 billion liters per year of a high-strength liquid waste called vinasse. One sustainable method of treating vinasse using environmental biotechnology is anaerobic digestion, which generates biogas that can be used as a renewable energy resource. Although a number of models have been developed for predicting biogas generation rates, no previous study has modeled liquid organic removal rates for vinasse treatment. The goal of this research was thus to develop models for predicting liquid-phase organic removal rates for anaerobic treatment of vinasse. 6-L laboratory-scale batch reactors were filled with vinasse of six different compositions and operated at three different mesophilic temperatures (30, 35, 40 °C). Biochemical and chemical oxygen demand (BOD and COD) were measured over time using Standard Methods 5210B and 5220C. Based on data collected, multiple linear regression equations (R² = 0.79 and 0.94) were developed to predict first-order rate constants k_BOD and k_COD as functions of temperature and vinasse composition (initial values of nitrogen, potassium, phosphorous, and sulfur). The first-order models developed require a small number of readily available input parameters. They apply to treatment of vinasse from ethanol produced from corn and milo; future work can test their applicability to ethanol produced from other feedstocks. The models can be used for sizing/design of reactors for anaerobic treatment of vinasse.     

Parameters affecting oleochemical production from waste bleaching earth via alcoholysis

The edible oil industry is one of the largest industries in the world. In the edible oil refining process, large amounts of waste are discarded every day. Evaluation of these wastes is vital for environmental issues. Most of this waste is due to the bleaching process in which bleaching earths are largely used. Due to its high adsorption capacity, bleaching earth adsorbs oil nearly 40% of its weight. In order to evaluate this waste for oleochemical production, alcoholysis reactions were investigated. Parameters affecting the reaction, such as catalyst type and amount, alcohol type, alcohol:oil molar ratio and temperature, were investigated. The reactions were conducted in the presence of different catalysts such as NaOH, NaOCH₃ and homogeneous alkali polymeric gel catalyst (HAPJEK) and performed at a temperature range of 60–78°C and in the presence of a catalyst (1–2% based on oil weight) at alcohol:oil molar ratios of 5:1–7:1. Based on optimisation by response surface methodology (RSM), the critical synthesis conditions for 210 min reaction time with a maximum of 85.8% methyl ester content were determined as temperature: 68.4°C, catalyst amount 1.5% based on oil weight and methanol/oil molar ratio: 6.4.     

Biological hydrogen production from sterilized sewage sludge by anaerobic self-fermentation

Due to richness in proteins and carbohydrates, the sewage sludge produced from the wastewater treatment processes is becoming a potential substrate for biological hydrogen production. In this study, sterilized sludge was employed to produce hydrogen by batch anaerobic self-fermentation without any extra-feeds and extra-seeds. Sterilization can screen hydrogen-producing microorganisms from sludge microflora and release organic materials from microbial cells of sludge. Experimental results suggested that sterilization could accelerate and increase the hydrogen production of sewage sludge in the anaerobic self-fermentation, and the biogas did not contain methane. The hydrogen yield was increased from 0.35 mL H₂/g VS (raw sludge) to 16.26 mL H₂/g VS (sterilized sludge). Although sterilization could fully inhibit the activity of methanogens in the sludge, the hydrogen consumption still occurred in the anaerobic self-fermentation of sterilized sludge due to the existence of other hydrogen-consuming actions. The decrease of pH in the anaerobic self-fermentation of sterilized sludge was very lower (from 6.81 to 6.56) because NH₄⁺ produced by degradation of proteins could neutralize organic acids produced in the process. The soluble chemical oxygen demand (SCOD) increase of sterilized sludge was higher than that of raw sludge. Volatile fatty acids (VFA) were the important by-products and acetate was the major composition. The hydrogen fermentation of carbohydrates was the major source of hydrogen production.     

Cyanide removal from cassava mill wastewater using Azotobactor vinelandii TISTR 1094 with mixed microorganisms in activated sludge treatment system

Cassava mill wastewater has a high organic and cyanide content and is an important economic product of traditional and rural low technology agro-industry in many parts of the world. However, the wastewater is toxic and can pose serious threat to the environment and aquatic life in the receiving waters. The ability of Azotobactor vinelandii TISTR 1094, a N₂-fixing bacterium, to grow and remove cyanide in cassava wastewater was evaluated. Results revealed that the cells in the exponential phase reduce the level of cyanide more rapidly than when the cells are at their stationary growth phase. The rate of cyanide removal by A. vinelandii depends on the initial cyanide concentration. As the initial cyanide concentration increased, removal rate increased and cyanide removal of up to 65.3% was achieved. In the subsequent pilot scale trial involving an activated sludge system, the introduction of A. vinelandii into the system resulted in cyanide removals of up to 90%. This represented an improvement of 20% when compared to the activated sludge system which did not incorporate the strain.     

Reduction and removal of Cr(VI) from aqueous solutions using modified byproducts of beer production

Biosorption, as an effective and low-cost technology treating industrial wastewaters containing Cr(VI), has become a significant concern worldwide. In this work, acid-modified byproducts of beer production (BBP) were used to remove Cr(VI) from aqueous solutions. Removal of Cr(VI) increases as the pH is decreased from 4.0 to 1.5, but the maximum of total Cr removal is obtained in a pH range from 2.0 to 2.5. Nearly 60% of the initial Cr(VI) (100 mg L(-1)) was adsorbed or reduced to Cr(III) within the first 10 min at pH 2.0. The Cr(VI) removal capability of acid-modified BBP materials was almost completely retained after regenerating with acid. FT-IR and XPS spectra revealed that carboxylate and carboxyl groups on the surface of modified BBP materials play a major role in Cr(VI) binding and reduction, whereas amide and other groups play a minor role in the Cr(VI) removal process.     

Hydrogen sulfide removal from coal gas by the metal-ferrite sorbents made from the heavy metal wastewater sludge

The metal-ferrite (chromium-ferrite and zinc-ferrite) sorbents made from the heavy metal wastewater sludge have been developed for the hydrogen sulfide removal from coal gas. The high temperature absorption of hydrogen sulfide from coal gas with the metal-ferrite sorbent in a fixed bed reactor was conducted in this study. The metal-ferrite powders were the products of the ferrite process for the heavy metal wastewater treatment. The porosity analysis results show that the number of micropores of the sorbents after sulfidation and regeneration process decreases and the average pore size increases due to the acute endothermic and exothermic reactions during the sulfidation–regeneration process. The FeS, ZnS, and MnS peaks are observed on the sulfided sorbents, and the chromium extraction of the CFR6 can fulfill the emission standard of Taiwan EPA. The suitable sulfidation temperature range for chromium-ferrite sorbent is at 500–600 °C. In addition, effects of various concentrations of H₂ and CO were also conducted in the present work at different temperatures. By increasing the H₂ concentration, the sulfur sorption capacity of the sorbent decreases and an adverse result is observed in the case of increasing CO concentration. This can be explained via water-shift reaction.     

Activated carbons from sewage sludge and discarded tyres: production and optimization

This is a study about making use of two residual materials such as sludges from a sewage treatment plant and discarded tyres to generate activated carbons and later optimize the production process. H2SO4 and ZnCl2 were used as chemical activating agents. Liquid-phase adsorption tests were made using the produced carbons to retain methylene blue and iodine. The best precursor was sludge activated with ZnCl2. After optimization studies, the best production methodology involved a 1:1 ratio of sludge and ZnCl2, a heating rate of 5 degrees C/min up to 650 degrees C and a residence time of 5 min. The resulting materials adsorbed up to 139.4 mg/g of methylene blue and 1358.5 mg/g of iodine. Nevertheless these carbons may leach Zn while using. To avoid this two treatments were carried out: one consisting of a coating with a polymer and another involving an intensive washing, which was seen to be more efficient.     

Ammonium removal by a novel magnetically modified excess sludge

Disposal of nitrogen nutrient and excess sludge is a keen concern in wastewater treatment plants. This study describes a simple method of preparing an economical adsorbent, i.e., magnetic excess sludge (MES) by compounding the excess sludge with Fe₃O₄ nanoparticles. Ammonia–nitrogen removal from simulated wastewater was investigated by using the MES as an adsorbent. The MES had an adsorption efficiency of up to 90% for ammonium removal. Highly efficient separation of adsorbed ammonium on the MES could be magnetically separated from wastewater within 30 s. The operating conditions for ammonium adsorption were optimized at MES dose of 20 g/L, initial ammonium concentration of 45 mg/L and operating temperature of 298–308 K. The equilibrium data of ammonium adsorption on the MES showed a good agreement with the Langmuir isotherm, while the kinetic data were best fitted by the pseudo-second-order model. FTIR analysis indicated that various functional groups, such as hydroxyl and carboxyl groups, existed on the surface of the MES and contributed to the excellent capability for ammonium adsorption. These results suggest that the MES is a promising candidate for removing ammonium from wastewater and recycling excess sludge to ease its disposal at low cost.     

Enhancing the dewaterability of anaerobically digested sludge using fibrous materials recovered from primary sludge: demonstration from a field study

Clean Technologies and Environmental Policy - Sludge dewatering is an important process for determining the operation cost of sludge disposal. Hence, improving the dewaterability of anaerobically...     

Noise removal from image data using recursive neurofuzzy filters

Neurofuzzy approaches are very promising for nonlinear filtering of noisy images. An original network topology is presented in this work to cope with different noise distributions and mixed noise as well. The multiple-output structure is based on recursive processing. It is able to adapt the filtering action to different kinds of corrupting noise. Fuzzy reasoning embedded into the network structure aims at reducing errors when fine details are processed. Genetic learning yields the appropriate set of network parameters from a collection of training data. Experimental results show that the proposed neurofuzzy technique is very effective and performs significantly better than well-known conventional methods in the literature