Influence of clinoptilolite rock on chemical speciation of selected heavy metals in sewage sludge

Modified bentonite as a conditioning agent for stabilising heavy metals and retaining nutrients in sewage sludge for agricultural uses

The management and disposal of excess sludge are emerging issues owing to the high costs associated with treatment. In this study, the viability of a modified bentonite was investigated as a conditioning agent for the stabilisation of heavy metals (i.e., Cu, Zn, Cr, Pb, and Cd) and the retention of nutrient species (i.e., total nitrogen (TN), total phosphorus (TP), available nitrogen (available N), and Olsen-phosphorus (Olsen-P)) in sewage sludge for agricultural use. Five grams of modified bentonite resulted in the highest stabilisation rate of heavy metals and strongly contributed to the stabilisation of heavy metals. However, increased amounts of modified bentonite might increase the TN, available N, and TP losses in the conditioned sewage sludge. Through the analytic hierarchy process modelling, optimal concentrations of nutrient species and heavy metals remaining in the conditioned sewage sludge were achieved when the ratio of bentonite to sewage sludge was 1:12.5 (4 g bentonite : 50 g sludge). Moreover, the optimal mixing ratio of the conditioned sewage sludge to the soil (1:2) was suggested for agricultural use. Based on these observations, modified bentonite allowed the sewage sludge to be used as a fertiliser in agriculture by stabilising heavy metals and retaining nutrient species.

Pretreatment with Ochrobactrum immobilizes chromium and copper during sludge pyrolysis

To increase the degree of immobilization of heavy metals subjected to sludge pyrolysis, we investigated the effects of pretreating sludge with Ochrobactrum supplementation on the immobilization of chromium (Cr) and copper (Cu) during sludge pyrolysis. The sequential extraction procedure was used to test the metallic forms of Cr and Cu. The immobilization of Cr and Cu was characterized with X-ray diffraction, scanning electron microscopy, Fourier transform infrared spectroscopy, etc. Results show that: 1) the addition of Ochrobactrum (1-8%) can accelerate the mineralization process in blank sludge and can accelerate the conversion of the oxidizable forms of Cr and Cu into the residual forms subjected to pyrolysis; 2) pretreatment with Ochrobactrum supplementation can inhibit the volatilization of Cr and Cu during sludge pyrolysis, particularly in the case of a high concentration of Cu. Notably, the pretreatment with Ochrobactrum can reduce 20.38-85.09% of the potential ecological risk of Cr and Cu. The pretreatment with Ochrobactrum contributes to the immobilization of Cr and Cu subjected to sludge pyrolysis and thus can prevent pollution of the environment. The results of this study can be used for harmless disposal of municipal sludge.

Use of clay minerals for sewage sludge stabilization and a preliminary assessment of the treated sludge's fertilization capacity

Preserving sewage sludge's N is important for its agronomic use and this could possibly be achieved by treating sludge with certain clay minerals. Nine clay minerals and additionally Ca(OH)₂ were added to dewatered sewage sludge at 0-30 % rates (wet weight basis) (treatments). After 70 days of equilibration, all mixtures were analyzed for certain properties and the mineral-sludge mixtures which showed the highest microbial load reduction were further assayed, along with the limed and untreated sludge. From all minerals' treatments, the fecal indicators of sludge treated with 30% of two bentonites, attapulgite, saponite-attapulgite, and zeolite decreased considerably compared to the control. These treatments were performed also well regarding sludge's retention capacity of available inorganic N, with the attapulgite and zeolite treatments containing the significantly highest amounts of NO₃-N and NH₄-N, respectively. For the water-soluble inorganic N, similar results were obtained for the zeolite treatment, whereas the treatments with the two bentonites had the significantly highest NO₃-N content. Also, considerable amounts of water-soluble P were obtained in all cases of the treated sludge with minerals. Limed sludge had the lowest content of the water-soluble inorganic N and P. As far as the micronutrients are concerned, only Zn and B were detectable in the water-soluble fraction of all five minerals' treatments. The heavy metals, which regulate sludge's agronomic use, were far below the respective permissible limits and lower than the untreated sludge, except for Ni and Cr in the attapulgite and saponite-attapulgite treatments. In conclusion, certain clay minerals, i.e., bentonite, attapulgite, mixed clay of saponite and attapulgite, and zeolite, seem promising materials for the stabilization of sewage sludge in the perspective of using them as a fertilizer. In addition, they seem to have higher fertilizing value than limed sludge. However, environmental (in respect of Ni and Cr) and agricultural (in respect of Zn and B) impacts must be considered.

A Review of Heavy Metal Contamination of Food Crops in Nigeria

Heavy metal contamination of food crops is an issue of global concern that ultimately results in toxicity and diseases in humans and animals through consumption of contaminated soils and food crops. With a population of 182 million people, Nigeria is regarded as the most populous country in Africa. The people suffer environmental pollution from high levels of heavy metal accumulation in the environment and in food crops. Heavy metals have atomic densities higher than 4 g/cm3, and these include lead (Pb), cadmium (Cd), zinc (Zn), mercury (Hg), arsenic (As), silver (Ag), chromium (Cr), copper (Cu), iron (Fe), and platinum (Pt). The high level of environmental contamination by these metals is dangerous because their uptake by plants and subsequent accumulation in food crops consumed by humans and animals is deleterious to health. There are many known sources of harmful metals, including the earth, which releases them into food, air, and water, and anthropogenic activities, such as the application of fertilizer in agriculture, the use of pesticides and herbicides, and irrigation. Other sources are automobile emissions, paints, cigarette smoking, industries, and sewage and waste disposal. Evidence shows that vegetables and other food crops consumed in Nigeria are contaminated by heavy metals, and this is associated with adverse health issues, such as cancer, which is currently on the rise in Nigeria. It is therefore vital that communities with high levels of heavy metal pollution avoid eating large quantities of these food items. There is also the need for the monitoring of levels of these injurious elements in food crops.

Distribution and risk assessment of heavy metals in sewage sludge after ozonation

In this paper, transformation of chemical forms of heavy metals (Cu, Zn, Ni, Pb, Cr, Cd, Mn, and Mg) in sewage sludge (SS) during ozonation was investigated. Meanwhile, the risk of heavy metals to environment in ozonated sludge (OS) and SS was estimated according to risk assessment code (RAC). The residual rates of heavy metals were over 72.8 %, which demonstrated that the heavy metals in SS were mainly existed in the OS after ozonation. The results indicated that the ozonation had an effect on the redistribution of heavy metals. The comparisons of the RAC between OS and SS indicated that the environmental risk of heavy metals in OS was aggravated compared to SS, except for Mg. Consequently, it was suggested that the OS should be pretreated before application.

Pollution control and metal resource recovery for low grade automobile shredder residue: a mechanism, bioavailability and risk assessment

Automobile shredder residue (ASR) is considered as hazardous waste in Japan and European countries due to presence of heavy metals. This study was carried on the extraction characteristics of heavy metals (Mn, Fe, Ni, and Cr) from automobile shredder residue (ASR). The effects of pH, temperature, particle size, and liquid/solid ratio (L/S) on the extraction of heavy metals were investigated. The recovery rate of Mn, Fe, Ni, and Cr increased with increasing extraction temperature and L/S ratio. The lowest pH 2, the highest L/S ratio, and the smallest particle size showed the highest recovery of heavy metals from ASR. The highest recovery rates were in the following order: Mn > Ni > Cr > Fe. Reduction of mobility factor for the heavy metals was observed in all the size fractions after the recovery. The results of the kinetic analysis for various experimental conditions supported that the reaction rate of the recovery process followed a second order reaction model (R(2) ⩾ 0.95). The high availability of water-soluble fractions of Mn, Fe, Ni, and Cr from the low grade ASR could be potential hazards to the environment. Bioavailability and toxicity risk of heavy metals reduced significantly with pH 2 of distilled water. However, water is a cost-effective extracting agent for the recovery of heavy metals and it could be useful for reducing the toxicity of ASR.

Priority and emerging pollutants in sewage sludge and fate during sludge treatment

This paper aims at characterizing the quality of different treated sludges from Paris conurbation in terms of micropollutants and assessing their fate during different sludge treatment processes (STP). To achieve this, a large panel of priority and emerging pollutants (n=117) have been monitored in different STPs from Parisian wastewater treatment plants including anaerobic digestion, thermal drying, centrifugation and a sludge cake production unit. Considering the quality of treated sludges, comparable micropollutant patterns are found for the different sludges investigated (in mg/kg DM - dry matter). 35 compounds were detected in treated sludges. Some compounds (metals, organotins, alkylphenols, DEHP) are found in every kinds of sludge while pesticides or VOCs are never detected. Sludge cake is the most contaminated sludge, resulting from concentration phenomenon during different treatments. As regards treatments, both centrifugation and thermal drying have broadly no important impact on sludge contamination for metals and organic compounds, even if a slight removal seems to be possible with thermal drying for several compounds by abiotic transfers. Three different behaviors can be highlighted in anaerobic digestion: (i) no removal (metals), (ii) removal following dry matter (DM) elimination (organotins and NP) and iii) removal higher than DM (alkylphenols - except NP - BDE 209 and DEHP). Thus, this process allows a clear removal of biodegradable micropollutants which could be potentially significantly improved by increasing DM removal through operational parameters modifications (retention time, temperature, pre-treatment, etc.).

Modified natural clinoptilolite detoxifies small mammal's organism loaded with lead I. Lead disposition and kinetic model for lead bioaccumulation

Zeolites, especially clinoptilolites, have wide application in removing heavy metals from different solutions and wastewater. The detoxification capacity of the clinoptilolite sorbent KLS-10-MA, a modified natural Bulgarian zeolite, applied as a food supplement in conditions of an ecotoxicological experiment with conventional food and lead was demonstrated for the first time. Laboratory mice, inbred imprinting control region strain, were used in a 90-day ecotoxicological experiment. Animals were divided into four experimental groups. Lead bioaccumulations in exposed and non-supplemented/supplemented with KLS-10-MA animals were compared. As additional control, healthy animals non-exposed to Pb were fed with conventional forage mixed with 12.5% KLS-10-MA. The dietary inclusion of the sorbent reduced Pb concentrations in exposed and supplemented mice by 84%, 89%, 91%, 77%, and 88% in carcass, liver, kidneys, bones, and feces, respectively. A mathematical model was proposed to outline the common trends of bone Pb bioaccumulation in exposed and non-supplemented/supplemented animals. Characteristic parameters of the kinetics of Pb concentrations were determined. Based on the model, the coefficient of absorption of Pb by gastrointestinal mucosa in the supplemented mice was found-η = 3.53% (versus η = 15% in non-supplemented ones). The present study clearly indicates that there is a realistic perspective to create a new drug based on modified natural clinoptilolites in cases of chronic heavy metal intoxication, without negatively affecting the environment.

Total concentrations and chemical speciation of heavy metals in liquefaction residues of sewage sludge

The risk (including bioavailability and eco-toxicity) of heavy metals (Pb, Zn, Cu, Cd, Cr and Ni) in liquefaction residues (LR) of sewage sludge (SS) was estimated, according to both the speciation of heavy metals and the local environmental characteristics. The amount of organic matters in LR was lower than that in SS, resulting in a smaller calorific value, while the total content of heavy metals in LR nearly doubled. High residual rates of heavy metals (about 80%) indicated that the heavy metals in SS were concentrated into LR after liquefaction. The comparisons of sequential extraction results between SS and LR showed that after liquefaction, the mobile and easily available heavy metal fractions (acid soluble/exchangeable and reducible fractions) were mainly transformed into the relatively stable heavy metal fractions (oxidizable and residual fractions). The bioavailability and eco-toxicity of heavy metals in LR were relieved, though the total concentrations of heavy metals increased.

Evaluation of factors affecting performance of a zeolitic rock barrier to remove zinc from water

This study examined the factors affecting the performance of zeolitic rocks as reactive media in a permeable reactive barrier (PRB) used to remediate groundwater contaminated with Zn. Serial batch kinetic and sorption tests were conducted on zeolitic rock samples under a variety of conditions (i.e., reaction time, pH, initial Zn concentration, and particle size) using Zn(NO(3))(2).6H(2)O solutions. Serial column tests were also conducted on zeolitic rock samples at various flow rates. The removal of Zn increased approximately from 20-60 to 70-100% with increasing pH from 2 to 4 and decreasing initial Zn concentration from 434 to 5mg/L. Zn removal was not affected by the particle size, regardless of the zeolitic rock samples used in this study. The Zn removal increased approximately from 20-70 to 60-100% with increasing the cation exchange capacity (CEC) from 124.9 to 178.5meq/100g and increasing zeolite (i.e., clinoptilonite and mordenite) and montmorillonite contents from 53.7 to 73.2%. The results from the column and batch tests were comparable. Increasing the flow rate caused the earlier breakthrough of Zn (sorbing cation) and a rapid decrease in the concentration of Na, Ca, and Mg (desorbing cations). The hydraulic conductivities of the samples were unaffected by the particle size and mineral components.

Sewage sludge bioleaching by indigenous sulfur-oxidizing bacteria: effects of ratio of substrate dosage to solid content

The aim of this work was to study the effect of ratio of substrate dosage to solid content (Sd/SC) on sewage sludge bioleaching. The inocula--indigenous sulfur-oxidizing bacteria were enriched and cultured from the fresh activated sludge to a wastewater treatment plant. The results showed that Sd/SC significantly influenced the sludge bioleaching process. With increase in Sd/SC the sludge bioleaching was enhanced, which was represented by the acceleration of sludge acidification, oxidizing environment formation, and substrate (sulfur) utilization. Higher Sd/SC was more efficient to solubilize the heavy metals and total phosphorus (TP) than lower Sd/SC, while total nitrogen (TN) release was not influenced by Sd/SC. Zinc and copper were efficiently bioleached because of sludge acidification and sludge oxidation, but lead was bioleached with a low efficiency because of the formation of low soluble PbSO(4) precipitates. After bioleaching the biotoxicity of sewage sludge greatly reduced.

Solid-liquid-solid extraction of heavy metals (Cr, Cu, Cd, Ni and Pb) in aqueous systems of zeolite-sewage sludge

This paper presents results of kinetic and equilibrium studies of the removal of heavy metals (Cr, Cu, Cd, Ni and Pb) from the sewage sludge using a new technique of solid-liquid-solid extraction with the adsorption-diffusion column filled by the zeolite. The metal extraction onto the zeolite from aqueous solution of the clinoptilolite and the sludge composition is characterized by three stages: intensive extraction, inversion and stabilization with the moderate extraction increase. Addition of 25% of the zeolite provides extraction efficiency of cadmium and lead of about 84%, chromium, copper and nickel of 66%, 61% and 50%, respectively. The estimated values of Gibbs free energy change DeltaG show that the metals extraction by the clinoptilolite may be considered as a physical adsorption. The negative values of DeltaG testify to an exothermic nature of the process. The difference between energetic potentials of the components is a driving force of the metal redistribution in the system "clinoptilolite-water-sludge".

Immobilization of selected heavy metals in sewage sludge by natural zeolites

This contribution presents the possibility of application of natural sorbent (Transcarpathian clinoptylolite (KL)) for immobilization of selected heavy metals in the sewage sludge. The influence of ion-exchange parameters (e.g. time, amount of zeolite) were discussed. Process of immobilization was performed using a static method (Batch). It was found that best possible conditions for immobilization of heavy metal ions were as follows: zeolite fraction 0.7-1.0mm, 5h of shaking, zeolite/sewage sludge ratio 2/98.