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Highlights • Geopolymers synthesized by metakaolin and tannery sludge. • The molar ratio of oxide is used as the formula calculation basis. • Long-term durability of solidified product is research. Abstract In this study, tannery sludge was used as a partial replacement material for a geopolymer. The best raw material composition of the geopolymer and durability of the solidified product were studied. Solidification effect was analyzed via compressive strength and total concentration of chromium leached. Its durability in terms of high-temperature resistance, acid/base resistance property, and resistance to acid rain erosion was studied. Through X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), Thermogravimetric Differential Thermal Analysis (TG-DTA) and scanning electron microscopy (SEM), the compressive strength and total concentration of chromium leached in different environments were analyzed. The results show that the mechanical properties of the solidified product were optimal when the silica/alumina mole ratio and sodium oxide/silica mole ratio were 2.45 and 0.37, respectively. The optimal raw material ratio of the above-mentioned product was used to synthesize a geopolymer containing 20% tannery sludge, with the solidified product showing high durability, as indicated by its good high-temperature resistance, high resistance to acids and alkalis, and great resistance to acid rain erosion. [ABSTRACT FROM AUTHOR]

This paper presents leaching behavior of chromium from the stabilized/solidified (S/S) matrixes of tannery sludge. S/S matrixes were formed using cement, and nanoparticles and nano-biocomposites. The chromium in tannery sludge was immobilized by ZVIN (zero-valent iron nanoparticles), MIN (magnetic iron oxide nanoparticles), ZVIN-SB (zero-valent iron nanoparticles/sugarcane bagasse composite) and MIN-SB (magnetic iron oxide nanoparticles/sugarcane bagasse composite). The semi-dynamic leachate tests such as ANS 16.1 and ASTM C 1308 were performed to evaluate the efficacy of S/S matrixes. The parameters such as leaching rate, cumulative fraction leached, effective diffusivity, leachability index and leaching mechanism were calculated for the S/S matrixes containing sludge stabilized by nanoparticles and nano-biocomposites and unstabilized sludge. The leaching rate of chromium from the test specimens showed the effectiveness of nanoparticles and nano-biocomposites. Diffusion studies from the S/S matrixes indicated immobility of chromium. The mean leachability index was found to be higher than 13 for all the test specimens which shows that the S/S matrixes can be effectively utilized for 'controlled applications.' Further, nanoparticles and nano-biocomposites increased compressive strength of the S/S matrixes. XRD, SEM/EDX and FTIR revealed that chromium could be chemically fixed into cement matrixes. [ABSTRACT FROM AUTHOR]

In this study, a sulfur-oxidizing community was enriched from activated sludge generated in tannery wastewater treatment plants. Bioleaching of tannery sludge containing 0.9–1.2% chromium was investigated to evaluate the effectiveness of the enriched community, the effect of chromium binding forms on bioleaching efficiency, and the dominant microbes contributing to chromium bioleaching. Sludge samples inoculated with the enriched community presented 79.9–96.8% of chromium leaching efficiencies, much higher than those without the enriched community. High bioleaching efficiencies of over 95% were achieved for chromium in reducible fraction, while 60.9–97.9% were observed for chromium in oxidizable and residual fractions. Acidithiobacillus thiooxidans , the predominant bacteria in the enriched community, played an important role in bioleaching, whereas some indigenous heterotrophic species in sludge might have had a supporting role. The results indicated that A. thiooxidans -dominant enriched microbial community had high chromium bioleaching efficiency, and chromium binding forms affected the bioleaching performance. [ABSTRACT FROM AUTHOR]

The presented work focuses on energy recovery through the photocatalytic conversion of sulfide-rich tannery sludge into hydrogen using CdS as a photocatalyst, platinum as a co-catalyst and visible light. Four reaction parameters were evaluated through a multivariate experimental design that included investigations of the mass of the photocatalyst (CdS), sacrificial reagent (tannery sludge) concentration, pH and amount of co-catalyst (Pt). The results demonstrated that the tannery sludge concentration and pH were the most important factors in producing the highest hydrogen levels. The strong interaction between these two factors is associated with the consumption of hydrogensulfide ions during the reaction, which can be replenished in basic medium. In contrast, the Pt content and mass of CdS were less relevant factors. The hydrogen production rate under optimal reaction conditions was only 12% lower than that obtained under simulated conditions after the first 5 h of irradiation. However, this rate decreased with longer reaction times. [ABSTRACT FROM AUTHOR]

Similarly to many powders of solids, dried sludge originated from tannery wastewater may result in a self-heating process, under given circumstances. In most cases, it causes a moderate heating (reaching 70–90 °C), but larger, off-design residence times in the drier, in a suboxic atmosphere, extremely reactive solids can be produced. Tannery waste contains several chemicals that mostly end up in the wastewater treatment sludge. Unexpected and uncontrolled self heating could lead to a combustion and even to environmental problems. Elaborating on previous studies, with the addition of several analytical determinations, before and after the self-heating, we attempted to formulate a mechanism for the onset of heating. We demonstrated that the system Fe/S/O has been involved in the process. We proved that the formation of small quantities of pyrophoric iron sulfides is the key. They are converted to sulfated by reaction with water and oxygen with exothermic processes. The pyrite/pyrrhotite production depends on the sludge drying process. The oxidation of sulfides to oxides and sulfates through exothermic steps, reasonably catalyzed by metals in the sludge, occurs preferentially in a moist environment. The mechanism has been proved by reproducing in the laboratory prolonged heating under anoxic/suboxic atmosphere. [ABSTRACT FROM AUTHOR]

Unlike food crops, essential oil-bearing crops in which the oil is extracted through hydro-distillation can be a suitable crop to be grown in heavy metal-polluted soils as the oil does not carry any heavy metal. In a field experiment conducted at CIMAP, Lucknow, India during 2011 and 2012, influence of six doses of tannery sludge viz 0, 10, 20, 30, 40, and 50 t ha were tested, taking sweet basil ( Ocimum basilicum) as the test crop. Maximum herb yield was obtained with the application of sludge at 20 t ha. While in root, accumulation of Cd and Pb increased significantly up to 20 t ha, Cr accumulation increased with increasing the dose of tannery sludge reaching maximum at 50 t ha. Essential oil yield of basil ( Ocimum basilicum) was significantly affected due to sludge application. Quality of essential oil, in term of chemical constituents, however, was marginally influenced due to tannery sludge application. [ABSTRACT FROM AUTHOR]

Tannery sludge is available in plenty and is hazardous to environment as well as plant and animal life. It is very important to manage the tannery sludge in an environmentally sound manner. The aim of this study was to assess the physico-chemical, microbial and biochemical properties of soil treated with different levels of sludge. In this study, Tagetes minuta an essential oil bearing crop was grown in two different textured soils treated with different levels of tannery sludge. Application of tannery sludge (TS) increased the growth and oil yield of plant and also the activity of urease and soil microbial biomass nitrogen (SMBN) when applied in 50:50 combinations of soil:sludge. The crop performed well in coarse soil with a soil:sludge ratio of 50:50. High concentration of tannery sludge exhibited inhibitory effect on SMBN and urease activity. Acid/alkaline phosphatase, dehydrogenase and soil microbial biomass carbon (SMBC) increased as the sludge concentration increased in soil. This may be due to high organic matter present in tannery sludge. Roots accumulated more metal than the shoot. No detectable amount of metal was found in oil of T.minuta. To test the relation between 20 characters principal component analysis (PCA) was performed. PCA analysis indicates that cation exchange capacity (CEC), SMBC, dehydrogenase, acid and alkaline phosphatases were grouped in group 1. SMBN, urease and cis-ocimene content in oil were in group 2 whereas biomasss, chlorophyll a, limonene, Z and E-tagetone were in group 3. PC-I contributes 54% of total variance and PC-II contributes 38% of the total variance. The results concluded that T.minuta can mitigate metal toxicity by root absorption. Microbial activity and biomass of plant was higher in coarse soil with TS than fine soil with TS. [ABSTRACT FROM AUTHOR]

Highlights: [•] We report simultaneous destruction of organics and recovery of chromium in tannery sludge by SCWO. [•] Destruction of COD increases with higher temperature and oxidant, with maximum value 96.5%. [•] Recovery efficiency of Cr from sludge to ash reaches more than 98% under all conditions. [•] Recovered chromium in solid ash is in amorphous structure under temperature 500°C. [•] Leaching toxicity of heavy metals like Cr is greatly reduced through stabilization. [ABSTRACT FROM AUTHOR]

The effectiveness of hydroxyapatite (HAP) on volatilization reducing of heavy metals during incineration of tannery sludge was investigated. The tannery sludge was treated through doped with different content of HAP, and then incinerated in the tube furnace at the temperature of 600 °C and 900 °C. The results showed that the volatilization rates decreased by 10.19 % for Pb, 10.17 % for Zn, 7.40 % for Cu and 5.33 % for Cr at 600 °C when the HAP content was raised to 20 %. At 900 °C, the volatilization rates of Pb, Cr and Cu decreased by about 40.0 %, 24.0 % and 9.0 %, respectively, while volatilization of Zn can be considered nearly unchanged at around 5 %. The heavy metals can be stabilized effectively in the incineration after the pyromorphite-like minerals were formed in the sludge doped with HAP. [ABSTRACT FROM AUTHOR]

Abstract: We experimentally studied the occurrence of spontaneous self-heating of sludge after drying, to understand its nature, course and remediation. The sludge originates from primary and biological treatment of both municipal and industrial wastewater, the latter largely dominant (approx. 90% total organic carbon, mainly from local tanneries). Dried sludge is collected into big–bags (approx. 1.5m3) and landfilled in a dedicated site. After several years of regular operation of the landfill, without any management or environmental issue, indications of local warming emerged, together with smoke and smelling emissions, and local subsidence. During a two year monitoring activity, temperatures locally as high as 80°C have been detected, 6–10m deep. Experiments were carried out on large quantities of dried sludge (∼1t), monitoring the temperature of the samples over long periods of time (months), aiming to reproduce the spontaneous self-heating, under different conditions, to spot enhancing and damping factors. Results demonstrate that air is a key factor to trigger and modulate the self-heating. Water, in addition to air, supports and emphasizes the heating. Unusual drying operation was found to affect dramatically the self-heating activity, up to spontaneous combustion, while ordinary drying conditions yield a sludge with a moderate self-heating inclination. Temperature values as well as heating time scales suggest that the exothermic process nature is mainly chemical and physical, while microbiological activity might be a co-factor. [Copyright &y& Elsevier]

Abstract: The present study revealed the role of earthworm in converting tannery sludge into a valuable product. Tannery sludge was toxic to earthworm, therefore it was mixed with cattle dung in different proportions viz. 0:100 (T 0), 10:90 (T 10), 25:75 (T 25), 50:50 (T 50) and 75:25 (T 75) on dry weight basis. The minimum mortality and highest population buildup of worms was in T 0 mixture. Nitrogen, sodium, phosphorus and pH increased from initial in the range of 7.3–66.6%, 16.90–70.58%, 8.57–44.8% and 2.8–13.65%, respectively. On the other hand potassium, organic carbon and electrical conductivity decreased in the range of 4.34–28.5%, 7.54–22.35% and 32.35–53.12%, respectively. C:N ratio decreased from 20.53% to 47.36% in the final products. Transition metals increased significantly from the initial value and within the permissible limit. The result indicated that vermicomposting with Eisenia fetida is better for changing this sludge into nutrient rich manure in a short period of time. [Copyright &y& Elsevier]

Abstract: Two new methods for treatment of tannery sludge were studied to achieve cost-effective and environmentally acceptable remediation solutions for high chromium containing tannery sludge. Quillaja bark saponin, a plant derived biosurfactant, was applied to dewatered tannery sludge for chromium recovery and a comparative assessment with H2O2 oxidative treatment method is presented. Tannery sludge samples were treated on a laboratory scale with saponin in the pH range 2–3. The effects of various factors like time, concentration of saponin, pH, and temperature on the extraction of chromium were studied. The treatment with saponin extracted 24% of Cr from tannery sludge at a pH around2, performing multiple wash of 6h, at 33°C. On the other hand, the H2O2 treatment, which include Cr(III) oxidation to Cr(VI) and extraction with sulfuric acid solution at pH 2, enabled to extract 70% of chromium within less than 4h at room temperature (21°C). The results indicate that the extraction efficiency of saponin was strongly dependent on the organic matter content of the sample, which affects chromium mobility by its high adsorption capacity. On the other hand hydrogen peroxide treatment is effective and the duration of the process is short and requires cheap chemicals and moderate conditions. [ABSTRACT FROM AUTHOR]

The effects of the use of tannery sludge as soil amendment material on the heavy metal content in sorghum and millet crops in the Challawa Industrial Estate (CIE), Kumbotso L.G.A. Kano State, were studied. Five farms (each 0.25 ha in size) on which both millet (Ex-Borno) and sorghum (Kaura) crops were cultivated and fertilized with tannery wastes for a period of five years were used for the study. The farm plots were designated TS1, TS2, TS3, TS4, and TS5. Samples (shoots and grains) were collected from these farms for two consecutive years and analysed for the following metals: Cr, Cu, Co, Pb, Mn, Fe, Zn and Ni. Results show that millet crop exhibited higher concentrations of Co, Pb, Zn, Cr and Cu than sorghum, indicating that with repeated applications of tannery wastes as sell amendment material, millet crops could accumulate heavy metals to toxic levels. The heavy metal content of the soils when matched against standard values, were found to be below the tolerance levels and hence posed no danger to man and livestock. Sorghum would be the most appropriate crop to be grown on tannery sludge fertilized lands as it accumulates less heavy metals than millet. [ABSTRACT FROM AUTHOR]

The aim of the present study was to examine Cr removal from tannery sludge by bioleaching method using indigenous sulfur-oxidizing bacteria with special emphasis on the influence of bioleaching process on sludge settleability. Chemical leaching with sulfuric acid was designed as the control. The results showed that the inoculation of sulfur-oxidizing bacteria and the addition of elemental sulfur were effective in removing Cr from tannery sludge. After 144 hours of bioleaching, 98% of Cr could be leached. Although it took only 8 hours to reduce the sludge pH from 7.8 to about 2.0 by chemical leaching as compared to 144 hours for bioleaching treatment, chemical leaching removed only 91% of the total Cr. Regardless of bioleaching and chemical leaching treatments, sludge settleability improved considerably with a decrease in sludge pH. Bioleaching treatment performed better than chemical leaching in terms of the percentage of settled sludge and the effluent suspended solids (ESS) content in sludge supernatant. Nevertheless, further work should be carried out to investigate the precise mechanisms leading to such enhanced sludge settleability during sludge bioleaching process. [ABSTRACT FROM AUTHOR]

We studied Cr fractionation in three semi-arid soils (cultivated, under-the-canopy, and outside-the-canopy soils). The soils were amended with: Cr3+, Cr6+, tannery sludge, Cr3+ +tannery sludge, and Cr6+ +tannery sludge and all soils were incubated for 30 and 120 days at 25°C. The Cr in three semi-arid soils was fractionated using sequential extraction (Tessier scheme). Data of Cr fractionation were used to find the correlations with microbial activities determined in previous work. The microbial activities: CO2–C evolved, dehydrogenase activity and nitrification were determined in the same soils amended with the same treatments. Tannery sludge was added at 0.0125gg−1 soil and Cr3+ or Cr6+ at 250μgg−1 soils. After 120 days of incubation, higher values of concentration of Cr were found in the residual fraction in the three soils amended with all the treatments, except cultivated and outside-the-canopy soils amended with Cr6+ +tannery. The non-residual fraction tended to decrease with time except in cultivated and outside-the-canopy soils amended with Cr6+ +tannery sludge. CO2–C evolved was significantly correlated (p <0.05 and p <0.001) with fractions bound to: Mn oxides, Fe oxides organic matter at 30 and 120 days of incubation (from r =0.827 to 0.979). Dehydrogenase activity was correlated with fractions bound to Fe oxides and bound to organic matter, and nitrification with fraction bound to organic matter at 30 days of incubation (r =0.874, 0.959, and 0.803, respectively). These results suggest that even in a sparingly available Cr fraction in semi-arid soils has effect on microbial activities. [Copyright &y& Elsevier]

Abstract: Bioleaching of Cr(III) from tannery sludge using the mixture of ingenuous iron-and sulfur-oxidizing bacteria was investigated in batch flasks. Experiments involved the adaptation of indigenous iron- and sulfur-oxidizing bacteria, the pre-acidification the sludge to pH 6.0 and the addition of energy substrates. Results showed the inoculation of mixture of ingenuous iron- and sulfur-oxidizing bacteria and co-addition of Fe2+ and elemental sulfur accelerated acid production and increase of oxidation-reduction potential originating from the bio-oxidation of Fe2+ and elemental sulfur. Dissolved Cr concentration increased concomitant with pH decreased in the sludge and reached its maximum removal of 95.6%. The amelioration of the odor of bioleached sludge could be noted. However, 20.4% of N, 24.5% of P and 14.3% of organic matter were lost in the bioleaching process. The residual Cr content in the leached tannery sludge was acceptable for use in agriculture. This study had shown the feasibility of applying the bioleaching process, developed for sewage sludge, to tannery sludge with high Cr. [Copyright &y& Elsevier]

Two different organophilic bentorutes obtained by cationic exchange with benzyldimethyloctadecylammonium chloride and trimethyloctadecylammonium chloride have been used to adsorb the organic fraction of a tannery sludge. The exchange process was carried out to different extents to obtain bentonite samples with different organophilicities and different interlayer spacings. Before adsorption, the organic matter was extracted by contacting the sludge with a Ca(OH)2 saturated solution. The adsorption capacity was found to increase with the amount of ammonium salt exchanged for both bentonites, but the one exchanged with benzyldimethyloctadecylammonium chloride proved to be more active: up to about 80% TOC could be removed from the contactingsolution. The adsorption of the organic matter caused a further increase of the bentonite interlayer spacing. In both cases, the adsorption isotherms were found to be of cooperative type, due to weak adsorbent-adsorbate interactions at low loading followed by increasing adsorbate-adsorbate interactions at increasing loading. The results may be applied to tannery sludge stabilization by cementitious systems. [ABSTRACT FROM AUTHOR]

Sludges formed as a result of chrome recovery process (A) and due tobasic tanning activities (B) have been characterized and speciated. The concentration of chromium in both of these sludges (A) and (B) iselevated, being 2,700 and 970 mug g-1, respectively. The sludge (A) has a major portion (48%) bound to inert sulfide form and 22%in the exchangeable fraction while the sludge (B) contains a sizeable fraction (46 %) of the metal in the organic phase. Though the organic bound chromium is apparently safe, analysis of some plants growing on this sludge shows elevated concentrations (1,200 ppm) of chromium. In a scenario like this, development of effective methods of chromium recovery from the sludges seems to be an important consideration. [ABSTRACT FROM AUTHOR]