Statistical Interpretation and Proling the Leaching Characteristic of Chromium in the Basic Chrome Sulphate (BCS) Sludge Dumping at Village Khanchandpur-Rania, District Kanpur Dehat, Uttar Pradesh (India)

Without immobilized hazardous waste contaminates soil and groundwater, which can further bio-accumulates and poses serious negative health impact on ora as well as fauna. The present investigation has been conducted to study of leaching behavior of chromium species in immobilized hazardous waste containing Basic Chrome Sulphate (BCS) dumped at dumping site Khanchandpur district of India. Results indicated that the pH of sludge ranged from 10.16–11.90 while EC ranged from 840-16160 dSm -1 in a different layer of the dumpsite and signicantly varies on increasing depth. A similar trend was also observed in TDS contents which strongly justied the leaching of salts in lower depth. Total Cr concentration (25029.94 mg kg -1 ) was observed in the top layer which was signicantly increased on increasing depth i.e., 36102.0 mg kg -1 and 42811.77 mg kg -1 while TCLP based concentration ( 216.44 mg kg -1 in top layer) was signicantly increased on increasing depth i.e., 406.25 mg kg -1 and 517.60 mg kg -1 . A similar trend was also observed in total and TCLP hexavalent and trivalent (Cr 6+ and Cr 3+ ) chromium concentration. Hierarchical Cluster Analysis is separated all sample based on depth into three different cluster based on dissimilarity. A signicant correlation was observed with TCLP Cr 6+ in TCLP Cr 3+ , EC, and TDS at 0.01 levels while EC, TDS, total Cr 6+ , and TCLP Cr were signicant correlated with TCLP Cr 3+ . The leaching behavior of Cr species was higher as well as increasing of depth in the dumping site.


Introduction
The rapid industrialization of India led to a geometrical rise in the level of air, water, and land pollution. Chromium is considered an environmentally hazardous element and classi ed as a class-A human carcinogen. Chromium is a naturally occurring element present in water, sediments, rocks, soils, plants, biota, animals, and volcanic emissions under various chemical, physical, and morphological forms (Siraj et al. 2012) which exist in several oxidation states (0-6). Only two of them, the Cr 3+ and Cr 6+ are stable and enough to occur in the environment (Ducros 1992;Shriver et al.1994), which differs from one another in charge, physicochemical properties as well as chemical and biological activities. Hexavalent chromium in the form of water-soluble complex anions in surface water undergoes reduction to Cr 3+ possessing a much shorter lifetime (Callahan et al. 1979). Cr 6+  Industrial applications of Cr include electroplating, pigment production, leather tanning (Fishbein 1971), and controlling bio lms in cooling towers (Lund 1971). Inadequate storage and improper disposal practices of Cr have caused incidents of soil and groundwater contamination in many areas (Nriagu & Nieboer 1988; Palmer and Wittbrodt, 1991). Once chromium enters the environment, it exists in the two most stable oxidation states i.e., Cr 3+ and Cr 6+ (Bartlett 1991). Among these trivalent form of chromium is comparatively offensive and nearly immobile, while hexavalent chromium moves rapidly through soil and water. This form of chromium generally acts as an irritant to plant and animal tissues and carcinogenic (Nieboer & Jusys 1988). Cr 3+ occurs primarily as a cation in solution and forms complexes with inorganic and organic ligands (Hartford 1979). It is considered an essential trace nutrient for animals and humans (Anderson 1993; Richard & Bourg 1991). Cr 6+ can be toxic to bacteria, plants, and animals (Anderson, 1995;Kimbrough 1999). The use of chromium and chromium compounds is increase due to fast growth through intensive industrialization. In the metallurgical industry, it is used for the manufacture of various alloys and steel. Chromate ore is also extensively used in making refractory materials like bricks.
Chromate is used in the chemical industry to make many chromium-containing chemicals. represents an inconvenience for the safe reuse of these sludge and a cost forming factor for their disposal as well as a real threat to the environment. Also, tanneries are doing illegal dumping of wastewater and sludge that causes serious environmental pollution. Tanning is one of the oldest and fastest-growing industries in India. There are about 2,000 tanneries located at different centers with a total processing capacity of 600,000 tons of hides and skins per year as per observed by Raju and Tandon (1999). Two major sources of Cr contamination are sludge-treated/amended soil (Dreiss 1986) and uncontrolled disposal of wastes (Makdisi 1991

Sample Collection
For sampling of hazardous waste standard methods was followed by CPCB manuals 2011. The samples were collected in polythene bags and transported to the laboratory after appropriate labeling for further analysis. A total of twenty-seven (27) samples were collected from nine places up to 150 cm depth and these depths were divided as D1:Top layer (0-15 cm), D2: Subsurface layer(15-75 cm), and D3: Lower depth(75-150 cm) in three vertical strata of the dumpsite. The personnel protective equipment was used during the collecting of samples. The sample was collected into the clean and air tight polybag which was air dry in the laboratory. After the air-drying sample was crushed through the porcelain motor and then sieved with a 10mm sieve. The samples were analyzed for the TCLP extraction method and total concentration of chromium oxide including bulk density (BD), pH, EC, and TDS.
TCLP Extraction based determination of chromium species TCLP designed to determine the mobility of both organic and inorganic analytes present in liquid, solid, and multiphasic wastes which is chemical analysis process used to determine whether there are hazardous elements present in a waste. The test involves a simulation of leaching through a land ll and can provide a rating that can prove if the waste is dangerous to the environment or not. This rating can dictate the waste management methodology that should be adopts to dispose of the waste afterward.
For the TCLP extraction, the test procedure was adopted as mentioned in USEPA SW-846 Test Method 1311: Toxicity Characteristic Leaching Procedure. Weight accurately 25.0 gm prepared test sample and slowly add 500 ml of extraction uid which is prepared by dilute 5.7 mL glacial CH3CH2OOH with reagent water to a volume of 1 liter. When correctly prepared, the pH of this uid will be 2.88 + 0.05 to the extractor vessel. Close the extractor bottle tightly, secure in rotary agitation device, and rotate it at 30 ± 2 rpm for 18 ± 2 hours. As de ne in Hazardous and Other Wastes (Management and Transboundary Movement) Rules, 2016 schedule-II note three, Cr6 + extractions was done using distilled water in place of the leaching media speci ed in the TCLP procedures. The leachable Total chromium concentration measured followed by Atomic absorption spectrophotometer make "analytical jena novAA-350" and hexavalent chromium was measured by spectrophotometer make Systronics-108.
Determination of total chromium hexavalent 2.5 gm of the moist sample was taken in a cleaned and labeled 250 ml beaker and added 50 ml digestion solution (20.0 ± 0.05 gm Sodium hydroxide, 30.0 gm ± 0.05 Sodium carbonate dissolve in 1000 ml distilled water). 392.18 mg MgCl 2 and 0.5 ml of 1.0 M phosphate buffer were added to the beaker and allow to stirrer without heat for at least 5 m by using a stirring bar. The sample was heated and maintains the temperature between 90-95 C with constant stirring for 60 minutes and cover all samples with a watch glass. Gradually allow cooling down each solution at room temperature, ltering the all solutions by using Whatman lter paper (0.45µm) and rinses to clean the 250 ml beaker and again place a magnetic stirrer into digested sample beaker and added the concentrated nitric acid solution drop wise with constant stirring. Adjust the pH 7.5 ± 0.5. Transfer quantitatively the content of the beaker to a 100 ml volumetric ask and make up the volume with double distilled water. The digested sample ready for analysis. 95 ml of the extract was transferred into a 100-mL volumetric ask. Diphenylcarbazide solution (2.0 mL) was added and mix properly. The pH was maintained upto 2 ± 0.5 by adding H 2 SO 4 solution and then volume was make up 100 mL with reagent water. Within 5 to 10 minutes full-color was developed.
Simultaneously blank was also run with distilled water for blank correction. Absorbance was measured at 540 nm by UV-spectrophotometer (make-systronics-108). Chromium was determined from the reference calibration curve.

Determination of pH, EC & TDS
For the characterization of the physical property i.e., bulk density (BD), pH, EC, and TDS were assessed by adopting standard methods USEPA SW-846; 9045D, 20 g of soil sample was taken in a 50-mL beaker and added 20 mL of double-distilled water, cover, and continuously stir the suspension for 5 min by stirrer. Additional dilutions were allowed if working with hygroscopic soils and salts or other problematic matrices. Let the soil suspension stand for about 1 hr to allow most of the suspended clay to settle down from the suspension or lter or centrifuge off the aqueous phase for pH measurement, the same aliquot is also used for measurement of electrical conductivity (EC) as well as TDS by gravimetric method.

Digestion of sample for total chromium analysis
The processed sludge sample was digested by nitric/hydrochloric acid digestion followed by metal analysis (SW 846 US EPA method 3050B). 2.0 g of samples was digested in 10 mL HNO 3 (1:1) by heating 95 o C up to 15 minutes. 5 mL HNO 3 added after cooling. Chromium was extracted from solid samples by covering the beaker with a watch glass and re uxing the sample in the dilute acid mixture for 30 minutes.
After extraction, extract was diluted to specify volumes with reagent water, mixed and either centrifuged or allowed to settle overnight before analysis. Diluted samples were to be analyzed by atomic absorption spectrometer (AAS) methods as soon as possible after digestion completed.

Statistical analysis
The SPSS software was used for the interpretation of descriptive statistics (Mean and SEM), Bivariates analysis of variance, LSD Post hoc test, Hierarchical cluster analysis (HCA), and Pearson correlation analysis.

Bivariates analysis of variance
The analysis of variance (ANOVA) was performed in the data set for comparing the mean and relative difference in the data set. It was a parametric statistical solution to nd out a signi cant difference in the individual and dependent variables. ANOVA has been performed in several ways but, It has three types namely univariate (One-way), bivariates (Two-way), and multivariates (K-way) analysis of variance. The univariate ANOVA test analyzing the group of data by using only one variable from the group. A variable is just a conditioned or subset that the groups of data fall into if the variables have more than one at a time it is called bivariates and variables further increase up to three or more it is called multivariate ANOVA (Gagné 2014). The bivariates analysis of variance (ANOVA) was performed in the SPSS software against the concentration of hexavalent and total chromium in TCLP extract of BCR sludge sample collected from deferent depth. In which is further multi comparison test conducted by Post hoc test.

Hierarchical cluster analysis (HCA)
The HCA is a useful technique for visual comparison in the data; it builds a tree plot where data participated within branches that are close together and dissimilar data separated in other branches (Sahu et al. 2018). The HCA was performed in the SPSS software against the physicochemical data of BCR sludge sample collected from the deferent depth the Linkage algorithm applied through ward linkage and distance was measured through rescaled distance cluster.

Pearson Correlation analysis
The correlation matrix is a Statistical tool to nding the relationship between data sets is signi cant or not at 0.01 and 0.05 level (Kumar et

Characterization of dumping site sludge
Results indicated that the pH of BCS sludge ranged from 10.16-11.90 which were signi cantly varied and shows alkali in nature (Table-1 Table 1).
The mean values of EC signi cantly increased on increasing depth due to leaching of salts in lower depth. Least EC at surface layer (935 dSm -1 ) while maximum in lower depth (3103.3dSm -1 ). A similar trend was also observed in TDS contents which strongly justi ed the nding. While bulk density was nonsigni cant variation was observed. Geelhoed et al. 2002 reported that during leaching, the pH decreased moderately from 12.3 to 11.7 (Rania COPR) and 12.6 to 12.1 (Chhiwali COPR). Considering that COPR has a high buffer capacity that alkaline pH values will prevail in the seepage water of COPR dumps in the next decades.

Total chromium and its different oxidation species
The BCS sludge from the dumping site indicated that the least concentration of total Cr was observed in the top layer which was signi cantly increased on increasing depth. The mean value of total Cr concentration was 26208.33 mg kg -1 in the top layer which was signi cantly increased 36102.0 mg kg -1 and 42811.77 mg kg -1 in the subsurface and the depth respectively (Fig. 2a). If we observe location-wise then the maximum concentration in the top layer was observed in the middle of the dumpsite while least concentration (25029.94 mg kg -1 ) in hind or towards village side of the top layer while in the subsurface layer it was observed least towards NH24 highway (34308.46 mg kg -1 ) and maximum (39482.59 mg kg -1 ) towards village side of dumpsite (Table 1). This variability in the concentration of total Cr at a different location in different depths may be due to the leachability of total Cr as per time duration and depth. But overall average mean values indicated that total Cr concentration increased signi cantly on increasing depth (Fig. 2a).
Total Cr 6+ showed a similar trend as observed in total Cr concentration which was signi cantly decreased on increasing depth at all locations. The average mean concentration was indicated that 9653.16 mg kg -1 , 24393.93 mg kg -1 , and 24946.88 mg kg -1 in the upper layer, subsurface, and depth respectively (Table 1& Fig. 2b) which showed minimum concentration in the top layer and maximum total Cr 6+ concentration in depth. There were insigni cant changes were observed in between subsurface and lower depth that may be due to either hindered rate of leaching of total Cr Cr 6+ on increasing depth (Fig. 2b).
The mean concentration of total Cr 3+ was indicated as 8951.24 mg kg -1 , 16560.96 mg kg -1 , and 20615.80 mg kg -1 in the upper layer, subsurface, and lower depth respectively which was signi cantly increased on increasing depth (Table 1& Fig. 2c)). Total Cr 3+ showed similar trends as observed in total Cr and Cr 6+ concentrations which were signi cantly decreased on increasing depth at all locations. If we thoroughly observed location-wise concentration of total Cr + 3 then the least concentrated in the upper layer was observed towards NH-2 of dumping site which was signi cantly increased towards the middle (L2) and village site (L3). This may be due to the time duration that Cr 3+ vertically moves downwards in earlier dumping hazardous waste (Table 1& Fig. 2c) i.e., towards NH2. A similar nding was also reported in which Cr concentration ranging between 2000 and 5000 mg/L in the aqueous e uent from the tanning industries which was very high than the recommended permissible limit of 2 mg/L while 0.05 mg/L in drinking water ( Mohan 2006). Singh et al. 2013 studied a detailed investigation about the status of hexavalent chromium in the area of sludge dump at village Umran, Rania -Jainpur area in Kanpur Dehat, UP, India where had long-standing problem due to indiscriminate disposal of high concentration chromium bearing BCS sludge and also due to improper drainage in the area. They observed that the quality of groundwater in bordering stockpiles and nearby villages was badly affected by hexavalent chromium (80mg/L) while BIS permissible limit is up to 0.05 mg/L. They marked the entire area alarming high concentration of Cr which was imparted strong pale yellow color to groundwater. Wang et al. 2004 reported that correlation was better between plant growth and available Cr than between plant growth and total Cr. It has long been recognized that the soluble, exchangeable, and loosely adsorbed metals are quite labile and hence more bioavailable for plants (Cary et al. 1977;Lasat 2004). Also, clayey soil might have high sorption capacity for Cr than other types of soils (Adriano 1986). Pendias and Pendias 1992 considered 75-100 mg/kg as a critical value/load for chromium in soils. The concentration in the lowest soil horizon is commonly used to represent the natural background value, which is representative of the individual soil pro le (Blaser 2000). Mandal et al. 2011 reported total Cr in sludge samples collected from the dumping site contained 377-1052 µg Cr/g sludge( acid digestion), whereas 413-1213 µg Cr/g sludge( microwave digestion), whereas sludge samples collected from the tannery contained 492-2941 µg Cr/g sludge (acid digestion), whereas 490-3540 µg Cr/g sludge ( microwave digestion). So, proper treatment and disposal of sludge in stockpile on priority have required simultaneously techno-feasibility must be explored for chemical treatment (immobilization) of chromium bearing sludge and its judicious disposal must be required.
TCLP based concentration of Cr and its different oxidation species TCLP or Toxicity Characteristic Leaching Procedure is a chemical analysis process used to determine whether there are hazardous elements present in the waste. The test involves a simulation of leaching through a land ll and can provide a rating that can prove if the waste is dangerous to the environment or not. This rating can dictate the waste management methodology that the company adopts to dispose of the waste afterward. In the present study TCLP based concentration of Cr and its different oxidation species were assessed. Results indicated that TCLP based concentration of Cr was very high in all locations which was signi cantly increased on increasing the depth of the dumping site. In the top layer, it was ranged from 126.32-294.64 mg kg -1 with an average mean value of 216.44 mg kg -1 which was signi cantly increased on increasing depth i.e., 406.25 mg kg -1 and 517.60 mg kg -1 in the subsurface and lower depth respectively (Table 1& Fig. 2d). These values of TCLP based Cr were manifold higher than the permissible limit. The same trend was also observed in the case of TCLP based Cr 6+ and Cr 3+ which concentration was observed minimum in the top layer (mean 108.43 mg kg -1 and 100.31 mg kg -1 respectively) and further these were signi cantly increased on increasing depth i.e., 153.06 mg kg -1 and 230.35 mg kg -1 respectively in subsurface layer while 198.47 mg kg -1 and 352.99 mg kg -1 respectively in the lower depth of dumping site (

Statistical Analysis
Pro ling of different oxidation states of chromium was executed in the different depth of dumped hazardous waste and following statistical interpretation conducted on the analyzed data.

Analysis of variance
In this study, the Bivariates analysis of variance had performed in SPSS software to identifying the leaching characteristic of chromium species in different depth i.e., the top layer (0-15 cm), subsurface layer (15- In a Bivariates ANOVA, the p values de ned the difference between groups are signi cant or not, but it failed to compare with each group such as signi cance between group 1 and group 2, Group 2 and group 3, and group 1 and group 3 respectively. The multiple comparisons have been done by LSD Post Hoc Test in the concentration of hexavalent chromium and total chromium in TCLP extract of deferent depth, 6 pairwise comparisons are given in Table 3. The p-value of all the tested groups has been less than 0.05 showing the signi cant differences in all the comparisons. The leaching behavior of Chromium species in different depths (0-15cm, 15-75cm, and 5-150cm) at duping site is signi cant means the leaching behavior of Chromium species is higher as well as increasing of depth of dumping site.

Hierarchical cluster analysis (HCA)
Hierarchical Cluster Analysis is an advanced helpful technique, which pulls together all the objects based on their similarity. HCA was performed using ward linkage with rescaling distance cluster combined as similarity a measure that is offered visually meaningful dendrogram and separate/cluster the groups (Sahu et al. 2018). HCA classi es physicochemical parameters of BCS sludge given in Fig. 3.1, physicochemical parameters clustered into two major groups that two major groups further divided into two sub-groups step by step. In this study, physicochemical parameters of BCS sludge were divided into four clusters, Bulk density (BD), pH, and hexavalent Chromium (TCLP Cr 6+ ) grouped in cluster 1, trivalent Chromium (TCLP Cr 3+ ), total Chromium (TCLP Cr), TDS and EC represent cluster 2. Trivalent Chromium (Cr 3+ ), and hexavalent Chromium (TCLP Cr 6+ ) formed cluster 3, while total Chromium was separated the cluster 4.
The dendrogram of HCA given in Fig. 3.2 represents the visual identity for the concentration of Chromium species at different depth levels in three sampling location. In this dendrogram, the triplicate sample of three deferent depth level at the dumping site was divided into two major clusters in which one major cluster is further divided into two sub-clusters; sample 1 and sample 2 at 0-15 cm depth contributes in sub-cluster 1, while sample 3 at 0-15 cm depth formed sub-cluster 2. The second major cluster was further divided into three sub-cluster; sample 1 and sample 2 at 15-75 cm depth contribute to sub-cluster   3 at 15-75 cm depth. Sample 3 at 15-75 cm depth and sample 2 at 75-150 cm depth both contributed  in sub-cluster 4, while sample 1 at 75-150 cm and sample 3 at 75-150 cm formed Sub-cluster 5. Pearson Correlation analysis Two tails Bivariates correlation was run through Pearson correlation methods in SPSS to nding the relation between a physicochemical variable of BCS sludge. In this study, statistical correlation analysis was done at 0.05 and 0.01 level which is given in  (15-75 cm), and lower depth (75-150 cm).. It was observed that sludge pH, EC, and TDS were signi cantly increased on increasing depth which strongly justi ed the leaching of salts in lower depth. Total Cr and its different oxidation species were also showed that concentration of Cr increased on increasing depth and TCLP based concentration was also signi cantly increased on increasing depth wise-versa similar trend was also observed in total and TCLP hexavalent and trivalent (Cr 6+ and Cr 3+ ) chromium concentration which showed high leaching tendency of sludge. Bivariates analysis of variance had performed to identifying the leaching characteristic of chromium species in different depth in which chromium species (Cr 6+ & total Cr) serves as variable Ist which showed a signi cant effect on depth factor F (2,12) = 37.334, p (0.000) < 0.05, and explain that there are signi cant differences in the TCLP concentration of chromium species within the group of different depth at the dumping site. Depth level of the dumping site was 2nd variable which also indicated a signi cant effect on Chromium species factor F (1,12) = 9.380, p (0.004) < 0.05, and the concentration of chromium species is treated as dependent variables and elucidate that there were signi cant differences in the TCLP concentration of chromium species within the group (Cr 6+ & Total Cr).
Hierarchical Cluster Analysis (HCA) showed that BD, pH, and TCLP Cr 6+ were grouped in cluster 1, TCLP Cr 3+ , TCLP Cr, TDS, and EC represented cluster 2. Cr 3+ and TCLP Cr 6+ formed cluster 3, while total Cr was separated in cluster 4. A signi cant correlation was observed with TCLP Cr 6+ in TCLP Cr 3+ , EC, and TDS at 0.01 level while EC, TDS, total Cr 6+ , and TCLP Cr were signi cant correlated with TCLP Cr 3+ . The leaching behavior of Cr species was higher as well as increasing of depth in the dumping site. So, it was concluded that BCS sludge required proper treatment, storage, and proper disposal facilities to avoid the contamination of soil and groundwater. Techno-economic feasibility must be explored for chemical treatment (immobilization) of chromium bearing sludge and its judicious disposal in either of two land-ll (TSDF) facilities operational in close proximity at village Khanchandpur Kharanja, Rania, Kanpur Dehat, UP, India. Figure 1 Geographical representation of sampling point at BCS sludge dumping site of Khanchandpur Kharanja, Rania, Kanpur Dehat, U.P., India. Figure 2