International Journal of Environmental Research University of Tehran ISSN: 1735-6865 EISSN: 2008-2304 Vol. 4, Num. 3, 2010, pp. 513-518

International Journal of Environmental Research, Vol. 4, No. 3, July-September, 2010, pp. 513-518

Article

Soil characteristics affected by long term application of sewage wastewater

Rana, L . , Dhankhar, R . * and Chhikara , S .

Ecology Laboratory, Department of Environmental Sciences, Maharishi Dayanand University, Rohtak, Haryana, India

Correspondence Address: *Ecology Laboratory, Department of Environmental Sciences, Maharishi Dayanand University, Rohtak, Haryana, India
dhankhar.rd@gmail.com

Date of Submission: 12-Jan-2009
Date of Decision: 05-Dec-2009
Date of Acceptance: 25-Mar-2010

Code Number: er10057

Abstract

Keywords: Sewage waste water, Irrigation, Soil properties, Correlation, Heavy metals

Introduction

The clean and safe environment is the basic re-quirement of human existence. Today, due to constraint in availability of fresh water for irrigation, waste water especially sewage water is being used for irrigation of agricultural fields. Various studies confirm that treated sewage waste water can be useful as an additional wa-ter resource for irrigation (Palese et al., 2009; Mehrdadi et al., 2007). Application of sewage water improved the physico-chemical properties and nutrient status of the soil and increases crop production as it supplies N, P and K and also valuable micronutrients than what crop requires (Panicker, 1995). On the other hand, the use of sewage water in agriculture is associated with health risks because of presence of pathogenic micro-organ-isms (Toze,2006), metallic contaminants like Cu, Ni, Cd, Cr, Zn (Misra & Mani,1991) and polychlorinated sub-stances (Bansal,1998). McGrath and Lane (1989) re-ported that more than 80% of toxic metals originally added were still present in top soil layers 25 years after sewage sludge application. Toxic effects of heavy met-als upon soil micro-organisms and microbial mediated processes have been reviewed by Duxbury (1985) and Doelman (1986).

In India, sewage water generation is 29000 million liters per day against the existing treatment capacity of 6000million liters per day (Central Pollution Control Board, 2004). The use of treated sewage in irrigation was emphasized in the Water (Prevention and Control of Pollution) Act, 1974.Due to lack of facilities; un-treated sewage water is being used by farmers to sat-isfy crop water needs. This indiscriminate continuous use of such effluent for crop production could result in the concentrations that may become phytotoxic (Ghafoor et al., 1999). Most of the crops and veg-etable species growing in metal polluted soils are un-able to avoid the absorption of these metals (Baker, 1981). Studies have shown that on applying sewage water to soil, Cu is among those metals that would quickly double its concentration in the top soils (Jorge et al., 2005). Bansal et al. (1992) compared the accu-mulation of Zn, Cu, Mn and Fe in soils irrigated with waste water and tube well water. Accumulation of heavy metals in agricultural soils is a subject of in-creasing concern due to food safety issues and po-tential health risks as well as detrimental effects on soil ecosystem (McLaughlin et al., 1999). There is a well recognized need to detect the level of pollution of soil given the increased use of sewage water in agri-cultural soils. It provides an indication of soil health. The Sewage effluent of the Rohtak city is discharged into two lined channels both of which join a larger channel. For the past 35 years, farmers owning land along these channels are making use of this untreated sewage effluent for irrigation purposes.The chosen agro-ecosystem, is intensively cultivated for growing veg-etables, pulses etc. In this paper, we have studied the long term influence of sewage water on soil properties and heavy metal concentrations. The comparison is also made between the various parameters of the soils irri-gated with sewage waste water and tube well water.

Materials and Methods

The study was conducted in Rohtak city which is located between 76°25' and 76°94' East longitudes and 28°35' and 28°80' North latitude, lying at 219.84 meters above sea level. The climate in this area is classified as continental with extremes of heat in summer and mark-edly cold in winters. The annual rainfall of Rohtak is 455mm, most of which is received during the last week of June to September contributed by South-west mon-soon. The soil samples at the depth of 0-10cm were collected from seven random spots of sewage irrigated agricultural fields of Rohtak city and of nearby fields irrigated by tube well water. Before chemical analysis, they were air dried, powdered and sieved through a 2mm sieve. Stones and plant materials were removed manually.The water samples were also collected in polythene bottles from the sewage disposal site and from four tube wells, located in tube well irrigated fields. The hydrogen ion concentration and electrical conduc-tivity of sewage water samples were determined imme-diately after collection by pH meter and electrical con-ductivity meter respectively. Dissolved oxygen, B.O.D., Ca ²⁺ , Mg ²⁺ , Chloride, Nitrate, sulphate and phosphorus were measured as per the method given by APHA (1992). Heavy metals like Ni, Cd, Zn, Cu, and Pb were estimated after wet digestion with 1:4 mixtures of HClO ₄ and HNO ₃ , followed by measurement of respective concentrations with the help of atomic absorption spectrophotometer. The pH of the soil samples was determined using glass electrode pH meter. Soil salinity was determined in soil extracts using conductivity meter and expressed as elec-trical conductivity (E.C.ds/m). Soluble captions (K ⁺ , Na ⁺ ) were determined by Flame photometer (Rhoades, 1982). Total alkalinity (CO ₃ and HCO ₃ ) and Cations (calcium and magnesium) were determined as per the method given in USDA Handbook No.60 (US Salinity Lab Staff, 1954). Organic carbon was determined by Walkley and Black rapid titration method. The method is based on organic matter oxidation by K-dichromate. Available Phosphorous was determined by the method prescribed by Bray and Kurtz, 1945. Chloride was determined by standard silver nitrate titration method (Jackson, 1967). All heavy metal concentrations in solution phase were determined by using atomic absorption spectrophotom-eter (AAS). Extractable metals were determined by AAS using DTPA as single extract ant (Lindsay & Norvell, 1978). The data obtained were subjected to mean and standard deviation. Correlation coefficient between physico-chemical parameters, metal concentrations and interaction of both was carried out in sewage irrigated soil samples and tested for significance following Rao and Richard (2001). The data were analyzed on Microsoft Excel and SPSS 7.5 software programs.

Results and Disscussion

The sewage effluent samples and tube well water samples were characterized as shown in [Table - 1]. Tube well water samples were analyzed to evaluate the suit-ability of sewage water as a source of irrigation. The tube well water exhibited almost neutral hydrogen ion concentration value (7.3) while the pH of sewage wa-ter is slightly alkaline in reaction (7.6). The enhance-ment of pH is due to addition of various soluble salts in sewage water. Despite the increase of 3.94%, the pH value of sewage waste water was within the permis-sible limits in respect of its use on agricultural lands(Desai et al.,1990).The salt content/E.C. of sew-age water (2.30ds/m) was 51.3% higher than that of tube well waters (1.12ds/m) indicating that industrial effluent discharged are brackish. The total dissolved solids in the sewage water were found to be 26.27% more than that of tube well waters. With respect to tube well water samples studied, the dissolved oxygen of sewage waste water sample (1.42g/l) was low. Low dissolved oxygen is indicative of higher value of bio-logical oxygen demand. Thereby, B.O.D. of sewage water was quite high compared to the tube well water samples; it also exceeded the prescribed limit of 100mg/ L. This condition of high biological oxygen demand value may pose problem to the use of sewage water for irrigation purpose.

The nutrient elements were present in high concentration in sewage waste water, with phosphorus (6.4 mg/L) content being 80.15% higher the content in well waters (1.27 mg/L) and nitrate content(25 mg/L) 94.4% more than that of tube well water(1.4 mg/L). Both were exceeding the prescribed limits of 5mg/L and 10mg/L for phosphorus and nitrate content respectively. High nitrate concentration may be due to the presence of urea[CO (NH ₂ ) ₂ ] which is the major source of nitrogen in sewage (Ganguly and Maiti, 2004). The sulphate content in sewage water was 125.68mg/L which is 48.13% higher than of tube well water samples (65.18 mg/L).The variation in the amount of nutrients present in the sewage water may be due to the variation in the mineralogical composition of their sources from where they are disposed off. The chloride content of sewage effluent (3.8 meq/L) was 24% higher than that of tubewell (5 meq/L) water samples. This parameter may not pose a problem for use as irrigation water. An alkalinity of the effluent seems to be due to bicarbonates (14 meq/L) only because carbonates were not observed in the effluent. The calcium and magnesium content of sewage effluent has increased by 35% compared to tube well water samples. This increase may be due to the addition of certain compounds (which imparts hardness) after domestic use of the water (Ganguly and Maiti, 2004). The concentration of heavy metals in sewage effluent depends on the nature of industries and domestic uses (Misra et al., 1992). High content of Cd and Ni have earlier been reported in sewage water contaminated with effluent discharge from electroplating industries (Narwal et al., 1990). In the present study, though the concentration of heavy metals viz. Ni, Cd, Zn, Cu, Pb and Fe were higher in sewage effluent with respect to ground water samples but still it is within the limits prescribed for land disposal. Physico-chemical properties of the soils are given in [Table - 2]. Repeated application of sewage effluent to agricultural lands can have significant effects on soil properties. The analysis of soil samples [Table - 3] reveals high chloride, bicarbonate, calcium and magnesium content of sewage irrigated soil compared to tube well irrigated soils.The carbonates in sewage irrigated soils form sparingly insoluble solid phases with many metals and have been observed to account for the major portion of several metals (Karpanagiotis et al., 1991). A strong positive correlation has been found between Fe and Cl content and between Cd and Cl content [Table - 4]>. The importance of chloride in increasing the mobilization and availability of Cd through the formation of Cd-chloro complexes has been reported to increase tissue Cd content of wheat and Swiss chard in soils amended with evaporative dried sludge (Weggler-Beaton et al., 2000). It has been suggested that high chloride levels in sewage water should be lowered before use on agricultural land.The soils irrigated with sewage water were weakly alkaline with a pH value of 7.84, 0.38 units less than that of tube well irrigated soils. The presence of significant quantities of mineralizable nitrogen and readily degradable organic matter in sewage sludge influences sludge pH. The soil pH influences the solubility and nutrient availability and also acts as prime factor affecting potential metal availability. In general, heavy metal cations are most mobile under acidic conditions (Christensen, 1984). As expected, all heavy metal ions show negative correlation with pH except Mn [Table - 4]. A significant positive correlation has been found between pH and Ca+Mg concentration and between pH and chloride [Table - 3]. The long term addition of sewage water to agricultural lands enhanced electrical conductivity value from 0.99ds/m for tube well irrigated to 1.65ds/m for sewage irrigated soil due to the high salt content present in the sewage effluents. Sewage application to soil may constitute a source of plant nutrients but simultaneously it may also increase heavy metal content. The electrical conductivity is positively correlated with all the heavy metals in soils and show significant positive correlation with Fe and Mn. A significant correlation was also observed between E.C. and chloride. High concentration of organic matter in sewage water reflected by high B.O.D. value has resulted in enhancement of available and total nutrients in soil over the years as compared to tube well irrigated soil. There is significant increase of 32.55%, 59.63% in available phosphorus and potassium content respectively in sewage irrigated soil. Sludge containing significant quantities of calcium and phosphorus has an increased quantity to retain heavy metals (Brown et al., 1997).Sodium was also accumulating in sewage irrigated soil. Sewage irrigated soil has 0.882% organic carbon compared to 0.707% of tube well irrigated soil. Most of the differences in organic matter content and electrical conductivity maybe attributed to long term application of waste water in soil (Ross et al., 1982).Organic carbon content have positive correlation with almost all nutrients and heavy metals but none of them was found to be significant as evident from the [Table - 3] and [Table - 4]. Thus, the availability of micronutrients and heavy metals can be increased with improving organic carbon status of soil (Trehan, 1996). The degradation of sludge organic matter may be a significant factor in release of heavy metals in sewage sludge amended soils (McBride, 1995). This is supported by the fact that Cd and Zn in sludge are largely associated with organic fractions (Karpanagiotis et al., 1991). The analysis of sewage irrigated soil samples showed that the contents of DTPA extractable micronutrients i.e. Zn, Cu, Fe and heavy metals Ni, Cd, Pb increased appreciably as compared to the tubewell irrigated soils since the sewage effluent contained higher concentration of these elements. In the present study, the Cu (82.93%) and Ni (92.73%) concentrations showed highest percent of increase while Pb (70.47%) showed the lowest percent of increase in sewage irrigated soils than that of tube well irrigated soils. However, Cd was found in soil samples from sewage irrigated fields only. The continuous use of sewage waste water for crop production result in accumulation of trace elements in concentration that may become phytotoxic (Kirkham, 1983). The increase in DTPA extractable metallic cations was also reported by Gupta et al., 1998. The extent of build up of metals in sewage water irrigated soils often depends on sewage water composition and the period of its application(Bansal et al.,1992), in this case being 35 years. In the present study, in spite of higher percentage increase in contents of heavy metals in sewage irrigated soils, they were all within the safe limits prescribed by WHO. The inter-metallic correlation as shown in [Table - 5] reveals significant positive correlation between Fe and Cu, Fe and Pb, Cu and Cd, Cu and Pb. The importance of Fe oxides and hydroxides in reducing the availability of sludge borne metals has been widely acknowledged (Smith 1996, Chaney et al., 2000).

Bioavailability of metals depends on the type and genetic features of soil forming rocks, soil composition, and amount of organic matter and other chemical and physical properties of soil (Lokeshwari and Chandrappa, 2006). It also depends on the concentrations of anions and chelating ligands present in water, pH, redox status and the presence of adsorbent sediments (Mido and Satake, 2003). Indeed, the concentration of free metal ions in soil solution has been shown to be closely linked to toxicity (Ma et al., 1999; McBride, 2001). This is because the free ion species of cationic metals is the dominant form absorbed by organisms (Kochian, 1991). Lokeshwari and Chandrappa 2006 reported highest bioavailability of Fe for plants and animals in sewage-fed lake water.

Conclusion

The present study reveals that the sewage waste water can be used as an alternative to fresh water irri-gation and as a source of fertilizers, since it has high contents of both organic matter and nutrients (N, P and K) and even after 35 years of its continuous use, heavy metals were found within the permissible limits in sewage irrigated soils. Nevertheless, the agricultural use of these effluents should be well controlled, be-cause of the persistence of metals in the soil in an extractable and plant available form for many years. For this reason, it is necessary to control the quality of both soils and waste water in order to adjust the dose applied. The present trend of indiscriminate use of untreated sewage water must be controlled. It should be treated before its use on land or it should be used after proper dilution.^[42]

References

Copyright 2010 - International Journal of Environmental Research

The following images related to this document are available:

Photo images