Heavy Metal Pollution from Treated Sewage Effluent

Heavy Metal Pollution from Treated Sewage Effluent

Available online at www.sciencedirect.com APCBEE Procedia 5 (2013) 344 – 348 ICESD 2013: January 19-20, Dubai, UAE Heavy Metal Pollution from Treat...

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Available online at www.sciencedirect.com

APCBEE Procedia 5 (2013) 344 – 348

ICESD 2013: January 19-20, Dubai, UAE

Heavy Metal Pollution from Treated Sewage Effluent S.K. Al-Musharafia , I.Y. Mahmoudb and S.N. Al-Bahryc a

Sur College of Applied Science, Sur, Oman Department of Biological Science and Chemistry, University of Nizwa, Nizwa, Oman c Department of Biology, College of Science, Sultan Qaboos University, Muscat, Oman b

Abstract Heavy metals were monitored from four sources: treated sewage effluent (TSE), sediment, snails, and grass roots. Using inductively coupled plasma optical emission spectrometer (ICP-OES), the results indicated that heavy metal values increase from the TSE to rest of the three sources. High values of heavy metals that were detected in the four sources were Cu, Ni and Zn. Many heavy metals exceeded the Minimum Permissible Levels (MPL) for wastewater discharge and reuse in Oman. Continuous monitoring of the heavy metal accumulation in the environment must be implemented to avoid health risk and further deterioration of the environment.

©2013 2013The Published ElsevierbyB.V. Selection © Authors.by Published Elsevier B.V. and/or peer review under responsibility of Asia-Pacific Chemical, Environmental Engineering Society Selection andBiological peer review&under responsibility of Asia-Pacific Chemical, Biological & Environmental Engineering Society Keywords: heavy metals; sewage effluent; sediment; pollution

1. Introduction It is well established that the ability of heavy metals binding to bimoleculaes is toxic to organisms. Some are known to be mutagens or carcinogens (He et al., 2005). Different types of heavy metals were reported from terrestrial and marine wild life in Oman [1, 2]. Sources of heavy metals include sewage water reclaimed for irrigation, land-applied wastewater sludge, municipal and industrial refuse [1, 2, 3]. Cu, Zn, Pb and Cd are the most environmentally concerning elements that have been often reported to cause contamination of soil, water, and food chains. The inherent persistence of this heavy metal is a reason for concern, as it

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2212-6708 © 2013 The Authors. Published by Elsevier B.V. Selection and peer review under responsibility of Asia-Pacific Chemical, Biological & Environmental Engineering Society doi:10.1016/j.apcbee.2013.05.059

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bioaccumulates throughout the ecosystem can be found at high levels in soil, surface water, sediments, and consequently reaching the food chain. Despite significant efforts to reduce trace metals loads in wastewater, municipal wastewater still conveys important amounts of trace metals into the environment. Although most of the wastewater treatment plants were initially designed to remove organic matter and nutrient load, most of the metals are efficiently retained in conventional activated sludge plants [4]. Heavy metals in Italy were detected only in low concentrations in the treated effluent, which came from two horizontal subsurface flow reed beds of 75 m2 each, treating dairy parlor effluent and domestic sewage [5]. Environmental implications in Spain showed that sediments inside the harbor of Ceuta were characterized by moderate levels of heavy metal pollution. There was no industrial activity around the harbor. However, the major sources of contamination are the sewage effluents of urban sites influence, antifouling paints and accidental oil spills during sheep loading and dumping [6]. The objective of this research is to investigate the levels of heavy metal contamination originating from industrial and residential sewage treatment plants and their consequent effect on the food chain. 2. Experimental Procedure Heavy metal pollution from the industrial sewage treatment plant (STP) was investigated in a small suburb of Muscat, Oman. Treated sewage effluent (TSE) from this plant was flowing in a small valley forming a water pond with growing grasses and grazing animals. TSE, sediment, shell and grass root samples were collected weekly for a period of three months. All samples were stored in a cooler at 10°C. TSE samples analyzed according to APHA, AWWA and WEP methods [7]. Sediment, shell and grass root samples were dried at 105 oC for 3 h. All samples (0.2 g) were weighed in perfluoroalkoxy polymer containers. The samples were then treated with 0.5ml of hydrofluoric acid and 4ml of concentrated nitric acid and heated in a microwave for 40 min. The samples were then diluted to 100 ml with Milli-Q water to give a final concentration of 1 g/l [8]. Samples were filtered and analysed for Al, Cd, Cr, Cu, Fe, Mn, Ni and Zn using (ICP-OES) type Perkin Elmer 3300 DV ICP (USA). Blank and certified reference solutions were used as controls. The concentrations of heavy metal were compared to the Omani Standard of Wastewater Reuse which was adapted from FAO guidelines for trace metals in irrigation water, (Table1). Unrestricted irrigation TSE is used for irrigation of vegetable, uncooked crops. TSE was also used to irrigate sports fields and public parks. Restricted irrigation TSE is used for cereal crops, industrial crops, fodder crops, pasture and trees [9]. Minimum Permissible Levels (MPL) for SB and Sc are absent in the Standard. Table 1. Heavy metal standards of wastewater reuse in Oman (1996) Minimum Permissible Levels (MPL) Metal Aluminum Arsenic Antimony Barium Boron Cadmium Chromium Copper Iron Mercury Manganes Nickel Lead


Unrestricted irrigation (mg/L)

Restricted irrigation (mg/L)

Al As Sb Ba B Cd Cr Cu Fe Hg Mn Ni Pb

5 0.1 1 0.5 0.01 0.05 0.05 1 0.001 0.1 0.1 0.1

5 0.1 2 1 0.01 0.05 1 5 0.001 0.5 0.1 0.2



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Scandium Selenium Zinc

Sc Se Zn

0.02 5

0.02 5

3. Results Generally, the majority of heavy metals in sediments, snails, aquatic grass roots were higher than the TSE values. Many of the heavy metals exceeded the MPL, Omani Standard, for the sewage water discharge. High concentrations of Cu, Ni, and Zn were detected in the four sources while other heavy metals were generally lower within the Omani Standard values (Table 1 and Figs 1-4). Some of the heavy metals values in snails were higher than the values in TSE and sediment samples (Fig 3). Most heavy metal concentrations in aquatic grass roots were similar to those of snail samples (Fig 4). Overall there is no specific trend relative to the values of heavy metals in the four sources.

Fig. 1. Heavy metal contamination from TSE. Note the high concentration of Ni, Cu followed by the rest of metals.

Fig 2. Heavy metal contamination from sediment. Note the high concentration of Ni, Cu, K, Pb followed by the rest of metals.

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Fig. 3. Heavy metal contamination from snails. Note the high levels of Ni, Cu, Pb, Zn followed by the rest of metals.

Fig. 4. Heavy metal contamination from grass roots. Note the high levels of Ni, Pb, Cu, Zn followed by the rest of metals.

4. Discussion Based on this study, the heavy metal values showed mixed results. Several have exceeded the MPL, Omani Standard, for the sewage water discharge. However, there is a trend in increasing heavy metal values from the TSE to sediment, snail and grass roots. Heavy metals are the most important wastewater contaminants which cannot be removed from treated effluent. Fortunately in recent years metal production has decreased in many countries due to stringent legislations, improved cleaning technology and altered industrial activities. A significant part of the anthropogenic emissions of heavy metals ends up in wastewater. Major industrial sources include surface treatment processes with elements such as Cu, Zn, Ni and Cr as well as industrial products that at the end of their use are discharged in wastes. Heavy metals contamination can be very dangerous. Many heavy metals and their compounds are toxic and some are also subject to biomagnification, which can lead to accumulation in the food chain. Animals at the higher food chain tend to accumulate higher concentration of toxicants in tissue from their food. Pb and Cd are currently being studied worldwide because of the danger they pose to animal and human food chains. Metals like Cd, Ni, Pb and Zn are known to be cumulative toxins that can affect animals including humans. High levels of these elements can be explained by their high mobility in the environment [10]. The continuous discharge of sewage treated effluent over an extended period can result in the accumulation of heavy metals in sediment and grass to levels that can be detrimental to the food chain [11]. In the study site, a variety of grasses grow locally enabling goats and sheep to graze. These animals are sources of milk and



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meat, thus creating a potential health risk to consumers. Extreme caution must be used to avoid excessive heavy metal accumulation and preventing further environmental deterioration. References [1] Al-Bahry S, Mahmoud I, Al-Rawahi S, Paulson J. 2011. Egg contamination as an indicator of environmental health. In: Impact of Egg Contamination on Environmental Health. Nova Science Publisher, Inc. New York, USA. ISBN: 978-1-62100-125-6. [2] Al-Musharafi SK, Mahmoud IY, Al-Bahry SN. 2012. Heavy metal contamination from treated sewage effluents. 11th International Conf. on Modelling, Monitoring and Management of Water Pollution. New Forest, UK. www.witpress.com, ISSN 17433541 (on-line). WIT Transactions on Ecology and The Environment, Vol. 164, ©2012 WIT Press. UK. Page 381-389. [3] Han FX, Banin A, Kingery WL, Triplett GB, Zhou LX, Zheng SJ, Ding WX. New approach to studies of heavy metal redistribution in soil. Advances in Environmental Research. 8, pp113- 120. 2003 [4] He ZL, Yang XE, Stoffella PJ. Trace elements in agroecosystems and impacts on the environment. J Trace Elem Med Bio 2005;19:125-140. [5] Mantovi P, Marmiroli M, Maestri E, Tagliavini S, Piccinini S, Marmiroli N. Application of a horizontal subsurface flow constructed wetland on treatment of dairy parlour wastewater. Bioresource Technol. 2003;88:85-94. [6] Guerra-Garcia, J. M. and Garcia-Gomez, JC. Assessing pollution levels in sediments of a harbour with two opposing entrances: environmental implications. J Environ Manage 2005;77:1-11. [7] APHA, AWWA, and WEF. (Clescerl LS, AE Greenberg, and AD Eaton (eds)). Standard Methods for the examination of water and wastewater. 20th ed. United book press. Washington. USA; 1998. [8] Moor C, Lymberopoulou T, Volker J, Dietrich V. Determination of heavy metals in soils, sediments and geological materials by ICP-AES and ICP-MS. Mikrochim Acta 20011;36:123-128. [9] Ministry of Regional Municipalities and Water Recourses (MEMWR). Standards for the minimization of pollution to air, water and soil. Ministry of Environment Decree No 52/1-Standards. Ministry of Environment: Oman, 1996. [10] Deroche B,

, Kerchief V. Impact of sewage sludge Spreading on heavy metal speciation in tropical soils (Réunion,

Indian Ocean) Chemosphere. 2006;65:286-293. [11] Madyiwa S, Chimbari M, Nyamangara J, Bangira C. Cumulative effects of sewage sludge and effluent mixture application on soil properties of a sandy soil under a mixture of star and Kikuyu grasses in Zimbabwe. Phys Chem Earth 2002;27:747-753.