1. 161 American Scientific Research Journal for Engineering, Technology, and Sciences (ASRJETS) ISSN (Print) 2313-4410, ISSN (Online) 2313-4402 © Global Society of Scientific Research and Researchers http://asrjetsjournal.org/ Physico-chemical Analysis of Groundwater Around Mai- Bela, Asmara, Eritrea Nahom Tesfalema*, Aron Tesfamariamb, Abel Okbaslasiec, Kibrom Tesfayd a,b,c,dEritrea Institute of Technology, Asmara, Eritrea aEmail: nahomtesfalem6@gmail.com bEmail: arontesfamariam34@gmail.com cEmail: abelokbaslasie@gmail.com dEmail: ktesfay206@gmail.com Abstract Groundwater quality studies were carried out inAsmaraaround Mai-Belaan area having a long history of waste water irrigation. The objective of this study is to identify the quality of groundwater where groundwater is used for domestic and agricultural purposes in Mai-Bela area. Samples from five locations were collected and analyzed. The present investigation is focused on the determination of Physico-Chemical parameters such as temperature, electrical conductivity, pH, hardness, total dissolved solids (TDS), alkalinity, salinity,sodium, potassium, calcium, magnesium, iron, manganese, bicarbonate, chloride, sulphate, nitrate, nitrite, ammonia, chemical oxygen demand (COD)and toxic metal determinations. Groundwater suitability for domestic and irrigation purposes was compared with World Health Organization (WHO) and Food and Agriculture Organization (FAO) standards. Most of the physico-chemical parameters were found above the permissible limit and so do the toxic metals except for COD, pH, temperature, Al, Cd, Cr, Cu and Zn which were found slightly lower than the standard limit which indicate the groundwater in most of the study sites were not suitable for drinking and irrigation purposes. This therefore, calls for appropriate treatment measures before the consumption of these waters by the populace to avoid long term accumulated health problems of these pollutants. Keywords: Groundwater; Physico-Chemical parameters; pollutants; toxic metals. ------------------------------------------------------------------------ * Corresponding author. http://asrjetsjournal.org/ American Scientific Research Journal for Engineering, Technology, and Sciences (ASRJETS) (2019) Volume 57, No 1, pp 161-186 162 1. Introduction Water is an important constituent of the ecosystem which is essential component of life. On earth 97.2% of water is salty and 2.8% is fresh water from which about 20% constitutesgroundwater [1]. Rapid growth of industrialization, population, and urbanization spoil the groundwater. The term groundwater pollution was defined in the International glossary of hydrology as: “Addition of pollutant to water.”(Pollutant was defined in the International glossary as: “A substance which impairs the suitability of water for a considered purpose ”[2]. Groundwater is used for domestic and industrial water supply and also for irrigation purposes in all over the world. In the last few decades, there has been a tremendous increase in the demand for fresh water due to rapid growth of population and the accelerated pace of industrialization. However, groundwater could be chemically, physically or microbiologically contaminated. According to WHO, about 80% of all the diseases in human beings are water borne diseases [3]. Ground water contamination is nearly always the result of human activity. There are many possible sources of chemical contamination. These include wastes from industrial chemical production, metal plating operations, domestic wastewater and pesticide runoff from agricultural lands. It is known that wastewater, depending on its source, contains dissolved salts, organic matter, oil, grease, detergents, essential minerals and toxic heavy metals…etc [4]. Asmara is the capital city and largest settlement of Eritrea. Home to a population of around 800,000 inhabitants, it sits at an elevation of 2,325 meters. The city is located at the tip of an escarpment that is both the north western edge of the Eritrean highlands and the Great Rift Valley in neighboringEthiopia. Whereas Mai-Bela is a river with a long history of wastewater drainage which originates from the heart of Asmara, containing the house hold and industrial effluents, and flows through the western escarpment which is a major tributary of the Anseba river. Finally Anseba river after flowing for 346 Km it merges with the Barka river near the border of Sudan and flow to Sudan altogether. The area around the waste water drainage of Asmara is called Mai-Bela which is well known for the agricultural practices, the waste water is the main source of water, and its characteristic unpleasant smell evolved from the effluent. It is expected that since the wells are located near the wastewater drainage in Mai-Bela, Asmara for long time; the ground water may be contaminated with inorganic and organic pollutants. Therefore, attention is paid to investigate the effect of domestic wastewater seepage on the physical and chemical properties of groundwater around Mai-Bela, Asmara. The sources of groundwater contamination are many and varied because, in addition to natural processes, practically every type of facility or structure installed by man and each and every human physical activity may eventually cause groundwater quality problems (Figure 1).The vulnerability of groundwater, especially of groundwater supplies, to existing or potential sources of contamination underscores the need for a systematic, detailed process by which these potential threats can be recorded and evaluated. zim://A/A/html/E/s/c/a/Escarpment.html zim://A/A/html/G/r/e/a/Great_Rift_Valley%2C_Ethiopia.html zim://A/A/html/E/t/h/i/Ethiopia.html American Scientific Research Journal for Engineering, Technology, and Sciences (ASRJETS) (2019) Volume 57, No 1, pp 161-186 163 Figure 1: Some potential sources of groundwater contamination taken from[2] In this study, groundwater samples were collected from five wells around Mai-Bela, Asmara. Various physico- chemical parameterswereanalyzed and compared with the WHO guideline values set for potable and other purposes of water. Based on the results of the analysis, the recommendations were made. Figure 2: Flow chart of water quality assessment parameters[5]. American Scientific Research Journal for Engineering, Technology, and Sciences (ASRJETS) (2019) Volume 57, No 1, pp 161-186 164 2. Literature review 2.1 International status Several research papers were referred on Physico-chemical analysis of ground water as well as surface water of different districts, cities and countries. Different Physico-chemical parameters were compared with WHO standards to determine the quality of water if it is suitable for drinking, irrigation and other domestic purposes [4]. carried out studies on domestic wastewater effect on the pollution of the ground water in rural areas in Egypt. The main aim was to analyze groundwater pollution as a consequence of wastewater discharging into permeable underground septic tanks. In the study, groundwater (from a well used for irrigation and drinking) samples were taken at the pumping level. A series of chemical analysis was carried out for water samples at different periods of time. Harmful effects of wastewater on the chemical compositions of groundwater were detected. In addition it was explained that, toxicity and chemistry of heavy metals increases in groundwater. Groundwater quality studies were carried out [6] in and around Namakkal District, Tamilnadu, India. The objective of the study was to identify the quality of groundwater especially in the town and rural areas where groundwater is used for domestic and agricultural purposes. Groundwater suitability for domestic and irrigation purposes was examined by using WHO standards, which indicates the groundwater of few areas, were not much suitable for drinking purposes. The work aimed to assess the quality of drinking water in some of local commercial water treatment plants in Jeddah city, five samples were taken from different water plants subjected to physical, chemical and biological analysis. The parameters Theseresults were compared with the maximum level of the World Health Organization (WHO), Saudi Specification and Standardization organization (SASO) and Gulf Countries Standards for drinking water (GCS). The results showed a compliance with the water quality standards regarding the physical, chemical and biological characteristics. Statistical tools such as average, standard deviation and the correlation coefficient (r), were also calculated for these water quality characteristics [7]. The assessment of the groundwater quality was carried out in the different wards of Indore City. The analysis was aimed at assessing the water qualityindex (WQI) for the ground water of Indore City and its industrial area .The ground water samples of all the selected stations from the wards were collected for a physiochemical analysis. The obtained results were compared with Indian Standard Drinking Water specification IS: 10500-2012. The study of physico-chemical and biological characteristics of this ground water sample suggests that the evaluation of water quality parameters as well as water quality management practices should be carried out periodically to protect the water resources [3]. The physico-chemical parameters of water from 12 boreholes in 12 different communities in Umuahia North Local Government Area, Abia State, Nigeria were determined [8] within the period of six months (February to July, 2011) to investigate their quality. The results of the study indicated that the water sources were contaminated and unfit for human consumption. It showed that, appropriate treatment measures before the consumption of the water should be done by the populace to avoid long term accumulative health problems of the pollutants present. Recommendations on the strategies to reduce/eliminate some of the pollutants were made [9], carried out the correlation and regression analysis on 12 physico-chemical parameters of groundwater revealed that all the parameters were more or less correlated with one another. A linear regression analysis technique has been proven to be a very useful tool for monitoring groundwater and has a good accuracy. The linear correlation is very useful to get fairly accurate idea of the quality of the groundwater by determining just a American Scientific Research Journal for Engineering, Technology, and Sciences (ASRJETS) (2019) Volume 57, No 1, pp 161-186 165 few examples experimentally and then predicting the remaining from correlation equation.[10] presented the levels of physico-chemical parameters in the well water samples collected from Dass, Kaltungo and Langtang North in Nigeria. The results showed that most of the parameters determined did not exceed the permissible limit of the WHO. The groundwater and river water from Lagbe town in Benin Republic were collected and analyzed [11] for physico-chemical and microbiological parameters. The surface water samples were treated with alum, Moringa oleifera seeds powder and the combination of alum and Moringa oleifera seeds. The groundwater samples analyzed were contaminated by nitrate due to the proximity of septic tanks next to wells for which the waters were sampled. The surface water turbidities were high in some places and mostly rich of organic matter. The groundwater and surface water presented a microbial pollution of faecal origin. It was recommended that those waters are not potable and cannot be consumed without adequate treatment. All standard permissible limits were adopted from WHO permissible limits [12]. 2.2 Physical Aspects of Water 2.2.1 Temperature Temperature is one of the important factors in an aquatic environment for its effects in chemical and biological reactions in organisms. The change in atmospheric temperature with change in season brought corresponding changes in water temperature. The difference in atmospheric temperature and groundwater temperature are under the influence of high specific heat of water. According to WHO standards temperature of groundwater should not exceed 25oC to use it for drinking purpose [13,14] 2.2.2 pH The pH is a measure of the intensity of acidity or alkalinity and measures the concentration of hydrogen ions in water. It has no direct adverse effect on health, however, a slight low value, below 6.5 will produce sour taste and slight higher value above 8.5 shows bitter taste. A pH range of 6.5 – 8.5 is normally acceptable as per guidelines suggested by WHO. As the pH value of water goes far apart from the suggested guideline it shows corrosive nature [3,10,13,14,15,16]. 2.2.3 Electrical Conductivity (EC) Electrical Conductivity is the measure of capacity of a substance or solution to conduct electric current. It is a useful toolto evaluate the purity of water. It is an excellent indicator of Total Dissolved Solids (TDS) andsalinity that affects the taste of potable water. The variation in electrical conductivity is based on sedimentary structure and composition of rock. Chemically pure water does not conduct electricity. Any rise in the electrical conductivity of water indicates pollution. It is a good and rapid measurementof contamination. Groundwater contamination often shows higher values of ECdue to the presence of ions like OH-, CO3-2, Cl-, Ca+2etc. As per the WHO and FAO standards the maximum permissible limits are 1000μS/cm, for drinking, and 3000μS/cm, for irrigation, purposes respectively [3,10,13,14]. 2.2.4Total Dissolved Solids (TDS) American Scientific Research Journal for Engineering, Technology, and Sciences (ASRJETS) (2019) Volume 57, No 1, pp 161-186 166 Total Dissolved Solids is a measure of the combined content of all inorganic and organic substances contained in waterTotal Dissolved Solids may be considered as salinity indicator forclassification of groundwater. The TDS in groundwater is due to the presence ofCalcium, Magnesium, Sodium, Potassium, Bicarbonate, Chloride and Sulphate ions.Primary sources for higher TDS in the groundwater might be due to agricultural runoff, discharge of waste from industries and other human activities. According to WHO permissible limit for TDS is 500 mg/L [3,10,13,14,16]. 2.3 Chemical aspects of water 2.3.1 Total Hardness (TH) Hardness is caused by multivalent metallic cations. The principal hardness causing cations are the divalent calcium and magnesium ions. The hardness in water is derived largely from contact with the soiland rock formations. Calcium and magnesium are the greatest portion of the hardnessoccurring in natural waters. Hardness of water is objectionable from the point ofviewwater use for laundry and domestic purposes since it consumes a large quantity of soap. Classification of groundwater Hardness is given in Table.1 whereas the maximum permissible limit of WHO is 500 mg/L. Table 1: Classification of groundwater Hardness TH Concentration (mg/L) Classification 0-60 Soft 61-120 Moderately Hard 121-180 Hard >180 Very Hard 2.3.2Total Alkalinity The alkalinity of water is a measure of its capacity to neutralize acids. Alkalinity values provide guidance in applying proper dose of chemicals in water and wastewater treatment processes particularly in coagulation and softening. The alkalinity in natural water is caused by bicarbonates, carbonates and hydroxides and can be ranked in order of their association with high pH values. However, bicarbonates represent the major form since they are formed in considerable amounts due to the action of carbonates with the basic materials in the water. Maximum permissible limit for the total alkalinity is 250 mg/L[3,14]. 2.3.3 Chloride Naturally, chlorides are found as salts such as sodium chloride (NaCl), potassium chloride (KCl), and calcium chloride (CaCl2). Chlorides are leached from different rocks into soil and water due to weathering. The chloride concentration can be used as an important parameter for detection of contamination by sewage. High chloride content in watermay harmmetallic pipes and structures aswell as growing plants. Chlorides in excess impart the zim://A/A/html/O/r/g/a/Organic_compound.html American Scientific Research Journal for Engineering, Technology, and Sciences (ASRJETS) (2019) Volume 57, No 1, pp 161-186 167 salty taste to water and people not accustomed to high chloride are subjected to laxative effect. Chloride as anion occurs in all natural waters in widely varying concentrations. The origin of chloride in ground water is from weathering and leaching of sedimentary rocks, domestic and industrials wastes discharge, municipal effluences etc. It is advisable to use water withchloride concentration less than 600 mg/Land 350 mg/L for drinking and irrigation purpose respectively as per the WHO and FAO standard limits [3,10,14,15,16]. 2.3.4Sulphate Naturally, Sulphates are found in various minerals, such as epsomite (MgSO4·7H2O), gypsum (CaSO4·2H2O) and barite (BaSO4). Such dissolved mineral constituents increases the mineral content in drinking water. Sulphates find their way into water through smelters in mines, also from Kraft pulp in paper mills, tanneries and textile mills. Sulphate of potassium, magnesium and sodium are highly soluble in water, while barium, calcium and various other heavy metal sulphates are less soluble. Sulphur dioxide & Sulphur trioxide also contribute to the Sulphate content of water to some extent. Cathartic effects are commonly reported to be experienced by people consuming drinking water containing sulphate with higher concentrations. Dehydration is another common side effect resulted by the ingestion of large amounts of sodium or magnesium sulphate containing water. So water with concentration above 400 mg/L is unfavourable for drinking [3,14,15]. 2.3.5Nitrate Relatively little amount of the nitrate found in natural waters is of mineral origin, most of it coming from organic and inorganic sources, the former includes waste discharges and the latter comprises chiefly artificial fertilizers. However, bacterial oxidation and fixing ofnitrogen by plants can both produce nitrate. Interest is centered on nitrate concentrations forvarious reasons. Most importantly, high nitrate level in water to be used for drinking will render it hazardous to infants as it induce the "blue baby" syndrome (methaemoglobinaemia). The nitrate itself is not a direct toxicant but is a health hazard because of its conversion to nitrite [see also below] which reacts with blood hemoglobin to cause methaemoglobinaemia. As per the WHO guidelines the nitrate concentration of potable groundwater should not exceed 50 mg/L [3,10,14,16,17]. 2.3.6 Nitrite Nitrite ion exists normally in very low concentrations and even in waste treatment plant effluents levels are relatively low, principally because the nitrogen will tend to exist in the more reduced (ammonia; NH3) or more oxidized (nitrate; NO3 - ) forms. Because nitrite is an intermediate in the oxidization of ammonia to nitrate, because such oxidation can proceed in soil, and because sewage is a rich source of ammonia nitrogen, waters which show any appreciable amounts of nitrite are regarded as being of highly questionable quality. Levels in unpolluted water is normally low, below 0.03 mg/L. Values greater than this may indicate sewage pollution. The significance of nitrite (at the low levels often found in surface waters) is mainly as an indicator of possible sewage pollution rather than as a hazard itself although, as mentioned above, under "Nitrate”, it is nitrite rather than nitrate which is the direct toxicant. There is, accordingly, a stricter limit for nitrite in drinking waters which is 0.5 mg/L. Concentration above this limit can cause methaemoglobinaemia. In addition, nitrites can give rise American Scientific Research Journal for Engineering, Technology, and Sciences (ASRJETS) (2019) Volume 57, No 1, pp 161-186 168 to the presence of nitrosamines by reaction with organic compounds and there may be carcinogenic effects [14]. 2.3.7Chemical Oxygen Demand (COD) COD is the oxygen required by the organic substances in water to oxidize them by a strong chemical oxidant. COD is related to organic and inorganic pollutants which causes unfavorable conditions for the growth of microorganisms. It is originated by natural or, more probably, added organic matter. COD measurement is useful as it gives a good figure about the water quality, it is applicable to wastewater and also heavily polluted waters. It has no direct hazard implication. The ideal value of the COD for drinking is 75 mg/L according to [14]. 2.4.8 Ammonia Ammonia is generally present in natural waters, though in very small amounts, as a result of microbiological activity which causes the reduction of nitrogen-containing compounds. When present in levels above 0.1 mg/L N, sewage or industrial contamination may be indicated. From the viewpoint of human health the significance of ammonia is marked because it indicates the possibility of sewage pollution and the consequent possible presence of pathogenic micro-organisms [14,18] 2.4.9 Salinity Salinity is the saltiness or dissolved salt content (such as sodium chloride, magnesium and calcium sulfates, and bicarbonates) of a body of water. Salinity is an important factor in determining many aspects of the chemistry of natural waters and of biological processes within it, and is a thermodynamic state variable that, along with temperature and pressure, governs physical characteristics like the density and heat capacity of the water[14]. 2.3.10 Sodium Absorption Ratio (SAR) If the proportion of sodium is high in groundwater for irrigation purpose, it can destroy soil structure. A simple method for evaluating the values of high-sodium is the Sodium Adsorption Ratio[14,16]. Table 2: Classification of the SAR values Type of water Classification SAR value Low Excellent <10 Medium Good 10-18 High Doubtful 18-26 Very high Unsuitable >26 2.4 Toxic Metals Metallic elements (mercury, arsenic, cadmium, barium, selenium, aluminum, tin and lead)which are able to zim://A/A/html/S/a/l/t/Salt_%28chemistry%29.html zim://A/A/html/S/o/d/i/Sodium_chloride.html zim://A/A/html/M/a/g/n/Magnesium_sulfate.html zim://A/A/html/C/a/l/c/Calcium_sulfate.html zim://A/A/html/B/i/c/a/Bicarbonate.html zim://A/A/html/W/a/t/e/Water.html zim://A/A/html/S/t/a/t/State_function.html zim://A/A/html/T/e/m/p/Temperature.html zim://A/A/html/P/r/e/s/Pressure.html zim://A/A/html/D/e/n/s/Density.html zim://A/A/html/H/e/a/t/Heat_capacity.html American Scientific Research Journal for Engineering, Technology, and Sciences (ASRJETS) (2019) Volume 57, No 1, pp 161-186 169 induce toxicity even at lower levels of exposure are considered as systemic toxicants whereas such metals are called toxic metals. Occupying the top position on the list of hazardous substances, the following sections provide insight into the mechanisms through which these metals exert their toxicity within the body of living organisms. 2.4.1 Manganese Manganese can be termed as a metal which is one of the most abundant on earth. Though it is not found in its natural form, it is actually a component of more than 100 minerals. Manganese can exist in 11 oxidative states. Manganese occurs naturally in many surface water and groundwater sources and in soils that may erode into these waters. However, human activities are also responsible for much of the manganese contamination in water in some areas. Ambient manganese concentrations in seawater have been reported to range from 0.4 to 10 μg/L, with an average of about 2 μg/L. Levels in fresh water typically range from 1 to 200 μg/L. Manganese has a median level of 16 μg/L in surface waters. Higher levels in aerobic water is usually associated with industrial pollution. Concentration of manganese in drinking water above 0.5 mg/L is beyond the tolerable limit of our body and results in generation of aesthetic effect [14,15,19]. 2.4.2 Iron Iron is present in significant amounts in soils and rocks, principally in insoluble forms. However, many complex reactions which occur naturally in ground formations can give rise to more soluble forms of iron which will therefore be present in water passing through such formations. Appreciable amounts of iron may therefore be present in ground waters. Severe problems can be caused in drinking water supplies by the presence of iron although there is normally no harmful effect on people consuming water with significant amount of iron. Rather, the problems are primarily aesthetic, as the soluble (reduced) ferrous (Fe2+) iron is oxidized in air to the insoluble ferric (Fe3+) form, resulting in color or turbidity (or, in severe cases, precipitate formation). Laundry becomes stained if washed in water with excessive iron, and vegetables likewise become discolored on cooking. Taste problems may also occur. When water rich in iron is used to make tea (in which tannins are present) there may be a reaction giving rise to off-color which may in severe cases resemble that of ink. So to avoid this problems WHO stated the maximum permissible limit to be 0.3mg/L [14,15]. 2.4.3 Mercury Mercury, considered the most toxic heavy metal, has become part of the environment owing to anthropogenic activities including agriculture, municipal wastewater discharge, mining, incineration, and discharges of industrial wastewater. Having different bioavailability and toxicities associated with them, it exists in nature as inorganic salts ,an elemental or metallic form, in andasorgano-mercurial compounds in which their toxicity varies in ascending order (ionic < metallic