Possibility of using Sewage Effluent from Different Water Treatment Plants in Different Cities of Saudi Arabia for Agricultural Reuse

A comparative study was conducted to test the efficiencies of 7 sewage water treatment plants, 4 in Jeddah, Bani-Malik, Al-Balad, Al-Khomrah, Hael, one in Makkah, one in Abha and one in Taif city in Saudi Arabia. The plants were installed for the treatment of the cities domestic and industrial wastewater effluent. The parameters studied included the physiological, chemical and biological characteristics treated sewage water (effluent) of the treatment plants. The 7 plants vary in their efficiencies to eliminate the studied parameters. The values of these parameters are within the range allowed according to the standards of the MWE ( 2005 ) and FAO ( 1985 ) except for the total coliform bacteria ( TCB ) which is high than the standards suggested (not to exceed 1000 colonies/100 ml), and also according to concentrations of TSS and according to concentrations of BOD and COD. So according to these results sewage water treatment plants working now in Saudi Arabia needed modernization to be more efficient in treatment of the raw waste water, so it can be used for irrigation and production of crop, fodder and vegetable plants. It is recommended to resort to treated sewage water for production of field crops, forages in general in Saudi Arabia.


INTRODUCTION
Saudi Arabia is an arid land country suffering shortage in fresh water for irrigation purposes, a reason that encouraged the Kingdom to search for alternatives, thus started using treated wastewater in agriculture sector. And throughout the world treated sewage water is now used in agriculture due to many benefits accompanying it, such as that it is a fresh water containing high level of organic matter and plant nutrients, (Al-Sha'lan, 2001). Saudi Arabia has more than 30 desalination water treatment plants with daily production of treated water reaching up to 3 million m3/day. Part of this water is reused in agriculture. Irrigation with treated sewage water saved up to 45% in fertilizers cost for wheat crop and 94% for alfalfa crop compared to irrigation using well water because it contains the essential plant nutrients, and the yield of these crops by 11 and 23%, respectively, compared to irrigation with well water (Al-Abdulqader and Al-Jaloud (2003). Due to scarcity of water that can be used in irrigation and production of plant crops most of the countries throughout the world restored to treated sewage water and started using it in irrigation for production of all types of crops, vegetables, seeds, fibers and trees from long time ago , as was shown by Culp et al. , 1978 ;Ongerth and Jopling , 1977 ;and Muller, 1977 (Dreschsel, et al., 2002). Well treated wastewater can be used irrigation of crops and produce very healthy crops (Najafi et al., 2003, Jimenez, 2005, Munir and Ayadi 2005, Esmailiyan et al., 2008and Zavadil, 2009.. Thus it is one of the aims of the Kingdom of Saudi Arabia to start using this source in irrigation of food products and forage production, due to deficiency of irrigation water and reduction of rainwater. Sewage effluents are contaminated and polluted with heavy metals, microbes and different other chemical and biological elements. Sewage water contains both the municipal and the industrial effluents. The organic materials in the sewage water are in the form of nonhomogenous mixture of compounds, most of it is nitrogenous, like urea, proteins, ammo acids, and nonnitrogenous materials like hydrocarbons, lipids, detergents, pesticides and soap residues (Arab Water World, 1995). Evaluation of wastewater for reusing m agriculture has been discussed by many researchers (Abdel Magid, 1996;Arafa et al., 2001;Al-Solaimani and Hashim, 2004;Emongor and Ramolemana, 2005). Abdel Magid (1996), tested the suitability of wastewater and effluent from Unayzah sewage treatment plant for reuse in irrigation and found that the physico-chemical parameters of that water fall within the local and international standards for irrigation reuse, but the total coliform bacteria count (TCB) was high rendering the effluent unacceptable for irrigation use. In another tests by Arafa et al., (2001), they evaluated the population of staphylococcus, coliform and fecal coliform bacteria and yeast and molds of the waste water of Makkah city, and concluded that the sewage water is acceptable for reuse in agriculture. There are some studies assessed the sewage water quality and its dilution at South Cornich in Jeddah City (Mudarries et al., 2006). There are always worries and precaution about the reverse affect of sewage water use in the irrigation of field crops for humans and animals (Toze, 2005). Thus, several international and local organizations have concerned about putting standards for sewage water reuse in agriculture. Nitrate is a threatening contaminant element in sewage water if found at high rates (Hallberg and Keeney, 1993). The U. S. Environmental Agency (USEPA) has set a maximum contaminant level for nitrate of 10 (mg/L) as nitrogen for drinking water (USEPA, 1991. The aim of this study is to compare the efficiencies of 7 sewage water treatment plants in numbers of Saudi Cities as regards to their capabilities to treat the disposed sewage water and the possibility of using this treated water in agriculture.

Sample Collection :
Treated sewage water samples were collected from the waste water treatment plant at Jeddah ( Bani-Malik, Al-Balad, Al-Khomrah and Hail) and waste water treatment plant in Makkah , Al-Taif and Abha. Six waste water samples were collected at the end of April and September 2017 at 10 cm below the water surface to avoid floating solids. Chemical analysis was performed in Al-Amri Laboratories in Jeddah according to APHA (1985). Biological analysis was performed at the microbiological lab, Faculty of Science, King Abdulaziz University also according to APHA (1985). Physical and Chemical Analysis of Biological Oxygen Demand (BOD) was measured using Dissolved Oxygen Meter, which measures the quantity of dissolved oxygen in the water sample using dissolved oxygen electrode before and after a five-day incubation period at 20° C. Total Dissolved Solids (TDS) was evaluated by filtering 50 ml of wastewater through standard glass fiber filter, then oven dried at 1800 C. Nitrates (N-No3) were measured using Nesslerization method with spectrophotometer at a wave length of 450mm. Chlorides (Cr) were evaluated using Argenometric method in which the water samples were titrated against AgNO3 solution applying potassium chromate as indicator showing the end point of the reaction between silver nitrate and the chloride. Light absorbance of the suspension was measured by spectrophotometer420 nm. For Determination of other elements such as Fe, Zn, Cu, Cd and Pb extracted using the perchloric-nitric digestion procedure of Shelton and Harper (1941), and the concentration of these elements were measured using the Atomic Absorption Spectrophotometer model 5000 Perkin Elmer.

Biological Analysis :
The standard plate count by serial dilution is used in determination of the total number of bacteria in sewage water on nutrient agar plates. For coliform bacteria, the Most Probable Number method was used on McKonkey broth for acid and gas detection.

RESULTS AND DICUSSION PHYSICAL CHARACTERISTICS
The pH Value: The results in table (1), shows that the pH values of the treated water of 6 of the treatment plants Al -Balad, Al -Khomrah, Hail, Makkah, Al-Taif and Abha are above 7, while that of Bani -Malik is below 7 (6.68). This means that the treated sewage water of the above 6 treatment plants is alkaline in nature, while that of Bani -Malik plant is some what acidic in nature PH is a logarithmic scale used to determine acidity or alkaline and measures the negativity of hydrogen activity in units per liter of water from hydrogen ions (Bates, 1973). Wallace and Cha (1977) noted that the pH of wastewater is an important factor in influencing the melting of heavy metals in the soil and thus their availability to the plant. Several previous studies have pointed to the wastewater base in Al-Khomra district south of Jeddah and that the pH in this water has exceeded 8 units (ROCERSGA, 2010; Al-Farraj et al., 2012). All these treated sewage waters can safely be used in agriculture based on their pH values. EC The results in table (1) show that EC values in Makkah , Al-Taif and Abha treated water reached 1130, 1061.44 and 455 U mhos / cm respectively, and all below standards of (MWE, 2005), (PME, 1989), (FAO, 1985). The degree of electrical conductivity is a numerical indication of the ability of the solution to transfer the electric current and depends on the quality and concentration of the ions in the solution. These ions are often non-salts and the electrical conductivity is expressed in micromes in the centimeter (U mhos / cm). In general, the amount of dissolved salts in water is indicated by the degree of electrical conductivity, which suggests the validity of water for use in different purposes. Accordingly these treated sewage waters can safely be used in agriculture based on their EC values.
Total suspended solids (TSS) and Total dissolved solids (TDS) : The total residues found in the sewage water are formed from both the total suspended solids(TSS) and the total dissolved solids (TDS). The sewage water treated by Abha treatment plant contained the least rate of (TSS) amounted to 5 mg/L, while the sewage water treated by Makkah treatment plant contained the highest (TSS) 162 mg/L, the others gave in between values (table 1). And all these treated sewage water by all these plants except Abha contain TSS above that recommended by (PME, 1989) and (MWE, 2005). TSS is the dry weight of suspended particles that have not been dissolved in water, a parameter used to assess the quality of waste water after and before treatment, and listed as conventional pollutants for clean water. Suspended solids (TSS) cause many problems, they prevent high light from reaching the plant and reduce the process of photosynthesis and thus reduce the dissolved oxygen content in the water and thus affected organisms living in water.

Nitrate ions ( NO3-):
More than 90% of the nitrogen present in sewage water is in the form of ammonia or its components. Recently the nitrogen compounds in the sewage water were considered one of the most important environmental concern due to the environmental problems accompanying these compounds, and one of them is their toxic effects on fishes and the other aquatic organisms, and activation of the dissolved oxygen in water. Consequently, abundance of nitrogen in sewage water is beneficial to plants. through treatment, and its increase in the sewage water is harmful to plants ( Russell et al., 1970), and irrigation with water rich in Na changes the soil to alkaline soil (Takashi, 1985). The results in table (1) 1985). Therefore these treated waters by these 7 plants can not be recommended for agricultural use, as the total coliform bacterial number that are allowed according to the FAO and MWE standards is 1.0 x 103 and 1.8 x 103 MPN/100 ml respectively.

Sodium adsorption ratio (SAR):
Sodium adsorption ratio refers to the ratio of the monovalent cations represented by Na and the bivalent cations represented by Ca and Mg. The lowest level of SAR was in the sewage water treated by Abha plant (2.58 mg*L), then Makkah (4.10 mg/L), Bani-Malik plant (5.35 mg/L) ,and the last was Hail plant with the highest SAR ( 12.02 mg/L), table (1). All the values of SAR in the sewage water treated by all of the 7 treatment plants fall below the permissible level suggested by FAO (1985) , and so they are safe and can be reuse in agricultural fields irrigation.
The heavy metals: The heavy metals or the micro-elements are important plant nutrients, but the toxic elements have toxic effects on plants, animals and humans. And the micro-elements become toxic and retarding to plant growth if their concentrations in water reached values higher than that permissible for agricultural use. The elimination of these elements from sewage water is practiced by advanced technical methods, like eliminating salts by irreversible collision or ionic exchange. The concentrations of the heavy metals (Fe, Mn, Cu, Zn, Cd, Pb, Ni) in the treated sewage water plants is shown in table (2).

a) The micro-elements:
The micro-elements are essential nutritive elements in plants, but are not required at high concentrations when treated water is used in irrigation, due to their harmful effects on humans and animals.  b) The toxic metals: As mentioned their presence in treated sewage water at levels lighter than those suggested by local and international organizations is harmful for use in agricultural purpose.

CONCLUSION
With regard to the physical parameters, the chemical parameters and the macro-elements, the values of the parameters studied in this research concerning their concentrations in the water treated by the 7 treatment plants ,Bani-Malik , Al-Balad , Al-Khomrah, Hail, Makkah, Al-Taif and Abha are within the range allowed according to the standards of the MWE ( 2005 ) and FAO ( 1985 ) except for the total coliform bacteria ( TCB ) which is high than the standards allowed by these organizations , (not to exceed 1000 colonies/100 ml), and also according to concentrations of TSS with exception of Abha, and according to BOD and COD with exception of Albaha and Al-Khomrah treatment plants. So according to these results the water treated by these 7 sewage treatment plants can easily and safely be used for irrigation of agricultural fields as regard their concentrations of pH, EC, chlorides, nitrates (NO3), SAR, Na, Fe, Mn, Cu, Zn, Cd, Pb, Ni, TSS and TDS (except Abha), , BOD and COD (except Abha and Al-Khomrah. But are not recommended for agricultural reuse as regard to their concentrations of the total coliform bacteria ( TCB).