1. Introduction

Several researches applied using several microorganisms to remove salts from water. Some artificial bacteria, which are still under research, were used for water desalination 3 years ago. In addition, researches from 5 years ago started application of some algae species under research manner to desalinate seawater with successful promising results.

Algae are simple plants without roots, stems, and leaves, which contain chlorophyll. They are a heterogeneous group of organisms and vary in size from microscopic unicellular forms to seaweeds of many feet in length with many different shapes. Algae can grow in water, whether it is saline water in seas or fresh water in rivers and lakes and under different weathers from snow weather to hot climatic. They can grow wherever they could synthesize their components and food by photosynthesis [1].

Scendesmus species growth successfully occurred in saline water as it absorbs salts and makes use of them in its metabolism. Chlorella and Scenedesmus are the most active Algae in stabilization ponds, because they can survive and commonly exhibit extremely wide range of salt tolerance in their habitat [2].

Micro-algae have a high capacity for inorganic nutrient uptake and can survive and grow in mass culture in outdoor solar bioreactors. Unicellular green algae such as Chlorella and Scendesmus have been widely used in wastewater treatment because they often colonize the ponds naturally, and they have fast growth rates and high nutrient uptake capabilities. However, one of the major drawbacks of using micro-algae in wastewater treatment is the harvesting of biomass [3].

Green algae was used for treatment of industrial waste water from natural gas production fields of 1500 m3 daily flow, which contains salinity up to 25000 ppm and oil content up to 100 ppm. The effluent could be re-used in irrigation of crops with a flow enough for about 60 fed./day. While the produced algae 1.5 ton/day was useful as a by-product for usage in medical industry, pigments for industry, functional food, bio-fertilizers, and animal or fish fodders [4].

Another algae application in stabilization ponds for industrial wastewater treatment of high salinity and oil content occurred through a pilot plant, which located in the site of N/D field in Abu-Mady north of Egypt. Several runs were made to ensure the results. The influent loads varied between 35000 & 10900 ppm for TDS, 250 & 65 ppm for Oil, 212 & 59ppm for BOD & 344 & 88ppm for COD. The effluent concentrations after 7 days retention time in the pond were ranged between 2750 & 2120 ppm for TDS, 2 & 0.5ppm for Oil, 7,4 ppm for BOD & 16 & 12 ppm for COD. These removal efficiencies proved the suitability of algae application for saline industrial wastewater treatment [5].

Desalination based on the use of algae in the removal of salts from saline water, and water production for use in different purposes is a new concept and it has been used and tested in previous researches in industrial wastewater treatment. The researches stated that using the algae reduced the cost to the minimum while maintained the efficiency with no reduction. The achieved results were promising and good in the desalination of seawater and were successful. Continuing the process made the removal efficiency reach up to 95% until the rates are relatively affordable for possible use in different purposes. This opens the door to a new direction that may succeed in solving the problem of water desalination with cost reduction to the minimum possible [6].

A study was made to assess the removal efficiencies of different nutrients in saline water by the means of the green algae Scenedesmus species. Total dissolved solids, Sodium, Chloride, and Phosphate removal efficiencies measured in the output of the reactor after 14 days reached around 97%. While the removal efficiencies of both Nitrate and Sulfate reached around 93% and all the parameters in the effluent were inside the permissible limits for potable water except the appear of some enzymes due to algae decay. This shows the success of this system to produce suitable potable water from seawater [7].

In March 2011, another study was made. The objective of this study was to assess the removal efficiencies of different nutrients in saline water by the means of the green algae Scenedesmus species through a continuous flow treatment system. The saline water used was from Red Sea, Ismailia Governorate, and had a TDS of 40000 ppm. Algae were added to two consecutive reactors for a retention time of 7 days for each reactor. The consecutive 7 days retention time for each reactor helped preventing the enzymes formations in the basins. The experiment in the continuous flow was repeated for 4 runs and the average values were taken into consideration. Analysis of growth media was daily determined. Total dissolved solids, Sodium, Chloride, and Phosphate removal efficiencies measured in the output of the second reactor reached around 97%. Moreover, the removal efficiencies of both Nitrate and Sulfate reached around 93% [8, 9].

2. Materials & Methods

A new system for decreasing the high salinity of brine water disposed from the desalination plants before its disposal to the sea was applied by using Algae for a natural, environment friendly and economic solution.

The Scendesmus algae species was the choice for operation process, thanks to its natural feature of growing very well in almost any mineral medium. The application was successfully worked under suitable conditions inside the lab as illustrated by El Nadi [5, 6, 9], El Sergany [5, 6], Saad [7] & Badawy [8]. In this study, the system was built outside the lab to meet the normal nature conditions.

The pilot plant located in open-air area in the environmental pilots Lab in Ain Shams university engineering faculty. The pilot plant consists of three storage tanks, three basins and it was equipped with manual algae separators units. Figure (1) illustrates the pilot photo.

Figure 1. Photo of the applied Pilot for algae Ponds

The pilot plant operated from August 2013 until November 2013 to obtain the system suitability under variable climatic conditions. It consisted of three runs, each with three different TDS concentrations for the three basins. Several concentrations of artificial saline water 80000, 75000, 70000, 65000, 60000, 55000, 50000, 45000 & 40000 ppm were applied three in each run. The feeding media for algae BG-11 solution was added to give algae enough nutrition with rate 0.1 lit/basin/run. Scendesmus algae were added by rate 0.4 lit/basin/run to treat the saline water for a retention time up to 7 days in each basin. Desalinated water came out as the effluent of the basin. Table (1) shows the chemical composition of BG-11 nutrient solutions.

Table (1). Chemical composition of BG-11 nutrient solutions Chemical BG-11(g/l) NaNO3 1.5 K2HPO4.3H2O 0.04 Na2CO3 0.02 MgSO4.7H2O 0.075 CaCl2.2H2O 0.036 EDTA-Na2 0.001 Fe(NH3)2Citrate 0.006 Citric acid 0.006

Samples were taken each day from each basin. The sample volume was 50 ml. Water samples were collected at 9:00 AM each morning periodically. They were analysed to investigate water quality during the examination period. The measured parameters were: Total dissolved solids (TDS), Air Temperature, Humidity, Sunlight period & Algae growth rate.

3. Results

The first run started with high salts concentrations. The feeding tanks had concentrations of 80000, 75000 and 70000 mg/l. The run was applied for 7 days for the three parallel basins. The second run worked with feeding concentrations 65000, 60000& 55000 mg/l. Moreover, the third run applied the lower concentrations from 50000, 45000 & 40000 mg/l. The process was repeated for four months to take the effect of climatic changes. The study measured the TDS concentrations at each basin effluent in addition to the climatic conditions during the run operation days. Tables (2), (3), (4), (5), (6), (7), (8) & (9) illustrate the results of the measured data during the first, second, third & fourth month's runs.

Table (2). Air climatic conditions during First Month Runs Run Date Air Climatic Conditions Temperature °C Humidity % Sun Light Period (hr) Day Night Run 1 1/8/13 37 22 54 16.00 2/8/13 38 22 42 16.02 3/8/13 39 27 62 16.05 4/8/13 41 30 59 16.07 5/8/13 39 29 60 16.10 6/8/13 40 31 59 16.12 7/8/13 38 29 64 16.15 Run 2 11/8/13 37 32 54 16.18 12/8/13 38 32 42 16.20 13/8/13 40 29 62 16.22 14/8/13 41 30 59 16.25 15/8/13 39 29 60 16.28 16/8/13 40 31 59 16.30 17/8/13 39 29 64 16.28 Run 3 21/8/13 39 32 54 16.20 22/8/13 39 32 42 16.18 23/8/13 39 29 62 16.16 24/8/13 41 30 59 16.14 25/8/13 41 33 60 16.11 26/8/13 40 31 59 16.09 27/8/13 39 29 64 16.07

4. Discussions

From tables (2, 3, 4 & 5) it can be seen that the algae role for removing salts from brine water was highly noticeable.

In general, the decrease in brine salinity is varied between 13-15% after first day, raised to 25-27.7% after the second day and gradually increased to 36-38.3 % after the third day and became 46 - 49% after the forth day then 54- 57% after the fifth day then finally reached 62-63% after the sixth day.

The variations in each day happened due to the effect of the nature conditions of temperature, humidity and sunlight period differences during the study period between August & November. The algae activity for desalination was higher in the hot climate more than cold one with small differences. In general, the variations were not too big to result in big differences.

Table (3). TDS measured during First Month Runs Run Date TDS mg/l Left Basin Middle Basin Right Basin Run 1 1/8/13 80000 75000 70000 2/8/13 68100 63800 59520 3/8/13 57790 54250 50580 4/8/13 49300 46060 42990 5/8/13 41000 39200 36550 6/8/13 34500 31370 28100 7/8/13 28170 25450 22500 Run 2 11/8/13 65000 60000 55000 12/8/13 55250 51100 46900 13/8/13 46980 43390 39840 14/8/13 39990 36900 33880 15/8/13 32980 30400 27800 16/8/13 25900 23700 20600 17/8/13 19540 16660 13900 Run 3 21/8/13 50000 45000 40000 22/8/13 42600 38500 33010 23/8/13 36400 32700 27970 24/8/13 29000 25800 21220 25/8/13 22280 17700 12740 26/8/13 16300 12100 7620 27/8/13 10050 8320 6630

Table (4). Air climatic conditions during Second Month Runs Run Date Air Climatic Conditions Temperature °C Humidity % Sun Light Period (hr) Day Night Run 1 1/9/13 37 22 54 16.00 2/9/13 36 22 55 15.58 3/9/13 36 27 65 15.55 4/9/13 35 23 65 15.53 5/9/13 35 24 70 15.50 6/9/13 35 22 59 15.48 7/9/13 35 24 54 15.46 Run 2 11/9/13 36 22 54 15.40 12/9/13 35 22 42 15.38 13/9/13 34 22 62 15.35 14/9/13 34 22 59 15.33 15/9/13 34 22 60 15.31 16/9/13 33 21 59 15.28 17/9/13 33 22 64 15.26 Run 3 21/9/13 33 22 54 15.20 22/9/13 33 22 42 15.18 23/9/13 32 21 62 15.16 24/9/13 31 20 59 15.14 25/9/13 31 21 60 15.11 26/9/13 30 21 59 15.09 27/9/13 30 21 64 15.07

Table (5). TDS measured during Second Month Runs Run Date TDS mg/l Left Basin Middle Basin Right Basin Run 1 1/9/13 80000 75000 70000 2/9/13 68300 64100 59980 3/9/13 58390 54950 50890 4/9/13 49980 46430 43590 5/9/13 41900 39990 37050 6/9/13 35700 32270 28810 7/9/13 29270 26460 23510 Run 2 11/9/13 65000 60000 55000 12/9/13 55960 51740 47500 13/9/13 47480 44090 40760 14/9/13 40390 37600 34480 15/9/13 34280 31100 28700 16/9/13 27000 24400 21400 17/9/13 20640 17660 14900 Run 3 21/9/13 50000 45000 40000 22/9/13 42480 38400 33180 23/9/13 35400 31700 28070 24/9/13 28400 25100 21870 25/9/13 21180 18100 13040 26/9/13 17300 12900 8120 27/9/13 11050 9320 7120

Table (6). Air climatic conditions during Third Month Runs Run Date Air Climatic Conditions Temperature °C Humidity % Sun Light Period (hr) Day Night Run 1 1/10/13 30 22 54 15.00 2/10/13 31 22 55 14.57 3/10/13 31 21 56 14.55 4/10/13 31 20 57 14.53 5/10/13 31 21 56 14.51 6/10/13 30 21 56 14.49 7/10/13 31 21 55 14.47 Run 2 11/10/13 30 21 56 14.45 12/10/13 30 22 55 14.42 13/10/13 29 21 56 14.40 14/10/13 29 20 57 14.37 15/10/13 29 21 56 14.35 16/10/13 28 21 57 14.33 17/10/13 28 21 55 14.31 Run 3 21/10/13 28 20 54 14.28 22/10/13 27 21 57 14.26 23/10/13 27 21 57 14.24 24/10/13 27 20 56 14.21 25/10/13 28 19 56 14.19 26/10/13 27 20 55 14.16 27/10/13 27 19 54 14.14

Table (7). TDS measured during Third Month Runs Run Date TDS mg/l Left Basin Middle Basin Right Basin Run 1 1/10/13 80000 75000 70000 2/10/13 68970 64800 60780 3/10/13 58890 55350 51290 4/10/13 50480 46830 43990 5/10/13 42500 40100 37450 6/10/13 36000 32670 29210 7/10/13 29670 26860 23910 Run 2 11/10/13 65000 60000 55000 12/10/13 56360 52140 47880 13/10/13 47850 44440 41060 14/10/13 41090 37990 34880 15/10/13 34780 31600 29100 16/10/13 27700 24900 21900 17/10/13 21340 18160 15600 Run 3 21/10/13 50000 45000 40000 22/10/13 42880 38700 33480 23/10/13 35700 31900 28270 24/10/13 28900 25600 22120 25/10/13 21780 18700 13540 26/10/13 18300 13900 8720 27/10/13 11950 9920 7630

Table (8). Air climatic conditions during Fourth Month Runs Run Date Air Climatic Conditions Temperature °C Humidity % Sun Light Period (hr) Day Night Run 1 1/11/13 27 18 54 14.10 2/11/13 28 18 54 14.08 3/11/13 27 17 54 14.05 4/11/13 27 17 54 14.03 5/11/13 26 18 55 14.01 6/11/13 26 17 55 13.58 7/11/13 25 17 55 13.56 Run 2 11/11/13 25 17 55 13.54 12/11/13 26 17 55 13.52 13/11/13 25 16 55 13.50 14/11/13 25 16 56 13.48 15/11/13 24 16 55 13.46 16/11/13 24 16 55 13.43 17/11/13 24 15 56 13.40 Run 3 21/11/13 24 17 54 13.38 22/11/13 23 17 54 13.36 23/11/13 23 17 54 13.33 24/11/13 22 16 54 13.30 25/11/13 22 16 54 13.28 26/11/13 21 16 54 13.26 27/11/13 21 15 54 13.23

Table (9). TDS measured during Fourth Month Runs Run Date TDS mg/l Left Basin Middle Basin Right Basin Run 1 1/11/13 80000 75000 70000 2/11/13 69670 65500 61680 3/11/13 59690 55950 51790 4/11/13 50980 47330 44690 5/11/13 43100 40600 38050 6/11/13 36700 33470 29810 7/11/13 30250 27560 24810 Run 2 11/11/13 65000 60000 55000 12/11/13 56960 52840 48480 13/11/13 48450 44990 41760 14/11/13 41890 38690 35580 15/11/13 35480 32400 29800 16/11/13 28500 25700 22600 17/11/13 22040 18990 16500 Run 3 21/11/13 50000 45000 40000 22/11/13 43680 39500 34580 23/11/13 36270 32500 28870 24/11/13 29700 26150 22920 25/11/13 22680 19400 14540 26/11/13 19370 14700 9710 27/11/13 12880 10890 8630

The results show that the effect of influent TDS concentration on the TDS removal by algae looks high. The increase of salinity in water increases the algae activity for TDS consuming under the same conditions of nutrient media quantity and algae quantity. The results show that the algae capability to consume salinity increases with the availability of this salinity.

From these results, it can be seen that a pond with water depth between 30-60 cm and retention time of one or two days, can be enough to return the brine salinity to the ordinary seawater source salinity. In addition, these proposed ponds could help in removing the brine water high temperature in all the thermal desalination plants.

5. Conclusions

Generally, results encourage the use of green algae for brine water treatment by desalination and decreasing its temperature. This put an easy environmental and economic solution for environmental problems occurred by brine water in desalination plants. The study had shown the following specific conclusions:-

1. Scendesmus species growth was successfully obtained in saline water as it uptakes salts and make use of them in its metabolism.

2. The system achieves high removals for salinity between 13% (for one day) to 63 % (for six days).

3. The effectiveness of the system increases as the starting total dissolved solids content increases.

4. The effect of the nature conditions of temperature, sunlight period was noticeable by about 2 % difference in removal efficiency between summer and winter.

5. The advantages of the proposed system are low cost, easy construction with low operation & maintenance cost, and no energy requirements in addition to environmental protection from brine effects.

6. The system gives low pollution to surrounding environment, with maximum benefit of by-products, besides it solves the problem of getting rid of the waste products.